Effect of procainamide on the induction of ventricular fibrillation by sequential ventricular stimulation

The effect of procainamide on ventricular vulnerability to fibrillation was studied in 13 anesthetized open-chest dogs. Epicardial electrograms were recorded through forty bipolar electrodes placed on the surface of exposed ventricles. Ventricular fibrillation (VF) was induced by sequential extrastimulation. The number of extrastimuli required to induce repetitive extrasystole (RE) or VF were defined as repetitive extrasystole threshold (RET) or ventricular fibrillation threshold (VFT). The epicardial electrograms at the onset of ventricular arrhythmia were divided every 100 msec after the last extrastimulation, and the ratio of recordings with activation time of more than 50 msec during each divided period was defined as "chaotic score". Intravenous injection of procainamide at the dose of 20 mg/kg failed to increase RET but successfully increased VFT from 4.4 +/- 0.9 to 7.0 +/- 1.8 in hearts with necrosis. Procainamide significantly reduced chaotic score from 36 +/- 12% to 14 +/- 7% at 5 sec after the induction of ventricular arrhythmias. We concluded that the antifibrillatory action of procainamide is based on a reduction of the number of chaotic multiple reentries, but not on the prevention of reentry per se.