Rapid suppression of spontaneous ventricular arrhythmias during oral amiodarone loading

To determine the time course of effects of amiodarone during an oral loading period.

A prospective, nonrandomized study.

Arrhythmia referral center at a university hospital.

Fifty patients with refractory sustained ventricular tachycardia (n = 44) or ventricular fibrillation (n = 6) and frequent (greater than or equal to 30/h) ventricular premature complexes.

Oral amiodarone, 1200 mg/d for 14 days and 400 mg/d thereafter.

Ambulatory electrocardiographic monitorings, 12-lead electrocardiograms, and amiodarone blood levels on days 3, 5, 7, 9, 11, 13, and 28.

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 less than 0.05 for all). Subsequent reductions of ventricular arrhythmias from day 3 to day 13 were more gradual but were still significant (P less than 0.05). A significant reduction of ventricular arrhythmias (greater than or equal to 70% reduction of ventricular premature complexes and greater than or equal to 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.

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.