III. TYPES OF GRAFTS
A. Saphenous Vein
The saphenous vein is ideal for bypass of occlusions of the right coronary and circumflex coronary arteries and for their diagonal branches. A saphenous vein graft is easily harvested and is used in emergency situations. These include bypass of the LAD because the internal mam¬mary artery is more difficult to mobilize in emergency situations. Saphenous vein grafts are superior or equal to radial artery grafts, but are much more vulnerable to occlusion compared with the internal mammary artery Approximately 10% of saphenous grafts become obstructed during the perioperative period. At 1 year approxmately 22% are obstructed and at 5 and 10 years, approximately 30% and greater than 55%, respectively, of these grafts become occluded. During the first year after implantation of the vein graft, there is proliferation and migration of smooth muscle cell into the intima. The migration of smooth muscle cells is nature’s method of healing and strengthening damaged vascular endothelium and is an early stage of atheromatous formation. In these lesions there are lipid-laden form cells, cholesterol clefts, and areas of calcification and thrombosis that are features of atherosclerosis. Late occlusions are due to accelerated atherosclerosis that occurs in saphenous vein grafts. The saphenous vein in the leg never develops atherosclerosis and the atheromatous process occurs only after the graft is exposed to the high arterial pressure that is present in the coronary and systemic circulation; the low pulsatile pressure in veins protects the vessel from the development of atherosclerosis. Beta-blocking agents decrease cardiac ejection velocity and pulsatile blood flow, and along with marked blood LDL cholesterol reduction, may favora¬bly influence saphenous vein graft occlusion. Fortunately, atherosclerosis is rare in internal mammary artery grafts.