Usefulness of changes in exercise tolerance induced by nitroglycerin in identifying patients with syndrome X

Abstract

Two exercise tests, one under basal conditions and one after sublingual nitroglycerin (NTG), were performed in 39 patients with stable angina pectoris—16 with critical coronary stenoses and 23 with normal coronary arteries (syndrome X). Under basal conditions, times at ischemic threshold, at peak exercise, and at complete ECG recovery were similar in the two groups. Peak ST depression was significantly higher in patients with coronary artery disease (CAD). In a similar proportion of patients, ST-segment depression developed earlier or at a low heart rate. Patterns of heart rate, blood pressure, and rate-pressure product during exercise and recovery were also similar. After NTG an increase in the ischemic threshold was observed in a significantly higher proportion of patients with CAD (93.8% vs 39.1%). Furthermore, a subgroup of patients with syndrome X showed a worsening of exercise performance. This suggests that NTG does not directly affect small coronary vessels. Our results confirm that no relevant differences exist in exercise responses between patients with CAD and those with syndrome X uncer basal conditions. NTG-induced changes in this response could be useful in indentifying patients with normal coronary arteries. Moreover, this test could be used as a guide to therapeutic approaches.