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A Concise History of the ECG

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Galvani's name is given to the 'galvanometer', an instrument for measuring (and recording) electricity - this is essentially what an ECG is; a sensitive galvanometer.
'''1788''' Charles Kite wins the Silver Medal of the Humane Society (awarded at the first prize medal ceremony of the Society, co-judged with the Medical Society of London) with an essay on the use of electricity in the diagnosis and resuscitation of persons apparently dead. This essay is often cited as the first record of cardiac defibrillation, but the use of electricity suggested by Mr Kite is much different. For example, on describing a case of drowning from 1785, in which resuscitation was attempted with artificial respiration, warmth, tobacco, "volatiles thrown into the stomach, frictions, and various lesser stimuli" for nearly an hour, he then recalls the use of electricity. "Electricity was then applied, and shocks sent through in every possible direction; the muscles through which the fluid [electricity] passed were thrown into strong contractions." He concludes that electricity is a valuable tool that can determine whether be used to resuscitate a person, apparently who appeared dead, can be successfully resuscitated. Annual Report 1788: Humane Society, London. pp 225-244. Kite C. An Essay on the Recovery of the Apparently Dead. 1788: C. Dilly, London.
[[Image:Alessandro_Volta.jpg|150px|thumb|left|Alessandro Volta]]'''1792''' Alessandro Volta, Italian Scientist and inventor, attempts to disprove Galvani's theory of "animal electricity'" by showing that the electrical current is generated by the combination of two dissimilar metals. [[Image:Voltaic_Pile.jpg|150px|thumb|Voltaic pile]]His assertion was is that the electrical current came comes from the metals and not the animal tissues. (We now know that both Galvani and Volta were right.) To prove his theory he develops the voltaic pile in 1800 (a column of alternating metal discs - zinc with copper or silver - separated by paperboard soaked in saline) which can deliver a substantial and steady current of electricity. Enthusiasm in the use of electricity leads to further attempts at reanimation of the dead with experiments on recently hanged criminals. Giovani Aldini (the nephew of Galvani) conducts an experiment at the Royal College of Surgeons in London in 1803. The executed criminal had has lain in a temperature of 30 degrees F for one hour and was is transported to the College. "On applying the conductors to the ear and to the rectum, such violent muscular contractions were executed, as almost to give the appearance of the reanimation". Aldini, J. Essai: Théorique et expérimental sur le Galvanisme, Paris (1804), Giovani Aldini. General Views on the Application of Galvanism to Medical Purposes Principally in cases of suspended Animation (London: J. Callow, Princes Street and Burgess and Hill, Great Windmill Street, 1819). Mary Shelly's Frankenstein was is published in 1818. Louis Figuier, Les merveilles de la Science (Paris, 1867), p.653
==1800 - 1895==
'''1819''' While demonstrating to students the heating of a platinum wire with electricity from a voltaic pile at the University of Copenhagen, Danish physicist Hans Christian Oersted notices that a nearby magnetized compass needle moves each time the electrical current is turned onapplied. He discovers electromagnetism , which is given a theoretical basis (with remarkable speed) by André Marie Ampère.
'''1820''' Johann (Johan) Schweigger of Nuremberg increases the movement of magnetized needles in electromagnetic fields. He found finds that by wrapping the electric wire into a coil of 100 turns multiplies the effect on the needle was multiplied. He proposed proposes that a magnetic field revolved around a wire carrying a current which . This was later proven by Michael Faraday. Schweigger had invented the first galvanometer and announced announces his discovery at the University of Halle on 16th September 1820.
'''1825''' Leopold Nobili, Professor of Physics at Florence, develops an 'astatic galvanometer'. Using two identical magnetic needles of opposite polarity, either fixed together with a figure of eight arrangment arrangement of wire loops (in earlier versions), or one moveable movable needle with a wire loop and one with a scale (in later versions), Nobili is able to compensate for the effects of the earth's magnetic field could be compensated for. In 1827, using this instrument, he managed manages to detect the flow of current in the body of a frog from muscles to spinal cord. He detected detects the electricity running along saline -moistened cotton thread joining the dissected frog's legs in one jar to its body in another jar. Nobili was working to support feels that this work proves the theory of animal electricity and this conduction, transmitted without wires, he felt demonstrated animal electricity.
[[Image:Matteucci.jpg|thumb|150px|left|Carlo Matteucci]]'''1838''' Carlo Matteucci, Professor of Physics at the University of Pisa, and a student of Nobili, shows that an electric current accompanies each heart beat. He used uses a preparation known as a 'rheoscopic frog' , in which the cut nerve of a frog's leg was is used as the electical electrical sensor and twitching of the muscle was is used as the visual sign of electrical activity. He also used uses Nobili's astatic galvanometer for the study of electricity in muscles , typically inserting one galvanometer wire in into the open end of the dissected muscle and the other on onto the surface of the muscle. He went goes on to try and to demonstrate conduction in nerve , but was is unable to do so (since his galvanometers were are not sensitive enough). <cite>Matteucci</cite>
'''1840''' Dr Golding Bird, a Physicianphysician, accomplished chemist and member of the London Electrical Society, opens an electrical therapy room at Guy's Hospital, London , treating a large range of diseases. Although the application of electricity was is popular , it was is not considered a subject worthy of serious investigation. Because of Bird's reputation as a researcher , electrical therapy achieved achieves popularity amongst among London Physicians physicians, including his mentor , Dr Thomas Addison. <cite>Bird</cite>
[[Image:Emil_Dubois.jpg|thumb|150px|left|Physiologist Emil Du Bois-Reymond]]'''1843''' German physiologist Emil Du Bois-Reymond describes an "action potential" accompanying each muscular contraction. He detected detects the small voltage potential present in resting muscle and noted notes that this diminished diminishes with contraction of the muscle. To accomplish this he had developed develops one of the most sensitive galvanometers of his time. His device had has a wire coil with over 24,000 turns - 5 km of wire. Du Bios Reymond devised devises a notation for his galvanometer which he called the 'disturbance curve'for his galvanometer. "oO" was the stable equilibrium point of the astatic galvanometer needle and p, q, r and s (and also k and h) were other points in its deflection. Du Bois-Reymond, E. Untersuchungen uber thierische Elektricitat. Reimer, Berlin: 1848.
'''1850''' Bizarre unregulated actions of the ventricles (later called ventricular fibrillation) is described by Hoffa during experiments with strong electrical currents across the hearts of dogs and cats. He demonstrated demonstrates that a single electrical pulse can induce fibrillation. <cite>Hoffa</cite>
'''1856''' Rudolph von Koelliker and Heinrich Muller confirm that an electrical current accompanies each heart beat by applying a galvanometer to the base and apex of an exposed ventricle. They also applied apply a nerve-muscle preparation, similar to Matteucci's, to the ventricle and observed observe that a twitch of the muscle occured occurs just prior to ventricular systole and also , followed by a much smaller twitch after systole. These twitches would will later be recognised recognized as caused by the electrical currents of the QRS and T waves. von Koelliker A, Muller H. Nachweis der negativen Schwankung des Muskelstroms am naturlich sich kontrahierenden Herzen. Verhandlungen der Physikalisch-Medizinischen Gesellschaft in Wurzberg. 1856;6:528-33.
'''1858''' William thompson Thompson (Lord Kelvin), Professor professor of Natural Philosophy natural philosophy at Glasgow University, invents the 'mirror galvanometer' for the reception of transatlantic telegraph transmissions. A small, freely rotating mirror, with magents magnets stuck to its back , is suspended in a fine copper coil and a reflected spot of light from this mirror 'amplifies' the small movements when electrical current is present. The whole apparatus was is suspended in an air chamber and the pressure inside could can be adjusted to vary the damping seen on the signals. This galvanometer was is sensitive enough for transatlantic telegraphy.
'''1867''' Thompson improves telegraph transmissions with the 'Siphon Recorder'. Before d'Arsonval (1880), Thompson uses a fine coil suspended in a strong magnetic magnetic field. Attached to the coil but isolated from it by ebonite (an insulator) was is a siphon of ink. The siphon was is charged with high voltage so that the ink was is sprayed onto the paper that , which moved over an earthed a metal surface. The siphon recorder could therefore not only detect currents ; it could also record them onto paper.
'''1869-70''' Alexander Muirhead, an electrical engineer and pioneer of telegraphy, may have a recorded possibly records a human electrocardiogram at St Bartholomew's Hospital, London but this is disputed. If he had he He is thought to have used a Thompson Siphon Recorder. Elizabeth Muirhead, his wife, wrote writes a book of his life and claimed , claiming that he refrained from publishing his own work for fear of misleading others. Elizabeth Muirhead. Alexander Muirhead 1848 - 1920. Oxford, Blackwell: privately printed 1926.
'''1872''' French physicist Gabriel Lippmann invents a capillary electrometer. It is a thin glass tube with a column of mercury beneath sulphuric acid. The mercury meniscus moves with varying electrical potential and is observed through a microscope.
'''1872''' Mr Green, a surgeon, publishes a paper on the resuscitation of a series of patients who had suffered cardiac and / or respiratory arrest during anaesthesia with chloroform. He uses a galvanic pile (battery) of 200 cells generating 300 Volts , which he applied applies to the patient as follows "One pole should be applied to the neck and the other to the lower rib on the left side." Green T. On death from chloroform: its prevention by galvanism. Br Med J 1872 1: 551-3. Although this has been reported as an example of cardiorespiratory resuscitation , it is unclear what the exact mechanism seems to be. It is unlikely to be electric cardioversion or external pacing. It seems to be another example of electrophrenic stimulation (See also Duchenne 1872).
[[image:Duchenne_de_belogne.jpg|thumb|150px|left|Guillaume Benjamin Amand Duchenne de Boulogne]]'''1872''' Guillaume Benjamin Amand Duchenne de Boulogne, pioneering neurophysiologist, describes the resuscitation of a drowned girl with electricity in the third edition of his textbook on the medical uses of electricity. This episode has sometimes been described as the first 'artificial pacemaker' but he used an electrical current to induce electrophrenic rather than myocardial stimulation. Duchenne GB. De l'electrisation localisee et de son application a la pathologie et la therapeutique par courants induits at par courants galvaniques interrompus et continus. [Localised electricity and its application to pathology and therapy by means of induced and galvanic currents, interrupted and continuous] 3ed. Paris. JB Bailliere et fils; 1872
'''1874''' A. Vulpian described ''mouvement fibrillaire'' in his article published in 1874, which would be the basis for the name ventricular fibrillation now used for this arrhythmia.<cite>Vulpian</cite>
'''1875''' Richard Caton, a Liverpool Physicianphysician, presents to the British Medical Association in July 1875 in Edinburgh. Using a Thompson 'mirror galvanometer' in animals he shows it was is possible to detect 'feeble currents of varying direction ... when the electrodes are placed on two points of the external surface, or one electrode on the grey matter and one on the surface of the skull'. This is the first report of the EEG (or electroencephalogram). Caton was proving another Physician's hypothesis, John Hughlings Jackson, who suggested in 1873 that epilepsy was due to excessive electrical activity in the grey matter of the brain. Caton R: The electric currents of the brain. BMJ 1875; 2:278, Mumenthaler, Mattle Eds. Neurology. 4th Edition. Stuttgart, Thieme: 2004.
'''1876''' Marey uses the electrometer to record the electrical activity of an exposed frog's heart. Marey EJ. Des variations electriques des muscles et du couer en particulier etudies au moyen de l'electrometre de M Lippman. Compres Rendus Hebdomadaires des Seances de l'Acadamie des sciences 1876;82:975-977
'''1884''' John Burden Sanderson and Frederick Page publish some of their recordings. Burdon Sanderson J, Page FJM. On the electrical phenomena of the excitatory process in the heart of the tortoise, as investigated photographically. J Physiol (London) 1884;4:327-338
[[image:Waller.jpg|thumb|150px|left|A.D. Waller with his famous bulldog Jimmy]]'''1887''' British physiologist Augustus D. Waller of St Mary's Medical School, London publishes the first human electrocardiogram. It is recorded with a capilliary electrometer from Thomas Goswell, a technician in the laboratory. <cite>Waller</cite> This was is shortly after the "Cruelty to Animals Act" had been is accepted in the British parliament, which lead leads to questions in the House of Commons.
Q. 'At a converzaione [sic] of the Royal Society at Burlington House on May 12th last, a bulldog was cruelly treated when a leather strap with sharp nails was wound around his neck and his feet were immersed in glass jars containing salts in solution, and the jars in turn were connected with wires to galvanometers. Such a cruel procedure should surely be dealt with under the "Cruelty to Animals Act" of 1876?'
A. 'The dog in question wore a leather collar ornamented with brass studs, and he was placed to stand in water to which some sodium chloride had been added, or in other words, common salt. If my honourable friend had ever paddled in the sea, he will appreciate fully the sensation obtained thereby from this simple pleasurable experience!'
'''1887''' McWilliam provided provides the first detailed description of VF, and demonstrated how VF in man could can be terminated by electric shocks applied through a large pair of electrodes: ; the first description of defibrillation in man.<cite>McWilliam1</cite><cite>McWilliam2</cite>
'''1889''' Dutch physiologist Willem Einthoven sees Waller demonstrate his technique at the First International Congress of Physiologists in Bale. Waller often demonstrated by using his dog "Jimmy" who would patiently stand with paws in glass jars of saline.
'''1890''' GJ Burch of Oxford devises an arithmetical correction for the observed (sluggish) fluctuations of the electrometer. This allows the true waveform to be seen , but only after tedious calculations. <cite>Burch</cite>
'''1891''' British physiologists William Bayliss and Edward Starling of University College London improve the capillary electrometer. They connect the terminals to the right hand and to the skin over the apex beat and show a "triphasic variation accompanying (or rather preceding) each beat of the heart". These deflections are later called P, QRS and T. <cite>Bayliss1</cite> and <cite>Bayliss2</cite> They also demonstrate a delay of about 0.13 seconds between atrial stimulation and ventricular depolarisation (later called PR interval). On the electromotive phenomena of the mammalian heart. Proc Phys Soc (21st March) in J Physiol (London) 1891;12:xx-xxi
'''1895''' Einthoven, using an improved electrometer and a correction formula developed independently of Burch, distinguishes five deflections which he names P, Q, R, S and T. <cite>Einthoven2</cite>
Why PQRST and not ABCDE? The four deflections prior to the correction formula were labelled are labeled ABCD and the 5 derived deflections were labelled are labeled PQRST. The choice of P is a mathematical convention (as used also by Du Bois-Reymond in his galvanometer's 'disturbance curve' 50 years previously) by using letters from the second half of the alphabet. N has other meanings in mathematics and O is used for the origin of the Cartesian coordinates. In fact Einthoven used uses O ..... X to mark the timeline time line on his diagrams. P is simply the next letter. A lot of work had has been undertaken to reveal the true electrical waveform of the ECG by eliminating the damping effect of the moving parts in the amplifiers and using correction formulae. If you look at the diagram in Einthoven's 1895 paper you will see how close it is to the string galvanometer recordings and the electrocardiograms we see today. The image of the PQRST diagram may have been be striking enough to have been be adopted by the researchers as a true representation of the underlying form. It would have then been be logical to continue the same naming convention when the more advanced string galvanometer started starts creating electrocardiograms a few years later.
'''1897''' Clement Ader, a French electrical engineer, reports his amplification system for detecting Morse code signals transmitted along undersea telegraph lines. It was is never intended to be used as a galvanometer. Einthoven later quoted quotes Ader's work but seems to have developed his own amplification device independently. <cite>Ader</cite>
'''1899''' Karel Frederik Wenckebach publishes a paper "On the analysis of irregular pulses" describing impairment of AV conduction leading to progressive lengthening and blockage of AV conduction in frogs. This will later be called Wenckebach block (Mobitz type I) or Wenckebach phenomenon.
'''1899''' Jean-Louis Prevost, Professor of Biochemistry, and Frederic Batelli, Professor of Physiology, both of Geneva , discover that large electrical voltages applied across an animal's heart can stop ventricular fibrillation. <cite>Prevost</cite>
'''1901''' Einthoven invents a new galvanometer for producing electrocardiograms using a fine quartz string coated in silver , based on ideas by Deprez and d'Arsonval (who used a wire coil). His "string galvanometer" weighs 600 pounds. Einthoven acknowledged acknowledges the similar system by Ader but later (1909) calculated calculates that his galvanometer was is in fact many thousands of times more sensitive. <cite>Einthoven3</cite>
'''1902''' Einthoven publishes the first electrocardiogram recorded on a string galvanometer. <cite>Einthoven4</cite>
Einthoven starts transmitting electrocardiograms from the hospital to his laboratory 1.5 km away via telephone cables. On March 22nd the first 'telecardiogram' is recorded from a healthy and vigorous man and the tall R waves are attributed to his cycling from laboratory to hospital for the recording.
'''1905''' John Hay , of Liverpool, publishes pressure recordings from a 65 year old man showing . The recording shows heart block in which AV conduction did does not seem to be impaired , since the a-c intervals on the jugular venous waves was is unchanged in the conducted beats. This is the first demonstration of what we now call Mobitz type II AV block. <cite>Hay</cite>
'''1906''' Einthoven publishes the first organised presentation of normal and abnormal electrocardiograms recorded with a string galvanometer. Left and right ventricular hypertrophy, left and right atrial hypertrophy, the U wave (for the first time), notching of the QRS, ventricular premature beats, ventricular bigeminy, atrial flutter and complete heart block are all described. Einthoven W. Le telecardiogramme. Arch Int de Physiol 1906;4:132-164 (translated into English. Am Heart J 1957;53:602-615)
'''1908''' Edward Schafer of the University of Edinburgh is the first to buy a string galvanometer for clinical use.
'''1909''' Thomas Lewis , of University College Hospital, London , buys a string galvanometer and so does Alfred Cohn of Mt Sinae Hospital, New York. Thomas Lewis publishes a paper in the BMJ detailing his careful clinical and electrocardiographic observations of atrial fibrillation. At one point Lewis identified identifies a fibrillating horse 's heart using the string galvanometer's electrocardigram recording. He then followed the horse to the slaughterhouse , where he could visually confirm the fibrillating atrium. <cite>Lewis</cite>
'''1909''' Nicolai and Simmons report on the changes to the electrocardiogram during angina pectoris. Nicolai DF, Simons A. (1909) Zur klinik des elektrokardiogramms. Med Kiln 5;160
'''1910''' Walter James, Columbia University and Horatio Williams, Cornell University Medical College, New York , publish the first American review of electrocardiography. It describes ventricular hypertrophy, atrial and ventricular ectopics, atrial fibrillation and ventricular fibrillation. The recordings were sent from the wards to the electrocardiogram room by a system of cables. There is a great picture of a patient having an electrocardiogram recorded with the caption "The electrodes in use".James WB, Williams HB. The electrocardiogram in clinical medicine. Am J Med Sci 1910;140:408-421, 644-669
'''1911''' Levy & Lewis demonstrated demonstrate that when VF occurred during chloroform anesthesia, it was often preceded by the appearance of multiform ventricular premature beats or ventricular tachycardia.<cite>Lewis</cite>
Thomas Lewis publishes a classic textbook. The mechanism of the heart beat. London: Shaw & Sons and dedicates it to Willem Einthoven.
'''1912''' Einthoven addresses the Chelsea Clinical Society in London and describes an equilateral triangle formed by his standard leads I, II and III later called 'Einthoven's triangle'. This is the first reference in an English article I have seen to the abbreviation 'EKG'that I have seen.Einthoven W. The different forms of the human electrocardiogram and their signification. Lancet 1912(1):853-861
Hoffman published the first ECG of ventricular fibrillation in man.<cite>Hoffman</cite>
'''1918''' Bousfield describes the spontaneous changes in the electrocardiogram during angina. <cite>Bousfield</cite>
'''1920''' Hubert Mann of the Cardiographic Laboratory, Mount Sinai Hospital, describes the derivation of a 'monocardiogram' , later to be called 'vectorcardiogram'. <cite>Mann</cite>
'''1920''' Harold Pardee, New York, publishes the first electrocardiogram of an acute myocardial infarction in a human and describes the T wave as being tall and "starts from a point well up on the descent of the R wave". <cite>Pardee</cite>
'''1924''' Woldemar Mobitz publishes his classification of heart blocks (Mobitz type I and type II) based on the electrocardiogram and jugular venous pulse waveform findings in patients with second degree heart block. Mobitz W. Uber die unvollstandige Storung der Erregungsuberleitung zwischen Vorhof und Kammer des menschlichen Herzens. (Concerning partial block of conduction between the atria and ventricles of the human heart). Z Ges Exp Med 1924;41:180-237.
'''1926''' A doctor from the Crown Street Women's Hospital in Sydney, who wished wishes to remain anonymous, resuscitates a new-born baby with an electrical device later called a 'pacemaker'. The doctor wanted wants to remain anoymous because of the controversy surrounding research that artificially extended extends human life.
'''1928''' Ernstine and Levine report the use of vacuum-tubes to amplify the electrocardiogram instead of the mechanical amplification of the string galvanometer. <cite>Ernstine</cite>
'''1928''' Frank Sanborn's company (founded 1917 and acquired by Hewlett-Packard in 1961 and since 1999, Philips Medical Systems) converts their table model electrocardiogram machine into their first portable version weighing 50 pounds and powered by a 6-volt automobile battery.
'''1929''' Sydney doctor Mark Lidwill, physician, and Edgar Booth, physicist, report the electrical resuscitation of the heart to a meeting in Sydney. Their portable device uses an electrode on the skin and a transthoracic catheter. Edgar Booth's design could deliver a variable voltage and rate and was is employed to deliver 16 volts to the ventricles of a stillborn infant.
[[image:White_stamp.gif|thumb|150px|left|Dr. Paul Dudley White]]'''1930''' Wolff, Parkinson and White report an electrocardiographic syndrome of short PR interval, wide QRS and paroxysmal tachycardias. Wolff L, Parkinson J, White PD. Bundle branch block with short P-R interval in healthy young people prone to paroxysmal tachycardia. Am Heart J 1930;5:685. Later, when other published case reports were are examined for evidence of pre-excitation, earlier examples of 'Wolff Parkinson White' syndrome , which were identified which had not been recognised recognized as a clinical entity at the time, are identified. The earliest example was published by Hoffmann in 1909. Von Knorre GH. The earliest published electrocardiogram showing ventricular preexcitation. Pacing Clin Electrophysiol. 2005 Mar;28(3):228-30
'''1930''' Sanders first describes infarction of the right ventricle. <cite>Sanders</cite>
'''1931''' Charles Wolferth and Francis Wood describe the use of exercise to provoke attacks of angina pectoris. They investigated investigate the ECG changes in normal subjects and those with angina , but dismissed the technique as too dangerous "to induce anginal attacks indiscriminately". <cite>Wood</cite>
'''1931''' Dr Albert Hyman patents the first 'artificial cardiac pacemaker' , which stimulates the heart by using a transthoracic needle. His aim was is to produce a device that was is small enough to fit in a doctor's bag and be able to stimulate the right atrial area of the heart with a suitably insulated needle. His experiments were are on animals. His original machine was powered by a crankshaft (it was is later prototyped by a German company but was is never successful). "By March 1, 1932 the artificial pacemaker had been used about 43 times, with a successful outcome in 14 cases." It was is not until 1942 that a report of its successful short term use in Stokes-Adams attacks was is presented. <cite>Hyman</cite>
'''1932''' Goldhammer and Scherf propose the use of the electrocardiogram after moderate exercise as an aid to the diagnosis of coronary insufficiency. Goldhammer S, Scherf D. Elektrokardiographische untersuchungen bei kranken mit angina pectoris. Z Klin Med 1932;122:134
'''1934''' By joining the wires from the right arm, left arm and left foot with 5000 Ohm resistors Frank Wilson defines an 'indifferent electrode' later called the 'Wilson Central Terminal'. The combined lead acts as an earth and is attached to the negative terminal of the ECG. An electrode attached to the positive terminal then becomes 'unipolar' and can be placed anywhere on the body. Wilson defines the unipolar limb leads VR, VL and VF where 'V' stands for voltage (the voltage seen at the site of the unipolar electrode). <cite>Wilson</cite>
'''1935''' McGinn and White describe the changes to the electrocardiogram during acute pulmonary embolism , including the S1 Q3 T3 pattern. <cite>McGinn</cite>
'''1938''' The American Heart Association and the Cardiac Society of Great Britain define the standard positions, and wiring, of the chest leads V1 - V6. The 'V' stands for voltage. Barnes AR, Pardee HEB, White PD. et al. Standardization of precordial leads. Am Heart J 1938;15:235-239
'''1938''' Tomaszewski notes changes to the electrocardiogram in a man who died of hypothermia. Tomaszewski W. Changements electrocardiographiques observes chez un homme mort de froid. Arch Mal Coeur 1938;31:525.
'''1942''' Emanuel Goldberger increases the voltage of Wilson's unipolar leads by 50% and creates the augmented limb leads aVR, aVL and aVF. When added to Einthoven's three limb leads and the six chest leads we arrive at the 12-lead electrocardiogram that is used today.
'''1942''' Arthur Master, standardises standardizes the two step exercise test (now known as the Master two-step) for cardiac function. Master AM, Friedman R, Dack S. The electrocardiogram after standard exercise as a functional test of the heart. Am Heart J. 1942;24:777
'''1944''' Young and Koenig report deviation of the P-R segment in a series of patients with atrial infarction. Young EW, Koenig BS. Auricular infarction. Am Heart J. 1944;28:287.
'''1947''' Gouaux and Ashman describe an observation that helps differentiate aberrant conduction from ventricular tachycardia. The 'Ashman phenomenon' occurs when a stimulus falls takes place during the relative or absolute refractory period of the ventricles and the aberrancy is more pronounced. In atrial fibrillation with aberrant conduction , this is demonstrated when the broader complexes are seen terminating a relatively short cycle that follows a relatively long one. The QRS terminating the shorter cycle is conducted 'more aberrantly' because it falls in the refractory period. The aberrancy is usually of a RBBB pattern. <cite>Gouaux</cite>
'''1947''' Claude Beck, a pioneering cardiovascular surgeon in Cleveland, successfully defibrillates a human heart during cardiac surgery. The patient is a 14 year old boy - 6 other patients had failed to respond to the defibrillator. His prototype defibrillator followed experiments on defibrillation in animals performed by Carl J. Wiggers, Professor of Physiology at the Western Reserve University. <cite>Beck</cite>

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