Clinical Electrocardiography: A Textbook (2012) PDF

Clinical Electrocardiography Bayes_ffirs.indd i 2/21/2012 1:00:04 PM  Companion website This book is accompanied by a website: www.wiley.com/go/bayes/electrocardiography...

Clinical Electrocardiography Bayes_ffirs.indd i 2/21/2012 1:00:04 PM  Companion website This book is accompanied by a website: www.wiley.com/go/bayes/electrocardiography The website includes: Helpful Multiple Choice Questions Bayes_ffirs.indd ii 2/21/2012 1:00:04 PM  Clinical Electrocardiography A Textbook FOURTH EDITION A N T O N I B AY É S D E L U N A Emeritus Professor of Cardiology, Autonomous University of Barcelona Senior Investigator, Institut Català Ciències Cardiovasculars Hospital Sant Pau Senior Consultant, Hospital Quiron Barcelona Spain With contributions from: A. B AY É S G E N I S , R. B R U G A D A , M. F I O L A N D W. Z A R E B A A John Wiley & Sons, Ltd., Publication Bayes_ffirs.indd iii 2/21/2012 1:00:04 PM  This edition first published 2012 © 2012 by John Wiley & Sons, Ltd Wiley-Blackwell is an imprint of John Wiley & Sons, formed by the merger of Wiley’s global Scientific, Technical and Medical business with Blackwell Publishing. 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Set in 9.25/12pt Palatino SPi Publisher Services, Pondicherry, India 1 2012 Bayes_ffirs.indd iv 2/21/2012 1:00:04 PM  Contents Preface, vii Part 4 Arrhythmias Foreword by Dr Eugene Braunwald, ix 14 Mechanisms, Classification, and Clinical Aspects Foreword by Dr Marcelo Elizari, x of Arrhythmias, 279 Recommended Reading, xi 15 Active Supraventricular Arrhythmias, 301 16 Active Ventricular Arrhythmias, 329 Part 1 Introductory Aspects 17 Passive Arrhythmias, 354 18 Diagnosis of Arrhythmias in Clinical Practice: 1 The Electrical Activity of the Heart, 3 A Step-by-Step Approach, 373 2 The History of Electrocardiography, 11 3 Utility and Limitations of the Surface Part 5 The Clinical Usefulness ECG: Present and Future, 16 of Electrocardiography 19 The Diagnostic Value of Electrocardiographic Part 2 The Normal ECG Abnormalities, 387 4 The Anatomical Basis of the ECG: From Macroscopic 20 The ECG in Different Clinical Settings of Ischemic Anatomy to Ultrastructural Characteristics, 25 Heart Disease, 402 5 The Electrophysiological Basis of the ECG: From Cell 21 Inherited Heart Diseases, 453 Electrophysiology to the Human ECG, 34 22 The ECG in Other Heart Diseases, 473 6 The ECG Recording: Leads, Devices, 23 The ECG in Other Diseases and Different and Techniques, 54 Situations, 494 7 Characteristics of the Normal Electrocardiogram: 24 Other ECG Patterns of Risk, 511 Normal ECG Waves and Intervals, 67 25 Limitations of the Conventional ECG: 8 Diagnostic Criteria: Sensitivity, Specificity Utility of Other Techniques, 523 and Predictive Value, 95 Index, 541 Part 3 Abnormal ECG Patterns Color plate section facing p. 276 9 Atrial Abnormalities, 103 10 Ventricular Enlargement, 123 11 Ventricular Blocks, 158 12 Ventricular Pre-excitation, 203 Companion website 13 Ischemia and Necrosis, 216 www.wiley.com/go/bayes/electrocardiography.com v Bayes_ftoc.indd v 2/21/2012 9:07:19 PM  Preface The 12-lead surface electrocardiogram (ECG) is the best the surface ECG. We also provide an overview of other technique to record the electrical activity of the heart and ECG techniques that we use to complement the diagnostic although it initially had a diagnostic value only, it has capacity of the 12-lead surface ECG. been demonstrated in recent years that it has very impor- After this preface, we provide a list of recommended tant clinical implications that are very useful for risk reading which will help the reader to better understand stratification as well as choosing the best management of the concepts discussed here. This list includes the classical different heart diseases. works that have greatly influenced me personally, in In this book we encompass all this new clinical knowl- addition to more recent books that provide new edge of the ECG with the aim of producing a clear text knowledge in all aspects of electrocardiology. After each that is easy to understand for clinicians and trainees. chapter there are also expanded references on the topics The first part is a review of the electrical activity of the discussed. heart, the history of electrocardiography, and its useful- Finally, this edition has an important innovation for ness and limitations. me. Although I have written the book alone, I have incor- In the second and third parts we discuss the origins porated contributions from A. Bayés-Genis, R. Brugada, of normal ECG patterns and the changes that various M. Fiol, and W. Zareba. They have completed and heart diseases produce in ECG morphology. This reviewed different sections. These doctors began as my includes the ECG patterns produced by atrial abnormali- fellows and collaborators and for the last 20 years have ties, ventricular enlargement, ventricular blocks, pre- excelled in different fields of cardiology that are very excitation, ischemia, and necrosis. In all these situations much related to the ECG. Their most valuable contribu- we identify the most important clinical implications tion throughout the years has been to inspire me to derived from these diagnoses. With regard to normal seach for new ideas in the field of electrocardiology. We and abnormal ECG patterns, we have attempted to have built a team that has adopted a similar philosophy reflect our conviction that ECG patterns should not be while adding new input and flavor to future editions memorized, but rather understood in terms of how they of the book. I am very much indebted to them for having are originated. The best way to demonstrate this is a accepted this task. deductive approach based on electrocardiographic–vec- My gratitude also goes out to other specific collab- torcardiographic correlations. However, when we under- orators including D. Goldwasser, J. Garcia Niebla, stand this correlation it is no longer necessary to record I. Cygankiewicz, A. Perez Riera, T. Martinez Rubio, VCG loops in order to improve on the information given M. Subirana, J. Guindo, V. de Porta, X. Viñolas, and by the ECG curves. J. Riba, among many others. My sincerest thanks to Part 4 deals with the ECG diagnosis of arrhythmias Professor E. Braunwald from United States who has been based on the changes produced by various arrhythmias in the greatest pioneer and master in so many fields of the surface ECG. A deductive approach is again the best Clinical Cardiology, and to Professor M. Elizari from way to diagnose arrhythmias. We briefly discuss the most Argentina, who also excels for his mastership in experi- important clinical implications of various arrhythmias. mental and clinical electrophysiology, both of whom have For further information, the reader should consult our been masters and friends and who have very generously book Clinical Arrhythmology (Wiley-Blackwell 2011), from written the forewords. which we have taken some of the ECG figures. The front cover illustrates the changes in the ECG Part 5 of the book deals with the clinical usefulness of recording of acute STEMI (see Figure 20.3) over the past electrocardiography. Here we explain the diagnostic 40 years. Underneath is the sillohuette of the “Sagrada value of different ECG alterations, the ECG changes in Familia” temple, “thrillering” arrhythmia (figure in itself), different heart diseases and situations, the ECG as a which still astonishes me every day as I make my way to marker of poor prognosis, and finally the limitations of work at my beloved Sant Pau Hospital in Barcelona. vii Bayes_fpref.indd vii 2/21/2012 7:55:39 PM  viii Preface I would also like to extend my thanks to Montse Saurí delve inside the book it will engage you like a passionate for her secretarial assistance, which she performed excel- novel. Finally, my sincerest thanks to Mr T. Hartman from lently and as usual, with a smile on her face. Wiley-Blackwell for his confidence in this project and also Finally I thank my family, especially my wife Maria to Cathryn Gates and Britto Fleming Joe for their excellent Clara, who has supported me patiently and lovingly work and patience during the long process to publish during so many hours of hard work in the last two years. their book. Now some words to my readers: do not be intimidated by the challenges of the first chapter. I hope that if you Antoni Bayés de Luna Bayes_fpref.indd viii 2/21/2012 7:55:39 PM  Foreword By Dr Eugene Braunwald Cardiovascular disease remains the leading cause of important help with this. It is in these parts of the book in mortality and serious illness in the industrialized world. which the enormous clinical experience of the author Efforts to improve cardiovascular diagnosis and therapy shines through, since it demonstrates how this very have never been more vigorous. However, despite the experienced clinician utilizes the electrocardiogram in development, sophistication, and improvement of a conjunction with the clinical profile and other diagnostic variety of imaging techniques in cardiovascular diagnosis, techniques in clinical evaluation. the electrocardiogram is still the most widely employed Professor Bayés de Luna has personally contributed to laboratory examination of the patient with known or many important areas of clinical electrocardiography, suspected heart disease. To aid in electrocardiographic including the description of the interesting syndrome of interpretation, Professor Bayés de Luna has authored this interatrial block with supraventricular arrhythmia and magnificent fourth edition of Clinical Electrocardiography: he has clarified our understanding and recognition of A Textbook. This volume, which builds upon its important intra-ventricular block. He has shown how Holter first three editions, will be enormously helpful to clinical recordings may be used to define patients at high risk of cardiologists, to internists responsible for the manage- cardiac arrhythmias. These subjects receive appropriate ment of patients with heart disease, and to cardiology attention. fellows. In the final analysis, the principal beneficiary of Clinical Electrocardiography is eminently readable and this excellent book will be the patient with established or successfully takes a middle course between the many suspected cardiovascular disease. brief manuals of electrocardiography which emphasize The author, Professor Bayés de Luna, is a master cardi- simple electrocardiographic pattern recognition, and the ologist who is the most eminent electrocardiographer in lengthy tomes which can be understood only by those the world today. As a clinician, he views the electrocardio- with a detailed background in electrophysiology. In an gram as the means to an end – the evaluation of the patient era of multi-authored texts which are often disjointed and with known or suspected heart disease – rather than as an present information that is repetitive and sometimes even end in itself. In accordance with this goal, the underlying contradictory, it is refreshing to have a body of informa- theme is to describe the clinical implications of electrocar- tion which speaks with a single authoritative, respected diographic findings. The core of this text is in parts 4 and voice. Clinical Electrocardiography is such a book. 5 on clinical arrhythmias and other cardiac conditions in which the electrocardiogram remains the principal diagnostic tool. The electrocardiogram is especially Eugene Braunwald, MD important in the recognition and localization of acute Harvard Medical School myocardial infarction, and this new edition provides Boston, MA, USA ix Bayes_flast.indd ix 2/18/2012 7:36:21 PM  Foreword By Dr Marcelo Elizari It was an unexpected and pleasant surprise to be invited resonance to a more refined judgment of the electrocardio- by Professor Antoni Bayés de Luna to write the gram. Hence, the electrocardiographic tracings analyzed introductory words for the fourth edition of his book on with all this information are extensively and easily clinical electrocardiography. Reviewing the foreword to understood in a better and more accurate manner. For all the previous editions makes it clear that the passage of these reasons, Bayés de Luna’s book is worth the highest time has not undermined the conviction of the comments merit since the reader will not only learn clinical and considerations expressed by those who were also electrocardiography but will also learn to interpret and awarded the honor to write the forewords to the Spanish apply it on a scientific basis. Moreover, Professor Bayés de and English versions of Antonio’s previous books. Luna has not limited himself to reproduce the works of The greatest impact on the field of electrocardiography others already presented in the literature but has also came in 1903 with Einthoven’s introduction of the string made original contributions to many subjects of the book. galvanometer. Thereafter, under the influence of Lewis As a cardiologist, Professor Bayés de Luna has occupied and Mackenzie in London and of Wenckebach and the most important seats of honour in the world cardiol- Rothberger in Vienna, the electrocardiogram emerged to ogy and has been a pioneer in the field. Notwithstanding, provide a valuable tool in the comprehension and he is, above all, a superb teacher and astute researcher clarification of cardiac arrhythmias. However, following with untiring devotion to the cause of electrocardiogra- the introduction and development of the clinical use of phy and arrhythmias. Electrocardiography continues to the chest leads by Wilson began a new era of great be an inexpensive, simple and highly reliable diagnostic progress in electrocardiography allowing the interpreta- tool for the cardiologist and this well planned book tion of the contour changes of the electrocardiogram for revives it and enhances the quality of its application. the diagnosis of physiologic and/or structural abnormali- Since there exist numerous texts, monographs and manu- ties of the heart under the whole spectrum of cardiac als on electrocardiography, what is then the reason for yet pathology. Thus, today the electrocardiogram may finally another book? The answer is very simple: there is always establish a correlation between the damage and the image. place for a good book and the need for a magisterial one This new edition of clinical electrocardiography will framing the scientific and technologic advances within immerse physicians and students in the underlying prin- the clinical practice. ciples and established facts of electrocardiography in a Sir William Osler one said: “To study medicine without simple and concise way focusing on those aspects of books is to sail an uncharted sea: whilst to study medicine immediate practical application. In fact, the book pro- only from books is not to go to sea at all.” vides enough theoretical and practical background to This book has been conceived from a clinician’s make the reader coherently acquainted with the reason- perspective and offers a balanced approach of great value ing involved in electrocardiographic interpretation. for students, residents and practitioners and it undoubt- Antoni Bayés de Luna, in single authorship, has edly deserves to be in every personal and public library. undertaken the challenge of bringing together the basic sciences, the clinical and pathologic knowledge, the elec- Marcelo Elizari, MD trocardiologic techniques, the hemodynamic findings and Head, Cardiology Service the application of nuclear medicine and nuclear magnetic Hospital Ramos Mejia, Buenos Aires, Argentina x Bayes_flast.indd x 2/18/2012 7:36:21 PM  Recommended Reading Bayés de Luna A, Cosín J (eds). Cardiac Arrhythmias. Pergamon Grant RP. Clinical Electrocardiography: The spatial vector approach. Press, 1978. McGraw-Hill, 1957. Braunwald’s. Heart diseases. A textbook of Cardiovascular Lipman BS, Marrie E., Kleiger RE. Clinical Scalar Electrocardiography, Medicine. 9th edn. Bonow RO, Mann DL, Zipes, DP, Libby P. 6th edn. Year Book Medical Publishers, 1972. Elsevier Saunders Pu. 2012. Macfarlane PW, Lawrie TDV (eds). Comprehensive Electrocardiology. Camm AJ, Lüscher TF, Serruys PW (eds). The ESC Textbook of Pergamon Press, 1989. Cardiovascular Medicine. Blackwell Publishing, 2006. Piccolo E. Elettrocardiografia e vettocardigorafia. Piccin Editore, Cooksey JD, Dunn M, Marrie E. Clinical Vectorcardiography and 1981. Electrocardiography. Year Book Medical Publishers, 1977. Rosenbaum M, Elizari M, Lazzari J. Los hemibloqueos. Editorial Fisch C, Knoebel S. Electrocardiography of Clinical Arrhythmias. Paidos, 1968. Futura, 2000. Sodi Pallares D, Bisteni A, Medrano G. Electrocardiografia y Friedman HH. Diagnostic Electrocardiography and Vectorcardiography, vectorcardiografia deductiva. La Prensa Médica Mexicana, 3rd edn. McGraw-Hill, 1985. 1967. Fuster V, Walsh RA, Harrington RA (eds). Hurst’s The Heart, Surawicz B, Knilans TK. Chou’s Electrocardiography in Clinical 13th edn. McGraw-Hill, 2010. Practice, 6th edn. WB Saunders Company, 2009. Gerstch M. The ECG: A two step approach for diagnosis. Springer Tranchesi J. Electrocardiograma normal y patológico. La Medica, 1968. 2004. Wagner GS. Marriott’s Practical Electrocardiography, 10th edn. Guidelines of AHA/ACC/HRS. Kligfield P, Gettes L, Wagner G, Lippincott Williams & Wilkins, 2001 Mason J, Surawicz B, Rautaharju P, Hancock E, et al. Circulation Zipes D, Jalife J. Cardiac Electrophysiology. From cell to bedside. 2007–2009. WB Saunders. Philadelphia, 2004. xi Bayes_flast.indd xi 2/18/2012 7:36:21 PM  Short axis (transverse) Vertical long axis Horizontal long axis (sagittal-like) 1 2 3 Plate 1 The three heart planes used by nuclear medicine experts (and other imaging techniques) to transect the heart: (1) the short-axis (transverse) view, (2), the vertical long-axis view (VLA) (oblique sagittal-like)and (3) the horizontal long-axis (HLA) view. A B Plate 2 (A) Normal scanner multislice showing normal LAD and LCX arteries. The latter is partially covered by the left appendix. The arrow points to the LAD. (B) Normal case: showing a normal dominant RCA. Plate 3 Patient with atypical precordial pain and a clearly positive exercise test (marked ST-segment depression) without pain during the test. The SPECT test was normal (see homogeneous uptake in red), as well as coronary angiography. It is a clear example of a false-positive exercise test. Clinical Electrocardiography: A Textbook, Fourth Edition. Antoni Bayés de Luna. © 2012 John Wiley & Sons, Ltd. Published 2012 by John Wiley & Sons, Ltd. Bayes_bins.indd 1 2/18/2012 7:33:11 PM  Plate 4 ECG with superoanterior hemiblock (SAH) and mild ST/T abnormalities. The patient presented with various myocardial infarctions—septal, anterior, and lateral—detected by contrast-enhanced cardiovascular magnetic resonance (CE-CMR) that masked each other. Plate 5 Rupture of inferior wall in a patient after 7 days of inferior myocardial infarction (MI) due to LCX occlusion. See the echocardiog- raphy showing large hematic pericardial effusion and the pathological aspect of the rupture. In spite of that, the ECG shows relatively small ECG changes (mild ST segment elevation in I and VL and mirror image of ST segment depression in V1–V3 that remains after a week of MI). Bayes_bins.indd 2 2/18/2012 7:33:16 PM  Chapter 1 The Electrical Activity of the Heart Basic concepts we will see that the repolarization process in this case starts in the opposite place to that of depolarization. This The heart is a pump that sends blood to every organ in explains why the repolarization of a single contractile cell the human body. This is carried out through an electrical is represented by a negative wave, whereas the repolari- stimulus that originates in the sinus node and is transmit- zation of the left ventricle expressing the human electro- ted through the specific conduction system (SCS) to cardiogram (ECG) is represented by a positive wave contractile cells. (Figure 5.28) (see Chapter 5, from cellular electrogram to During the rest period, myocardial cells present an equi- human ECG). librium between the positive electrical charges outside and the negative charges inside. When they receive the stimulus propagated from the sinus node, the activation How can we record the electrical process of these cells starts. The activation of myocardial activity of the heart? cells is an electro-ionic mechanism (as explained in detail in Chapter 5) that involves two successive processes: There are various methods used to record the electrical depolarization, or loss of external positive charges that activity of the heart. The best known method, the one we are substituted by negative ones, and repolarization, examine in this book, is electrocardiography. An alter- which represents the recovery of external positive charges. native method, rarely used in clinical practice today but The process of depolarization in a contractile myocar- very useful in understanding ECG curves and therefore dial cell starts with the formation of a depolarization helpful in learning about ECGs, is vectorcardiography. dipole comprising a pair of charges (−+) that advance The latter and other methods will be briefly dis- through the surface cell like a wave in the sea, leaving cussed in Chapter 25. These include, among others, behind a wave of negativity (Figure 1.1A). When the body mapping, late potentials, and esophageal and entire cell is depolarized (externally negative), a new intracavitary electrocardiography. In addition, normal dipole starting in the same place is formed. This is ECGs can be recorded during exercise and in long known as a dipole of repolarization (+−). The process of recordings (ECG monitoring and Holter technology). repolarization, whereby the entire cell surface is supplied For more information about different techniques see with positive charges, is then initiated (Figure 1.1B). Chapter 3, The Future of Electrocardiography or consult The expression of the dipoles is a vector that has its our book Clinical Arrhythmology (Bayés de Luna 2011), head in the positive charge and tail in the negative one. and other ECG reference books (Macfarlane and Lawrie An electrode facing the head of the vector records positiv- 1989; Wagner 2001; Gertsch 2004; Surawicz et al. 2008) ity (+), whereas when it faces the tail it records negativity (see page X). (−) (Figures 1.1–1.3; see also Figures 5.24, 5.25, and 5.28). The deflection originating with the depolarization process is quicker because the process of depolarization is an What is the surface ECG? active one (abrupt entry of Na ions, and later Ca) and the process of repolarization is much slower (exit of K) The ECG is the standard technique used for recording the (see Chapter 5, Transmembrane action potential). electrical activity of the heart. We can record the process If what happens in one contractile cell is extrapolated of depolarization and repolarization through recording to the left ventricle as the expression of all myocardium, electrodes (leads) located in various places. Clinical Electrocardiography: A Textbook, Fourth Edition. Antoni Bayés de Luna. © 2012 John Wiley & Sons, Ltd. Published 2012 by John Wiley & Sons, Ltd. 3 Bayes_c01.indd 3 2/27/2012 7:04:38 PM  4 Introductory Aspects A D E P O Sense of ph. L Vector A R Dipole –+ ++++++ –––––––+ I Z +––––––– +++++++– A T I O N B R Sense of ph. E P Vector O L Dipole +––––––– +++++++ – Figure 1.1 Depolarization and repolari- A R – + + + + + ++ ––––––– + zation of the dipole in an isolated I Z myocardium cell. We see the onset and A T end of the depolarization and repolariza- I O tion processes and how this accounts for N the positivity and negativity of corre- sponding waves (see text and Chapter 5). A B C –– + 1 + + 2 – – 3 + 2 + P 1 3 T QRS Figure 1.2 The origin of P, QRS, and T deflections. When an electrode faces the head (+) of a vector of depolariza- P T tion (P, QRS) or repolarization (T), it records positivity. When an electrode faces the tail of a vector (−), it records negativity. Atrial repolarization is D hidden in the QRS (shadow area) QRS (see text and Chapter 5). The depolarization process of the heart, atria and ven- (vector). The process of ventricular depolarization, tricles (see Chapter 5 and Figures 5.16 and 5.18) starts which occurs later when the stimulus arrives at the with the formation of a dipole of depolarization (− +), ventricles, usually presents as three deflections ( ), known which has a vectorial expression ( ) that advances as the QRS complex, caused by the formation of three con- through the surface of the myocardium and seeds the secutive dipoles (vectors). The first vector appears as a entire surface of the myocardial cells with negative small and negative deflection because it represents the charges. A recording electrode facing the head of the vec- depolarization of a small area in the septum and is usu- tor records positivity (Figure 1.2). Later, the repolariza- ally directed upwards and to the right and recorded from tion process starts with the formation of a repolarization the left ventricle as a small negative deflection (“q”). Next, dipole (+ −), which also has a vectorial expression. During a second important and positive vector is formed, repre- this process the positive charges of the outside surface of senting the R wave. This is the expression of depolariza- the cells are restored. tion in most of the left ventricular mass. The head of this These two processes relate to specific characteristics vector faces the recording electrode. Finally, there is a of the atria and ventricles (Figure 1.2). The process of third small vector of ventricular depolarization that depo- atrial depolarization, when recorded on the surface of the larizes the upper part of the septum and right ventricle. It body in an area close to the left ventricle (Figure 1.2), is directed upwards and to the right and is recorded by presents as a small positive wave called the P wave ( ). the recording electrode in the left ventricle zone as a small This is the expression of the atrial depolarization dipole negative wave (“s”) (Figure 1.2). Bayes_c01.indd 4 2/27/2012 7:04:38 PM  The Electrical Activity of the Heart 5 A B FP FP I (X) I (X) VF (Y) VF (Y) V6 V6 HP HP V2 (Z) V2 (Z) C D Figure 1.3 Four locations of a vector FP FP and their projection in frontal (FP) and horizontal planes (HP). A and B have the same projection in FP but not in HP. C and D has the same projection I (X) I (X) in HP but not in FP. Different positive and negative morphologies appear according to these projections. The locations of the orthogonal leads X, Y VF (Y) VF (Y) and Z perpendicular to each other are similar to I, VF, and V2 leads. Vertical lines correspond to the positive V6 V6 hemifields of VF and V2, and horizontal lines correspond to the positive hemifields of leads I and V6. HP HP FP lead I (X) = 0°; VF (Y) = +90°; HP V2 (Z) V2 (Z) V2 (Z) = +90°; V6 = 0°. After depolarization of the atria and ventricles, the The successive recording of the ECG is linear and the process of repolarization starts. The repolarization of distance from one P–QRS–T to another can be measured in the atria is usually a smooth curve that remains hidden time. The frequency of this sequence is related to heart rate. within the QRS complex. The ventricular repolarization The heart is a three-dimensional organ. In order to see curve appears after the QRS as an isoelectric ST segment its electrical activity on a two-dimensional piece of paper and a T wave. This T wave is recorded as a positive wave or screen, it must be projected from at least two planes, from the left ventricle electrode because the process of the frontal plane and the horizontal plane (Figure 1.3). ventricular repolarization, as already mentioned and The shape of the ECG varies according to the location later explained in detail (see Chapter 5, From cellular (lead) from which the electrical activity is recorded. In electrogram to the human ECG and Figures 5.24 and general, the electrical activity of the heart is recorded 5.25), appears very differently from what happens in an using 12 different leads: six on the frontal plane (I, II, III, isolated contractile cell (see Figure 5.9). Repolarization VR, VL, VF), located from +120° to −30° (the VR is usually starts on the opposite side to that of depolarization. Thus, recorded in the positive part of the lead that is located the recording electrode faces the positive part of the in −150°) (see Figures 6.10 and 6.11), and six on the hori- dipole, or head of the vector, and will record a positive zontal plane (V1–V6) located from +120° to 0° (see Chapter deflection, even though the dipole moves away from it 6, Leads and Figures 6.10 and 6.13). (Figures 1.2C; see also Figures 5.24 and 5.25). Therefore, Each lead has a line that begins where the lead is repolarization of the left ventricle in a human ECG placed, 0° for lead I or +90° for lead VF in the frontal plane (the T wave) is recorded as a positive wave, just as occurs (FP) and 0° for lead V6 and +90° for lead V2 in the hori- with the depolarization complex (QRS) in leads placed zontal plane (HP), for example (see Figure 6.10), and ends close to the left ventricle surface ( ). at the opposite side of the body, passing through the Bayes_c01.indd 5 2/27/2012 7:04:39 PM  6 Introductory Aspects A B C I I I 1 3 P 2 QRS FP HP O E P O J T X X E T J D Figure 1.4 The origin of P, QRS, and T loops. The vectorcardiographic curve Y Z is the union of the heads of multiple vectors that form during the consecutive processes of depolarization and EO = P loop; OJ = QRS loop; JE = T loop; OJ = ST vector repolarization (see text and Figure 5.23). center of the heart. By tracing each perpendicular line as in the sagittal plane. Made of the joined heads of that passes through the center of the heart, we may the multiple vectors that form during the consecutive divide the electrical field of the body into two hemi- processes of depolarization and repolarization of the fields for each lead, one positive and one negative heart (Figure 1.4), VCG loops are obtained from three (Figure 1.3). A vector that falls into the positive hemifield orthogonal (perpendicular to each other) leads, X, Y, and records positivity, while one that falls into the negative Z, which are placed in positions similar to those of leads hemifield records negativity. When a vector falls on the I, VF, and V2, respectively (see Figure 1.3 and Chapter 25). line of separation between hemifields, an isodiphasic The VCG curve is a plot of voltage against voltage of the curve is recorded (see Chapter 6, Figures 6.14 and 6.16). different waves generated by the heart (P, QRS, T loops), The different vectors are recorded as positive or negative and therefore it is not possible to measure the time depending on whether they are projected onto positive or between the beginning of the P loop and the beginning of negative hemifields of different leads (Figures 1.3 and 1.5). the QRS loop (PR interval), or the beginning of QRS and This is a key concept for understanding the morphology the end of the T loop (QT interval). However, we can of ECG curves in different leads and is explained in interrupt the loops of P, QRS, and T by cutting the tracing Chapter 6 in more detail (Figure 6.14). every 2.5 ms, which allows the duration of each loop to be measured (see Figures 10.6–10.10 and 10.22–10.25). One advantage of the VCG is that the different rotations The ECG and its different morphologies can be explained using the following sequence: of the loop can be visualized, which is important to know Dipole → Spatial vectors → Projection in frontal (FP) if the stimulus follows a clockwise or counter-clockwise and horizontal (HP) planes rotation when one complex or wave is diphasic. Figure 1.5B shows how the mean vector of a loop directed to +0° that falls within the limit between the positive or negative What is vectorcardiography? hemifields in lead “Y” (VF) may present a +−( ) or a −+ ( ) deflection. The direction of the mean vector of the loop The vectorcardiogram (VCG) is the closed curve or loop does not solve one important problem: a +− deflection is that records the entire pathway of an electrical stimulus normal, but a −+ deflection may be the expression of myo- from the depolarization of the atria (P loop) and ventri- cardial infarction. The correct morphology will be shown cles (QRS loop) to the repolarization of the ventricles by the direction of loop rotation, however (Figure 1.5). In (T loop). These loops are recorded in FP and HP, as well addition, the mean vector of the QRS loop, which Bayes_c01.indd 6 2/27/2012 7:04:39 PM  The Electrical Activity of the Heart 7 A B – en I y VF + en I – en VF b I I – en I a + en VF + en I y VF VF VF +90˚ +90˚ a b C D a b I I Figure 1.5 The concept of the hemifield. We see how a morphology may be +− or −+ with the same vector but a different b a loop rotation (B and C) (A and B). The recording of the initial and terminal deflections of qRs are well understood VF VF with the correlation of the loop and hemifields in D (see I and VF). +90˚ +90˚ VF VF VF VF V2 V2 V2 V2 Figure 1.6 Correlation of a vectorcardio- graphic loop with an electrocardiographic morphology in VF and V2. expresses the sum of all vectors of depolarization, does and end) that falls in the opposite hemifield of the main not indicate the direction of the small initial and final vector can explain the complete ECG morphology with forces when these forces are opposed to a mean vector initial (q) and final small (s) deflections (Figures 1.5 and (Figure 1.5). However, the small part of the loop (beginning 1.6; see also Figures 7.10 and 7.11). Bayes_c01.indd 7 2/27/2012 7:04:40 PM  8 Introductory Aspects correlation) is understood and used, we are able to derive The VCG can be described using the following sequence: the same information that VCGs provide by just looking The head of multiple vectors → Spatial loops → Projection in FP and HP at the ECG. For example, it has been reported (Benchimol et al. 1972) that VCGs are essential for the diagnosis of superoanterior fascicular block (hemiblock) associated with inferior myocardial infarction (MI). However, as ECG–VCG correlation discussed in Chapter 13, the same information can be obtained from the ECG if we recognize the exact path- Bearing in mind the abovementioned information, it is way of the stimulus in both cases (inferior MI alone or clear that to better understand the morphology of an associated with hemiblock) and we make a good ECG– ECG we must consider the stimulus pathway through VCG correlation (see Figure 13.98). Furthermore, many the heart (VCG loop) in different normal and pathologi- details provided by amplified VCG loops (the degree of cal conditions and identify the projection of these loops ST shifts, onset of pre-excitation, characteristics of the P in FP and HP. It is important to understand how the wave, etc.) can also be obtained from surface ECGs different parts of the loop that fall into the positive or through amplification of the ECG waves, if necessary negative hemifields of each lead correspond to the differ- (see Figures 9.20 and 13.24) (Bayés de Luna 1998; Bayés de ent deflections of an ECG curve (Figures 1.5 and 1.6; see Luna and Fiol-Sala 2008). also Figures 4.60 and 4.61) (ECG–VCG correlation). This The VCG is not useful in the diagnosis of arrhyth- allows the ECG curves to be drawn from the VCG loops mias. Even information about the ectopic P wave may be and vice versa. correctly obtained from ECG curves. Computerization of ECG data and not of VCG has become dominant and, despite current limitations, it has The key concepts around how ECG curves can be a great future. However, as we see later on (Chapter 3, obtained from the VCG loops and vice versa (ECG–VCG Limitations) it is necessary to improve the results with correlation) are defined using the following sequence: better technology and the inclusion of new data (clinical Dipole → Vector → Loop → Projection in different hemifields → ECG patterns setting, etc.). The ECG is used more than the VCG for estimating the size of an MI (Selvester QRS scoring system) (Selvester et al. 1972; Wagner et al. 1982). However, in the era of ECG- Why do we record ECG curves imaging correlations it is necessary to improve the methodol- and not VCG loops? ogy of QRS score measurement to obtain a better correlation with contrast-enhanced cardiovascular magnetic resonance Although ECG–VCG correlation is used in this book to measurements (see later and Chapter 3, Limitations). explain how the different ECG patterns are produced, ECG and not VCG patterns have already been the recording of vectorcardiographic loops for diagnostic correlated with imaging techniques, especially corona- purposes is rarely used in clinical practice at present. graphy and contrast-enhanced cardiovascular magnetic There are many reasons for the superiority of ECG resonance (CE-CMR). The correlation of ECG patterns curves over VCG loops, the main ones being as with coronagraphy has allowed us to better locate follows: the occlusion and determine the severity of ischemia in The established diagnostic criteria of ECG in differ- different types of acute coronary syndromes (leads with ent pathologies are more defined and agreed-upon, different ST shifts) (Sclarovsky 1999; Wellens et al. 2004; compared with the VCG criteria. They are also easier Bayés de Luna and Fiol-Sala 2008). It is also possible to to apply. Furthermore, it has not been clearly demon- obtain better classification and location of Q-wave MI strated by experts in ECG/VCG interpretation that VCG (leads with abnormal Q or R waves as mirror image) criteria provide more diagnostic information than that using CE-CMR–ECG correlation (Bayés de Luna et al. taken from ECGs, even in an era when VCG criteria were 2006a, 2006b; Cino et al. 2006; Bayés de Luna 2007; Rovai most used (Simonson et al. 1967; Rautaharju 1988; Van et al. 2007; Bayés de Luna and Fiol-Sala 2008; Van der Weg Bemmel et al. 1992). et al. 2009). Similar correlations have not been done with VCG loops do not show an appreciation of time VCG loops. Currently, a good estimation of infarction size (PR and QT interval), as previously mentioned. using CE-CMR has been obtained (Kim et al. 1999; Moon The ECG curves–VCG loop correlation gives us all et al. 2004). However, the correlation of infarct size meas- the detailed information obtainable from VCG loops. urement performed by surface ECG (QRS scoring system) In fact, if the origin of the ECG curve interpretation (Selvester et al. 1972) with CE-CMR is not very consistent, based on the projection of VCG loops in the positive and the CE-CMR shows larger values than the QRS score and negative hemifields of different leads (ECG–VCG estimation (Weir et al. 2010). We hope that in the future Bayes_c01.indd 8 2/27/2012 7:04:40 PM  The Electrical Activity of the Heart 9 it will be possible to improve these results with new curves of an ECG. Both ECG curves and VCG loops, equations (see Chapter 3, The future). Good results however, are completely connected so that the ECG curve have also recently been shown by Montant et al. (2010) may be easily deduced from the VCG loop, and vice using a contrast-enhanced three-dimensional echocardi- versa (see ECG–VCG correlation, Figures 1.5 and 1.6). As ography compared with CE-CMR to identify and quantify already mentioned, this approach is considered to be the myocardial scars (positive and negative predictive best way to understand both the normal ECG and all the value (PV) > 90%). morphological changes that different pathologies intro- Young physicians should realize that ECG–VCG duce to the ECG. correlation is a basis for better understanding ECG The correlation between VCG loops and projection curves. This does not mean that they need to know specific of this on different hemifields to understand the ECG VCG criteria, such as the number of milliseconds the loop pattern (dipole → vector → loop → hemifield sequence) is going up and down, because these data obtained from will no doubt remain a cornerstone of the teaching of the the VCG does not add too much diagnostic information. ECG (Grant and Estes 1952; Sodi-Pallares and Calder Therefore, a recorded VCG loop alone is not clinically 1956; Cooksey et al. 1957; Cabrera 1958; Bayés de Luna efficient. However, it is important to remember that the 1998; Gertsch 2004). ECG–VCG correlation is a key point for better under- standing of how ECG curves are originated (see below). Currently, there are very few devices that still correctly 1. The deduction of the ECG from the VCG loops is record VCG curves. At the Electrocardiology Congress crucial to better recognizing how both normal ECG held in 2009, titled with the subheading “VCG sympo- curves and the many ECG changes found in different sium,” it was decided that this subheading should be heart diseases and under special circumstances suppressed (Macfarlane 2009). “Signum temporis” stated originate. the first organizers (Sobieszczańska and Jagielski 2010). 2. Although the deductive method for teaching elec- The number of VCG papers published in Medline in the trocardiography is fundamentally based on the cor- 1970s and 1980s reached more than 800 per decade; today, relation that exists between ECG curves and VCG in the first decade of this century, there are fewer than 60. loops, VCG criteria are not used for diagnosis. It appears that the VCG loops taken from the orthogo- 3. In the majority of diagrams used to show the use- nal leads do not give much more information from a clini- fulness of VCG loop–ECG wave correlations, the path- cal point of view than a conventional 12-lead surface way of the electrical stimulus is represented as a curve ECG. They are also time consuming and need special with a continuous line. When we record original trac- devices. Although we presume that VCG devices will no ings, however, dashes every 2.5 ms in the VCG loops longer serve as an independent tool in the future, the are shown. Examples of this may be seen throughout VCG loops are very useful for teaching purposes and for this book (see, for example, Figures 11.25, 11.36, and some diagnostic, prognostic, and research purposes (Kors 11.40). et al. 1990, 1998; Rautaharju et al. 2007; Pérez Riera 2009; Lazzara 2010). It may be that incorporating VCG loops synthesized directly from 12-lead surface ECG recordings would be an interesting option (see Chapter 3). References Bayés de Luna A. Textbook of Clinical Electrocardiography. Futura, Why do we use ECG–VCG correlations 1998. to understand ECG patterns? Bayés de Luna A. New heart wall terminology and new electrocar- diographic classification of Q-wave myocardial infarction based Electrocardiography and vectorcardiography are two on correlations with magnetic resonance imaging. Rev Esp methods for recording the electrical activity of the heart. Cardiol 2007;60:683. As explained above, the ECG is a linear curve based on Bayés de Luna A. Clinical Arrhythmology. Wiley-Blackwell, 2011. the positive and negative deflections recorded when an Bayés de Luna A, Fiol-Sala M. Electrocardiography in Ischemic Heart Disease. Blackwell Futura, 2008. electrode faces the head or the tail of a depolarization and Bayés de Luna A, Wagner G, Birnbaum Y, et al. A new terminology repolarization dipole, the expression of which is a vector, for left ventricular walls and location of myocardial infarcts that from leads placed in frontal and horizontal planes. The present Q wave based on the standard of cardiac magnetic reso- VCG is a loop that represents the outline of the joining of nance imaging: A statement for healthcare professionals from a multiple dipoles (vectors) formed along the electrical committee appointed by the International Society for Holter and stimulus pathway through the heart. The projection of Noninvasive Electrocardiography. Circulation 2006a;114:1755. these loops in frontal and horizontal planes is a closed Bayés de Luna A, Cino JM, Pujadas S, et al. Concordance of curve that is different in morphology from the linear electrocardiographic patterns and healed myocardial infarction Bayes_c01.indd 9 2/27/2012 7:04:40 PM  10 Introductory Aspects location detected by cardiovascular magnetic resonance. Am Pérez Riera A. Learning easily Frank vectorcardiogram. Editora J Cardiol 2006b;987:443. Mosteiro. Sao Paulo, 2009. Benchimol A, Desser KB, Schumacher J. Value of the vectorcardio- Rautaharju PM. A hundred years of progress in electrocardio- gram for distinguishing left anterior hemiblock from inferior graphy. 2: the rise and decline of vectorcardiography. Can J infarction with left axis deviation. Chest 1972;61:74. Cardiol 1988;4:60. Braunwald E, Bonow RO, Mann DL, Zippes D, Libby P. Heart Rautaharju P, Prineas R, Zhang Z-M. A simple procedure for esti- Disease, 11th edn. Elsevier Saunders, 2012. mation of the spatial QRS/T angle from the standard 12-lead Cabrera E. Teoría y práctica de la Electrocardiografía. Edic INC México, ECG. J Electrocardiol 2007;40:300. La Prensa Médica Mexicana, 1958. Rovai D, Di Bella G, Rossi G, et al. Q-wave prediction of myocardial Camm J, Luscher TF, Serruys PW (eds). The ESC Textbook of infarct location, size and transmural extent at magnetic reso- Cardiovascular Medicine. Blackwell, 2006. nance imaging. Coronary Artery Dis 2007;18:381. Cino J, Pons-Lladó G, Bayés de Luna A, et al. Utility of contrast- Sclarovsky S. Electrocardiography of Acute Myocardial Ischaemic enhanced cardiovascular magnetic resonance (CE-CMR) to Syndromes. Martin Dunitz, 1999. assess how likely is an infarct to produce a typical ECG pattern. Selvester RH, Wagner JO, Rubin HB. Quantitation of myocardial J Cardiovasc Magn Reson 2006;8:335. infarct size and location by electrocardiogram and vectorcardio- Cooksey J, Dunn M, Massie E. Clinical Vectorcardiography and gram. In Snelin HA (ed.) Boerhave Course in Quantitation in Electrocardiography, 2nd edn. YearBook MP, 1957. Cardiology. Leyden University Press, 1972, p. 31. Fuster V, Walsh RA, Harrington RA (eds). Heart’s. 13th edition. Simonson E, Tune N, Okamoto N, et al. Vectorcardiographic McGraw-Hill, 2010. criteria with high diagnostic accuracy. Z Kreislaufforsch Gertsch M. The ECG: A two step approach for diagnosis. Springer, 2004. 1967;56:1243. Grant R, Estes EH. Spatial Vector Electrocardiography. Blakston Co., Sodi-Pallares D, Calder R. New Bases of Electrocardiography. Mosby, 1952. 1956. Kim RJ, Fieno D, Parrish T, et al. Relationship of CE-CMR to irre- Sobieszczańska M, Jagielski J. The International Society of versible injury, infarct age and contractile function. Circulation Electrocardiology: A 50 year history originated in Poland. 1999;100:1992. J Electrocardiol 2010;43:187. Kors JA, Van Herpen G, Sitting AG, et al. Reconstruction of the Surawicz B, Knilans TK, Te-Chuan Chou. Chou’s Electrocardiography Frank VCG from the standard ECG leads. Eur Heart J in Clinical Practice, 6th edn. Saunders, 2008. 1990;11:1083. Van Bemmel JH, Kors JA, van Herpen G. Combination of diagnos- Kors JA, De Bruyne MC, Hoes AW. T axis as an independent indi- tic classifications from ECG and VCG computer interpretations. cator of risk of cardiac events in elderly people. The Lancet J Electrocardiol 1992;25(suppl):126. 1998;352:361. Van der Weg K, Bekkers S, Gorgels A, et al. The R in V1 in non- Lazzara R. Spatial vectorcardiogram to predict risk for sudden anterior wall infarction indicates lateral rather than posterior arrhythmic death: Phoenix risen from the ashes. Heart Rhythm involvement. Results from ECG/MRI correlations. Eur Heart 2010;1614. J 2009;30(suppl):P2981. Macfarlane PW. Interview with Peter W Macfarlane by Ljuba Wagner GS (ed.) Marriott’s Practical Electrocardiography, 10th edn. Bacharova. J Electrocardiol 2009;42:223. Lippincott Williams & Wilkins, 2001. Macfarlane PW, Lawrie TDV (eds). Comprehensive Electro- Wagner G, Freye C, Palmer ST, et al. Evaluation of QRS scoring cardiography. Pergamon Press, 1989. system for estimating myocardial infarction size. Circulation Montant P, Chenot F, Gaffinet C, et al. Detection and quantification 1982;65:347. of myocardial scars using CE-3D-echocardiography Circulation Weir R, Martin T, Wagner G. Comparison of infarct size and LVEF CV Imag 2010;3:415. by CE-CMR and ECG scoring in reperfused anterior STEMI. Moon JC, De Arenaza DP, Elkington AG, et al. The pathologic basis J Electrocardiol 2010;43:230. of Q-wave and non-Q-wave myocardial infarction: a cardiovas- Wellens H, Doevedans P, Gorgels A. The ECG in Acute Myocardial cular magnetic resonance study. J Am Coll Cardiol 2004;44:554. Infarction and Unstable Angina. Kluwer Academic, 2004. Bayes_c01.indd 10 2/27/2012 7:04:41 PM  Chapter 2 The History of Electrocardiography Electrical phenomena have been observed by humans for he was able to predict the correct form of the human ECG more than 2500 years. Thales of Miletus in Greece (sixth (Figure 2.2C) and he proved his findings using a string century BC) noted that amber rubbed with wool attracts galvanometer developed in 1902. light objects. In fact, the ancient Greek name for amber is Einthoven’s string galvanometer (Figure 2.2D) consisted elektron. As early as the end of the sixteenth century, the of a silver-coated quartz filament suspended between the English physician William Gilbert postulated the relation- two poles of an electromagnet. The fixed magnetic field ship between electricity and magnetism. He was followed created by the electromagnet established a strong constant by Benjamin Franklin, who discovered the lightning rod in about 1750. At the end of the eighteenth century, the Italian Luigi Galvani discovered that electricity in animals is generated via “an electric fluid.” Galvani believed that electrical stimulus preceded muscle contraction. He would become the world’s first electrophysiologist (Rosen 2002; Rosen and Janse 2006). The electrical activity of the heart was first recorded in the late nineteenth century by Augustus D Waller (Figure 2.1), who in 1887 recorded the curves of electrical activity of the human heart using saline-filled tube electrodes and the capillary electrometer developed by Gabriel Lippmann (Figure 2.2A,B). The first human ECG was taken to Thomas Goswell, a technician in his laboratory. Initially he used his dog Jimmy to perform ECG recordings, but was accused of cruelty to animals because of the belts used and the practice of putting the dog’s extremities in saline water. Although Waller was credited with being the first to record the electrical activity of the heart, he did not have much faith in the usefulness of electrocardiography, stating “I do not imagine the electrocardiography is likely to find any very extensive use … just occasionally to record some rare anomaly of cardiac action” (Burch and DePasquale 1964). In the last years of the nineteenth century, Willem Einthoven (1860–1927) (Figure 2.3) (Einthoven 1912; Snellen 1977; Moukabary 2007; Kligfield 2010) began to study animal action potentials using the capillary electrometer. Because he was dissatisfied with the records obtained, he made several modifications that greatly improved the tracing quality by using differential equations to correct the poor frequency response of the Figure 2.1 Dr AD Waller recorded many ECG tracings using his original design (Figure 2.2A). With these modifications, dog Jimmy, resulting in accusations of animal cruelty. Clinical Electrocardiography: A Textbook, Fourth Edition. Antoni Bayés de Luna. © 2012 John Wiley & Sons, Ltd. Published 2012 by John Wiley & Sons, Ltd. 11 Bayes_c02.indd 11 2/21/2012 6:22:15 PM  12 Introductory Aspects A B t t h h c c 0,5 sec C Hg C D A B H CO 0,1 sec S R D T Figure 2.2 (A) Lippmann’s capillary P electrometer consisted of a mercury O X reservoir ending in a glass capillary S with the upper half filled with mercury Q and the lower half and reservoir filled with sulfuric acid. (B) Waller’s E cardiogram recorded using a capillary electrometer. t = time; h = external pulsation from heart beat; c = electrical activity of heart. (C) Einthoven’s recording using a capillary electrometer. Upper: A, B, C, and D waves; lower: mathematically corrected waves, now designated PQRST. (D) A string galvanometer. Upper: Poles P and P1 of electromagnet and aperture for string. Note holes for viewing via microscopes. Lower: electromagnet with string in place and two microscopes. (E) Einthoven’s ECG recordings. A B Figure 2.3 Dr Willem Einthoven in his laboratory early in his career (A) and years later (B) while visiting Frank N Willem Einthoven (1860–1927) Wilson in Ann Arbor, Michigan. Bayes_c02.indd 12 2/21/2012 6:22:16 PM  The History of Electrocardiography 13 force moving from one pole to the other. Currents from A the heart registered from the surface of the body were conducted through the quartz string, thereby creating a varying magnetic field of force around the long axis of the string. The interaction between the two magnetic fields, one between the poles of the electromagnet and the other depending on the magnitude of the current that flowed through the string, resulted in movements of the string that were recorded as sharp deflections. The first electrocardiogram recorded using the string galvanometer was published in 1902. The quality of B the tracings was undoubtedly very good and similar to today’s tracings (Figure 2.2E). It is interesting to note that because Einthoven’s laboratory was more than a mile from the academic hospital in Leyden, he developed a method for recording the ECG from a distance, which he called “Telecardiogramme.” Unlike Waller, Einthoven intuited the great potential of electrocardiography, stating that “A new chapter has been opened in the study of heart diseases … by which suffering mankind is helped.” In fact, by 1906 he had already published his first paper presenting normal and abnormal ECGs (Einthoven 1912). With this new tech- nique, the recording of ECG curves had a high fidelity and sensitivity and represented an undistorted, directly read- able graphic record of the electrical activity of the heart. Figure 2.4 (A) The first manufactured ECG machine. (B) The Einthoven labeled the detailed wave deflections “PQRST,” second model (table model manufactured by Cambridge Scientific instead of using the “ABCD” notations used for the waves Instrument Company in 1911) (see text). taken with the capillary electrometer (Figure 2.2C). This avoided confusion between uncorrected and corrected In hindsight it is clear that the Nobel Prize Einthoven records and allowed the addition of further letters if other received in 1924 was very well deserved. He had a fasci- earlier or later wave forms should be discovered. Starting nating and creative personality added to his genius. He with “P” to describe the first wave avoided the use of the only looked for the truth. He once stated “What you or I letters “N” and “O,” which were already in use for other think is not important. What is important is the truth” mathematical/geometrical conventions. (Burch and De Pasquale 1964). The diagnostic technique introduced by Einthoven over Prior to the discovery of the ECG, the diagnosis of heart 100 years ago was soon manufactured by the Cambridge rhythm disorders had been performed by clinical exami- Scientific Instrument Company, founded by Horace nation and polygraphic recordings of arterial and venous Darwin, younger son of the great biologist Charles Darwin pulsations. The most important studies in this field were and the first to officially commercialize ECG machines. performed by the physicians Sir James Mackenzie and The first manufactured ECG machine was supplied to EA Karel F Wenckebach in the late nineteenth century. In the Schafer in Edinburgh in 1908 (Figure 2.4A). The second early days of electrocardiography they were naturally model, the table model, was manufactured in 1911. Figure suspicious of this new technique, probably because they 2.4B shows how the recording of tracings with this huge thought that it might interfere with careful observation machine was performed. One of the three first complete and the physical diagnosis of heart diseases. However,