Effects of propafenone on sinus nodal and ventricular automaticity: In vitro and in vivo correlation

Abstract

The electrophysiologic effects of the new antiarrhythmic drug, propafenone, were evaluated in anesthetized closed-chest dogs and on isolated cardiac tissues with the microelectrode technique. Propafenone (2 to 4 mg/kg intravenously) had no effect on sinus rate or on sinus nodal recovery time, but caused a dose-dependent significant decrease in the rate of idioventricular rhythm and increased the duration of ventricular overdrive suppression in dogs (n = 8) with complete atrioventricular block. On isolated canine Purkinje fibers (n = 8) manifesting automaticity with resting membrane potential less negative than −70 mV, propafenone reduced the slope of phase 4 depolarization and reduced the rate of automatic impulse initiation in a concentration-dependent manner (10 −6M–4.10 −5M). At these concentrations, propafenone had no effect on rabbit sinus nodal automaticity (n = 8) or on sinoatrial conduction. However, significant depression of sinus nodal automaticity occurred with propafenone concentrations above 5.10 −6M in the presence of cholinergic or complete autonomic blockade with atropine (10 −6M) and propranolol (5.10 −5M). Propafenone caused a concentration-dependent decrease in the disparity of Purkinje fiber-ventricular muscle action potential duration (APD), mainly by shortening Purkinje fiber APD. We conclude: (1) that propafenone suppresses idioventricular rhythm in the intact dog, most likely by depressing Purkinje fiber automaticity; (2) the depressant effect of propafenone on sinus nodal automaticity is evident only during cholinergic receptor blockade; and (3) the antiarrhythmic properties of propafenone may include removal of APD disparity by selective shortening of Purkinje fiber and not of ventricular muscle APD.