Relative effect of chronic ischemia and a myocardial revascularization procedure on the ventricular fibrillation threshold.

THE commonest cause of death following coronary occlusion, certainly in the experimental animal if not in the human being, is ventricular fibrillation. We wish to report the relative effect of chronic ischemia alone and of a myocardial revascularization procedure on the susceptibility of the heart to ventricular fibrillation. Two questions in this regard that might be answered by the measurement of ventricular fibrillation thresholds are: 1. Can we, by operative means, increase the stability of the heart after coronary occlusion over that which might occur in time without operation? 2. Is a return of fibrillation threshold to normal after coronary occlusion necessarily associated with revascularization of the ischemic area? Wiggers and co-workers first demonstrated that coronary occlusion caused a decrease in the fibrillation threshold in the area of distribution of the vessel occluded. In our laboratory, in a study of 93 dogs, we have found a decrease from 21 milliamperes (mean) to 4.9 milliamperes (mean) in the fibrillation threshold after occlusion of the anterior descending branch of the left coronary artery. Previous studies have established also that while there is considerable variation of the fibrillation threshold among dogs, this is a very precise determination which remains constant in any given dog. Repeat determinations of the ventricular fibrillation threshold up to 6 times on the same day or on subsequent days have