FLOW-MEDIATED VASODILATOR RESPONSE TO TACHYCARDIA OF EPICARDIAL CORONARY-ARTERIES IS PRESERVED IN HEART-TRANSPLANT RECIPIENTS

Background. Increasing blood flow through conduit arteries induces vas odilation through endothelium-dependent mechanisms. In humans, flow-me diated dilation of angiographically normal epicardial coronary arterie s has been observed during tachycardia, this response being impaired i n the presence of atherosclerosis. Methods and Results. To evaluate wh ether the endothelium-dependent physiological vasodilatory response of epicardial coronary arteries to tachycardia is preserved in heart tra nsplant recipients, 22 patients with angiographically smooth coronary arteries were studied with quantitative angiography. A total of 14 pat ients had undergone cardiac transplantation more than 1 year (mean, 28 +/-18 months) before the study, and 8 patients were nontransplant pati ents with atypical chest pain and normal exercise tests (control group ). Angiograms of the left coronary artery were obtained on 35-mm cinef ilms at 3-minute intervals in basal conditions, during pacing-induced tachycardia (150 beats per minute), and after intracoronary injection of 1.5 mg of isosorbide dinitrate. During tachycardia, the mean lumina l diameter of the midsegment of the left anterior descending coronary artery increased by 8.9+/-6.1% from 2.64+/-0.56 to 2.88+/-0.62 mm (P<. 001) in transplant recipients and by 7.5+/-5.0% from 2.37+/-0.54 to 2. 53+/-0.50 mm (P<.025) in the control group (transplant vs control pati ents, NS). A further coronary dilation was observed in all patients af ter isosorbide dinitrate, up to 124.8+/-8.1% of basal lumen diameter i n transplant recipients and up to 129.1+/-16.1% of basal diameter in t he control group. Conclusions. The vasodilator response of epicardial coronary arteries to tachycardia is preserved in heart transplant reci pients. This suggests that the functional response of the endothelium to an increase in coronary blood flow remains normal in these patients .