Effect of basal epicardial tone on endothelium-independent coronary flow reserve measurement

Increased basal epicardial tone may attenuate the coronary flow reserve (CFR) by causing vasodilatation of resistance vessels. We examined the effect of basal epicardial tone on the endothelium-independent CFR measurements in subjects with nonobstructive coronary disease. Patients underwent evaluation of endothelium-independent CFR using adenosine (18-36 μg) and endothelium- dependent CFR using acetylcholine (10^-6M-10^-4M), both administered intracoronary. CFR to adenosine, presented as the ratio of Doppler flow velocities post- and pre-adenosine, was measured at baseline and after intracoronary nitroglycerin (200 μg). Nitroglycerin increased the coronary artery diameter by 19.7 ± 2.5%, and decreased the coronary vascular resistance from 3.0 ± 0.2 mm Hg/ml/min to 1.8 ± 0.1 mm Hg/ml/min (p < 0.0001). The response to adenosine at baseline and after nitroglycerin was similar (CFR ratio of 2.52 ± 0.09 and 2.57 ± 0.10, respectively, p = NS). The effect of nitroglycerin on the response to adenosine did not correlate with coronary endothelial function (r² = 0.06, p = 0.13). The basal epicardial tone does not affect CFR measurements in patients with angina and nonobstructive coronary disease.