Ischemic ventricular fibrillation: The importance of being spontaneous

Abstract Although the energy level required to defibrillate normal myocardium is low and constant, as determined from studies of induced ventricular fibrillation, little is known of the specific energy requirements in regionally ischemic hearts for spontaneous or induced ventricular fibrillation. In this study the lowest energy threshold for defibrillation was determined in 10 open chest dogs with reversible 10 minute coronary occlusions at various sites for each of 44 events of ventricular fibrillation, using apical and superior vena caval electrodes with a generator providing variable output of 1 to 30 watt seconds. The ischemic mass, quantitated from postmortem angiographic and planimetric data, was 52 ± 9 percent (mean ± standard deviation) of the left ventricle in dogs with induced ventricular fibrillation (Group I), 52 ± 12 percent in dogs with spontaneous ventricular fibrillation after occlusion (Group II) and 54 ± 9 percent in dogs with spontaneous ventricular fibrillation after reperfusion (Group III). Defibrillation thresholds in watt seconds were 9 ± 7 in Group I (n = 12), 19 ± 10 in Group II (n = 13) and 18 ± 10 in Group III (n = 19). (Group I versus Groups II and III, probability [p]