Key Questions in Congenital Cardiac Surgery [1 ed.] 190337894X, 9781903378946

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Key Questions CCS_Key Questions CCS v2.qxd 01/02/2022 13:11 Page 1

systematic overview of the important topics in contemporary congenital cardiac surgical practice. This illustrated concise

text is a practical and clinically focused book that covers all

the key questions in congenital cardiac surgery. Whilst being

an ideal reference for cardiothoracic surgical trainees and

residents, especially when undertaking their cardiothoracic surgery board examinations, this book is also of great value to

all the specialties involved in the peri-operative care of

congenital cardiac surgical patients, including congenital cardiac surgeons, paediatric cardiologists, congenital cardiac

anaesthetists, intensive care unit specialists, radiologists,

nurses and physiotherapists. ISBN 978-1-903378-94-6

9 781903 378946

Moorjani, Viola and Caldarone Key Questions in CONGENITAL CARDIAC SURGERY

Key Questions in Congenital Cardiac Surgery provides a

tf m

Key Questions in

CONGENITAL CARDIAC SURGERY

Narain Moorjani Nicola Viola

Christopher A. Caldarone

Foreword by William J. Brawn

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Key Questions in

CONGENITALCARDIACSURGERY

Narain Moorjani Nicola Viola

Christopher A. Caldarone

Foreword by William J. Brawn

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Key Questions in CONGENITAL CARDIAC SURGERY

tfm Publishing Limited, Castle Hill Barns, Harley, Shrewsbury, SY5 6LX, UK Tel: +44 (0)1952 510061; Fax: +44 (0)1952 510192 E-mail: [email protected]; Web site: www.tfmpublishing.com

ii

Design & Typesetting: First Edition:

Nikki Bramhill BSc (Hons) Dip Law © 2022

Paperback

ISBN: 978-1-903378-94-6

E-book editions: ePub Mobi Web pdf

© 2022 ISBN: 978-1-910079-46-1 ISBN: 978-1-910079-47-8 ISBN: 978-1-910079-48-5

The entire contents of ‘Key Questions in CONGENITAL CARDIAC SURGERY’ is copyright tfm Publishing Ltd. Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may not be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, digital, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher. Neither the authors nor the publisher can accept responsibility for any injury or damage to persons or property occasioned through the implementation of any ideas or use of any product described herein. Neither can they accept any responsibility for errors, omissions or misrepresentations, howsoever caused. Whilst every care is taken by the authors and the publisher to ensure that all information and data in this book are as accurate as possible at the time of going to press, it is recommended that readers seek independent verification of advice on drug or other product usage, surgical techniques and clinical processes prior to their use. The authors and publisher gratefully acknowledge the permission granted to reproduce the copyright material where applicable in this book. Every effort has been made to trace copyright holders and to obtain their permission for the use of copyright material. The publisher apologises for any errors or omissions and would be grateful if notified of any corrections that should be incorporated in future reprints or editions of this book. Printed by Gutenberg Press Ltd., Gudja Road, Tarxien, GXQ 2902, Malta Tel: +356 2398 2201; Fax: +356 2398 2290 E-mail: [email protected]; Web site: www.gutenberg.com.mt

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Contents =======================

é~ÖÉ vi

Preface

Foreword

Acknowledgements Contributors

Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9

Chapter 10 Chapter 11 Chapter 12

x xii

Abbreviations Chapter 1

viii

xxii Congenital cardiac anatomy Congenital cardiac physiology

1 61

Congenital cardiac pharmacology

101

Congenital echocardiography

127

Congenital cardiac imaging

171

Congenital angiography and catheter interventions

205

Anaesthesia and congenital heart disease

241

Paediatric cardiac intensive care

277

Adult congenital cardiac intensive care

337

Cardiopulmonary bypass

351

Extracorporeal membrane oxygenation

385

Informed consent in congenital cardiac surgery 427

iii

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Key Questions in CONGENITAL CARDIAC SURGERY

Chapter 13 Chapter 14 Chapter 15 Chapter 16 Chapter 17 Chapter 18 Chapter 19 Chapter 20 iv

Chapter 21 Chapter 22 Chapter 23 Chapter 24 Chapter 25 Chapter 26

Chapter 27 Chapter 28 Chapter 29 Chapter 30 Chapter 31

Atrial septal defects

451

Ventricular septal defects

477

Atrioventricular septal defects

519

Anomalous pulmonary venous connections

537

Ebstein’s anomaly

565

Tricuspid atresia

595

Hypoplastic right heart

613

Right ventricular outflow tract

639

Tetralogy of Fallot

675

Pulmonary atresia with ventricular septal defect 703 Transposition of the great arteries

729

Congenitally corrected transposition of the great arteries

759

Double-outlet right ventricle

781

Hypoplastic left heart syndrome

811

Congenital abnormalities of the mitral valve

839

Left ventricular outflow tract lesions

863

Truncus arteriosus

907

Anomalies of coronary arteries and coronary fistulae

935

Aortopulmonary window

961

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Contents Chapter 32 Chapter 33 Chapter 34 Chapter 35 Chapter 36 Chapter 37 Chapter 38 Chapter 39 Chapter 40 Chapter 41 Index

Vascular rings and slings

979

Patent ductus arteriosus

995

Aortic coarctation

1019

Interrupted aortic arch

1047

Univentricular heart

1057

Surgical palliation in congenital heart disease

1073

Heart and lung transplantation

1087

Surgery for cardiac arrhythmias

1111

Cardiac tumours

1139

Infective endocarditis

1157 1177

v

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Preface Congenital cardiac surgery is a continually expanding field with the development of novel techniques and operations, as well as the refinement of well-established surgical procedures. These developments fuel the demand for knowledge regarding congenital cardiac surgical disease processes and the optimal therapeutic strategies currently available. Although several large-volume texts exist, there are none which aim to deliver this knowledge base in one concise book, and that address the important questions pertaining to congenital cardiac surgery.

vi

hÉó=nìÉëíáçåë=áå=`çåÖÉåáí~ä=`~êÇá~Å=pìêÖÉêó systematically covers all the main topics involved in the contemporary practice of a congenital cardiac surgeon, using numerous illustrations to enhance the understanding of the reader. The book incorporates the current international guidelines for practice, with up-to-date information based on current scientific literature and experience from established congenital cardiac surgical units. Each chapter contains important references for further reading and greater in-depth study. The chapters have been written by practising international specialists in congenital cardiac surgery, congenital cardiology, congenital cardiac anaesthesia and intensive care, to reflect the truly interdisciplinary nature of congenital cardiac practice. The images have been drawn from an operative perspective where appropriate. This book is relevant to all cardiothoracic surgical trainees and residents, at any stage of their training programme, as it provides them with the necessary knowledge base to carry out their daily duties. Paediatric cardiologists, adult congenital cardiologists, congenital intensive care unit specialists, radiologists, nursing staff, physiotherapists and other allied professionals working with congenital cardiac surgical patients, either preoperatively or postoperatively, will also find this book key to facilitating their understanding of the principles surrounding congenital cardiac surgical disease management. Importantly, the book is also an ideal revision aid for trainees and residents undertaking their cardiothoracic surgery board examinations around the world. Its concise yet complete coverage of the important topics make it the perfect guide to answer the key questions in congenital cardiac surgery that are often asked within the confines of an

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Preface examination. In summary, this book is a succinct yet encompassing congenital cardiac surgical text, which allows the reader to obtain information in an easily readable format. Furthermore, this book completes the key question series of cardiothoracic surgical textbooks, following on from the successful publication of hÉó= nìÉëíáçåë= áå= `~êÇá~Å= pìêÖÉêó and hÉó= nìÉëíáçåë= áå qÜçê~ÅáÅ=pìêÖÉêó.

Narain Moorjani MB ChB MRCS MD FRCS (CTh) MA

Royal Papworth Hospital University of Cambridge, UK káÅçä~=sáçä~=ja= University Hospital Southampton University of Southampton, UK `ÜêáëíçéÜÉê=^K=`~äÇ~êçåÉ=ja= Texas Children’s Hospital and Baylor College of Medicine Houston, Texas, USA

vii

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Foreword I have been a congenital heart surgeon for over 35 years during which time there have been tremendous advances in the management of patients of all ages with congenital heart disease. It is a pleasure, therefore, to contribute a foreword for hÉó=nìÉëíáçåë=áå=`çåÖÉåáí~ä=`~êÇá~Å=pìêÖÉêó as it covers these advances in which I have had the privilege to have been involved.

viii

This book is the third volume in the ‘Key Questions’ series after hÉó nìÉëíáçåë=áå=`~êÇá~Å=pìêÖÉêó and hÉó=nìÉëíáçåë=áå=qÜçê~ÅáÅ=pìêÖÉêó. The Key Question format, so successful in the first two volumes, is very suited to enable an understanding of the management of congenital heart disease. This is because the question and answer format allows the reader to more easily navigate through the complexities of congenital cardiac abnormalities. The editors have gathered world-class contributors to write each chapter and the chapters are clearly written and comprehensively cover the abnormal cardiac morphologies and their diagnosis and treatment. Each chapter is clearly illustrated with easily understandable diagrams and photographs — all of superb quality. Importantly, the cardiac anatomy and congenital malformations are clearly described and illustrated with outstanding, coloured illustrations and photographs. Some chapters cover the important topics of cardiopulmonary bypass, physiology and diagnostic techniques. A separate chapter is devoted to the issue of consent, particularly important now for patients with complex lesions where difficult palliative surgery may be the only surgical option. This is an exceptional textbook and its main strength is the question and answer format, clear description of the congenital heart defect and the excellent illustrations and photographs. hÉó= nìÉëíáçåë= áå= `çåÖÉåáí~ä `~êÇá~Å= pìêÖÉêó= contains all the basic information to enable a clear understanding of the complex subject of congenital heart disease and

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Foreword provides a sound foundation in the subject. At the end of each chapter, selected references have been included that will guide the reader to further exploratory reading.

hÉó= nìÉëíáçåë= áå= `çåÖÉåáí~ä= `~êÇá~Å= pìêÖÉêó is essential reading for surgical and medical trainees and all other professionals involved in the care of patients with all forms of congenital heart disease.

William J. Brawn CBE FRCS

Honorary Consultant in Congenital Heart Surgery Birmingham Women’s and Children’s NHS Trust Birmingham, UK

ix

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Acknowledgements We are grateful to the numerous congenital cardiac specialists who have authored the chapters in this book. The expert knowledge that they have imparted has made this a truly comprehensive text. We would also like to thank Nicki Averill and Nicola Viola for providing the majority of the illustrations used in the book. As regards the individual chapters, we are appreciative of the numerous medical and surgical colleagues, whom we have acknowledged in the appropriate chapters, for providing some of the images and photographs. These are as follows:

• x

• •

• • • • • • • • • • • •

Diane E. Spicer, Heart Institute, Johns Hopkins All Children’s Hospital; Professor Robert H. Anderson, Biosciences Institute, Newcastle University; Mr. Nicola Viola, Dr. Tara Bharucha, Dr. Trevor Richens, Dr. Andrew Ho, Mr. Antonio Ravaglioli, Dr. James Shambrook, Dr. Shankar Sadagopan, Dr. Charles Peebles, Dr. Kevin Roman, Dr. Lindsay Smith, Mr. Pietro Malvindi and Mr. Theo Velissaris — all from University Hospital Southampton; Dr. Dhaval Parekh, Texas Children’s Hospital; Professor Gurleen Sharland, Evelina London Children’s Hospital; Dr. Will Regan, Evelina London Children’s Hospital; Dr. Soha Romeih, Aswan Heart Centre, Egypt; Dr. Fahad Alhabshan and Ms. Norah Al-Otaibi, National Guard Health Affairs, Riyadh, Saudi Arabia; Dr. Francisco Gonzales-Bartalay, Bristol Royal Hospital for Children; Dr. Simon Bamforth, Newcastle University; Professor Antoon F. M. Moorman and Dr. Aleksander Sizarov, Academic Medical Center, Amsterdam; Dr. Tom Semple, Royal Brompton Hospital, London; Professor John Lamberti, Lucile Packard Children’s Hospital Stanford, Palo Alto, California; Gemma Price, Gemma Price Designs, Cobham, Surrey; Professor Anthony Hlavacek, Medical University of South Carolina.

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Acknowledgements We are also grateful to the following for granting permission to reprint copyrighted images:

• • • • • • • • • • • • • •

Abbott; Berlin Heart Inc.; BioIntegral Surgical; Cambridge Unversity Press; Edwards Lifesciences Corporation; Elsevier; Getinge; Mayo Foundation for Medical Education and Research; Medtronic; Springer; St. Jude Medical; Steinkopff Verlag; Texas Children’s Hospital; Wessex Heartbeat 3D Heart Library.

In addition, we would like to thank Mr. Nick Small, Cardiac Physiology Unit, University Hospital Southampton NHS Foundation Trust, Professor Subhasis Chakraborty, Children’s Hospital, Oxford University Hospital NHS Trust and Mr. Nicola Viola, University Hospital Southampton NHS Foundation Trust, for providing the images and photograph on the front cover. Finally, we are deeply indebted to Nikki Bramhill from tfm publishing for her expert production of this congenital cardiac surgical text and ongoing enthusiasm for the ‘Key Question’ series of textbooks.

xi

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Contributors Abdullah A. Alghamdi, MD MSc FRCSC Head, Cardiac Surgery Assistant Professor of Surgery King Abdulaziz Medical City, National Guard Health Affairs, Riyadh, Saudi Arabia David R. Anderson, MA MB BChir FRCS FRCS Edinb Professor of Congenital Cardiac Surgery King’s College London, UK Consultant Cardiac Surgeon Evelina London Children’s Hospital, Guy’s & St Thomas’ NHS Foundation Trust, London, UK xii

Robert H. Anderson, BSc MD PhD (Hon) FRCPath FRCS Ed (Hon) Visiting Professorial Fellow Biosciences Institute, Newcastle University, Newcastle-upon-Tyne, UK Hiroko Asakai, MD Research Fellow The Royal Children’s Hospital, Parkville, Melbourne, Australia Conal B. Austin, FRCS Congenital Cardiac Surgeon St Thomas’ Hospital, London, UK Carles Bautista, MD MSc PhD Paediatric Cardiology Consultant, Interventional Cardiology The Royal Brompton Hospital, part of Guy’s and St Thomas’ NHS Foundation Trust, London, UK Lale Begum, BSc MSc PgDip Lead Clinical Perfusion Scientist Royal Brompton Hospital, London, UK Tara Bharucha, MA (Cantab) MBBChir FRCP FESC Consultant Paediatric and Fetal Cardiologist Congenital Cardiac Centre, University Hospital Southampton, Southampton, UK

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Contributors Mark S. Bleiweis, MD Professor of Surgery and Pediatrics, University of Florida Congenital Heart Center, Division of Cardiovascular Surgery, Departments of Surgery and Pediatrics, University of Florida, Gainesville, Florida, USA William J. Brawn, CBE FRCS Honorary Consultant in Congenital Heart Surgery Birmingham Women’s and Children’s NHS Trust, Birmingham, UK Harold M. Burkhart, MD Professor and Chief, Division of Cardiac, Thoracic & Vascular Surgery University of Oklahoma, Oklahoma, USA Christopher A. Caldarone, MD Donovan Chair, Professor, and Chief of Congenital Heart Surgery Texas Children’s Hospital and Baylor College of Medicine, Houston, Texas, USA Sian Chivers, MBChB MRCPCH Paediatric Cardiology Registrar The Royal Brompton Hospital, part of Guy’s and St Thomas’ NHS Foundation Trust, London, UK Melanie A. Connett, BN (Hons) MSc Paediatic Intensive Care Advanced Nurse Practitioner Southampton Children’s Hospital, Southampton, UK Miriam Conway, MBBS BSc (Hons) MRCP Specialist Registrar in Cardiology Royal Brompton Hospital, London, UK Antonio F. Corno, MD FRCS FACC FETCS Professor of Research in Pediatric and Congenital Heart Surgery University of Texas Health, Houston, Texas, USA Jennifer Co-Vu, MD Attending Pediatric Cardiologist Congenital Heart Center, Division of Pediatric Cardiology, Department of Pediatrics, University of Florida, Gainesville, Florida, USA

xiii

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Key Questions in CONGENITAL CARDIAC SURGERY

Adrian Crucean, MD MS PhD Consultant in Cardiac Morphology Specialty Doctor in Congenital Heart Surgery Birmingham Women’s and Children’s Hospital NHS Foundation Trust, Birmingham, UK Barbara J. Deal, MD MSc Professor Emerita of Pediatrics Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA Joseph A. Dearani, MD Professor of Surgery Mayo Clinic, Rochester, Minnesota, USA

xiv

Eric Devaney, MD Chief, Pediatric Cardiac Surgery University Hospitals Rainbow Babies & Childrens Hospital, Cleveland, Ohio, USA Nigel E. Drury, BM (Hons) PhD FRCS (CTh) Hunterian Professor & Consultant in Paediatric Cardiac Surgery Birmingham Children’s Hospital, Birmingham, UK Saravanan Durairaj, MBBS DCH MRCPCH Consultant Paediatric Cardiologist East Midland Congenital Heart Centre, University Hospitals of Leicester NHS Trust, Leicester, UK Pirooz Eghtesady, MD PhD Professor of Surgery and Chief of Pediatric Cardiothoracic Surgery St. Louis Children’s Hospital/Washington University in St. Louis, St. Louis, Missouri, USA Shakil Farid, MBBS FCPS MRCS Ed FRCS (CTh) MBA Consultant Cardiac and Aortic Surgeon Royal Papworth Hospital, Cambridge, UK Charles D. Fraser, Jr., MD Professor of Surgery and Perioperative Care, and Pediatrics Chief, Pediatric and Congenital Cardiothoracic Surgery Director, Texas Center for Pediatric and Congenital Heart Disease Dell Medical School at The University of Texas at Austin/Dell Children’s Medical Center, Austin, Texas, USA

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Contributors Simone Ghiselli, MD Research Fellow ASST Niguarda, Milan, Italy Jorge M. Giroud, MD Retired Attending Pediatric Cardiologist All Children’s Hospital, Saint Petersburg, Florida, USA Sarah Goring, MSc LCCP Clinical Perfusionist Wythenshawe Hospital, Manchester, UK Michael J. Griksaitis, MBBS(Hons) MSc MRCPCH FFICM Consultant Paediatric Intensivist & Honorary Senior Clinical Lecturer Southampton Children’s Hospital, Southampton, UK Faculty of Medicine, University of Southampton, UK Kimberly A. Holst, MD Chief Cardiothoracic Surgery Resident Mayo Clinic, Rochester, Minnesota, USA Osami Honjo, MD PhD Cardiovascular Surgeon, Associate Professor The Hospital for Sick Children, University of Toronto, Toronto, Canada Hatem Hosny, FRCS (CTh) FEBCTS (Cardiac) FEBCTS (Congenital) Consultant Cardiac Surgeon Aswan Heart Centre, Magdi Yacoub Foundation, Aswan, Egypt Golnaz Houshmand, MD FSCMR Cardiac Imaging Fellow Royal Brompton Hospital, UK Cardiology Consultant Rajaie Cardiavascular, Medical and Research Center, Iran Unversity of Medical Science, Tehran, Iran Jeffrey P. Jacobs, MD FACS FACC FCCP Professor of Surgery and Pediatrics, University of Florida Congenital Heart Center, Division of Cardiovascular Surgery, Departments of Surgery and Pediatrics, University of Florida, Gainesville, Florida, USA Sian Jaggar, MBBS BSc FRCA FFPMRCA CertMedEd MD Consultant in Anaesthesia & Critical Care Royal Brompton Hospital, London, UK

xv

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Key Questions in CONGENITAL CARDIAC SURGERY

Robert D. B. Jaquiss, MD Chief of Pediatric and Congenital Heart Surgery Pogue Distinguished Chair in Pediatric Cardiac Surgery Research Professor of Thoracic and Cardiovascular Surgery and Pediatrics Children’s Medical Center/UT Southwestern Medical Center Dallas, Texas, USA Natasha E. Khan, FRCS (CTh) Consultant Cardiac Surgeon Birmingham Children’s Hospital, Birmingham, UK

xvi

Ergin Kocyildirim, MD Pediatric Cardiothoracic Surgeon Assistant Professor University of Pittsburgh, Pennsylvania, USA Department of Cardiothoracic Surgery, Children’s Hospital of Pittsburgh, McGowan Institute of Regenerative Medicine, Pittsburgh, Pennsylvania, USA Igor E. Konstantinov, MD PhD FRACS Professor, Department of Paediatrics University of Melbourne, Australia Senior Research Fellow Heart Research, Murdoch Children’s Research Institute, Melbourne, Australia Director, Melbourne Centre for Cardiovascular Genomics and Regenerative Medicine, Melbourne, Australia Consultant Cardiothoracic Surgeon The Royal Children’s Hospital, Parkville, Melbourne, Australia Timothy S. Lancaster, MD MS Fellow in Congenital Cardiac Surgery Mott Children’s Hospital/University of Michigan, Ann Arbor, Michigan, USA Michael Lavrsen, MD Consultant Paediatric & Adult Congenital Cardiac Surgeon University Hospital Southampton, Southampton, UK Andrew J. Lodge, MD Associate Professor of Surgery and Pediatrics Duke University Health System, Durham, North Carolina, USA Spiros Loggos, MD MSc Senior Congenital Cardiac Fellow Alder Hey Children’s Hospital, Liverpool, UK

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Contributors Attilio A. Lotto, MD MCh FRCS (CTh) Consultant and Professor in Congenital Cardiac Surgery Alder Hey Children’s and Liverpool Heart and Chest Hospital Liverpool John Moores University, Liverpool, UK Stefano M. Marianeschi, MD Consultant Congenital Surgeon ASST Niguarda, Milan, Italy Christopher E. Mascio, MD Professor and Chief, Division of Pediatric Cardiothoracic Surgery Executive Director WVU Medicine Children’s Heart Center West Virginia University, West Virginia, USA Constantine Mavroudis, MD Chief of Pediatric Cardiothoracic Surgery Peyton Manning Children’s Hospital, Indianapolis, Indiana, USA Professor Emeritus of Surgery Johns Hopkins University School of Medicine, Baltimore, Maryland, USA Carlos M. Mery, MD MPH Surgical Director, Coronary Anomalies Program Associate Chief, Pediatric and Congenital Cardiothoracic Surgery Associate Professor, Surgery and Perioperative Care, and Pediatrics Texas Center for Pediatric and Congenital Heart Disease Dell Medical School at The University of Texas at Austin/Dell Children’s Medical Center, Austin, Texas, USA Jacob R. Miller, MD Instructor of Surgery St. Louis Children’s Hospital/Washington University in St. Louis, St. Louis, Missouri, USA Branko Mimic, MD PhD Consultant Congenital Cardiac Surgeon University Hospitals of Leicester, Leicester, UK Saeed Mirsadraee, MD MRCS FRCR FRCPE PhD Consultant Radiologist Royal Brompton and Harefield Hospitals, UK

xvii

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Key Questions in CONGENITAL CARDIAC SURGERY

Narain Moorjani, MB ChB MRCS MD FRCS (CTh) MA Consultant Cardiac Surgeon and Clinical Lead for Cardiac Surgery Royal Papworth Hospital, Cambridge, UK Associate Lecturer, University of Cambridge, UK Victor O. Morell, MD Eugene S. Weiner Endowed Professor and Chair of Pediatric Cardiothoracic Surgery Surgeon-in-Chief Children’s Hospital of Pittsburgh, Pittsburgh, Pennsylvania, USA Executive Director UPMC Heart and Vascular Institute, Pittsburgh, Pennsylvania, USA Michael O. Murphy, MA MD MRCP FRCS Congenital Cardiac Surgeon Royal Brompton Hospital, London, UK xviii

Raghav Murthy, MD DABS FACS FACC Assistant Professor, Pediatric Cardiac Surgery Mount Sinai Hospital, New York, USA Shafi Mussa, MA MD FRCS (CTh) Consultant Congenital Cardiac Surgeon Bristol Royal Hospital for Children and Bristol Heart Institute, Bristol, UK Phillip Naimo, BSc MD PhD Research Fellow The Royal Children’s Hospital, Parkville, Melbourne, Australia Masakazu Nakao, MD FRCS (CTh) Consultant Cardiac Surgeon KK Women’s and Children’s Hospital, Singapore, Singapore Nitha Naqvi, BSc (Hons) MBBS (Hons) MSc FRCPCH FRCP Paediatric Cardiology Consultant with special interest in echocardiography The Royal Brompton Hospital, part of Guy’s and St Thomas’ NHS Foundation Trust, London, UK Thieu Nguyen, MD Attending Pediatric Cardiologist Johns Hopkins All Children’s Hospital, Saint Petersburg, Florida, USA

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Contributors Giles J. Peek, MD Professor of Surgery and Pediatrics, University of Florida Congenital Heart Center, Division of Cardiovascular Surgery, Departments of Surgery and Pediatrics, University of Florida, Gainesville, Florida, USA Susanna Price, MBBS BSc PhD FRCP EDICM FFICM FESC RCPathME Consultant Cardiologist & Intensivist Royal Brompton Hospital, London, UK National Heart & Lung Institute, Imperial College, London, UK Eric Y. Pruitt, MD Cardiovascular Surgical Resident Congenital Heart Center, Division of Cardiovascular Surgery, Department of Surgery, University of Florida, Gainesville, Florida, USA Michael Puntis, MB BChir MA MRCS FRCA FFICM FHEA Consultant Intensivist St George’s University Hospitals NHS Foundation Trust, London, UK David N. Ranney, MD Fellow in Cardiovascular and Thoracic Surgery Duke University Medical Center, Durham, North Carolina, USA Antonio Ravaglioli, MD Congenital Cardiac Surgeon University Hospital Southampton, Southampton, UK Syed M. Rehman, MBBS BSc (Hons) MRCS FRCS (CTh) Cardiothoracic Surgeon Hammersmith Hospital, London, UK Vanessa J. C. Rogers, BSc (Hons) MBBS MRCS FRCS (CTh) Consultant Thoracic Surgeon Queen Elizabeth Hospital, Birmingham, UK Kelly Rosso, MD MS FACS Consultant Breast Surgeon Banner MD Anderson Cancer Center, Sun City West, Arizona, USA Kasra Shaikhrezai, MD MSc MRCS FETCS MD (Res) FRCS (CTh) Consultant Cardiac Surgeon Golden Jubilee National Hospital, Glasgow, UK

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Key Questions in CONGENITAL CARDIAC SURGERY

Simone Speggiorin, MD Consultant Congenital Cardiac Surgeon Evelina’s Hospital, Guy’s and St Thomas’ NHS Foundation Trust, London, UK Diane E. Spicer, PA(ASCP)CM Cardiac Morphologist Heart Institute, Johns Hopkins All Children’s Hospital, St. Petersburg, Florida, USA Curator of the Van Mierop Congenital Cardiac Archive Congenital Heart Center, University of Florida, Gainesville, Florida, USA Paraskevi Theocharis, MD PhD Consultant in Paediatric Cardiology Evelina London Children’s Hospital, Guy’s and St Thomas’ NHS Trust, London, UK xx

Jess L. Thompson, MD Managing Partner Yavapai Cardiac Surgery, Prescott, Arizona, USA Victor Tsang, MS MSc FRCS Consultant Cardiac Surgeon Great Ormond Street Hospital for Children St Bartholomew’s Hospital, London, UK Professor of Cardiac Surgery University College London, London, UK Nicola Uricchio, MD Consultant Congenital Surgeon ASST Papa Giovanni XXIII, Bergamo, Italy Carin van Doorn, MD FRCS (CTh) Consultant Cardiac Surgeon Leeds Teaching Hospitals NHS Trust, Leeds, UK Nicola Viola, MD Consultant Congenital Cardiac Surgeon University Hospital Southampton, Southampton, UK Clinical Lead for Cardiovascular Surgery Southampton Children’s Hospital, Southampton, UK Honorary Senior Lecturer University of Southampton, Southampton, UK

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Contributors Pascal Vouhé, MD PhD Professor of Pediatric Heart Surgery Necker Hospital for Sick Children, Paris, France Robert A. Wheeler, MBBS FRCS MS LLB(Hons) LLM Consultant Neonatal & Paediatric Surgeon Associate Medical Director, Department of Clinical Law University Hospital Southampton, Southampton, UK Neil Wilson, MD FSCAI Pediatric Interventional Cardiologist University of Colorado, Aurora, Colorado, USA Jenny E. Zablah, MD FACC FAAP FSCAI FPICS Assistant Professor of Pediatrics University of Colorado, Aurora, Colorado, USA Congenital Interventional Cardiologist Children’s Hospital Colorado, Aurora, Colorado, USA

xxi

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Abbreviations

xxii

2VC 3DRA AAo AAOCA AC ACEI ACHD ACT aEEG AHA AI AKI AL ALCA ALCAPA AMVL Ao AoV AP APACHE II APM APTTR APTT AR ARCA ARDS ARSA ART aRV AS ASD ASL ATP AV AVM AVN AVR AVSD BART BAS BAV

two-ventricle circulation three-dimensional rotational angiography ascending aorta anomalous aortic origin of a coronary artery aortic component angiotensin-converting enzyme inhibitor adult congenital heart disease activated clotting time amplitude-integrated electroencephalography American Heart Association aortic insufficiency; aortic incompetence acute kidney injury anterior leaflet (of the tricuspid valve) anomalous left coronary artery anomalous left coronary artery from the pulmonary artery anterior mitral valve leaflet aorta aortic valve aortopulmonary; anteroposterior; atriopulmonary Acute Physiology and Chronic Health Evaluation II anterior papillary muscle activated partial thromboplastin time ratio activated partial thromboplastin time aortic regurgitation anomalous right coronary artery acute respiratory distress syndrome aberrant right subclavian artery antidromic reciprocating tachycardia atrialised portion of the right ventricle aortic stenosis atrial septal defect anterosuperior leaflet (of the tricuspid valve) adenosine triphosphate atrioventricular; arteriovenous; apical vessel arteriovenous malformation atrioventricular node aortic valve replacement atrioventricular septal defect Blood Conservation Using Antifibrinolytics in a Randomized Trial balloon atrial septostomy bicuspid aortic valve

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Abbreviations BCA BCPS b.d. BDG BIS BiVAD BJV BoH BOS BP bPAB BSA BTS BTTS BVF CaO2 CAPP CAPRIE CAT CAV CAVV CCAM ccTGA CFAM cGMP CHD CI CMR CNS CO CO2 CoA CORSA CPB CPET CPR CPV CRRT CS CT CTA CUF CURE CVP CVVH

brachiocephalic artery bidirectional cavopulmonary shunt Äáë=ÇáÉ=ëìãÉåÇìã, twice daily bidirectional Glenn (procedure) bispectral index biventricular assist device bovine jugular vein bundle of His bronchiolitis obliterans syndrome blood pressure bilateral pulmonary artery banding body surface area Blalock-Taussig shunt Blalock-Thomas-Taussig shunt bulboventricular foramen arterial content of oxygen coronary artery perfusion pressure Clopidogrel versus Aspirin in Patients at Risk of Ischaemic Events common arterial trunk cardiac allograft vasculopathy common atrioventricular valve cystic congenital adenomatoid malformation congenitally corrected transposition of the great arteries cerebral function-analysing monitor cyclic guanosine monophosphate congenital heart disease cardiac index cardiac magnetic resonance central nervous system cardiac output carbon dioxide coarctation of the aorta cervical origin of the right subclavian artery cardiopulmonary bypass cardiopulmonary exercise testing cardiopulmonary resuscitation common pulmonary vein continuous renal replacement therapy coronary sinus computed tomography computed tomography angiography continuous ultrafiltration Clopidogrel in Unstable Angina to Prevent Recurrent Events central venous pressure central veno-venous haemofiltration

xxiii

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Key Questions in CONGENITAL CARDIAC SURGERY

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Cx CXR CW DA DAA DAo DHCA DILV DIRV DKS DO2 DORV DPG DV EA EACTS ECC ECG ECLS ECMO ECPR ED EDP EDV EEG EF EFE ELSO ERA ERO ESC ESV ETCO2 FA FAC FBC FDG FFP FiO2 FISH FO FRC FRISC fRV FV GABA GCS

circumflex artery chest X-ray continuous wave ductus arteriosus double aortic arch descending aorta deep hypothermic circulatory arrest double-inlet left ventricle double-inlet right ventricle Damus-Kaye-Stansel (procedure) oxygen delivery double-outlet right ventricle disphosphoglycerate descending vein Ebstein’s anomaly European Association for Cardiothoracic Surgery extracardiac conduit electrocardiogram extracorporeal life support extracorporeal membrane oxygenation extracorporeal cardiopulmonary resuscitation Ehlers-Danlos end-diastolic pressure end-diastolic volume electroencephalography ejection fraction endocardial fibroelastosis Extracorporeal Life Support Organization endothelin receptor antagonists effective regurgitant orifice European Society of Cardiology end-systolic volume end-tidal carbon dioxide femoral artery fractional area change full blood count fluorodeoxyglucose fresh frozen plasma inspired oxygen concentration fluorescence áå=ëáíì hybridization foramen ovale functional residual capacity Fragmin in Unstable Coronary Artery Disease Study functional right ventricle femoral vein gamma-aminobutyric acid Glasgow Coma Scale

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Abbreviations GI GOSE HACEK

Hb HCM Hct HF HIT HLA HLH HLHS HOCM HR HRH HRHS HRV HV IA IAA IAC IAS IC ICD-11 ICP ICU IE Ig IHC IM iNO INR IPCCC IPPV IR IRMER IS ISNPCHD IV IVC IVS IVSd IVSs

gastrointestinal Great Ormond Street Echocardiography score e~ÉãçéÜáäìë=é~ê~áåÑäìÉåò~ÉI=eK=~éÜêçéÜáäìëI=eK=é~ê~éÜêçéÜáäìëI eK= áåÑäìÉåò~ÉI= ^ÅíáåçÄ~Åáääìë= ~ÅíáåçãóÅÉíÉãÅçãáí~åëI `~êÇáçÄ~ÅíÉêáìã=ÜçãáåáëI=báâÉåÉää~=ÅçêêçÇÉåëI=háåÖÉää~=âáåÖ~ÉI ~åÇ=hK=ÇÉåáíêáÑáÅ~åë haemoglobin hypertrophic cardiomyopathy haematocrit hemi-Fontan (procedure); heart failure heparin-induced thrombocytopaenia human leukocyte antigen hypoplastic left heart hypoplastic left heart syndrome hypertrophic obstructive cardiomyopathy heart rate hypoplastic right heart hypoplastic right heart syndrome hypoplasia of the right ventricle hepatic vein innominate artery; intersegmental artery interrupted aortic arch interatrial communication interatrial septum intracardiac Eleventh Iteration of the International Classification of Diseases intracranial pressure intensive care unit infective endocarditis immunoglobulin inner heart curvature intramuscular inhaled nitric oxide international normalised ratio International Paediatric and Congenital Cardiac Code intermittent positive pressure ventilation infrared Ionising Radiation Medical Exposure Regulations infundibular septum The International Society for Nomenclature of Paediatric and Congenital Heart Disease intravenous; innominate vein inferior vena cava; interventricular communication interventricular septum interventricular septum in diastole interventricular septum in systole

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JET LA LAA LAD LAO LAP LAS LAVV LBBB LCA LCC LCCA LCOS LCS LCX LIVC LLPV LMCA LMWH LPA LPM LPV LSCA LSCV LSVC LT LUPV LV LVEDP LVEDV LVH LVIDd LVIDs LVNC LVOT LVOTO LVPWd LVPWs MA MAP MAPCAs mBT MCS MDT MECC MIP mLV

junctional ectopic tachycardia left atrium left atrial appendage; left aortic arch left anterior descending (coronary artery) left anterior oblique left atrial pressure lung allocation score left atrioventricular valve left bundle branch block left coronary artery; left carotid artery left coronary cusp (of the aortic valve) left common carotid artery low cardiac output state left coronary sinus left circumflex (coronary artery) left inferior vena cava left lower pulmonary vein left main coronary artery low-molecular-weight heparin left pulmonary artery litres per minute left pulmonary vein left subclavian artery left superior caval vein left superior vena cava lateral tunnel left upper pulmonary vein left ventricle left ventricular end-diastolic pressure left ventricular end-diastolic volume left ventricular hypertrophy left ventricular internal diameter in diastole left ventricular internal diameter in systole left ventricular non-compaction left ventricular outflow tract left ventricular outflow tract obstruction left ventricular posterior wall in diastole left ventricular posterior wall in systole maximum amplitude mean arterial pressure major aortopulmonary collateral arteries modified Blalock-Taussig mechanical circulatory support multidisciplinary team minimal extracorporeal circulation maximum intensity projection morphological left ventricle

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Abbreviations MOF MPA MPAP MPR MR MRI MRSA mRV MS mTOR MUF MV MVP MVr MVR nAo NBTE NCC NCHDA NEC NeoPV NICOR NIRS NO nPA NSAID NSF NVE NYHA O2 o.d. OPTN OR ORT OS PA PAB PaCO2 PAD PA-IVS PaO2 PAPVC PAPVD PASP PA-VSD PC PCA

multi-organ failure main pulmonary artery mean pulmonary artery pressure multiplanar projection mitral regurgitation magnetic resonance imaging methicillin-resistant pí~éÜóäçÅçÅÅìë=~ìêÉìë morphological right ventricle mitral stenosis mammalian target of rapamycin modified ultrafiltration mitral valve mitral valve prolapse mitral valve repair mitral valve replacement neo-aorta non-bacterial thrombotic endocarditis non-coronary cusp (of the aortic valve) National Congenital Heart Disease Audit necrotising enterocolitis neopulmonary valve National Institute for Cardiovascular Outcomes Research near-infrared spectroscopy nitric oxide neopulmonary artery non-steroidal anti-inflammatory drug nephrogenic systemic fibrosis native valve endocarditis New York Heart Association oxygen çãåÉ=áå=ÇáÉ, once daily Organ Procurement and Transplantation Network odds ratio orthodromic reciprocating tachycardia outlet septum pulmonary artery; posteroanterior pulmonary artery band partial pressure of carbon dioxide patent arterial duct pulmonary atresia with intact ventricular septum partial pressure of oxygen partial anomalous pulmonary venous connection partial anomalous pulmonary venous drainage pulmonary artery systolic pressure pulmonary atresia with ventricular septal defect pulmonary component patient-controlled analgesia

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PCWP PD PDA PDE PEARS PEEP PET PFO PGE PHT PICU PL PM PMEA PMVL p.o. POCUS PPHN PPVI PRA PRIMACORP PS PT PTFE PV PVC PVE PVL PVR PW q.d.s. QIP Qp Qs RA RAA RACHS-1 RAO RAP RAVV RBBB RBCA RCA RCC RCCA RCS

pulmonary capillary wedge pressure peritoneal dialysis patent ductus arteriosus phosphodiesterase personalised external aortic root support positive end-expiratory pressure positron emission tomography; polyethylene terephthalate patent foramen ovale prostaglandin E pulmonary hypertension paediatric intensive care unit posterior leaflet (of the tricuspid valve) perimembranous para-methoxy-N-ethylamphetamine posterior mitral valve leaflet éÉê=çë, by mouth point-of-care ultrasound persistent pulmonary hypertension of the newborn percutaneous pulmonary valve implantation panel reactive antibody PRophylactic Intravenous use of Milrinone After Cardiac OpeRation in Pediatrics pulmonary stenosis pulmonary trunk polytetrafluoroethylene pulmonary vein; pulmonary valve; pulmonary venous. polyvinyl chloride prosthetic valve endocarditis paravalvar leak pulmonary vascular resistance; pulmonary valve replacement pulsed wave èì~íÉê=ÇáÉ=ëìãÉåÇìã, four times a day quality improvement programme pulmonary blood flow systemic blood flow right atrium right atrial appendage; right aortic arch Risk Adjustment for Congenital Heart Surgery right anterior oblique right atrial pressure; retrograde autologous priming right atrioventricular valve right bundle branch block right brachiocephalic artery right coronary artery; right carotid artery right coronary cusp (of the aortic valve) right common carotid artery right coronary sinus

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Abbreviations REV RIJV RLPV RMPV ROTEM® RPA rpm RPV RRT RSCA RSVC RUPV RV RVEDP RVEDV RVEDVi RVESVi RVH RVOT RVOTO SAM SAN SaO2 Sats SCPC SCV SFA SIRS SL SMR SMT SPECT SSFP STJ STS sTV SV SV ASD SVC SvO2 SVR TA TAH TAP TAPSE TAPVC TAPVD

réparation à l’etage ventriculaire right internal jugular vein right lower pulmonary vein right middle pulmonary vein rotational thromboelastometry right pulmonary artery revolutions per minute right pulmonary vein renal replacement therapy right subclavian artery right superior vena cava right upper pulmonary vein right ventricle right ventricular end-diastolic pressure right ventricular end-diastolic volume right ventricular end-diastolic volume indexed right ventricular end-systolic volume indexed right ventricular hypertrophy right ventricular outflow tract right ventricular outflow tract obstruction systolic anterior motion (of the mitral valve) sinoatrial node arterial oxygen saturation oxygen saturation levels superior cavopulmonary connection superior caval vein superficial femoral artery systemic inflammatory response syndrome septal leaflet (of the tricuspid valve) supramitral ring septomarginal trabeculation single photon emission computed tomography steady-state free precision sinotubular junction Society of Thoracic Surgeons straddling tricuspid valve stroke volume sinus venosus atrial septal defect superior vena cava mixed venous saturation systemic vascular resistance truncus arteriosus; tricuspid atresia total artificial heart transannular patch tricuspid annular plane systolic excursion total anomalous pulmonary venous connection total anomalous pulmonary venous drainage

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TAPVR TAV TCPC TDI t.d.s. TEG® TGA THAM TIMI TNPAI TOE TOF TPN Tr TR TRALI TRV TTA TTE TV TVO Tx TXA UAV uAVSD UNOS VA VACTERL VAD VAP VF VIF V/Q VSD VT VTE VA VS VV WPW ZBUF

total anomalous pulmonary venous return tricuspid aortic valve total cavopulmonary connection tissue Doppler indices íÉê=ÇáÉ=ëìãÉåÇìë, three times a day thromboelastography® transposition of the great arteries tromethamine Thrombolysis in Myocardial Infarction Total NeoPulmonary Artery Index transoesophageal echocardiography tetralogy of Fallot total parenteral nutrition trachea tricuspid regurgitation transfusion-associated lung injury true right ventricle true tricuspid annulus transthoracic echocardiography tricuspid valve; truncal valve true valve orifice transplant tranexamic acid unicuspid aortic valve unbalanced atrioventricular septal defect United Network for Organ Sharing ventriculo-arterial vertebral anomalies, anal atresia, cardiac defects, tracheoesophageal fistula and/or oesophageal atresia, renal and radial anomalies, and limb defects ventricular assist device ventilator-associated pneumonia ventricular fibrillation ventriculo-infundibular fold ventilation/perfusion ventricular septal defect ventricular tachycardia venous thromboembolism veno-arterial ventricular septum vertical vein; veno-venous Wolff-Parkinson-White zero-balance ultrafiltration

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Chapter 1

Congenital cardiac anatomy Robert H. Anderson, Diane E. Spicer

1 • •

What are the embryological origins of the components of the definitive heart?

The primary and secondary heart fields represent the heart-forming area of the mesodermal layer of the embryonic disc. Cardiomyocytes migrate from the primary heart field to produce a linear tube within the pericardial cavity (Figure 1), which is responsible for forming the left ventricle and part of the ventricular septum. Developing right ventricle

Presumptive left ventricle

Developing atrial component

Figure 1. Scanning electron micrograph of a

mouse embryo on the 9th day of development demonstrating an essentially straight linear tube, which is eventually responsible for formation of little more than the definitive left ventricle.

1

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With ongoing development, new material from the second heart field invades the pericardial cavity at both the venous and arterial poles of the linear tube. This is responsible for formation of the atrioventricular canal and the primary atrial chamber at the venous pole, and the primordium of the right ventricle, along with the outflow tract, at the arterial pole (Figure 2). Developing right ventricle

Developing outflow tract

2

Developing left ventricle

Figure 2. Scanning electron micrograph of a mouse embryo during the 10th day of development demonstrating looping of the ventricular component of the linear tube in front of the developing atrial component, produced by ongoing addition of material from the heartforming areas at both the arterial and venous poles. Ballooning from the cavity at the atrial level then produces the atrial appendages (white stars), while ballooning from the ventricular loop produces the apical components of the developing right and left ventricles.

•

Ingrowth at both poles results in lengthening of the tube, which contributes to formation of the ventricular loop. Subsequent to looping, the tube retains a solitary lumen, which is lined with endocardial jelly. At this early stage, the entirety of the tube, including the outflow tract, possesses exclusively myocardial walls.

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• •

The cardiomyocytes forming the walls of the tube have their own phenotype and can be recognised as forming primary myocardium. The definitive atrial and ventricular chambers are formed by expansion of pouches from the cavity of the primary tube, with the newly formed walls built from phenotypically different cardiomyocytes, which give rise to secondary, or chamber, myocardium. Outpouching or ballooning of the primary atrial chamber occurs in a symmetrical fashion and gives rise to the atrial appendages (Figure 2). The ventricular pouches, in contrast, balloon in series, one from the inlet of the ventricular loop, and the other from the outlet (Figure 3).

Dorsal mesocardium

Pharyngeal mesenchyme

3

AV canal

Outlet

Inlet

Figure 3. Episcopic image of a mouse embryo during the 11th day of development demonstrating ballooning of the atrial appendages (large white arrows) in parallel from the atrial component of the primary tube, while the ventricular components are ballooning apically from the inlet and outlet components of the ventricular loop. At this initial stage, the atrioventricular (AV) canal opens exclusively to the inlet part of the loop.

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• •

4

The pouch ballooning from the inlet of the loop will become the apical component of the left ventricle, while the ballooning from the outlet component provides the apical part of the right ventricle. The apical muscular ventricular septum appears concomitant with the formation of the two pouches. By the time the ballooning has taken place, the endocardial jelly has itself undergone a process of endothelial-to-mesenchymal transformation, producing cushions in the atrioventricular canal and throughout the outflow tract. These cushions will eventually remodel to become the cardiac valves. Additional remodelling within the lumen of the initial primary heart tube then permits the right atrium to gain access to the developing right ventricle by expansion of the atrioventricular canal (Figure 4), with the aorta subsequently being transferred to the left ventricle.

Inferior AV cushion

Developing RV

Primary atrial septum

Developing LV

Figure 4. Episcopic image of a mouse embryo during the 12th day of development demonstrating expansion of the atrioventricular (AV) canal, which permits the right atrium to connect directly with the cavity of the developing right ventricle (large white arrow).

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2 • • •

Only after this remodelling has taken place is it possible to close the embryonic interventricular communication, thereby completing the separation of the systemic and pulmonary ventricular blood streams.

Describe the connection of the atrial chambers with the ventricular mass and the ventricles with the arterial trunks The key part of the analysis of congenitally malformed hearts is to describe the arrangement of the ‘segments’ (atrial, ventricular and arterial components) and how they are joined together. Subsequent to remodelling of the embryonic interventricular communication, the cavities of the atrial chambers are in continuity with those of the underlying ventricles, whilst the cavities of the ventricles are continuous with those of the intrapericardial arterial trunks. The walls of the various components, however, are not directly contiguous, due to the presence of ‘connecting segments’, with atrioventricular canal myocardium interposing between the walls of the atrial segment and the inlet of the ventricular loop, while the proximal part of the outflow tract (conus) is supported exclusively by the developing right ventricle (Figure 5). eìã~å=Ô=`~êåÉÖáÉ=ëí~ÖÉ=NP

Left atrium

Right atrium

AV canal Left ventricle

Conus

Figure 5. Episcopic image of a human embryo during

the 6th week of development demonstrating the developing atrioventricular junctions and the proximal part of the outflow tract (conus).

5

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• • • • •

With ongoing development, the myocardium of the atrioventricular canal becomes incorporated into the atrial chambers, forming the vestibules of the tricuspid and mitral valves. The proximal myocardium of the outflow tract (conus) forms the myocardium supporting the arterial roots above their respective ventricles, and is an integral part of the ventricular myocardium. Subsequent to these changes, it is possible to recognise the definitive atrioventricular and ventriculo-arterial junctions, which delimit the extent of the ventricular mass. Hence, the cavities of the atrial chambers connect with those of the ventricles across the atrioventricular junction, and the chambers of the ventricles are in direct connection with those of the arterial trunks. It is less accurate to use the term ‘alignments’ to describe these features, since the cavities of the atrial and ventricular chambers can be aligned one to the other, as in tricuspid atresia, without being connected (Figure 6).

6

Right atrium

Right ventricle

Figure 6. Macroscopic image demonstrating alignment of the right atrium with an incomplete right ventricle in a patient with tricuspid atresia but the absence of connection between the atrial and ventricular cavities.

3 •

What are heterotaxy and isomerism?

Heterotaxy is defined as an abnormal arrangement of the internal thoracic or abdominal organs across the left-right axis of the body.

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•

• • • • • •

Most complex congenital cardiac lesions are found in hearts with the variant of so-called heterotaxy in which there is evidence, in the thorax, of an isomeric arrangement of all or parts of the organs. Isomerism describes the situation in which the right- and left-sided structures within the body are mirror images of each other. The hands are the perfect example of bodily isomerism. In the mirrorimaged arrangement, often described as ‘situs inversus’, all the organs are lateralised, but are positioned in mirror-imaged fashion compared to the usual arrangement. In the isomeric arrangement, seen best in the thoracic organs, the lungs and bronchi, and the atrial appendages, are mirror images of each other in the same individual. Both the isomeric and mirror-imaged variants represent disorders of laterality. The right and left sides of the body develop their individual anatomical features in response to genes located on the left side of the developing embryo, such as Cited2 and Pitx2, and which are prevented from reaching the right side by other genes, such as Lefty2 and Sonic hedgehog. Within the heart, it is only the atrial appendages that respond in differential fashion to these genes, which explains why only the atrial appendages show evidence of isomerism. As emphasised above, the lungs and bronchi are also able to develop in isomeric or mirror-imaged fashion, but this is not the case for the abdominal organs, which can develop in a mirrorimaged or jumbled-up fashion. The syndrome currently described by many as ‘visceral heterotaxy’ is best addressed on the basis of the isomeric arrangement of the lungs, bronchi and atrial appendages, although the isomeric features are not always universally present. For appropriate description of the cardiac findings, analysis should begin with establishment of the presence of isomerism, as opposed to usually arranged or mirror-imaged atrial appendages. This should then be followed by full sequential segment analysis, with particular attention paid to the veno-atrial connections, which can never be anatomically normal in hearts having isomeric appendages, although the patterns of venous return can be quasi-usual or quasimirror-imaged.

7

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4 • • • •

8

•

• •

What is the significance of ventricular looping?

As new material is added to the initial heart tube by ongoing migration to the arterial and venous poles from the heart-forming area, the ventricular component of the tube elongates and turns to the right, which represents ventricular looping. The next stage of ventricular development is ‘ballooning’ of the apical components of the right and left ventricles from the outlet and inlet components of the ventricular loop, respectively. With normal development, this places the right ventricle to the right of the developing left ventricle. Rightward expansion of the atrioventricular canal provides the inlet to the developing right ventricle. This means that, subsequent to the formation of the right ventricular inlet, it is the palmar surface of the right hand that can be placed on the developing septum, such that the fingers are in the outlet and the thumb is in the inlet component. This is called right-handed ventricular topology, and is the consequence of rightward ventricular looping Should the ventricular part of the developing heart tube loop to the left, then in association with leftward expansion of the atrioventricular canal, the situation is produced in which it is the developing left atrium that is placed into continuity with the developing right ventricle, and the right ventricle is then formed in leftward position relative to the left ventricle. In this situation, it is the palmar surface of the left hand, rather than the right, which is placed on the septal surface of the developing right ventricle with the thumb in the inlet and the fingers in the outlet. This produces left-handed ventricular topology (Figure 7). This means that, in almost all patients with usual atrial arrangement and concordant atrioventricular connections, the ventricular mass shows right-handed topology. In patients with concordant atrioventricular connections and mirror-imaged atrial arrangement, however, the ventricular mass shows left-handed topology. It then follows that, when the atrioventricular connections are discordant, there is left-handed topology in the setting of usual atrial arrangement, but right-handed topology with mirror-imaged atrial arrangement. These conventions are the basis for description of segmental anatomy in the approach to analysis promoted by Van Praagh and his colleagues, with the arrangements described as

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1 Congenital cardiac anatomy

Right-handed ventricular topology

Left-handed ventricular topology

Figure 7. Features of right-handed (left panel), as opposed to lefthanded ventricular topology (right panel).

• •

(S,L,*) and (I,D,*), the asterisk representing the topological arrangement of the arterial segment. For those using sequential segmental analysis, it can be presumed that the topological arrangement of the ventricular mass is in keeping with the atrioventricular connections. In the setting of isomerism of the atrial appendages, however, it is necessary always to describe the ventricular topology, since the atrioventricular connections themselves are always mixed when the atrial appendages are isomeric (Figure 8).

9

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Key Questions in CONGENITAL CARDIAC SURGERY

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10

Figure 8. Combinations of atrial arrangement and ventricular topology

that produce the various biventricular atrioventricular connections. When the atrial appendages are isomeric, the atrioventricular connections are always mixed. In this setting, therefore, it is always necessary to specify topology so as to provide a complete description.

5 • • • • •

What is the origin of the pulmonary veins?

The atrial component of the developing heart tube is attached to the pharyngeal mesenchyme through the dorsal mesocardium (Figure 3). At this stage, neither the lungs nor any boundaries between the atrial component of the heart tube and the systemic venous tributaries have been formed. Once the venous valves have formed, it becomes possible to recognise the boundaries of the systemic venous sinus. Associated with this, a strand of tissue forms in the midline of the pharyngeal mesenchyme. Subsequent canalisation of this mid-pharyngeal strand provides a connection between the developing intraparenchymal pulmonary veins and the left atrium, with the newly formed channel opening into the left atrium between the folds showing the dorsal mesocardial connection. This newly formed pulmonary vein opens into the left atrium through a myocardial portal with atrial characteristics. The walls at the site of connection are different from the walls of the systemic venous tributaries. The initial opening of the pulmonary vein is adjacent to the left atrioventricular junction. Only at a much later stage does it become possible to recognise separate openings for the right and left pulmonary veins. Following formation of the separate pulmonary

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•

venous orifices, the superior interatrial fold develops, which provides the superior rim of the oval fossa. The walls of the pulmonary veins possess a myocardial phenotype and have never had any relationship with the walls of the systemic venous sinus (Figure 9).

Superior caval vein

Left superior caval vein

A

Left atrium Venous valve Right atrium

Outflow tract

eìã~å=ÉãÄêóç=Ô=`~êåÉÖáÉ=ëí~ÖÉ=NQ Superior caval vein

B

Left superior caval vein

Dorsal mesocardium

Coloured to show NKX 2.5

Venous valve

Opening of pulmonary vein eìã~å=ÉãÄêóç=Ô=`~êåÉÖáÉ=ëí~ÖÉ=NQ

Coloured to show TBX18

Figure 9. Human embryo sections (at Carnegie stage 14) demonstrating: A) myocardium (using staining of the gene NKX 2.5); and B) walls of the systemic venous tributaries, derived from the sinus venosus (using staining of the gene TBX18). The pulmonary vein opens into the myocardium, with no relationship to the derivatives of the systemic venous sinus. The original images were prepared in collaboration with Professor Antoon F. M. Moorman and Dr.

Aleksander Sizarov, Academic Medical Center, Amsterdam, The

Netherlands, and are reproduced with their permission.

11

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6 • •

• • 12

• • • •

Describe the development of the atrial septum

The first signs of atrial septation is the formation of a ridge in the roof of the atrial component of the heart tube. As it grows towards the orifice of the atrioventricular canal, this first septum (septum primum) carries a cap of mesenchyme on its leading edge. The atrioventricular canal itself is divided into right and left parts by the fusion within its cavity of the superior and inferior atrioventricular cushions. As the primary atrial septum grows towards the cushions, the space between the mesenchymal cap on its leading edge and the cushions represents the primary atrial foramen (foramen primum). With ongoing growth of the primary septum and its mesenchymal cap towards the cushions, there is a concomitant decrease in the size of the primary foramen, which is eventually closed by fusion of the cap with the cushions. By the time the primary foramen has been obliterated, however, the upper edge of the primary septum has broken away from the atrial roof to form the secondary atrial foramen (foramen secundum, Figure 10). As the primary foramen closes, a new mesenchymal structure develops from the dorsal margin of the mesocardium, known as the vestibular spine. With ongoing development, the vestibular spine and the mesenchymal cap muscularise, forming the inferoanterior buttress of the oval fossa (fossa ovale). The primary septum itself then forms the floor of the newly formed oval fossa. Its superior rim is formed by an infolding of the atrial roof between the attachments of the pulmonary veins to the left atrium and the caval veins to the right atrium. The oval foramen (foramen ovale) is the space between the infolded superior interatrial fold and the cranial margin of the primary septum, with the primary septum itself forming a flap valve over the foramen (Figure 11).

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1 Congenital cardiac anatomy Mesenchymal cap

A

Primary septum

Left atrium Right atrium

Atrioventricular canal

Developing LV

Developing RV

Venous valves

B

Secondary foramen Primary septum Primary foramen

Mesenchymal cap

Superior AV cushion

Figure 10. Initial stages of development of the

atrial septum in the human heart: A) growth of the primary septum, with its mesenchymal cap, from the roof of the atrial component of the heart tube; B) growth of the primary septum towards the atrioventricular (AV) cushions, with its upper part breaking down to form the secondary atrial foramen. The primary foramen is the space between the mesenchymal cap and the atrial margins of the atrioventricular cushions. LV = left ventricle; RV = right ventricle.

13

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Key Questions in CONGENITAL CARDIAC SURGERY Vestibular spine

A

Primary septum Mesenchymal cap

Primary foramen

Inferior atrioventricular cushion Venous valves

14

Interventricular communication Pulmonary veins

B

Left SCV

Primary septum

Right atrium

Inferoanterior buttress

Oval fossa

Right ventricle

Figure 11. Later stages of development of the atrial septum in a mouse heart: A) growth of the vestibular spine; B) completion of atrial septation with infolding of the superior atrial roof that forms the cranial margin of the oval fossa (white arrow with black borders). The mesenchymal cap and the vestibular spine have muscularised to form the inferoanterior buttress of the oval fossa. SCV = superior caval vein.

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7 •

1 Congenital cardiac anatomy What is the difference between an atrial septal defect and an interatrial communication? The normal atrial septum has two components: a) b)

•

True atrial septal defects are produced either because of deficiencies or fenestrations of the floor of the oval fossa, or because of inappropriate formation of the anteroinferior buttress, including: a)

b)

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floor of the oval fossa, which is derived from the primary atrial septum; anteroinferior buttress, which is formed by muscularisation of the mesenchymal cap carried on the primary septum and the vestibular spine.

oval fossa (ostium secundum) defects — which represent deficiencies or fenestrations of the floor of the fossa resulting from inappropriate formation of the primary atrial septum. They should be distinguished from persistent patency of the oval foramen (PFO), when the flap valve of the fossa overlaps but fails to fuse with the anterosuperior interatrial fold. Such persistent patency is found in around 25% of normal individuals; vestibular defects — which are much rarer and secondary to improper fusion of the muscularising components of the anteroinferior buttress of the oval fossa (Figure 12).

Interatrial communications represent lesions outside the confines of the atrial septum, including: a)

b)

c)

sinus venosus defects — which are the commonest of these extraseptal communications and are the consequence of an anomalous connection of one or more pulmonary veins to a caval vein, with the pulmonary veins retaining their left atrial connection. Sinus venosus defects can be found in the openings of either the superior or inferior caval veins. On occasion, they can be distant from the atrial orifice of the systemic venous channel (Figure 13); coronary sinus defect — which is the rarest interatrial communication outside the confines of the atrial septum. This lesion permits shunting across the right atrial orifice of the sinus because of fenestration, or absence, of the walls that usually interpose between the cavities of the coronary sinus, or a persistent left superior caval vein, and the left atrium; ostium primum defect — which is an atrioventricular rather than an atrial septal defect.

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A

Deficient flap valve

Perforated flap valve

Vestibular defect

Coronary sinus

16

B

Anterosuperior border

Flap valve

Left atrium

Right atrium

Figure 12. Atrial septal defects: A) true defects within the oval fossa (yellow oval) and a vestibular defect within the anteroinferior buttress; B) persistent patency of the oval foramen, with the flap valve of sufficient size to cover the margins of the fossa (double-headed white arrow) but fails to fuse with the anterosuperior margin, leaving a potential interatrial communication (doubleheaded white arrow with red borders). Shunting across the communication is only possible when right atrial pressure exceeds that in the left atrium.

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1 Congenital cardiac anatomy Anomalously connected pulmonary vein

Venovenous conduit

A

Normal arrangement of the atrial septum LSCV

B

Opening of the coronary sinus

Oval fossa

Figure 13. Interatrial communications outside the atrial septum, including: A) sinus venosus defect, in proximity to the opening of the superior caval vein; and B) coronary sinus defect, which is caused by failure of formation of the walls that normally separate a left superior caval vein (LSCV) or coronary sinus, from the cavity of the left atrium (red dotted lines).

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What are the phenotypic features of an atrioventricular septal defect?

The commonality of the atrioventricular junction, along with the trifoliate configuration of the left atrioventricular valve are the fundamental phenotypic features of an atrioventricular septal defect (AVSD), which is also known as an atrioventricular canal defect. During gestation, the bridging leaflets of the common atrioventricular valve, as typically seen in the atrioventricular septal defect, are derived from the superior and inferior atrioventricular cushions, which when fused separate the atrioventricular canal into the right and left atrioventricular orifices (Figure 14). In the past, the left component of the common atrioventricular valve or junction was usually described as a ‘cleft mitral valve’, which is incorrect. This is because the left half of the persisting common atrioventricular junction is guarded by a trifoliate valve (Figure 14B) rather than a bifoliate valve, even when the common atrioventricular junction itself is divided into separate valvar orifices for the right and left ventricles, as in the case of an AVSD without ventricular septal defect (Figure 15). The building blocks of the left half of the common atrioventricular valve are the same as those producing the aortic leaflet (or anterior leaflet) of the mitral valve in normal hearts. In AVSD, the commonality of the atrioventricular junction and the trifoliate configuration of the left atrioventricular valve are present irrespective of the level of shunting across the septal defect, hence above the valve plane, below the valve plane or both. Comparable arrangements are also found when there is a common valve guarding the common junction, or when the bridging leaflets are themselves fused to produce separate right and left valvar orifices for the right and left ventricles (Figure 16). In most cases, the bridging leaflets float more or less freely within the atrioventricular septal defect. This permits shunting at both atrial and ventricular levels. When the bridging leaflets are themselves fused to the crest of the muscular ventricular septum, the arrangement confines the potential for shunting across the atrioventricular septal defect at atrial level, producing a so-called ‘ostium primum’ defect. Less frequently, the bridging leaflets can be attached to the leading edge of the atrial septum, thus producing an atrioventricular septal defect with exclusively ventricular shunting. In this latter setting, the heart retains the common atrioventricular junction, along with the trifoliate configuration of the left atrioventricular valve. In rare circumstances, the atrioventricular septal defect can close spontaneously. This produces the arrangement of a heart with intact septal structures, but with a common atrioventricular junction and a trifoliate left atrioventricular valve.

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1 Congenital cardiac anatomy A Outflow cushions

Right lateral cushion Subaortic outflow tract

B

Superior AV cushion

Left lateral cushion

Inferior AV cushion Superior bridging leaflet

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Right ventricular leaflets

Inferior bridging leaflet

Left mural leaflet

Figure 14. A) Atrioventricular cushions as seen in a developing mouse embryo sacrificed at embryonic day 12, just prior to fusion of the superior and inferior cushions that lie edge-to-edge within the atrioventricular canal. B) Atrioventricular septal defect with the common atrioventricular junction guarded by a common atrioventricular valve. There is an obvious similarity between the arrangements of the bridging leaflets and the superior and inferior atrioventricular (AV) cushions. The ‘trifoliate’ arrangement of apposition of the left ventricular cushions in the developing mouse heart (white dotted lines) parallels the configuration of the leaflets that guard the left half of the common atrioventricular junction in the specimen with deficient atrioventricular septation. In the developing mouse, however, the outflow tract remains undivided, whereas the subaortic root is committed to the left ventricle in the specimen with an atrioventricular septal defect. Both images are viewed from the ventricular apex looking towards the base of the ventricular mass.

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Key Questions in CONGENITAL CARDIAC SURGERY A

Subaortic outflow tract

Inferior AV cushion

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Subaortic outflow tract

B

Inferior AV cushion

Superior AV cushion

Left lateral cushion

Superior AV cushion

Left lateral cushion

Figure 15. A) Atrioventricular septal defect with separate valvar orifices for the left and right ventricles (‘ostium primum defect’); and B) a normal heart in mouse embryos sacrificed at embryonic day 15.5. Both short-axis images are viewed from the ventricular apex looking towards the base. The mouse with the atrioventricular septal defect has maintained the trifoliate configuration of the left half of the common atrioventricular junction despite the commitment of the aortic root to the left ventricle, whereas the normal mouse, subsequent to closure of the embryonic interventricular communication, has formed a bifoliate left valve. The black dotted line shows the line of fusion between the superior and inferior atrioventricular cushions in the normal mouse, whereas the left ventricular components of the cushions have remained unfused in the mouse with the atrioventricular septal defect.

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1 Congenital cardiac anatomy Superior bridging leaflet A

Left mural leaflet Superior bridging leaflet B

Left mural leaflet

Right anterosuperior leaflet Right inferior leaflet

Inferior bridging leaflet Right anterosuperior leaflet Right inferior leaflet

Inferior bridging leaflet

Figure 16. The images show the commonality of the atrioventricular junction in hearts with an atrioventricular septal defect, when the junction is guarded by: A) a common valve; or B) when the bridging leaflets have themselves fused to produce separate valvar orifices for the right and left ventricles (star), and are additionally fused to the crest of the muscular ventricular septum. The area previously considered to represent a ‘cleft’ in the mitral valve (double-headed arrow in B) can be seen to be the zone of apposition between the left ventricular components of the bridging leaflets (compare with double-headed arrow in A). The dotted white lines shown the location of the crest of the muscular ventricular septum.

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What is the origin of the membranous septum?

The normal ventricular septum is almost exclusively a muscular entity, with a small part within the left ventricular outflow tract that is fibrous (known as the membranous septum). Most often, it is crossed on its right ventricular aspect by the hinge of the septal leaflet of the tricuspid valve, which divides it into atrioventricular and interventricular components (Figure 17). Membranous septum Aorta

Mitral valve

Atrioventricular component

Left ventricular outflow tract

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Interventricular component

Hinge of TV Muscular septum

Figure 17. ‘Four-chamber’ section through the

aortic root, with the non-coronary sinus and its leaflet removed. The hinge of the septal leaflet of the tricuspid valve (TV) crosses the membranous septum, dividing it into its atrioventricular and interventricular components.

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During normal development, the expansion of the atrioventricular canal allows the connection of the developing right atrium with the right ventricle. During this process, the ventricular outflow tract, which is separating to form the aortic and pulmonary roots, remains supported above the cavity of the right ventricle. In order to close the ventricular septum, the developing aortic root, still supported above the cavity of the right ventricle, needs to come into continuity with the cavity of the left ventricle. This is achieved by creating a shelf within the cavity of the right ventricle by fusion of the proximal parts of the cushions dividing the

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1 Congenital cardiac anatomy outflow tract into the aortic and pulmonary components. At the same time, this process begins to transfer the larger part of the persisting interventricular communication into the outflow tract for the left ventricle (Figure 18). A Aortic root

Left ventricle

Tertiary interventricular communication B

Secondary interventricular communication

Aortic root

Tubercles of AV cushions

Left ventricular outflow tract

Figure 18. Process of transfer of the aortic root to the left ventricle in the developing mouse heart: A) embryonic day 13.5, where the greater part of the embryonic interventricular communication is remodelling so as to connect the aortic root with the left ventricle. This can be considered to represent the secondary interventricular communication. A persisting third component of the communication is then seen between the rightward part of the aortic root and the right ventricle; B) embryonic day 14.5, where this communication is closed by fusion of so-called tubercles derived from the superior and inferior atrioventricular (AV) cushions. This produces the membranous part of the ventricular septum and commits the secondary interventricular communication to the outflow tract for the left ventricle.

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This part of the embryonic interventricular communication can be considered as a secondary channel, since part of the initial, or primary, interventricular communication has already been remodelled to form the inlet of the right ventricle. Subsequent to the remodelling of the secondary embryonic interventricular communication to become the subaortic outflow tract, a persisting third part of the communication remains as a channel between the cavities of the right and left ventricles. It is this channel that is then closed by growth of so-called tubercles from the atrioventricular cushions to produce the membranous part of the ventricular septum. When initially closed, the septal leaflet of the tricuspid valve has yet to delaminate from the surface of the ventricular septum. It is only subsequent to the delamination of this leaflet that it becomes possible to recognise the atrioventricular and interventricular components of the membranous septum.

Is there a muscular outlet septum in the normal heart?

There is no muscular septal component interposed between the ventricular outflow tracts in the normal heart. Moreover, by virtue of the wedging of the aortic root between the mitral valve and the ventricular septum, the inlet of the right ventricle is separated from the outlet, rather than the inlet, of the left ventricle. This is despite the fact that the proximal parts of the outflow cushions fuse to produce a shelf in the roof of the right ventricle. This process provides a channel between the developing aortic root and the cavity of the left ventricle (Figure 19). As part of this process, the shell of these proximal cushions achieves a myocardial phenotype. At the same time, however, the core of the cushions attenuates. The disappearance of the core of the cushions then produces an extracavitary area that interposes between the muscularising shell and the developing sinuses of the aortic root. The muscularising shell of the proximal cushions, therefore, becomes the freestanding infundibular sleeve. This lifts the pulmonary root away from the base of the ventricular mass. The formation of the freestanding infundibular sleeve makes it possible to remove the entirety of the pulmonary root and use it as an autograft in the Ross procedure. This would not be possible in the normal heart had there been formation of a muscular outlet septum.

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1 Congenital cardiac anatomy A Developing aortic root

Secondary interventricular communication

Muscularising parietal cushion Right ventricle B

Septal cushion Pulmonary root

Aortic root

Right atrium

Right ventricle Closing interventricular foramen

Figure 19. Stages in development of the freestanding infundibular sleeve of the right ventricle: A) fusion of the proximal cushions at embryonic day 13.5. This process builds a shelf in the roof of the right ventricle, committing the aortic root to the left ventricle through the secondary interventricular communication; B) oblique subcostal equivalent section at embryonic day 14.5, at the stage of closure of the tertiary interventricular communication. The shell of the muscularising proximal cushion mass is transforming into the subpulmonary infundibulum (black dashed line). The core of the cushion mass (white star with red borders) is attenuating to produce an extracavitary area between the developing infundibular sleeve and the forming sinuses of the aortic root.

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Is a ventricular septal defect (VSD) the same as an interventricular communication?

During the development of the heart, there is extensive remoulding of the initial embryonic interventricular communication. The first, or primary, interventricular communication is the portal for passage of all the blood entering the developing left ventricle ultimately to reach the undivided outflow tract. The defects originating from a primary interventricular communication include: a) b)

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defects in the setting of double-inlet left ventricle with doubleoutlet from the right ventricle; defects seen with straddling and overriding of the tricuspid valve.

The secondary interventricular communication is the embryonic interventricular channel underneath both outflow tracts where, during the normal expansion of the atrioventricular canal and formation of the right ventricular inlet, they remain supported above the cavity of the developing right ventricle. Defects originating from the secondary interventricular communication are found between the ventricles in the setting of double-outlet right ventricle. The tertiary interventricular communication is the route by which the rightward margin of the developing aortic root remains in communication with the cavity of the right ventricle, during the process of connection of the aortic root with the left ventricular cavity, with the secondary interventricular communication remoulded to become the left ventricular outflow tract. The tertiary interventricular communication is eventually closed during normal development by formation of the membranous part of the septum from the so-called tubercles of the atrioventricular cushions. Failure to close the tertiary communication results in production of a perimembranous ventricular septal defect. It follows that the channels found in the setting of double-outlet right ventricle, double-inlet left ventricle with DORV and perimembranous VSD represent the different stages of the remoulding of the embryonic interventricular communication and therefore cannot be considered all the same ventricular septal defects.

Describe the defects that open into the inlet of the right ventricle

There are four phenotypically different defects that open to the inlet of the right ventricle. The location of the atrioventricular conduction axis differs markedly in all of them.

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1 Congenital cardiac anatomy

• • • •

It is now well established that the ‘septum of the atrioventricular canal’ is the muscularising vestibular spine. The formation of this structure during normal development, along with its fusion with the atrioventricular cushions, divides the initial atrioventricular canal into the orifices of the tricuspid and mitral valves. One type of inlet defect results from a process of malalignment of the muscular component of the interventricular septum, by virtue of incomplete expansion of the atrioventricular canal, relative to the atrial septum. This defect is also perimembranous, since it is characterised by fibrous continuity between the leaflets of the mitral and tricuspid valves. It is found in the setting of straddling and overriding of the tricuspid valve. Because of the septal malalignment, the atrioventricular conduction axis arises from an anomalous posteroinferior atrioventricular node (Figure 20).

Triangle of Koch in atrial septum

Straddling tricuspid valve

Malaligned muscular septum

Figure 20. Right ventricular inlet defect found in the setting of straddling and overriding of the tricuspid valve. It is a perimembranous defect with malalignment between the atrial septum and the muscular ventricular septum. The atrioventricular conduction axis (red dashed line) no longer originates from the regular atrioventricular node (red star with white borders). Instead, it takes origin from an anomalous inferior node (white star with red borders).

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Apex of triangle of Koch

A

Medial paillary muscle

Muscular inlet defect

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B

Perimembranous inlet defect

Triangle of Koch deviated inferiorly

Figure 21. Macroscopic images demonstrating the arrangement of the atrioventricular conduction axis (red dashed line) in the setting of defects opening to the inlet of the right ventricle with: A) exclusively muscular borders; and B) perimembranous. The perimembranous defect shown in B) differs from the one shown in Figure 20 because of the presence of alignment between the atrial septum and the inferior part of the muscular ventricular septum.

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1 Congenital cardiac anatomy

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A second type of inlet defect is where the opening into the inlet of the right ventricle exclusively has muscular margins. In these instances, the conduction axis courses in cranial fashion relative to the defect. A third type is the one represented by perimembranous defects extending to open to the inlet of the right ventricle. They are characterised by a fibrous continuity between the leaflets of the mitral and tricuspid valves forming their posterior margin but with alignment between the atrial and muscular ventricular septal structure. In this defect, the conduction axis is deviated inferiorly but it continues to arise from a regular atrioventricular node at the apex of the triangle of Koch. The triangle is itself deviated inferiorly due to the hypoplasia of the inferior component of the muscular ventricular septum (Figure 21). The fourth type is an atrioventricular septal defect opening directly to the inlet of the right ventricle with the potential only for ventricular shunting. This occurs when the bridging leaflets of the common atrioventricular valve abut against the leading edge of the atrial septum during ventricular systole. In this instance, the atrioventricular conduction axis will arise from an inferiorly deviated atrioventricular node.

What is the phenotypic feature of a supracristal ventricular septal defect?

For some time, ventricular septal defects were categorised on the basis of being supracristal or infracristal. Examination of the defects distinguished in this fashion shows a lack of logic, since rather than the defects opening in different fashion to the right ventricle, it is the structure nominated as the ‘crista’ that varies. The majority of supracristal defects open into the right ventricle between the limbs of the septomarginal trabeculation (SMT), also known as the septal band (Figure 22A). In this setting, the feature nominated as the ‘crista’ is the myocardial structure produced by fusion of the caudal limb of the septal trabeculation with the ventriculo-infundibular fold, the latter structure being derived from the inner heart curvature. The feature nominated as the ‘crista’ in an infracristal defect is the supraventricular crest. This is formed by the freestanding subpulmonary muscular infundibulum, along with the right ventricular margin of the inner heart curvature, which is known as the ventriculoinfundibular fold (Figure 22B). The differences between the appearance of the two defects is now well explained on the basis of the development of the normal right ventricular outflow tract. The normal supraventricular crest is formed in its larger part by muscularisation of the proximal outflow cushions, which subsequently become the freestanding subpulmonary infundibulum (Figure 23A).

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Key Questions in CONGENITAL CARDIAC SURGERY A Aortopulmonary continuity

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Ventriculo-infundibular fold

B

Supraventricular crest

Tricuspid-mitral continuity

Septal defect

Septomarginal trabeculation Septal defect

Septomarginal trabeculation

Figure 22. Ventricular septal defects defined by the ‘crista’, rather than location: A) in the so-called ‘supracristal defect’, the myocardial structure identified as the ‘crista’ is produced by fusion of the ventriculo-infundibular fold with the caudal limb of the septomarginal trabeculation (white star with red borders). The phenotypic feature of this defect is the fibrous continuity between the leaflets of the aortic and pulmonary valves in the roof of the defect; B) in the so-called ‘infracristal defect’, the structure identified as the ‘crista’ is the supraventricular crest.

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1 Congenital cardiac anatomy Muscularised outflow cushions

Septal defect

A

Tricuspid-mitral continuity Hypoplastic non-muscularised

B outflow cushions

Septomarginal trabeculation

Pulmonary root

Aortic root

Inner heart curvature

Septal defect

Septomarginal trabeculation

Figure 23. A) The defect described by some as being ‘infracristal’ lies inferior to the structure derived by muscularisation of the proximal outflow cushions. B) In the defect described by some as being ‘supracristal’, the proximal outflow cushions have failed to muscularise. The difference between the two defects, therefore, reflects the varying maturation of the proximal outflow cushions, rather than the way the defects open relative to the ventricular septum.

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This explains the phenotypic feature of the supracristal defect, which is better described as being doubly committed and juxta-arterial. The distinguishing feature is the fibrous continuity between the leaflets of the aortic and pulmonary valves.

What are the phenotypic features of tetralogy of Fallot?

Tetralogy of Fallot is a combination of four morphological features, namely an interventricular communication, biventricular connection of the aortic root, subpulmonary stenosis and right ventricular hypertrophy. There is a wide range of combinations of these morphological features, resulting in no two cases being morphologically identical. For some time, it was thought that anterocephalad malalignment of the muscular outlet septum or its fibrous remnant, was the unifying feature of the tetralogy spectrum. Such a feature, however, is to be found not only in the setting of tetralogy of Fallot but also in an Eisenmenger ventricular septal defect, which is a perimembranous outlet defect associated with overriding of the pulmonary trunk. The additional finding required to produce the phenotypical feature of tetralogy is the anomalous formation of the septoparietal trabeculations. In the tetralogy spectrum, the trabeculations are usually hypertrophied. It is the combination of these two features that produces the characteristic narrowing at the mouth of the subpulmonary infundibulum (Figure 24). Hearts with this phenotypical feature can show morphological variability in terms of the: a)

b) c) d)

type of interventricular communication which can: i) be perimembranous; ii) have a muscular posteroinferior rim; iii) be doubly committed and juxta-arterial; extent of override of the aortic root; degree of obstruction of the subpulmonary outflow tract; right ventricular hypertrophy — which is recognised to be a haemodynamic consequence of the subpulmonary narrowing.

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1 Congenital cardiac anatomy A

Malaligned outlet septum Pulmonary root

Aortic root

Unobstructed outflow tract

B

Malaligned outlet septum

Septoparietal trabeculations

Pulmonary root Aortic root

Subpulmonary obstruction

Septoparietal trabeculations

Figure 24. Images demonstrating malalignment of the muscular outlet septum, which in isolation, does not produce the phenotypical feature of tetralogy of Fallot: A) Eisenmenger defect where the subpulmonary outflow tract is unobstructed despite the presence of malalignment of the outlet septum, along with well-formed septoparietal trabeculations; B) tetralogy of Fallot, characterised by the phenotypical narrowing between the malaligned muscular outlet septum and the septoparietal trabeculations.

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What are the phenotypical characteristics of defects associated with systemic-to-pulmonary collateral arteries?

In the setting of pulmonary atresia, the pulmonary arterial supply is derived most frequently either through a persistently patent arterial duct or via systemic-to-pulmonary collateral arteries (Figure 25). Systemic-to-pulmonary is a better descriptor of the collateral arteries than major aortopulmonary collateral arteries (MAPCAs), since the collateral arteries can arise not only from the aorta but also from the coronary or brachiocephalic arteries. These two sources hardly ever supply the same lung. Indeed, it is a good working rule that, if systemic-to-pulmonary collateral arteries are found supplying one or both lungs, the arterial duct will be absent, unless it provides the sole supply to one lung through a discontinuous intrapericardial pulmonary artery. The pulmonary arterial supply via the persistently patent arterial duct is almost without exception found in pulmonary atresia with intact ventricular septum. Pulmonary supply via an arterial duct can also be found in cases of pulmonary atresia with ventricular septal defect, as in the context of: a) b) c)

transposition of the great arteries; congenitally corrected transposition of the great arteries; isomerism with a VSD.

Instead, the supply of blood to the lungs through systemic-topulmonary arteries is found with frequency only with pulmonary atresia in the context of tetralogy of Fallot. It is a subset of the hearts that collectively can be described as pulmonary atresia with ventricular septal defect. The pulmonary arterial supply in tetralogy with pulmonary atresia can also be through a persistently patent arterial duct. If via a duct, however, there will be a unifocal supply to all the bronchopulmonary segments. Pulmonary arterial supply through systemic-to-pulmonary collateral arteries is multifocal, since hardly ever does a solitary collateral artery supply all the bronchopulmonary segments. Instead, the supply is either direct, or else through anastomoses with intrapericardial pulmonary arteries. In rare circumstances, the pulmonary arterial supply in tetralogy with pulmonary atresia can be through an aortopulmonary window, or via coronary arterial fistulous communications. Discontinuous pulmonary arteries can be fed through bilateral arterial ducts, or through a duct

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1 Congenital cardiac anatomy A Confluent intrapericardial pulmonary arteries

Aorta

B

Arterial duct

Systemic-to-pulmonary collateral arteries

Aorta

Confluent intrapericardial pulmonary arteries

Figure 25. Images demonstrating systemic-to-pulmonary collateral

arteries in the setting of pulmonary atresia, with a supply through: A) a persistently patent arterial duct to confluent intrapericardial pulmonary arteries (where the intrapericardial pulmonary arteries supply all of the bronchopulmonary segments in a unifocal fashion); and B) systemic-topulmonary collateral arteries arising from the descending intrathoracic aorta, with coexisting confluent intrapericardial pulmonary arteries, which anastomose with the collateral arteries. In these instances, the intrapericardial arteries have a limited multifocal supply to some, but not all, of the bronchopulmonary segments.

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in one lung and systemic-to-pulmonary collateral arteries in the other lung. In the past, arterial ducts with an unusual origin were described as ‘arteries of the 5th pharyngeal arch’. It is now known that the socalled ‘5th arch’ does not exist. It remains to be proven as to whether the systemic-to-pulmonary arteries are hypertrophied bronchial arteries. It is a mistake to seek to distinguish the intrapericardial pulmonary arteries as being ‘native’, as the systemic-to-pulmonary collateral arteries are equally ‘native’.

What is double-outlet right ventricle?

Double-outlet right ventricle (DORV) is the situation in which the larger part of both arterial roots are supported by the morphologically right ventricle. The definition of the arrangement existing when both arterial trunks arise from the morphological right ventricle has long been contentious. The resolution of these discussions has been provided by the concept of the ‘morphological method’, which stated that one variable feature in the heart should not be defined on the basis of another feature that is itself variable. As a result, only the proportion of the overriding arterial trunk supported by the right, as opposed to the left ventricle, is the determinant of the precise ventriculo-arterial connection, and DORV is no more than one of the possible ventriculo-arterial connections in the setting of overriding of either the aortic or the pulmonary root, or in some instances both arterial roots. In this setting, the channel overridden by the arterial root will have right and left ventricular borders. Whether the root is supported predominantly by the right ventricle, and hence in the setting of double outlet, can be determined by whether the surgeon considers that they are able to close the right ventricular border. If this is the case, the ventriculo-arterial connections will have been either concordant or discordant and the surgeon will have closed the ‘ventricular septal defect’. If the surgeon considers that they have had to tunnel the right ventricular border of the overriding root to the crest of the muscular ventricular septum, then the ventriculo-arterial connection will initially have been that of double-outlet right ventricle. The leftward border of the defect will then have been an interventricular communication, rather than a ‘ventricular septal defect’ (Figure 26).

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1 Congenital cardiac anatomy A

B

C

Figure 26. Relative position of the plane of an interventricular

communication (red dotted line) and the patch (in yellow) used to close it, where: A) the aorta is committed to the left ventricle in a simple ventricular septal defect and the patch coincides with the plane of the interventricular communication; B) there is 50% aortic override in tetralogy of Fallot and the plane of the interventricular communication is to the left of the plane of the patch. The patch includes a small portion or the right ventricular cavity to redirect the flow from the left ventricle to the aorta; and C) the aorta is committed to the right ventricle and the plane of the interventricular communication and that of the patch are on the opposite sides of the aortic root, as in double-outlet right ventricle. A large portion of the right ventricular cavity is required to redirect the flow from the left ventricle to the aorta.

17 •

•

What is a functionally univentricular heart?

A functionally univentricular heart is characterised by an incomplete ventricle, which is of insufficient size to support independently either the pulmonary or the systemic circulation, such as with a: a) b)

dominant left ventricle and an incomplete right ventricle; dominant right ventricle and an incomplete left ventricle.

Very few congenitally malformed hearts are found with a solitary chamber within the ventricular mass. If found, such solitary ventricles are of indeterminate ventricular morphology, although occasionally

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hearts can be found with a dominant right ventricle when the accompanying left ventricle is so small as to escape clinical detection. The majority of hearts that, in the past, were described as ‘single ventricles’ have a dominant left ventricle, with incomplete formation of the right ventricle due to absence of its inlet component. This is found either when both atrioventricular junctions are connected to the dominant left ventricle (double-inlet left ventricle, [DILV]), or when there is an absence of either the right-sided or the left-sided atrioventricular connection. The latter arrangement is seen most frequently in the setting of tricuspid atresia. These hearts with a double-inlet ventricle, or with absence of either the right-sided or the left-sided atrioventricular connections, together make up the group of hearts with univentricular atrioventricular connections. Hearts with biventricular atrioventricular connections can also produce a functionally univentricular arrangement. This occurs when either the morphological right or the morphological left ventricle, although normally constituted, is too small as to support the systemic or the pulmonary circulation, such as hypoplastic left heart syndrome (HLHS), pulmonary atresia with intact ventricular septum (PA-IVS) and hypoplastic right ventricle, or severely unbalanced AVSD. Other hearts with complex circulatory patterns may be deemed to be functionally univentricular and hence better suited for surgical repair by means of construction of the Fontan circulation.

What is the phenotypic feature of tricuspid atresia?

Atresia, when defined literally, is either the absence or abnormal closure of a bodily communication. Both of these phenotypes are to be found in the setting of tricuspid atresia, since the lesion can be produced either by an imperforate tricuspid valve or by the absence of the right atrioventricular connection in the setting of a usual atrial arrangement with the left atrium connected to a dominant left ventricle (Figure 27). The arrangement with the absence of the right atrioventricular connection is by far the commonest variant found in patients with tricuspid atresia. By virtue of the absence of the right atrioventricular connection, the right ventricle in this setting is incomplete, since it lacks its inlet component. The arrangement as seen in postnatal life reflects the situation as seen during the initial stages of normal development, when the atrioventricular canal is supported exclusively by the developing

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1 Congenital cardiac anatomy A Left atrium

Left ventricle

Right atrium

Hypoplastic right ventricle

Imperforate tricuspid valve B Left atrium

Right atrium

Left ventricle

Absent AV connection

Incomplete right ventricle

Figure 27. Macroscopic images demonstrating the difference between

tricuspid atresia produced by: A) an imperforate valve; and B) absence of the right atrioventricular (AV) connection.

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Aorta

Subpulmonary infundibulum

Absent AV connection

Incomplete right ventricle

A

Right atrium

40

Undivided outflow tract

B

Developing right atrium

Absent connection Embryonic IVC Right ventricular apical component

Figure 28. Images demonstrating the commonest variant of tricuspid atresia, where: A) the right atrioventricular (AV) connection is absent; and B) the atrioventricular canal remains supported exclusively by the developing left ventricle. The developing right ventricle at this early stage receives its blood through the embryonic interventricular communication (IVC), although it already possesses its apical component.

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morphological left ventricle, and the developing right ventricle gives rise to the entirety of the developing outflow tract (Figure 28). The differences in morphology between the two phenotypic variants of tricuspid atresia serve to illustrate the differences between the hypoplastic right ventricle found in the setting of the imperforate valve, and the incomplete ventricle found in the absence of the right atrioventricular connection. Both variants, however, produce functionally univentricular hearts.

What is the developmental background of common arterial trunk?

The phenotypic feature of common arterial trunk is the commonality of the ventriculo-arterial junction, rather than the presence of a common intrapericardial arterial component or ‘truncus’. The essential feature of common arterial trunk, therefore, is persistence of the undivided embryonic ‘conus’, specifically the intermediate and proximal components of the outflow tract, rather than lack of division of its distal component (Figure 29). When the term ‘persistent truncus arteriosus’ was first introduced, it was used to describe the distal part of the developing outflow tract, which is separated by the development of a protrusion from the dorsal wall of the aortic sac to produce the intrapericardial arterial trunks. It is the manner of separation of the distal part of the outflow tract that, traditionally, has been used to subcategorise the examples of common arterial trunk. In the initial approach, four types were described by Collett and Edwards according to the origin of the pulmonary arteries. Type IV was subsequently recognised to be a solitary arterial trunk, rather than a common trunk, since it was defined on the basis of absence of the intrapericardial pulmonary arteries. In the revised version proposed by Van Praagh and Van Praagh, Types I and II of the Collett and Edwards classification were unified as Types 1 and 2. The Van Praaghs then introduced new Types 3 and 4, to account for variants with discontinuous pulmonary arteries and hypoplasia of the aortic component of the trunk, respectively. At the same time, the Van Praaghs pointed out that a simpler approach was to separate the variants according to the dominance of the aortic as opposed to the pulmonary component of the common arterial trunk. The concept of aortic as opposed to pulmonary dominance provides a much simpler categorisation. It is pulmonary dominance that is

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Systemic arteries

Pulmonary arteries Common VA junction

Coronary artery

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Hypoplastic aortic component

Common AV junction

LSCA

B

Dominant pulmonary component

Arterial duct

Common VA junction

Figure 29. Embryological images demonstrating two embryonic mice genetically modified so as to produce common arterial trunk, defined on the basis of a trunk that gives rise directly to the systemic, pulmonary and coronary arteries: A) following knock-out of the Tbx1 gene, there has been no separation of the distal outflow tract, so that the trunk has an aortic dominance; B) following disruption of the Furin enzyme, the aortopulmonary septum (white arrow) has grown so as to divide the distal outflow tract disproportionately in favour of the pulmonary component of the trunk. The aortic arch is interrupted (white star with red borders), with the descending aorta fed through the persistently patent arterial duct. The left subclavian artery (LSCA) arises from the descending aorta. AV = atrioventricular; VA = ventriculo-arterial.

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accompanied by interruption of the aortic arch or severe coarctation. When there is aortic dominance, it then becomes necessary to describe with precision the origin of the pulmonary arteries. In the majority of cases, the pulmonary arteries arise in close proximity to each other from the posterior or leftward component of the aortic dominant trunk, meaning that frequently they are described as ‘Type 1½’ using traditional classifications. The origin of the pulmonary arteries, however, can involve one of the sinuses of the truncal root, whilst the right and left pulmonary arteries can cross as they extend towards the mediastinum.

What is transposition?

Transposition literally means ‘placed across’ and it refers to the placement of the arterial roots across the ventricular septum, such that they arise from morphologically inappropriate ventricles. Irrespective of the atrioventricular connections, which can be concordant, discordant, mixed in the setting of isomeric atrial appendages, or univentricular, the transposition is always ‘complete’ in the sense that each of the arterial trunks is completely placed across the septum. The commonest variant is now simply described as ‘transposition’. In most instances, it is usually qualified to include ‘of the great arteries’. The latter part, however, is redundant. The discordant ventriculo-arterial connections can be found with various relationships of the arterial trunks and with varied infundibular morphology. The combination of discordant ventriculo-arterial connections with concordant atrioventricular connections can itself be found in usual or mirror-imaged variants. Most usually, the aortic root is found anteriorly and to the right. It can, nonetheless, be found in a leftward location. The latter relationship is the rule when transposition is found in its mirror-imaged variant. It is inappropriate, therefore, to use ‘d-transposition’ as being the default option for transposition. The presence of a ventricular septal defect, or obstruction of the ventricular outflow tracts, are the associated malformations of greatest clinical significance. The developmental defect underscoring the production of the discordant ventriculo-arterial connections is the fusion of the major outflow cushions in the outflow tract in a straight as opposed to their normal spiralling fashion (Figure 30). The fusion of the outflow cushions in a straight as opposed to spiralling fashion serves to join the rightward component of the

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Aorta

Pulmonary trunk

A

Right ventricle

Spiralling cushions

44

Aorta

Pulmonary trunk

B

Parallel cushions Right ventricle

Figure 30. Embryological images demonstrating the arrangement of the outflow cushions in a: A) control mouse; and B) mouse with knock-out of the Ptx1 gene. Ongoing development in the mice with the knock-out gene produces either transposition or double-outlet right ventricle with subpulmonary interventricular communication. It is the fusion of the outflow cushions in a straight as opposed to spiralling fashion that underscores these changes.

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proximal outflow tract to the aortic component of the aortic sac, and the leftward component to the pulmonary component. It is then the leftward component of the outflow tract, which is closest to the embryonic interventricular communication that is transferred to the developing left ventricle, thus producing the discordant ventriculoarterial connections.

How can transposition be congenitally corrected?

When discordant ventriculo-arterial connections (transposition) are associated with concordant atrioventricular connections, the systemic and pulmonary circulations are arranged in parallel, rather than in series. Connections across the atrioventricular junctions, in a discordant fashion as opposed to concordant, serve to ‘correct’ the discordant ventriculo-arterial connections. By virtue of the double discordance, the circulations are then again in series, even though the arterial trunks are supported by morphologically inappropriate ventricles. This occurs as a consequence of looping of the ventricular component of the heart tube in a mirror-imaged fashion compared to normal. In the usual situation, the ventricular component of the heart tube loops to the right. Expansion of the atrioventricular canal then places the developing right atrium in communication with the developing right ventricle, hence ensuring the formation of concordant atrioventricular connections. If the ventricular component of the heart tube should loop to the left, in contrast, expansion of the atrioventricular canal will similarly take place in a leftward direction. This will serve to connect the developing left atrium to the right ventricle, which is derived from the outlet component of the heart tube. It will be positioned in a left-sided position subsequent to leftward ventricular looping. In the setting of a mirror-imaged atrial arrangement, it will be rightward looping of the ventricular component of the heart tube that will produce discordant, rather than concordant, atrioventricular connections. Almost always, the formation of discordant atrioventricular connections sets the scene for associated formation of discordant ventriculo-arterial connections. On occasion, nonetheless, the ventriculo-arterial connection can be that of a double-outlet right ventricle. On rare occasions, furthermore, the ventriculo-arterial connections can be concordant. The latter combination will produce the haemodynamic picture of regular transposition.

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What is the classification system used to describe the origin of the coronary arteries?

Almost always, the major coronary arteries arise from one or other, but usually both, of the sinuses of the aortic root that are adjacent to the pulmonary root. Endothelial stems grow out from the developing aortic root, which occurs during the separation of the intermediate part of the outflow tract into its aortic and pulmonary components. The stems initially develop distal to the myocardial turret that surrounds the intermediate part of the outflow tract. They are incorporated into the sinuses, as the sinuses themselves expand proximally relative to the myocardial boundary of the developing outflow tract. The major coronary arteries themselves are formed within the atrioventricular and interventricular grooves, producing in this way the right, anterior interventricular and circumflex arteries. With normal development, the endothelial stem growing from the leftward of the two aortic valvar sinuses formed adjacent to the pulmonary root joins with the anterior interventricular and circumflex arteries. The stem from the rightward adjacent sinus joins with the right coronary artery. According to the Leiden classification, as viewed by an observer standing upright (figuratively speaking) in the sinus that is not adjacent to the pulmonary trunk, one of the sinuses will be to their right hand. This sinus is conventionally nominated as #1. The other sinus will be to the left hand of the observer and it is nominated as #2 (Figure 31). This arrangement of the aortic valvar sinuses, as seen by the observer standing in the non-adjacent sinus, will remain constant irrespective of the relationship of the arterial roots to each other. On this basis, the arrangement of the right, circumflex and anterior interventricular arteries can be described in constant fashion in terms of their origin from either the right-handed (#1) or left-handed (#2) aortic sinuses. According to their relationship to the arterial pedicles, each of the arteries can arise from either of the adjacent valvar sinuses. In the setting of transposition, the commonest pattern is for the main stem of the left coronary artery to arise from sinus #1, and to divide into the anterior interventricular and circumflex arteries. The right coronary artery then takes its origin from sinus #2. Any arrangement is possible, including the crossing of coronary arteries so as to arise from seemingly inappropriate sinuses. The arteries can also cross between the arterial roots with an interarterial course, usually with an intramural location within the wall of the aortic

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1 Congenital cardiac anatomy A

Left-hand sinus #2

Left coronary artery

Right coronary artery

Right-hand sinus #1 B Right coronary artery

Left-hand sinus #2

Right-hand sinus #1

Anterior interventricular artery

Circumflex artery

Anterior interventricular artery

Figure 31. Classification of the origin of the coronary arteries. The images show how the origin of the coronary arteries can be described in terms of the view obtained by the surgeon ‘standing upright’ in the non-adjacent sinus and looking towards the adjacent aortic valvar sinuses. Irrespective of the relationship of the arterial trunks, one sinus will always be to the right hand of the surgeon, which is then nominated as #1. The other sinus will be to the left hand, and it is nominated as #2. The arrangements shown are as seen in the: A) normal heart (1R,2LCx); and B) commonest variant of transposition (1LCx,2R).

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root. In most instances, nonetheless, the coronary arteries will arise from their closest sinus according to the relationship of the arterial roots.

What is the aortopulmonary septum?

In the postnatal heart, each of the aortic and pulmonary pathways can be considered as possessing a ventricular outflow tract, an arterial root, and then intrapericardial and extrapericardial arterial components. At present, it is usual to assess the developing outflow tract in terms of its components labelled as the ‘truncus’ and ‘conus’, along with an extrapericardial aortic sac. If we presume that the ‘conus’ gives rise to the ventricular outflow tracts and the ‘truncus’ to the intrapericardial arterial trunks, with the extrapericardial arterial pathways derived from the aortic sac, however, the current categorisation makes no provision for the arterial roots. A better approach considers the outflow tract as possessing proximal, intermediate and distal components, with the cavity of the distal component becoming continuous with the cavity of the aortic sac at the margins of the pericardial cavity. The intermediate component can be recognised in anatomic terms by the appearance within its lumen of the intercalated swellings. The distal ends of these swellings, along with the major outflow cushions, will cavitate to produce the leaflets of the arterial valves, with the arterial roots forming within the intermediate component of the outflow tract (Figure 32). Earlier in development, the aortic sac is the manifold that gives rise to the arteries of the pharyngeal arches, which will themselves transform into the extrapericardial components of the aortic and pulmonary pathways. The arteries of the 3rd and 4th arches will form the systemic pathways, while the arteries of the pulmonary arches will give rise to the right and left pulmonary arteries, which develop within the pharyngeal mesenchyme. At this stage, it is the dorsal wall of the aortic sac that represents the aortopulmonary septum (Figure 33). With ongoing development, the dorsal wall of the aortic sac grows and protrudes into the cavity of the distal outflow tract, separating it into the intrapericardial components of the aorta and the pulmonary trunk. The protrusion is the aortopulmonary septum.

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1 Congenital cardiac anatomy Ventral protrusion Distal Fused distal cushions

Intermediate Proximal

Unfused proximal cushions Right ventricle

Figure 32. Long axis of the developing outflow tract of

the mouse heart, subsequent to the formation of the socalled intercalated swellings (white stars with red borders). The proximal part will become separated into the ventricular outflow tracts, with the intermediate part being transformed into the arterial roots, and the distal part forming the intrapericardial arterial trunks. The dotted white line shows the site of fusion between the aortopulmonary septum and the major cushions within the outflow tract. This obliterates the embryonic aortopulmonary foramen.

• • •

The protrusion eventually fuses with the distal ends of the major outflow cushions to obliterate the embryonic aortopulmonary foramen. The major cushions themselves fuse with each other so as to separate, the arterial roots distally, and the right and left ventricular outflow tracts proximally. Failure of fusion of the protrusion with the ends of the major outflow cushions results in persistence of an aortopulmonary window. Failure of fusion of the major outflow cushions themselves produces a common arterial trunk.

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Key Questions in CONGENITAL CARDIAC SURGERY Third arch artery

A

Fourth arch arteries

Third arch artery

Pulmonary arch arteries

50

Distal extent of outflow cushions

Intrapericardial pulmonary trunk

Ventral protrusion

B

Intrapericardial aorta

Developing right ventricle

Distal outflow cushions

Figure 33. Stages of formation of the aortopulmonary septum in the developing mouse: A) early stage, in which the arteries of the 3rd and 4th pharyngeal arches are bilaterally symmetrical, and separated from the arteries of the pulmonary arches by the dorsal wall of the aortic sac (white star with red borders). The white arrows with red borders show the junction between the distal outflow tract and the aortic sac at the margins of the pericardial cavity; B) the dorsal wall of the aortic sac has protruded into the cavity of the distal outflow tract, separating the intrapericardial components of the developing aorta and pulmonary trunk. The white arrows with red borders continue to show the margins of the pericardial cavity. The protrusion has become the aortopulmonary septum. At this stage, the space between the protrusion and the edges of the major outflow cushions

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1 Congenital cardiac anatomy (double-headed white arrow) is an aortopulmonary foramen. It is closed at the later stage to separate the intrapericardial pulmonary arteries. The major cushions fuse to separate the intermediate and proximal parts of the outflow tract.

24 • •

Describe the embryological origin of vascular rings

Multiple arrangements of the extrapericardial branches of the aorta are known to encircle the trachea-oesophageal pedicle and produce ‘dysphagia lusorum’. All of these patterns are well explained on the basis of the hypothetical double arch as proposed by Edwards (Figure 34).

Right arch

Descending aorta

51

Left arch

Subclavian artery

Subclavian artery

Common carotid artery

Common carotid artery Arterial duct

Arterial duct

Aorta

Pulmonary trunk

Figure 34. Hypothetical double aortic arch (as hypothesised by

Edwards), which encircles the tracheo-oesophageal pedicle and unites posteriorly to form a neutral descending aorta. Each arch gives rise to a common carotid artery and a subclavian artery from its cranial surface, and an arterial duct from its dorsal surface. The various vascular rings, along with isolation of the brachiocephalic arteries, are all explained on the basis of attenuation and disappearance of the different components of the double arch, including the arterial ducts.

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Examination of the evolution of the arteries extending through the pharyngeal arches of the developing embryo provides validation for the correctness of the hypothesis as put forward by Edwards. Although six sets of pharyngeal arch arteries tend to be shown in the classical diagram based on the investigation of Rathke, carried out in the 19th century, in fact it is only the arteries of the 3rd, 4th and pulmonary arches that provide the vessels as shown by Edwards in the hypothetical model (Figure 34). During early development, these arteries are bilaterally symmetrical and encircle the developing tracheo-oesophageal pedicle. With ongoing normal development, the right-sided components of these bilateral symmetrical primordiums undergo attenuation and the components encircling the pedicle to join the descending aorta disappear. During the stages of attenuation, nonetheless, a pattern can be visualised that provides the validation of the concept advanced by Edwards (Figure 35).

Right third arch artery

Right fourth arch artery

Right horn of aortic sac

Left third arch artery

Pulmonary trunk Aorta Pulmonary arteries

Regressing right pulmonary arch artery

Left horn of aortic sac

Left fourth arch artery Left pulmonary arch artery

Figure 35. Reconstruction of the developing arteries of the pharyngeal arches in the mouse at embryonic day 12.5. There is clear bilateral symmetry of the arteries of the 3rd and 4th arches, which both join the right- and left-sided descending aortas. The arteries of the pulmonary arch are also bilateral at this stage, although the right-sided artery is beginning to regress. The pattern is remarkably similar to the hypothetical double arch as proposed by Edwards. Image created and reproduced with permission by Dr. Simon Bamforth, Newcastle

University, UK.

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1 Congenital cardiac anatomy What is the origin of the arterial duct?

The arterial duct (also known as the ‘ductus arteriosus’) is an integral part of the foetal circulation. Its presence ensures that the deoxygenated systemic venous return of the foetus, having passed through the right ventricle, is returned to the placenta, thus bypassing the lungs during foetal life. From a developmental standpoint, the arterial duct is derived from the artery of the pharyngeal arch previously described as being ‘6th’. We now know that there is never a 5th arch. The so-called ‘6th arch’, therefore, is better described as being the pulmonary arch. During early development, the arteries of the pharyngeal arches are bilaterally symmetrical. By the time that the arteries of the pulmonary arches are recognisable, however, the arteries of the 1st and 2nd arches have effectively disappeared, becoming incorporated into the arteries supplying the head and face. It is possible, nonetheless, to recognise symmetrical arteries extending through the 3rd, 4th and pulmonary arches (Figure 36). With ongoing development, the right-sided components of the bilateral symmetrical arrangement largely disappear. This leaves the left pulmonary arch artery as the arterial duct, with the left 4th arch artery forming the transverse component of the aortic arch (Figure 37). When first formed, the subclavian arteries, derived from the 7th cervical intersegmental arteries, take their origin from the descending aorta. It is only later in development that these arteries migrate cranially so as to arise from the transverse aortic arch. They cross the insertion of the duct to the descending aorta during this process. The isthmus of the aortic arch is the component between the origin of the left subclavian artery and the junction with the arterial duct. It cannot be defined until the left subclavian artery achieves its definitive position. The right and left pulmonary arteries develop within the pharyngeal mesenchyme, taking their origin from the caudal component of the aortic sac, which gives rise initially to the bilaterally symmetrical arteries of the pulmonary arches.

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Cranial dorsal aortas Regressing second arch arteries Third arch arteries Fourth arch arteries

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Pulmonary arch arteries

Pulmonary arteries Dorsal aortas 7th segmental arteries

Figure 36. Arrangement of the arteries of the pharyngeal arches in the

developing mouse at embryonic day 10.5. The arteries of the 3rd, 4th and pulmonary arches are bilaterally symmetrical. They extend through the pharyngeal mesenchyme before merging dorsally to form the descending aorta. The 7th cervical intersegmental arteries, which will become the subclavian arteries, arise from the dorsal aorta at this early stage of development. Image created and reproduced with permission by Dr. Simon Bamforth, Newcastle University, UK.

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1 Congenital cardiac anatomy

Pulmonary valve

Intrapericardial pulmonary trunk

Aortic valve

Transverse aortic arch

Right and left pulmonary arteries

Arterial duct

Figure 37. Reconstruction of the cavities of the right (blue) and left

(brown) ventricles, along with the extent of the pericardial cavity (green) in the developing mouse at the end of embryonic day 12.5. The artery of the left pulmonary pharyngeal arch has become the arterial duct, while the artery of the left 4th arch has become the transverse aortic arch. Note that the right and left pulmonary arteries develop within the pharyngeal mesenchyma, taking their origin from the caudal component of the aortic sac. The developing subclavian artery (white arrow with red borders) still retains its origin from the descending aorta at this stage of development. Image created and reproduced with permission by Dr. Simon Bamforth, Newcastle University, UK.

26 • •

Is there an artery of the 5th pharyngeal arch?

It is frequent to find aberrant arterial channels in patients with congenitally malformed hearts interpreted in terms of ‘5th arch arteries’. The classical diagram for the developing arteries of the pharyngeal arches does, indeed, illustrate six pairs of bilaterally symmetrical channels (Figure 38).

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1-4

?5

?5 6

56

Aortic sac

6

Figure 38. Classical ‘Rathke’ diagram showing the developing arteries of the pharyngeal arches. The purported 5th arch arteries are shown with dotted lines, since their existence remains contentious. The 7th cervical intersegmental arteries (white arrows with red borders) originate from the descending aorta (white star with red borders) and later in development become the subclavian arteries.

• •

To the best of the authors’ knowledge, there is but a solitary example thus far identified of an attenuating artery of the 5th arch, enclosed within its own segment of pharyngeal mesenchyme (Figure 39). Arteries extending between the aortic sac and the descending aorta at the site of the postulated 5th pharyngeal arch are exceedingly rare.

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1 Congenital cardiac anatomy

Left third arch artery

Left fourth arch artery

Collateral channel

Left horn of aortic sac Left pulmonary arch artery

Figure 39. Reconstruction from the left side of the pharyngeal region of a development human embryo at Carnegie stage 15. It demonstrates attenuation of the left-sided artery that initially coursed between the aortic sac and the descending aorta parallel to the arteries of the left 4th and left pulmonary arches. This arterial channel was embedded within its own segment of pharyngeal mesenchyme. Although initially interpreted as a ‘5th arch artery’, we now consider it better described as a persisting collateral channel.

• •

Collateral channels extending between the posterior terminations of the arteries of the 4th and pulmonary arches, in contrast, are found in up to half of all developing mouse embryos, and in a comparable number of human embryos. The majority of vascular channels interpreted as persistence of the hypothetical artery of the 5th pharyngeal arch is better explained on the basis of presence of such collateral channels, or else as remodelling of the walls of the aortic sac.

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58

A

Describe the anatomy of the sinus node and atrial conduction To this day, no evidence has ever been presented to show that postulated internodal atrial conducting tracts or ‘specialised internodal pathways’ extending through the atrial myocardium to join the sinus and atrioventricular nodes have been identified and isolated from the remainder of the atrial myocardium. Instead, histological examination has demonstrated the sinus node to be a well-defined anatomical entity. The sinus node can be recognised as occupying the epicardial aspect of the terminal groove at the superior cavoatrial junction, usually located inferior to the crest of the right atrial appendage. Its borders are well demarcated, with no extensions of nodal cardiomyocytes identifiable as extending into the adjacent atrial myocardium (Figure 40).

B

Figure 40. A) Operative image demonstrating the superior cavoatrial

junction, with terminal groove (yellow dotted line) and anticipated location of the sinus node (yellow oval). B) Histological section (taken from the site of the yellow solid line) demonstrating the sinoatrial node aggregated around a prominent artery. It has a discrete boundary (blue dashed line) from the adjacent myocardium of the terminal crest and superior caval vein. There are no insulated tracts identifiable extending from the node into the adjacent atrial wall.

•

The specialised cardiomyocytes activate the adjacent atrial myocardium at the margins of the node. The prominent myocardial bundles within the right atrium, such as the terminal crest,

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Bachman’s bundle and the margins of the oval fossa, then serve to conduct the impulse generated within the sinus node towards the atrioventricular node, at the apex of the triangle of Koch. The pathways within the major myocardial atrial bundles are all composed of ordinary working atrial cardiomyocytes. There is nothing ‘specialised’, either histologically or electrophysiologically, regarding these pathways. Rather, the preferential conduction through the major pathways is dictated by the parallel alignment of the working cardiomyocytes making up the bundles.

Describe the anatomical atrioventricular conduction axis

location

of

the

Although the specialised conduction tissues themselves are invisible to the cardiac surgeon, the landmarks regarding their anatomical disposition are now sufficiently robust to permit recognition in all patients with concordant atrioventricular connections. The atrioventricular node is located at the apex of the triangle of Koch. The atrial border of the triangle is demarcated by the extension from the Eustachian valve into the myocardium separating the inferior border of the oval fossa from the orifice of the coronary sinus. The ventricular border is formed by the attachment of the septal leaflet of the tricuspid valve. These borders come together at the site of the atrioventricular component of the membranous septum, which forms the apex of the triangle. The atrioventricular bundle, or bundle of His, passes through the atrioventricular component of the membranous septum to reach the crest of the muscular ventricular septum. It branches on the crest of the septum, or just below it, into the right and left bundle branches. The right bundle branch then courses through the muscular ventricular septum, emerging on the right ventricular surface in relation to the medial papillary muscle, also known as the muscle of Lancisi, or the conal papillary muscle. A line drawn from the apex of the triangle of Koch to the medial papillary muscle shows the anticipated course of the atrioventricular conduction axis (Figure 41). Providing the surgeon keeps all operative manoeuvres outside the boundaries of the triangle of Koch, no damage will be inflicted to the atrioventricular node. The landmarks indicating the site of the axis remain consistent in all hearts with deficient ventricular septation when the atrioventricular connections are concordant. The connecting atrioventricular node does not occupy the apex of the triangle of Koch in the setting of malalignment between the atrial and

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Key Questions in CONGENITAL CARDIAC SURGERY Tendon of Todaro

Membranous septum

Medial papillary muscle

Oval fossa

Conduction axis

Eustachian valve

Coronary sinus

Hinge of tricuspid valve

Figure 41. Macroscopic image depicting the location of the atrioventricular conduction axis in a heart with concordant atrioventricular connections. The right atrioventricular junction is shown, in an attitudinally appropriate orientation, from the right side, having opened the junction and reflected its parietal wall. The location of the axis is shown by the red line joining the apex of the triangle of Koch with the medial papillary muscle.

60

• •

ventricular septal components, nor in the setting of double-inlet left ventricle or discordant atrioventricular connections. The connecting node is found at the site of insertion of the malaligned ventricular septum to the inferior atrioventricular junction when there is straddling of the tricuspid valve. The node is anterior and beneath the mouth of the right atrial appendage in the setting of double-inlet left ventricle or discordant atrioventricular connections.

Recommended reading 1.

Anderson RH, Webb S, Brown NA, Lamers W, Moorman A. Development of the

2.

Moorman A, Webb S, Brown NA, Lamers W, Anderson RH. Development of the

3.

heart: (2) septation of the atriums and ventricles. eÉ~êí 2003; 89(8): 949-58.

heart: (1) formation of the cardiac chambers and arterial trunks. eÉ~êí= 2003; 89(7): 806-14.

Spicer DE, Bridgeman JM, Brown NA, Mohun TJ, Anderson RH. The anatomy and

development of the cardiac valves. `~êÇáçä=vçìåÖ 2014; 24(6): 1008-22.

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Chapter 2

Congenital cardiac physiology Carin van Doorn, Hatem Hosny

1 • • •

Describe the foetal circulation (Figure 1)

The fundamental difference between the foetal circulation and adult circulation is that gas exchange occurs in the placenta and not in the lungs. The placenta receives the foetal deoxygenated blood via the umbilical arteries and returns oxygen-rich blood via the umbilical vein to the foetal circulation. The foetal circulation flows as follows: a)

b) c) d)

e)

•

oxygenated blood returning from the placenta via the umbilical vein bypasses the liver through the ductus venosus to drain into the inferior vena cava (IVC), with oxygen saturation levels of approximately 70%; IVC blood streams by the Eustachian valve to cross from the right atrium (RA) to the left atrium (LA) through the patent foramen ovale; LA blood passes into the left ventricle (LV), from where it is pumped into the ascending aorta (supplying the coronary arteries) and aortic arch (supplying the head vessels); deoxygenated blood from the superior vena cava (SVC), with oxygen saturation levels of approximately 40%, preferentially enters the right ventricle (RV), and from there it is pumped into the pulmonary artery (PA); most of the blood from the PA is diverted through the ductus arteriosus to the descending aorta (as the pulmonary vascular resistance in the foetus is high) and returns to the placenta via the umbilical arteries.

Most of the highly oxygenated blood is delivered to myocardium and brain. This is achieved by preferential streaming, and intracardiac and extracardiac shunting.

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62

High oxygen saturation

Medium oxygen saturation

Figure 1. Foetal circulation.

•

Low oxygen saturation

The foetal circulation allows shunting at four points, including the: a) b) c)

placenta — which has a low vascular resistance and receives about 55% of the combined left and right ventricular foetal cardiac output; ductus venosus — which allows shunting from the umbilical vein to the IVC, bypassing the liver; foramen ovale — which allows unidirectional shunting of blood from the RA to the LA by a valve-like flap;

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2 Congenital cardiac physiology d)

2 • •

ductus arteriosus — which allows shunting from the PA to the aorta.

Describe the circulatory changes that occur at birth

At birth, the neonate starts breathing that results in lung expansion, which together with the pulmonary vasodilatation caused by a high alveolar PO2, leads to a sharp decline in pulmonary vascular resistance. As pulmonary vascular resistance decreases, more blood from the PA enters the lungs instead of the descending aorta (Figure 2).

63

Figure 2. Pressure, blood flow and resistance in the pulmonary circulation before, at and after birth. The progressive decline in pulmonary vascular resistance can be seen over the first 5-7 weeks after birth.

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•

As the intracardiac shunts close, the systemic and pulmonary circulation are now separated, including: a)

b) c) d)

• 64

•

3 • • • •

closure of the ductus arteriosus, as a result of smooth muscle contraction in its wall in response to increased arterial oxygen saturation levels and decreased levels of circulating prostaglandin (which came from the placenta); clamping of the umbilical cord and the removal of the low resistance placenta can result in increased systemic vascular resistance and reduced return to the IVC and RA; closure of the sphincter of the ductus venosus, which forces blood to return via the liver to the RA; closure of the flap valve foramen ovale as LA pressure rises, as a result of the increased pulmonary blood flow.

The ductus arteriosus initially functionally closes due to smooth muscle contraction. This becomes permanent after 3 weeks because of anatomical changes in the endothelium and subintimal layers of the ductus. Ductal closure can be manipulated in the initial period with the use of prostaglandins. The foramen ovale closes passively by the increased LA pressure and is permanently closed in most infants within 6 months. In about 20% of cases, complete fusion of the foramen ovale flap does not occur, leaving a patent foramen ovale (PFO), which does not normally allow for significant shunting from left-to-right due to the valve-like mechanism.

What is the ductus arteriosus?

The ductus arteriosus, which is also known as the ductus Botalli, is a vascular channel connecting the main pulmonary vascular trunk with the descending aorta. During foetal life, the ductus arteriosus allows shunting of mostly deoxygenated blood from the PA to the aorta. Maintaining ductal patency after birth can be lifesaving as initial palliation in neonates with duct-dependent congenital heart disease. In patients with left-sided obstruction, such as severe aortic coarctation, right-to-left shunting through the ductus maintains lower body perfusion. Percutaneous oxygen measurement will show a differential in oxygen saturation levels, with lower saturations in the lower body compared to the upper body (duct-dependent systemic circulation).

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• •

4 • • • •

5 • • • •

In those with right-sided obstruction, such as pulmonary atresia, retrograde flow through the ductus allows filling of the pulmonary arteries (duct-dependent pulmonary circulation). In transposition of the great arteries, where there are parallel circulations, ductal patency aids mixing between the systemic and pulmonary circulations (duct-dependent mixing).

How is ductal closure and opening regulated?

In full-term infants, the ductus closes 24-48 hours after birth due to an increase in arterial pO2, breakdown of circulating PGE2 in the lungs, and lowering of intraluminal ductal pressure due to falling pulmonary vascular resistance. In preterm infants, the ductus is less responsive to oxygen, which explains the higher incidence of duct patency in these young babies. Prolonged patency of the ductus results in pulmonary overflow and low systemic perfusion. Ductal constriction can be promoted through inhibition of prostaglandin synthesis via the cyclo-oxygenase pathway. The cyclooxygenase inhibitors, indomethacin and ibuprofen, are used in clinical practice to promote ductal closure in premature infants. To maintain ductal patency in a neonate with a duct-dependent circulation, a continuous intravenous infusion of synthetic prostaglandin E1 is used (0.005-0.1µg/kg/min).

Describe the changes in pulmonary vascular resistance that occur during normal development

In the full-term foetus, the lungs are collapsed and there is minimal blood flow through the pulmonary vascular bed. After birth, lung expansion and increased alveolar PO2 cause a rapid initial decline in the pulmonary vascular resistance (PVR). In the fullterm infant shortly after birth, the PVR is nearly equal to the systemic vascular resistance. During the first 6-8 weeks of life, there is a gradual decrease in PVR with reduction in PA pressures. If any intracardiac communications are present, there will be increasing shunting from the left to the right side of the circulation, with resultant pulmonary overflow. A further fall in PVR occurs after 2 years of age, when it will reach levels that remain constant throughout adulthood.

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•

Persistent neonatal pulmonary hypertension, also called persistent foetal circulation, can be caused by: a) b)

•

6 66

• • •

c)

Persistent neonatal pulmonary hypertension needs to be distinguished from morphological cardiac defects that cause pulmonary venous obstruction, such as obstruction of pulmonary venous return, veno-occlusive disease or mitral stenosis.

Describe the factors that control pulmonary vascular resistance

Oxygen, hypocapnia and alkalosis act as pulmonary arterial vasodilators, whereas hypoxia, hypercapnia and acidosis are associated with vasoconstriction. Pharmacological treatment of arterial pulmonary hypertension involves manipulation of endothelium-derived vasodilators (such as nitric oxide) and vasoconstrictors (such as endothelin-1). Nitric oxide (NO): a) b)

•

lack of normal physiological relaxation of the pulmonary vascular bed, such as due to hypoxaemia or acidaemia; increased vascular smooth muscle in the pulmonary vascular bed; inadequate number of blood vessels in the lung parenchyma.

endothelium-derived NO — which is produced locally in the lungs and has profound effects on smooth muscle relaxation and proliferation; exogenous NO — which can be administered in closed ventilation circuits at 1-20 parts per million for use as a shortacting pulmonary vasodilator.

Phosphodiesterase (PDE) inhibitors: a)

b)

milrinone — which is a PDE Type 3 inhibitor that increases the bioavailability of cyclic adenosine monophosphate (cAMP), resulting in smooth muscle relaxation, with resultant pulmonary and systemic vasodilatation. Intravenous milrinone is widely used as an inodilator in neonates; sildenafil — which is a PDE Type 5 inhibitor that prevents the hydrolysis of cyclic guanosine monophosphate (cGMP), the second messenger of nitric oxide, allowing a more sustained effect of endogenous nitric oxide.

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2 Congenital cardiac physiology

•

Prostacyclines: a)

b)

•

7

prostacyclin — which is a naturally occurring prostaglandin synthesised in the vascular endothelium from arachnidonic acid via the cyclo-oxygenase pathway. It is a short-acting, potent vasodilator throughout the vascular system, and also has antiplatelet effects; synthetic prostacyclin analogues — which can be delivered via a continuous intravenous infusion, such as epoprostenol, or intermittent inhalation, such as iloprost.

Endothelin receptor antagonists (ERA) — which are used to block the action of endothelin-1, a peptide that is produced by the vascular endothelium with potent vasoconstrictive and proliferative paracrine actions on vascular smooth muscle cells. An example is bosentan, which is administered orally.

What are the normal values for vital signs in the paediatric population (Table 1)?

Table 1. Normal values for heart rate, respiratory rate and blood pressure, according to age. ^ÖÉ

eÉ~êí=ê~íÉ EÄéãF

oÉëéáê~íçêó ê~íÉ=EêéãF

póëíçäáÅ éêÉëëìêÉ EããeÖF

aá~ëíçäáÅ= éêÉëëìêÉ EããeÖF

kÉçå~íÉ= EYOU=Ç~óëF

100-205

90-160

67-84

35-53

fåÑ~åí= 100-190 EN=ãçåíÜJN=óÉ~êF

30-53

72-104

37-56

qçÇÇäÉê= ENJO=óÉ~êëF

98-140

22-37

86-106

42-63

mêÉëÅÜççä= EPJR=óÉ~êëF

80-120

20-28

89-112

46-72

pÅÜççäJ~ÖÉ= ESJNN=óÉ~êëF

75-118

18-25

97-115

57-76

^ÇçäÉëÅÉåí= ENOJNR=óÉ~êëF

60-100

12-20

110-131

64-83

67

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8

What are the normal values for weight, height and body surface area in the paediatric population (Table 2)?

Table 2. Normal values for weight, height and body surface area, according to age *.

jÉÇá~å=ïÉáÖÜí EâÖF

j~äÉë

jÉÇá~å=ÜÉáÖÜí EÅãF

cÉã~äÉë j~äÉë

jÉÇá~å=ÄçÇó ëìêÑ~ÅÉ=~êÉ~=EãOF

3.2

3.0

51

51

0.21

0.21

5.6 fåÑ~åí= EN=ãçåíÜJN=óÉ~êF

5.7

60

58

0.30

0.31

qçÇÇäÉê= ENJO=óÉ~êëF

14

12

94

87.5

0.60

0.53

mêÉëÅÜççä= EPJR=óÉ~êëF

19

17.5

110

107.5

0.76

0.73

pÅÜççäJ~ÖÉ= ESJNN=óÉ~êëF

30

29

137

136

1.07

1.05

^ÇçäÉëÅÉåí= ENOJNR=óÉ~êëF

63

52

174

162

1.75

1.54

^ÖÉ

kÉçå~íÉ= EYOU=Ç~óëF

68

cÉã~äÉë j~äÉë

cÉã~äÉë

* Height and weight are affected by genetic make-up, nutrition, hormones, activity levels and medical conditions.

9 • • • • •

What is the average circulating blood volume in the paediatric population? Premature neonates 95mL/kg. Full term neonates 85mL/kg. Infants 80mL/kg. Adult male 75mL/kg. Adult female 65mL/kg.

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10 • •

• • •

11 • • • • •

2 Congenital cardiac physiology Describe the relationship between blood flow and vascular resistance

Blood flow (Q) is the amount of blood volume passing through a vessel per unit time and is often expressed as mL/min. Blood flow is directly proportionate to the pressure drop (P) over the vessel and inversely proportionate to the vascular resistance (R), as per the equation: Q = P R In the normal adult circulation, the pulmonary vascular resistance is much lower than the systemic vascular resistance, hence the pressure required for the blood to cross the pulmonary circulation is much lower than that required for the same amount of blood for the systemic circulation. This is also reflected in that the muscle mass of the right ventricle is substantially less than that of the left ventricle. In the neonate, as the pulmonary vascular resistance is high and equals systemic vascular resistance, both the right and left ventricles need to generate high pressure. As the pulmonary vascular resistance drops in the early weeks of life, there is a concomitant reduction in right ventricular pressure, and this is accompanied by a reduction in the right ventricular mass. In patients with transposition of the great arteries, in whom the morphological left ventricle is the subpulmonary ventricle, it is the left ventricle that will reduce in mass.

What are the anatomical characteristics of the normal adult circulation?

The normal circulation consists of a systemic circulation and a pulmonary circulation, each supported by a dedicated pumping chamber (i.e. a biventricular circulation). All the usual cardiovascular structures are present and of normal size, and are connected in normal sequence, with the SVC and IVC connecting to the right atrium, then right ventricle, pulmonary artery, pulmonary vascular bed, left atrium, pulmonary veins, left ventricle, aorta and systemic vascular bed. The systemic and pulmonary circulations are separated, with no intracardiac communications. The systemic and pulmonary blood flow are in series, where the blood goes sequentially through the systemic then pulmonary vascular bed. Blood that leaves the heart via the aorta is distributed to major organ arteries, including the carotid, brachial, superior mesenteric, renal and iliac arteries, which are in parallel with each other.

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• •

The exception are the gut and hepatic circulations, which are partly in series as the venous drainage from the intestines drains into the portal vein that supplies most of the inflow to the liver. Within each organ, there is a microcirculation arranged as a series of in-parallel and in-series vessels (Figure 3).

70

Figure 3. Normal adult circulation.

12 • • • •

What are the principles of a biventricular circulation?

A biventricular circulation has two adequately sized functioning ventricles. One ventricle supports the pulmonary circulation, the other supports the systemic circulation and, in the absence of any intracardiac shunts, these circulations are connected in series. Usually, the morphological right ventricle is the subpulmonary ventricle and the morphological left ventricle is the subaortic ventricle. Each ventricle provides a step-up in blood pressure that allows the propulsion of blood through the downstream vascular bed.

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•

As the systemic circulation normally has a much higher resistance than the pulmonary circulation, the subaortic ventricle needs to generate a much higher step-up in blood pressure than the subpulmonary ventricle (Figure 4).

71

Figure 4. Step-up in systemic and pulmonary blood pressure by the left and right ventricles.

13 • •

Describe the principles of calculating systemic and pulmonary vascular resistance

Vascular resistance represents the opposition to blood flow in the circulation. Although resistance cannot be directly measured, vascular resistance is calculated as: R = P Q

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•

R = resistance; P = change in pressure across the circulation loop from its beginning (immediately after exiting the ventricle) to its end (entering the atrium); Q = flow through the vasculature. Systemic vascular resistance (SVR) can be calculated as: SVR (dynes.sec/cm5) = (MAP – CVP) x 80 CO SVR (Wood units) = (MAP – CVP) CO

• 72

MAP = mean arterial pressure (mmHg); CVP = central venous pressure (mmHg); CO = cardiac output (L/min). Normal SVR is 770-1500 dynes.sec/cm5 or 10-20 WU. Pulmonary vascular resistance (PVR) can be calculated as: PVR (dynes.sec/cm5) = (MPAP – LAP) x 80 CO PVR (Wood units) = (MPAP – LAP) CO

14 • • • •

MPAP = mean pulmonary arterial pressure (mmHg); LAP = left atrial pressure (or pulmonary venous wedge pressure) (mmHg); CO = cardiac output (L/min). Normal PVR is 20-120 dynes.sec/cm5 or 0.25-1.5 WU.

Discuss the regulation of peripheral vascular resistance in the systemic circulation

Within the body as a whole, and in individual organs, the circulation is made up of both in-series and in-parallel vascular elements. The major distributing arteries from the aorta (e.g. carotid, brachial, superior mesenteric, renal, iliac) are in parallel with each other. The notable exception is the liver, which is partly in series with the gut. Within individual organs, the arteries branch out, terminating in microvascular vascular beds comprising of small arteries (A), arterioles (a), capillaries (c), venules (v) and veins (V) (Figure 5). The Poiseuille equation (R = 8Lη/.r4 ) dictates that resistance in an individual segment of vessel (R) is directly proportional to the length (L) of the vessel and inversely proportional to the radius to the fourth power (r4).

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2 Congenital cardiac physiology

73

Figure 5. Distribution of systemic blood flow.

• • • •

When vascular segments are connected in series, the total vascular resistance in this system equals the sum of the individual resistances. In the typical microvascular bed, the relative contributions to the total resistance (RT) of the bed are approximately RA = 20%, Ra = 50%, Rc = 20%, Rv = 6%, RV = 4% (Figure 6). Small arteries and arterioles comprise approximately 70% of the total resistance in most organs, and changes in the diameter, and therefore resistance, of these arteries are the major determinants of the vascular resistance in an organ. For body arteries that are in a parallel arrangement, including the distribution of the aortic blood flow, the total resistance of such vascular networks can be calculated (Figure 7).

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RT = RA + Ra + Rc + Rv + RV

Figure 6. Calculation of the vascular resistance with vessels in series. 74

Figure 7. Calculation of vascular resistance with vessels in parallel.

• •

In principle, adding a vascular bed in series to a circulation increases its total vascular resistance, while adding a vascular bed in parallel decreases the total resistance. For the body as a whole, the large distributing arteries comprise only approximately 1% of the total vascular resistance, and therefore, unlike arterioles, changes in the diameter have a relatively small effect on total resistance. Although a 50% reduction in radius should

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2 Congenital cardiac physiology

15 •

increase the resistance in the individual vessel 16-fold according to the Poiseuille equation, the overall resistance will only increase by about 15% as the relative contribution of the vessel to the overall resistance is small.

What is collateral circulation?

A collateral circulation is an alternate circulation, which develops around an obstruction or occasionally lack of development, of an artery or vein. Some examples encountered in congenital cardiac surgery include the: a) b)

c)

d)

• • •

collateral arterial circulation that develops via intercostal arteries in patients with coarctation of the aorta, which provides blood flow to organs distal to the coarctation; veno-veno collateral vessels in patients with a superior vena cava to pulmonary artery shunt (Glenn shunt), with blood flowing from the higher pressure SVC to the lower pressure IVC territory. The resultant bypassing of the pulmonary vascular bed results in desaturation; major aortopulmonary collateral arteries (MAPCAs), which are systemic collateral arteries from the aorta or subclavian artery, that perfuse the lung parenchyma if the central pulmonary arteries are underdeveloped or absent, thereby enabling blood delivery for pulmonary gas exchange. Longstanding highpressure MAPCAs lead to the development of pulmonary vascular disease; arteriovenous malformations in the lung, which are abnormal connections between pulmonary arteries and veins bypassing the capillary system and leading to central cyanosis.

The collateral circulation connects a high-pressure proximal vascular bed to a lower-pressure vascular bed. In the event of an arterial occlusion, it helps to provide oxygenated blood to the downstream area. The collateral blood flow may occur via pre-existing redundancy or via new branches formed between adjacent blood vessels (neovascularisation). Collateral blood flow may result in significant volume loading of the circulation.

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16 • • • • •

76

17 • • • •

What is cardiac output?

Cardiac output (CO) is the volume of blood ejected by the heart per unit of time, and is usually expressed as litres/minute (L/min). Cardiac output can be calculated as: CO = Stroke volume x Heart rate. Stroke volume is the volume of blood ejected by the ventricle in a single beat. In neonates, as ventricular volumes are small and the ventricles are poorly compliant, the stroke volume is fixed within narrow margins. Hence, any decrease in heart rate will result in a decrease in cardiac output. In adults, however, the ventricles are much more compliant. When the heart rate decreases, there will be more blood entering the heart, and thus stroke volume will increase (according to Starling’s law) and cardiac output remains unaffected (within limits).

What are the principles of cardiac shunting?

In the normally connected circulation, the pulmonary and systemic blood flow are separated and arranged in series. The blood must pass through the pulmonary vascular bed to reach the systemic circulation, and vice versa. In the absence of shunts, the amount of pulmonary blood flow (Qp) is equal to that of systemic blood flow (Qs), hence the ratio of pulmonary to systemic flow (Qp/Qs) = 1. Shunting of blood between the systemic and pulmonary circulations occurs when the normal flow of blood is diverted because of an intracardiac communication and the blood goes back to the same capillary bed that it came from. Some cardiac shunting may occur in normal states, including: a) b)

•

anatomic shunting — which occurs when bronchial arterial blood returns to the left atrium; physiological shunting — which occurs in the lungs due to the effect of gravity, where more blood flows to the lung bases, which are not well ventilated, and bypasses the alveoli.

Cardiac shunts are common in congenital heart disease. They can present as communications at the level of the: a)

atria — atrial septal defect (ASD);

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•

• •

18 • • • •

19 •

b) c)

ventricles — ventricular septal defect (VSD); great arteries — patent ductus arteriosus (PDA).

The blood flow across the shunt is pressure driven. In the case of a VSD, this is directly related to the pressure difference between the ventricles at any time during the cardiac cycle, whereas for an ASD, the pressure difference between the atria is governed by the ventricular end-diastolic pressure. Since this pressure is normally higher in the thick-walled, relatively non-compliant left ventricle, an ASD will usually shunt from the left to right atrium. In patients with a cardiac communication and otherwise normally connected circulation, oxygenated blood will shunt from the highpressure left side to the low-pressure right side, representing a leftto-right shunt, where the patient is not cyanosed (pink). If a VSD is associated with severe pulmonary stenosis, such as in tetralogy of Fallot, the obstruction to pulmonary blood flow forces the blood to pass through the VSD from the RV to the LV, representing a right-to-left shunt, where the patient is cyanosed (blue).

Describe the changing physiology of a cardiac shunt in the first few months following birth

In patients with congenital heart disease, changes in pulmonary vascular resistance in the neonatal period affect the direction and magnitude of the shunt flow. Immediately after birth, as pulmonary vascular resistance is high and there is little difference between pulmonary and systemic pressure, there will be minimal overall blood flow across the cardiac communication. After the pulmonary vascular resistance drops in the first few weeks of life, the pressure difference between the systemic and pulmonary circulations increases, causing an increase in flow from left to right across the shunt, with a Qp/Qs ratio of >1. Patients with a right-to-left shunt have lower pulmonary flow than systemic flow, with a Qp/Qs ratio of 1 or 100mmHg; cardiac causes of cyanosis only produce a slight rise in PaO2 of 10-30mmHg and it does not go above 100mmHg, because of the deoxygenated blood that continues to bypass the lung.

What are the sequelae of chronic cyanosis? Polycythemia. Clubbing.

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• • • •

40 •

Central nervous system complications, such as a brain abscess and cerebrovascular stroke. Bleeding tendency, as well as increased risk of thromboembolism. Hypercyanotic spells. Hyperuricaemia and gout.

Describe the oxygen-haemoglobin dissociation curve (Figure 20)

The oxygen-haemoglobin dissociation curve describes the relationship between the partial pressure of oxygen (PO2) and

Oxyhaemoglobin (% saturation)

98

PaO2 (mmHg)

Figure 20. Oxygen-haemoglobin dissociation curve, where a left shift represents a greater affinity of haemoglobin for oxygen (blue curve) and a right shift represents a reduced affinity of haemoglobin for oxygen (red curve). DPG = disphosphoglycerate.

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• • • • • • • •

41 • • • • •

oxygen saturations (percentage of haemoglobin binding to oxygen), which is not linear but rather sigmoid. Above a PO2 of 8kPa (60mmHg), changes in the PO2 make very little difference to oxygen saturation levels. Below a PO2 of 8kPa (60mmHg), however, a small drop in the PO2 produces a large fall in the oxygen saturation levels. The PO2 at which 50% of haemoglobin is saturated has been chosen as the reference point, called P50. The position of the dissociation curve is an expression of the affinity of haemoglobin for oxygen. Shift of the curve to the left denotes an increased affinity of haemoglobin to oxygen, where the same oxygen saturation levels occur at a lower PO2 and more oxygen is bound to haemoglobin. Shift to the right denotes decreased affinity of haemoglobin to oxygen. Foetal haemoglobin has a higher affinity to oxygen (shifting of the curve to the left) to allow better oxygen extraction from the placenta. Factors that causes the curve to be shifted to the right (less affinity of haemoglobin to oxygen) include low pH, high temperature, high CO2 and high levels of 2,3-disphosphoglycerate (2,3-DPG). These factors occur at tissue level, so more oxygen is released from haemoglobin to be taken up by the tissues.

Describe how oxygen content in blood is calculated

Oxygen content represents the actual amount of oxygen present per volume of blood. Oxygen is carried in blood either bound to haemoglobin or dissolved in plasma. Dissolved oxygen accounts for only 2% of the total oxygen content in blood. Dissolved oxygen concentration is rather constant at 0.003mL O2/100mL blood/mmHg but is dependent on its partial pressure. Thus, with a PO2 of 100mmHg, the concentration of dissolved oxygen will increase to 0.3mL O2/100mL. The remaining 98% of the total oxygen content of blood is reversibly bound to haemoglobin. The oxygen-binding capacity of haemoglobin is the maximum amount of oxygen that can be bound to haemoglobin per volume of blood. Assuming that haemoglobin is 100% saturated, 1g of haemoglobin can bind 1.34mL oxygen.

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•

Hence, to calculate the amount of oxygen per volume of blood: Oxygen content = (oxygen-binding capacity x O2 saturation) + dissolved oxygen Oxygen content = (1.34 x Hb [g/dL] x O2 saturation) + (0.003 x PO2)

Acknowledgement

We would like to thank Soha Romeih for her help with the cardiac imaging.

Recommended reading

100

1.

Kappanayil M, Kannan R, Kumar RK. Understanding the physiology of complex

2.

Sommer RJ, Hijazi ZM, Rhodes JF. Pathophysiology of congenital heart disease in the

3.

Rhodes JF, Hijazi ZM, Sommer RJ. Pathophysiology of congenital heart disease in the

4. 5.

congenital heart disease using cardiac magnetic resonance imaging. ^åå= mÉÇá~íê

`~êÇáçä 2011; 4(2): 177-82.

adult: part III: complex congenital heart disease. `áêÅìä~íáçå 2008; 117(10): 1340-50. adult, part II. Simple obstructive lesions. `áêÅìä~íáçå 2008; 117(9): 1228-37.

Sommer RJ, Hijazi ZM, Rhodes JF Jr. Pathophysiology of congenital heart disease in the adult: part I: Shunt lesions. `áêÅìä~íáçå 2008; 117(8): 1090-9.

Chowdhury D. Pathophysiology of congenital heart diseases. ^åå= `~êÇ= ^å~ÉëíÜ

2007; 10(1): 19-26.

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Chapter 3

Congenital cardiac pharmacology Shakil Farid, Kasra Shaikhrezai, Narain Moorjani

1 • • • • • •

2 • •

What are the pharmacological properties of aspirin?

Class of drug: cyclo-oxygenase inhibitor. Mechanism of action: aspirin irreversibly inhibits thromboxane A2 production in platelets via acetylation of cyclo-oxygenase and inhibiting it. Inhibition of thromboxane A2 production reduces the adhesiveness of platelets. Indications: prophylaxis against clot formation after cardiac surgery, prophylaxis of stroke in children with high risk, Kawasaki syndrome. Cautions: asthma, peptic ulcer disease, renal impairment, concomitant use of a non-steroidal anti-inflammatory drug or anticoagulant (warfarin). Side effects: gastrointestinal effects, such as nausea, vomiting, bleeding, epigastric distress, bronchospasm, respiratory depression and hyperthermia in toxic doses, hypersensitivity, Reye syndrome (which can happen in children under 16 years of age, characterised by fulminant hepatitis with cerebral oedema). Dose p.o.: a) b) c)

neonate: 1-5mg/kg o.d.; child (1 month-12 years): 1-5mg/kg (usual maximum dose 75mg) o.d.; child (12-18 years): 75mg o.d.

What are the pharmacological properties of clopidogrel?

Class of drug: platelet ADP (adenosine diphosphate) receptor antagonist. Mechanism of action: clopidogrel irreversibly modifies the platelet ADP receptor thereby directly inhibiting the binding of ADP and subsequent ADP-mediated activation of the glycoprotein IIb/IIIa complex. Platelets exposed to clopidogrel are ineffective for the remainder of their lifetime (5-7 days).

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• • • •

Indications: primary and secondary prevention of cardiovascular and cerebrovascular disease (CAPRIE trial). It is also used as dual therapy in combination with aspirin for acute coronary syndrome (CURE trial) and long-term anti-thrombotic prophylaxis for drugeluting stents. Cautions: active bleeding. Side effects: haemorrhage, neutropenia. Dose:

3

What are the pharmacological properties of heparin?

• 102

• • • •

a) b)

child (0-24 months): 0.2mg/kg/day (maximum 75mg per dose); child (2-17 years): 0.2-1mg/kg/day (maximum 75mg per dose).

Mechanism of action: heparin is a mucopolysaccharide that: a) b) c)

inactivates activated factor X; inhibits conversion of prothrombin to thrombin; prevents fibrin formation from fibrinogen.

Indications: treatment and prophylaxis of deep venous thrombosis and pulmonary embolism; unstable angina; anticoagulation during cardiopulmonary bypass; temporary anticoagulation for prosthetic valve patients Cautions: active bleeding. Side effects: haemorrhage, hyperkalaemia, osteoporosis, thrombocytopaenia and hypersensitivity. Dose: a) b)

prophylactic — 100 units/kg b.d. (maximum per dose 5000U) by subcutaneous injection; therapeutic: i) neonate (up to 35 weeks corrected gestational age): initially 50 units/kg, then 25 units/kg/hour continuous IV infusion, adjusted according to APTT; ii) neonate: initially 75 units/kg, then 25 units/kg/hour continuous IV infusion, adjusted according to APTT; iii) child (1-11 months): initially 75 units/kg, then 25 units/kg/hour continuous IV infusion, adjusted according to APTT; iv) child (1-17 years): initially 75 units/kg, then 20 units/kg/hour continuous IV infusion, adjusted according to APTT;

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3 Congenital cardiac pharmacology c)

•

4 • • • • •

5 •

• • •

full cardiopulmonary bypass — 300U/kg bolus; minimal extracorporeal circulation (MECC) — 200U/kg.

Heparin can be reversed with protamine sulphate.

What are the protamine?

pharmacological

properties

of

Mechanism of action: protamine antagonises the anticoagulant effects of heparin. Indications: reversal of the effects of overdose with intravenous unfractionated or low-molecular-weight heparin. Cautions: excessive doses can have an anticoagulant effect, increased risk of allergic reaction to protamine (previous treatment with protamine or protamine insulin, allergy to fish, adolescent males who are infertile). Side effects: hypersensitivity (including angioedema, anaphylaxis), dyspnoea due to pulmonary oedema, flushing, bradycardia and hypotension. Dose: a)

child (1 month-18 years): by intravenous injection (rate not exceeding 5mg/minute) to neutralise each 100 units of unfractionated heparin 1mg if less than 30 minutes has lapsed since overdose, 500-750µg if 30-60 minutes has lapsed, 375500µg if 60-120 minutes has lapsed, 250-375µg if over 120 minutes has lapsed (maximum 50mg).

What are the pharmacological properties of lowmolecular-weight heparins (LWMHs)? Mechanism of action: LMWH has a similar action to heparin except:

a) b) c) d)

LWMH has a longer half-life than heparin; LWMH does not require monitoring (APTTR is unaffected); LMWH has a greater anti-factor Xa activity; LMWH has a lower incidence of thrombocytopaenia and osteoporosis.

Indications: acute coronary syndrome (FRISC trial, TIMI IIB trial) and prophylaxis for deep vein thrombosis. Cautions: active bleeding. Side effects: haemorrhage, hyperkalaemia, osteoporosis, thrombocytopaenia and hypersensitivity.

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•

Dose: a)

b)

104

6 • • • • •

Dalteparin (Fragmin®): i) therapeutic dose: neonate: 100 units/kg twice daily; child (1 month-11 years): 100 units/kg b.d.; child (12-17 years): 200 units/kg o.d. (maximum 18,000 units); ii) prophylactic dose: neonate: 100 units/kg o.d.; child (1 month-11 years): 100 units/kg o.d.; child (12-17 years): 2500-5000 units o.d.; Enoxaparin (Clexane®): i) therapeutic dose: neonate: 1.5-2mg/kg b.d.; child (1-2 months): 1.5mg/kg b.d.; child (2 months-17 years): 1mg/kg b.d.; ii) prophylactic dose: neonate: 750µg/kg b.d.; child (1-2 months): 750µg/kg b.d.; child (2 months-17 years): 500µg/kg b.d. (maximum 40mg per day).

What are the pharmacological properties of warfarin?

Mechanism of action: warfarin is a coumarin derivative that interferes with vitamin K metabolism. Vitamin K is a cofactor in the hepatic production of numerous proteins including coagulation factors II, VII, IX and X. Indications: prophylaxis and treatment for thromboembolism with deep vein thrombosis, pulmonary embolism, atrial fibrillation, mechanical prosthetic valves, left ventricular thrombus and transient ischaemic attacks. Cautions: hepatic impairment; peptic ulcer disease; warfarin interacts with numerous drugs including amiodarone, antibiotics (such as rifampicin), anticonvulsants, non-steroidal anti-inflammatory drugs and statins. Side effects: haemorrhage. Dose (induction): a)

neonate: initially 200µg/kg for 1 dose on day 1; then reduced to 100µg/kg once daily for 3 days; subsequent doses are dependent upon INR levels; if the INR is above 3.5, a dose should be omitted;

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3 Congenital cardiac pharmacology b)

•

7 • • • • •

Warfarin can be reversed with vitamin K, fresh frozen plasma or Beriplex® (human prothrombin complex concentrate).

What are the pharmacological properties of vitamin K?

Mechanism of action: vitamin K acts as a cofactor in the hepatic production of several protein coagulation factors including II, VII, IX and X. Indications: bleeding in neonates and infants due to blood clotting factors and vitamin K deficiency, warfarin-induced bleeding. Cautions: allergic reactions, risk of vascular collapse (should be given very slowly). Side effects: allergic reactions, haemolytic anaemia and cytotoxicity in liver cells. Dose: a) b)

c)

8 • • •

child: initially 200µg/kg (maximum per dose 10mg) for 1 dose on day 1; then reduced to 100µg/kg once daily (maximum per dose 5mg) for the following 3 days; subsequent doses are adjusted according to the INR levels; if the INR is above 3.5, a dose should be omitted.

neonatal hypoprothrombinaemia or vitamin K deficiency bleeding: by intravenous injection 1mg, repeated 8-hourly if necessary; for reversal of coumarin anticoagulation when continued anticoagulation is required or if no significant bleeding in a child (1 month-18 years): 15-30µg/kg (maximum 1mg) as a single-dose intravenous injection, repeated as necessary; for reversal of coumarin anticoagulation when continued anticoagulation is not required or if significant bleeding; treatment of haemorrhage associated with vitamin K deficiency in a child (1 month-18 years): 250-300µg/kg (maximum 10mg) as a single-dose intravenous injection.

What are the pharmacological tranexamic acid?

properties

of

Class of drug: lysine analogue antifibrinolytic agent. Mechanism of action: tranexamic acid binds to plasminogen, thereby inhibiting fibrinolysis. Indications: prophylaxis to reduce bleeding and the use of blood products following cardiac surgery. Tranexamic acid is also used following massive haemoptysis and in haemophiliacs.

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• • •

9 •

Cautions: renal impairment, disseminated intravascular coagulation, thromboembolic disease. Side effects: renal function, graft patency. Dose: 30mg/kg/5 minutes loading bolus (maximum 2g) followed by a 5-10mg/kg/hr maintenance IV infusion; 30mg/kg added to the prime volume of the cardiopulmonary bypass circuit.

What are the dopamine?

b)

c)

• • • •

• •

of

very high doses — can cause vasoconstriction by activating α1 receptors; moderate doses — stimulates β1 receptors of the heart having both inotropic and chronotropic effects. With this moderate dose in older children, there is an increase in myocardial contractility and cardiac output; however, in neonates, this moderate dose causes a reduction in cardiac output; low doses — dilates renal and splanchnic arterioles by activating dopaminergic receptors, thereby increasing blood flow to the kidneys and other viscera.

Indications: cardiogenic shock and septic shock. Cautions: tachyarrythmias, neonatal pulmonary hypertension, phaeochromocytoma, patients on mono-amine oxidase inhibitors. Side effects: tachycardia, vasoconstriction, hypotension, rarely hypertension, dyspnoea. Dose: a) b)

10

properties

Mechanism of action: dopamine can activate α- and β-adrenergic receptors: a)

106

pharmacological

neonate: initially 3µg/kg/min, adjusted according to response (maximum 20µg/kg/min); child (1 month-18 years): initially 5µg/kg/min, adjusted according to response (maximum 20µg/kg/min).

What are the dobutamine?

pharmacological

properties

of

Mechanism of action: dobutamine is a direct-acting catecholamine that acts as a β1 receptor agonist. One of the stereoisomers has a stimulatory effect and increases the cardiac rate and output. Indications: inotropic support after cardiac surgery, increase cardiac output in acute congestive heart failure.

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3 Congenital cardiac pharmacology

• • •

11 • • • • •

12 •

• •

Cautions: tachyarrhythmias, phaeochromocytoma, marked obstruction of cardiac ejection (such as idiopathic hypertrophic subaortic stenosis). Side effects: tachyarrhythmias, bronchospasm, nausea, hypertension. Dose: initially 5µg/kg/min, adjusted according to response to 220µg/kg/minute by intravenous infusion.

What are the adrenaline?

pharmacological

properties

of

Mechanism of action: adrenaline increases the contractility of the myocardium (positive inotropic β1 action) and increases its rate of contraction (positive chronotropic β1 action). At low doses, it causes systemic vasodilatation and bronchodilation by β2 effects but at higher doses its α-adrenergic vasoconstriction effects predominate. Indications: low cardiac output syndrome, cardiopulmonary resuscitation, anaphylaxis, acute hypotension, bradycardia (unresponsive to atropine). Cautions: obstructive cardiomyopathy, aortic stenosis, occlusive vascular disease, arrhythmias, hypertension, phaeochromocytoma, glaucoma, diabetes mellitus, arrhythmias. Side effects: tachycardia, arrhythmias, hypertension, metabolic acidosis, central nervous system disturbances, such as anxiety, fear, tension, headache, tremor. Dose: initially 100ng/kg/min adjusted according to response, higher doses up to 1.5µg/kg/min can be used.

What are the noradrenaline?

pharmacological

properties

of

Mechanism of action: noradrenaline is a potent α1-adrenergic agonist, causing a rise in peripheral resistance due to intense vasoconstriction of most vascular beds. It is also a β1-adrenergic agonist producing increased myocardial contractility and increased heart rate, although it has minimal effects áå=îáîç. In practice, when the drug is given in therapeutic doses in humans, the α-adrenergic receptor is most affected. Indications: shock or low systemic vascular resistance due to sepsis, vasodilatation or anaphylaxis, low cardiac output following cardiac surgery. Cautions: peripheral vascular thrombosis, hyperthyroidism, diabetes mellitus, extravasation at the injection site causing necrosis, susceptibility to angle-closure glaucoma, uncorrected hypovolaemia.

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• •

13 •

• 108

• • •

14 • • • • •

15 • •

Side effects: hypertension, tachyarrhythmias, anorexia, nausea, vomiting, tremor, psychosis. Dose: 20-100ng/kg/minute intravenous infusion adjusted according to response, maximum 1µg/kg/minute.

What are the vasopressin?

pharmacological

properties

of

Mechanism of action: vasopressin has both antidiuretic and vasopressor effects. In the kidney, it binds to the V2 receptor to increase water permeability and reabsorption in the collecting tubules. The vasoconstrictor effect is mediated by the V1 receptor that is located in vascular smooth muscle; it also remains in liver and other tissues. Indications: diabetes insipidus, bleeding from oesophageal varices or colonic diverticula. Cautions: coronary artery disease, epilepsy, asthma, heart failure, conditions that might be aggravated by water retention. Side effects: vascular disease, chronic nephritis, fluid retention, peripheral ischaemia, hypersensitivity reactions. Dose: for acute massive haemorrhage of the gastrointestinal tract: a)

child (1 month-18 years): initially 0.3 units/kg (maximum 20 units) over 20-30 minutes, then 0.3 units/kg/hour, adjusted according to response (maximum 1 unit/kg/hour).

What are the phenylephrine?

pharmacological

properties

of

What are the levosimendan?

pharmacological

properties

of

Mechanism of action: phenylephrine is a selective α1-adrenergic receptor agonist, which produces systemic vasoconstriction. Indications: acute hypotension; to maintain systemic blood pressure whilst on cardiopulmonary bypass. Cautions: severe hyperthyroidism. Side effects: hypertension, peripheral ischaemia, headache. Dose: 500µg-1mg IV boluses whilst on cardiopulmonary bypass.

Class of drug: calcium sensitizer. Mechanism of action: myocytes become more sensitive to calcium, hence increasing contractility.

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3 Congenital cardiac pharmacology

• • • •

16 • •

• • • •

17 • • • • •

Indications: severe congestive heart failure. Cautions: hepatic and renal impairment. Side effects: dysrrhythmia, hypokalaemia, myocardial ischaemia. Dose: 0.05-0.2µg/kg/min intravenous infusion.

What are the enoximone?

pharmacological

properties

of

Class of drug: phosphodiesterase inhibitor. Mechanism of action: enoximone is a type 3 phosphodiesterase inhibitor that acts as an inodilator by reducing systemic and pulmonary vascular resistance, as well as having moderate positive inotropic effects. They increase intracellular calcium by increasing the intracellular concentration of cyclic AMP, thereby improving cardiac contractility. Indications: low cardiac output following cardiac surgery, especially in the presence of pulmonary hypertension or right ventricular failure. Cautions: hypertrophic cardiomyopathy, stenotic or obstructive valvular disease, or other outlet obstruction (such as aortic stenosis), hypotension. Side effects: tachyarrhythmias, hypotension, thrombocytopaenia, ectopic beats, ventricular tachycardia, supraventricular arrhythmias. Dose: initial loading dose of 500µg/kg by slow intravenous injection, followed by 5-20µg/kg/min by continuous intravenous infusion over 24 hours adjusted according to the response; maximum 24mg/kg over 24 hours.

What are the pharmacological properties of nitric oxide?

Mechanism of action: nitric oxide is a potent and selective pulmonary vasodilator, which causes relaxation of pulmonary artery smooth muscle by acting on cyclic guanosine monophosphate (cGMP). Indications: persistent neonatal pulmonary hypertension and other forms of arterial pulmonary hypertension. Cautions: methaemoglobin should be measured regularly, particularly in neonates. Side effects: risk of haemorrhage by inhibiting platelet aggregation, methaemoglobinaemia. Dose: 20 ppm.

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18 • • • • • •

What are the pharmacological properties of sildenafil?

Class of drug: phosphodiesterase inhibitor. Mechanism of action: sildenafil relaxes the pulmonary arterial wall by inhibiting the cyclic guanosine monophosphate specific phosphodiesterase type 5 enzyme that promotes degradation of cGMP. Indications: pulmonary arterial hypertension. Cautions: hepatic impairment, renal impairment, concurrent use of nitric oxide donors, hypotension, hereditary degenerative retinal disorders, left ventricular outflow obstruction, pulmonary venoocclusive disease. Side effects: headache, flushing, dyspepsia, nasal congestion, disturbances in colour vision and photophobia. Dose: a) b)

110

19 • • • • • •

neonate-1 year: initially 250-500µg/kg every 4-8 hours, maximum 30mg/day; child (1-18 years): i) body weight 50% and aorto-mitral discontinuity. RV = right ventricle; LA = left atrium; Ao = aorta. 160 A

B

^ç

m^

os=

G

is

Figure 35. Subcostal views demonstrating a: A) Taussig-Bing anomaly, characterised by a double-outlet right ventricle with the aorta lying to the right of the pulmonary artery and completely arising from the RV, and a subpulmonary ventricular septal defect (*); and B) the pulmonary artery with flow (red) from a patent ductus arteriosus, allowing it to be distinguished from the aorta, on the corresponding colour flow Doppler image. RV = right ventricle; LV = left ventricle; Ao = aorta; PA = pulmonary artery.

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23 •

4 Congenital echocardiography What are the principles of assessing vascular rings on echocardiography?

Vascular rings are usually diagnosed with suprasternal echocardiographic views and often confirmed by CT or MRI (Figure 36).

A

B ^ç

G

G

om^

m^

G

im^

G

Figure 36. Suprasternal view colour flow Doppler images demonstrating

a: A) double aortic arch (*); and B) left pulmonary artery sling, with the left pulmonary artery (LPA) originating (arrow) from the right pulmonary artery (RPA), rather than its usual origin (*) at a symmetrical bifurcation with the right pulmonary artery. Ao = aorta; PA = pulmonary artery.

•

24 • • • •

Vascular rings can be diagnosed by foetal sonographers, such as a right aortic arch with aberrant left subclavian artery and left ductus arteriosus.

What are the principles of assessing isomerism on echocardiography?

Isomerism refers to the atrial appendages and not the entire atria. As the appendages are not usually seen on echocardiography, the situs is inferred from the arrangement of the aorta and IVC or azygos and hemiazygos venous systems on the subcostal view (Figure 37). On echocardiography, right isomerism is characterised by an absent coronary sinus and totally anomalous pulmonary venous connection. In addition, there is often an AVSD, poorly formed atrial septum, DORV with pulmonary stenosis or atresia, bilateral vena cavae, rightsided heart and left-handed ventricular topology. On echocardiography, left isomerism is characterised by an interrupted IVC and azygos continuation. In addition, there is often an AVSD and bilateral vena cavae.

161

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Key Questions in CONGENITAL CARDIAC SURGERY A

B s

s

^

^

péáåÉ

páíìë=ëçäáíìë=Ô=ìëì~ä C

páíìë=ëçäáíìë=Ô=ìëì~ä D

s ^

162

oáÖÜí=~íêá~ä=áëçãÉêáëã

E ^

e

iÉÑí=~íêá~ä=áëçãÉêáëã

^

s

jáêêçê=áã~ÖÉ

Figure 37. Isomerism identification on echocardiography determined by the relationship between the aorta (A) and the inferior vena cava (V), or in the case of left atrial isomerism, the aorta and the hemiazygos (H) vein: A) echocardiographic subcostal situs views demonstrating the usual atrial arrangement with the aorta lying posterior and to the left of the inferior vena cava. Schematic illustrations of: B) situs solitus; C) right atrial isomerism; D) left atrial isomerism; and E) mirror image.

•

In addition, other malformations associated with isomerism include: a) b) c)

common atrioventricular junction — which are frequent with both right and left isomerism; double-inlet connection — which is more frequent with right isomerism; biventricular connections — which is more frequent with left isomerism;

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4 Congenital echocardiography d) e)

25 •

concordant connections with coarctation — which is more frequent with left isomerism; discordant or double-outlet connections along with pulmonary atresia or stenosis — which is expected with right isomerism.

What are the principles of assessing tricuspid atresia on echocardiography?

Anatomically, the valve can be imperforate or there may be an absent connection, which appears echocardiographically as a thick band of the atrioventricular groove separating the atrium from the ventricle (Figure 38).

A o^

i^

B

o^

163 os=

os= is=

Figure 38. Apical four-chamber view demonstrating tricuspid atresia

characterised by a: A) thick band between the right atrium (RA) and the rudimentary right ventricle (RV), consistent with an absent right connection; and B) flow across the open mitral valve but no flow across the absent right connection on the corresponding colour flow Doppler image. LV = left ventricle; LA = left atrium.

•

26 •

It is associated with a rudimentary RV, and the left atrium connected to a dominant LV. Ventriculo-arterial connections can be concordant or discordant.

What are the principles of assessing double-inlet ventricle on echocardiography?

Echocardiography uses the relationship of the rudimentary ventricle to the main ventricle (not usually by the ventricular trabecular pattern

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Key Questions in CONGENITAL CARDIAC SURGERY

that is much harder to distinguish) to distinguish the three types of double-inlet ventricle: a)

double-inlet LV (DILV, commonest) — which is diagnosed by finding a rudimentary anterosuperior RV either on the left or right hand side of the main ventricle (Figure 39);

164

Figure 39. Apical view (in adult

orientation with the apex up) demonstrating a double-inlet to a dominant left ventricle (LV). TV = tricuspid valve; MV= mitral valve.

b)

•

27 •

c)

double-inlet RV — which is associated with a rudimentary posteroinferior LV; double-inlet to a solitary, usually indeterminate, ventricle (rare).

The Holmes heart is a DILV with a rudimentary RV and ventriculoarterial concordance.

What are the principles of assessing hypoplastic left heart syndrome on echocardiography?

Echocardiographic assessment of a patient with hypoplastic left heart syndrome is used to identify a number of features (Figure 40), including:

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4 Congenital echocardiography A

B o^

os=

C

i^

G

o^

G

os=

D

E m^

aÉëÅ ^ç

aÉëÅ ^ç

Figure 40. Echocardiography images of hypoplastic left heart syndrome: A)

apical four-chamber view demonstrating a globular left ventricle (*), with bulging of the interatrial septum into the right atrium (RA), suggestive of a restrictive interatrial communication; B) apical four-chamber view demonstrating a slit-like LV (*); and C) tricuspid regurgitation (blue jet) on the corresponding colour flow Doppler image; D) parasternal short-axis view demonstrating a very small aorta (arrow) relative to the enlarged pulmonary artery (PA); E) suprasternal view demonstrating a small ascending aorta and transverse arch (arrow) relative to the descending aorta (Desc Ao), which is fed by the patent ductus arteriosus. RV = right ventricle; LA = left atrium.

a) b) c) d) e) f)

hypoplastic left ventricle; distinguishing aortic valve stenosis from aortic atresia by assessing colour flow across the aortic valve; distinguishing mitral valve stenosis from mitral atresia; hypoplastic aortic arch and aortic coarctation; patent ductus arteriosus size — which is essential for neonatal survival; restrictive secundum ASD — which worsens prognosis and may require an urgent balloon atrial septostomy;

165

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Key Questions in CONGENITAL CARDIAC SURGERY

g) h) i) j)

28 •

tricuspid regurgitation; coronary artery fistulae; pulmonary venous stenoses or anomalous pulmonary venous drainage (levoatrial cardinal vein); RV function, using tricuspid annular plane systolic excursion (TAPSE) and RV fractional area change (FAC).

What are the principles of assessing aortopulmonary window on echocardiography? An aortopulmonary (AP) window is best visualised in the parasternal short-axis or suprasternal arch views, anywhere from just above the semilunar valves to the more distal ascending aorta and main pulmonary artery (Figure 41).

166

G

^ç

m^

om^

Figure 41. Parasternal short-axis view demonstrating an aortopulmonary window (*), which inserts into the origin of the right pulmonary artery (RPA). Ao = aorta; PA = pulmonary artery.

• •

Left heart dilatation due to volume overload from left-to-right shunting will also be present and is best seen in the apical and subcostal fourchamber views. The most common lesions associated with AP window are interrupted aortic arch (classically Type A) and coarctation.

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29 •

4 Congenital echocardiography What are the principles of assessing anomalous origin of the left coronary artery from the pulmonary artery on echocardiography?

The anomalous left coronary artery typically arises from the left inferolateral aspect of the main pulmonary artery just beyond the pulmonary valve and is best seen in the parasternal short-axis view (Figure 42). It then courses toward the interventricular groove and branches into the left anterior descending (LAD) and left circumflex (LCX) arteries.

A

B

167

m^ m^ ^ç

^i`^m^

^ç

i^a i`u

Figure 42. Parasternal short-axis view demonstrating: A) an anomalous

left coronary artery from the pulmonary artery (ALCAPA); with B) ALCAPA originating from the pulmonary artery (PA) and dividing into the left anterior descending (LAD) and left circumflex (LCX) coronary arteries, on the corresponding colour flow Doppler image. Ao = aorta.

• • • •

The retrograde flow from the left coronary artery to the main pulmonary artery is well depicted on echocardiogram and is a characteristic finding of the steal phenomenon. The right coronary artery is often dilated. An impression of endocardial fibroelastosis is also often seen with brightness of the LV myocardium, especially the papillary muscles. Left heart dilation occurs, often associated with functional mitral regurgitation, and is best seen in the apical four-chamber view.

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30 •

What are the principles of assessing Ebstein’s anomaly on echocardiography?

Ebstein’s anomaly is best seen on the apical (Figure 43) and subcostal four-chamber views, which illustrate the key features, including: a) b)

c) d)

168

inferior displacement of the proximal attachments of the septal and posterior leaflets of the tricuspid valve; rightward and anterior rotational displacement of the valve — which results in ‘atrialisation’ of the proximal portion of the right ventricle, resulting in a reduction in the size of the functional right ventricle and tricuspid regurgitation; secundum ASD — which is a frequent association and may show right-to-left shunting on echocardiography; non-compaction of the left ventricle — which is a known association.

A

B i^

o^ is=

^ç

~os

Ños

Figure 43. Apical four-chamber view of Ebstein’s anomaly demonstrating: A) inferior displacement of the septal tricuspid valve leaflet (green arrow), compared to the normally positioned anterior tricuspid valve leaflet origin (red arrow) and septal mitral valve leaflet (blue arrow), thereby creating an atrialised portion of the right ventricle (aRV), whilst the functional portion of the right ventricle (fRV) is small; and B) severe tricuspid regurgitation, on the corresponding colour flow Doppler image. RA = right atrium; LA = left atrium; LV = left ventricle.

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4 Congenital echocardiography

•

The outflow echocardiographic views, namely the subcostal right anterior oblique and parasternal short-axis views, are used to assess the: a)

•

b)

anterior tricuspid valve leaflet — which is frequently redundant and curtain-like, and may cause right ventricular outflow obstruction; presence of any anatomical or functional pulmonary atresia.

An echocardiographic score to assess the severity of Ebstein’s anomaly with prognostic implications has been used in neonates, which involves calculating the ratio of the combined area of the right atrium and atrialised right ventricle to that of the functional right ventricle and left heart in a four-chamber view in end-diastole.

Recommended reading 1.

Colan SD. The why and how of z scores. g=^ã=pçÅ=bÅÜçÅ~êÇáçÖê 2013; 26(1): 38-

2.

Silvestry FE, Cohen MS, Armsby LB, Burkule NJ, Fleishman CE, Hijazi ZM, Lang RM,

40.

Rome JJ, Wang Y. Guidelines for the echocardiographic assessment of atrial septal

defect and patent foramen ovale: from the American Society of Echocardiography and

Society for Cardiac Angiography and Interventions. g= ^ã= pçÅ= bÅÜçÅ~êÇáçÖê 2015;

3. 4. 5. 6. 7. 8.

28(8): 910-58.

Jacobs JP, Burke RP, Quintessenza JA, Mavroudis C. Congenital heart surgery

nomenclature and database project: ventricular septal defect. ^åå=qÜçê~Å=pìêÖ 2000;

69(3): 25-35.

Rastelli GC, Ongley PA, Kirklin JW, McGoon DC. Surgical repair of the complete form of persistent common atrioventricular canal. g=qÜçê~Å=`~êÇáçî~ëÅ=pìêÖ 1968; 55(3):

299-308.

Need LR, Powell AJ, del Nido P, Geva T. Coronary echocardiography in tetralogy of

Fallot: diagnostic accuracy, resource utilization and surgical implications over 13

years. g=^ã=`çää=`~êÇáçä=2000; 36(4): 1371-7.

Hanley FL, Sade RM, Blackstone EH, Kirklin JW, Freedom RM, Nanda NC.

Outcomes in neonatal pulmonary atresia with intact ventricular septum. A

multiinstitutional study. g=qÜçê~Å=`~êÇáçî~ëÅ=pìêÖ 1993; 105(3): 406-23.

Craig JM, Darling RC, Rothney WB. Total pulmonary venous drainage into the right

side of the heart; report of 17 autopsied cases not associated with other major

cardiovascular anomalies. i~Ä=fåîÉëí 1957; 6(1): 44-64.

Wernovsky G, Sanders SP. Coronary artery anatomy and transposition of the great

arteries. `çêçå=^êíÉêó=aáë 1993; 4(2): 148-58.

169

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Key Questions in CONGENITAL CARDIAC SURGERY 9. 10. 11.

introduction to normal and congenitally malformed hearts. eÉ~êí 2001; 86 Suppl 2: II3-

11.

Van Praagh R, Papagiannis J, Grunenfelder J, Bartram U, Martanovic P. Pathologic anatomy of corrected transposition of the great arteries: medical and surgical implications. ^ã=eÉ~êí=g 1998; 135(5 Pt 1): 772-85.

Anderson RH, Cook AC. Morphology of the functionally univentricular heart. `~êÇáçä

vçìåÖ 2004; 14 Suppl 1: 3-12.

12.

Khairy P, Poirier N, Mercier LA. Univentricular heart. `áêÅìä~íáçå 2007; 115(6): 800-

13.

Backer CL, Mavroudis C. Surgical management of aortopulmonary window: a 40-year

14.

170

Ho S, McCarthy KP, Josen M, Rigby ML. Anatomic-echocardiographic correlates: an

12.

experience. bìê=g=`~êÇáçíÜçê~Å=pìêÖ 2002; 21(5): 773-9.

Dodge-Khatami A, Mavroudis C, Backer CL. Anomalous origin of the left coronary artery from the pulmonary artery: collective review of surgical therapy. ^åå= qÜçê~Å

pìêÖ 2002; 74(3): 946-55.

15.

Martinez RM, O’Leary PW, Anderson RH. Anatomy and echocardiography of the

16.

Celermajer DS, Dodd SM, Greenwald SE, Wyse RK, Deanfield JE. Morbid anatomy

normal and abnormal tricuspid valve. `~êÇáçä=vçìåÖ 2006; 16 Suppl 3: 4-11.

in neonates with Ebstein’s anomaly of the tricuspid valve: pathophysiologic and clinical implications. g=^ã=`çää=`~êÇáçä=1992; 19(5): 1049-53.

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Chapter 5

Congenital cardiac imaging Saeed Mirsadraee, Golnaz Houshmand

1 • • • • •

•

Describe the principles of computed tomography

A computed tomography (CT) scan combines a series of X-ray images taken from different projections and the attenuation data are used to reconstruct cross-sectional images. Different tissues and organs are differentiated by their inherent variation in attenuation; bone has high attenuation, air has the lowest attenuation and water has intermediate attenuation. Iodinated contrast agents are used to enhance visualisation of the blood pool, such as vessels and body organs. CT plays an important role in the characterisation of congenital cardiovascular anomalies and complications post-corrective surgery. CT exposes patients to potentially harmful ionising radiation, especially the potential risk of cancer. The Ionising Radiation Medical Exposure Regulations (IRMER) has set out responsibilities for practitioners and operators to ensure that the benefits of the exposure to ionising radiation outweigh the risks, and that the radiation dose is kept ‘as low as reasonably practicable’ for their intended use. The main risks of exposure to iodinated contrast medium are: a) b)

allergic reaction, with anaphylactic reaction reported in 24 per 1000; renal impairment, which occurs in 40mmHg or an echocardiographic peak instantaneous gradient >60mmHg; clinically significant pulmonary valvular obstruction in the presence of RV dysfunction.

The technique of pulmonary valvuloplasty includes: a) b)

general anaesthesia but can be performed under sedation in older patients; vascular access via the femoral vein. At the discretion of the operator, an arterial line may be used to monitor the arterial blood pressure;

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Key Questions in CONGENITAL CARDIAC SURGERY

c)

biplane right ventricular angiogram that is performed to confirm the site of the obstruction, to measure the pulmonary valve annulus diameter (Figure 11) and to evaluate the function of the right ventricle;

**

MPA

RVOT

220

RV

Figure 11. Angiographic evaluation of the pulmonary

valve annulus in the lateral projection after a right ventricular angiogram demonstrating thickened pulmonary valve leaflets with the valve doming (asterisks). RV = right ventricle; RVOT = right ventricular outflow tract; MPA = main pulmonary artery; A = pulmonary valve annulus.

d) e)

•

haemodynamic assessment of the pulmonary valve gradient; selection of the appropriate balloon size. Accepted practice is to use a balloon that is 1.2-1.4 times the diameter of the pulmonary valve annulus. Longer balloons give more stability during valvuloplasty, with 20mm-long balloons generally used in neonates and infants, 30mm-long balloons in children and 40mm-long balloons in adolescents and adults.

Balloon pulmonary valvuloplasty is generally a safe and effective procedure, with a low complication rate. Complications are more

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6 Congenital angiography and catheter interventions

• •

14 • • •

common in neonates or infants with the most severe pulmonary valve stenosis. Rare complications include right bundle branch block, femoral venous obstruction, injury to the tricuspid valve, pulmonary regurgitation and balloon rupture. A flow-directed catheter, such as a balloon wedge catheter, can be used to cross the tricuspid valve and subsequently a soft-tipped wire to cross the pulmonary valve prior to positioning the balloon angioplasty catheter. Whilst this may be difficult or time consuming in very small patients, the risk of not doing so could result in the catheter and or wire passing through the chordae of the tricuspid valve. This in turn may result in damage to these structures when the balloon catheter is advanced or retrieved through the right ventricle.

What are the indications for pulmonary artery angioplasty and stent placement?

Abnormalities of the pulmonary arteries are involved in a wide variety of congenital heart defects. In the clinical setting, stenotic or hypoplastic arteries may lead to a pressure burden on the right ventricle. Balloon angioplasty alone is indicated for both severe main pulmonary artery and severe branch pulmonary artery stenosis, particularly in very small patients or in those with pulmonary arteries with very complicated anatomy in whom primary stent implantation is not a viable option. Significant stenosis is obvious when there is a: a) b) c)

• • •

measurable gradient of 20-30mmHg across the stenotic area; elevation of the right ventricular or proximal main pulmonary artery pressure > two thirds of systemic pressure, secondary to more distal obstruction; relative flow discrepancy between the two lungs of 35%/65% or worse.

In low pulmonary flow situations, such as with Glenn shunts and a Fontan circulation, the gradient in the pulmonary bed is an unreliable determinant of the degree of stenosis. A similar situation presents when there is decompression run-off to a compliant contralateral artery. In this context, the pressure gradient alone is not a good indicator of severity. Pulmonary artery stents are indicated in main or branch pulmonary artery stenosis that is not expected to have, or has not had, an

221

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Key Questions in CONGENITAL CARDIAC SURGERY

adequate or persistent response to pulmonary artery balloon dilation (Figure 12). A

222

LPA stenosis

B

LPA post-stent

Figure 12. Lateral projection angiogram demonstrating: A) stenosis of the

left pulmonary artery (LPA)(arrow); and B) improvement of the LPA diameter (arrow) following treatment with balloon angioplasty and stent placement.

• • • • •

It is ideal that the stents placed into the central branch pulmonary arteries have adult-size potential. The use of smaller stents are recognised as a palliative procedure and a commitment for surgical removal or potential of enlargement at a future date. The risks of pulmonary angioplasty and stent placement include vessel perforation, arrhythmia during manipulation of the catheters and wires, and bleeding. The risks of the stents specifically include misplacement, embolisation and jailing of the adjacent branch vessels. Embolisation to the ventricle may require an emergent surgical approach for removal of the stent. Placement of a pulmonary artery stent can represent a significant burden to subsequent surgical interventions, which can be indicated by in-stent stenosis, or other surgical indications, such as pulmonary valve interventions. Stents placed beyond the bifurcation can produce complex branches stenosis, including lobar bifurcations requiring extensive reconstructions. The use of pulmonary artery branch stenting should

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6 Congenital angiography and catheter interventions

15 •

be discussed at a multidisciplinary team meeting, with both interventional cardiology and surgical teams present.

What are the indications for angioplasty or stent placement? Pulmonary vein stenosis can present as: a) b) c) d)

• •

• • • • •

pulmonary

vein

an isolated congenital lesion or in association with other cardiac defects; an acquired lesion after corrective surgery for anomalous pulmonary venous connections; a complication of extreme prematurity; a complication of pulmonary vein isolation ablation in adult patients with atrial fibrillation.

Comparison data of balloon angioplasty versus stent dilation suggest that stents achieve better results and have longer patency rates. Final stent diameter is an important factor, with a greater end diameter being associated with a better outcome. Paediatric pulmonary vein ballooning and stenting yields generally poorer results in the mid to long term, as compared to vein interventions in adults following ablation. Pulmonary vein interventions in children with congenital, progressively obstructing disease are rarely curative, with or without the addition of surgical interventions. Pulmonary artery wedge angiograms with follow through to the levophase are useful in this diagnosis, if transseptal access to the pulmonary veins is not available. The angioplasty technique requires appropriate balloon diameter selection. More recently, cutting and drug-eluting balloons have been used. Stent implantation can be considered if there is elastic recoil of the lesion or if vessel dissection is noted. A variety of stents are available but the goal is to place a stent which may be subsequently dilated (Figure 13). Complications are similar to angioplasty and stenting of other vascular structures and include vessel dissection, stent malposition or embolisation. Pulmonary haemorrhage after intense intervention on the pulmonary veins is not uncommon. Blood is cross-matched and available, and very frequently patients are monitored in a critical care area after intervention.

223

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Key Questions in CONGENITAL CARDIAC SURGERY A

B

* Figure 13. Angiographic images demonstrating: A) left pulmonary vein

stenosis at the site of the veno-atrial junction (arrow), and venous collateralisation (asterisk); and B) unobstructed drainage in the atrial cavity (arrow) following stent placement. 224

16 •

What are the indications for ductus arteriosus stent placement? Stenting of the ductus arteriosus has been used to establish a reliable source of pulmonary blood flow for the palliation of: a) b) c)

• • •

cyanotic heart disease, notably patients with severe tetralogy of Fallot and all forms of pulmonary atresia, as an alternative to aortopulmonary surgical shunts; neonates with hypoplastic left heart syndrome (HLHS), as part of the hybrid procedure, in an alternative to the Norwood procedure; neonates with non-HLHS lesions, where a single-stage repair may be contraindicated.

Current literature suggests that ductus stenting is most favourable in neonates with a morphologically straight ductus (no more than one to two bends), requiring a reliable palliation for 3-6 months. In full-term neonates, a stent diameter of 3.5-4mm generally provides adequate palliation of pulmonary blood flow without leading to excessive pulmonary blood flow. In patients weighing less than 3kg, a diameter of 3mm may be adequate. Complications of the procedure include those associated with cardiac catheterisation in neonates, particularly femoral vessel injury or occlusion.

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6 Congenital angiography and catheter interventions

• • •

17 • •

• • •

In patients with ductal-dependent pulmonary blood flow, there is a risk of requiring extracorporeal membrane oxygenation or bypass in cases of injury to the duct during manipulation or unexpected spasm compromising adequate pulmonary blood flow. Stent malposition or embolisation can occur, requiring surgical intervention. Hybrid procedures required in HLHS and non-HLHS patients involve surgical placement of bilateral branch pulmonary artery bands and stent delivery through a median sternotomy, normally performed without cardiopulmonary bypass.

What are the general principles of patent ductus arteriosus closure?

The indications for PDA occlusion vary depending on the physiological context at the time of presentation. In small and premature neonates (80mL/m2; iii) RV ejection fraction 20mmHg or in the presence of significant collateral vessels and suitable angiographic anatomy, irrespective of patient age; patients with a univentricular heart or significant ventricular dysfunction may not exhibit high gradients but are candidates for intervention.

It is reasonable to consider balloon angioplasty of native coarctation (Figure 24) as a palliative measure to stabilise a patient irrespective of age when extenuating circumstances are present, such as

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Key Questions in CONGENITAL CARDIAC SURGERY A

238

B

Figure 24. Lateral view angiographic images demonstrating: A) a tight and

discrete hour-glass coarctation (arrows); and B) improvement (red arrows) following balloon angioplasty.

• •

severely depressed ventricular function, severe mitral regurgitation, low cardiac output, end-organ dysfunction (such as renal failure), or systemic disease affected by the cardiac condition. The recurrence rate is higher for younger patients (20mmHg.

Where possible, a stent that can be expanded to an adult size should be used. Current limiting factors are the size of the sheath required to deliver such a stent. The availability of surgical expertise and stent technology should dictate local institutional practice. Balloon and/or stent angioplasty of coarctation carries a serious risk of vessel disruption and bleeding. Covered stent technology offers some protection from this complication and many operators use the

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6 Congenital angiography and catheter interventions A

B

*

Before stent

After stent

Figure 25. Lateral view angiographic images demonstrating: A) a tight hour- 239 glass coarctation with mild pre-stenosis dilatation; and B) improvement following balloon angioplasty and stent insertion (asterisk).

covered CP Stent™ (Figure 26) by choice, accepting that the sheaths required to deliver such stents may limit their use to teenage and adult patients.

Figure 26. Covered CP Stent™ used for

coarctation of the aorta.

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Key Questions in CONGENITAL CARDIAC SURGERY

•

If transverse arch hypoplasia accompanies discrete coarctation, it may also be tackled using stent angioplasty with the recognised problems of crossing the major head and neck vessels. In such circumstances, open cell design stents are ideally suited.

Recommended reading 1.

Jayaram N, Beekman RH, Benson L, Holzer R, Jenkins K, Kennedy KF, Martin GR, Moore JW, Ringel R, Rome J, Spertus JA, Vincent R, Bergersen L. Adjusting for risk

associated with pediatric and congenital cardiac catheterization: a report from the

240

NCDR® IMPACT™ Registry. `áêÅìä~íáçå 2015; 132(20): 1863-70.

2.

Zahn EM, Nevin P, Simmons C, Garg R. A novel technique for transcatheter patent

3.

Prabhu S, Anderson B, Ward C, Karl T, Alphonso N. A simplified technique for

4.

ductus arteriosus closure in extremely preterm infants using commercially available technology. `~íÜÉíÉê=`~êÇáçî~ëÅ=fåíÉêî 2015; 85(2): 240-8.

interventional extracardiac Fontan. tçêäÇ=g=mÉÇá~íê=`çåÖÉåáí=eÉ~êí=pìêÖ 2017; 8(1): 92-8.

Cheatham JP, Hellenbrand WE, Zahn EM, Jones TK, Berman DP, Vincent JA, McElhinney DB. Clinical and hemodynamic outcomes up to 7 years after transcatheter

pulmonary valve replacement in the US melody valve investigational device exemption

5.

trial. `áêÅìä~íáçå 2015; 131(22): 1960-70.

Feltes TF, Bacha E, Beekman RH 3rd, Cheatham JP, Feinstein JA, Gomes AS, Hijazi

ZM, Ing FF, de Moor M, Morrow WR, Mullins CE, Taubert KA, Zahn EM; American

Heart Association Congenital Cardiac Defects Committee of the Council on Cardiovascular Disease in the Young; Council on Clinical Cardiology; Council on

Cardiovascular Radiology and Intervention; American Heart Association. Indications for cardiac catheterization and intervention in pediatric cardiac disease: a scientific statement from the American Heart Association. `áêÅìä~íáçå 2011; 123(22): 2607-52.

6.

Meadows J, Minahan M, McElhinney DB, McEnaney K, Ringel R; COAST

7.

Kang SL, Jivanji S, Mehta C, Tometzki AJ, Derrick G, Yates R, Khambadkone S, de

Investigators. Intermediate Outcomes in the Prospective, Multicenter Coarctation of the Aorta Stent Trial (COAST). `áêÅìä~íáçå 2015; 131(19): 1656-64.

Giovanni J, Stumper O, Dhillon R, Bhole V, Slavik Z, Rigby M, Noonan P, Smith B,

Knight B, Richens T, Wilson N, Walsh K, James A, Thomson J, Bentham J, Hayes N,

Nazir S, Adwani S, Shauq A, Ramaraj R, Duke C, Taliotis D, Kudumula V, Yong SF,

Morgan G, Rosenthal E, Krasemann T, Qureshi S, Crossland D, Hermuzi T, Martin RP.

Outcome after transcatheter occlusion of patent ductus arteriosus in infants less than

6kg: a national study from United Kingdom and Ireland. `~íÜÉíÉê= `~êÇáçî~ëÅ= fåíÉêî 8.

2017; 90(7): 1135-44.

Hascoët S, Baruteau A, Jalal Z, Mauri L, Acar P, Elbaz M, Boudjemline Y, Fraisse A.

Stents in paediatric and adult congenital interventional cardiac catheterization. ^êÅÜ

`~êÇáçî~ëÅ=aáë 2014; 107(8-9): 462-75.

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Chapter 7

Anaesthesia and congenital heart disease Michael Puntis, Sian Jaggar

1 • • • •

Describe the involvement of anaesthetists in the care of patients with congenital heart disease

During pre-operative planning and peri-operative care of patients undergoing cardiac surgical interventions. Providing general anaesthesia or sedation for patients undergoing percutaneous interventions in the cardiac catheter laboratory. Providing intensive care support for both adult and paediatric patients. Providing anaesthesia for non-cardiac interventions, including: a) b) c)

2 •

•

specialist interventions — such as pain management or vascular access; general surgical interventions unrelated to the cardiac disease; obstetric interventions — where the greatly increased physiological demands of pregnancy may precipitate cardiac problems, requiring close liaison between medical, obstetric and anaesthetic staff.

Describe the factors that determine the use of anaesthesia or sedation Patient factors:

a) b) c)

age; comorbidity; cognitive and psychological considerations.

Procedural factors: a) b) c)

position required; duration; degree of invasiveness.

241

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3 •

What are the differences between neonates and older children from an anaesthetic point of view?

Airway — the neonatal airway is more challenging to manage because the: a) b) c)

•

Breathing — in the neonate, hypoxia occurs much more rapidly; this is affected by: a) b)

242

c) d) e) f)

•

prominent occiput pushes the neck into flexion when supine; tongue is relatively large; epiglottis is floppy and U-shaped, and the larynx is relatively cephalad.

neonatal respiratory centres — which although mature are more easily suppressed by drugs or hypothermia; intercostal and diaphragmatic muscles — which contain fewer Type I (slowly contracting, highly oxidative) muscle fibres and are easily fatigued; reduced mechanical advantage — as the ribs are relatively horizontal, requiring a greater contribution from the diaphragm; reduced functional residual capacity (FRC) — which usually provides a store of oxygen. This results from low lung compliance, despite a relatively compliant chest wall; higher airway resistance with increased work of breathing — which consumes more of the inspired oxygen; foetal-type acetylcholine receptors, expressed in neonates — which are more sensitive to depolarising muscle relaxants, hence, normal respiratory function may take longer to recover.

Circulation — which requires different management because: a) b) c)

neonatal cardiac output is particularly rate-dependent, as stroke volume cannot readily be increased; neonatal myocardium is relatively stiff and less able to increase contractility or respond to preload; neonates have a proportionally much greater cardiac output, due to an increased heart rate (400mL/kg/min at birth, 150mL/kg/min at 8 weeks and 70mL/kg/min at puberty).

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7 Anaesthesia and congenital heart disease

•

Pharmacology — where many important pharmacokinetic factors are less well developed, including: a) b) c) d)

•

•

4 •

Temperature control — neonates and infants have an increased surface area to volume ratio, favouring heat loss. Steps to maintain normothermia include ensuring adequate ambient temperature and the use of forced air warmers. Generating heat to maintain body temperature causes a dramatic increase in metabolic demands on the neonate. Communication — as cognitive function develops, a child’s ability to understand, communicate and reason improves. The developmental stage impacts upon interaction with both the child and parents.

What are the principles of pre-operative assessment and preparation of paediatric cardiac surgical patients for anaesthetists? Information should be gathered first, including: a)

b) c)

• •

absorption — neonatal drug absorption is altered by increased gastric pH, slower gastric emptying and increased intestinal transit time; distribution — the blood-brain barrier is less well developed and sedative drugs may cross more easily; metabolism — neonates can metabolise most drugs but more slowly than older children; excretion — renal excretion is impaired, especially in the preterm neonate. Some drugs, such as aminoglycosides, need to be administered less frequently.

history — review of the case notes and discussion with the patient/parents for information about the cardiac diagnosis, other related comorbidity and history of any previous anaesthesia (both for the child and family members); examination — especially considering ease of airway management and potential vascular access sites; investigations — especially those relevant to the cardiovascular and respiratory status.

All correctable medical conditions should be optimised prior to surgery and any issues that cannot be changed must be accepted. The risk level should be stratified to plan for peri-operative care. Critical care is mandatory for most cardiac surgical procedures and

243

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• • •

244

•

5 • •

more common for many other procedures than for patients without congenital heart disease. Rapport must be established with both the patient and their family. Anxious patients suffer more adverse events, such as laryngospasm, during anaesthesia and premedication may help. Induction using intravenous or inhalational agents should be discussed with the child and parents, to aid compliance. Patients and parents should be aware of and accept the risks associated with the planned techniques, including invasive monitoring. Details of starvation times should be documented, especially as patients with congenital heart disease are at particular risk from dehydration, potentially caused by excessive starvation times. The usual rules are: a) b) c)

clear (non-fizzy) fluids — 1 hour before anaesthesia; breast milk — 4 hours before anaesthesia; other milk or food — 6 hours before anaesthesia.

Options for analgesia and their relevant risks should also be discussed.

Which investigations are helpful to the anaesthetist in the pre-operative assessment?

Many routine investigations are performed to screen for unidentified problems and to provide a baseline assessment of the patient’s physiology and metabolic status. Although most pre-operative investigations are performed primarily for surgical reasons, they provide useful anaesthetic information. Blood tests, including: a) b)

c)

full blood count (FBC) — which establishes the presence of polycythaemia or anaemia. Cyanotic patients require higher haemoglobin levels for adequate oxygen delivery; haemoglobinopathy screen (including HbSS) — which should be performed in the relevant patient groups, especially if cooling is planned, which may cause a sickle crisis. In cases where hypothermia presents significant risks, the surgeons, anaesthetists and perfusionists may agree to maintain a normal body temperature on bypass; platelet count and coagulation studies — especially as cyanotic patients are prone to bleeding, even when laboratory findings are normal. Ordering products early helps to ensure rapid and effective management;

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7 Anaesthesia and congenital heart disease d)

e)

• •

Electrocardiogram (ECG) — to identify signs of any conduction abnormalities or arrhythmias, which may require peri-operative pacing interventions (temporary or permanent). Chest radiograph (CXR) — which provides information regarding the: a) b) c) d)

•

6 • • • •

urea & electrolytes — as abnormalities increase the risk of myocardial irritability or indicate underlying renal dysfunction. Arrhythmias are particularly important when cardiac function is borderline; pregnancy test — which is indicated for all female patients post-menarche. Careful communication is vital for these patients.

lower airway — including the size of the lungs; other anatomical abnormalities — such as sequestrated lung or diaphragm anomalies; respiratory disease — such as acute airways or parenchymal infections requiring treatment; non-infectious lung disease — which may or may not require therapy but might affect peri-operative risk or affect prognosis.

Specific investigations, such as cardiac catheterisation and echocardiography, which define abnormal anatomy and physiology can also identify high-risk lesions that may influence the conduct or risk of anaesthesia.

What psychological, social and legal issues may arise when assessing paediatric patients for anaesthesia?

A patient’s understanding varies quite considerably, depending on age, educational level, cognitive ability and complexity of the lesion. Some patients have great insight into their condition, while others will have little or none. Anxieties or phobias may develop following multiple interventions and admissions. These should be actively managed prior to further intervention and the anaesthetist should be involved at an early stage. Younger patients and those with learning difficulties may need information provided in differing formats, including for postoperative care and appropriate pain-scoring tools. Language barriers can present insurmountable obstacles to communication, and in these cases, interpreters are required during anaesthetic assessment, as they are during surgical consenting.

245

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7 • •

246

•

•

8 • •

Which comorbidities or patient factors should be discussed with the anaesthetic team early?

Some situations require additional planning and surgery may be delayed if the anaesthetist is unaware of issues until the day of surgery. Abnormal airways — patients with congenital heart disease may have associated abnormal airway anatomy, making conventional laryngoscopy difficult. Further airway assessment or alternative techniques may need to be planned. In adults, a number of tests are able to predict difficult intubation, although none are particularly specific or sensitive. Similar tests are not validated in children. Conditions known to be associated with difficult intubation include: a) b) c)

trisomy 21; Pierre-Robin syndrome; DiGeorge syndrome.

Significant comorbidity, such as pulmonary disease, may necessitate prolonged postoperative critical care and therefore require advanced planning. Patients with congenital heart disease with varying degrees of learning difficulties, or other neuropsychological issues, may be poorly compliant with postoperative care, including respiratory care, mobility and medications. Psychological problems, such as anxiety or needle phobia, may require addressing pre-operatively. Older children and patients in transitional age may present significant problems with compliance, especially those with previous surgical experiences.

Describe how congenital heart disease is broadly classified for planning of anaesthetic management

A normal circulation is characterised by equal pulmonary and systemic flow in functionally serial circulations. This may be disrupted in patients with congenital heart disease. Pathology can be considered in terms of how changes in pulmonary and systemic vascular resistances influence flow: a)

increased pulmonary blood flow — with systemic to pulmonary shunting of blood (Figure 1). This type of shunt lesion includes: i) atrial septal defects (ASD); ii) ventricular septal defects (VSD); iii) atrioventricular septal defects (AVSD); iv) patent ductus arteriosus (PDA);

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7 Anaesthesia and congenital heart disease

Figure 1. Systemic to pulmonary (left to right) shunt through an atrial

septal defect causes increased pulmonary blood flow, as well as right atrial and right ventricular volume overload. RA = right atrium; RV = right ventricle; LA = left atrium; LV = left ventricle.

b)

These are usually initially acyanotic conditions, mostly characterised by volume overload and congestive heart failure but pulmonary hypertension (PHT) may appear and cause reversal of the shunt and cyanosis; decreased pulmonary blood flow — with pulmonary to systemic (often right to left) shunting of blood (Figure 2). This occurs when the resistance to flow is higher through the pulmonary than the systemic circulation and includes: i) tetralogy of Fallot; ii) pulmonary atresia with or without VSD; iii) double-outlet right ventricle (DORV) of tetralogy type; iv) DORV of transposition of the great arteries (TGA) type. These are typically cyanotic lesions, due to the mixing of blood from the systemic venous return into the systemic circulation. In some cases, the mixing is obligated and complete (such as in pulmonary atresia), whereas in others, the degree of mixing depends on the degree of obstruction of the outflow tract and can vary in different physiological conditions (such as in tetralogy of Fallot);

247

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248

Figure 2. Higher resistance to pulmonary blood flow (mechanical or

physiological) results in pulmonary to systemic (right to left) shunting (through an atrial septal defect) and reduced arterial oxygen saturations. RA = right atrium; RV = right ventricle; LA = left atrium; LV = left ventricle.

c)

d)

decreased systemic blood flow — which is often associated with systemic hypoperfusion (Figure 3). This condition is associated with a few anomalies, such as: i) coarctation of the aorta; ii) hypoplastic left heart syndrome (HLHS); iii) congenital severe aortic stenosis; iv) total anomalous pulmonary venous connections (TAPVC) with obstruction to left atrial inflow; v) TGA with a small PDA or restrictive ASD; balanced parallel circulation — where pulmonary and systemic blood flow are well balanced but not necessarily equal (Figure 4). This type of physiology is seen in: i) functionally single-ventricle circulations — HLHS, absent interventricular septum, unbalanced AVSD, hypoplastic right heart syndrome (HRHS); ii) truncus arteriosus with a large VSD. In these cases, the balancing of the two circulations is due to the relative resistance of the two vascular beds. In some cases, there may be a mechanical obstruction to the pulmonary circulation preventing the circulation to overflow to the lungs.

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7 Anaesthesia and congenital heart disease

Figure 3. Decreased systemic blood flow distal to an obstruction (left

ventricular outflow tract obstruction). RA = right atrium; RV = right ventricle; LA = left atrium; LV = left ventricle.

Figure 4. Balanced circulation with total mixing of blood in a ‘common ventricular cavity’. The oxygen saturations of blood entering the systemic and pulmonary circulations are the same. RA = right atrium; RV = right ventricle; LA = left atrium; LV = left ventricle.

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9 •

Many precipitants, such as infection, pulmonary hypertension or systemic vasodilatation, acutely disrupt this equilibrium, exacerbating cyanosis or congestive heart failure.

What are the principles of anaesthesia for patients with congenital heart disease? The circulation may be destabilised by many events that occur during anaesthesia, including: a) b) c) d) e)

250

• • • • • • • •

reduced venous return to the right ventricle; reduced myocardial function; increased pulmonary vascular resistance — with subsequent reduced venous return to the left ventricle; decreased systemic vascular resistance — with reduced aortic root pressure, potentially impairing coronary artery blood flow; abnormal temperature or glucose availability — altering enzyme function in the myocardium and other tissues.

As patients are usually hypovolaemic, secondary to pre-operative starvation and vasodilatation caused by anaesthetic agents, venous return must be carefully monitored. Excess bleeding, potentially due to failed haemostatic management, may cause reduced preload and circulatory instability. Many anaesthetic agents suppress myocardial function. These effects are minimised by balanced anaesthetic techniques, typically utilising opioids, sedatives and a muscle relaxant. Induction and extubation are high-risk periods, requiring extra vigilance, as both hypoventilation and positive intrathoracic pressure causing hypercapnia can increase pulmonary vascular resistance (PVR). Hypothermia and hyperthermia are a hazard to the circulation and metabolic homeostasis. Effective temperature control includes active warming or cooling, both off and on cardiopulmonary bypass. Adequate temperature control helps to minimise coagulation abnormalities. Neonates have minimal ability to store glycogen and glucosecontaining fluids may be required. Endocarditis is a risk and prophylactic antibiotics should always be considered. Patients with abnormal connections between the left and right heart are at risk of paradoxical emboli from intravenous injections.

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10 •

7 Anaesthesia and congenital heart disease What are the principles of anaesthesia in the presence of a cyanotic lesion?

Cyanosis occurs when arterial blood contains deoxyhaemoglobin at concentrations greater than 20g/L. In cyanotic lesions, it can worsen when: a)

• • • • • •

11 • •

b)

oxygen saturation in the pulmonary veins is reduced due to a ventilation-perfusion mismatch, such as with ventilatory failure, pulmonary oedema or pneumonia; excessive right-to-left shunting.

Management of cyanosis involves manipulation of ventilation and vascular resistance. Right-to-left shunting is encouraged by a rise in PVR, a fall in systemic vascular resistance (SVR) or a combination of both. PVR elevation may be caused by hypoxia, hypercarbia or acidosis. Positive end-expiratory pressure (PEEP) during intermittent positive pressure ventilation (IPPV) directly increases PVR but may indirectly decrease it by avoiding alveolar collapse and subsequent hypoxia. Poor fluid resuscitation results in acidosis and increased PVR, whereas fluid overload causes pulmonary oedema, hypoxia and increased PVR. Extubation is a particularly challenging period. Although early extubation avoids coughing and increased PVR, due to irritation from the endotracheal tube, it risks hypoxia and hypercarbia. Anaesthetic agents frequently reduce SVR and systemic vasopressors may be needed to maintain the balance between PVR and SVR.

What are the principles of management in a patient undergoing repair of an Ebstein’s anomaly?

Ebstein’s anomaly occurs when the tricuspid valve leaflets fail to delaminate from the myocardium. The functional annulus is displaced into the right ventricle with varying degrees of ‘atrialisation’ of the right ventricle, tricuspid regurgitation and right atrial dilatation. Cardiac output may fall due to increased regurgitant flow. The main anaesthetic risks include: a) b) c)

poor cardiac output; right-to-left shunting through an interatrial communication; increased susceptibility to arrhythmias.

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• • •

12 • 252

The goals are to minimise PVR, optimise preload and maintain myocardial contractility. Maintaining sinus rhythm and right ventricular preload more effectively supports cardiac output than using inotropes or vasopressors. Some authors advocate the use of a small dose of a vasopressor agent to maintain adequate systemic perfusion pressure and avoid the administration of a large amount of fluid, thus preventing further dilatation of the right ventricle.

What are the principles of managing a neonate with hypoplastic left heart syndrome?

•

Neonates with HLHS have a single functional (right) ventricle. Mixed pulmonary and systemic venous blood is ejected into systemic and pulmonary circulations (Figure 5). Flow distribution to the two circulations is dependent on PVR and SVR. In these patients, neonatal PVR is too high to allow passive pulmonary flow, making conversion to a parallel circulation impossible. The first operation is usually a Norwood procedure with a neo-aorta constructed from pulmonary artery and is performed within the first week of life. The pulmonary circulation is provided by a BlalockTaussig shunt or a RV-to-PA conduit (Sano modification, Figure 6). Pre-operatively, the goals are to optimise:

•

The peri-operative challenges include:

• •

a) b)

a) b) c)

pulmonary function, especially to avoid infection; systemic perfusion, by: i) maintaining a patent ductus arteriosus using prostaglandin E2; ii) keeping the SVR low and PVR high to maintain balance; iii) using inotropes.

balancing pulmonary and systemic perfusion in the context of pulmonary hyper-reactivity. This can potentially be achieved by modifying ventilation parameters; managing myocardial dysfunction and ischaemia; minimising cerebral hypoxia during circulatory arrest — which can be improved by increasing the: i) perfusion pressure;

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253

Figure 5. Hypoplastic left heart syndrome, characterised by hypoplasia

of the mitral valve, aortic valve, left ventricle and ascending aorta. The systemic circulation is maintained by flow across a large patent ductus arteriosus. Blood circulates both antegradely in the descending aorta and retrogradely into the aortic arch and coronary arteries. A drop in pulmonary vascular resistance will favour circulation into the lungs and reduce flow into the systemic circulation. RA = right atrium; RV = right ventricle; LA = left atrium; LV = left ventricle; IVC = inferior vena cava; SVC = superior vena cava; Asc Ao = ascending aorta; PDA = patent ductus arteriosus; MPA = main pulmonary artery.

•

ii) iii)

haemoglobin; arterial carbon dioxide tension.

Near-infrared spectroscopy (NIRS) is useful to monitor cerebral saturations.

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Figure 6. Circulation following the Norwood procedure, where pulmonary venous (red) and systemic venous (blue) blood mix in the atria via an atrial septal defect, resulting in mixed blood ejected into common outflow with a balanced circulation. RA = right atrium; RV = right ventricle; LA = left atrium; LV = left ventricle; IVC = inferior vena cava; SVC = superior vena cava; Neo-Ao = neo-aorta; BTS = Blalock-Taussig shunt.

13 • •

What are the anaesthetic considerations for a patient with a single ventricle?

Single ventricles provide flow to both the pulmonary and systemic circulations, acting as systems in parallel, with flow depending on the relative resistances in the circuits. A bidirectional Glenn procedure (Figure 7) can usually be performed by the age of 6 months. Pressure monitoring from internal jugular lines then reflects pulmonary artery pressures.

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255

Figure 7. Bidirectional Glenn procedure, where the superior vena cava is anastomosed to the pulmonary artery. Oxygenated blood (red) enters the right atrium through an atrial septal defect and mixed blood (purple) is ejected into the systemic circulation. BTS = Blalock-Taussig shunt; PA = pulmonary artery; SVC = superior vena cava.

• •

Total cavopulmonary connection (TCPC) is usually achieved by 4 years. As blood flow through the lungs is then entirely passive, minimising the PVR is vital (Figure 8). When managing a TCPC circulation, it is important to avoid an elevation in PVR due to: a) b) c) d)

hypoxia; hypercarbia; acidosis; drugs (e.g. ketamine).

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Figure 8. Total cavopulmonary connection (TCPC) circulation, where venous blood (blue) flows passively from the superior and inferior vena cavae into the pulmonary circulation. Oxygenated blood (red) returns to the right ventricle via an atrial septal defect and is ejected into the systemic circulation. PA = pulmonary artery; IVC = inferior vena cava; SVC = superior vena cava.

• • •

Hypovolaemia is poorly tolerated in passive circulations. As the risk of arrhythmias is increased in this patient population and is poorly tolerated, maintenance of sinus rhythm is paramount. This is particularly problematic where the whole right atrium is within the circuit (classical Fontan) rather than only the vena cavae (TCPC). Often the function of the systemic ventricle, which is a morphological right ventricle, is impaired and responds poorly to increased metabolic demand. Over time, hypertrophy and dilatation occur and response to inotropes is poor.

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7 Anaesthesia and congenital heart disease

•

14 • • • • • • •

15 • • • •

Central venous lines are a very significant risk, especially for thrombosis or post-surgical line obstruction to venous drainage.

What are the principles of anaesthesia in a patient undergoing repair of coarctation of the aorta with poor left ventricular function?

All obstructions to systemic blood flow causing a severe increase in afterload lead to upper body hypertension and congestive heart failure. In patients with coarctation of the aorta, the obstruction can cause severe impairment of left ventricular function in the early days, especially when the PDA spontaneously closes. When preparing for surgery in these patients, the blood pressure may be monitored above and below the coarctation via the right radial and femoral arteries. Pre-operative inotropes may be required to support ventricular contractility and cardiac output. Significant proximal hypertension with cross-clamping of the aorta may require vasodilators. Some centres use a small dose of heparin during the procedure to prevent stasis-related clotting in the proximity of the vascular clamps. Hyperventilation should be avoided throughout, as it causes vasoconstriction with reduced cerebral and spinal perfusion. Postoperative analgesia provides comfort and control of hypertension. Intercostal blocks can be sited under direct vision intra-operatively to effect this.

What are the principles of anaesthesia for a patient with pulmonary atresia and an intact ventricular septum?

Pulmonary atresia with intact ventricular septum (PA-IVS) is one of the most challenging conditions that an anaesthetist might need to face (Figure 9). It is characterised by right ventricular hypertrophy and hypoplasia, capable of generating supra-systemic pressures, and varying degrees of tricuspid valve hypoplasia. The degree of hypoplasia of the tricuspid valve is directly linked to the presence of coronary sinusoids. These ventriculo-coronary fistulae render myocardial perfusion dependent on intracavitary pressures. As a result, any change in preload, central venous pressure and systemic vascular resistance, can affect myocardial perfusion, especially when coronary arteries present with significant stenoses.

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Figure 9. Pulmonary atresia with intact ventricular septum. As blood

cannot be ejected from the right ventricle, all pulmonary flow occurs through a patent ductus arteriosus. Venous blood (blue) enters the left atrium via an atrial septal defect, mixing with oxygenated blood (red) from the pulmonary veins. Note the right ventricular dependent sinusoids feeding the coronary circulation. ASD = atrial septal defect; PDA = patent ductus arteriosus.

• • • •

Pulmonary flow is PDA-dependent, requiring pre-operative prostaglandin E2. Although radiofrequency perforation and dilatation of the valve may be possible, tamponade is a recognised risk and adequate vascular access is required pre-procedure. Total atresia of the infundibulum requires a modified Blalock-Taussig shunt (BTS) to produce a balanced circulation. Inotropes are associated with an increased subpulmonary gradient and should be avoided where possible.

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16 • • • • • • • •

17 •

7 Anaesthesia and congenital heart disease What are the principles of anaesthesia for ligation of a patent ductus arteriosus in a preterm neonate?

Patency of the ductus arteriosus in preterm infants is inversely proportional to gestational age. Approximately 50% of preterm infants 7.5% suggest antifibrinolytics (such as tranexamic acid or aprotinin) may be required.

What are the advantages and disadvantages of early tracheal extubation following surgery for congenital heart disease?

Patients are routinely ventilated following complex cardiac surgery. Prolonged ventilation increases the risk of complications.

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• •

Pulmonary blood flow, particularly passive flow, such as in a Fontan circulation, is determined by the pressure gradient between the pulmonary arteries and capillaries. This is reduced by intermittent positive pressure ventilation and a return to spontaneous ventilation improves pulmonary blood flow and cardiac output. Reducing the duration of ventilation is associated with:

•

Prolonged ventilation is associated with complications, including:

272

a) b) c)

a) b) c) d)

•

d)

•

ventilator-associated pneumonia (VAP); subglottic stenosis; adverse events, such as accidental extubation, kinking or obstruction; side effects of sedation and neuromuscular blockade, which are necessary to facilitate toleration of the endotracheal tube.

For some patients, early extubation is inappropriate and a more gradual weaning from mechanical ventilation is required, including in patients with: a) b) c)

29

shorter hospital stay; increased patient comfort and parental satisfaction; early recovery of communication, feeding, bowel function and mobility.

prolonged cardiopulmonary bypass time; significant inotrope requirement; significant comorbidities — such as pulmonary hypertension, heart failure, chronic lung disease or liver failure; a high risk of TRALI, acute respiratory distress syndrome (ARDS) or multi-organ failure (MOF) — who tolerate reintubation poorly and early extubation may not be helpful.

What are the features of an effective handover from anaesthesia to the paediatric intensive care unit team?

Although personal styles vary, certain key information must be conveyed in a concise and relevant summary, including: a) b)

basic patient identifiers, including hospital number, date of birth, age and weight; diagnostic issues, including underlying condition, pre-operative conditions, previous procedures and allergies;

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7 Anaesthesia and congenital heart disease c)

d) e)

f)

g) h)

30 •

i)

information on the procedure performed, including repair or palliation, current anatomical and physiological status, presence or absence of residual lesions and their description, relevant information on cardiopulmonary bypass, information regarding the use of blood and blood products, presence or absence of arrhythmias, need for pacing, and position and function of drains; airway issues: i) ease of mask ventilation and laryngoscopy; ii) endotracheal tube size and depth; ventilator requirements: i) ventilator mode and airway pressures; ii) oxygen requirement; iii) need for nitric oxide; circulatory issues: i) site and size of intravascular lines; ii) details of cardiopulmonary bypass, including duration of bypass, cross-clamp and deep hypothermic circulatory arrest; iii) inotrope and pacing requirements, including underlying rhythm and function; iv) use of blood and products and current availability; v) available or outstanding results; vi) use of ultrafiltration; antibiotics, analgesia and fluids administered; plans should be discussed, including ideal haemodynamic parameters; contact details should problems arise.

What are the negative effects of poorly controlled postoperative pain?

Pain stimulates a neuroendocrine stress response with wide-ranging adverse physiological and emotional consequences. Many effects reflect increased levels of circulating catecholamines, including: a) cardiovascular: i) increased myocardial workload due to increased heart rate, SVR, PVR and oxygen requirements; ii) PVR is increased by raised intrathoracic pressure induced by crying. Shunting may be altered; b) respiratory: i) increased atelectasis, increasing the risk of pneumonia; ii) hypocapnia (and altered PVR) with prolonged crying;

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c)

d)

31 • • 274

• • • • •

What systems may be used to ensure quality control in anaesthesia services for congenital heart disease?

Quality can be defined as “the degree to which health services increase the likelihood of desired health outcomes and are consistent with current professional knowledge”. Assessing quality requires robust, relevant and measurable outcomes. The complexity of healthcare makes this difficult. Currently, popular parameters include outcome data, such as mortality, complications and satisfaction surveys. Measuring quality in anaesthesia is challenging. Confounding factors make identifying meaningful measurable metrics, specific to the delivery of anaesthesia, difficult. Committing to ongoing quality improvement programmes (QIP) leads to maintenance of high standards. Areas for improvement may be identified from the analysis of adverse events, anecdotal reports or morbidity and mortality reviews. Once a problem has been identified, a proposed standard should be defined. Data should be collected defining current practice and suggesting improvements. Following any change, the process must be repeated to evaluate impact (Figure 16). The QIP cycle may have both positive and negative effects: a) b)

•

central nervous system: i) aversion to future procedures complicating ongoing care; ii) impaired communication; general: i) impaired wound healing due to reduced subcutaneous oxygen partial pressure; ii) poor mobilisation, increasing complications and delaying discharge from ICU and hospital.

positive — such as identify resource deficiencies or educational needs to increase efficiency; negative — such as frequent changes in practice come at a cost, including staff disengagement.

The costs and benefits must be balanced. Identifying key improvement areas will yield the greatest benefits.

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7 Anaesthesia and congenital heart disease Define standards

Observe and compare current practice to standards

Local or national

Define relevant local metrics

mêçÄäÉã= áÇÉåíáÑáÉÇ Reobserve and compare practice to standards Using relevant local metrics

Implement change Ensure ‘buy-in’ from whole team

Figure 16. The quality improvement cycle (previously known as the audit cycle).

Recommended reading 1. 2. 3.

Yamamoto T, Schindler E. Anaesthesia management for non-cardiac surgery in

children with congenital heart disease. ^å~ÉëíÜÉëáçä=fåíÉåëáîÉ=qÜÉê 2016; 48(5): 305-

13.

Subramaniam R. Anaesthetic concerns in preterm and term neonates. fåÇá~å= g

^å~ÉëíÜ 2019; 63(9): 771-9.

Checketts MR, Alladi R, Ferguson K, Gemmell L, Handy J, Klein A, Love N, Misra U, Morris C, Nathanson M, Rodney G, Verma R, Pandit J. Standards of monitoring during

anaesthesia and recovery. London, UK: The Association of Anaesthetists of Great

4.

Britain and Ireland, 2015.

Odegard KC, Vincent R, Baijal R, Daves S, Gray R, Javois A, Love B, Moore P,

Nykanen D, Riegger L, Walker SG, Wilson EC. SCAI/CCAS/SPA expert consensus

statement for anesthesia and sedation practice: recommendations for patients

undergoing diagnostic and therapeutic procedures in pediatric and congenital cardiac

5. 6. 7.

catheterization laboratory. `~íÜÉíÉê=`~êÇáçî~ëÅ=fåíÉêî 2016; 88(6): 912-22.

Liu Y, Chen K, Mei W. Neurological complications after cardiac surgery: anesthetic

considerations based on outcome evidence. `ìêê= léáå= ^å~ÉëíÜÉëáçä= 2019; 32(5): 563-7.

Shen L, Tabaie S, Ivascu N. Viscoelastic testing inside and beyond the operating

room. g=qÜçê~Å=aáë 2017; 9(suppl4): S299-S308.

Andropoulos DB. Effect of anesthesis on the developing brain: infant and fetus. cÉí~ä

aá~Öå=qÜÉê 2018; 43(1): 1-11.

275

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Key Questions in CONGENITAL CARDIAC SURGERY 8.

Haller G, Bampoe S, Cook T, Fleisher LA, Grocott MPW, Neuman M, Story D, Myles

P, on behalf of the StEP-COMPAC Group. Systematic review and consensus definitions for the standardised endpoints in perioperative medicine initiative: clinical indicators. _ê=g=^å~ÉëíÜ 2019; 123(2): 228-37.

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Chapter 8

Paediatric cardiac intensive care Michael J. Griksaitis, Melanie A. Connett

1 • • •

What are the principles of practice for a cardiac intensive care unit?

Cardiac intensive care units are highly specialised units providing intensive care to a wide range of clinical scenarios and needs. Some hospitals operate specialised cardiac intensive care (paediatric and adult) and some care for patients with cardiac disease as part of the general intensive care practice. Regardless of the structural model, specialists in cardiac intensive care are called to deal with a child or adult with a cardiac condition, admitted: a) b)

•

c)

with an acute medical problem including stabilisation prior to cardiotomy; following cardiac operations and/or catheter-based procedures (diagnostic or therapeutic, electrophysiology interventions); after non-cardiac surgery.

This chapter will focus on children with cardiac conditions, with the principles of intensive care for the adult congenital heart disease population described in the following chapter.

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2

What are the monitoring tools that are available to the paediatric intensivist (Table 1)?

Table 1. Common monitoring tools used in the paediatric intensive care unit.

mf`r=ãçåáíçêáåÖ=íççä

aÉëÅêáéíáçå

ECG

All patients have a rhythm strip displayed on their monitor, allowing the determination of heart rate and rhythm. Many machines allow for a variety of leads to be selected and can also determine ST segment changes from the baseline.

Invasive arterial pressure

Invasive arterial lines measure the arterial blood pressure beat-by-beat. The pulse pressure can give an indication of the systemic vascular resistance or diastolic run-off. The pulse pressure variation (change in peak amplitude of the systolic pressure), also known as a ‘swing’, can suggest volume depletion. The trace itself can indicate myocardial contractility; a steep upstroke implies a greater change in pressure per unit of time, which therefore suggests good contractility and vice versa. Cardiac output (CO) can also be calculated from the arterial waveform (see CO monitor). Two invasive arterial lines can be used to monitor for residual gradients across a vessel (e.g. pre- and post-ductal lines following hypoplastic aortic arch repair). The arterial line also allows ease of sampling for arterial blood gases and other blood investigations. Arterial lines are not without risk, particularly in smaller infants. This includes distal perfusion problems.

Central venous pressure (CVP)

Internal jugular central venous lines can be transduced to measure the central venous pressure (CVP), which in turn is an estimation of the right atrial pressure and in the absence of tricuspid valve disease is an estimation of right ventricular end-diastolic pressure. The CVP is often used as an indirect measure of preload and volume status. However, tricuspid stenosis/regurgitation will affect the CVP as well as right ventricle disease, such as the restrictive right ventricular physiology. The normal CVP waveform consists of a variety of waves (3 in systole and 2 in diastole), which are altered in the face of arrhythmia or tricuspid valve disease, leading to characteristic changes that can be helpful diagnostically. The CVP line also allows administration of irritant drugs (e.g. vasopressors, TPN) more safely than peripheral access.

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8 Paediatric cardiac intensive care Table 1 continued. Common monitoring tools used in the paediatric intensive care unit.

Left atrial pressure (LAP)

LA pressure lines are left áå=ëáíì following certain congenital cardiac surgical procedures (e.g. arterial switch). The pressure reading is a surrogate marker for the left ventricular end-diastolic pressure and gives an indicator of LV preload, contractility and afterload. Normal LAP is slightly higher than the RAP (measured via the CVP) at 5-10mmHg. LAP lines are not routinely left áå=ëáíì as they are associated with risks of air entrainment or thromboembolic events directly to the systemic circulation and bleeding on removal. If an air bubble is seen in the line it must be clamped immediately and action taken.

Pulse oximeter saturation levels (SpO2)

This is a standard monitoring tool and uses the transmission of light at two different frequencies through pulsatile tissues to assess the oxygen saturation levels of haemoglobin. The original calibration means that SpO2 accuracy is less with extremes of hypoxia (90 minutes associated with a greater risk of bleeding; major transfusion intra-operatively; consumption of platelets and coagulation factors during cardiopulmonary bypass; inadequate heparin reversal; haemodilution; hypothermia; surgical bleeding.

The management requires a multidisciplinary, systematic approach which can improve patient outcomes, avoid unnecessary use of blood products and prevent surgical re-exploration. Most units use institution-based protocols and major haemorrhage policies. The level of intervention needed is dependent on the severity of bleeding and level of cardiovascular compromise. Haemorrhagic shock is a clinical emergency and needs to be managed aggressively and promptly. Although the severity of bleeding definition varies, a general rule can be based on chest drain losses in relation to body weight (Table 3).

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8 Paediatric cardiac intensive care Table 3. Classification for severity of bleeding post-cardiopulmonary bypass.

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Nil — check drains are not blocked Minimal Moderate High Very severe — assume surgical bleeding

0 1-2mL/kg/hr 2-5mL/kg/hr 5-10mL/kg/hr >10mL/kg/hr

•

The management of bleeding on the PICU includes: a) b)

c) d) e) f) g) h) i)

•

• •

resuscitation — to ensure adequate oxygen delivery to tissues despite blood loss; replacement of lost blood volume — which needs to be warmed and a mix of red blood cells, platelets, fresh frozen plasma and cryoprecipitate to replace the whole blood lost. Pump blood or cell-saved blood can also be used; correction of any residual coagulopathy; early antifibrinolytic treatment (tranexamic acid) — which has been shown to significantly reduce the need for transfusion with minimal risk of venous thrombosis; ensuring normothermia; restore ionised calcium to normal levels; further reversal of heparin with protamine; correcting acidosis; considering the possibility of surgical bleeding or cardiac tamponade, which may require chest re-exploration.

If initial resuscitative measures have failed to control a major haemorrhage, then more potent thrombin generators can be considered including recombinant factor VIIa (rFVIIa). The administration of rFVIIa should only be used in extreme circumstances and where all surgical sources of bleeding have been corrected. As the use of rFVIIa has been associated with increased adverse events, including arterial thrombi, it should be used with caution. Although coagulation studies are useful to direct a focused transfusion strategy, resuscitation should not be delayed waiting for results. Only few coagulation tests will provide meaningful information on whole blood function, as the majority of them look at specific parts of the coagulation cascade (e.g. INR, APTTR).

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•

Two bedside examples of whole blood coagulopathy screens include: a)

activated clotting time (ACT) — a bedside test of fibrin formation in whole blood that is used to monitor heparin anticoagulation but not specific to it. It provides a limited amount of information about clotting. The normal range for the ACT is 100-140 seconds; thromboelastogram (TEG®) (Figure 5) — which can provide a detailed whole blood clotting test to help determine the cause of coagulopathy and thereby guide which blood product to administer. It can be difficult, however, to differentiate between thrombocytopaenia and hypofibrinogenaemia.

b)

`äçí=Ñçêã~íáçå

cáÄêáåçäóëáë ivPM

α

296 o=íáãÉ

`äçííáåÖ=íáãÉ

Time zero

h

`äçí=âáåÉíáÅë

Time to MA

Parameter

j^

30 mins

`äçí=ëí~Äáäáíó

Description

Reaction time (R time) Normal 5-10 minutes

Time to first significant clot formation/fibrin initiation

K value Normal 1-5 mins

Clot formation/time to clot firmness of 20mm amplitude

α-angle

Speed of fibrin accumulation

Maximal amplitude (MA) 55-73mm

Maximum clot strength Highest vertical amplitude of TEG

53-72°

Lysis at 30 minutes (LY30) 0-8%

Degradation of clots 30 mins after MA/indicator of excess fibrinolysis

Clot lysis time

Clinical implications

áR time = âcoagulation factors ­ Affected by anticoagulation FFP or protamine áK time = âplatelets and/or fibrinogen Affected by anticoagulation

âα-angle = âfibrinogen and/or platelets Affected by anticoagulation âMA = âplatelets Affected by antiplatelet drugs áLY30 = áclot breakdown Consider antifibrinolytics, e.g. tranexamic acid (TXA)

Figure 5. Thromboelastogram (TEG®) and its interpretation.

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13 • •

•

•

8 Paediatric cardiac intensive care What are the characteristic findings and management of a patient with post-cardiotomy low cardiac output state? Low cardiac output state (LCOS) describes a common phenomenon seen on the PICU following congenital cardiac surgery. The cardiac output falls, causing a significant impairment of delivery of oxygen to the tissues. LCOS occurs in approximately 25% of children following cardiac surgery. One major study involving 122 neonates undergoing the arterial switch procedure for transposition of the great arteries, showed that 25% had a cardiac index 1.1mmol/L when enterally fed; lymphocytes >80%; chylomicrons.

A chylothorax can occur secondary to: a)

damage to the central lymphatic system (often the thoracic duct), such as during aortic arch surgery;

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8 Paediatric cardiac intensive care b)

•

c)

The principles of managing a chylothorax include: a) b) c) d)

e) f)

17 • • •

elevated systemic venous pressures, associated with the Glenn or Fontan procedure, SVC obstruction or thrombosis, or right ventricular failure; congenital abnormalities in the lymphatic system.

chest drain insertion to remove the effusion; treating any reversible causes, such as SVC thrombosis; monitoring of biochemical markers, serum proteins and immunoglobulins; nutritional management. If tolerated, continue with normal enteral feed (especially breast milk) but if losses increase, then change feed to medium chain triglyceride feed, which is not absorbed via the lymphatic system. If drain losses continue to be high, intravenous parenteral nutrition should be considered. It is important to ensure that a dietician is involved; IV octreotide, if the losses are persistently high; surgical options — which are used in recurring chylothorax and include: i) thoracic duct ligation; ii) pleurodesis; iii) pleurectomy.

What are the principles of intensive care unit postoperative management for a neonate with biventricular anatomy following a palliative operation?

Pulmonary artery (PA) banding is a procedure used to limit pulmonary blood flow and is often performed to protect the pulmonary vascular bed from high flow in patients with a large left-toright shunt, until the child is large enough for a full correction of their original lesion. Upon return to the PICU, the management strategy will depend on the degree of obstruction produced by the band. Loose PA bands, producing mild to moderate obstruction to pulmonary blood flow, are accepted if planned for a long period of time. This will allow the child to grow and with the subsequent increase of cardiac output result in a progressively tighter band. The immediate postoperative management is therefore generally orientated to minimising the left-to-right shunt and reducing pulmonary oedema. If unresponsive, surgical recalibration may be required.

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• • •

• 306

PA bands producing moderate to severe obstruction may result in right ventricular failure, hypoxia and low cardiac output, especially in the post-bypass setting, associated with myocardial stunning. They may require PVR reducing interventions to increase pulmonary blood flow, inotropic support, and if unresponsive, surgical recalibration. Infants following isolated PA banding can generally be extubated quickly, although it is useful to allow a period of time to assess the band’s clinical effect. Aortopulmonary shunts, such as a modified BT shunt, can be used to provide pulmonary blood flow in situations when a full biventricular repair cannot take place immediately. A key question for the intensivist to determine is whether the BT shunt provides the only source of pulmonary blood flow. It is important to assess shunt dependency, as the consequence of shunt failure would lead to no pulmonary blood flow and rapid arrest. Management of the infant post-BT shunt includes: a) b) c) d)

18 • • •

appropriate anticoagulation with heparin, which is then converted to aspirin; balancing of the circulations; rapid extubation, if this was the only procedure performed; support nutrition and promote growth prior to the child’s definitive surgery.

What are the principles of intensive care unit management for a neonate or infant following surgical repair of transposition of the great arteries?

An arterial switch is performed in neonates with ventriculo-arterial discordance but the operation may also include a VSD closure, repair of the atrial septum or PDA closure. The two key aspects to consider for PICU management are: a) b)

a neonate undergoing cardiopulmonary bypass; reimplantation of the coronary arteries.

The postoperative complications that can be seen following an arterial switch include: a) b) c)

standard complications of cardiopulmonary bypass; low cardiac output, which typically occurs 6-12 hours postbypass; coronary artery complications;

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8 Paediatric cardiac intensive care

•

d) e)

arrhythmia; pulmonary hypertension.

The management of these infants requires appropriate knowledge of the coronary artery perfusion pressure. During systole, the left coronary artery is almost occluded, and most perfusion occurs during diastole. In normal health, the right ventricle is perfused in both systole and diastole due to the lower force of contraction. If the RV pressure is elevated, however, such as with pulmonary hypertension, then the perfusion is only in diastole. Coronary artery perfusion pressure (CAPP) can be approximately calculated using this formula: Left or right CAPP = Aortic diastolic BP – Left or right ventricular end-diastolic pressure In the absence of mitral lesions, LVEDP can be assumed to be equal to the left atrial pressure, which is measured with a direct left atrial line that is inserted in theatre and left áå=ëáíì for PICU care. In the absence of tricuspid lesions, the RVEDP can be assumed to be equal to the CVP, measured by the internal jugular central venous line. Left CAPP = Aortic diastolic BP – Left atrial pressure

• •

Right CAPP = Aortic diastolic BP – Central venous pressure Coronary artery problems are more likely in infants with single coronary systems or coronary arteries with an intramural course. The general management strategy of neonates following an arterial switch operation include: a) b) c)

d)

managing general cardiopulmonary bypass complications; monitoring for cardiac ischaemia by assessing ST segments on serial ECGs and regional wall motion on echocardiography; managing low cardiac output by: i) milrinone with adrenaline and/or dopamine; ii) reducing metabolic demand with ventilation, sedation and normothermia; iii) consideration of mechanical support, such as ECMO; maintaining coronary perfusion pressure by: i) adding a low-dose vasopressor (such as noradrenaline/vasopressin) to prevent diastolic hypotension;

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ii) e) f) g)

19 • • 308

• • •

•

avoiding fast or large fluid boluses, as they will increase the left atrial pressure and central venous pressure, thereby reducing coronary perfusion; managing arrhythmias; administering diuretics, restricting fluid input and consideration of renal replacement therapy; consideration of cardiac catheterisation for coronary angiography if clinical deterioration or ventricular arrhythmias ensue.

What are the principles of intensive care unit management for a neonate with total anomalous pulmonary venous drainage? Abnormal connections of all four pulmonary veins usually presents in the neonatal age and may present to the PICU prior to surgery. The appropriate assessment of the pre-operative clinical status needs to include the presence and severity of possible obstruction to blood drainage from the lungs. This can present at the level of the pulmonary veins, veno-atrial connection or interatrial communication, and will result in pulmonary venous hypertension, pulmonary arterial hypertension, pulmonary oedema, hypoxia and shock. In the presence of no or minimal obstruction, there may be increased pulmonary blood flow or signs of congestive cardiac failure. Obstructed TAPVC is a true paediatric cardiac surgical emergency, which requires immediate surgical correction, as medical management is only a temporising measure. Non-obstructed TAPVC can be managed with conventional heart failure treatment until surgery. Following TAPVC repair surgery, the common problems seen include: a) b) c) d) e)

standard complications of cardiopulmonary bypass; pulmonary hypertension crisis; persistent residual pulmonary venous obstruction; pleural effusion or chylothorax; arrhythmias.

Management strategies for TAPVC repair patients may include: a) b) c) d) e)

managing the general complications of cardiopulmonary bypass; careful monitoring and treatment of pulmonary hypertension; managing arrhythmias; administration of diuretics, fluid restriction or renal replacement therapy; managing low cardiac output state.

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20 • • • • •

8 Paediatric cardiac intensive care What are the principles of intensive care unit management for a neonate or infant following surgical repair of an anomalous left coronary artery from the pulmonary artery? The anomalous origin of the left main coronary artery produces a state of chronic ischaemia during gestation, as the myocardium is perfused with poorly oxygenated blood. The left ventricle can appear dilated and poorly contracting at birth. Although elevated PVR immediately after birth can prevent or limit coronary flow steal into the pulmonary circulation, when PVR does drop, the myocardium is not only poorly oxygenated but is also poorly perfused. This often leads to acute myocardial ischaemia or infarction, with a dilated poorly functioning left ventricle and mitral regurgitation, either physiological or due to papillary muscle infarction. Many of these children may already be on the PICU pre-operatively due to their poor clinical status. This makes them a high-risk group of patients. The postoperative issues that can be seen include: a) b) c) d) e)

•

general complications of cardiopulmonary bypass; low cardiac output — which may be related due to the poor LV function pre-operatively, as well as the effect of cardiopulmonary bypass; coronary artery spasm or anatomical issues with the reimplantation; mitral valve regurgitation; arrhythmia — which are often atrial or nodal rhythms. If VF or VT ensure, it is important to ensure that there are no underlying coronary perfusion problems.

The general management strategy of neonates following surgical repair of an anomalous coronary artery include: a) b) c)

d)

managing the general complications of cardiopulmonary bypass; monitoring for cardiac ischaemia by assessing ST segments on serial ECGs and regional wall motion on echocardiography; managing low cardiac output by: i) milrinone with adrenaline and/or dopamine; ii) reducing metabolic demand with ventilation, sedation and normothermia; iii) consideration of mechanical support, such as ECMO; maintaining coronary perfusion pressure;

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e) f) g)

21 • • • 310

• • • •

managing arrhythmias; administering diuretics, restricting fluid input and consideration of renal replacement therapy; consideration of cardiac catheterisation for coronary angiography if the clinical condition deteriorates or ventricular arrhythmias ensue.

What are the principles of intensive care unit management for a neonate or infant with a fully repaired left-to-right shunt? Following closure of a left-to-right shunt, the circulation should return to normal. Postoperative concerns relate to the consequences of pre-operative high pulmonary blood flow. The expected complications of these operations include: a) b)

c) d)

standard complications of cardiopulmonary bypass; pulmonary hypertension (either persistent or as a crisis), with an increased risk in cases of: i) high pre-operative Qp:Qs; ii) smaller neonates or infants; iii) delayed closure of the shunt; iv) pre-operative heart failure; v) trisomy 21; vi) pulmonary hypoplasia and possible associated upper airway obstruction; vii) Eisenmenger syndrome (reversal of left-to-right shunt secondary to pulmonary hypertension); arrhythmias and heart block; residual lesions.

The management is partly related to the degree of pre-operative heart failure, the risk of pulmonary hypertension and the age or size of the child. All children require diuresis. Low-pressure, high-volume shunts, such as atrial septal defects, AVSD with no ventricular component, unobstructed TAPVC, PAPVC, are at a low risk of complications and can often be extubated quickly with minimal challenges. Children with pressure-loading shunts, such as VSD, multiple VSD, complete AVSD, AP window and truncus arteriosus, often require milrinone post-cardiopulmonary bypass.

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•

22 • • •

Those at a higher risk of pulmonary hypertension may require ventilation for a longer period of time to observe for stability. Signs of pulmonary hypertension can then be managed accordingly.

What are the principles of intensive care unit management for a patient with a fully repaired rightto-left shunt and restrictive right ventricular physiology? Restrictive right ventricular physiology results from a right ventricle with severe diastolic dysfunction that is stiff, non-compliant, with small intracavitary volume. It is characterised by end-diastolic antegrade flow during atrial contraction in the main pulmonary artery, as seen on Doppler echocardiography. This physiology is typically seen in patients following repair of tetralogy of Fallot and it is often the result of underlying RV hypertrophy and the effects of cardiopulmonary bypass. A restrictive RV results in: a) b) c)

•

impaired diastolic filling that produces reducing stroke volume and forward cardiac output; central venous hypertension as a result of high right atrial pressures and RVEDP; poor end-organ perfusion as a result of the reduced pressure gradient, especially in the kidneys and gut.

The main complications seen after corrective surgery of these lesions includes: a) b)

c) d) e) f)

standard complications of cardiopulmonary bypass; residual lesions, such as: i) pulmonary regurgitation (especially with the use of a transannular RVOT patch); ii) residual RVOT obstruction; iii) residual shunts; iv) tricuspid valve dysfunction; arrhythmias, especially JET; low cardiac output — which is worsened by restrictive RV physiology, residual lesions (PR, RVOTO, VSD) and reduced RV systolic function (if a ventriculotomy was performed); pulmonary hypertension; pleural effusion or chylothorax.

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•

The management considerations will vary for these children depending on the age or size of the patient, degree of RVOTO/RV hypertrophy and the surgery performed, and may include: a) b) c)

d) e) 312

f) g)

23 •

• •

managing the general complications of cardiopulmonary bypass; observing for and rapidly treating any arrhythmias. The tachycardia with JET is not well tolerated due to the diastolic impairment and subsequent reduced filling of the RV; ventilation considerations, such as ventilation with the lowest possible mean airway pressure to maintain adequate gas exchange is useful, especially as positive pressure ventilation may exacerbate RV afterload; optimising preload (important due to the RV restrictive physiology) with the judicious use of fluids and vasopressors, such as noradrenaline or vasopressin; using inodilators, such as milrinone, to help improve a low cardiac output state, as well as providing lusitropic properties for the right ventricle; ensuring any chylothorax or pleural effusions are evacuated; providing adequate diuresis, including early renal replacement therapy.

What are the principles of intensive care unit management for a neonate or infant following a Norwood operation, with either a modified BT shunt or Sano shunt? The Stage I Norwood operation includes: a) b) c) d)

atrial septectomy; reconstruction of the aortic arch; creation of the neo-aorta; systemic to pulmonary shunt (modified BT or Sano).

The key principle of managing an infant following a Stage I Norwood procedure is to ensure an adequate cardiac output with a balanced Qp:Qs and to deal with the standard complications of cardiopulmonary bypass. It is generally considered that the Sano modification provides a more stable haemodynamic behaviour on the PICU postoperatively when compared to the modified BT shunt. The main reason for the apparent advantage of the Sano modification is attributed to the fact

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8 Paediatric cardiac intensive care

• •

that in this case pulmonary flow is systolic and does not affect diastolic pressure in the systemic circulation. As a result, flow distribution is not completely reliant on the difference in vascular resistance between the two circulations, and coronary flow is superior as it is not affected by the drop in mean arterial pressure, as with the BT shunt. A Sano procedure, however, is not completely immune to problems with balancing Qp:Qs in the immediate postoperative period nor does it seem to provide a significant net advantage to longer-term morbidity or mortality of the patient. Issues that can occur with either shunt include: a)

b)

c) d)

e)

•

•

standard complications of cardiopulmonary bypass, but in particular: i) low cardiac output state; ii) cardiac tamponade (the chest is often left open electively); iii) myocardial dysfunction; high pulmonary blood flow, as a result of: i) high SVR due to insufficient inodilation, pain, hypothermia or spontaneous fluctuations; ii) low PVR due to hypocarbia, too high FiO2, BTS/BSA mismatch or excessive pulmonary vasodilation; low pulmonary blood flow, as a result of: i) shunt obstruction or even blockage; ii) pulmonary hypertension episodes, often spontaneous; anatomical complications, such as: i) pulmonary venous drainage obstruction; ii) residual aortic arch narrowing; iii) atrioventricular valve regurgitation; iv) neo-aortic valve regurgitation; non-cardiac complications, such as: i) ischaemic colitis; ii) sepsis.

Multimodal monitoring of these infants is mandatory to guide adequate oxygen delivery treatment. This is typically in the form of standard continuous monitoring of parameters such as ECG, BP, CVP, oxygen saturations, end-tidal CO2, NIRS of cerebral oxygen saturation, urinary output, blood lactate levels, and arteriovenous saturation gradient to allow the calculation of Qp:Qs directly, assuming normal lung oxygenation. It is important to understand that isolated arterial blood desaturation can be precipitated by several causes, including: a)

decreased pulmonary blood flow and reduced O2 pick-up;

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b) c)

•

The general management strategy for these infants includes: a) b) c) d) e) f) g) h)

314

i)

j) k)

24 •

reduced mixed venous saturation; pulmonary venous desaturation, as a result of poor lung function.

managing the general complications of cardiopulmonary bypass; balancing Qp:Qs, by maintaining an adequate PVR-SVR gradient (ideally, in the postoperative setting the Qp:Qs should be 30 days old

O

Repair of VSD, tetralogy of Fallot, vascular ring, Glenn shunt, AP window, coarctation of aorta repair 400 seconds. It is prone to haemolysis and haemodilution, utilises an arterial filter and its oxygenator can be only used for a relatively short time. Traditionally, it uses a roller pump and has a blood reservoir (except in mini-bypass circuits) and is able to provide a wide range of temperature change. ECMO, however, can only be used to perform a limited number of extracardiac procedures and not open heart procedures but is a smaller machine, portable and usable by the patient’s bedside, which only requires a small amount of priming volume and smaller doses of heparin (50-100 IU/kg), with a lower desired ACT of 150-220 seconds. It has limited haemolytic effects and limited haemodilution, no separate arterial filter and its oxygenator can be used for longterm support. It has a centrifugal pump, no reservoir and a limited capability to cool or warm patients.

Table 1. Differences between cardiopulmonary bypass (CPB) and extracorporeal membrane oxygenation (ECMO). ACT = activated clotting time. Ideal use Size and portability Pumping mechanism Priming volume Arterial filters Venous reservoir Thermoregulation Anticoagulation requirements Haemodilution/haemolysis Adaptable to haemofiltration Risk of air embolism

`m_

b`jl

Cardiac operating theatre Large, poorly mobile Roller pumps Large Yes Yes Wide range High (ACT >400) Few hours No Low

Bedside Small, highly mobile Centrifugal pump Small No No Limited range Low (ACT 150-220) Few days Yes High

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7 •

•

388

8 •

What are the differences between veno-arterial and veno-venous extracorporeal membrane oxygenation?

VA ECMO can be used to support a patient with both respiratory and cardiac failure, maintain higher systemic blood pressures, provide a variable degree of circulatory support but requires venous and arterial cannulation. It provides a high O2 delivery capacity, has a low pulse pressure on full flow, and reduces cardiac workload by reducing preload but it increases the afterload. Coronary perfusion can be affected by ejection of deoxygenated blood; if not appropriately vented it can provoke LV distension, and may cause LV stunning on prolonged use. VV ECMO, however, cannot be used to support cardiac failure, does not affect directly systemic blood pressure but only requires venous cannulation (either single or double cannulation). It only provides a moderate O2 delivery capability, does not reduce cardiac workload, the pulse pressure is unaffected but increases O2 delivery to the coronary and pulmonary circulation.

What are the components of an extracorporeal membrane oxygenation circuit?

A typical VA ECMO circuit is a complex system (Figure 1), composed of: a) b) c) d) e) f) g)

arterial and venous cannulae; circuit to connect the venous cannula draining from the patient to the centrifugal pump; from the pump to the oxygenator; and from the oxygenator to the arterial cannula; magnetically levitating impeller (centrifugal pump) mounted on a rotating magnet device, controlled by a console (Figure 2); membrane oxygenator to which both the venous and arterial sides of the circuit are connected (Figure 3); heat exchanger for temperature regulation; air and O2 mixer (blender) and sweep gas flow regulator to optimise O2 and CO2 gas exchange (Figure 4); side ports (pigtails) used for a wide variety of functions, including: i) administration of heparin continuously; ii) pressure monitoring before and after the oxygenator; iii) sampling for blood gas analysis; iv) connecting the venous and arterial sides of the circuit (bridge) to temporarily isolate the patient from the ECMO pump without stopping the flow (Figure 5);

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11 Extracorporeal membrane oxygenation

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Figure 1. Veno-arterial extracorporeal membrane oxygenator (VA ECMO) circuit: with pigtail 1 used for the venous side of the bridge; pigtail 2 used for inlet pressure monitoring and a large air and fluid line; pigtail 3 used for activated clotting time (ACT) measurement and central venovenous haemofiltration (CVVH) access; pigtail 4 used for CVVH return; pigtail 5 used for pre-membrane pressure monitoring and heparin infusion; pigtail 6 used for air removal and addition of volume; pigtail 7 used for post-membrane pressure, gas samples, clotting products (if there is no patient access); and pigtail 8 used for the arterial side of the bridge. v)

h)

connecting the circuit to a continuous renal replacement unit (CVVH); flow sensors.

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390

Figure 2. Centrifugal pump consisting of control monitors, primary and back-up control panels, rotating driver devices and centrifugal impellers.

Reproduced with permission from Abbott, © 2020. All rights reserved. CentriMag™,

Thoratec Corporation and Thoratec Corporation Logo are trademarks of Abbott or

its related companies.

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11 Extracorporeal membrane oxygenation 1

6 10

2 3

7

8

9

4

5

391

Figure 3. Membrane oxygenator and its connections. 1 = vent port; 2 = water outlet; 3 = oxygen supply tube; 4 = membrane oxygenator; 5 = water inlet; 6 = sampling ports; 7 = recirculation port; 8 = arterial outlet; 9 = flow sensor; 10 = venous inlet.

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Figure 4. Air and oxygen blender, with sweep gas regulator.

392

Figure 5. Bridge between the arterial and venous cannulae in an open state.

9 •

Describe the different types of pump that are used in an extracorporeal membrane oxygenation circuit

Semi-occlusive roller pumps are rarely used currently, as they are more traumatic to blood components, especially when used for longer periods.

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•

They have been replaced by magnetically levitated centrifugal pumps, which are mounted on a rotating magnet driver (Figure 6).

393

Figure 6. Centrifugal propeller.

• • • •

This pump provides less trauma to blood components and can be employed for longer period of times. By spinning, a vortex effect is created with low pressure in the apex of the pump removing blood from the patient. The vortex creates a positive pressure at the bottom of the pump, returning blood to the patient. Therefore, centrifugal pumps are preload-dependent and afterloadsensitive. Given the prolonged use and dependency of the patient’s circulation and respiratory function, drivers are always provided with a back-up for quick replacement in case of failure (Figure 7).

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Figure 7. Centrifugal pump mounted on the rotating magnetic device, with the mandatory back-up device adjacent for immediate transfer of the propeller.

394

10 •

What are the main factors affecting extracorporeal membrane oxygenation flow?

•

The pump provides a blood flow rate (L/min) delivered at a given amount of revolutions per minute (rpm). Factors that can affect the blood flow rate include:

11

What is pump cavitation?

• • • •

a) b) c) d) e) f)

preload and afterload; size of the cannulae; size of the cannulated vessels and compliance; body surface area (BSA) of the patient; haematocrit; transmembrane gradient (which represents the pressure gradient across the oxygenator).

The pump generates a negative pressure on the patient’s venous side, which drives the flow rate, as it provides the inflow into the propeller. Past the point of maximal inflow, the negative pressure in the venous system causes the venous vessels or the right atrial wall to temporarily collapse, potentially occluding blood inflow altogether. When the pressure in the venous side builds back up again, the pump is able to flow again, which might generate a pulsing blood flow and cavitation of the pump. The first intervention to avoid further cavitation is to reduce the pump rpm and therefore the suction effect on the venous return.

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11 Extracorporeal membrane oxygenation

•

Other manoeuvres that might be needed to maintain pump blood flow include: a) b) c) d) e)

12 •

correcting the hypovolaemia status; changing the positioning of the patient; ensuring that there is no kinking or malposition of the cannula; checking for the presence of thrombus or clotting in the circuit; increasing the size of the venous cannulae or adding additional venous access for drainage.

What is recirculation?

Recirculation is a phenomenon that occurs in VV ECMO when a single intra-atrial double-lumen cannula is used, where reinfused oxygenated blood is withdrawn through the venous drainage cannula and therefore does not reach the systemic circulation (Figure 8).

A

Double-lumen cannula

B

RA

RV

Figure 8. Flow within a single VV ECMO double-lumen cannula: A) in the correct position and functioning properly, the cannula draws deoxygenated blood from the inferior vena cava and right atrium, while the outlet lumen ejects fully oxygenated blood towards the tricuspid valve. This increases forward flow with high oxygen saturation across the pulmonary circulation to reach the left atrium; B) recirculation occurring with the arterial output drained from the cannula instead of reaching the right ventricle, resulting in reduced forward flow to the pulmonary valve and reduced oxygen saturation. RA = right atrium; RV = right ventricle.

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•

If the patient is dependent on ECMO for oxygenation, recirculation can pose a clinical problem. In this situation, solutions to be considered include: a) b)

13 • • 396

• •

c) d)

What is Harlequin syndrome?

Harlequin syndrome represents a phenomenon occurring in VA ECMO, when there is significant residual native cardiac output with impaired native gas exchange. In such cases, poorly oxygenated blood ejected from the heart will supply the upper body, whereas the lower body is perfused by oxygenated blood from the arterial cannula of the ECMO circuit, in particular when a femoral cannula is employed. Blood returning to the venous drainage is more saturated than expected and may be interpreted as a form of recirculation, but as the blood has already passed through the systemic circulation, it is not considered recirculation. Possible solutions to this include: a) b) c) d)

14 • • •

changing the position of the cannulae; changing the configuration of the cannulae by adding an extra drainage cannula; changing the position of the reinfusion cannula; decreasing ECMO flow (if possible).

increasing the ECMO flow; increasing ventilation support (if possible); repositioning the arterial cannula more proximally in the aorta (if central cannulation has been used) or adding an additional arterial cannula for the upper body, such as an axillary artery cannula; improving left atrial decompression with a left atrial vent or atrial septostomy.

Describe the types of extracorporeal membrane oxygenation arterial cannulae that are used

ECMO is instituted using specific cannulae that are produced to be site-specific. Most centres use a uniform size to flow ratio, according to the patient’s body weight or body surface area (Tables 2 and 3). The size and shape of the venous and arterial cannulae vary when used for central or neck cannulation, as compared to peripheral sites, such as the femoral vein (Figures 9 and 10). The use of heparin-coated cannulae and heparin-bonded circuits is variable.

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11 Extracorporeal membrane oxygenation Table 2. Arterial cannula size chart according to flow and body weight. cäçï= EãiLãáåF=

páòÉ= EcêF=

bñíÉêå~ä= _çÇó=ïÉáÖÜí `~ååìä~ Çá~ãÉíÉê=EããF EâÖF ëáòÉ=EcêF

0-400 400-700 700-1200 1200-1700 1700-2000 2000-2500 2500-3500 >3500

8 10 12 14 15 17 19 >21

2.66 3.33 4 4.66 5 5.66 6.33 >7

40

8 to 10 10 to 14 12 to 16 14 to 19 17 to 21 >21

Table 3. Venous cannula size chart according to flow and body weight. cäçï= EãiLãáåF=

páòÉ= EcêF=

bñíÉêå~ä= _çÇó=ïÉáÖÜí `~ååìä~ Çá~ãÉíÉê=EããF EâÖF ëáòÉ=EcêF

0-350 350-600 600-1000 1000-1400 750-1000 1000-1500 1500-2000 2000-2500 2500-3000 3000-3600 3600-4500 4500-

8 10 12 14 15 17 19 21 23 25 27 29

2.66 3.33 4 4.66 5 5.66 6.33 7 7.66 8.33 9 9.66

40

8 to 10 10 to 16 14 to 17 17 to 19 19 to 23 21 to 28

397

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Key Questions in CONGENITAL CARDIAC SURGERY A

B

398

Figure 9. Arterial cannulae used for paediatric extracorporeal membrane oxygenators: A) an 8Fr cannula used for central and neck cannulation, with a single orifice at the cannula tip, which is placed in the aortic arch or root of the right brachiocephalic artery; B) a 15Fr cannula used for femoral cannulation, with a multi-orifice tip, that is more effective in the abdominal aorta.

• •

Generally, venous cannulae tend to be larger than the arterial cannulae to prevent venous collapse and to accommodate the higher distensibility of the venous vessels. In respiratory ECMO, when the VA set is used, the cannulae tend to be of the same size.

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11 Extracorporeal membrane oxygenation A

B

399

Figure 10. Venous cannulae used for paediatric extracorporeal membrane oxygenators: A) an 8Fr cannula used for neck cannulation, with multiple openings and markers to identify the cannula position within the superior vena cava, right atrium (RA) and inferior vena cava (IVC); B) a long 15Fr cannula used for femoral vein cannulation, with a multiorifice tip, that is placed at the RA-IVC area.

•

Although single cannulae (double-lumen) are used in VV ECMO, their use in small babies is limited (Figures 11 and 12).

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Figure 11. Avalon Elite® bi-caval double-lumen catheter. Reproduced with permission from Getinge.

400

Figure 12. ParaGlide™ ECLS adult veno-veno doublelumen cannula (Chalise Medical, Worksop, UK).

15 • • •

Describe the priming solution used for the institution of extracorporeal membrane oxygenation

Priming of the entire circuit, oxygenator and pump is performed before cannulating the patient. Carbon dioxide is flushed through the circuit to displace atmospheric oxygen and nitrogen, followed by an infusion of a balanced crystalloid prime. Albumin is then added to coat the prosthetic surfaces and decrease platelet and fibrinogen adherence.

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11 Extracorporeal membrane oxygenation

• • •

16 •

Finally, blood is used to displace the crystalloid to prevent haemodilution, especially in small patients, with the ideal haematocrit between 30-40%. A blood gas analysis of the priming solution is made before connecting the patient to the circuit, with adjustments of the priming pH and electrolytes frequently required. When blood is added to the prime, heparin is added to initiate anticoagulation (100 units of heparin per unit of packed red blood cells), followed by a buffer solution, such as sodium bicarbonate.

What are the different cannulation strategies for extracorporeal membrane oxygenation? Central cannulation — which is performed via a median sternotomy and usually involves an arterial cannula in the ascending aorta and a right-angled venous cannula in the right atrium. In some cases, an additional cannula is inserted through the left atrial appendage or the right upper pulmonary vein to vent the left atrium. Indications include: a)

•

b)

Neck cannulation — which can be used for: a)

b)

•

post-cardiotomy heart failure, refractory to increasing inotropic support; post cardiac arrest, refractory to conventional CPR (ECPR).

VA ECMO — where the arterial cannula is placed in the right common carotid artery (RCCA) and advanced to the aortic arch, and the venous cannula is placed in the right internal jugular vein (RIJV) and advanced to the right atrium-IVC junction. It is mostly used in non-post-cardiotomy neonates and infants requiring both cardiac and respiratory support. The right-sided vessels are preferred but in exceptional circumstances the left neck vessels can be used. If this cannulation is employed, it is important to ensure patency of the contralateral arterial and venous vessels; VV ECMO — where a double-lumen cannula is inserted in the right internal jugular vein and advanced into the right atrium. In neonates and infants, this is performed by open dissection of the vessels. In larger patients, the cannulation can be done percutaneously, using the Seldinger wire technique.

Femoral cannulation — which is used for larger patients, where higher flows are needed both on the venous and/or arterial side. In VA ECMO, the arterial cannula is placed in the femoral artery and the

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venous cannula in the femoral vein, preferably on the opposite side. In patients who are supported with ECMO for a prolonged period, the risk of leg ischaemia, distal to the femoral artery cannulation site, can be significant. This can be mitigated by the (Figure 13): a) b)

use of a side graft anastomosed on the femoral artery, which is subcutaneously tunnelled and exteriorised 4 to 5cm inferiorly, with a separate incision; positioning of a retrograde reperfusion catheter (smaller in size to restrict the flow) in the superficial femoral artery, connected to the femoral arterial cannula.

A

Inguinal ligament

B

FA

402

Distal arm

FV

Proximal arm Interposition tube graft

SFA

Figure 13. Strategies to reduce the risk of leg ischaemia during

prolonged periods of ECMO, including: A) an arterial cannula inserted into an interposition graft anastomosed to the femoral artery, which prevents occlusion of the artery; and B) a retrograde reperfusion cannula inserted in the superficial femoral artery to provide distal perfusion. FA = femoral artery; FV = femoral vein; SFA = superficial femoral artery.

•

In VV ECMO, if a double-lumen cannula is not used via the right internal jugular vein in larger children, bilateral femoral venous

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•

17 • •

cannulation is used, to drain venous blood from one, and infuse oxygenated blood into the other. A combination of neck and femoral vein cannulation can be used to improve venous drainage.

What are the indications for a left heart vent in venoarterial extracorporeal membrane oxygenation? Adequate drainage of the right atrium should reduce left ventricular preload, so that even in the absence of significant ejection, the left ventricle should not distend. In certain circumstances, however, the left ventricle can distend significantly, even when the pulmonary forward flow is substantially reduced, where a left atrial vent is beneficial, including: a) b) c) d) e) f) g)

• •

severe LV dysfunction with a prolonged lack of contraction and ejection — where venting may support recovery by reducing cardiac workload; mitral regurgitation — where the ejecting ventricles are subject to volume overload; cyanotic patients — where the pulmonary return may be increased due to arteriovenous collaterals; significant ventricular return and lack of adequate interatrial shunting; single ventricle circulations — where deoxygenated blood, due to mixing, could be ejected into the coronary system, affecting myocardial recovery; severe ventricular arrhythmias; any situation requiring venting, where percutaneous septal fenestration cannot be obtained.

These indications are weighted against adding a second inflow line to the venous drainage with a ‘Y’ connector and the consequent increased risk of air embolisation in the circuit. The left atrium can be accessed via the: a) b) c) d) e)

right upper pulmonary vein; Waterston’s groove; left atrial roof; let atrial appendage; left ventricular apex (uncommon).

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18 • • •

What are the principles of transitioning a patient from cardiopulmonary bypass to extracorporeal membrane oxygenation?

Following cardiac surgery with the patient still in the operating theatre, mechanical support should be considered when cardiac function is inadequate despite maximal medical therapy. The institution of ECMO, however, should only be considered when the causes of failure are not attributable to residual surgical lesions, in which case these should be addressed first. The decision should be a multidisciplinary team decision, involving the surgeon, anaesthetist, cardiologist and intensivist. Once all correctable lesions have been excluded, ECMO may be indicated with: a) b)

404

c) d) e)

•

One of the challenges faced in such conditions is the choice of the transition method from CPB onto ECMO and depends mainly on the haemodynamic and respiratory status of the patient. The options include: a)

b)

•

severe right or left ventricular failure (normally myocardial stunning), with the inability to separate from CPB; rapid haemodynamic deterioration, unresponsive to increasing inotropic and vasopressor support; rapid deterioration in respiratory function, unresponsive to conventional ventilation; severe pulmonary hypertensive crisis, unresponsive to inhaled nitric oxide; cardiac arrest immediately after chest closure, unresponsive to chest reopening and CPR, or responsive but with residual myocardial stunning.

completely weaning from CPB, administration of protamine with blood products and then controlled transition to ECMO. This is usually used for patients where respiratory failure is the predominant issue; immediate (or almost immediate) transition from CPB to ECMO, administering protamine to reach an ACT of approximately 200 seconds. This is usually used for patients who do not separate from CPB.

Blood loss while on ECMO cannot be saved and reinfused, leading to multiple blood transfusions and ECMO flow instability. In addition, surgical haemostasis is more difficult whilst on ECMO and surgical

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19 •

manipulation of the heart can impair ECMO flow. A heparin-free run on ECMO for a limited period of time is an acceptable strategy to limit severe blood loss in these circumstances.

What are the indications for the use of extracorporeal membrane oxygenation in the intensive care unit? According to current national standards, fully operational congenital heart disease surgical units are expected to provide ECMO support for a range of clinical situations, including: a) b) c)

•

d)

There are two main scenarios in which ECMO is initiated and these can present on the basis on any of the above conditions: a)

b)

•

haemodynamic and/or respiratory support for patients with congenital heart disease following cardiac surgery; support for patients with or without structural heart disease, with acute medical cardiac conditions, such as myocarditis, malignant arrhythmias, cardiac arrest or failure of the newborn; support for patients with or without structural heart disease with acute medical non-cardiac conditions, such as sepsis; respiratory support for patients with respiratory failure.

cardiac arrest and cardiopulmonary resuscitation — where ECMO is normally instituted due to a failure to re-establish an adequate circulation or to support a stunned heart following the arrest. If after 5 minutes of internal CPR, the heart function has not regained, an ECPR protocol is deployed with central cardiac VA cannulation and initiation of ECMO. In non-surgical patients, cardiac surgical patients in whom established adhesions may delay central cannulation or patients with a significant risk of bleeding, closed massage and VA ECMO via neck cannulation should be considered; progressive deterioration of haemodynamic and/or respiratory function despite full medical support — where controlled cannulation and initiation of VA ECMO should be performed, with: i) neck cannulation for non-cardiac surgical patients; ii) central cannulation for cardiac surgical patients, provided there is an acceptable risk of bleeding.

In the majority of units, paediatric cardiac surgeons provide surgical support for institution of ECMO, including participating in the decision-making process and the provision of surgical cannulation.

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•

20 • • •

406

• • • • •

21 • • •

Non-cardiac ECMO cannulation is also provided by general surgeons, interventional cardiologists and cardiac anaesthetists.

What additional cardiorespiratory support is required for a patient whilst on veno-arterial extracorporeal membrane oxygenation?

In general, VA ECMO provides cardiorespiratory support and the need for inotropic, vasopressive and respiratory treatments are reduced. After initiation of ECMO, cardiorespiratory medical support is gradually weaned, according to the haemodynamic state of the patient and ECMO flows. Whilst adrenaline can be reduced to small doses in the first hour, vasopressors are often still needed in the first few hours following initiation of ECMO support and in some cases, longer. It is required to counteract vasodilatation that non-pulsatile flow induces on organ perfusion, with a non-ejecting heart, especially if concomitant sepsis is present, where severe vasodilatation could be seen after starting ECMO flow. Once ECMO flow balance between preload and afterload is achieved, the need for vasopressor and inotropic support is reduced. After initiation of ECMO, respiratory support is also reduced but minimal ventilation (on the resting setting) is maintained to guarantee oxygenation of the blood reaching the left heart, which will allow oxygenated blood to perfuse the coronary arteries, in case of heart ejection. The circulatory management of respiratory VV ECMO can be quite different from the cardiac support required with VA ECMO in the surgical population. Patients with patent BT shunts may require increased flows and the medical support needed to compensate for the resulting left-to-right shunting and reduction in systemic perfusion. Patients with a single-ventricle circulation may require more afterload reduction to compensate for desaturation and limited systemic output.

What are the exclusion criteria for neonatal extracorporeal membrane oxygenation support? Gestational age 60 minutes; vi) repeated cardiac arrests; vii) failed CPR with evidence of severe multi-organ failure; viii) unwitnessed cardiac arrest; ix) out-of-hospital arrest (in some centres); respiratory conditions, such as: i) >7-10 days on the ventilator, depending on age; ii) escalating ventilator settings, with PEEP >15cmH2O, mean airway pressure >25cm H2O, peak inspiratory pressure >45cm H2O; iii) severe anatomical lesions or injury; iv) fixed elevated PVR; v) chronic lung disease; haematological conditions, such as: i) major life-threatening haemorrhage; ii) uncontrolled coagulopathy; iii) immunosuppression; iv) disseminated intravascular coagulopathy; neurological conditions, such as: i) severe central nervous system injury; ii) infection; iii) hypoxic damage; iv) trauma; v) toxic insult; metabolic conditions, such as: i) severe chronic organ dysfunction, involving the hepatobiliary, renal and respiratory systems; ii) severe metabolic failure (autoimmune disease); iii) oncological diseases of poor prognosis; iv) chromosomal abnormalities; infective conditions, such as: i) uncontrolled septic shock.

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24 •

A

11 Extracorporeal membrane oxygenation Which imaging modalities are used for patients whilst on extracorporeal membrane oxygenation? Chest radiography can be used to confirm the position of cannulae (Figure 14), immediately after cannulation and thereafter at set intervals depending on institutional protocols. It is important to note that cannulae differ slightly in their appearance on the chest radiograph.

B

409

Figure 14. Chest radiograph in different patients on veno-arterial extracorporeal membrane oxygenation, immediately following: A) central cannulation, with a right-angled venous cannula in the right atrium and a straight arterial cannula in the aorta; and B) neck cannulation, with the venous cannula longer, reaching the RA, and armed until approximately 5cm from the tip, which is not radiopaque.

• • • •

It is often the first line of investigation to assess cannula dislodgment or malposition, and can also identify any kinks or damage. It can also be helpful to visualise the endotracheal tube, lung pathology, pleural collections and cardiac shadow. Echocardiography is critical to confirm the position of the cannulae, cardiac function, the presence of any atrial communication and the diagnosis of any congenital defect not yet identified (Figure 15). Importantly, it is also used to indicate the progression of the patient on ECMO and allows plans to be made for weaning and disconnection from ECMO support.

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B

RA

RA

Cannula

Figure 15. Echocardiographic images demonstrating venous cannula

position for: A) veno-veno extracorporeal membrane oxygenation; and B) veno-arterial extracorporeal membrane oxygenation. RA = right atrium.

410

• • • •

25 • • •

Computed tomography (CT) scanning can be used to investigate the cardiac and respiratory systems, whilst the patient is on ECMO. It is also useful in assessing the central nervous system, if any neurological symptoms are present. CT angiography allows visualisation of cardiac structures and the adequacy of surgical repair. In such cases, a brief period of reduced or no ECMO flow can be employed to fill the cardiac structures, while ventilating the patient fully. Angiography is occasionally used to visualise anatomy and also to perform cardiac interventions, as required. Ultrasound scanning is used to diagnose involvement of the central nervous system and intra-abdominal organs, and Doppler scanning to visualise distal limb perfusion in patients with femoral cannulation.

What are the ventilation settings on extracorporeal membrane oxygenation?

Whilst on ECMO, full gas exchange in the lung is not required and ventilation is usually adjusted to rest settings. This allows for the lungs to be ventilated with lower volumes and pressures, facilitating lung recovery by preventing barotrauma. The usual settings of a patient on ECMO are FiO2 30%, PEEP 35cm H2O, respiratory rate 5-10 rpm, tidal volume 5-10mL/kg, with adjustments made according to the patient’s requirements.

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•

26 • • • • • • • • •

27 • • • • • •

In patients with cardiac ejection whilst on VA ECMO, it is advisable to increase the mechanical ventilation settings, given the increased pulmonary venous return, to allow for adequate coronary perfusion with oxygenated blood.

What procedures can be performed whilst on extracorporeal membrane oxygenation?

Chest drain insertion for pneumothorax, haemothorax or chylothorax. Insertion of central lines, arterial lines or a vascular catheter (for haemofiltration). Orotracheal intubation. Balloon atrial septostomy. Diagnostic or interventional cardiac catheterisation. Computed tomography scan. Transoesophageal and transthoracic echocardiogram. Bronchoscopy. Abdominal procedures and peritoneal dialysis catheter placement.

Describe the principles of anticoagulation management whilst on extracorporeal membrane oxygenation

One major advantage of ECMO compared to CPB is the lower heparin requirement and lower activated clotting time (ACT). The ACT, however, needs to be checked regularly to avoid under- or overheparinisation. Generally, an ACT of 250 seconds is required to start ECMO and this is obtained with heparin 100 IU/kg administered just prior to cannulation, depending on local protocols. Regular checks are carried out at 15-minute intervals for the first 2 hours, every 30 minutes for the next hour and finally hourly if the ACT is within the desired parameters. A heparin infusion is then started at 0.5mL/hr or 10 IU/kg/hr and titrated accordingly, to maintain an ACT of 220-250 seconds (or 180200 seconds, if bleeding is present). In the event of a low ACT, the heparin infusion is increased by 0.2mL/hr and the ACT is checked every 15 minutes until stable. If a bolus is required, 5-10 IU/kg is administered in addition to increasing the infusion by 0.2mL/hr and the ACT is rechecked every 15 minutes.

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•

• • •

412

•

28 • •

A higher ACT may be required when: a) b) c)

increasing clot or fibrin formation is visible within the circuit; less than ideal flows are reached; during weaning and trial off ECMO.

A lower ACT may be required in the presence of persistent bleeding, despite optimising clotting factors or after surgical intervention. If bleeding is persistent, the heparin infusion can be stopped, and correction of the coagulation status is achieved by administration of platelets, fresh frozen plasma and cryoprecipitate, according to the clotting results. Careful management of the circuit with monitoring of clot formation and fibrous strands within the circuit should be performed. The membrane oxygenator is the most vulnerable component of the circuit at risk of clotting. Monitoring of the transmembrane gradient is paramount to prevent sudden clotting of the oxygenator, causing the pump to acutely fail. Once bleeding is corrected, the heparin infusion should be restarted, as above.

What are the principles of weaning a patient from extracorporeal membrane oxygenation?

Weaning a patient from ECMO is a complex and difficult procedure, which requires a multidisciplinary team approach. The respiratory, cardiac, renal and general status of the patient need to be taken into consideration before attempting separation from cardiorespiratory support. Prior to the commencement of a weaning trial, the following conditions should be evaluated: a)

b)

pulmonary function — to assess chest mechanics, the presence of any pleural effusions, pneumothorax, pleural effusions, residual lesions and airway problems by chest radiography, and lung compliance by manual ventilation of the patient. Occasional, inhaled nitric oxide may be required to reduce pulmonary vascular resistance; cardiac function — by serial echocardiography to assess regional and global function, myocardial contractility and ventricular compliance at rest before the weaning process. In cases where ECMO is required for cardiac failure, a more indepth analysis of cardiac function in response to progressive loading might be required before embarking on a full weaning process (i.e. 12-24 hours before). This is called a ‘stress echo’

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c)

d)

e) f) g) h)

• • • •

and it is achieved by temporarily increasing the ACT to 250 seconds, starting conventional ventilation and progressively reducing the flow by 25% decrements until the circulation is stopped for 30-60 seconds. In cases where a left heart vent is present, it is reasonable to clamp it for the duration of the stress echo which should be kept short (2-3 minutes) to avoid clot formation in the circuit. While the ECMO flows are reducing, an echocardiogram is continuously performed to assess myocardial systolic and diastolic function, global and regional contractility and any valve dysfunction. In our experience, a stress echo provides important information about progression in the recovery of cardiac function and the timing of the ECMO wean; renal function — where alternative strategies should be considered following a successful weaning (peritoneal dialysis, peripheral CVVH), if replacement therapy was used on ECMO via the side ports; fluid balance — increasing oncotic pressure and the use of vasopressor drugs may be required to limit or reverse fluid extravasation as a consequence of the inflammatory response to ECMO; vascular function — with inotropic and vasopressor support, started before an attempt at weaning; metabolic status — with worsening lactic acidosis, unstable glycaemia and evidence of worsening multi-organ failure on ECMO being poor predictors of a successful wean; neurologic status — where head ultrasound or magnetic resonance imaging may be required to document intracranial anatomy and functional status; infective conditions — where worsening signs of sepsis prior to weaning is a poor predictor of outcomes.

The ACT is generally raised to 300 seconds by increasing the heparin infusion, to reduce clot formation in the cannulae and circuit whilst reducing flow. The process of weaning requires a gradual reduction of the flow, so that over the course of 1-2 hours, the ECMO flow is reduced in steps of 25%. During the weaning period, blood gas analysis is performed regularly and the ventilation parameters are adjusted accordingly. Systemic lactate levels are taken into account as part of the assessment of systemic perfusion. Weaning from the ECMO circuit is completed by clamping the venous line, unclamping the bridge and then clamping the arterial line, following which the child is isolated from the circuit and the heart takes over the systemic perfusion.

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• • •

The cannulae are left in place and the ECMO circuit continues to run via the bridge, in case the child fails the weaning trial. Every 15-20 minutes, the cannulae are flushed to avoid blood stagnation and clot formation. Signs of early failure of an ECMO weaning trial include: a)

b) c) d) e)

• 414

• •

29 •

f)

poor haemodynamic performance with declining systemic arterial pressure; increasing right and/or left atrial pressure; poor ventricular function on echocardiogram; arrhythmias; poor peripheral perfusion with increasing systemic lactate, hypoxia, hypercarbia and acidosis; poor oxygenation and high end-tidal CO2.

In some cases, a ‘one-way wean’ strategy is adopted, where ECMO will not be reinstituted in the case of early failure. This is a difficult decision that must be taken by the most senior multidisciplinary team and adopted in cases of manifest inadequacy of the native cardiorespiratory system. Given the nature of active withdrawal of care, it is important to involve the parents in the decision-making process. If the trial is successful, the patient is decannulated. In patients with central cannulation via a median sternotomy, a policy of ‘delayed sternal closure’ is employed. In patients with neck decannulation, vessel reconstruction should be attempted but if no reasonable patency is obtained, vessel ligation may be required. An ACT is then performed and protamine is administered to reverse heparin to reach an ACT of 100-120 seconds.

What are the outcomes of patients undergoing extracorporeal membrane oxygenation following paediatric cardiac surgery?

In general, survival to hospital discharge following cardiac ECMO is 40-50% and is influenced by several factors:

a)

b) c)

time spent on ECMO — where increased duration of ECMO support is associated with a lower survival. Beyond an ECMO duration of 7 days, the odds of mortality increase by 12% per every extra day on ECMO; pre-operative conditions — where low weight, preterm birth, pre-operative necrotising enterocolitis are recognised risk factors for mortality; postoperative complications — where renal failure requiring renal replacement therapy, neurological impairment, bleeding and developing necrotising enterocolitis whilst on ECMO, all carry higher mortality;

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30

neurological sequelae — where longer CPB (>400 minutes) and the use of deep hypothermic circulatory arrest at the cardiac operation, are determinants of an increased risk of a neurological insult, if the patient needs VA ECMO postoperatively.

What are the outcomes of extracorporeal membrane oxygenation in the neonatal paediatric population (Table 4)?

Table 4. Outcomes following paediatric extracorporeal membrane

oxygenation produced by the Extracorporeal Life Support Organization (ELSO) in 2018.

Neonatal Pulmonary Cardiac ECPR Paediatric Pulmonary Cardiac ECPR

31 • •

•

qçí~ä=êìåë

pìêîáîÉÇ=b`ip

pìêîáîÉÇ=íç=ÇáëÅÜ~êÖÉ= çê=íê~åëÑÉê

30,934 7794 1718

25,990 5063 1140

84% 64% 66%

22,662 3281 708

73% 42% 41%

8820 10,462 3946

5953 7177 2262

67% 68% 57%

5131 5447 1675

58% 52% 42%

What are the potential complications of extracorporeal membrane oxygenation?

As complications of ECMO are common, each patient is likely to develop an ECMO-related complication. Although circuit-related complications are rare, they are significant. Complications that occur during cannulation include: a) b) c) d) e)

damage to the cannulating vessels, including dissection; haemothorax, pneumothorax (Figure 16); haemopericardium and tamponade; accidental dislodgement of the cannulae or malposition; limb ischaemia, especially in femoral cannulation.

Complications that occur whilst the child is on ECMO include: a) b)

bleeding (both minor and major); thrombus in the circuit (tubing, oxygenator), or haemolysis;

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416

Figure 16. Chest radiograph demonstrating a

pneumothorax following venous cannulation for extracorporeal membrane oxygenation.

Figure 17. An axial computed tomography scan demonstrating a significant cerebral bleed in a child whilst on extracorporeal membrane oxygenation.

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11 Extracorporeal membrane oxygenation c) d) e) f) g) h) i) j) k)

air within the circuit; motor failure, pump failure or console failure; oxygenator failure; tubing rupture or failure of the line components; cerebral bleed, infarction or oedema (Figure 17); infection; accidental displacement and decannulation (Figure 18); complications from other systems, especially renal and gastrointestinal; general ICU-related complications.

417

Figure 18. Chest radiograph demonstrating

accidental arterial decannulation of a child whilst on extracorporeal membrane oxygenation.

32 •

Describe the principles of managing emergency extracorporeal membrane oxygenation scenarios Veno-veno ECMO hypoxia:

a)

check that the pump flow is over two-thirds of the patient’s cardiac output;

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b)

•

c) d) e) f) g) h)

Veno-veno ECMO hypercarbia: a) b) c)

418

•

•

d) e) f)

check that the pump flow is over two-thirds of the patient’s cardiac output; increase the O2 flow to the oxygenator to twice the pump flow rate; increase the pump flow rate (otherwise consider that recirculation may be occurring); increase ventilation; cool the patient; administer muscle relaxants.

Veno-veno ECMO shunting or recirculation: a) b) c)

observe the cannula position as pump flow may not improve oxygenation; check that the pre-membrane (venous) pO2 is 150mmHg; increase pump flow; increase ventilation; cool the patient; administer muscle relaxants; maintain haemoglobin levels; add a second access line to reduce the shunt.

c) d) e)

check the arterial blood gas from the right radial arterial line and O2 saturation measured on the right hand or forehead; ensure proper functioning of the oxygenator return line pO2 >150mmHg; increase the pump flow as high as possible; increase ventilation, PEEP and inspired O2 concentration; readjust or replace the arterial line, if required.

Veno-arterial ECMO hypercarbia: a) b)

check for adequate pump flow (over two-thirds of the patient’s cardiac output); adjust the supply of O2 to the oxygenator, to twice the pump flow rate;

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•

c) d) e) f)

Veno-arterial ECMO bleeding: a) b)

•

c) d) e)

prevention is the primary objective by meticulous haemostasis and monitoring coagulation status (ACT, APTT, FBC, D-dimer, fibrinogen); maintain an APTT of 50-75 seconds with a heparin infusion (but can be withheld if the patient is bleeding). Heparin-coated circuits can run for a couple days without heparin; transfuse platelets, cryoprecipitate, FFP, packed cells as needed; administer antifibrinolytic agents, such as IV tranexamic acid; consider surgical exploration.

Veno-arterial ECMO haemolysis — which may be caused by a clot in the circuit or near the cannula orifice, obstruction at the circuit, increased speed of the pump, deranged coagulation cascade or liver dysfunction. Presenting signs include haematuria, hyperkalaemia, renal failure, jaundice (late sign) and shaking of the lines due to changes in pressure (cavitating). Management includes the following: a) b) c) d)

•

increase the pump flow rate; increase ventilation; cool the patient; administer a muscle relaxant.

e)

monitor haemoglobin, liver function tests, urea & electrolytes and clotting screen; replace the volume; adjust the pump flow; a transoesophageal echocardiogram (TOE) to ensure that the cannulae are not obstructed; circuit change, if required.

Unable to maintain veno-arterial ECMO flow: a) b) c) d) e) f)

check the position of the cannulae and volume status and improve if possible; check for any kinking of the lines or cannulae; blood sample from pre- and post-oxygenator; perform an echocardiogram and chest radiograph to identify the intracardiac position of the cannulae; optimise fluid status, preload, afterload and contractility; decrease the pump speed to reduce the suction on the catheter, followed by increasing the speed to normal as smoothly and quickly as possible;

419

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•

g)

Pump failure: a) b) c) d) e) f)

g)

420

•

•

•

consider changing faulty components.

call for help from the PICU, surgical and perfusion teams; ventilate conventionally to support the respiratory system; haemodynamic support with inotropes and vasoconstrictor agents; if there is no flow, consider the risk of thrombus formation whilst the ECMO is not working; if pump head failure is the cause, use the back-up console, battery and check the wall power; if an electrical issue is the cause, clamp the lines and turn off the pump, commence hand cranking and evaluate the integrity of the pump head. Consider changing the pump head, turning the pump to the minimal settings of 1000-1500 rpm, remove the clamps, and then gradually increase the rpm. Check for thrombus; if pump head failure is the cause, clamp the lines and stop the pump, replace the pump head, turn the pump to the minimal settings of 1000-1500 rpm, remove the clamps, and then gradually increase the rpm. Check for thrombus.

Cardiac arrest on VV ECMO: a) b) c) d)

call for help; CPR; consider and check for reversible causes; DC shock if in shockable rhythm.

Cardiac arrest on VA ECMO. Cardiac arrest has little effect on ECMO support, if flows are maintained: a) b)

call for help; DC shock if in shockable rhythm.

Accidental decannulation. On VV ECMO, it may be accompanied by profound hypoxia, hypovolaemic shock and cardiac arrest, whereas VA ECMO may be accompanied by cardiac arrest and hypovolaemic shock: a) b) c) d)

call for help; clamp the circuit; turn off the pump; commence cardiopulmonary resuscitation;

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•

e) f) g)

Air in the circuit. Air can find its way through various ports, connections, as well as faults in the circuit and cannulae. The presence of a significant amount of air will compromise ECMO flows and performance: a) b) c) d)

•

e)

33 •

clamp the arterial line; stop the pump; place the patient in a head-down position; commence inotropic and ventilatory support, including volume replacement; examine possible entry points and call for help, if required.

Circuit rupture, which is accompanied by massive blood loss, air entry to the circuit, and haemodynamic and respiratory compromise: a) b) c) d) e) f)

•

ventilate; administer volume and cardiovascular support; prepare for surgical intervention.

clamp the circuit; stop the pump; call for help; support the cardiovascular and respiratory systems; replace volume lost; prepare for surgical intervention if required or change all or parts of the circuit.

Thrombus in the circuit. Although this is the most common complication, meticulous management of anticoagulation can help to reduce the risk. Some small-size thrombi may cause problems with the ECMO support. Thrombi of any size pose a danger when present in the outflow portion of the circuit but less so when in the inlet portion, unless large, as they will end up in the oxygenator. Management involves maintaining an optimal ACT, monitoring the circuit for thrombus, and if required, clean or change the affected component of the circuit

Describe the steps when stopping and recommencing extracorporeal membrane oxygenation In a circuit with a roller head pump:

a) b)

clamp the venous line above the bridge; open the bridge clamp;

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c) d)

clamp the arterial line above the bridge; stop the flow.

To return to ECMO flow: a) b) c) d)

open the arterial clamp; clamp the bridge; open the venous cannula; return to the previous pump head speed (rpm).

In a circuit with a centrifugal pump: a) b) c) d) e) f)

close the post-oxygenator clamp; clamp the venous line above the bridge; open the bridge; clamp the arterial line; release the post-oxygenator clamp; maintain ECMO flow through the bridge.

To return to ECMO flow: a) b) c) d) e) f) g)

close the post-oxygenator clamp; clamp the bridge; open the arterial clamp; open the venous clamp; increase the pump head speed (rpm); remove the post-oxygenator clamp; clear the bridge.

What are the general parameter guidelines for paediatric extracorporeal membrane oxygenation support?

ACT 160-220 seconds. PaO2 60-80mmHg (VA), 45-80mmHg (VV). Haemoglobin 13-15g/dL (VA), 15g/dL (VV). Haematocrit >40 (VA), >45 (VV). pH 7.35-7.45. PaCO2 35-45mmHg. Platelet count >75 x 109/L. Urine output >2mL/kg/hour. Heparin 25-50 units/kg/hour (but may need to be adjusted according to renal function, bleeding and the presence of a haemofilter).

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Venous O2 saturation 70-75%. Fluid requirements 20-100mL/kg/day (20kg 20mL). Calorie requirements 60-90/kg/day. Maintain serum sodium, potassium and calcium levels at normal values. VA ECMO flow 100mL/kg/min x 0.8 (80% of estimated cardiac output). VV ECMO flow 80-120mL/kg/min (but may need to be adjusted according to the recirculation flow and the effective flow).

Describe the steps when commencing extracorporeal membrane oxygenation After completing the cannulation process, check the circuit, including the position of the cannulae and the patient, ensuring that the cannulae are secure. Open the clamp on the venous line above the bridge. Close the clamp on the bridge. Open the clamp on the arterial line above the bridge. Slowly increase the blood flow. Monitor the cardiovascular response. Wean off the ventilation support. Wean off the inotropic support. Re-evaluate the circuit for the presence of air bubbles. Check all the connections and ports. Check that the console, transducers and all other electrical components are operational. Perform the calculations regarding flow, sweep, FiO2, drug and fluid infusions. Check the ACT or APTT and adjust heparin, as appropriate. Optimise the clotting profile. Inform all personnel involved about the set parameters and alarms. Recheck that the cannulae are secure. Request an echocardiogram and chest radiograph, as appropriate.

What are the principles of daily management for a patient requiring extracorporeal membrane oxygenation?

Daily routine checks and evaluation of all the organ systems are crucial not only for optimal support but also for survival.

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It is important to regularly check the cannulation site, cannulae and circuit (mechanical and electrical components). Ensure that the position of the patient’s head is in the midline, up to 30°. Cardiovascular system: a) b) c) d) e)

maintain systemic perfusion and intravascular volume; monitor urine output, central venous pressure, physical signs of perfusion, and body weight; use echocardiography, as required; check the circuit for the presence of clots and overall integrity; regular ECG and relevant blood tests.

•

Respiratory system:

•

Renal system:

a) b) c)

a) b)

•

c)

in the first 48 hours, there is a high incidence of acute tubular necrosis and oliguria. Thereafter, the urine output usually increases to >2mL/kg/hr; if renal function does not improve, however, renal support can be added to the circuit with continuous renal replacement therapy (CRRT); a renal blood test may be required daily, according to function.

Central nervous system (CNS): a) b)

c)

•

ventilation settings; evaluate arterial blood gases and chest radiograph; avoid build-up of secretions in the endotracheal tube and pulmonary hygiene with flexible bronchoscopy, as required.

avoid paralytic agents; perform regular sedation holding and neurologic examinations, including pupil size and reaction, reflexes, level of consciousness, and the presence of normal or abnormal movements; a head US or CT may be required, although CT requires transporting the patient to the radiology department on ECMO.

Infection control: a)

all procedures and interventions should follow aseptic techniques;

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11 Extracorporeal membrane oxygenation

•

b) c) d)

Fluids, electrolytes and nutrition: a) b)

•

check all sites for infection; send appropriate cultures of blood, sputum and urine; antibiotics, as indicated.

regular monitoring of electrolytes, including magnesium, calcium and phosphorus levels; close monitoring of fluid balance, high calorie intake and nutritional support, as required.

The surgical team should perform daily checks of the cannulation site, cannulae, circuit, assist in dressing changes, be available to transport the patient, and be available to perform any invasive procedure.

Recommended reading 1. 2. 3. 4. 5.

Brogan TV, Lequier L, Lorusso R, MacLaren G, Peek G. bñíê~ÅçêéçêÉ~ä=iáÑÉ=pìééçêíW

qÜÉ= bipl= oÉÇ= _ççâ, 5th ed. MI, USA: Extracorporeal Life Support Organization (ELSO); 2017.

Short BL, Williams L. b`jl=péÉÅá~äáëí=qê~áåáåÖ=j~åì~ä. MI, USA: Extracorporeal Life

Support Organization (ELSO); 2010.

Pappalardo F, Montisci A. What is extracorporeal cardiopulmonary resuscitation? g

qÜçê~Å=aáë 2017; 9(6): 1415-9.

Schmidt M, Pellegrino V, Combes A, Scheinkestel C, Cooper DJ, Hodgson C. Mechanical ventilation during extracorporeal membrane oxygenation. `êáí=`~êÉ 2014;

18(1): 203.

Barbaro RP, Guner Y. Pediatric Extracorporeal Life Support Organization Registry International Report 2016. ^p^fl=g 2017; 63(4): 456-63.

6.

Yam N, McMullan DM. Extracorporeal cardiopulmonary resuscitation. ^åå=qê~åëä=jÉÇ

7.

Chan T, Thiagarajan RR, Frank D, Bratton SL. Survival after extracorporeal

8.

2017; 5(4): 72.

cardiopulmonary resuscitation in infants and children with heart disease. g= qÜçê~Å

`~êÇáçî~ëÅ=pìêÖ 2008; 136(4): 984-92.

Kane DA, Thiagarajan RR, Wypij D, Scheurer MA, Fynn-Thompson F, Emani S, del

Nido PJ, Betit P, Laussen PC. Rapid-response extracorporeal membrane oxygenation

to support cardiopulmonary resuscitation in children with cardiac disease. `áêÅìä~íáçå 9.

2010; 122(11 Suppl): S241-8.

Extracorporeal Life Support Organization. Guidelines for ECMO centres, training and

continuous education. Available at http://www.elso.org. Accessed 26.02.21.

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Key Questions in CONGENITAL CARDIAC SURGERY 10.

Trummer G, Foerster K, Buckberg GD, Benk C, Mader I, Heilmann C, Liakopoulos

O, Beyersdorf F. Superior neurologic recovery after 15 minutes of normothermic cardiac arrest using an extracorporeal life support system for optimized blood

426

pressure and flow. mÉêÑìëáçå 2014; 29(2): 130-8.

11.

Booth KL, Roth SJ, Thiagarajan RR, Almodovar MC, del Nido PJ, Laussen PC.

12.

Makdisi G, Wang I. Extracorporeal membrane oxygenation (ECMO) review of a

13.

Rood KL, Teele SA, Barrett CS, Salvin JW, Rycus PT, Fynn-Thompson F, Laussen

Extracorporeal membrane oxygenation support of the Fontan and bidirectional Glenn circulations. ^åå=qÜçê~Å=pìêÖ 2004; 77(4): 1341-8.

lifesaving technology. g=qÜçê~Å=aáë 2015; 7(7): E166-76.

PC, Thiagarajan RR. Extracorporeal membrane oxygenation support after the Fontan operation. g=qÜçê~Å=`~êÇáçî~ëÅ=pìêÖ 2011; 142(3): 504-10.

14.

Gomez D, Duffy V, Hersey D, Backes C, Rycus P, McConnell P, Voss J, Galantowicz

15.

Conrad SA, Rycus PT. Extracorporeal membrane oxygenation for refractory cardiac

16.

Khorsandi M, Davidson M, Bouamra O, McLean A, MacArthur K, Torrance I, Wylie G,

M, Cua CL. Extracorporeal membrane oxygenation outcomes after the comprehensive

stage II procedure in patients with single ventricles. ^êíáÑ=lêÖ~åë 2017; 41(1): 66-70.

arrest. ^åå=`~êÇ=^å~ÉëíÜ 2017; 20(Supplement): S4-10.

Peng E, Danton M. Extracorporeal membrane oxygenation in pediatric cardiac surgery: a retrospective review of trends and outcomes in Scotland. ^åå= mÉÇá~íê

17. 18.

`~êÇáçä 2018; 11(1): 3-11.

Gupta P, Robertson MJ, Beam B, Gossett JM, Schmitz ML, Carroll CL, Edwards JD, Fortenberry JD, Butt W. Relationship of ECMO duration with outcomes after pediatric cardiac surgery: a multi-institutional analysis. jáåÉêî~=^åÉëíÜÉëáçä 2015; 81: 619-27.

Balasubramanian SK, Tiruvoipati R, Amin M, Aabideen KK, Peek GJ, Sosnowski AW,

Firmin RK. Factors influencing the outcome of paediatric cardiac surgical patients during extracorporeal circulatory support. g=`~êÇáçíÜçê~Å=pìêÖ=2007; 2: 4.

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Chapter 12

Informed consent in congenital cardiac surgery Robert A. Wheeler

1 • • • • • •

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•

What is the role of consent in modern society?

Choice has achieved a high priority in our society. Citizens’ choices in education, transport structure and healthcare provision, to name a few, are constantly and publically acknowledged. The necessity for choice reflects the fundamental role of autonomy: the right of every citizen to influence their own destiny. In this context, the need to choose to accept (consent) the otherwise unwanted physical contact of any type (touch) is self-evident. In fact, unwelcome attentions from another person who tries to touch you against your wishes are considered repellent. There are times when certain contacts or touches are unavoidable, such as in packed trains, shops and sidewalks. In some cases, there is little choice but to resign yourself to being touched. But in any less frenetic circumstances, there is an absolute understanding that we are entitled to choose who touches us, and when.

Why is consent necessary in health care?

One important consequence of the need for consent is that a patient, or their parent, must agree in advance of physical touching, before any intervention can ensue. The teenage patient, who is lying on his or her hospital bed, when suddenly confronted with a surgeon who puts his or her hand on the apex beat without first asking for permission, would justifiably complain that the treatment fell below the reasonable standard one would be entitled to expect. Clearly, such behaviour is simple rudeness, irrespective of the legal context. However, the legal context is suddenly placed into stark relief when a patient complains that an intimate examination was performed without consent; and further still when such an examination was irrelevant to his or her clinical presentation.

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These latter actions move the lack of consent into the arena of professional disciplinary regulation, as well as civil litigation and potentially criminal prosecution. Several medical defence organisations’ case reports are a testament to this not infrequent and devastating error of judgement. Plainly, interventions required in congenital cardiac surgery are more complex and threatening than the simple touch. But the need for consent, based on disclosure as to what is entailed and why it is necessary, is built upon this elementary foundation.

Is consent needed for anything other than treatment interventions?

In paediatric cardiac surgery, the patient or parent must agree, in advance, before any of the confidential information that they impart when dealing with their surgeon can be further disclosed. Clearly, it is consent for surgical intervention that is uppermost on the surgeon’s mind, and rightly so. But the rules of consent encompassing aspects of care, such as competence or capacity, correct disclosure and appropriate recording, are equally applicable to both clinical interventions and to confidentiality. Consent is the legal key that makes both physical intervention and sharing of information lawful.

What is a child, under English law?

From the legal perspective, a child is someone who has not yet reached 18 years of age. Legal synonyms include ‘minor’ and ‘infant’. The latter is instructive, since it is derived from the Latin, áåÑ~åë, unable to speak. This reflects the legal rule preventing children from speaking for themselves in court, although this impediment has been at least partly addressed over the last two decades. Nevertheless, this definition begs a fundamental question; as to whether children can provide their own consent, or whether they depend upon their parents to provide it for them.

What is a ‘young person’ under English law?

It is becoming more common in England to describe citizens of 16 and 17 years as ‘young people’. This acknowledges that they are still children from the legal perspective, whilst at the same time accepting

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that as they approach majority, their autonomy is emerging, reflected by certain legal rights. For instance, the Mental Capacity Act 2005 applies to those who are 16 years and over, prescribing measures to be taken if they lack capacity. Nevertheless, those with parental responsibility for young people retain parallel rights to consent on their behalf, although these rights diminish as the child achieves competence or capacity.

What is a ‘looked after child’ under English Law?

Children are described as being ‘looked after’ by the local authority (LA) when either: a) b)

• •

• •

7 •

they have been made the subject of a care order by a family court, which obliges the local authority to look after the child; the local authority provides the child with accommodation, in the absence of a care order.

In both cases, the child’s local authority passport, generally provided by the foster parent should make clear into which category the child falls. Clearly, children who are a subject of a care order will usually also be accommodated by the local authority. The existence of the care order is of great importance, since it directs the local authority to share parental responsibility for the child with the parent(s), who before the start of the order had parental responsibility for the child. Since only those with parental responsibility for the child can provide consent for his or her treatment, it is vital to ascertain which adults hold parental responsibility. If no care order is in place, consent needs to be sought from the parents. If an order is in place, the local authority passport will indicate whether the local authority has restricted the scope of the birth parents’ parental responsibility. If they continue to bear parental responsibility for medical decisions, they can provide consent. If the local authority appears to have restricted the parents from giving consent, advice should be sought.

Who can provide consent for surgery?

A person with parental responsibility has the right to provide consent where necessary. The child’s mother (the woman who gave birth to the baby, but not the person who provided the egg from which

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he/she was conceived, if different) automatically has parental responsibility. The child’s father gains parental responsibility automatically if married at the time of the birth registration. Since 2003, unmarried fathers also get parental responsibility automatically, when they register the birth. Alternatively, parental responsibility can be later acquired by the unmarried father, either with the agreement of the child’s mother, by application to a court or by marrying the mother. Parental responsibility is passed to adoptive parents on legal adoption. It may be shared with guardians appointed by parents or with local authorities, and is linked to various legal orders.

How does the parent decide whether to provide consent?

The person with parental responsibility who provides consent for a child’s surgery must act in the child’s best interests in so doing. These interests are usually self-evident, and the agreement between parents and surgeon is reached after full disclosure of the relevant information. This agreement is not invariable. In a case concerning a child with biliary atresia, the clinicians wished to perform a liver transplant, and considered the prospects of success to be good. The parents refused their consent, on the grounds that the surgery was not in the child’s best interests. The Court of Appeal held that the assessment of the child’s best interests went wider than the narrower medical best interests, and that the child’s connection with his family held great weight in this regard. Accordingly, the Court refused to enforce the hospital’s request that the mother would bring her child in for surgery. The judgement could be criticised, in failing to differentiate between the interests of the child and those of his mother. The case, however, provides an example of the balancing act performed by courts.

Can children under 16 provide consent independent of their parents?

Depending on their maturity and the intervention that is proposed, children from a young age may be able to provide independent consent. For example, a 4-year-old child may be able to consent to a blood pressure measurement, a 6-year-old to a venepuncture and a 10-year-old to the removal of a chest drain. There is no suggesting that the parents should be excluded from this process and such an exclusion should be avoided, if possible. It is

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for the family as a whole to decide what part the child’s potential competence should play in the consenting process. But the involvement of children in this process will strengthen the therapeutic relationship and is to be encouraged. A child’s previous experience is of great importance. It is submitted that following the very recent diagnosis of structural cardiac disease in a 15-year-old, who has been asymptomatic up to this point, the child will be so horrified by the dissolution of his comfortable and well organised life as to be incoherent, likely incapable of consenting for the necessary cardiac catheter investigations. By contrast, another 15-year-old has been teetering on the brink of cardiac failure for many years. He has already undergone multiple cardiac interventions, including a sternal dehiscence 3 years ago. He knows a great deal about cardiac surgery and has seen its complications and disadvantages wreak havoc in his congenital cardiac peer group. Now facing his transplant, it is possible he will be competent to provide independent consent. Therefore, it is important objectively to determine whether a child of 15 years or younger has the necessary experience to inform his or her competence to provide independent consent for the proposed intervention.

How is the competence of a child younger than 16 established?

For this assessment, the Gillick test is widely used. The test derives from a landmark case where it was established that a child who is competent to provide consent should be allowed to do so, independently of their parents. The test requires that the child has sufficient understanding and intelligence to enable him or her to understand fully what is involved in a proposed intervention. Thus, if a child can understand: a) b) c) d) e)

that a choice exists; the nature and purpose of the procedure; the risks and side effects; the alternatives to the procedure; and is able to: i) retain the information long enough; ii) weigh the information; iii) arrive at a decision; iv) and to be free from undue pressure. Then he or she would be deemed competent for the proposed intervention. It will be seen that competence rests on intelligence, maturity and experience. Not on age.

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Gillick provides a high threshold for consent, consistent with public policy. It would be highly undesirable to allow incompetent children to provide consent for interventions which they could not fully understand. The fact that a child has to ‘prove’ their competence places a barrier to children that is never experienced by adults, whose capacity is presumed.

Is ‘Fraser’ competence synonymous with ‘Gillick’ competence?

During the Gillick case, an additional set of guidelines were suggested by Lord Fraser, specifically for doctors who assist with reproductive decision-making by children under 16. It should be noted that these do not replace the Gillick test, nor are they synonymous with it.

Can a Gillick competent child refuse treatment?

The vast majority of Gillick competent children who refuse treatment are refusing relatively trivial procedures. You may be entitled to rely upon their parent’s consent if necessary, but it is a matter for clinical judgement whether the procedure could be deferred, to allow the child further time to consider, and be reconciled with what is likely to be an inevitable outcome. (The problem of refusal in Gillick competent children is dealt with in the same way as for the 16- and 17-year age group, below.) The Gillick competent child, however, does not enjoy an equal right to refuse treatment. Only those cases in which the refusal of lifesaving treatments in these children is at issue have reached the court. Given the opportunity, courts have resolutely denied the (otherwise) competent minor the right to choose death: a)

A 15-year-old girl refusing her consent for a life-saving heart transplant had her refusal overridden by the courts. M’s reason was that she “…would rather die than have the transplant and have someone else’s heart. …I would feel different with someone else’s heart… that’s a good enough reason not to have a heart transplant, even if it saved my life…” Nevertheless, balancing the child’s undoubted resentment against the certainty of her death in the absence of a transplant, the court was obliged to act in her best interests, and keep her alive. Accordingly, the court authorised the operation;

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14 • • •

In another case, a 14-year-old girl required a blood transfusion. She was a Jehovah’s Witness, and refused the treatment. The court found that even if she had been Gillick competent, her grave condition would have led the court to authorise the transfusion. As it was, the girl was unaware of the manner of death from anaemia and was basing her views on those of her congregation, rather than on her own experiences. For these reasons, she was judged incompetent to make this decision for herself.

Can young people provide independent consent?

People of 16 and 17 years of age are presumed to have the capacity to provide consent for surgical, medical and dental treatment. Made possible by the Family Law Reform Act 1969, this recognised that the ‘lifestyle’ decisions that teenagers were taking in that era contrasted sharply with the age of majority (21 years) at the time. The new law reduced the age of majority to 18 years, and introduced the notion that 16- and 17-year-olds had äÉÖ~ä= Å~é~Åáíó. This was built upon by the Mental Capacity Act 2005, which provided the presumption of ãÉåí~ä=Å~é~Åáíó for this age group. Young people are thus able to provide consent for treatment in the absence of their parents. However, the parental right to provide consent for treatment lasts until the end of childhood. This has the effect of providing a ‘safety net’, allowing 16- and 17-year-olds the opportunity of consent for themselves or deferring to parents if they see fit. Once these children reach adulthood on their 18th birthday, all parents’ rights disappear. For the rest of their life, they alone can provide consent, either directly in person, or in some circumstances, by a proxy method.

How to deal with a young person who wishes to have a treatment with which her parents disagree?

If parents and a child of this age disagree, it is wise to exercise caution. If a 16- or 17-year-old wishes to exercise his or her right to consent, whilst parents oppose the decision, then one would be entitled to rely on this consent. However, it would be important to understand the basis for their disagreement. For instance, if one suspected that the young person was not capacitous, the presumption (that the child’s consent could be relied upon) should be challenged. This can simply be done by establishing whether all the relevant information is properly understood, and that information can be retained, believed and weighed up. Finally, that a decision could be appropriately communicated. If the young person can, then he or she has capacity.

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But it is still wise to tease out where the problem lies, since this is a most unusual situation, and it would be in the young person’s best interests to resolve the issue before surgery, if that is feasible.

How to deal with a young person who refuses a treatment that his parents wish him to have?

The problem, reversed, is of a young person who refuses treatment but who is accompanied by a parent who provides consent. Valid parental consent will make the procedure ‘legal’ but clinical judgement should be exercised as to whether proceeding with the treatment against the young person’s wishes is both practicable and in his or her best interests. Modern English law views parental responsibility as a dwindling right, steadily eroded by the maturing child’s increasing autonomy. For elective procedures, it is recommended that these should be abandoned until the dispute is resolved. For emergency or life-saving procedures, alternative ways to administer treatment that are still consistent with the young person’s best interests should be explored. However, if life or limbs were under threat, and there was no valid alternative choice but to provide a definitive operation, then reluctantly, restrain and proceed could be the only way forward. A postoperative embolism that has resulted in an ischaemic hand could be an example of this situation. It should be noted that in reality, the amount of resistance that a child of any age puts up is usually inversely proportional to their malaise and discomfort. In the gravely ill, refusal is rare. For urgent procedures, if a 16- or 17-year-old refuses treatment for the preservation of her life, such as the transfusion of blood, courts invariably choose to override the child’s autonomy and provide an order which allows lawful provision of the treatment against the child’s wishes. This either upholds the parental wishes for treatment or overrides parental refusal. Although these cases are rare, the timescale within which the decision needs to be made allows sufficient time for the court to be contacted, providing the surgeon with the necessary authority.

Does the young person’s right to consent extend to research activities?

The 1969 law did not extend this right to consent for research or interventions that do not potentially provide a direct health benefit to the individual concerned. However, if competent along ‘Gillick’ lines, a young person may be able to provide consent for these activities.

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12 Informed consent in congenital cardiac surgery How can consent be obtained from ‘incapacitated adult patients’ requiring interventions for congenital heart disease? All patients who are 18 years or over are presumed to have capacity. Where there is a suspicion that the adult about to give consent lacks capacity, that presumption may be rebutted if, on the basis of the Mental Capacity Act 2005, it has been established that they lack capacity to make the relevant decision; for instance, the decision to agree or refuse cardiac surgery. Both the local trust’s mandatory training or that of the General Medical Council are helpful and ubiquitous sources of information concerning the use of the Mental Capacity Act 2005. If the adult in question has capacity, it is important to realise that no consent can be provided from any source. In most situations, there will be universal agreement between the family, friends, acquaintances, doctors and nurses that the procedure is in the best interest of the patient. In this common situation, it will be completely acceptable to proceed on this basis. Although no consent will be available, the procedure will be lawful if performed in the patient’s best interests. However, there are circumstances in which despite universal agreement, the Court of Protection should be consulted, including: a) b) c) d)

• •

•

organ donation; non-therapeutic sterilisation of incapacitated adults; foreseeable necessity for forceful restraint; use of treatments that are innovative or experimental, or involve an ethical dilemma.

If the incapacitated adult is unbefriended, with no accompanying persons, the Mental Capacity Act 2005 insists that an Independent Mental Capacity Advocate should be nominated, to ensure that the patient’s circumstances have been subject to all reasonable scrutiny, before the best interests of the patient can be determined. In the unusual circumstances where there is dissent from any quarter, then resolving the dispute before proceeding is strongly advised. If the dispute cannot be transformed into an agreement from the dissonant parties, (irrespective of whether they are clinical or family) then a declaration from the Court of Protection will be required. There are circumstances where patients may, during an adult era of capacity, have made advanced decisions (that anticipate their own incapacity) to refuse treatment. If such a decision exists, then advice should be sought.

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Equally, the capacitous adult may have created a lasting power of attorney, embodied in a friend or relative (donee), to be activated by the advent of their incapacity, authorising the donee to give or refuse consent to the carrying out or continuation of a treatment on their behalf. In these circumstances, advice should be sought. Less likely, the Court of Protection may have appointed a deputy to make decisions on behalf of the incapacitated patient but it is unlikely to have given the deputy powers to make medical decisions, since the courts prefer to reserve these difficult decisions for themselves. Social services have no role in the provision or withholding of consent in this group of patients.

Why is it necessary to disclose information when seeking consent?

Clinicians must supply the patient or parent with enough information to make an informed decision as to whether they wish to undergo the proposed intervention. This is entirely separate from the need to ensure that patients are not subjected to an unwanted touch. Whilst training ensures that surgeons are acutely aware of surgical hazards, our patients are not. As a consequence, doctors often fail to appreciate how little patients understand about the consequences of intervention. Examples are numerous, including: a) b)

c)

• •

probably only a few patients appreciate that surgery on their back may lead them to urinary and faecal incontinence, or failure to move their legs; that misdirection of a subclavian needle may lead to a thoracotomy, to arrest the haemorrhage thus caused; that a difficult inguinal hernia repair could lead to loss of the ipsilateral testicle.

The process of consent, with disclosure of risks and side effects, is designed to allow patients an insight into the risks that they and the surgeon jointly face. Furthermore, patients cannot be expected to anticipate the limitations of treatment or the possible alternatives. Disclosing alternatives to treatment may be very important to a patient who is otherwise unaware that they had a choice; for example: a)

a man facing excision of pulmonary metastases from osteosarcoma may be blissfully unaware that cure is unlikely. If he had known, he might have chosen an alternative route and avoided thoracic intervention;

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a woman planning on going to her daughter’s wedding tomorrow might just elect, tonight, to have her acute appendicitis treated only with antibiotics, at least for 24 hours, and take the risk.

What should be disclosed when seeking consent?

Most hospitals provide consent forms that guide the clinician as to what should be discussed, broadly categorised as the benefits and disadvantages of the proposed operation, together with the benefits and disadvantages of alternative treatments, including those of no treatment at all (Figure 1). This position was articulated in the case of Pearce v United Bristol Healthcare NHST [1999], 48 BMLR 118, and provided the foundations for the standards for disclosure of risk: “If there is a significant risk which would affect the judgement of a reasonable patient, then in the normal course it is the responsibility of a doctor to inform the patient of that significant risk, if the information is needed so that the patient can determine for him or herself as to what course he or she should adopt.” This judgement, with some embellishment, was adopted in Montgomery v Lanarkshire Health Board [2015], UKSC 11. This judgement was reflected by the General Medical Council in 2008, which emphasised the importance of a discussion that leads to consent, rather than a soliloquy delivered by a surgeon. The legal prescription for the necessary disclosure was provided by the Supreme Court in 2015, after a woman claimed that she would have chosen a Caesarean section if it had been offered to her, thereby avoiding neurological injury to her son. In this fundamental case (Montgomery v Lanarkshire, 2015), the Supreme Court took the opportunity to endorse and confirm various strands of previously decided court decisions, pertaining to the disclosure of information to patients prior to seeking their consent for surgery. In so doing, the Supreme Court reiterated existing advice from the General Medical Council. These various aspects of consent law in England are set out in all the following sections. The doctor is under a duty to take reasonable care to ensure that the patient is aware of any material risks involved in any recommended treatment, and of any reasonable alternatives or variant treatment. The test of materiality is whether, in the circumstances of the particular case, a reasonable person in the patient’s position would be likely to attach significance to the risk, or the doctor is or should be aware that the particular patient would be likely to attach significance to it (Figures 2, 3 and 4).

437

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438

Figure 1. Guidance provided to clinicians on the back of a standard consent form. Such forms are used widely across NHS hospitals.

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12 Informed consent in congenital cardiac surgery

439

Figure 2. Standard consent form for investigation or treatment in use in a tertiary centre. This form is used by clinicians when patients are able and entitled to provide their own consent, for example, adult congenital heart disease patients. Continued overleaf.

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440

Figure 2 continued. Standard consent form for investigation or treatment in use in a tertiary centre. This form is used by clinicians when patients are able and entitled to provide their own consent, for example, adult congenital heart disease patients.

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12 Informed consent in congenital cardiac surgery

441

Figure 3. Standard consent form for investigation or treatment in use in a tertiary centre. This form is used by clinicians when patients are children or a young person. The patient is still able to sign for his or her own agreement, but the signature of a parent or legal guardian is required to render the form legally valid. Continued overleaf.

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442

Figure 3 continued. Standard consent form for investigation or

treatment in use in a tertiary centre. This form is used by clinicians when patients are children or a young person. The patient is still able to sign for his or her own agreement, but the signature of a parent or legal guardian is required to render the form legally valid. Continued overleaf.

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12 Informed consent in congenital cardiac surgery

443

Figure 3 continued. Standard consent form for investigation or

treatment in use in a tertiary centre. This form is used by clinicians when patients are children or a young person. The patient is still able to sign for his or her own agreement, but the signature of a parent or legal guardian is required to render the form legally valid.

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444

Figure 4. Form in use in a tertiary centre for consent in situations where the patient is incapable to provide his or her consent due to severe limitations (see point “B” on the form). Continued overleaf.

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12 Informed consent in congenital cardiac surgery

445

Figure 4 continued. Form in use in a tertiary centre for consent in situations where the patient is incapable to provide his or her consent due to severe limitations (see point “B” on the form). Continued overleaf.

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446

Figure 4 continued. Form in use in a tertiary centre for consent in situations where the patient is incapable to provide his or her consent due to severe limitations (see point “B” on the form).

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20 •

21 •

•

22 • •

12 Informed consent in congenital cardiac surgery To what extent is dialogue with the patient or parents required? When concerning the consent process, dialogue is mandatory. Both courts and regulators consider open discussion between clinician and patients to be of the greatest importance.

Is there an exception to the imperative for disclosure prior to consent?

There is an exception to the imperative of disclosure, but it is highly restrictive. The court in Montgomery acknowledged the rare situation where the disclosure would be seriously detrimental to the patient’s health. Plainly, this exception primarily refers to the health of a person making a decision about their own treatment, so would be unlikely to apply to a parent. Nevertheless, it is foreseeable that adults suffering from congenital cardiac disease might fall into the category where disclosure would seriously harm their health. This ‘therapeutic exception’, however, should be used only with great caution and would require a second opinion, as a matter of urgency.

How do courts deal with patients’ claims that insufficient information was disclosed to allow an informed decision?

It is very unusual for cases where patients claim that they were not provided with valid disclosure (and thus their consent was invalid) to reach court. When this happens, however, English courts do not rely on expert witnesses to set the standard for what the appropriate disclosure should have been. The trend is in contradistinction to the great majority of clinical negligence cases, where a medical expert will be asked to set the standard of care, against which the defendant doctor will be judged. But it also gives an insight into the importance that the judiciary set on disclosure for consent. Judges tend to put themselves in the shoes of the ‘reasonable’ patient and enquire what such a person would want to know, before giving consent in the particular set of clinical circumstances.

447

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23 • • •

448

24 • •

•

•

What should be the appropriate course of action if doubts remain that a proposed elective operation is appropriate? Seeking consent from a person who is fully aware of the clinical risks and benefits should concentrate the mind of both surgeon and patient. If the process has failed to dispel doubts in either mind that intervention is the right thing to do, the procedure should be abandoned, the situation should be reconsidered, and a different course should be pursued. At any stage, seeking a colleague’s opinion, promoting discussion at multidisciplinary team (MDT) meetings and a pro-active stance towards obtaining a formal second opinion are valid strategies to reach a consensus and obtaining consent.

What is the role of multidisciplinary team deliberations in congenital cardiac surgery?

In the NHS, there is no legal provision for shared responsibility. Each patient is treated under the name of an identified consultant, who in the first instance bears responsibility for the patient’s outcome. Any conclusions reached and advice given following an MDT discussion will have been based on individual contributions by the specialists within the group. If the MDT conclusions or advice are later challenged, a record of these contributions needs to be available to assess whether the individual contributions were reasonable. It is foreseeable that an MDT might reach a majority conclusion that a particular procedure or operation is in the best interests of the patient but the consultant surgeon to whom the patient is now referred to disagrees with this proposal. The surgeon should make this known to the MDT, giving reasons. On no account should a surgeon perform an operation which they believe to be counter to the patient’s interests. When an agreement cannot be reached, it is advisable to consider the opinion or intervention of a surgeon colleague. In any case, the disclosure of information prior to seeking consent is the responsibility of the surgeon who is going to perform the procedure. Whilst the sum of the information in relation to benefits, risks and alternatives may reflect advice garnered at an MDT, the ‘consenting’ surgeon carries all the responsibility for the choices they make when selecting what information to disclose.

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25 • •

• •

• •

26 •

•

12 Informed consent in congenital cardiac surgery How should information be disclosed to a pregnant mother?

Anything which is not proscribed by English law is lawful. No laws prevent pregnant women from hang-gliding, bungee jumping, taking drugs, smoking or driving in F1 racing cars, although all of these activities may be highly prejudicial to the mother and her baby. Equally, if a woman with congenital heart disease wishes to run the risk that pregnancy might pose to her own health, she is entitled to do so and a matter only for her to decide upon. In fact, this decision falls outside the remit of consent for medical treatment, since the conception is usually achieved without medical assistance. It has to be very clear that the responsibility of carrying the risk to her own health and that of the unborn child remains with the mother. This is because until the baby is born and has a separate existence from the mother, it has no legal personality and is considered a part of the mother. Therefore, child protection laws do not apply to a foetus. There are examples of women whose rights to refuse caesarean section despite the certain consequent death of their baby have been steadfastly upheld by English courts. Reasonable steps, however, need to be taken to inform the putative mother of the risks that she runs and if she requests information relating to the risk she plans to run, the consulting doctor must provide it. With respect to the health of her putative foetus, if a prospective mother with congenital heart disease seeks information regarding the wisdom of becoming pregnant, any and all risks to the foetus that derive either from her cardiac diagnosis (such as heritability) or her cardiac health must be disclosed, insofar as that may have a bearing on her ability to carry the baby to full term, or to adequately provide circulation to the unborn child.

What is the role of a numeric threshold in choosing what to disclose?

The assessment of whether a risk is ‘material’ cannot be reduced to percentages. The significance of a given risk will reflect not only its magnitude but also other factors. The nature of the risk, the effect which its occurrence would have upon the life of the patient, the importance to the patient of the benefits sought to be achieved by the treatment, the alternative therapies available and the risks involved in those alternatives, all play a part. This assessment therefore depends on the facts of the case and upon the characteristics of the patient. Basing a clinical decision

449

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whether or not to disclose an operative risk solely upon whether or not it crosses a numerical threshold of 1, 0.1 or 0.001 percent is arbitrary and unreasonable.

Recommended reading 1.

2.

3.

4. 5.

6.

450

Bainham A. `ÜáäÇêÉåW=qÜÉ=jçÇÉêå=i~ïK Bristol: Jordan Publishing, 2005.

Wheeler RA. Gillick or Fraser? A plea for consistency over competence in children.

_jg=2006; 332: 807.

Family Law Reform Act 1969 s8.

General Medical Council. Consent: patients and doctors making decisions together. GMC: London, 2008.

Wheeler RA. Numeric threshold for risk. ^åå=oçó=`çää=pìêÖ=båÖä=2012; 94(2): 81-2.

Wheeler RA. `äáåáÅ~ä=i~ï=Ñçê=`äáåáÅ~ä=mê~ÅíáÅÉK London: CRC Press, Taylor & Francis,

2020.

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Chapter 13 Atrial septal defects Narain Moorjani, Nicola Viola

1 •

2 •

What is an atrial septal defect (ASD)?

An atrial septal defect is a congenital lesion that results in communication and therefore shunting of blood between the left and right atria.

How is the atrial septum formed embryologically?

The cavity of the primitive atrium is initially subdivided into right and left chambers by the septum primum, which is a crescentic fold of endocardial tissue that begins to develop at day 28 in utero (Figure 1).

Septum primum Membrane erosions

Ostium primum Endocardial cushions

Figure 1. Development of the septum primum.

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• • •

The septum primum grows downwards to close the primary interatrial foramen by fusing with the endocardial cushions by approximately day 35, leaving an opening below its free margin (ostium primum). By programmed cell death (apoptosis), a second opening (ostium secundum or foramen ovale) develops in the upper part of the septum primum at day 33. This opening persists until birth. At a similar time (day 33), a second endocardial fold (septum secundum), semilunar in shape, develops and descends towards but never reaches the endocardial cushions, thereby forming the fossa ovalis (Figure 2).

Ostium secundum

452

Septum secundum

Septum secundum

Septum primum

Fused endocardial cushions

Foramen interventricularis Endocardial cushions

Figure 2. Development of the septum secundum.

• •

Shortly after birth, the foramen ovale closes following fusion of the septum secundum with the septum primum (Figure 3). Hence, the component parts of the final true atrial septum (Figure 4) include the: a) b)

floor of the fossa ovalis — which is derived from the septum primum; anteroinferior muscular rim of the fossa ovalis.

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13 Atrial septal defects Septum secundum

Sealed ostium secundum

Sealed ostium secundum

Septum secundum Valve of foramen ovale Crux of the heart

Figure 3. Closure of the foramen ovale resulting in separation of the left and right atrial chambers.

Superior rim of the fossa (Waterston’s groove)

True interatrial septum:

Floor of the fossa ovalis Anteroinferior muscular rim of the fossa ovalis

453

Aortic rim of the fossa Membranous septum

Tricuspid valve Atrial component of the atrioventricular septum

Sinus septum

Figure 4. Components of the true interatrial septum (in white) and surrounding structures.

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3 •

How are atrial septal defects classified (Figure 5)? Defects of the interatrial septum: a)

b)

•

454

Defects outside the interatrial septum: a)

b)

• • •

4 • • •

fossa ovalis defects (75%): i) patent foramen ovale (Vieussens valve) — superiorly placed; ii) ostium secundum defect — centrally placed, can be single or multi-fenestrated (Figure 5B); vestibular defect (40 years old.

Figure 6. Electrocardiogram of a patient with an ostium secundum defect, demonstrating an rSR’ pattern in V1.

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12 •

13 Atrial septal defects What are the radiological features of atrial septal defects (Figure 7)? Chest radiography may demonstrate:

a) b)

cardiomegaly (due to right atrial and right ventricular enlargement); prominent pulmonary arteries (dilated hilar vessels) with increased pulmonary vascular markings (Figure 7);

A

B

Figure 7. Chest radiographs demonstrating increased pulmonary

vascular markings, hilar congestion and a distended right atrium in: A) an 18-month-old child with a large ostium secundum defect; and B) a 67year-old patient with a superior sinus venosus defect.

c) d)

•

in patients with ostium primum defects, left atrial enlargement may be observed if significant mitral regurgitation is present; in patients with sinus venosus defects, proximal dilation of the superior vena cava may be seen.

Cardiac magnetic resonance imaging (MRI) may be useful to further delineate associated anomalies and the haemodynamic consequences of volume overload of the right heart and pulmonary circulation (Figure 8).

os=

os= is=

is=

Figure 8. Cardiac MRI in a patient with a sinus venosus defect demonstrating an enlarged right ventricle (RV). LV = left ventricle.

459

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13 • •

A

What are the echocardiographic features of atrial septal defects? Echocardiography can be used to definitively diagnose the type of anatomical defect with 2D and 3D images (Figure 9). Colour-flow Doppler is used to quantify the shunt across the atrial septum (Figure 10).

ps`

B

lëíáìã= ëÉÅìåÇìã= ÇÉÑÉÅí

460

i^

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fs`

C

fs` i^

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Figure 9. Transthoracic echocardiography, with: A) 3D images demonstrating a large ostium secundum defect with a multi-fenestrated fossa membrane; and 2D images demonstrating: B) an ostium primum defect, with alignment of both atrioventricular valves on the same plane, which is typical of a partial atrioventricular septal defect; and C) an inferior sinus venosus defect. SVC = superior vena cava; IVC = inferior vena cava; RA = right atrium; LA = left atrium; LAVV = left atrioventricular valve; RAVV = right atrioventricular valve.

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13 Atrial septal defects

i^=

o^

Figure 10. Transoesophageal echocardiogram demonstrating

a moderate-large left-to-right shunt across the interatrial septum on colour-flow Doppler. RA = right atrium; LA = left atrium.

•

Echocardiography can also demonstrate the haemodynamic consequences of the defect, including: a)

•

b) c) d)

right ventricular chamber size and function (degree of dilatation and dysfunction) (Figure 11); right atrial enlargement; pulmonary artery dilatation; tricuspid regurgitation.

It is also important to identify any associated cardiac abnormalities, including: a) b) c)

cleft mitral and mitral regurgitation (in ostium primum defects); persistent left-sided superior vena cava (in coronary sinus defects); anomalous pulmonary venous drainage (in sinus venosus defects) (Figure 12).

461

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Key Questions in CONGENITAL CARDIAC SURGERY A

B os=

os=

is=

is=

Figure 11. Parasternal: A) long-axis; and B) short-axis transthoracic

echocardiographic images demonstrating right ventricular dilatation, secondary to volume overload in a patient with an ostium secundum defect. RV = right ventricle; LV = left ventricle.

462

orms

ps` i^

o^=

páåìë îÉåçëìë ÇÉÑÉÅí

Figure 12. Doppler echocardiography demonstrating flow across the superior cavo-atrial junction, inflow from an anomalous right upper pulmonary vein (RUPV) into the right atrium and a shunt across a sinus venosus defect. SVC = superior vena cava; RA = right atrium; LA = left atrium.

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14 • •

13 Atrial septal defects Describe the bubble test (Figure 13)

Sterile saline is agitated by passing it between two syringes to produce tiny bubbles. Following intravenous injection of the saline, echocardiographic images of the left and right atrium are monitored.

A _ìÄÄäÉë=áå=o^Los

is=

i^

B

_ìÄÄäÉë=áå=i^

C

_ìÄÄäÉë=áå=is

Figure 13. Bubble test demonstrated

on serial transthoracic apical fourchamber images: A) the right atrium (RA) and ventricle (RV) are filled with bubbles; B) during a Valsalva manoeuvre, the bubbles fill the left atrium (LA) first; and then C) the left ventricle (LV).

463

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• •

15 • • • 464

If the atrial septum is intact, the bubbles should remain on the right side. Bubbles within the left atrium indicate a communication between the atria, suggestive of an atrial septal defect.

What are cardiac catheterisation findings of atrial septal defects? Routine cardiac catheterisation is unnecessary in children with a previously diagnosed uncomplicated atrial septal defect. For patients with pulmonary hypertension, associated congenital abnormalities or age over 40 with suspected coronary artery disease, cardiac catheterisation is an important component of the surgical work-up. Oxygen saturation measurements in the systemic and pulmonary circulations will reveal a step-up in right ventricular and pulmonary artery oxygen saturations (Table 1).

Table 1. Cardiac catheterisation data demonstrating a step-up in right atrial

(RA) oxygen saturations in an adult patient with an ostium secundum defect. SVC = superior vena cava; MPA = main pulmonary artery; LPA = left pulmonary artery; FA = femoral artery; RUPV = right upper pulmonary vein; BCV = brachiocephalic vein; IVC = inferior vena cava; EDP = end-diastolic pressure.

mêÉëëìêÉ ~åÇ=çñóÖÉå=ë~íìê~íáçå=Ç~í~

páíÉ

p~í B

SVC RA MPA LPA FA RUPV BCV High SVC Low SVC Mid RA Low RA High RA Low IVC High IVC

65 96 79.3 78.8 93 97.4 63.9 64.3 61.7 96 76.3 67.7 68.8 68.2

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75

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13 Atrial septal defects

• •

16 •

High oxygen saturations in the superior vena cava may indicate the presence of a sinus venosus defect. Cardiac catheterisation also allows the size of the shunt to be quantified by calculating the shunt fraction.

How do you calculate the shunt fraction (Qp:Qs) (Figure 14)? Using the Fick principle: Flow =

O2 consumption arteriovenous O2 concentration difference

Flow =

O2 consumption (arteriovenous O2 sats difference x Hb x 1.34 x 10)

Pulmonary flow =

O2 consumption [(PV sats - PA sats) x Hb x 1.34 x 10]

Systemic flow =

O2 consumption [(Ao sats - RA sats) x Hb x 1.34 x 10]

As O2 consumption and Hb are the same in both equations Pulmonary flow: systemic flow ratio (shunt ratio) Qp:Qs = (Ao sats - RA sats) (PV sats - PA sats) RA sats = (3 x SVC sats) + (1 x IVC sats) 4 PV = pulmonary vein; PA = pulmonary artery; Ao = aorta; RA = right atrium; SVC = superior vena cava; IVC = inferior vena cava; Hb = haemoglobin; sats = oxygen saturations.

465

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VVB

SQB

UOB

VVB

VVB VVB

466

SUB

UOB

Figure 14. Shunt calculation based on the Fick principle. RA sats = ([3 x 64] + [1 x 68]) / 4 = 65%. Measured PA saturations = 82%. Measured PV saturations = 99%. Assuming aortic and PV saturation are equal, the Qp:Qs shunt in this patient will be: (99 - 65) / (99 - 82) = 34 / 17 = 2:1.

17 •

What are the therapeutic options for a patient with an atrial septal defect? Conservative management:

a) b) c)

•

infants with an ostium secundum defect 12 WU).

Medical therapy — to optimise patients with atrial arrhythmias and right ventricular volume overload prior to intervention.

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13 Atrial septal defects

• •

18 • • • • •

19 • •

20 •

• • • • •

Percutaneous closure. Surgery.

What are the indications for therapeutic closure of an atrial septal defect?

A Qp:Qs ratio of >2. Atrial arrhythmia. Reversible pulmonary hypertension. Right ventricular dysfunction. Patent foramen ovale in patients with a demonstrated right-to-left shunt (by saturations or bubble study) and recurrent paradoxical cerebral emboli.

What are the contraindications for therapeutic closure of an atrial septal defect?

Asymptomatic patient with a clinically insignificant atrial septal defect (Qp:Qs 60mmHg, PVR >12 WU).

What are the principles of device closure for an atrial septal defect (Figure 15)? Device closure is only suitable in patients with: a) b) c)

ostium secundum defects (within the fossa ovalis); 5mm rim from the defect to the valves and major veins; defect 2:1; ventricular dilatation (even if the left-to-right shunt is 8 units/m2, who show no response to pulmonary arterial vasodilatation, are not candidates for surgical closure. (These patients often have a history of some previous clinical improvement due to the decreased left-to-right shunt in response to the increased pulmonary vascular resistance.) Asymptomatic patients with a small VSD and Qp:Qs 1.6m/s may suggest a

549

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ms= ÅçåÑäìÉåÅÉ

G

ps`

i^

o^

Figure 8. Echocardiographic subcostal view demonstrating a 550

significant interatrial communication (green asterisk) with an obligatory right-to-left shunt across the interatrial septum in a patient with total anomalous pulmonary venous connection. SVC = superior vena cava; RA = right atrium; LA = left atrium; PV = pulmonary venous.

fs ps`

^ç orms oims

m^ ms= ÅçåÑäìÉåÅÉ

m^ irms

^ç

fs ss

ps`

iims

Figure 9. Echocardiographic parasternal short-axis views demonstrating a

supracardiac total anomalous pulmonary venous connection, with all four pulmonary veins draining into a venous confluence and then via the vertical vein (VV) and innominate vein (IV) into the superior vena cava (SVC). RUPV = right upper pulmonary vein; RLPV = right lower pulmonary vein; LUPV = left upper pulmonary vein; LLPV = left lower pulmonary vein; Ao = aorta; PA = pulmonary artery; PV = pulmonary venous.

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16 Anomalous pulmonary venous connections A

B

^ç ps`

m^

ss

G

ms= ÅçåÑäìÉåÅÉ

C

551

Figure 10. Echocardiographic images in a patient with obstructed supracardiac total anomalous pulmonary venous connection: A) parasternal short-axis view with; B) colour flow Doppler image demonstrating turbulent flow at the anatomical narrowing (green asterisk) between the left pulmonary artery and ascending vertical vein (VV); C) continuous wave Doppler image demonstrating the peak flow velocity of the pulmonary venous flow is approximately 2m/sec and the Doppler waveform does not return to baseline. SVC = superior vena cava; Ao = aorta; PA = pulmonary artery; PV = pulmonary venous.

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Key Questions in CONGENITAL CARDIAC SURGERY A

B om^

ms= ÅçåÑäìÉåÅÉ

ps`

G

i^

o^

`p

Figure 11. Echocardiographic subcostal view of an intracardiac total 552

anomalous pulmonary venous connection, demonstrating: A) a typical ‘whale’s tail’ appearance, dilated coronary sinus (CS) and a significant interatrial communication (green asterisk) on 2D imaging; and B) a rightto-left shunt on the corresponding colour flow Doppler image. RA = right atrium; LA = left atrium; SVC = superior vena cava; RPA = right pulmonary artery; PV = pulmonary venous.

i^ o^

is

os

Figure 12. Echocardiographic apical fourchamber view demonstrating a dilated right atrium (RA) and right ventricle (RV) in a patient with total anomalous pulmonary venous connection. LA = left atrium; LV = left ventricle.

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16 Anomalous pulmonary venous connections functionally significant obstruction (Figure 13). It can also demonstrate shunts across the foramen ovale or an atrial septal defect (Figure 14).

Hepatic portal system

iáîÉê o^

ss

Figure 13. Echocardiographic subcostal view

demonstrating turbulent flow in the descending vertical vein (VV), which drains into the hepatic portal system suggesting the presence of an obstructed infradiaphragmatic total anomalous pulmonary venous connection. RA = right atrium.

SVC

RUPV

SV ASD LA

RA

Figure 14. Colour flow Doppler echocardiography

demonstrating flow across the superior cavo-atrial junction, inflow from an anomalous right upper pulmonary vein (RUPV) into the right atrium and a shunt across a sinus venosus atrial septal defect (SV ASD). SVC = superior vena cava; RA = right atrium; LA = left atrium.

553

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Key Questions in CONGENITAL CARDIAC SURGERY

•

14 •

• 554

• •

15 •

Transoesophageal echocardiography may provide a more accurate assessment of pulmonary venous anomalies, particularly in obese adult patients where transthoracic images may not be adequate.

What are the cardiac catheterisation features of anomalous pulmonary venous connection?

Routine cardiac catheterisation is not necessary in PAPVC. If performed, features may include normal right heart pressures in paediatric patients and higher oxygen saturations in the right atrium compared to the superior vena cava, which suggest anomalous pulmonary venous drainage to the right atrium in the absence of an atrial septal defect. Selective right and left pulmonary artery angiography also delineates the anatomy of the anomalous pulmonary venous connections. In cor triatriatum, cardiac catheterisation may show pulmonary hypertension without a left-to-right shunt, high pulmonary artery wedge pressures and normal left atrial pressures. Pulmonary artery angiography reveals an opacified pulmonary venous chamber draining into the left atrium. In pulmonary vein stenosis, there may be no antegrade flow of contrast dye through the veins and there may even be retrograde flow into arteries that drain into less stenotic veins. Nonoccluded veins may be visualised directly via transseptal catheterisation.

Describe the pulmonary vein stenosis score (Table 1)

Each vein is evaluated on 2D echocardiographic images and colour Doppler assessment of the pressure gradient (mmHg) across the veno-atrial junction. This is correlated with macroscopic operative findings, including measurement of the pulmonary vein diameter (mm).

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16 Anomalous pulmonary venous connections Table 1. Pulmonary vein stenosis echocardiographic and operative findings.

score

correlated

pÅçêÉ bÅÜç=Oa= ëíÉåçëáë

jÉ~å=açééäÉê Öê~ÇáÉåí=EããeÖF

0

No stenosis

4 Woods units; left ventricular end-diastolic pressure or left atrial pressure >12mmHg; significant pulmonary artery hypoplasia.

When should atrial septal defect subclosure or nonclosure be considered? Residual interatrial communication is an intermediate option to bypass the RV in situations with poor RV function, although this does not provide as significant RV unloading as with BCPS. It should be used: a) b) c)

routinely in the neonate/infant; selectively in the child/young adult; rarely in the adult, especially when there is an increased risk of paradoxical emboli.

When should tricuspid valve replacement be considered in the surgical management of Ebstein’s anomaly?

Older patients (>60 years of age). Pulmonary hypertension. Significant LV dysfunction. In these situations, a bioprosthesis is preferred to a mechanical prosthesis due to the good durability of a biological valve in the TV position and as it is associated with less thromboembolic complications. The valve suture line is placed on the atrial side of the membranous septum and AV node (generally marked with the vein of D) to avoid conduction injuries. The sutures should be tied with heart beating to readily identify injury to the conduction system (Figure 23).

chapter 17_KQCCS.qxd 01/02/2022 14:59 Page 591

17 Ebstein’s anomaly Junction of smooth and trabeculated portions of the atrium

A

Membranous septum CS Vein of D

B

Figure 23 Suture line placement for a tricuspid valve replacement in Ebstein’s anomaly: A) the coronary sinus (CS) can be left to drain normally into the right atrium if there is sufficient distance between the coronary sinus and AV node; B) if the coronary sinus and conduction tissue are close, the suture line can be deviated into the right atrium to avoid iatrogenic injury, with the coronary sinus then draining into the right ventricle. Copyright © Mayo Foundation for Medical Education and Research.

591

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Key Questions in CONGENITAL CARDIAC SURGERY

31 •

What are the special considerations for the perioperative care of patients with Ebstein’s anomaly? RV preload and RV afterload must be optimised by: a)

b) c)

592

32 • • • •

33 • •

d)

adjusting intravascular volume — using tachycardia (HR 100120 with atrial pacing if needed) and relative hypovolaemia (RA pressures 10mm) in V1 and differentiates it from pulmonary atresia with intact ventricular septum where the right ventricle is diminutive (Figure 5).

Figure 5. Electrocardiogram of a patient with pulmonary atresia with ventricular septal defect demonstrating right axis deviation and right ventricular hypertrophy.

chapter 22_KQCCS.qxd 25/01/2022 18:29 Page 711

22 Pulmonary atresia with ventricular septal defect

•

12 •

Left atrial enlargement and biventricular hypertrophy — which are caused by an increase in pulmonary venous return.

What are the radiological features of pulmonary atresia with ventricular septal defect? Chest radiograph (CXR) may demonstrate: a)

boot-shaped heart, due to the small or absent left pulmonary artery creating a concavity of the left heart border below the aortic arch, and right ventricular hypertrophy leading to uplifting of the cardiac apex from the dome of the diaphragm (Figure 6);

711

Figure 6. Chest radiograph of a neonate with

pulmonary atresia with ventricular septal defect who required intubation, demonstrating a boot-shaped heart with concavity of the left heart border and uplifting of the cardiac apex.

b) c)

right aortic arch (25-50%); pulmonary vascular markings may be decreased or increased, dependent on the pulmonary blood flow, and have a typical reticular pattern in the presence of MAPCAs.

chapter 22_KQCCS.qxd 25/01/2022 18:29 Page 712

Key Questions in CONGENITAL CARDIAC SURGERY

•

Computed tomography (CT) scanning and magnetic resonance imaging (MRI) are emerging as alternatives to cardiac catheterisation and may provide: a)

b) c)

A

anatomical definition of the right ventricular outflow tract, main pulmonary artery, branch pulmonary arteries and stenoses, ductus arteriosus and number, location and course of the MAPCAs; functional assessment (MRI) of the percentage of blood flow to each lung; 3D reconstruction (CT) of the MAPCAs, which may be useful for operative planning (Figure 7).

B

712

Figure 7. Radiological imaging demonstrating a large U-shaped major

aortopulmonary collateral artery (MAPCA) arising from the mid-descending thoracic aorta and passing over the left main bronchus, entering the lung at the hilum and supplying most of the left upper lobe on: A) computed tomography 3D reconstruction (posterior view); and B) cardiac catheterisation.

13 • •

What are the echocardiographic features pulmonary atresia with ventricular septal defect?

of

Echocardiography is the key investigation for determining intracardiac anatomy but has a limited ability to define the nature of the pulmonary circulation. Echocardiography can define the pulmonary atresia with absent flow between the right ventricular outflow tract and pulmonary trunk (Figure 8), and its association with a variable degree of hypoplasia of

chapter 22_KQCCS.qxd 25/01/2022 18:29 Page 713

22 Pulmonary atresia with ventricular septal defect A

B

os

^ç

^ç

is

oslq m^ a^

i^

C m^ oslq

i^ is

Figure 8. Transthoracic echocardiographic views in a patient with 713 pulmonary atresia with ventricular septal defect: A) parasternal long-axis view of a malalignment VSD and large overriding aorta; B) parasternal short-axis view of a shelf-like obstruction at the level of the pulmonary valve with a lack of flow from the right ventricular outflow tract to the pulmonary trunk but turbulent flow originating from the ductus arteriosus (red-yellow) into the branch pulmonary arteries (blue); C) subcostal view of the shelf-like obstruction with turbulent ductal flow into the pulmonary trunk (red-yellow). Ao = aorta; DA = ductus arteriosus; LA = left atrium; LV = left ventricle; PA = pulmonary artery; RV = right ventricle; RVOT = right ventricular outflow tract.

•

the subpulmonary infundibulum and main pulmonary artery, ranging from an intact membrane to complete absence of the intrapericardial pulmonary arteries. A comprehensive examination will adhere to the standard assessment of the heart and intrapericardial vessels as per segmental anatomical sequence. In particular, echocardiography will provide information on the: a)

type i) ii) iii)

of ventricular septal defect: large and unrestrictive VSD (often); malalignment VSD; perimembranous VSD with outlet extension (most often);

chapter 22_KQCCS.qxd 25/01/2022 18:29 Page 714

Key Questions in CONGENITAL CARDIAC SURGERY

b) c) d) e) f)

g)

h) 714

14 •

What are the cardiac catheterisation features of pulmonary atresia with ventricular septal defect? Cardiac catheterisation remains a key investigation for delineating the pulmonary circulation (Figure 9). It provides information on the intrapericardial pulmonary arteries, including the:

a) b)

•

anterior deviation of the infundibular septum with a varying degree of aortic override in the tetralogy type; degree of right ventricular hypertrophy and cavity size; type of interatrial communication and direction of shunt: i) secundum atrial septal defect; ii) patent foramen ovale (50%); presence of right aortic arch and mirror branching; anatomy of the coronary arteries, which are usually normal but in some cases, there is an anomalous origin of the left coronary artery from the right coronary artery, passing across the right ventricular outflow tract; anatomy of the intrapericardial pulmonary arteries: i) presence or absence of intrapericardial branching, continuous or contiguous to the ventricular mass; ii) confluent or discontinuous branches; iii) size and possible stenoses of the branches; direction of the colour Doppler flow in the central pulmonary arteries when detectable: i) antegrade flow coming from the ductus arteriosus (which joins the pulmonary artery in the mediastinum); ii) retrograde flow coming from MAPCAs (which feed into the pulmonary tree at the hilum of the lung).

c) d) e)

presence of the main pulmonary artery; confluence of the left and right pulmonary arteries — ‘seagull’ appearance with diminutive but confluent pulmonary arteries; size of vessels and side disparity; number of lung segments supplied; presence of distal stenoses.

A retrograde pulmonary vein wedge injection may be required in the presence of hypoplastic intrapericardial pulmonary arteries to demonstrate intrapericardial arborisation within the lung parenchyma.

chapter 22_KQCCS.qxd 25/01/2022 18:29 Page 715

22 Pulmonary atresia with ventricular septal defect A

B

Figure 9. Cardiac catheterisation demonstrating different anatomical

presentations of intrapericardial pulmonary arteries: A) diminutive but confluent central pulmonary arteries (white arrow); B) large confluent central pulmonary arteries.

•

Cardiac catheterisation can also provide information regarding any MAPCAs (Figure 10): a) b) c) d) e)

A

number; size of vessels; origin from systemic circulation; number of lung segments supplied; presence of proximal stenoses;

B

Figure 10. Cardiac catheterisation demonstrating a large residual MAPCA supplying the right lower lobe on an: A) anteroposterior projection; and B) lateral projection.

715

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Key Questions in CONGENITAL CARDIAC SURGERY

f)

•

15 • • 716

•

16 • • •

elevated distal pressure (mean >20-25mmHg) suggesting significant pulmonary vascular occlusive disease within the affected lung segments.

In addition, it can also delineate the coronary anatomy and provide information regarding the pulmonary vascular resistance and transpulmonary gradient. RV pressure is invariably systemic due to the presence of an unrestrictive VSD.

Describe the medical management for a patient with pulmonary atresia with ventricular septal defect

Neonates with a duct-dependent pulmonary circulation require prostaglandin E1 to maintain patency of the ductus arteriosus until surgical intervention. Those presenting acutely with shock following closure of the ductus arteriosus also need immediate resuscitation and may require ventilation. Medical treatment with a diuretic and an ACE inhibitor may be required in patients presenting in congestive heart failure due to excessive pulmonary blood flow.

What are the principles of surgical repair of pulmonary atresia with ventricular septal defect?

The primary aim of surgery is to improve on the predicted natural history of the disease for each patient. Heterogeneity of the condition precludes a standardised approach to all patients, as this is determined by the individual morphology, pathophysiology and presentation. The ideal outcome is the creation of a septated biventricular circulation with low pulmonary vascular resistance and low right ventricular pressures. This can be achieved by intervening on all the repairable lesions and malformations of the conditions by: a)

increasing pulmonary blood flow, increasing oxygen saturation and encouraging growth of the intrapericardial pulmonary arteries with a: i) systemic-pulmonary shunt; ii) right ventricular-pulmonary artery conduit; iii) aortopulmonary window;

chapter 22_KQCCS.qxd 25/01/2022 18:29 Page 717

22 Pulmonary atresia with ventricular septal defect b)

A

early or interval unifocalisation of the MAPCAs to connect as many lung segments as possible to the central pulmonary arteries, thus maximising the size and run-off of the pulmonary vascular bed (Figure 11); B

Figure 11. Cardiac catheterisation demonstrating the variable nature of

single and dual supply to different lung segments: A) small but confluent intrapericardial pulmonary arteries supplying most of the right lung (white arrow) and the left lower lobe (green arrow); B) MAPCAs supplying the right lower lobe (white arrow) and the left upper and lower lobes (green arrow).

c) d)

• •

securing a long-term source of blood from the right ventricle to the pulmonary tree using, in most cases, a valved conduit, which is preferably oversized; closing the VSD to prevent shunting, avoid volume overload and prevent or reduce pulmonary hypertension. The VSD should not be closed if a low pulmonary vascular resistance cannot be guaranteed, to avoid acute and chronic right ventricular failure.

Surgical strategies should aim to minimise the need for surgical or catheter-based reinterventions. The approach for achieving these goals remains controversial with different surgical centres pursuing radically different strategies. Long-term outcome data are awaited to determine the optimal approach.

717

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Key Questions in CONGENITAL CARDIAC SURGERY

17 •

What are the surgical therapeutic options for a patient with pulmonary atresia with ventricular septal defect? Surgical approaches in the absence of MAPCAs (Type A) are normally performed via sternotomy: a)

b)

718

•

single-stage complete repair — which will typically involve a tetralogy-type repair with minor interventions or no interventions on the pulmonary arteries and implantation of a right ventricular-pulmonary artery valved conduit. In some cases, a REV (réparation à l’etage ventriculaire) type repair (patch across the RVOT) can be used. In addition, the VSD is closed; staged repair — which initially involves a systemic-pulmonary artery shunt to increase intrapericardial pulmonary artery blood flow and encourage growth. Subsequently, the shunt is taken down, a right ventricular-pulmonary artery valved conduit is implanted and the VSD closed.

Surgical approaches in the presence of MAPCAs (Type B/C) are carried out using a combination of a thoracotomy and sternotomy, including: a)

b)

single-stage complete repair — which will involve repair of all the lesions in one session, including: i) unifocalisation of MAPCAs; ii) central pulmonary artery augmentation or reconstruction; iii) implantation of a right ventricular-pulmonary artery valved conduit; iv) closure of the VSD; although some authors advocate the measurement of intra-operative pulmonary vascular resistance to determine whether the VSD should be closed; staged repair — which can be achieved using several different strategies, such as: i) initially, surgical shunt to increase pulmonary artery blood flow and encourage growth of the intrapericardial or reconstructed central pulmonary arteries, or unifocalisation of MAPCAs (ligation in some cases); ii) later, implantation of a right ventricular-pulmonary artery valved conduit, with concurrent or subsequent VSD closure.

chapter 22_KQCCS.qxd 25/01/2022 18:29 Page 719

18 • • • • •

19 •

22 Pulmonary atresia with ventricular septal defect What are the key anatomical features to be considered for surgical decision-making in pulmonary atresia with ventricular septal defect?

Suitability of complete repair, including closure of the VSD, is dependent upon adequacy of the pulmonary vascular tree, pulmonary vascular resistance and postoperative RV pressure. Size of the intrapericardial pulmonary arteries and the extent of peripheral arborisation. Number, origin, course and segments supplied by each MAPCA, may determine the approach, such as sternotomy versus a staged thoracotomy and sternotomy. Location of the stenosis within the intrapericardial pulmonary arteries and collaterals. Post-stenotic pressure in the collaterals, predictive of subsequent pulmonary vascular resistance.

How is the adequacy of the intrapericardial pulmonary arteries assessed to predict the adequacy of postoperative pulmonary vascular resistance? Although there are several different indices/ratios that can be used, they are all limited as they do not take account of the distal pulmonary vascular bed, which is a key determinant of pulmonary vascular resistance. These ratios and indices include: a)

b)

c)

McGoon’s ratio = (Proximal RPA diameter + Proximal LPA diameter) Descending aortic diameter above the diaphragm A ratio >1.2 is adequate for complete repair, whereas 150mm2/m2 is adequate for complete repair without a shunt. The index, however, is not useful in patients with MAPCAs, as it does not account for unifocalisation; Total NeoPulmonary Artery Index (TNPAI) = Nakata index + Cross-sectional area of significant MAPCAs Body surface area An index >200mm2/m2 correlates with low postoperative RV pressure.

719

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Key Questions in CONGENITAL CARDIAC SURGERY

•

•

20 •

720

Intra-operative functional assessment after completion of unifocalisation and a distal RV-PA conduit can be obtained using a perfusion cannula and pulmonary artery catheter inserted via the conduit and increased up to full flow. If the pulmonary artery pressure remains 30mm)

Urgent

IIa

B

Aortic or mitral NVE or PVE with isolated large vegetations (>15mm) and no other indication for surgery d

Urgent

IIb

C

Aortic or mitral NVE or PVE with severe regurgitation or Urgent obstruction causing symptoms of HF or echocardiographic signs of poor haemodynamic tolerance

1168

`ä~ëëÄ iÉîÉäÅ

OK=råÅçåíêçääÉÇ=áåÑÉÅíáçå Locally uncontrolled infection (abscess, false aneurysm, fistula, enlarging vegetation)

PK=mêÉîÉåíáçå=çÑ=ÉãÄçäáëã Aortic or mitral NVE or PVE with persistent vegetations >10mm after one or more embolic episode despite appropriate antibiotic therapy

a Emergency surgery: surgery performed within 24 h; urgent surgery: within a few days; elective surgery: after at least 1-2 weeks of antibiotic therapy. b Class of recommendation. c Level of evidence. d Surgery may be preferred if a procedure preserving the native valve is feasible.

chapter 41_KQCCS.qxd 01/02/2022 21:17 Page 1169

41 Infective endocarditis

c)

A

abscesses have been excluded. Some evidence now exists that blood cultures remaining positive after 48-72 hours of antibiotics is associated with poor prognosis and surgery could be considered at 3 days; ii) paravalvular extension (including abscess formation, pseudoaneurysm formation or fistulae) is particularly common with aortic valve IE or prosthetic valve IE, as well as in cases with pí~éÜK= ~ìêÉìë as the infecting organism. Paravalvular extension is associated with a high mortality; prevention of systemic or pulmonary embolism. Left-sided vegetations commonly embolise to the brain or spleen, whereas right-sided vegetations (including those from pacemaker leads) commonly embolise to the lungs. Embolic events typically occur in the first few days after starting antibiotic therapy and are relatively rare after 2 weeks of therapy. There is a higher risk of embolisation in the presence of: i) large vegetation (>10mm for left-sided IE, >20mm for right-sided IE) (Figure 1); B

Figure 1. A) A large staphylococcal vegetation (black arrow) seen in the left ventricular outflow tract in a 16-year-old boy with no known cardiac anomaly. B) An operative specimen following surgical resection of the vegetation.

1169

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Key Questions in CONGENITAL CARDIAC SURGERY

15 • • •

ii) iii) iv) v)

What are the principles of surgery for infective endocarditis?

The decision to operate is individualised, with factors such as size and mobility of the vegetation, previous embolism, type of microorganism and duration of antibiotic therapy taken into account. A multidisciplinary team including a cardiothoracic surgeon, a cardiologist and a microbiologist should be involved in the decisionmaking process. The aims of surgery include: a)

1170

b)

•

mobile vegetation seen on echocardiography; previous embolic event; underlying atrial fibrillation; pí~éÜK=~ìêÉìë as the infecting organism.

total removal of the vegetations and all infected material, in order to reduce the risk of recurrent infections and failure of the repair; reconstruction of the cardiac structures.

If there is an anatomical cardiac defect, such as a ventricular septal defect or patent ductus arteriosus, it should be addressed when the infection is controlled or at the time of vegetectomy.

A

B

APM

CS

Figure 2. Operative images demonstrating: A) a large vegetation (black arrow) deep within the right ventricular cavity below a small untreated ventricular septal defect; and B) the excised vegetation. APM = anterior papillary muscle; CS = coronary sinus.

chapter 41_KQCCS.qxd 01/02/2022 21:17 Page 1171

41 Infective endocarditis

•

Repair of any involved valves should be performed when possible, especially in very young patients, to avoid implanting a small prosthetic valve. Surgical repair is often established on the basis of the intra-operative findings and the conditions of the heart once removal of the infected tissue is complete. In some cases, removal of the vegetation is sufficient (Figure 2). Both autologous tissues and heterologous tissues can be used for repair of valves and blood vessels (Figure 3).

• • • A

B

AL

*

C

1171 SL

D

Figure 3. Operative images demonstrating: A) a large vegetation seen on the anterior leaflet (AL) of the tricuspid valve (black arrow) and seeding vegetations on the septal leaflet (SL); B) complete excision of the vegetation and involved leaflet tissue, including the commissural subvalvular apparatus (white asterisk); C) closure of the ventricular septal defect, reconstruction of the valve with autologous pericardium and resuspension of the commissure with artificial chordae; and D) a competent valve on saline static testing.

chapter 41_KQCCS.qxd 01/02/2022 21:17 Page 1172

Key Questions in CONGENITAL CARDIAC SURGERY

• •

When valve replacement is unavoidable, both tissue and mechanical prostheses can be used, without a substantial difference in the rate of recurrent infection. In cases of prosthetic valve endocarditis, the valve is removed and the annulus cleared of infection prior to the reimplantation of a new prosthesis (Figure 4).

*

1172

Figure 4. Operative image demonstrating prosthetic mitral valve infective endocarditis, with a large vegetation seen on the valve leaflets (black asterisk) as well as along the sewing ring (black arrow). Removal of the valve revealed an abscess beneath the annulus.

16 • •

What are the outcomes of surgery for infective endocarditis?

Although improvements in diagnosis, advances in antibiotic therapy and aggressive treatment of IE have improved survival, mortality remains substantial (10-25%). Peri-operative mortality of patients undergoing IE surgery depends on comorbidities, degree of left ventricular impairment, infective agent, extent of destruction of cardiac structures and anatomical defects.

chapter 41_KQCCS.qxd 01/02/2022 21:17 Page 1173

41 Infective endocarditis

• • • • •

17 • •

No pre-operative risk score currently in use has been validated for the assessment of the operative risk in patients with IE. Operative mortality is 5-15% for patients with native valve IE. If surgery is performed early in the disease process (first week of antibiotic therapy), in-hospital mortality is 15%. The in-hospital mortality in patients with prosthetic valve IE is 20-40%. The cause of death may be intractable sepsis or multi-organ failure and is often multifactorial. Long-term survival is 60-90% at 10 years for native heart endocarditis and slightly less for prosthetic valve cases at 50-70%. The risk of recurrence (relapse or reinfection) is 2-6% amongst survivors.

What are the principles of prophylaxis for infective endocarditis?

The American Heart Association and the European Society of Cardiology both recommend antibiotic prophylaxis for patients with the highest risk of developing infective endocarditis undergoing highrisk procedures. High-risk patients include those with: a) b) c)

• •

prosthetic valve or prosthetic material used for cardiac valve repair, including transcatheter deployed valves; previous episode of infective endocarditis; congenital heart disease, including: i) any type of cyanotic lesion; ii) any congenital lesion repaired with prosthetic material, placed surgically or percutaneously, up to 6 months after the procedure (until endothelialisation occurs) or lifelong if a residual shunt or valve regurgitation remains.

High-risk procedures include dental procedures that involve manipulation of gingival tissue, periapical region of teeth or perforation of the oral mucosa, including scaling and root canal work. Antibiotic prophylaxis, however, is no longer recommended for: a) b) c) d)

procedures involving incision of the respiratory mucosa; gastrointestinal or urogenital procedures; transoesophageal echocardiography; skin and soft tissue procedures, including tattooing and piercing.

1173

chapter 41_KQCCS.qxd 01/02/2022 21:17 Page 1174

Key Questions in CONGENITAL CARDIAC SURGERY

• • •

18 1174

• •

Antibiotic therapy is advised when invasive procedures are performed in the context of active infection. Education of patients regarding the prevention and recognition of IE is the most effective prophylaxis, either after the first episode in patients with structurally normal hearts and as primary prevention in patients with congenital heart disease, prosthetic valves or intravascular devices. Patients should be advised regarding the importance of good dental hygiene, regular dental check-ups, avoidance of tattoos and body piercings, as well as recognition of the signs and symptoms of IE, and avoidance of self-medication with antibiotics.

Describe the antibiotic prophylaxis regimes used for patients with prosthetic cardiac valves used prior to a dental procedure

The main target of oral antibiotic prophylaxis in high-risk patients before dental procedures is oral píêÉéíçÅçÅÅìë species, with suggested antibiotic regimes described in Table 3. Instead of ampicillin, alternative cephalosporins can be used, including: a) b)

cephalexin — 2g IV (adults) or 50mg/kg IV (children); cefazolin or ceftriaxone — 1g IV (adults) or 50mg/kg IV (children).

Table 3. Oral antibiotic prophylaxis in high-risk patients before dental procedures.

mÉåáÅáääáå=~ääÉêÖó

^åíáÄáçíáÅ

páåÖäÉ=ÇçëÉ=PMJSM=ãáåìíÉë=ÄÉÑçêÉ éêçÅÉÇìêÉ ^Çìäíë `ÜáäÇêÉå

NO allergy to penicillin Amoxicillin or 2g orally or IV or ampicillin ampicillin Allergy to penicillin or ampicillin

Clindamycin

600mg orally or IV

50mg/kg orally or IV 20mg/kg orally or IV

chapter 41_KQCCS.qxd 01/02/2022 21:17 Page 1175

41 Infective endocarditis Recommended reading 1.

Wilson W, Taubert KA, Gewitz M, Lockhart PB, Baddour LM, Levison M, Bolger A, Cabell CH, Takahashi M, Baltimore RS, Newburger JW, Strom BL, Tani LY, Gerber

M, Bonow RO, Pallasch T, Shulman ST, Rowley AH, Burns JC, Ferrieri P, Gardner T, Goff D, Durack DT; American Heart Association Rheumatic Fever, Endocarditis, and Kawasaki

Disease

Committee;

American

Heart

Association

Council

on

Cardiovascular Disease in the Young; American Heart Association Council on Clinical

Cardiology; American Heart Association Council on Cardiovascular Surgery and Anesthesia; Quality of Care and Outcomes Research Interdisciplinary Working

Group. Prevention of infective endocarditis: guidelines from the American Heart Association: a guideline from the American Heart Association Rheumatic Fever, Endocarditis, and Kawasaki Disease Committee, Council on Cardiovascular Disease

in the Young, and the Council on Clinical Cardiology, Council on Cardiovascular Surgery and Anesthesia, and the Quality of Care and Outcomes Research

2.

Interdisciplinary Working Group. `áêÅìä~íáçå 2007; 116(15): 1736-54.

Habib G, Lancellotti P, Antunes MJ, Bongiorni MG, Casalta JP, Del Zotti F, Dulgheru

R, El Khoury G, Erba PA, Iung B, Miro JM, Mulder BJ, Plonska-Gosciniak E, Price S,

Roos-Hesselink J, Snygg-Martin U, Thuny F, Tornos Mas P, Vilacosta I, Zamorano JL;

ESC Scientific Document Group. 2015 ESC Guidelines for the management of

infective endocarditis: The Task Force for the Management of Infective Endocarditis of the European Society of Cardiology (ESC). Endorsed by: European Association for Cardio-Thoracic Surgery (EACTS), the European Association of Nuclear Medicine

3.

(EANM). bìê=eÉ~êí=g 2015; 36(44): 3075-128.

Nishimura RA, Carabello BA, Faxon DP, Freed MD, Lytle BW, O'Gara PT, O'Rourke

RA, Shah PM, Bonow RO, Carabello BA, Chatterjee K, de Leon AC Jr, Faxon DP, Freed MD, Gaasch WH, Lytle BW, Nishimura RA, O'Gara PT, O'Rourke RA, Otto

CM, Shah PM, Shanewise JS, Smith SC Jr, Jacobs AK, Buller CE, Creager MA,

Ettinger SM, Krumholz HM, Kushner FG, Lytle BW, Nishimura RA, Page RL,

Tarkington LG, Yancy CW Jr; American College of Cardiology/American Heart

Association Task Force. ACC/AHA 2008 guideline update on valvar heart disease:

focused update on infective endocarditis: a report of the American College of

Cardiology/American Heart Association Task Force on Practice Guidelines: endorsed

by the Society of Cardiovascular Anesthesiologists, Society for Cardiovascular

Angiography and Interventions, and Society of Thoracic Surgeons. `áêÅìä~íáçå 2008; 4. 5.

118(8): 887-96.

Rushani D, Kaufman JS, Ionescu-Ittu R, Mackie AS, Pilote L, Therrien J, Marelli AJ.

Infective endocarditis in children with congenital heart disease: cumulative incidence

and predictors. `áêÅìä~íáçå 2013; 128(13): 1412-9.

Chu VH, Park LP, Athan E, Delahaye F, Freiberger T, Lamas C, Miro JM, Mudrick DW,

Strahilevitz J, Tribouilloy C, Durante-Mangoni E, Pericas JM, Fernández-Hidalgo N,

Nacinovich F, Rizk H, Krajinovic V, Giannitsioti E, Hurley JP, Hannan MM, Wang A;

International Collaboration on Endocarditis (ICE) Investigators*. Association between

1175

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Key Questions in CONGENITAL CARDIAC SURGERY surgical indications, operative risk, and clinical outcome in infective endocarditis: a prospective study from the International Collaboration on Endocarditis. `áêÅìä~íáçå

2015; 131(2): 131-40.

1176

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Index ablation therapies for arrhythmia 1112, 1115–16, 1117–18, 1119, 1120, 1121–2 intra-operative 1122–30 prophylactic 1130–6 for pulmonary atresia 656 ABO-incompatible transplantation 1092 acid-base balance 320, 373–4 activated clotting time 296, 411–12 adenosine 116 adrenaline 107 adult circulation (normal) 69–71 adults with CHD aortic coarctation 1026–7, 1033–4, 1035, 1037, 1045 atrial fibrillation 1130 consent when incapacitated 435–6, 444–6 CPB 369, 379 intensive care 337–50 LVOT defects 899–901 PDA closure 1012–13 pregnancy 449, 1070 airway compression 201, 922, 931, 982–3, 984, 985–9 airway management 242, 246, 264, 293 alpha stat strategy 374 alprostadil 118 amiodarone 113–14, 302, 592 Amplatzer™ devices 226, 229, 232–3, 469, 1015, 1016 anaesthesiology 241–75 anaesthesia or sedation 241 anaesthetists 241 drugs 119–22 peri-operative management 250–74 pre-operative assessment 243–50 quality control 274–5 analgesia 122–3, 273–4 anatomy 1–60 adult circulation 69–71 aortopulmonary septum 48–51, 962

1177

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Key Questions in CONGENITAL CARDIAC SURGERY

1178

atrial septum 12–14, 451–3 conduction system 26–9, 58–60, 488–90, 763–4, 788 coronary arteries 46–8, 730–3, 935–7 ductus arteriosus 53–5, 997, 1000–1 embryological development 1–12, 961–3 foetal circulation 61–3, 997–8 LVOT 863–6 mitral valve 839–40 pharyngeal arch arteries 48, 52, 53, 55–7 pulmonary veins 10–11, 537–9 RVOT/pulmonary valve 639–43 ventricular septum 22–5 ëÉÉ=~äëç=ìåÇÉê=áåÇáîáÇì~ä=~åçã~äáÉë aneurysms berry aneurysms of circle of Willis 1026 coronary artery 957–60 PDA 1008 angiography 206–9 aortic stenosis 872 after arterial switch 754 coronary arteries 950, 956, 958–9 Fontan fenestrations 230, 231 HLHS 827, 829, 831 PDA 227, 1006–7 tetralogy of Fallot 697, 699, 700 valvular repair/replacement 219, 220, 235, 236, 237 VSD 207, 233 angioma 1154 angioplasty ëÉÉ balloon angioplasty/valvuloplasty angiotensin-converting enzyme (ACE) inhibitors 111 anomalous aortic origin of a coronary artery (AAOCA) 946–55 anomalous left coronary artery from the pulmonary artery (ALCAPA) 167, 174, 309–10, 937–45 anomalous PV connections ëÉÉ pulmonary venous anomalies antenatal diagnosis ëÉÉ prenatal diagnosis anti-arrhythmic agents 111–12, 113–16, 301–2, 592 antibiotics 123–4, 1166–7, 1173–4 anticoagulants 102–5, 893 in CPB 359 in ECMO 411–12 reversal 103, 378–9 antidiuretic hormone (vasopressin) 108 antifibrinolytics 105–6, 356, 380 antiplatelet agents 101–2 aortic arch double 51, 981, 983, 985, 990–2 hypoplasia 240, 1020, 1036, 1040, 1042–3

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Index interrupted 1047–56 anatomy 1047–8 associated conditions 911, 966–7, 976, 977, 1048 investigations 196–7, 1050–1 management 361, 1049–50, 1051–6 outcomes and complications 1056 symptoms and signs 1049 left, with an aberrant right subclavian artery 982 right, with left ligamentum 981, 983, 993 ëÉÉ=~äëç vascular rings and slings aortic coarctation 1019–45 anatomy 1019–21 associated conditions 1023–4 epidemiology 1024 genetics 1022 investigations 154–6, 194–6, 209, 1027–33 management 195–6, 237–40, 257, 344, 1033–45 outcomes and complications 1025–7, 1043–5 pathophysiology 1024–5 symptoms and signs 1027 aortic complications after TA repair 929–30 aortic dominant common arterial trunk 41–3 aortic pressure waveform 213–14 aortic root 23, 197, 864, 866, 898–904 aortic valve anatomy 864–5, 866 bicuspid 1023 regurgitation 870–1, 877, 883, 885 management 889, 899–904 stenosis 869–70, 888 in HLHS 813, 822 investigations 139–41, 877–83, 885 management 217–19, 888–9, 890–3, 897–9, 905, 1084 aortopulmonary septum 48–51, 962 aortopulmonary shunts, surgical 306, 350, 1074–81 ëÉÉ=~äëç Blalock-Taussig (BT) shunt aortopulmonary window 961–78 associated conditions 964–8 classification 963–5 embryology 961–3 epidemiology 966 investigations 166, 202, 970–3 management 973–8 outcomes and complications 969, 976–7 pathophysiology 969 symptoms and signs 969–70 aprotinin 356, 380

1179

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Key Questions in CONGENITAL CARDIAC SURGERY

1180

arrhythmias 263, 1111–36 anti-arrhythmic agents 111–12, 113–16, 301–2, 592 atrial fibrillation 577, 1119–20, 1129, 1130 atrial re-entry tachycardia 1111–12, 1122–8 atrioventricular nodal re-entry tachycardia 1116–18 atrioventricular re-entrant tachycardia 1113–16 Ebstein’s anomaly 576–7 focal atrial tachycardia 1118–19 postoperative 322 JET 299–302 TCPC/Fontan 633, 637 VSD repair 515 prophylactic surgery 1130–6 right-sided lesions 1129–30 ventricular tachycardia 1120–2 arterial compliance 83–4 arterial duct ëÉÉ ductus arteriosus; patent ductus arteriosus (PDA) arterial pressure monitoring 278, 358 arterial switch procedures 306–8, 360, 746, 748, 750–6, 804, 900 double-switch 774–6 arteriovenous ECMO 386 ASD ëÉÉ atrial septal defects aspirin 101 atenolol 112 atrial appendages 3 isomerism 7, 10 atrial embryology 2–6, 12–14 atrial fibrillation 577, 1119–20, 1129, 1130 atrial pressure 209–11, 279, 358 atrial re-entry tachycardia (atrial flutter) 1111–12, 1122–8 atrial septal defects (ASD) 451–74 adult patients 344 aetiology 454–6 associated conditions 456 classification 454 in Ebstein’s anomaly 590 embryology 12–15, 451–3 epidemiology 456 investigations 133–5, 175–7, 216, 458–66 management 228–30, 261–2, 466–74 outcomes and complications 457, 473–4 pathophysiology 77, 85–6, 456, 465–6 symptoms and signs 457–8 ëÉÉ=~äëç patent foramen ovale atrial septostomy 227–8, 745–6, 1082 atrial septum 12–14, 451–3 atrial switch procedures 746–9 double-switch 774–5

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Index Senning/Rastelli 777 atrioventicular canal 2, 4, 5–6, 12, 27 atrioventricular conduction axis 26–9, 59–60 atrioventricular nodal re-entry tachycardia 1116–18 atrioventricular re-entrant tachycardia 1113–16 atrioventricular septal defects (AVSD) 519–36 anatomy 18–21, 519–23 associated conditions 523–4 classification 519–20 investigations 147–9, 178–9, 526–9, 533–4, 615 management 344, 521, 529–36, 629–30 outcomes and complications 525, 534–6 partial (ostium primum defect) 18, 20, 454, 460, 472 pathophysiology 524–5 symptoms and signs 525–6 unbalanced 523, 536, 614, 615, 629–30, 1058 atropine 116–17

B-mode echocardiography 128 bacterial infections antibiotics 123–4, 1166–7, 1173–4 infective endocarditis 1008, 1026, 1157–74 balanced parallel circulation 248–50 balloon angioplasty/valvuloplasty aorta 237–8 aortic valve 217–19, 888–9, 890, 905 pulmonary artery 221–3, 725 pulmonary valve 219–21, 658–9 pulmonary vein 223–4 balloon atrial septostomy 227, 745–6 BCPS ëÉÉ bidirectional cavopulmonary shunt benign tumours 1140, 1152–5 Bentall procedure 899–901 benzodiazepines 121 Berlin Heart EXCOR® Pediatric VAD 1093–4 beta-blockers 111–12, 302, 691 bidirectional cavopulmonary shunt (BCPS; Glenn shunt) 1079–80 complications 636, 835–6 one-and-a-half ventricles 82, 589–90 postoperative management 314–16, 1080–1 single ventricle 254–5, 602, 634, 826–8, 1067–8 Birmingham modification of the Norwood procedure 826, 833 bispectral index 280 Blalock-Taussig shunt (BTS) 1065, 1074–6, 1078–9 complications 636, 1076 intensive care 306, 350 used in 603, 633, 693, 723, 770, 801, 1075

1181

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Key Questions in CONGENITAL CARDIAC SURGERY

1182

blood flow classification of pathologies 246–50 in CPB 363 Doppler echo 128 in ECMO 394–5 in a modified BTS 1078–9 in PDA 1001–2 Qp/Qs ratio 80, 90, 92–4 ASD 465–6 single ventricle 80, 285–7 restrictive/non-restrictive defects 84 and vascular resistance 69 blood gases 96, 373–4 blood loss 294–6, 320, 379–81 ëÉÉ=~äëç anticoagulants; coagulation blood pressure adults with CHD 341 monitoring in the PICU 278 physiological 67, 71 blood tests 244–5, 292 blood transfusions 261 blood volume 68 body surface area 68 bosentan 67, 110 brain monitoring neurological function 265–7, 280, 330, 424 protection during CPB 372–4, 375–7 breathing 242, 264–5, 293 Bretschneider solution 366–7 BTS ëÉÉ Blalock-Taussig shunt bubble test 463–4 bulboventricular foramen 622–3, 632

calcium gluconate 113 calcium metabolism 263 cancer 1139–52 radiation exposure 206 carbon dioxide (CO2) ETCO2 280 hypercarbia in ECMO 418, 418–19 permissive (post-Glenn) 315 cardiac arrest 319–22, 420 cardioplegia/DHCA 365–8, 374–7 ëÉÉ=~äëç sudden cardiac death cardiac mixing 79 cardiac output (CO) 76, 92 in CPB 363

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Index management of low CO 297–9, 347 monitoring 279, 341–2 cardiac shunts 76–7 ëÉÉ=~äëç=ëéÉÅáÑáÅ=ÅçåÇáíáçåë cardiac tumours 1139–55 classification 1139–40 epidemiology 1141 investigations 1141–9 management 1149–55 symptoms and signs 1141 cardiomegaly 89, 459, 498, 527, 570–1, 940, 971, 1003, 1143 cardiomyopathy 291–3, 1087, 1098 cardioplegia 365–8 cardiopulmonary bypass (CPB) 351–82 anticoagulation 359 reversal 378–9 in aortopulmonary shunt 381–2 blood conservation 379–81 cannulation procedures 359–62 cardioplegia 365–8 cerebral protection 372–4, 375–7 circuit components 351–5 complications 261, 369–71 DHCA 374–7 and ECMO 387, 404–5 flow rate 363 gas exchange 363–4 in interrupted aortic arch 361, 1052 monitoring 356–8 myocardial protection 364–5, 370, 945 patient characteristics 358–9 primers 356 renal protection 377–8 temperature control 358, 368, 371–2 in truncus arteriosus 923–4 venting the heart 362–3 weaning from 262–3 cardiotomy, complications of 293–305, 319–22 care orders 429 carvedilol 112 catecholamines 106–8, 301 catheterisation ablation therapies 1112, 1115–16, 1117–18, 1119, 1120, 1121–2 angiography 206–9 aorta coarctation 209, 237–40, 1030, 1034 interrupted arch 1050–1

1183

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Key Questions in CONGENITAL CARDIAC SURGERY

1184

aortopulmonary window 973, 977–8 ASD 228–30, 261–2, 464–5, 467–9 atrial septostomy 227–8, 745–6 AVSD 529 coronary artery anomalies 942, 950, 956, 957, 958–9 Fontan fenestration closure 230–1 HRH 619–20 L-to-R shunts 91 LVOT defects 887–8 aortic valvuloplasty 217–19, 888–9, 890, 905 mitral valve defects 849, 857 and non-invasive imaging 199–200, 215–17 PA angioplasty/stenting 221–3, 725 PA-VSD 714–16, 724–5 PDA 1006–7 closure 225–7, 1009, 1013–16 stenting 224–5, 801, 831 pressure measurements 209–15 pulmonary valve replacement 235–7, 668–70 stenosis 219–21, 652–3, 656, 658–9, 697 pulmonary veins anomalous connections 554, 555–6 stenosis 223–4 Qp/Qs ratio 92–3 radiation exposure 205–6 tetralogy of Fallot 689–90, 696–8 TGA 742, 745–6 tricuspid atresia 602 truncus arteriosus 918–19 univentricular heart 1062, 1063 VSD 231–4, 501, 506–8 cavopulmonary circulation ëÉÉ Fontan circulation ccTGA ëÉÉ congenitally corrected transposition of the great arteries cefuroxime 123 central shunt 1077 central venous access 267–9 central venous pressure 278 centrifugal pumps 354 cerebral function monitoring 265, 280, 330, 424 cerebral oximetry 265–7 cerebral protection during CPB 372–4, 375–7 chest radiography ALCAPA 940 anomalous PV connections 193, 548 aortic coarctation 194, 1028 aortic regurgitation 883

index_KQCCS.qxd 26/01/2022 13:08 Page 1185

Index aortopulmonary window 971 ASD 175, 459 AVSD 178, 526–7 cardiac tumours 1142–3 ccTGA 188, 761, 764–5 DORV 792 Ebstein’s anomaly 198, 570–1, 582 in ECMO 409, 416, 417 Eisenmenger syndrome 95 HLHS 820 HRH 619–20 L-to-R shunts 88 mitral valve defects 848 PA-VSD 711 PDA 1003, 1010 pre-operative 245 tetralogy of Fallot 684 TGA 185, 738 tricuspid atresia 600–1 truncus arteriosus 914 univentricular heart 1060 vascular rings 984–5 VSD 89, 177, 497–8 chylothorax 304–5 circulation monitoring 265 normal adult 69–71 foetal 61–3, 997–8 neonatal 63–4, 242 venous return 80 one-and-a-half-ventricle 81–2, 589–90 postoperative complications 293 in series or in parallel 69–70, 74, 79–80 single ventricle 80–1 cleft mitral valve 18, 21, 142, 842, 855 clonidine 301 clopidogrel 101–2 coagulation 261, 346 antifibrinolytics 105–6, 356, 380 postoperative bleeding 295–6 pre-operative checks 244 thromboelastograms 270–1, 296 ëÉÉ=~äëç anticoagulants coarctation of the aorta ëÉÉ aortic coarctation coils (for PDA closure) 225, 1014–15

1185

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Key Questions in CONGENITAL CARDIAC SURGERY

1186

collateral arteries 75 in aortic coarctation 1024 MAPCAs 34–6, 620, 707–8, 715–16, 718, 721 colloids 356 common arterial trunk ëÉÉ truncus arteriosus communication with patients/carers 244, 245, 436–7, 447, 449–50 compliance 83–4 compression syndromes in truncus arteriosus 922, 931 vascular rings and slings 51, 200–1, 979–94 computed tomography (CT) 171 ALCAPA 942, 944 anomalous PV connections 192, 549 aorta coarctation 195–6, 1025, 1030–2, 1034, 1037 interrupted arch 196–7 vascular slings/rings 201, 985–6, 992 aortopulmonary window 202, 973 ASD 176–7 AVSD 178 and catheterisation 199–200, 216–17 ccTGA 189 coronary artery anomalies 172, 942, 944, 949–50 DORV 183–5, 796–8 Ebstein’s anomaly 198, 199, 575 in ECMO 410 Fontan procedure 190 L-to-R shunt 90 LVOT defects 874, 886 neurological status 330 PA-VSD 712 tetralogy of Fallot 179, 180–2 TGA 186, 187, 188, 743–4, 756 truncus arteriosus 919–22, 931 univentricular heart 1061 VSD 177–8 conduction system 58–60 in ccTGA 763–4 in RV inlet anomalies 26–9 in VSD 488–90, 788 ëÉÉ=~äëç arrhythmias congenitally corrected transposition of the great arteries (ccTGA) 759–79 anatomy 45, 759–61, 763–4 associated conditions 761–2 investigations 157–9, 188–9, 761, 762, 764–8 management 504, 629, 768–79 outcomes and complications 778–9 pathophysiology 615, 764

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Index connective tissue disorders 871, 899 consent 427–50 contrast agents 171, 172, 343, 346 cor triatriatum 143–4, 541–2, 543, 544–5, 546, 547, 554 coronary artery anomalies 935–60 ALCAPA 167, 174, 309–10, 937–45 anatomy 730–3, 935–7, 938, 946 aneurysms 957–60 anomalous aortic origin 946–55 and aortopulmonary window 967–8, 975–6 classification 46–8, 730–1, 937 epidemiology 937 fistulae 955–7 in HLHS 812 investigations 167, 172–5, 939–42, 948–50, 951, 955–6, 958–9 management 943–5, 951–5, 956–7, 959–60 perfusion pressure 307 in pulmonary atresia (sinusoids) 643–5, 657–8 stenosis 871 sudden cardiac death 947, 951, 955 symptoms and signs 939, 948, 955, 958 in tetralogy of Fallot 150, 679, 688 in TGA 46, 154, 158, 307, 730–3, 741, 752–3 in truncus arteriosus 913, 919, 933 coronary sinuses 864 defects 15, 17, 454, 472–3, 893 corticosteroids 119, 299 covered CP Stent™ 238, 239 CPB ëÉÉ cardiopulmonary bypass cross-clamp fibrillation 368 cryoablation ëÉÉ ablation therapies crystalloid 356, 400 CT ëÉÉ computed tomography cyanosis/cyanotic heart disease 96–8, 617 in adults 345–6 anaesthesia 251 compared with PPHN 284 management 289–90, 655 R-to-L shunts 77, 247, 289–90 ëÉÉ=~äëç=áåÇáîáÇì~ä=ÅçåÇáíáçåë cyclo-oxygenase inhibitors 65, 101, 118–19

dalteparin 104 Damus-Kaye-Stansel anastomosis 623, 632, 825, 1056 David V reimplantation 901, 902 death and dying 335–6 deep hypothermic circulatory arrest (DHCA) 374–7

1187

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Key Questions in CONGENITAL CARDIAC SURGERY

1188

dexmedetomidine 301 diagnosis ëÉÉ echocardiography; imaging dialysis 303–4 DiGeorge syndrome 911, 912, 1048 DILV (double-inlet left ventricle) 38, 163–4, 614, 621–3, 632, 1058 disclosure of information 245, 436–7, 447, 449–50 diuretic agents 117–18, 691 diverticulum of Kommerell 983, 987 dobutamine 106–7 documentation (consent forms) 437–46 dopamine 106, 301 Doppler echocardiography 128, 215, 461 DORV ëÉÉ double-outlet right ventricle double aortic arch 51, 981, 983, 985, 990–2 double-inlet left ventricle (DILV) 38, 163–4, 614, 621–3, 632, 1058 double-outlet right ventricle (DORV) 781–809 anatomy 26, 36–7, 781–8 associated conditions 160, 783–4 epidemiology 792 investigations 159–60, 183–5, 792–8 management 799–809 outcomes 792, 808 pathophysiology 78, 788–92 symptoms and signs 792 and VSD 477–8, 784–6, 788–92, 802–8 double-switch procedure 774–6 Down’s syndrome 524, 525 ductus arteriosus anatomy 53–5, 997, 1000–1 foetal 53, 61, 995, 997–8 physiological closure 64, 65, 998 ëÉÉ=~äëç patent ductus arteriosus ductus venosus 62, 64 Duke criteria 1162–4 dyspnoea 85 ëÉÉ=~äëç airway compression Ebstein’s anomaly 565–92, 627–8 aetiology 566 anatomy 565–6, 628 associated conditions 566–7 epidemiology 567 investigations 168–9, 198–9, 570–6, 762 management 251–2, 345, 573, 577–92, 627 outcomes 567, 568–9, 592 pathophysiology 567 symptoms and signs 568, 570

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Index ECG ëÉÉ electrocardiography echocardiography (ëÉÉ=~äëç imaging) 127–70 anomalous PV connections 143–7, 549–54 aorta coarctation 154–6, 194, 1028–30, 1044 interrupted arch 1050 aortopulmonary window 166, 971–2 ASD 133–5, 216, 460–4 AVSD 147–9, 527–8, 533–4 cardiac tumours 1142, 1144–7 ccTGA 157–9, 762, 767–8 coronary artery anomalies AAOCA 948 ALCAPA 167, 940 diagnostic principles 127–33 DILV/DIRV 163–4 DORV 159–60, 792–5 Ebstein’s anomaly 168–9, 568–9, 571–3, 762 in ECMO 409–10, 412–13 HLHS 164–6, 816, 819, 820, 821–2, 826, 832, 1058 HRH 618–19, 1058 infective endocarditis 1163, 1164–5 isomerism 161–3 L-to-R shunts 88–90 LVOT obstruction 139–41, 878–83, 896, 897 mitral valve 142–3, 821, 841, 842, 843, 844, 845, 847, 848, 853 PA-IVS 151 PA-VSD 152, 712–14 PDA 135–6, 688, 1004–5 pressure gradients 215 pulmonary stenosis 650–1 tetralogy of Fallot 149–50, 680, 684–9, 692, 695 TGA 152–4, 739–42 transoesophageal 127–8, 215–16, 269–70 transthoracic 127, 130–2 tricuspid atresia 163, 601–2, 1058 truncus arteriosus 156–7, 914–17, 928, 929 vascular rings 161 VSD 136–9, 159, 498–501 ECLS (extracorporeal life support) 385 ECMO (extracorporeal membrane oxygenation) 385–425 anticoagulation 411–12 blood flow 394–5 cannulation 396–400, 401–3, 409, 415, 417, 420–1 cardiorespiratory support 406 circuit components 388–94, 420 and CPB 387, 404–5

1189

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Key Questions in CONGENITAL CARDIAC SURGERY

1190

ECPR 386 exclusion criteria 406–7, 407–8 history 385–6 imaging 409–10, 412–13 indications 407, 1093 in intensive care 302, 405–6 left heart vent 403 outcomes and complications 396, 414–21 patient parameters 422–3 primers 400–1 recirculation 395–6, 418 routine checks 423–5 starting and stopping 421–2, 423 in transplant patients 1093, 1100, 1104–5 types 386, 388 ventilation settings 410–11 weaning from 412–14 Edwards SAPIEN XT/3/Ultra™ valves 235–236, 668 Eisenmenger syndrome 94–6, 260, 1003 VSD 32, 33, 495 electrocardiography (ECG) 278 ALCAPA 939 anomalous PV connections 548 aortic coarctation 1027 aortic stenosis 877–8 aortopulmonary window 970 ASD 458 AVSD 526 cardiac tumours 1144 ccTGA 765–6 Ebstein’s anomaly 575–6 JET 300–1 LV failure 292 mitral valve defects 848, 850 PA-VSD 710–11 PDA 1004 pulmonary stenosis 649 tetralogy of Fallot 683 TGA 738–9 tricuspid atresia 600 truncus arteriosus 914 univentricular heart 1062 VSD 496–7 electroencephalography 280 electrolytes 245, 320, 425 embolism thrombotic 321, 421 vegetations in IE 1161, 1169–70

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Index embryology 1–14, 22–5, 48–55 aorta 1048 aortic valve 866 aortopulmonary window 961–3 ASD 12–15, 451–3 AVSD 520–1 coronary arteries 46, 936–7 DORV 782–3 ductus arteriosus 53–5, 997 HLHS 815–16 HRH 614–15 mitral valve 839 PDA 53–5, 997 pulmonary veins 10–11, 537–9 RVOT 639–43 tetralogy of Fallot 676 tricuspid atresia 596 truncus arteriosus 912, 961, 963 vascular rings 51–2, 979–80 VSD 26, 491–2 enalapril 111 end-of-life care 335–6 end-tidal CO2 (ETCO2) 280 endarteritis ëÉÉ infective endocarditis endocardial fibroelastosis 167, 813, 897 endothelin receptor antagonists 67, 110 enoxaparin 104 enoximone 109 epicardial echocardiography 128 epidemiology ëÉÉ=ìåÇÉê=áåÇáîáÇì~ä=ÅçåÇáíáçåë epinephrine (adrenaline) 107 esmolol 112, 302 ethics of consent 427–8 exercise stress testing 951 extracardial conduit 635 extracorporeal cardiopulmonary resuscitation (ECPR) 386 extracorporeal life support (ECLS) 385 extracorporeal membrane oxygenation ëÉÉ ECMO extubation 251, 271–2 factor VIIa, recombinant 295 Fallot’s tetralogy ëÉÉ tetralogy of Fallot femoral cannulation 401–3 fenestration (Fontan circulation) 230–1, 609 fibroma 1153–4 flecainide 114 fluid management 251, 425 hypovolaemia 318, 320, 341

1191

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Key Questions in CONGENITAL CARDIAC SURGERY

1192

focal atrial tachycardia 1118–19 foetal circulation 61–3, 997–8 and LVOTO 875–6 foetal haemoglobin 99 foetal legal status 449 Fontan circulation 80–1, 312–19, 1064–9, 1082–4 in adults 348–9 complications 609, 633, 835–6, 1069 cryoablation 1126–9 fenestration 230–1, 609 HLHS 252, 824–36 HRH 625, 632–3, 635, 637 hybrid procedure 225, 831–2, 833, 1066, 1084–5 imaging 190–1 Stage I (Norwood/BTS) 252, 312–14, 825–6, 833, 1064–7 Stage II (Glenn/BCPS) 254, 314–16, 826–8, 835–6, 1067–8, 1079–81 Stage III (TCPC) 255–7, 316–19, 605–6, 632–3, 635, 828–31, 1068–9 tricuspid atresia 602–11, 625 Fontan conversion 610–11 foramen ovale 12, 62 patent 15, 16, 64, 133 fossa ovale 12, 15, 16 Fraser competence 432 fungal endocarditis 1159, 1167 furosemide 117, 691 genetics

aortic coarctation 1022 PDA 999–1000 sidedness 7 truncus arteriosus 911, 912 univentricular lesions 616 gentamicin 123–4 Gerbode defect 488 Gillick competence 431–3 Glenn shunt 1079 bidirectional ëÉÉ bidirectional cavopulmonary shunt GOSE score 568–9

haematocrit 356, 357–8 haemodialysis 303–4 haemofiltration 378 haemoglobin cyanosis 96–7 O2-Hb dissociation curve 98–9

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Index haemoglobinopathy screen 244 haemolysis 419 haemostasis 294–6, 379–81 on ECMO 419 ëÉÉ=~äëç=anticoagulants; coagulation handover procedures 272–3 Harlequin syndrome 396 heart block in AVSD 534 in ccTGA 615, 764, 766, 770 heart murmurs 496, 526, 683, 710, 848, 914, 970, 1002, 1027 heart rate, normal 67 heart transplantation 824, 1070, 1087–1101 heart-lung transplantation 1102 height, normal 68 hemi-Fontan procedure 634–5, 827 hemitruncus arteriosus 963 heparin 102–4, 359, 411–12 hepatic function 343, 345 heterotaxy 6–7, 630 HLHS ëÉÉ hypoplastic left heart syndrome Holmes heart 164 HRH ëÉÉ hypoplastic right heart hypercarbia in ECMO 418, 418–19 permissive (post-Glenn) 315 hyperoxia test 97, 282 hypoplastic left heart syndrome (HLHS) 811–36 anatomy 811–16 associated conditions 816–17 epidemiology 817 investigations 164–6, 197, 816, 819–22, 1058 management 224–5, 252–4, 822–36, 895 outcomes and complications 818, 835–6, 877 pathophysiology 817–18 symptoms and signs 818–19 hypoplastic right heart (HRH) 613–37 aetiology 615 associated conditions 615–16 ccTGA 615, 629 DILV 38, 163–4, 614, 621–3, 632, 1058 embryology 614–15 investigations 616–17, 618–21, 1058 management 621, 623, 624–7, 630–7 outcomes and complications 636–7 pulmonary atresia 151, 628–9, 654–5, 656–8 sTV 614, 621–3

1193

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Key Questions in CONGENITAL CARDIAC SURGERY

symptoms 617 types 613–14 unbalanced AVSD 614, 615, 629–30 ëÉÉ=~äëç=Ebstein’s anomaly; tricuspid atresia hypothermia 301, 320 in CPB 368, 373–4 DHCA 374–7 hypovolaemia 318, 320, 341 hypoxia/hypoxaemia 316, 320 in ECMO 417–18, 418

1194

IE ëÉÉ infective endocarditis imaging (ëÉÉ=~äëç echocardiography) 171–202 angiography 206–9 anomalous PV connections 192–3, 548–54 aorta coarctation 194–6, 1021, 1025, 1028–33, 1034, 1037 interrupted arch 196–7, 1050–1 root pathology 197 vascular slings/rings 200–1, 984–6, 992 aortopulmonary window 202, 971–3 ASD 175–7, 459–64 AVSD 178–9, 526–8, 615 cardiac tumours 1142–3, 1147–9 and catheterisation 199–200, 215–17 ccTGA 188–9, 761, 764–5 coronary artery anomalies 172–5 AAOCA 173, 948–50 ALCAPA 167, 174, 940–1 aneurysms 958–9 fistulae 955–6 DORV 183–5, 792, 796–8 Ebstein’s anomaly 198–9, 570–5, 582 in ECMO 409–10 Eisenmenger syndrome 95 HLHS 197, 820, 821 HRH 617, 619–20 L-to-R shunts 88–90 LVOT defects 874, 883–6 mitral valve defects 848–9 neurological status 330 PA-VSD 711–12 PDA 227, 1003, 1005–6, 1010 point-of-care US 331–2 pre-operative 245 pulmonary stenosis 650 tetralogy of Fallot 179–83, 684

index_KQCCS.qxd 26/01/2022 13:08 Page 1195

Index TGA 185–8, 738, 743–4, 756 tricuspid atresia 600–1, 625 truncus arteriosus 914, 919–22 univentricular heart 1060–1 VSD 89, 177–8, 207, 497–501 immunosuppressants 1098, 1106–7 indomethacin 118–19, 1009 infective endocarditis (IE) 1157–74 classification 1157–8 diagnostic criteria 1162–4 echocardiography 1163, 1164–5 epidemiology 1008, 1026, 1158 management 1166–73 microbiology 1159–60, 1163, 1165–6 pathogenesis 1159 in PDA 1008 prophylaxis 1173–4 symptoms and signs 1161–2 informed consent 427–50 infracristal VSD 29–31 infundibular sleeve 24–5 injectable pulmonary valve implantation 670–3 innominate artery compression syndrome 984, 988, 993 inotropic agents 106–8, 108–9, 263, 301 intensive care, adult 337–50 intensive care, paediatric (PICU) 277–336 ALCAPA 309–10 biventricular palliative procedures 305–6 cardiac arrest 319–22 duct-dependent pulmonary circulation 282–3 duct-dependent systemic circulation 280–2 ECMO 302, 405–6 end-of-life care 335–6 handover to 272–3 interventional cardiologists 328–9 L-to-R shunts 288–9, 310–11 long-term patients 329 LV failure 291–3 monitoring 278–80, 330 non-cardiac patients 328 nutrition 333–4 outcomes 322–4 point-of-care US 331–2 postoperative complications 293–305 PPHN 283–5 principles 277 pulmonary hypertension 310, 321, 325–7

1195

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Key Questions in CONGENITAL CARDIAC SURGERY

R-to-L shunts 289–90, 311–12 single ventricle 285–7, 312–19 TAPVC 308 TGA 290–1, 306–8 ventilation 271–2, 324–5 interatrial communication 15, 17, 454, 472–3 interrupted aortic arch ëÉÉ aortic arch, interrupted interventricular communication 26, 36–7 intracardiac lateral tunnel conduit 635 intubation 246 ischaemic colitis 334 isomerism 7, 9–10, 161–3, 630 junctional ectopic tachycardia (JET) 299–302

Kawasaki disease 958, 959 kidney ëÉÉ renal function Konno modification 899

1196

left ventricle (LV) compliance 83 double-inlet 38, 163–4, 614, 621–3, 632, 1058 embryology 1–6 failure 291–3 training 774 ëÉÉ=~äëç hypoplastic left heart syndrome left ventricular outflow tract (LVOT) defects 863–906 anatomy 863–6 obstruction (LVOTO) associated conditions 524, 534–5, 772–3, 873–4 causes 868–70, 871–3, 874, 1022 interrupted aortic arch 1048, 1056 investigations 139–41, 874, 877–88 management 217–19, 772–3, 888–9, 890–9 outcomes and complications 877, 904–6 pathophysiology 875–6 symptoms and signs 876 ëÉÉ=~äëç aortic coarctation regurgitation 870–1, 877, 883, 885 management 889, 899–904 subaortic 863, 868–9, 879, 880, 881, 884, 888, 895–7, 905 supravalvular 864, 871–3, 880, 886, 893–4, 905 types 866–7 valvular ëÉÉ aortic valve left-handed ventricular topology 8–10 left-to-right shunts, congenital 246–7 in ASD 85, 456

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Index in AVSD 524–5 CPB 381–2 Eisenmenger syndrome 94, 260, 495 imaging 88–91 intensive care 288–9, 310–11 in PDA 87–8, 995, 1001–2 in tetralogy of Fallot 681–2 in truncus arteriosus 912–13 in VSD 86–7, 494, 495–6 left-to-right shunts, surgical 306, 350, 1074–81 ëÉÉ=~äëç Blalock-Taussig shunt legal issues 427–50 Leiden classification of coronary arteries 46, 730–1 levosimendan 108–9 lidocaine 114–15, 367 liver function 343, 345 low cardiac output state (LCOS) 297–9 low molecular-weight heparin (LWMH) 103–4 lung pulmonary oedema 331–2 transplantation 1101–8 LV ëÉÉ left ventricle LVOT(O) ëÉÉ left ventricular outflow tract (obstruction)

M-mode echocardiography 128 magnesium 366 magnetic resonance imaging (MRI) 172 ALCAPA 941 anomalous PV connections 192–3, 549 aorta coarctation 195, 1021, 1030–1, 1033 interrupted arch 196–7, 1050 root pathology 197 ASD 176, 459 AVSD 178, 529 cardiac tumours 1147–9 and catheterisation 216–17 ccTGA 188–9 coronary artery anomalies 172–4, 941, 949 DORV 183 Ebstein’s anomaly 198–9, 573–5 Fontan procedure 190 HLHS 197 L-to-R shunts 90 LVOT defects 883–5 mitral valve defects 848–9 neurological status 330

1197

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PDA 1005 tetralogy of Fallot 179, 183 TGA 185–6, 187–8 truncus arteriosus 919–22, 930, 932, 933 univentricular heart 1061 VSD 177 major aortopulmonary collateral arteries (MAPCAs) 34–6, 75, 620, 707– 8, 715–16, 718, 721 malignant tumours 1139–52 radiation exposure 206 mannitol 356 Maquet Quadrox iD® membrane oxygenator 1105 McGoon ratio 607, 719 mechanical assist devices 836, 1070 heart transplantation 1093–4, 1100–1 lung transplantation 1104–6 ëÉÉ=~äëç ECMO mechanical valves 667–8, 857, 859, 860 medicolegal issues 427–50 Medtronic Contegra™ pulmonary valved conduit 663–4, 720 Medtronic Freestyle™ bioprosthesis 663, 664 Medtronic Melody™ valves 237, 668, 857, 860 Melbourne shunt 1077 membranous septum 22–4 microbiology antibiotics 123–4, 1166–7, 1173–4 IE 1159–60, 1163, 1165–6 midazolam 121 milrinone 66, 263, 297–8 minors, consent 428–9, 430–4 mitral valve anomalies 839–60 anatomy 839–40 associated conditions 846, 873 classification 840–5 cleft mitral valve 18, 21, 142, 842, 855 epidemiology 846 investigations 142–3, 821, 848–9, 850 management 850–60, 1084 outcomes and complications 857–9 pathophysiology 839, 846–7 prolapse 849–50 regurgitation 841, 846, 851, 854–6, 859 stenosis 813, 846, 850, 851–4, 859, 1084 symptoms and signs 847–8, 850 monitoring adults with CHD 341–2 CPB 356–8

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Index intra-operative 264–7 neurological function 265, 280, 330, 424 in the PICU 278–80, 330 morphine 122 MRI ëÉÉ magnetic resonance imaging multidisciplinary teams 323–4, 448 muscle relaxants 120–1 Mustard procedure 747 myectomy 896 myocardium protection/damage in CPB 364–5, 370, 945 signs of dysfunction 263 myxoma 1146, 1152–3

Nakata index 608, 719 near-infrared spectroscopy (NIRS) 253, 280, 358 neck cannulation 401 neonates ALCAPA 309–10 anaesthesia 242–3, 259 aorta coarctation 1026, 1033, 1035, 1036 interrupted arch 1047–56 ccTGA 770–1 circulation 63–4, 242 cyanosis 655 DORV 792, 799, 808 duct-dependent pulmonary circulation 282–3 duct-dependent systemic circulation 280–2 ductus arteriosus closure 64–5, 118–19, 225, 259, 998, 1009, 1010–12 Ebstein’s anomaly 568–9, 571, 578–82 ECMO 406–7, 415 HLHS 252–4, 817–18, 825–6, 831–2 HRH 631–2 L-to-R shunt 310–11 LVOT defects 877, 888, 889, 890, 905 normal values 67, 68 pharmacokinetics 243 PPHN 66, 283–5 pulmonary stenosis 655–8 single ventricle 285–7 tetralogy of Fallot 683, 691, 695 TGA 290–1, 306–8, 736–7 truncus arteriosus 912–13, 922–3 neurological function monitoring 265, 280, 330, 424 nitric oxide (NO) 66, 109

1199

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non-infective endocarditis 1160 non-restrictive cardiac defects 84 noradrenaline (norepinephrine) 107–8 Norwood procedure (Fontan stage I) 252, 312–14, 825–6, 833, 835 Nunn procedure 532 nutrition after a chylothorax 305 in the PICU 333–4 pre-operative starvation 244, 260

1200

oesophageal compression 201, 981, 984, 985–6, 990 one-and-a-half-ventricle circulation 81–2, 589–90 opiates 122–3 ostium primum defects 18, 20, 454, 460, 472 ostium secundum defects ëÉÉ atrial septal defects outcomes adult patients 338 paediatric patients 322–4 ëÉÉ=~äëç=ìåÇÉê=áåÇáîáÇì~ä=ÅçåÇáíáçåë oxygen content in blood 99–100 delivery in CPB 372–4, 375–7 in LCOS 298–9 ëÉÉ=~äëç ECMO hypoxia 316, 320 O2-Hb dissociation curve 98–9 PaO2 97, 357 saturation in CPB 357 L-to-R shunts 91 measurement 96, 265–7, 279 and Qp/Qs ratio 92–4

PA-IVS ëÉÉ pulmonary atresia with intact ventricular septum PA-VSD ëÉÉ pulmonary atresia with VSD pacing 302, 342–3 packed RBCs 356 pain relief 122–3, 273–4 palliative operations 1073–85 in aortic stenosis 1084 atrial septectomy/septostomy 227–8, 745–6, 1082 in ccTGA 770–1 in mitral stenosis 1084 systemic-to-pulmonary shunts 306, 350, 633, 770, 800–1, 1073–81 ëÉÉ=~äëç Fontan circulation; pulmonary artery, banding

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Index parachute mitral valve 843–4, 852 parental consent 429–30, 441–3 parenteral nutrition 334 partial anomalous pulmonary venous connection (PAPVC) 539–40, 543, 544 management 556, 557–9, 563 symptoms and signs 545–6, 546–7 patent ductus arteriosus (PDA) 995–1016 aetiology 999–1000 anatomy 53–5, 996, 997, 1000–1 associated conditions 688, 995, 998 closure 65, 118–19, 225–7, 259, 1008–16 epidemiology 999, 1008 investigations 135–6, 1003–7, 1010 maintaining patency (duct-dependent circulations) 118, 280–3, 995, 1049 stenting 224–5, 801, 831 outcomes and complications 1007–8, 1013, 1015 pathophysiology 64–5, 87–8, 995–8, 1001–2, 1024 normal closure 64, 65, 998 symptoms and signs 1002–3 patent foramen ovale (PFO) 15, 16, 64, 133 pathophysiology ëÉÉ=ìåÇÉê=áåÇáîáÇì~ä=ÅçåÇáíáçåë patient-controlled analgesia 122 PDA ëÉÉ patent ductus arteriosus pentalogy of Fallot 678 peripheral vascular resistance 72–5 peritoneal dialysis 303 persistent pulmonary hypertension of the newborn (PPHN) 66, 283–5 personalised external aortic root support 903–4 pH stat strategy 374 pharmacology 101–24 neonatal pharmacokinetics 243 in pre-transplant cardiac failure 1088–9 after repair of Ebstein’s anomaly 592 pharyngeal arch arteries 48, 52, 53, 55–7 phenylephrine 108 phosphodiesterase (PDE) inhibitors 66, 109, 110, 263, 297–8 physiology 61–100 neonatal 63–5, 67, 242–3 ëÉÉ=~äëç pathophysiology ìåÇÉê=áåÇáîáÇì~ä=ÅçåÇáíáçåë PICU ëÉÉ intensive care, paediatric placenta 62 platelet receptor antagonists 101–2 pneumothorax 320, 416 point-of-care ultrasound 331–2 Poiseuille equation 72

1201

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1202

postoperative care 273–4, 293–322 potassium chloride 366 Potts shunt 1076 prednisolone 119 pregnancy tests 245 pregnancy in women with CHD 449, 1070 prenatal diagnosis aortopulmonary window 971 cardiac tumours 1141–2, 1155 HLHS 197, 819–20 HRH 616 TGA 737 pre-operative care 243–50, 285–91 pressure load 82–4 weaning from bypass 262 procainamide 115 propofol 119–20 prostacyclines 67 prostaglandins 65, 118, 281, 691, 716, 744, 890, 1049 prosthetic valves aortic valve 892, 897 endocarditis 1160, 1167, 1172 mitral valve 856–7, 860 pulmonary valve 235–7, 665–73 pulmonary valved conduits 662–5, 720, 726, 927 tricuspid valve 590–1 protamine 103, 378–9 pseudocoarctation of the aorta 1021, 1040 psychological problems 245, 246 pulmonary artery anatomy 53 angioplasty/stenting 221–3, 725 banding 305–6, 1081–2 in AVSD 530, 1066 in ccTGA 504, 771, 774 in DORV 799–800 in HRH 633–4, 636 in VSD 502–4 in pulmonary atresia 152 sizing 607–8, 719–20 slings 982, 983, 989, 993 in tetralogy of Fallot 679, 685, 700, 701 in truncus arteriosus 908, 911 pulmonary atresia with intact ventricular septum (PA-IVS) 151, 628–9, 647 coronary sinusoids 643–5, 657–8 management 257–8, 654, 656–7 pulmonary atresia with tetralogy of Fallot 34, 681, 682, 693, 705

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Index pulmonary atresia with VSD (PA-VSD) 703–26 aetiology 705 anatomy 703–5, 707–8, 719 associated conditions 705–6 classification 706–7 epidemiology 705 investigations 152, 710–16 management 716–26 outcomes and complications 709, 723–4 pathophysiology 708 symptoms and signs 709–10 pulmonary capillary wedge pressure (PCWP) 212–13 pulmonary dominant common arterial trunk 41–3 pulmonary hypertension in the PICU 310, 321, 325–7 PPHN 66, 283–5 pulmonary oedema 331–2 pulmonary stenosis aetiology 645 associated conditions 646 classification 645 in DORV 800–2 epidemiology 646 with intact ventricular septum (PS-IVS) 643–5 investigations 649–53 management 653–62 balloon valvuloplasty 219–21, 658–9 valve replacement 235–7, 665–73, 698 valved conduits 662–5 valvotomy 659–60 outcomes and complications 648, 659 pathophysiology 646–8 symptoms and signs 648–9 pulmonary vascular resistance (PVR) cyanosis 251 in Eisenmenger syndrome 94, 260 and heart transplantation 1089–90 in HLHS 252, 817 after PA-VSD repair 719–20 physiology 63, 65–7, 72 in TCPC 255 univentricular anatomy 285–7, 349 pulmonary vein stenosis 542, 543, 545, 546, 547, 554–5 management 223–4, 562, 564 pulmonary venous anomalies 537–64 aetiology 542 associated conditions 543

1203

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classification 539–42 embryology 10–11, 537–9 epidemiology 544 investigations 143–7, 192–3, 548–55 management 223–4, 259–60, 308, 555–64 outcomes and complications 545, 562–4 pathophysiology 544–5 symptoms and signs 545–7 pulse oximetry 96, 279 pumps in CPB 354–5 in ECMO 392–4, 420 PVR ëÉÉ pulmonary vascular resistance

quality improvement cycle 274–5

1204

radiation exposure during procedures 171, 205–6 radiofrequency ablation ëÉÉ ablation therapies radiography ëÉÉ chest radiography Rastelli procedure 187, 777, 806 refusal of treatment 432–3, 434 remifentanyl 122–3 renal function and contrast agents 171, 172, 343, 346 in ECMO 424 monitoring 265 protection during CPB 377–8 renal replacement therapy 302–4 reperfusion injury 370 research, consent for 434 respiratory system monitoring 264–5 in neonates 242 normal respiratory rates 67 postoperative complications 293, 369 pulmonary oedema 331–2 ventilation 271–2, 324–5, 343, 349 restrictive cardiac defects 84 REV procedure 806–7, 927 rhabdomyoma 1152 rib notching 1028 right ventricle (RV) dilatation 85, 135, 151 double-inlet 164 double-outlet ëÉÉ double-outlet right ventricle embryology 1–6 failing, in adults 346–8

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Index hypoplastic ëÉÉ hypoplastic right heart inlet defects 26–9 one-and-a-half-ventricle circulation 81–2, 589–90 pressure waveform 211–12 restrictive physiology 311–12 RV-PA conduits/shunts 723, 726, 801, 825, 826 systemic in TGA 348, 734, 746–7 in tetralogy of Fallot 680 tricuspid atresia 38, 40 right ventricular outflow tract (RVOT) 639–73 in DORV 800–2 embryology 639–43 in tetralogy of Fallot 676, 679–80, 681–2, 685, 692–3, 696–8, 699 in truncus arteriosus 929, 933 ëÉÉ=~äëç pulmonary atresia; pulmonary stenosis right-handed ventricular topology 8–10 right-to-left shunts 77, 247–8 Eisenmenger syndrome 260 intensive care 289–90, 311–12 PDA 995 tetralogy of Fallot 682 VSD 496 risk assessment adult patients 338 paediatric patients 323 Roesler sign 194 roller pumps 354 Ross II procedure 857 Ross/Ross-Konno procedures 892, 898–9, 905 RV ëÉÉ right ventricle RVOT ëÉÉ right ventricular outflow tract safety

contrast agents 171, 172, 343, 346 CPB equipment 353–4 radiation exposure 171, 205–6 St. Thomas’ solution 366 Sano modification of Norwood procedure 312–13, 826, 833 semilunar valves 642–3 Senning procedure 748, 774–5, 777 sevoflurane 121–2 shock, cardiogenic 291–3 Shone syndrome 843–4, 873 signs ëÉÉ=ìåÇÉê=áåÇáîáÇì~ä=ÅçåÇáíáçåë sildenafil 66, 110

1205

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1206

single ventricle ëÉÉ univentricular heart sinotubular junction 865–6 sinus node 58–9 sinus venosus defects 15, 17, 134, 454, 460, 472 situs inversus 761, 764, 1096–7 situs solitus 760, 763 sotalol 112 spironolactone 118, 691 Starnes procedure 579, 580 starvation times, pre-operative 244, 260 stented biprosthetic valves 666 stents aorta 238–40, 1034 ductus arteriosus 224–5, 801, 831 pulmonary artery/RVOT 221–3, 696–7, 725, 801–2 pulmonary vein 223–4 steroids 119, 299 straddling tricuspid valve (sTV) 614, 621–3 streaming 77–8, 790 stroke volume 76 subclavian arteries 53, 982 sudden cardiac death 947, 951, 955 superior cavopulmonary connection (SCPC) 632, 634–5, 1079 ëÉÉ=~äëç bidirectional cavopulmonary shunt supracristal VSD 29–32 suxamethonium 120–1 Swiss cheese (ventricular) septum 492, 513–14 symptoms ëÉÉ=ìåÇÉê=áåÇáîáÇì~ä=ÅçåÇáíáçåë systemic hypoperfusion 248 systemic vascular resistance (SVR) 72–5 systemic-to-pulmonary collateral arteries ëÉÉ major aortopulmonary collateral arteries (MAPCAs) systemic-to-pulmonary shunts ëÉÉ left-to-right shunts

tachycardia ëÉÉ arrhythmias Takeuchi procedure 944–5 tamponade 321 TAPVC ëÉÉ total anomalous pulmonary venous connection Taussig-Bing anomaly 160, 783–4, 804–7 TCPC (total cavopulmonary connection) 80–1, 255–7, 316–19, 605–6, 632–3, 635, 828–31, 1068–9 temperature control 243, 250, 263 in CPB 358, 368, 371–2 DHCA 374–7 tension pneumothorax 320 teratoma, intrapericardial 1154–5 tetralogy of Fallot (TOF) 675–701

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Index anatomy 32–3, 34, 675–6, 676–8 associated conditions 678–9 epidemiology 676 investigations 149–50, 179–83, 680, 683–90 management 150, 523–4, 690–701 adults 344–5 outcomes and complications 682–3, 699–701 pathophysiology 679–82 symptoms and signs 683 TGA ëÉÉ transposition of the great arteries thoracotomy, complications of 293–305, 319–22 three-dimensional echo 132 three-dimensional rotational angiography 208–9 thromboelastograms 270–1, 296 thromboembolism 321, 421 thromboprophylaxis 101–3 topical haemostatic agents 380–1 total anomalous pulmonary venous connection (TAPVC) 541, 543, 544 investigations 144–7, 549–54 management 259–60, 308, 555–6, 559–61, 563 symptoms and signs 546, 547 total cavopulmonary connection (TCPC) 80–1, 255–7, 316–19, 605–6, 632–3, 635, 828–31, 1068–9 total mixing of blood 80, 93–4, 249 Total NeoPulmonary Artery Index (TNPAI) 719 tracheal compression 201, 922, 931, 982–3, 984, 985–9 tranexamic acid 105–6, 380 transoesophageal echocardiography (TOE) 127–8, 215–16, 269–70 transplantation heart 824, 1070, 1087–1101 heart-lung 1102 lung 1101–8 transposition of the great arteries (TGA) 729–56 anatomy 43–5, 729–33 classification 733 coronary arteries 46, 154, 158, 307, 730–3, 741, 752–3 epidemiology 733–4 investigations 152–4, 185–6, 738–44 management 154, 159, 186–8, 290–1, 306–8, 348, 360, 744– 56, 1095 outcomes and complications 737–8, 753–6 pathophysiology 598–9, 734–7 symptoms and signs 737 ëÉÉ=~äëç congenitally corrected transposition of the great arteries transthoracic echocardiography (TTE) 127, 130–2 triangle of Koch 29, 59, 488 tricuspid atresia 595–611

1207

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1208

anatomy 38–41, 595–6, 597, 624 associated conditions 597 classification 597 epidemiology 596 investigations 163, 600–2, 625, 1058 management 602–11, 624–7 outcomes and complications 599–600, 609–10 pathophysiology 79, 80, 597–9, 624 symptoms and signs 600 tricuspid valve atresia ëÉÉ tricuspid atresia in ccTGA 504, 764, 773 stenosis 629, 656–7 straddling 614, 621–3 ëÉÉ=~äëç Ebstein’s anomaly truncal valve 908, 923, 927, 932 truncus arteriosus (TA) 907–33 aetiology 911–12 anatomy 41–3, 907–9, 912, 961, 963 associated conditions 910–11 classification 41, 909–10 epidemiology 912 investigations 156–7, 914–22 management 922–33 outcomes and complications 913, 927–33 pathophysiology 912–13 symptoms and signs 913–14 two-dimensional angiographic projections 206–7 two-dimensional echo modes 128–9

ultrasound cranial 330 point-of-care 331–2 prenatal diagnosis 197, 616 umbilical arteries/veins 61 univentricular heart 1057–70 in adults 348–50 pregnancy 449, 1070 anatomy 37–8, 1057 causes 616, 1057–8 epidemiology 1058 investigations 1060–3 management 254–7, 285–7, 1063–70 cryoablation 1126–9 Fontan ëÉÉ Fontan circulation heart transplantation 824, 1070, 1094, 1095–6 outcomes and complications 536, 808, 1069

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Index pathophysiology 80, 80–1, 1059 ëÉÉ=~äëç=áåÇáîáÇì~ä=Å~ìëÉë urea & electrolytes 245

vancomycin 124 vascular resistance 69, 71–5 ëÉÉ=~äëç pulmonary vascular resistance vascular rings and slings 979–94 anatomy 51–2, 979–80 associated conditions 983 double aortic arch 51, 981, 983, 985, 990–2 innominate artery compression syndrome 984, 988, 993 investigations 161, 200–1, 984–90 management 990–4 PA slings 982, 983, 989, 993 right aortic arch with left ligamentum 981, 983, 993 symptoms and signs 984 vasopressin 108 VATER complex/VACTERL 968 venae cavae, anomalies in heart transplantation 1095, 1096–7 veno-arterial (VA) ECMO 386, 388 cannulation 397–9, 401 cardiorespiratory support 406 circuit components 388–94 emergencies 418–21 Harlequin syndrome 396 left heart vent 403 veno-venous (VV) ECMO 386, 388 cannulation 399–400, 401, 402–3 emergencies 417–18, 420 recirculation 395–6, 418 venous compliance 83–4 ventilation 271–2, 324–5, 343, 349 ventricles ëÉÉ left ventricle; right ventricle; univentricular heart ventricular assist devices (VADs) 836, 1070, 1093–4, 1101 ventricular looping 8–10, 45 ventricular septal defects (VSD) 477–516 aetiology 491–2 anatomy 29–32, 483–8 associated conditions 493 in ccTGA 159, 504, 772 classification 478–83 conduction system 488–90, 788 definitions 477–8, 482–3 and DORV 477–8, 784–6, 788–92, 802–8 in Eisenmenger syndrome 32, 33, 495 epidemiology 493

1209

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1210

investigations 89, 136–9, 159, 177–8, 207, 496–501 management 927 closure 139, 231–4, 504–16, 722, 772, 1055–6 medical 501–2 palliative 502–4 outcomes and complications 494–5, 514–16 pathophysiology 77, 78, 86–7, 494 perimembranous 136, 483, 489, 499, 506, 509–11 with pulmonary atresia ëÉÉ pulmonary atresia with VSD symptoms and signs 495–6 in tetralogy of Fallot 680, 685, 687 and tricuspid atresia 597, 598 in truncus arteriosus 908 ventricular tachycardia 1120–2 vestibular defects 15, 454 vestibular spine 12, 27 visceral heterotaxy 7 vitamin K 105 volume overload 82–4, 85–8, 262–3 VSD ëÉÉ ventricular septal defects

Warden operation 557–9 warfarin 104–5 Waterston-Cooley shunt 1076–7 weight, normal 68 Williams syndrome 645, 871, 887 Wilms’ tumour 1150–1 Wolff-Parkinson-White (WPW) syndrome 576, 1113 X-rays ëÉÉ chest radiography

Yacoub remodelling 901, 902 ‘young people’ (16-17 years), consent 428–9, 433–4

Z-score 132–3, 618–19, 654

Key Questions CCS_Key Questions CCS v2.qxd 01/02/2022 13:11 Page 1

systematic overview of the important topics in contemporary

congenital cardiac surgical practice. This illustrated concise

text is a practical and clinically focused book that covers all

the key questions in congenital cardiac surgery. Whilst being

an ideal reference for cardiothoracic surgical trainees and

residents, especially when undertaking their cardiothoracic

surgery board examinations, this book is also of great value to

all the specialties involved in the peri-operative care of

congenital cardiac surgical patients, including congenital cardiac surgeons, paediatric cardiologists, congenital cardiac

anaesthetists, intensive care unit specialists, radiologists, nurses and physiotherapists.

Moorjani, Viola and Caldarone Key Questions in CONGENITAL CARDIAC SURGERY

Key Questions in Congenital Cardiac Surgery provides a

tf m

Key Questions in

CONGENITAL CARDIAC SURGERY

Narain Moorjani

Nicola Viola

Christopher A. Caldarone Foreword by William J. Brawn