ABC OF CLINICAL ELECTRO- CARDIOGRAPHY FRANCIS MORRIS JUNE EDHOUSE WILLIAM J BRADY JOHN CAMM BMJ Books ABC OF CLINICAL ELECTROCARDIOGRAPHY ABC OF CLINICAL ELECTROCARDIOGRAPHY Edited by FRANCIS MORRIS Consultant in Emergency Medicine, Northern General Hospital, Sheffield JUNE EDHOUSE Consultant in Emergency Medicine, Stepping Hill Hospital, Stockport WILLIAM J BRADY Associate Professor, Programme Director, and Vice Chair, Department of Emergency Medicine, University of Virginia, Charlottesville, VA, USA and JOHN CAMM Professor of Clinical Cardiology, St George’s Hospital Medical School, London © BMJ Publishing Group 2003 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording and/or otherwise, without the prior written permission of the publishers. First published in 2003 by BMJ Books, BMA House, Tavistock Square, London WC1H 9JR www.bmjbooks.com British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN 0 7279 1536 3 Typeset by BMJ Electronic Production Printed and bound in Spain by GraphyCems, Navarra Cover image depicts a chest x ray and electrocardiogram trace Composite image of an electrocardiogram trace showing termination of atrioventricular nodal re-entrant tachycardia, overlaid onto a false-coloured chest x ray With permission from Sheila Terry/Science Photo Library v Contents Contributors vi Preface vii 1 Introduction. I—Leads, rate, rhythm, and cardiac axis 1 Steve Meek, Francis Morris 2 Introduction. II—Basic terminology 5 Steve Meek, Francis Morris 3 Bradycardias and atrioventricular conduction block 9 David Da Costa, William J Brady, June Edhouse 4 Atrial arrhythmias 13 Steve Goodacre, Richard Irons 5 Junctional tachycardias 17 Demas Esberger, Sallyann Jones, Francis Morris 6 Broad complex tachycardia—Part I 21 June Edhouse, Francis Morris 7 Broad complex tachycardia—Part II 25 June Edhouse, Francis Morris 8 Acute myocardial infarction—Part I 29 Francis Morris, William J Brady 9 Acute myocardial infarction—Part II 33 June Edhouse, William J Brady, Francis Morris 10 Myocardial ischaemia 37 Kevin Channer, Francis Morris 11 Exercise tolerance testing 41 Jonathan Hill, Adam Timmis 12 Conditions affecting the right side of the heart 45 Richard A Harrigan, Kevin Jones 13 Conditions affecting the left side of the heart 49 June Edhouse, R K Thakur, Jihad M Khalil 14 Conditions not primarily affecting the heart 53 Corey Slovis, Richard Jenkins 15 Paediatric electrocardiography 57 Steve Goodacre, Karen McLeod 16 Cardiac arrest rhythms 61 Robert French, Daniel DeBehnke, Stephen Hawes 17 Pacemakers and electrocardiography 66 Richard Harper, Francis Morris 18 Pericarditis, myocarditis, drug effects, and congenital heart disease 70 Chris A Ghammaghami, Jennifer H Lindsey Index 75 William J Brady Associate Professor, Programme Director, and Vice Chair, Department of Emergency Medicine, University of Virginia, Charlottesville, VA, USA Kevin Channer Consultant Cardiologist, Royal Hallamshire Hospital, Sheffield David Da Costa Consultant Physician, Northern General Hospital, Sheffield Daniel De Behnke Department of Emergency Medicine, Medical College of Wisconsin, Milwaukee, WI, USA June Edhouse Consultant in Emergency Medicine, Stepping Hill Hospital, Stockport Demas Esberger Consultant in Accident and Emergency Medicine, Queen’s Medical Centre, Nottingham Robert French Department of Emergency Medicine, Medical College of Wisconsin, Milwaukee, WI, USA Chris A Ghammaghami Assistant Professor of Emergency and Internal Medicine, Director, Chest Pain Centre, Department of Emergency Medicine, University of Virginia Health System, Charlottesville, VA, USA Steve Goodacre Health Services Research Fellow, Accident and Emergency Department, Northern General Hospital, Sheffield Richard Harper Assistant Professor, Department of Emergency Medicine, Oregon Health and Science University, Portland, Oregon, USA Richard A Harrigan Associate Professor of Emergency Medicine, Temple University School of Medicine, Associate Research Director, Division of Emergency Medicine, Temple University Hospital, Philadelphia, PA, USA Stephen Hawes Department of Emergency Medicine, Wythenshaw Hospital, Manchester Jonathan Hill Specialist Registrar in Cardiology, Barts and the London NHS Trust Richard Irons Consultant in Accident and Emergency Medicine, Princess of Wales Hospital, Bridgend Richard Jenkins Specialist Registrar in General Medicine and Endocrinology, Northern General Hospital, Sheffield Kevin Jones Consultant Chest Physician, Bolton Royal Hospital Sallyann Jones Specialist Registrar in Accident and Emergency Medicine, Queen’s Medical Centre, Nottingham Jihad M Khalil Thoracic and Cardiovascular Institute, Michigan State University, Lancing, MI, USA Jennifer H Lindsey Fellow, Division of Cardiology, Department of Pediatrics, University of Virginia Health System, Charlottesville, VA, USA Karen McLeod Consultant Paediatric Cardiologist, Royal Hospital for Sick Children, Glasgow Steve Meek Consultant in Emergency Medicine, Royal United Hospitals, Bath Francis Morris Consultant in Emergency Medicine, Northern General Hospital, Sheffield Corey Slovis Professor of Emergency Medicine and Medicine, Vanderbilt University Medical Center, Department of Emergency Medicine, Nashville, TN, USA R K Thakur Professor of Medicine, Thoracic and Cardiovascular Institute, Michigan State University, Lancing, MI, USA Adam Timmis Consultant Cardiologist, London Chest Hospital, Barts and the London NHS Trust vi Contributors vii Preface To my mind electrocardiogram interpretation is all about pattern recognition. This collection of 18 articles covers all the important patterns encountered in emergency medicine. Whether you are a novice or an experienced clinician, I hope that you find this book enjoyable and clinically relevant. Francis Morris Sheffield 2002 1 Introduction. I—Leads, rate, rhythm, and cardiac axis Steve Meek, Francis Morris Electrocardiography is a fundamental part of cardiovascular assessment. It is an essential tool for investigating cardiac arrhythmias and is also useful in diagnosing cardiac disorders such as myocardial infarction. Familiarity with the wide range of patterns seen in the electrocardiograms of normal subjects and an understanding of the effects of non-cardiac disorders on the trace are prerequisites to accurate interpretation. The contraction and relaxation of cardiac muscle results from the depolarisation and repolarisation of myocardial cells. These electrical changes are recorded via electrodes placed on the limbs and chest wall and are transcribed on to graph paper to produce an electrocardiogram (commonly known as an ECG). The sinoatrial node acts as a natural pacemaker and initiates atrial depolarisation. The impulse is propagated to the ventricles by the atrioventricular node and spreads in a coordinated fashion throughout the ventricles via the specialised conducting tissue of the His-Purkinje system. Thus, after delay in the atrioventricular mode, atrial contraction is followed by rapid and coordinated contraction of the ventricles. The electrocardiogram is recorded on to standard paper travelling at a rate of 25 mm/s. The paper is divided into large squares, each measuring 5 mm wide and equivalent to 0.2 s. Each large square is five small squares in width, and each small square is 1 mm wide and equivalent to 0.04 s. The electrical activity detected by the electrocardiogram machine is measured in millivolts. Machines are calibrated so that a signal with an amplitude of 1 mV moves the recording stylus vertically 1 cm. Throughout this text, the amplitude of waveforms will be expressed as: 0.1 mV = 1 mm = 1 small square. The amplitude of the waveform recorded in any lead may be influenced by the myocardial mass, the net vector of depolarisation, the thickness and properties of the intervening tissues, and the distance between the electrode and the myocardium. Patients with ventricular hypertrophy have a relatively large myocardial mass and are therefore likely to have high amplitude waveforms. In the presence of pericardial fluid, pulmonary emphysema, or obesity, there is increased resistance to current flow, and thus waveform amplitude is reduced. The direction of the deflection on the electrocardiogram depends on whether the electrical impulse is travelling towards or away from a detecting electrode. By convention, an electrical impulse travelling directly towards the electrode produces an upright (“positive”) deflection relative to the isoelectric baseline, whereas an impulse moving directly away from an electrode produces a downward (“negative”) deflection relative to the Throughout this article the duration of waveforms will be expressed as 0.04 s = 1 mm = 1 small square Sinoatrial node Electrically inert atrioventricular region Left bundle branch Left anterior hemifascicle Left posterior hemifascicle Right atrium Left atrium Right ventricle Left ventricle Atrioventricular node Right bundle branch The His-Purkinje conduction system V5 V5 Role of body habitus and disease on the amplitude of the QRS complex. Top: Low amplitude complexes in an obese woman with hypothyroidism. Bottom: High amplitude complexes in a hypertensive man Speed : 25 mm/s Gain : 10 mm/mV Standard calibration signal 1