Bretylium tosylate and electrically induced cardiac arrhythmias during hypothermia in dogs

Abstract

The effect of bretylium tosylate on plasma catecholamines and on electrically induced arrhythmias was evaluated in anesthetized hypothermic dogs. Bretylium at a dose of 7.5 mg/kg was administered prior to cooling from 37 degrees C to 27 degrees C. During cooling, the ventricular arrhythmia threshold (VAT) in control animals decreased from 10.1 +/- 1.9 to 4.4 +/- 1.3 impulses, while the VAT in bretylium-treated animals increased from 9.8 +/- 2.9 to 23.2 +/- 2.7 impulses. Catecholamine levels increased during cooling in all animals. In control animals, the epinephrine/norepinephrine ratio was unchanged, but in animals treated with bretylium tosylate, the ratio increased more than 10-fold (from 0.48 +/- 0.1 to 5.49 +/- 0.32 at 29.9 degrees C). The demonstrated increase in catecholamine levels during hypothermia suggests that the protection offered by bretylium tosylate against cardiac arrhythmias is not explained by modification of catecholamine levels, and is more likely due to an alteration of the electrophysiologic properties of cardiac tissues.