Stability of electrophysiological parameters after acute amiodarone loading: implications for patient management

The appropriate timing of electrophysiological study in patients treated with amiodarone is uncertain. Twenty patients with coronary artery disease in whom sustained ventricular tachycardia was still inducible after 9 +/- 1 days of amiodarone loading (1,200-1,400 mg/day) underwent repeat electrophysiological testing after an additional month of maintenance therapy (400 mg/day). Compared with baseline, both short- and long-term amiodarone therapy caused significant changes in QTc, right ventricular effective refractory period, and ventricular tachycardia cycle length. However, there was no significant change in electrophysiological parameters between the end of the acute amiodarone loading period and 1 month of additional therapy. Sustained ventricular tachycardia remained inducible in 19 of 20 patients after 1 month of maintenance therapy. Amiodarone and desethylamiodarone plasma concentrations remained stable after amiodarone loading, but did not correlate with the magnitude of electrophysiological changes from baseline. These data suggest that electrophysiological testing after 9 days of high dose amiodarone therapy may accurately reflect long-term electrophysiological effects.