Effects of diltiazem on vulnerability to atrial and ventricular reentrant arrhythmias in the normal and ischemic heart.

In experiments on 20 artificially ventilated anaesthetized dogs, the effects of the new calcium antagonist diltiazem on the stimulation thresholds to repetitive extrasystoles and fibrillation of the atria and the ventricles, respectively, and on ventricular dysrhythmias 6-24 h after acute coronary occlusion were investigated. The electrophysiological studies were performed using different methods of programmed stimulation of the heart. The results show that therapeutic doses of diltiazem provide no protection against stimulus-induced supraventricular reentrant arrhythmias with the AV-node not involved in the reentrant circus, and have no antifibrillatory efficacy in electrically induced ventricular arrhythmias in the non-ischemic heart. In acute myocardial infarction there is no antiarrhythmic effect either. Our results can be explained by the fact that diltiazem is a specific calcium antagonist and that the slow response plays only a minor role in the arrhythmias investigated.