In patients with angiographically detectable atherosclerosis or in those with risk factors for coronary artery disease, intracoronary acetylcholine causes coronary constriction instead of endothelium-derived relaxing factor-mediated dilation. Therefore, it has been hypothesized that diffuse endothelial dysfunction precedes development of coronary atherosclerosis. We tested this hypothesis in a systematic investigation of the effects of ascending doses of acetylcholine on the diameters of nonstenotic segments of the left coronary artery in patients with advanced atherosclerosis and coronary risk factors.Methods and Results
Effects of intracoronary infusion of acetylcholine (10−6 to 10−4 mol/L) on diameters of proximal, middle, and distal nonstenotic segments of the left coronary artery were studied in 28 consecutive patients with chronic stable angina, positive exercise tests, and angiographic evidence of obstructive atherosclerosis (≥50% reduction in lumen diameter in at least one vessel). Two patterns of response to the maximal acetylcholine dose (10−4 mol/L) were observed. In 21 patients (group 1), only constriction was observed in all left anterior descending and circumflex artery segments studied (16±3%, 19±4%, and 23±4%, respectively; P < .01 compared with control). In 7 other patients (group 2), both constriction and dilation were observed in adjacent segments of the same vessel; maximal acetylcholine dose caused constriction in 14 left anterior descending artery segments from a control diameter of 1.94±0.19 to 1.33±0.26 mm (37% reduction, P < .01) and dilation in 16 other segments from 1.63±0.22 to 1.93±0.21 mm (25% increase, P < .01). In the circumflex artery, this dose caused constriction in 16 segments from a control diameter of 1.88±0.14 to 1.33±0.17 mm (31% reduction, P < .01) and dilation in 12 segments from 1.37±0.12 to 1.71±0.09 mm (34% increase, P < .01).Conclusions
In 25% of patients studied with advanced angiographic coronary atherosclerosis and coronary risk factors, coronary segments with acetylcholine-inducible dilatation are present. In these patients, the endothelium is not diffusely dysfunctional as currently believed but rather shows marked segmental heterogeneity in the response to acetylcholine reflecting degrees of endothelial dysfunction.