Characterization and localization of ventricular arrhythmias resulting from myocardial ischemia and infarction.

Electrocardiograms and electrograms were recorded in 18 dogs anesthetized with sodium pentobarbital. Using endocardial and epicardial plunge wire electrodes in normal and ischemic or infarcted areas, activation of Purkinje and regular muscle tissue was studied within the first 20-30 minutes and 24 hours after anterior descending coronary artery ligation. The ventricular arrhythmias in the first 20 minutes were abolished during vagally induced atrial arrest, but ventricular automaticity was unchanged from that during the control period. These rate-related arrhythmias were uniformly associated with marked diminution and delay of epicardial activation in the ischemic zone. Slowing of the heart rate caused recovery of the timing, form, and duration of these epicardial potentials with the coincident disappearance of ventricular arrhythmias. The ventricular arrhythmias of the early phase spontaneously subsided with time 20-30 minutes after ligation; concurrently, epicardial activation in the ischemic zone improved. The ventricular arrhythmias noted 24 hours after coronary artery ligation were revealed by vagally induced atrial slowing and suppressed by rapid atrial pacing, indicating the existence of enhanced ventricular automaticity. There was a loss of endocardial muscle activation; Purkinje tissue was depressed but viable in the infarcted zone. The sequence of firing during many of the multifocal ventricular ectopic beats showed that the earliest activation arose from Purkinje tissue in the infarcted zone. However, other ectopic beats appeared to arise from infarcted epicardial muscle.