Epicardial mapping of polymorphous ventricular tachycardias induced in the canine heart with procainamide

To elucidate the mechanisms of the arrhythmogenic and antifibrillatory action of procainamide, 24 episodes of polymorphous ventricular tachycardia were analyzed. They were induced electrically in 12 canine hearts before and after the administration of 40 mg/kg of procainamide. The isochronal maps of the epicardial activation sequence were successfully constructed by 40 simultaneously recorded bipolar electrograms in 14 of 17 episodes after procainamide. The isochronal maps showed a possible macroreentrant circuit in 12 episodes, and in four of them the functional block was noticed to have disappeared before the termination of tachycardia. This study suggests that procainamide predisposes the ventricle to reentrant tachyarrhythmias and that the dimension of the reentrant circuit induced is too large to be fragmented into multiple reentries, which results in the prevention of the development of ventricular fibrillation.