Effect of quinidine and bretylium on defibrillation energy requirements

Abstract

We examined the effect of bretylium and quinidine on the energy requirements for internal defibrillation in 14 pentobarbital-anesthetized dogs. Bretylium, 6 or 10 mg/kg (n = 6), did not affect the relation between energy and the likelihood of successful defibrillation. The mean energy required to achieve 50% success (E 50) or 90% success (E 90) in defibrillation was not significantly altered; E 50 was 5.3 ± 1.9 J (x ± s.d) before and 6.1 ± 3.5 J after bretylium (n.s.), and E 90 was 7.2 ± 2.1 J before and 8.6 ± 3.3 J after drug (n.s.). Quinidine was administered in a series of two loading and maintenance infusions to achieve mean plasma concentrations of 2.4 ± 0.63 and 2.95 ± 0.88 μg/ml, respectively (n = 8). No significant effect on defibrillation energy requirement was observed; mean E 50 before and after treatment was 6.3 ± 3.3 J and 6.2 ± 2.9 J, respectively, and mean E 90 was 8.3 ± 4.4 J and 8.3 ± 4.1 J, respectively. Similarly, saline administration to control dogs (n = 12) resulted in no change in E 50 or E 90. At concentrations or doses similar to those in patients with serious arrhythmias, neither quinidine nor bretylium appears to have consistent effects on the energy requirements for internal defibrillation in our dog model.