Effects of acute intravenous and chronic oral amiodarone on defibrillation energy requirements.

Amiodarone is commonly used with the automatic implantable defibrillator to treat recurrent ventricular tachyarrhythmias. The effects of acute intravenous and chronic oral amiodarone on the energy requirements for successful defibrillation were evaluated in 12 dogs chronically instrumented with right atrial spring and left ventricular patch defibrillation electrodes. Multiple shocks of varying energy were applied in balanced random order to construct curves of percent successful defibrillation vs energy (DF curves) on each test day. Dogs were studied on days 1, 11, 18, 25, and 32. On day 11, DF curves were determined before and after infusing saline (n = 6) or amiodarone (n = 6), 10 mg/kg loading and 0.33 mg/kg/min maintenance doses. Dogs administered intravenous amiodarone were continued on oral drug (300 mg twice daily) for the remainder of the study. Data were analyzed by logistic regression and the energy required for 50% (E50) and 80% (E80) successful defibrillation were compared. Differences between controls and animals receiving chronic oral amiodarone were not significant on any day. After acute intravenous infusion, dogs given amiodarone had a 21.7 +/- 12.8% decrease in E50 (p less than 0.01) and a 19.7 +/- 17.8% decrease in E80 (p less than 0.05), while controls had an 11.4 +/- 30.5% increase (p = NS) in E50 and 6.30 +/- 30.5 increase in E80 (p = NS). It is concluded that the energy required for successful defibrillation is decreased by acute intravenous amiodarone, while chronic oral administration has no significant effect.