Regular ventricular rhythms in patients with symptomatic paroxysmal atrial fibrillation.

Paroxysmal atrial fibrillation is a grossly irregular tachycardia. Forty-nine patients with paroxysmal atrial fibrillation who were taking a variety of antiarrhythmic medications including the class IC agents propafenone and flecainide were followed up for a median of 371 days with use of transtelephonic electrocardiogram (ECG) monitoring to document symptomatic rhythms. Eighteen patients had 96 episodes of regular tachycardia; the cumulative incidence rate was 25% at 6 months, 33% at 1 year and 41% at 18 months. Eighty of the 96 episodes occurred with a heart rate less than or equal to 180 beats/min and could have been explained by atrial flutter with 2:1 block. However, nine patients had a total of 16 episodes with a rate greater than 180 beats/min that were probably not due to atrial flutter with block; the cumulative incidence rate of these fast regular tachycardias was 14% at 6 months, 17% at 1 year and 25% at 18 months. QRS duration during the first episode of regular tachycardia was significantly longer in patients taking a class IC drug (median 105 vs 90 ms, p less than 0.001 Wilcoxon rank sum test). In contrast to drug therapy with amiodarone or the combination of digoxin and verapamil, the QRS duration of regular tachycardias during class IC therapy was directly related to the tachycardia heart rate (Spearman's rank, p less than 0.01). All episodes of fast, regular tachycardias with a QRS duration greater than 120 ms occurred in patients taking a class IC drug. Clinicians treating patients with paroxysmal atrial fibrillation should expect a substantial incidence of regular tachycardia in addition to atrial fibrillation.