Effects of angiotensin-converting enzyme inhibition on exercise-induced angina and ST segment depression in patients with microvascular angina

Department of Cardiological Sciences, St. George's Hospital Medical School, London, England, United Kingdom.

OBJECTIVES. This study was conducted to test the hypothesis that angiotensin-converting enzyme inhibition may lessen myocardial ischemia in patients with microvascular angina. BACKGROUND. Patients with syndrome X (angina pectoris, positive findings on exercise testing and normal coronary arteriogram) have a reduced coronary vasodilator reserve ("microvascular angina") and may show an increased sympathetic drive. Angiotensin-converting enzyme inhibition attenuates sympathetic coronary vasoconstriction in patients with coronary artery disease. METHODS. Ten patients (seven women and three men, mean age [+/- SD] 53 +/- 6 years) with syndrome X and a reduced coronary flow reserve underwent a randomized, single-blind, crossover, placebo-controlled study of the effects of the angiotensin-converting enzyme inhibitor enalapril on angina and exercise-induced ST segment depression. Assessment was by symptom-limited treadmill exercise testing after 2 weeks of treatment with 10 mg/day of enalapril and after 2 weeks of placebo administration. RESULTS. All patients had positive findings on exercise testing (> or = 1 mm ST segment depression and angina) while taking placebo, whereas six patients had a positive test result (four with angina) during enalapril therapy. Total exercise duration and time to 1 mm of ST segment depression were prolonged by enalapril over those obtained with placebo (mean 779 +/- 141 vs. 690 +/- 148 s, p = 0.006 and 690 +/- 204 vs. 485 +/- 241 s, p = 0.007, respectively). The magnitude of ST segment depression was also less with enalapril than with placebo (mean 1.1 +/- 0.4 vs. 1.5 +/- 0.2 mm, p = 0.004). Heart rate and blood pressure at peak exercise and at 1 mm of ST depression were not significantly different during placebo and enalapril treatment. CONCLUSIONS. Angiotensin-converting enzyme inhibition lessens exercise-induced ischemia in patients with syndrome X and microvascular angina, probably by a direct modulation of coronary microvascular tone, which results in an increased myocardial oxygen supply.

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