Evidence of endothelial dysfunction in coronary resistance vessels in patients with angina pectoris and normal coronary angiograms.

This study determines whether an impaired endothelium-mediated vasodilation in coronary resistance vessels exists in patients with microvascular angina. In 23 patients with clinically suspected coronary artery disease and smooth coronary arteries in the angiogram, coronary flow in response to an endothelium-related (acetylcholine) and endothelium-unrelated (dipyridamole) vasodilation was measured. Coronary flow was determined by the gas-chromatographic argon method (1) before, (2) with intracoronary acetylcholine infusion, and (3) after dipyridamole administered intravenously. In 8 patients, acetylcholine did not significantly increase coronary flow (from 91 +/- 28 to 118 +/- 37 ml/min.100 g), whereas flow was greatly increased after administration of dipyridamole (258 +/- 97 ml/min.100 g), indicating an endothelium-related vasodilator defect. In 6 patients, neither acetylcholine nor dipyridamole caused a significant increase in coronary flow, indicating an impaired coronary vasodilation on the vascular site. In 6 patients, coronary flow increased markedly after both administration of both acetylcholine and dipyridamole (from 81 +/- 26 to 191 +/- 68 and 234 +/- 87 ml/min.100 g). In 3 patients given acetylcholine, coronary artery constriction occurred. No significant correlation was found between the response to acetylcholine and that to dipyridamole (r = 0.40, p = not significant). The results indicate that in a subgroup of patients with smooth coronary arteries angina can be caused by an abnormality of the endothelial function in the microcirculation.