Comparison of the effects of calcium channel blockers and antiarrhythmic drugs on digitalis-induced oscillatory afterpotentials on canine Purkinje fiber.

We studied the effects of Ca channel blockers and 3 antiarrhythmic drugs on the digitalis-induced oscillatory afterpotential (OAP). The OAP was observed in Purkinje fibers stimulated by pulse trains, with cycle lengths ranging from 1,000 to 300 msec. The Ca channel blockers verapamil, diltiazem and nifedipine (2.0 x 10(-6) M) depressed OAP significantly and abolished triggered activity. Verapamil was more effective than diltiazem. However, nicardipine and nitrendipine (2.0 x 10(-6) M) had no depressant effects on OAP or triggered activity. The antiarrhythmic drugs procainamide (1.0 x 10(-4) M), mexiletine (1.0 x 10(-5) M) and propranolol (1.0 x 10(-4) M) depressed both OAP and triggered activity. There were no significant differences in the depressant effects between the Ca2+ antagonists (except for nitrendipine and nicardipine) and the other antiarrhythmic drugs. The OAP coupling interval was prolonged by verapamil, diltiazem, propranolol, procainamide and mexiletine. Although the APD50 was shortened by verapamil, diltiazem and nifedipine, it was prolonged by propranolol. It is concluded that nifedipine, verapamil, diltiazem, procainamide, mexiletine and propranolol may be effective for digitalis-related arrhythmia.