REGULAR VENTRICULAR RHYTHMS BEFORE CONVERSION OF RECENT-ONSET ATRIAL-FIBRILLATION TO SINUS RHYTHM

The incidence of fast atrial tachycardias with regular Ventricular rhy thm was assessed in a population of 243 patients with recent onset (< 72 hours) atrial fibrillation (AF), without heart failure, randomly tr eated with single loading oral dose of propafenone (600 mg), flecainid e (300 mg), digoxin (1 mg), or placebo for acute conversion to sinus r hythm (SR). Fast atrial arrhythmias developed in 14 (6%) patients: 6/9 2 treated with propafenone, 3/34 treated with flecainide, 1/25 treated with digoxin, and 4/92 who received placebo (P = NS). Heart rate > 17 5 beats/min with 1:1 AV conduction ensued in 4 cases: 2 treated with f lecainide and 2 treated with placebo; in the other cases 2:2 AV conduc tion was observed. Widening of QRS during regular tachycardia was obse rved in 4 patients; 3 who received propafenone and 1 who received flec ainide. Conversion to SR within 4 hours was achieved in 55/92 (60%) pa tients treated with propafenone, 20/34 (59%) patients treated with fle cainide, 7/25 (28%) patients treated with digoxin, and 19/92 (20%) tre ated with placebo (P < 0.001 propafenone vs placebo and flecainide vs placebo; P < 0.05 propafenone vs digoxin and flecainide vs digoxin). P eriods of regular tachycardia are expected in recent onset AF and may not necessarily represent a proarrhythmic effect of Class 1C drugs, ra ther than mark the transition from AF to SR. Class 1C agents are proba bly responsible for widening of the QRS complex seen during these tach ycardias. Propafenone and flecainide appear equally effective in conve rting recent onset AF.