[Electrophysiologic studies on reentrant ventricular arrhythmia in the late myocardial infarction period]

The mechanisms of reentrant ventricular tachycardia were studied in canine post-infarction model. In 15 dogs that weighed 10-20 kg, the anterior descending coronary artery was ligated. 3 to 7 days after coronary artery occlusion, the dogs were reoperated to set up a composite electrode or a patch electrode with 32 bipolar electrodes. The composite electrode was utilized to record ventricular late potentials (VLPs) from the epicardial surface of the infarction zone (IZ) and adjacent normal zone (NZ). The bipolar electrodes were used to record the epicardial isochronal maps. 16 bipolar electrodes were placed over the area of infarction and its bordering zone and the other 16 bipolar electrodes were distributed over the remaining surface of the ventricle. Reentrant ventricular tachycardias were induced by programmed electrical stimulation. The VLPs and epicardial isochronal activation were recorded by SC-16 oscillograph and computerized mapping system during sinus rhythm and programmed stimulation. The experiments showed; 1) VLPs were demonstrated in 11 of the 15 dogs (73.3%) during programmed stimulation. 2) The reentrant circuit has a characteristic figure-8 configuration in the form of two circulating wave-fronts around arcs of functional conduction block that coalesce into a slow commun reentrant wave-front. One of the two synchronous circuits traveled clockwise and the other counter-clockwise. 3) VLPs represent a delayed depolarization at the ischemic myocardium, where the impulse conducts slowly in the reentrant circuit. It is clear that the present study may increase the understanding of the mechanism of ventricular arrhythmias in the late myocardial infarction period.