In a placebo-controlled study the effects on ventricular rate regulation and exercise performance of
xamoterol, 100 mg two times a day and 200 mg two times a day, and slow-release
verapamil, 240 mg once a day, were assessed in 21 patients with chronic
atrial fibrillation. The mean ventricular rate from noon to 6:00 PM was 101 +/- 20 beats/min with placebo, 95 +/- 17 beats/min with
xamoterol 100 mg two times a day (not significant), 90 +/- 16 beats/min with
xamoterol 200 mg two times a day (p less than 0.001 vs placebo) and 78 +/- 19 beats/min with
verapamil (p less than 0.001 vs each other treatment). The mean ventricular rate from midnight to 6:00 AM was 69 +/- 16 beats/min with placebo, increased with
xamoterol 100 mg two times a day and 200 mg two times a day to 75 +/- 15 beats/min and 74 +/- 16 beats/min, respectively (p less than 0.001 vs placebo), but decreased with
verapamil to 62 +/- 15 beats/min (p less than 0.001 vs each other treatment). The number of ventricular pauses greater than 2.0 seconds was increased by
verapamil (p less than 0.05). All active treatments reduced exercise ventricular rates (p less than 0.001), but the decrease was more pronounced with
verapamil. The anaerobic threshold was reached significantly earlier with
verapamil than with placebo (72 +/- 32 W vs 79 +/- 37 W; p less than 0.01).
Xamoterol is preferable to
verapamil for treatment of patients with chronic
atrial fibrillation who exhibit both
bradycardia at rest and excessive
tachycardia during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)