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Electrocardiography (ECG in British English〔(ECG ). American Heritage Dictionary〕 and EKG in American English〔(Electrocardiography ). Columbia Electronic Encyclopedia〕〔(EKG ). Collins Dictionary〕 *) is the process of recording the electrical activity of the heart over a period of time using electrodes placed on a patient's body. These electrodes detect the tiny electrical changes on the skin that arise from the heart muscle depolarizing during each heartbeat. In a conventional ''12 lead ECG'', ten electrodes are placed on the patient's limbs and on the surface of the chest. The overall magnitude of the heart's electrical potential is then measured from twelve different angles ("leads") and is recorded over a period of time (usually 10 seconds). In this way, the overall magnitude and direction of the heart's electrical depolarization is captured at each moment throughout the cardiac cycle.〔(【引用サイトリンク】 title=ECG- simplified. Aswini Kumar M.D. )〕 The graph of ''voltage'' versus ''time'' produced by this noninvasive medical procedure is referred to as an electrocardiogram (abbreviated ''ECG'' or ''EKG''). During each heartbeat, a healthy heart will have an orderly progression of depolarization that starts with pacemaker cells in the sinoatrial node, spreads out through the atrium, passes through the atrioventricular node down into the bundle of His and into the Purkinje fibers spreading down and to the left throughout the ventricles. This orderly pattern of depolarization gives rise to the characteristic ECG tracing. To the trained clinician, an ECG conveys a large amount of information about the structure of the heart and the function of its electrical conduction system.〔Walraven, G. (2011). ''Basic arrhythmias'' (7th ed.), pp. 1–11〕 Among other things, an ECG can be used to measure the rate and rhythm of heartbeats, the size and position of the heart chambers, the presence of any damage to the heart's muscle cells or conduction system, the effects of cardiac drugs, and the function of implanted pacemakers.〔Braunwald E. (ed) (1997), ''Heart Disease: A Textbook of Cardiovascular Medicine, Fifth Edition'', p. 108, Philadelphia, W.B. Saunders Co.. ISBN 0-7216-5666-8.〕 ==History== The etymology of the word is derived from the Greek ''electro'', because it is related to electrical activity, ''kardio'', Greek for heart, and ''graph'', a Greek root meaning "to write". Alexander Muirhead is reported to have attached wires to a feverish patient's wrist to obtain a record of the patient's heartbeat in 1872 at St Bartholomew's Hospital.〔Ronald M. Birse,(rev. Patricia E. Knowlden ) Oxford Dictionary of National Biography 2004 (Subscription required) – (original source is his biography written by his wife – Elizabeth Muirhead. Alexandernn Muirhead 1848–1920. Oxford, Blackwell: privately printed 1926.)〕 Another early pioneer was Augustus Waller, of St Mary's Hospital in London. His electrocardiograph machine consisted of a Lippmann capillary electrometer fixed to a projector. The trace from the heartbeat was projected onto a photographic plate that was itself fixed to a toy train. This allowed a heartbeat to be recorded in real time. An initial breakthrough came when Willem Einthoven, working in Leiden, the Netherlands, used the string galvanometer he invented in 1901. This device was much more sensitive than both the capillary electrometer Waller used and the string galvanometer that had been invented separately in 1897 by the French engineer Clément Ader. Einthoven assigned the letters P, Q, R, S, and T to the various deflections, and described the electrocardiographic features of a number of cardiovascular disorders. In 1924, he was awarded the Nobel Prize in Medicine for his discovery. Though the basic principles of that era are still in use today, many advances in electrocardiography have been made over the years. Instrumentation has evolved from a cumbersome laboratory apparatus to compact electronic systems that often include computerized interpretation of the electrocardiogram. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Electrocardiography」の詳細全文を読む スポンサード リンク
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