Endothelium-dependent and endothelium-independent vasodilator response of left and right internal mammary and internal thoracic arteries used as a composite Y-graft

Objective: The manner in which a blood vessel is for used as a coronary graft may be important in maintaining a viable and functional endothelial lining. Composite internal thoracic arteries (ITAs) in a Y-graft configuration are characterized by the connection of an in situ left ITA with preserved innervation and lymphatics and of a free semi-skeletonized right ITA. Methods: To determine whether endothelial function differs between left and right ITA segments in a Y-graft configuration, 11 patients were studied 3 years after surgery. The endothelium-dependent vasodilator substance P was selectively infused (1.4-22.4pmolmin ^-1 in doubling dose increments) in the ostium of ITA Y-grafts. A maximal endothelium-independent vasodilatory response was then obtained by intragraft infusion of 2mg isosorbide dinitrate (ISDN). Biplane angiograms obtained at 3-min intervals using an automated contrast injection system with fixed preset volume and pressure parameters were analyzed off-line using a quantitative analysis system (CAAS, Pie Medical). Results: A similar dose-dependent vasodilatory response to substance P was observed in the left and in the right ITA. No difference in maximal endothelium-dependent response to substance P (7.4±4.3% in the left ITA and 8.1±5.3% in the right ITA) or in maximal endothelium-independent response to ISDN (12.2±4.4% in the left ITA and 10.6±8.1% in the right ITA) was observed. Conclusions: The endothelium-dependent and the endothelium-independent vasodilator capacity of the two branches of a Y-graft ITA configuration appear similar 3 years after bypass surgery. This suggests that the preservation of the ITA pedicle does not significantly affect basal vasomotor tone, long-term endothelial function, or vasodilator reserve.