Effects of verapamil on reoxygenation and programmed electrical stimulation-induced ventricular arrhythmias in the isolated heart

The antiarrhythmic effect of verapamil was tested on spontaneous ventricular arrhythmias during reoxygenation after 15 min of glucose-free hypoxia and on programmed electrical stimulation-(8 stimuli + 1 or 2 extrastimuli) induced ventricular fibrillation in isolated Langendorff perfused guinea pig hearts. Verapamil (1 mg/l) added during hypoxia and reoxygenation significantly reduced, during reoxygenation, the incidence of arrhythmias (46%, N = 13 vs. controls 87%, N = 30; P less than 0.01), of ventricular fibrillation (0%, N = 13 vs. controls 70%, N = 30; P less than 0.001) and of programmed stimulation-induced ventricular fibrillation (0%, N = 10 vs. controls 100%, N = 16). No effect was observed on programmed stimulation-induced ventricular fibrillation during hypoxia (90%, N = 10 vs. controls 100%, N = 10). Verapamil added during reoxygenation reduced the incidence of reoxygenation arrhythmias and ventricular fibrillation (47% and 29%, N = 17, P less than 0.01 and P less than 0.05 vs. controls, respectively) but it had no effect on programmed stimulation-induced ventricular fibrillation (100%, N = 10). It is likely that verapamil exerts its antiarrhythmic effect by preventing cellular calcium overload during hypoxia and reoxygenation.