786-3 Adenosine Causes Flow-Mediated Epicardial Vessel Dilation in Humans

The predominant effect of intracoronary adenosine (Ad) is vasodilation of the microcirculation, but Ad also increases epicardial coronary artery diameter. It is not known whether epicardial dilation is a direct action of Ad or an indirect effect mediated by increased flow or shear stress. We reasoned that changes in the diameter of the left anterior descending (LAD) artery upstream to the site of Ad delivery must reflect an indirect effect. whereas downstream vasodilation would reflect the sum of direct and indirect effects. We therefore compared changes in upstream and downstream LAD diameter in 11 patients without significant coronary artery disease in whom LAD flow increased at least three-fold (n = 6) or remained unchanged (n = 5) in response to Ad 10 -4 M infused via a 3F Doppler catheter. LAD diameter was assessed by quantitative angiography 2.5 upstream and 2.5 mm downstream to the site of Ad delivery. LAD flow was calculated as the product of downstream cross-sectional area and Doppler velocity. LAD diameter (mm) is shown as mean ± standard error of the mean. Flow Increased Flow Unchanged Baseline Adenosine p Baseline Adenosine p Downstream 2.08 ± 0.22 248 ± 0.30 0.06 1.97 ± 0.16 1.99 ± 0.14 0.16 Upstream 2.38 ± 0.20 2.65 ± 0.21 0.004 2.28 ± 0.26 2.18 ± 0.26 0.23 Thus, epicardial vessel dilation in response to Ad occurs only in the presence of an increase in coronary blood flow, and there is significant dilation upstream from the site of Ad infusion. Conclusions Adenosine causes flow-mediated epicardial vessel dilation in humans, with little or no direct effect on epicardial vessel diameter.