Comparison of exercise testing with studies of coronary flow reserve in patients with microvascular angina

Abnormal small coronary artery function may cause limited coronary flow responses to stress, resulting in anginal symptoms and ischemia in some patients with chest pain despite angiographically normal coronary arteries. To assess the exercise hemodynamic correlates of coronary flow abnormalities measured in the cardiac catheterization laboratory, 105 patients with microvascular angina (defined as an increase in coronary vascular resistance during pacing stress after ergonovine administration in the absence of significant epicardial constriction and associated with provocation of the patient's typical chest pain) and 27 patients without any coronary flow abnormality (normal) were analyzed. Of the 105 patients with microvascular angina, 75 had normal electrocardiographic responses to treadmill exercise testing, 22 had ischemic responses, and eight had bundle branch block during exercise. All 27 normal patients had normal electrocardiographic responses to exercise. Patients with ischemic electrocardiographic responses (0±7%,p<0.01), and those with bundle branch block (-2±6%,p<0.01) had abnormal left ventricular ejection fraction responses to exercise compared with the normal group, who demonstrated an 8±6% increase in left ventricular ejection fraction by radionuclide angiography during exercise, and microvascular angina patients with a normal electrocardiographic response to exercise, who demonstrated a 5±7% increase in ejection fraction. Although the microvascular response to ergonovine was no different among the three microvascular angina exercise groups, the administration of dipyridamole caused less coronary vasodilation in those patients with apparently ischemic or bundle branch block responses to exercise compared with those with normal electrocardiograms during exercise. Thus, the limited coronary flow response to dipyridamole may be closely related to the limited ejection fraction response to exercise and the abnormal electrocardiographic response during exercise, presumably reflecting reduced maximum coronary flow available to the myocardium during exercise stress. However, the electrocardiographic and ejection fraction responses to exercise did not separate patients with varying degrees of sensitivity to a vasoconstrictor stimulus such as ergonovine during stress.