Differential effects of xamoterol and verapamil on ventricular rate regulation in patients with chronic atrial fibrillation.

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)