Factors Concerned in Electrical Defibrillation of the Heart, Particularly Through the Unopened Chest

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Abstract
An attempt to determine optimal conditions for electrical defibrillation of the heart, particularly through the unopened chest, has been made. Sixty-cycle current for a duration of 0,1-0.2 seconds has been found to be the most suitable defibrillatory stimulus from among a number of different types of stimuli tested. The use of electrodes larger than the heart itself promotes the greatest density of current flow at the lowest possible voltage; small electrodes may require several times as high voltage as do large electrodes to achieve the same results. Also, in the opened chest, compressing the heart between the electrodes considerably lowers the voltage needed. It is reasoned that trains of relatively weak stimuli stop fibrillation not by throwing the entire ventricular muscle into refractoriness at one time but simply by blockage of fibrillation action potentials as they momentarily enter the effective field of the stimuli. Defibrillation of an otherwise normal heart, through the unopened chest as well as with electrodes applied directly to the heart, almost always results in recovery of the animal,provided that fibrillation has not persisted for more than 1 minute.

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