Exercise testing in patients with microvascular angina

The widespread use of exercise testing for the detection of myocardial ischemia in patients suspected of having coronary artery disease led to the detection of ischemic changes in many subjects who subsequently were found to have angiographically normal epicardial vessels - the false positive response. Such a result is usually interpreted as indicating that the subject's chest pain is of noncardiac origin. For the past several years, we have studied the mechanism of pain resembling angina that occurs in patients with normal epicardial coronary arteries demonstrated by angiography; we believe these studies have shed some light on this problem. Patients with angiographically normal coronary arteries who present because of a history of angina-like pain and/or ischemic changes detected during exercise electrocardiogram testing were evaluated by measuring great cardiac vein flow (under baseline conditions and after cardiac pacing, with and without intravenous administration of ergonovine) and by radionuclide angiography before and during exercise. We found that a substantial number of these subjects showed inadequate coronary vasodilator reserve and had exercise-induced left ventricular dysfunction suggestive of myocardial ischemia. We concluded from our results that there is a distinct clinical syndrome of myocardial ischemia caused by abnormal resistance responses of the prearteriolar coronary microvasculature. We now refer to this syndrome as microvascular angina. In a series of 115 patients with documented microvascular angina, we also found that only 10% had ischemic ST changes with exercise testing (2% of the men and 17% of the women developed ischemic ST segment changes). However, almost 70% of these patients had one or more abnormalities of left ventricular systolic function during exercise as assessed by radionuclide angiography. The low sensitivity of the electrocardiogram for detecting ischemia probably is caused by the ischemia being mild in such patients, and possibly by the existence of a diffuse pattern of ischemia obviating the development of a net electrical vector. We conclude that a positive exercise stress test cannot be considered false positive merely because coronary angiography discloses no epicardial coronary artery disease; the possibility of microvascular angina must be raised and appropriate studies conducted.