A single-blind, placebo-controlled study of effects of atenolol on transient ischemia in "mixed" angina.

The efficacy of atenolol in preventing episodes of transient ischemia during daily life was evaluated in 10 patients with "mixed" angina who underwent a 4-week, single-blind, double-crossover placebo-controlled trial. On day 6 and 7 of each treatment phase, continuous ambulatory electrocardiographic monitoring was performed for 48 hours. On day 7 an exercise test was also performed. Two-hundred and sixty-four ischemic episodes (79% "silent") were recorded during placebo treatment; 98 were recorded during atenolol treatment (63% decrease, p less than 0.01). In agreement with previous observations, most ischemic episodes observed during placebo (156 or 59%) were not preceded by an increase in heart rate. Surprisingly, the beneficial effects of atenolol were more pronounced for these episodes than for those preceded by an increase in heart rate and apparently caused by an increase in myocardial demand (decreases of 72% and 48%, respectively). Painful and painless episodes were decreased by a similar extent. In all patients, the heart rate recorded at the beginning of ST-segment depression was widely variable and significantly lower with atenolol (64 +/- 14 beats/min) than with placebo (81 +/- 13 beats/min, p less than 0.05). During both placebo and atenolol treatment, the highest incidence of ischemic events was observed between 6 A.M. and 9 P.M., in coincidence with the highest levels of the heart rate resting.(ABSTRACT TRUNCATED AT 250 WORDS)