Effects of Atenolol, Verapamil, and Xamoterol on Heart Rate and Exercise Tolerance in Digitalised Patients with Chronic Atrial Fibrillation

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Abstract
The aim of the study was to compare the effects of atenolol (50 mg b.i.d.), verapamil (80 mg b.i.d.), xamoterol (200 mg b.i.d.), and matching placebo on heart rate (HR) and exercise tolerance in digitalised patients with chronic atrial fibrillation. Each treatment was taken for 4 weeks, and digoxin was continued throughout the study. During treatment with placebo (digoxin alone), the mean postexercise heart rate was 164 beats/min, and four subjects had rates of 2≥170 beats/min. Atenolol, verapamil, and xamoterol achieved significantly better control of exercise-induced tachycardia, mean postexercise heart rates being reduced to 120, 131, and 130 beats/min, respectively (p < 0.01 for each). However, minimum HRs ≤ 45 beats/min occurred during treatment with placebo, atenolol, and verapamil, whereas treatment with xamoterol was associated with a minimum heart rate of 56 beats/min. Treatment with atenolol was associated with a marked reduction in maximum treadmill walking distance (mean 356 m) as compared both with placebo (mean 421 m, p < 0.01) and verapamil (mean 439 m, p < 0.01). Xamoterol reduced maximum walking distances as compared with verapamil (402 vs. 439 m; p < 0.05) but not placebo (402 vs. 421 m; NSS). Thus, atenolol, verapamil, and xamoterol achieved better control of exerciseinduced tachycardia than digoxin, but atenolol clearly impaired exercise tolerance whereas verapamil did not. Xamoterol achieved more even control of ventricular response rates and prevented the resting bradycardias that occurred with the other treatments. However, walking distances were significantly lower than those noted during treatment with verapamil.