Studies of Ventricular Fibrillation Caused by Electric Shock:

Abstract 1. 1. The natural course of events from the onset of fibrillation following faradic excitation to complete diastolic rest was studied by recording electrocardiograms and moving pictures simultaneously. In addition, intraventricular pressure curves were optically recorded during a number of experiments. The changes taking place when fibrillation was inhibited by intraventricular injections of 5 per cent KCl and the process of recovery following similar injections of 5 per cent CaCl2 solutions combined with massage, were investigated by the same means. 2. 2. Fibrillation induced by faradic stimulation continues naturally for fifteen to fifty minutes and may be divided into 4 stages, on the basis of surface changes, electrocardiographic deflections and intraventricular pressure variations. 3. 3. The initial stage of tachysystole lasts less than one second and is characterized by the spread of rapidly recurring but coordinated contraction waves, by large electrocardiographic deflections with steep gradients and by definite if small intraventricular pressure variations. 4. 4. The second stage of convulsive incoordination ordinarily lasts fifteen to forty seconds and is characterized by rapid irregular localized contractions which spread short and variable distances over the heart. They are accompanied by large electrical deflections, 600 or more per minute, which vary considerably in size, amplitude and contour. 5. 5. The third stage of tremulous incoordination ordinarily continues two or three minutes and is characterized by multitudes of irregular yet forceful shivering or trembling motions, each speading very short distances and with highly variable frequencies over different surface regions. They give rise to small irregular electrocardiographic oscillations having frequencies between 1100 and 1700 per minute, and are capable of increasing the intraventricular pressure level slightly. 6. 6. The fourth stage of atonic incoordination is characterized by feeble wavelets of contraction spreading irregularly and at slow rates over small areas until more and more areas become quiescent, and finally the very slightest movements remain in a few areas only. The electrical deflections perhaps become slightly more regular in contour and spacing, but their amplitude becomes progressively smaller, and their frequency is gradually reduced to 400 per minute or less. 7. 7. Potassium chloride injected into both ventricular cavities does not modify the stages through which fibrillation naturally passes; it merely hastens the process so that fibrillation stops within an average period of 2.4 minutes. 8. 8. Intraventricular injections of CaCl2 after potassium inhibition combined with massage, first inaugurate a coordinated idioventricular rhythm, characterized by slow waves of contraction sweeping over the two ventricles asynchronously but in coordinated fashion. After a short interval, a supraventricular rhythm is reestablished, the electrocardiogram regaining all its normal characteristics.