A method for quantitating antifibrillatory effects of drugs after coronary reperfusion in dogs: improved outcome with bretylium.

We developed a quantitative approach to assess the antifibrillatory effects of short-term interventions in a canine preparation of ventricular fibrillation caused by coronary reperfusion, and applied it to evaluate the antifibrillatory effects of bretylium tosylate. Twenty-five dogs were given 10 mg/kg infusions of bretylium over 10 min, subjected to a 20 min proximal left anterior descending coronary artery ligation followed by sudden release, and compared with 25 animals given saline placebo. Drug infusion was begun 90 min before reperfusion to avoid evaluation of outcome during the phase of drug-induced catecholamine release and to allow adequate time for bretylium uptake in the myocardium. The relationship between the likelihood of ventricular fibrillation during reperfusion and the amount of myocardium perfused by the occluded vessel (myocardium at risk) was analyzed with the logistic risk-regression model. This model was developed to control for the effects of amount of myocardium at risk on outcome. For both the bretylium and the placebo groups the incidence of ventricular fibrillation correlated significantly with amount of myocardium at risk. However, animals treated with bretylium had an improved outcome for a given amount of myocardium at risk. In other words, the curve relating outcome to myocardium at risk was shifted significantly to the right. The amount of myocardium at risk required for half the placebo-treated animals to fibrillate was 20.3 g and that required for half the bretylium-treated animals to fibrillate was 27.9 g, or 37% more than that for the placebo group. This logistic risk-regression analysis format permits quantification of treatment effects while accounting for variability in amount of myocardium at risk.