EFFECTS OF LONG-TERM AMIODARONE THERAPY ON THE DEFIBRILLATION THRESHOLD AND THE RATE OF SHOCKS OF THE IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR

The effects of long-term amiodarone therapy on the defibrillation thresholds and the rate of shocks were evaluated in 62 patients who had implantation of an automatic cardioverter-defibrillator (n = 53) or prophylactic implantation of patch electrodes (n = 9) who were survivors of sudden cardiac death (n = 34) or had refractory rapid ventricular tachycardia (n = 28). There were 53 men and 9 women, with ages ranging from 18 to 76 years (mean +/- SD, 60 +/- 12). Coronary artery disease occurred in 50 patients (80.6%), cardiomyopathy occurred in six (9.7%), valvular heart disease developed in two (3.2%), primary electrical disease developed in two (3.2%), hypertensive heart disease materialized in one (1.6%), and Ebstein's anomaly occurred in one (1.6%). The left ventricular ejection fraction varied from 10% to 75% (mean, 37 +/- 17%). All patients had failed a mean of 3.9 +/- 1.6 antiarrhythmic drugs prior to implantation of the device. Twenty-eight patients (45%) were taking amiodarone up to the time of surgery, with a mean daily dose of 406 +/- 147 mg (range 200 to 800) and for a mean duration of 6.0 +/- 6.7 months (range 1 to 36 months). The mean defibrillation threshold (DFT) was 12.0 +/- 4.4 joules (range 5 to 20) in the group taking amiodarone and was not significantly different from that of the group not taking amiodarone (n = 32) (mean DFT 12.3 +/- 5.5 joules, range 5 to 30; p = 0.77). After discharge from the hospital, 53 patients were followed for a mean of 17.8 +/- 14.4 months (range 1 to 63), and 25 (47%) of them were continued on a regimen of amiodarone with a mean daily dose of 344 +/- 122 mg (range 100 to 600). A total of 179 presumable appropriate shocks were registered in 8 of 25 patients (32%) taking amiodarone and 126 appropriate shocks were given in 8 of 28 patients (29%) who were not taking amiodarone. This study suggests that (1) long-term amiodarone therapy does not increase the defibrillation thresholds in patients undergoing implantation of an automatic cardioverter-defibrillator and (2) a significant number of patients receiving long-term amiodarone therapy continue to suffer from ventricular tachyarrhythmias and require repeated shocks from the device.