Comparative effects of epanolol and diltiazem on exercise performance and respiratory gas exchange in angina pectoris

The effects of epanolol (a new selective beta-adrenoceptor antagonist), diltiazem and placebo were compared in a group of 16 patients with chronic stable angina pectoris. Each patient received each treatment in random order. Diltiazem reduced weekly angina attack rate from 7.2 (95% CI 3.9-10.5) to 3.9 (1.9-5.9) (P less than 0.01), whereas a lesser reduction was observed after epanolol. Both drugs produced a small but significant (P less than 0.05) increase in treadmill exercise time (placebo 474 s (374-574), epanolol 527 s (431-623) and diltiazem 554 s (462-646). However, aerobic work capacity, assessed by peak achieved oxygen consumption, was not different from the placebo value of 21.2 (18.0-24.4) ml.min-1.kg-1, and clearly subnormal when compared to age- and sex-matched controls (33.0 (30.1-35.9) ml.min-1.kg-1). Ventilatory abnormalities and increased lactate levels on active treatment were observed at peak exercise only. We conclude that the cardiodepressant effects of both active drugs limit blood supply to working skeletal muscle, and that chest pain may be replaced by dyspnoea or fatigue as the limiting factors to exercise.