Incidence and clinical significance of transformation of atrial fibrillation to atrial flutter in patients undergoing long-term antiarrhythmic drug treatment

Aims: To investigate the rate of transformation of atrial fibrillation to atrial flutter in patients taking antiarrhythmic drugs for the prophylaxis of atrial fibrillation, we retrospectively analysed data from 305 consecutive patients with paroxysmal atrial fibrillation (155 male; mean age 63 ± 11 years) treated with ventricular rate controlling drugs, antiarrhythmic drugs, or without drugs. Methods and Results: At a mean follow-up of 9 months (range 1-24) all patients experienced recurrence of arrhythmia: 48 (14·6%, Group A) suffered Type 1 atrial flutter, and 257 (85·4%, Group B) atrial fibrillation. The relative rate of recurrence of atrial flutter vs atrial fibrillation was similar in patients without treatment or with ventricular rate controlling drugs (from 6·8% to 14·6%, P=ns). However, recurrence was higher (25%) in patients administered antiarrhythmic drug therapy. The relative risk in these patients was 3·02 times greater, compared with patients without treatment, or treated with rate controlling drugs (P<0.001). There were no differences between groups concerning the baseline clinical characteristics and the clinical consequences of the recurrence; patients with atrial flutter had a lower rate of conversion to sinus rhythm (42% vs 64%) and a higher rate of hospital admission (69% vs 36%) compared with those with atrial fibrillation. Six patients (8·5%) experienced 1:1 atrioventricular conduction during atrial flutter with a ventricular rate of 240-280 beats.min-1. Conclusion: Our data suggest that the use of antiarrhythmic drugs for the prophylaxis of atrial fibrillation is associated with a threefold increase in the probability of Type 1 atrial flutter recurrence, as opposed to atrial fibrillation, which may have important clinical consequences, but which did not in our study.