Effect of caffeine on the ventricular fibrillation threshold in normal dogs and dogs with acute myocardial infarction

The effect of caffeine administration on the VFT was studied in normal dogs and in dogs with acute myocardial infarction. Two methods were employed; the first utilized impulses delivered through the chest wall of the intact animal and the second used epicardial electrodes implanted four to seven days previously. Caffeine produced a decrease in VFT starting 15 minutes after injection and this effect lasted about 60 minutes. Propranolol and practolol prevented the caffeine-induced decrease of VFT. In dogs with acute myocardial infarction the VFT was lower than normal and was further decreased after caffeine administration. Although the dose of caffeine utilized in this study is higher than that usually consumed by humans, it is possible that lower doses have a significant effect when combined with other agents. The various factors that affect the VFT which might have arrhythmogenic effects are presently under study. There is suggestive evidence that a number of factors might be cumulatively significant in susceptible individuals. These factors may include cigarette smoking, various degrees of stress effects due to anxiety and exertion, various drugs—i.e., isoproterenol, ephedrine, and several sympathomimetic agents, and caffeine. The role of caffeine requires further study in this regard.