Background: The aim of this study was to investigate both endothelium-dependent and endothelium-independent vasodilatation in syndrome X patients. Recently selective impairment of endothelium-dependent function has been reported in a small number of syndrome X patients. However, other investigators have reported impaired endothelium-independent function.
Methods: We infused the endothelium-independent vasodilators papaverine and glyceryl trinitrate, and endothelium-dependent vasodilator acetylcholine in the left coronary artery of 35 patients with syndrome X and in 17 control subjects (atypical chest pain, negative exercise test, and normal coronary angiograms). Coronary blood flow was measured with an intracoronary Doppler catheter positioned in the proximal left anterior descending coronary artery, and the artery diameter was assessed using quantitative coronary angiography.
Results: The mean increase in coronary blood flow in response to a 12 mg dose of papaverine was significantly less in the syndrome X group (185 +/- 74% vs 411 +/- 59%, P < 0.001). The increase in coronary blood flow in response to acetylcholine, at doses of 1, 3, 10, and 30 micrograms.min-1, was also significantly lower in the syndrome X group (12 +/- 13 (P < 0.05), 41 +/- 33, 57 +/- 68, and 124 +/- 87% (P < 0.001)) as compared to the control group (76 +/- 49, 214 +/- 116, 355 +/- 115, and 361 +/- 74%).
Conclusion: These findings demonstrate that both endothelium-dependent and endothelium-independent dilatation of the coronary microvasculature is impaired in syndrome X.