Exacerbation of coronary occlusion induced ventricular arrhythmias by the vagolytic effect of procainamide

The influence of the vagolytic effect of procainamide on the early ventricular arrhythmias induced by left anterior descending coronary (LAD) occlusion was studied in chloraloseanaesthetised cats. All control animals developed a ventricular arrhythmia (1119 +/- 166 PVCs per hour), with a consistent onset time, duration, and overall mortality due to ventricular fibrillation (ie 20%). In 18 animals pretreated with procainamide (0.5 mg.kg-1.min-1 for 50 min), there was no effect on the ventricular arrhythmia in terms of ectopic frequency (1020 +/- 180 PVCs per hour), time to onset of arrhythmia, duration of arrhythmia, and mortality incidence (ie 16.7%). However, subdividing the data according to whether or not vagal blockade had been produced by procainamide revealed that animals exhibiting complete vagal blockade demonstrated significantly more ectopic beats (1606 +/- 310 PVCs per hour) and 33% developed ventricular fibrillation. Treated animals without complete vagal blockade exhibited an ectopic frequency rate of 620 +/- 98 PVCs per hour and none of the animals developed ventricular fibrillation. The haemodynamic parameters were similar between both procainamide treated subgroups. These results suggest that an important factor in response of the ischaemic heart to the cardiac rhythm effects of procainamide is the degree of vagal blockade induced by this agent.