Vascular biology of coronary bypass grafts.

Clinical studies on the natural history of coronary bypass grafts strongly suggest that biologic properties of the vessels used importantly affect their function and patency. The endothelium is a source of substances regulating vascular tone, platelet function, and vascular growth; it produces nitric acid from L-arginine, which is a potent vasodilator and inhibitor of platelet function and has antiproliferative properties. Nitric oxide and prostacyclin, which have a similar profile of action, are released in greater amounts in arterial than venous coronary bypass vessels. Vascular smooth muscle cells are primary regulators of local blood flow and contribute to proliferative responses. The right gastroepiploic artery exhibits more pronounced contractions than the mammary artery but has a similar sensitivity to vasoconstrictors. Proliferative responses in coronary bypass vessels appear to be induced by changes in transmural pressure (particularly in veins), endothelial damage, and in turn, local release of platelet-derived growth factors, low-density lipoproteins, and intrinsic characteristics of the blood vessels. Thus, biologic properties of the endothelium and vascular smooth muscle significantly contribute to the function and patency of coronary bypass grafts. While the mammary artery has near-ideal characteristics, the right gastroepiploic artery exhibits marked contractile responses and the saphenous vein has unsatisfactory antithrombotic properties and more pronounced proliferative responses.