Antiarrhythmic and antifibrillatory action of diltiazem on early and late phase ventricular arrhythmias following coronary artery occlusion and on reperfusion ventricular arrhythmias.

The effects of diltiazem on ventricular arrhythmias and ventricular vulnerability for fibrillation, both in the very beginning of myocardial ischemia and in the early stage of myocardial necrosis, were evaluated in 13 mongrel dogs. In part I of the study, repeated coronary occlusions were performed. Time course and extent of ventricular ectopy were continuously recorded, and changes in ventricular fibrillation threshold were assessed, both after coronary artery occlusion and release. In part II, a permanent coronary artery occlusion was performed, and the changes in frequency of ventricular arrhythmias were assessed. Diltiazem displayed strong antiarrhythmic and antifibrillatory effects on early ventricular occlusion arrhythmias. The drop in ventricular fibrillation threshold 5 min after coronary occlusion was significantly attenuated. Following the release of coronary artery obstruction, diltiazem failed to reduce the frequency of ventricular fibrillation immediately after the onset of reperfusion. However, during the early postreperfusion period, the drug was able to accelerate significantly the increase in the ventricular fibrillation threshold. Late phase ventricular arrhythmias were not influenced by the drug even when high doses were applied. The different antiarrhythmic actions of diltiazem on early and late phase ventricular arrhythmias can be assumed to be due to differences in the arrhythmogenesis at the very onset of myocardial ischemia compared to the stage of myocardial necrosis.