Morphine suppression of digitalis-induced ventricular arrhythmias

The purpose of the study was to investigate the effect of morphine on digitalis-induced arrhythmias. Seventeen normokalemic dogs [serum potassium 3.9 ± 0.3 mEg/L (±1 S.D.)] and 19 hypokalemic dogs (serum potassium 2.2 ± 0.3 mEg/L) were allocated to a morphine pretreatment group (morphine sulfate 3 mg/kg) or to a control group without morphine. Ouabain was administered by a constant infusion of 150 μg/kg/hr following an initial bolus of 20 μg/kg until animals developed ventricular tachycardia. In hypokalemic dogs, morphine pretreatment significantly (p < 0.05) increased the digitalis dose required to initiate ventricular tachyarrhythmias (66 ± 14 vs 37 ± 11 μg ouabain/kg). In normokalemic dogs morphine did not affect the relationship between digitalis dose and arrhythmias. Thus, morphine pretreatment reduces the tendency for hypokalemia to potentiate digitalis-induced ventricular arrhythmias.