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Early in the 20th century, the Consolidated Edison Electrical Company of New York, concerned by accidental electrocutions of its line workers, supported research on the mechanisms and treatment of electrical accidents. Investigators at Johns Hopkins Hospital developed techniques of defibrillation—the termination of ventricular fibrillation—by an electrical shock in the 1930s.1 The first human defibrillation in the operating room was performed by Claude Beck in 1947.2 Transchest defibrillation using alternating current became a clinical reality when introduced by Paul Zoll in 1956,3 and direct current defibrillation was pioneered by Bernard Lown in 1962.4 The work of Zoll and Lown, in combination with the description of closed-chest cardiac massage by Jude and colleagues in 1960,5 has formed the foundation of cardiopulmonary resuscitation from cardiac arrest for 50 years.

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Lown used a damped sinusoidal waveform, which—at the usually encountered human transthoracic impedance (60-90 ohms)—was effectively monophasic. In the Soviet Union, Gurvich described an underdamped sinusoidal waveform that was effectively biphasic6; this waveform was not used in the West.

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More recently, truncated exponential biphasic waveforms have become the standard for transchest defibrillation; this is discussed further on.

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In this review, the term defibrillation refers to the electrical termination of ventricular fibrillation (VF); cardioversion refers to the electrical termination of atrial fibrillation, atrial flutter, and supraventricular and ventricular tachycardias.

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How does an electric shock terminate a cardiac arrhythmia? There are three principal hypotheses. The critical mass hypothesis suggests that some proportion of the myocardium (not necessarily all) must be depolarized, so that the remaining muscle is inadequate to maintain the arrhythmia.7 The upper limit of vulnerability hypothesis argues that a sufficient current density throughout the ventricle must be achieved lest fibrillation be reinitiated by a subthreshold current density.8 Jones' group9 hypothesized that defibrillating shocks must achieve an extension of refractoriness in sufficient myocardium to terminate VF. These concepts are not mutually exclusive; all may be applicable. Whether they also apply to the atrial myocardium for the termination of atrial fibrillation by electrical shock is not known. More organized arrhythmias, such as ventricular tachycardia and atrial flutter, terminate with lower energy than VF and atrial fibrillation,10 likely because only regional depolarization in the path of an advancing wavefront is required.

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VF, a lethal arrhythmia, requires prompt termination as a lifesaving maneuver. For many years the American Heart Association encouraged immediate defibrillation of a victim of VF upon the arrival of personnel equipped with a defibrillator. However, recent investigations by Cobb et al11 and Wik et al12 have shown that if the initial application of shock is delayed, a brief period of cardiopulmonary resuscitation (CPR; ventilation, closed-chest compression) before the first shock will favorably enhance outcome. (A third clinical trial, by Jacobs et al,13 did not find that a period of CPR before defibrillation facilitates resuscitation.) These observations led Weisfeldt and Becker14 to propose ...

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