Effect of metoprolol on the submaximal stress test performed early after acute myocardial infarction

To determine the effect of β-adrenergic blockade on the submaximal stress test after acute myocardial infarction (AMI), 36 post-AMI patients performed their treadmill test on 2 separate days, with and without metoprolol, in a double-blind, placebo-controlled, crossover design study. Rest and peak submaximal exercise heart rate was diminished by 100 mg of metoprolol administered twice daily (from 84 ± 3 to 68 ± 2 beats/min, p < 0.001, and from 126 ± 3 to 97 ± 2 beats/min, p < 0.001, respectively) compared with placebo. Rest and peak submaximal systolic blood pressure was also decreased (from 121 ± 3 to 108 ± 2 mm Hg, p < 0.001, and from 151 ± 4 to 124 ± 3 mm Hg, p < 0.001). Exercise-induced ST-segment depression of 1 mm or more from baseline occurred in 12 patients taking placebo. However, only 4 of these patients had ST depression when they exercised while taking metoprolol (p < 0.05). Angina pectoris occurred in 4 patients taking placebo but in only 1 of these taking a β-blocking drug. It is concluded that β-blocking therapy renders the post-AMI submaximal stress test less sensitive for markers of exercise-induced ischemia than if the test is performed without the drug. Therefore, when using the prognostic information of published studies, it is important to define the conditions surrounding the exercise test.