Conversion of recent onset paroxysmal atrial fibrillation to normal sinus rhythm: the effect of no treatment and high-dose amiodarone - A randomized,placebo-controlled study

Background Spontaneous conversion of recent onset paroxysmal atrial fibrill ation to normal sinus rhythm occurs commonly and is not affected by low-dos e amiodarone treatment. Methods In a randomized, placebo-controlled trial of 100 patients with paro xysmal atrial fibrillation of recent onset (<48 h) we compared the effects of treatment with continuous intravenous amiodarone 125 mg per hour (total 3 g) and intravenous placebo. Patients in the placebo group who did not con vert to normal sinus rhythm within 24 h were started on amiodarone therapy. Results Conversion to normal sinus rhythm occurred within 24 h in 32 of 50 patients (64%) in the placebo group, most of whom converted within 8 h. Low er conversion rates were observed in patients with hypertension, ischaemic heart disease or congestive heart failure and in patients with echocardiogr aphic findings of left atrial diameter above 45 mm, ejection fraction below 45% or significant mitral regurgitation. However, in most patients these c linical or echocardiographic risk factors of decreases in conversion rate w ere not present. In such patients the spontaneous conversion rate was appro ximately 90%. The conversion rate during 24 h of treatment in the amiodaron e group was 92% (P=0.0017, compared to the placebo group). In this group, t he conversion rate was largely unaffected by baseline characteristics. Of t he 18 patients who did not convert with placebo, 15 (85%) converted after b eing crossed over to amiodarone. All patients not responding to high-dose a miodarone were in chronic atrial fibrillation within 1 month. In patients s till in atrial fibrillation after g h of treatment, the pulse rate decrease d significantly more in the amiodarone as compared to the placebo group (83 +/- 15 vs 114 +/- 20 beats.min(-1), P=0.0014). Conclusion The spontaneous conversion of recent onset paroxysmal atrial fib rillation is high and approaches 90% in specific clinical and echocardiogra phically defined subgroups. Intravenous high-dose amiodarone safely facilit ates conversion of paroxysmal atrial fibrillation. However, such treatment should be reserved for patients with unfavourable risk factor profiles, not converting during sh of observation or requiring rate control. (Eur Heart J 1999; 20: 1833-1842) (C) 1999 European Society of Cardiology.