Rapid suppression of spontaneous ventricular arrhythmias during oral amiodarone loading

Objective: To determine the time course of effects of amiodarone during an oral loading period. Design: A prospective, nonrandomized study. Setting: Arrhythmia referral center at a university hospital. Patients: Fifty patients with refractory sustained ventricular tachycardia (n = 44) or ventricular fibrillation (n = 6) and frequent (≥ 30/h) ventricular premature complexes. Intervention: Oral amiodarone, 1200 mg/d for 14 days and 400 mg/d thereafter. Measurements: Ambulatory electrocardiographic monitorings, 12-lead electrocardiograms, and amiodarone blood levels on days 3, 5, 7, 9, 11, 13, and 28. Results: Dramatic reductions of ventricular arrhythmias were noted during the first 72 hours of the therapy. Average ventricular premature complexes/h, couplets/h, and nonsustained ventricular tachycardias/24 h were 524 ± 1224/h, 16 ± 61/h, and 167 ± 611/24 h, respectively, at baseline, and reduced to 140 ± 243/h, 11 ± 50/h, and 33 ± 117/24 h, respectively, on day 3 (P < 0.05 for all). Subsequent reductions of ventricular arrhythmias from day 3 to day 13 were more gradual but were still significant (P < 0.05). A significant reduction of ventricular arrhythmias (≥ 70% reduction of ventricular premature complexes and ≥ 90% reduction of nonsustained ventricular tachycardias) was noted in 50% of patients on day 3, in 65% on day 7, and in 83% on day 13. Prolongation of the QT interval exhibited a similar time course. There were no further differences in reduction of ventricular premature complexes or QT intervals between day 13 and day 28. Conclusions: Oral amiodarone given in loading doses produces rapid and dramatic reductions in spontaneous ventricular arrhythmias within 72 hours. Subsequent reductions of spontaneous arrhythmia were gradual and less dramatic.