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 at rial 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 dru gs, or without drugs. Methods and Results At a mean follow-up of 9 months (range 1-24) all patien ts experienced recurrence of arrhythmia: 48 (14.6%, Group A) suffered Type 1 atrial flutter, and 257 (85.4%, Group B) atrial fibrillation. The relativ e rate of recurrence of atrial flutter vs atrial fibrillation was similar i n patients without treatment or with ventricular rate controlling, drugs (f rom 6.8% to 14.6%, P=ns). However, recurrence was higher (25%) in patients administered antiarrhythmic drug therapy. The relative risk in these patien ts was 3.02 times greater, compared with patients without treatment, or tre ated with rate controlling drugs (P<0.001). There were no differences betwe en groups concerning the baseline clinical characteristics and the clinical consequences of the recurrence, patients with atrial flutter had a lower r ate of conversion to sinus rhythm (42% vs 64%) and a higher rate of hospita l admission (69% vs 36%) compared with those with atrial fibrillation. Six patients (8.5%) experienced 1:1 atrioventricular conduction during atrial f lutter with a ventricular rate of 240-280 beats.min(-1) Conclusion Our data suggest that the use of antiarrhythmic drugs for the pr ophylaxis of atrial fibrillation is associated with a threefold increase in the probability of Type I atrial flutter recurrence. as opposed to atrial fibrillation, which may have important clinical consequences, but which did not in our study. (C) 1999 The European Society of Cardiology.