The effect of the combination of quinidine and propranolol upon atrial and ventricular automatically in dogs.

The effects of quinidine, propranolol and their combination on atrial and ventricular automaticity were studied in pentobarbital-anesthetized dogs with complete heart block produced by injection of 40% formalin. The indices of atrial and ventricular automaticity were the intrinsic rate and the asystole interval, 10-beat period, and beats per 30 seconds after cessation of a 2-minute overdrive. Potentiation was considered to be a response produced by the combination of a half-dose of quinidine plus a half-dose of propranolol significantly greater than that produced by the full dose of either drug. Two combinations were studied: combination I consisted of 1.0 mg/kg of quinidine and 0.04 mg/kg of propranolol while combination II consisted of 2.0 mg/kg of quinidine and 0.08 mg/kg of propranolol. Neither combination potentiated the action of the individual drugs on the ventricle. Both combinations produced a potentiation of the individual drug effects on atrial intrinsic rate, asystole interval, and 10-beat period while only combination II potentiated the individual drug effects on atrial beats per 30 seconds. These studies indicate that the enhanced effect of the quinidine-propranolol combination in conversion of atrial tachyarrhythmias to sinus rhythm may be a function of its potentiation of the ability of the individual drug to depress atrial automaticity.