Effects of (-), (+/- ), and (+) verapamil on coronary occlusion-induced mortality and infarct size

In a blind and randomised study, (-), (+/- ), and (+) verapamil were compared for their abilities to reduce mortality induced by occlusion of the left anterior descending coronary artery in conscious rats. In addition, effects on infarct size were also measured. In a separate experiment, the ability of an observer to detect ventricular fibrillation (VF) on the basis of changes in behaviour alone was established; (+/- ) verapamil statistically significantly reduced total mortality compared with controls, while (-) verapamil produced a similar, but non-statistically significant reduction. Both (+/- ) and (-) verapamil reduced mortality caused by VF; (-) verapamil was more effective than (+/- ) verapamil. Neither (-), (+/- ), nor (+) verapamil reduced infarct size in 24-h survivors; (-) verapamil produced the highest incidence of morbidity and associated cardiovascular depression (hypotension, bradycardia, and P-R interval prolongation), whereas (+) verapamil produced the least. Since (-) verapamil is a more potent calcium antagonist than (+) verapamil, the results of this study support the hypothesis that calcium antagonism was responsible for the observed antiarrhythmic actions.