Effects of propafenone, quinidine, and their combination on ventricular fibrillation threshold in dogs

The effects of propafenone (Pro), a new Ic anti-arrhythmic agent (AAA), quinidine (Qui), and their combination on ventricular fibrillation threshold (VFT) and other electrophysiological properties were evaluated in 20 dogs. VFT was determined by a train of pulses, 4 ms in duration, delivered at 10 ms intervals. The results showed that in normal anesthetized, open-chest dogs: (1) Pro decreased VFT by 21.4%; (2) Qui increased VFT by 75.5%; (3) the Pro-induced decreased VFT was abolished by simultaneous administration of Qui; and (4) the above effects of the two drugs used separately or in combination on VFT were not related to their effects on ventricular effective refractory period and atrioventricular conduction time.