Effect of chronic amiodarone therapy on defibrillation energy requirementsin humans

Introduction: The effect of oral amiodarone therapy on defibrillation energ y requirements in patients with an implantable defibrillator has not been e stablished. Methods and Results: Twenty-one Consecutive patients with implantable bipha sic waveform defibrillators underwent a step-down determination of the defi brillation energy requirement 211 +/- 12 days before and 73 +/- 22 days aft er initiation of amiodarone therapy (mean total dose 26.7 +/- 11.1 g). Seru m amiodarone and desethylamiodarone concentrations were measured at the tim e of defibrillation energy requirement determination. The mean defibrillati on energy requirement before amiodarone therapy was 9.9 +/- 4.6 J. After in itiation of amiodarone therapy, the mean defibrillation energy requirement increased to 13.7 +/- 5.6 J (P = 0.004). A linear relationship between the amiodarone (P = 0.02, r = 0.6), desethylamiodarone (P = 0.02, r = 0.6), and combined amiodarone-desethylamiodarone concentrations (P = 0.01, r = 0.6) and the defibrillation energy requirement was noted. Stepwise regression an alysis demonstrated that the combined amiodarone-desethylamiodarone concent ration was the only independent predictor of increase in the defibrillation energy requirement. Conclusion: Chronic oral amiodarone therapy increases the defibrillation en ergy requirement by approximately 62% in patients with an implantable defib rillator. The combined amiodarone-desethylamiodarone concentration is direc tly related to the increase in the defibrillation energy requirement.