Effect of coronary occlusion on arrhythmias and conduction in the ovine heart

The proximal left circumflex coronary artery was occluded for 1 h in 16 open-chest sheep anesthetized with pentobarbital sodium. Epicardial conduction was monitored at three or four sites within the ischemic zone and one site in the normal zone. Eight of the sheep developed ventricular fibrillation within the first 15 min of occlusion; the remaining sheep survived the 1-h observation period. In the sheep that developed spontaneous ventricular fibrillation, the circumflex perfused a significantly greater amount of the left ventricle (44 +/- 3 vs. 39 +/- 3%; P = 0.008). The occurrence of spontaneous ventricular fibrillation was invariably preceded by a period of sustained (0.5-4 min) ventricular tachycardia. Six of the surviving sheep developed episodes of sustained (2-10 min) tachycardia that were self-terminating. The ischemic zone electrograms showed continuous fractionated electrical activity during both self-terminating tachycardias and tachycardias ending in fibrillation. The continuous epicardial electrical activity did not appear to cause the tachycardias but rather occurred as a result of the tachycardias. The genesis of ventricular tachycardia and fibrillation in this model may involve mechanisms different from ischemia-induced ventricular tachycardia and fibrillation in canine and porcine hearts.