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 fibrillation to normal sinus rhythm occurs commonly and is not affected by low-dose amiodarone treatment. Methods. In a randomized, placebo-controlled trial of 100 patients with paroxysmal 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 convert 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. Lower conversion rates were observed in patients with hypertension, ischaemic heart disease or congestive heart failure and in patients with echocardiographic findings of left atrial diameter above 45 mm, ejection fraction below 45% or significant mitral regurgitation. However, in most patients these clinical or echocardiographic risk factors of decreases in conversion rate were not present. In such patients the spontaneous conversion rate was approximately 90%. The conversion rate during 24 h of treatment in the amiodarone group was 92% (P = 0.0017, compared to the placebo group). In this group, the conversion rate was largely unaffected by baseline characteristics. Of the 18 patients who did not convert with placebo, 15 (85%) converted after being crossed over to amiodarone. All patients not responding to high-dose amiodarone were in chronic atrial fibrillation within 1 month. In patients still in atrial fibrillation after 8 h of treatment, the pulse rate decreased 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 fibrillation is high and approaches 90% in specific clinical and echocardiographically defined subgroups. Intravenous high-dose amiodarone safely facilitates conversion of paroxysmal atrial fibrillation. However, such treatment should be reserved for patients with unfavourable risk factor profiles, not converting during 8 h of observation or requiring rate control.