Flow-mediated vasodilator response to tachycardia of epicardial coronary arteries is preserved in heart transplant recipients

Background. Increasing blood flow through conduit arteries induces vasodilation through endothelium-dependent mechanisms. In humans, flow- mediated dilation of angiographically normal epicardial coronary arteries has been observed during tachycardia, this response being impaired in the presence of atherosclerosis. Methods and Results. To evaluate whether the endothelium-dependent physiological vasodilatory response of epicardial coronary arteries to tachycardia is preserved in heart transplant recipients, 22 patients with angiographically smooth coronary arteries were studied with quantitative angiography. A total of 14 patients had undergone cardiac transplantation more than 1 year (mean, 28±18 months) before the study, and 8 patients were nontransplant patients with atypical chest pain and normal exercise tests (control group). Angiograms of the left coronary artery were obtained on 35-mm cinefilms 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 luminal 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 patients, NS). A further coronary dilation was observed in all patients after isosorbide dinitrate, up to 124.8±8.1% of basal lumen diameter in transplant recipients and up to 129.1±16.1% of basal diameter in the control group. Conclusions. The vasodilator response of epicardial coronary arteries to tachycardia is preserved in heart transplant recipients. This suggests that the functional response of the endothelium to an increase in coronary blood flow remains normal in these patients.