Morphologic observations in biologic conduits between aorta and coronary artery.

This report describes morphologic observations in autogenous saphenous veins, autogenous internal mammary arteries, radial arteries and arterial heterografts used as aortocoronary bypass conduits. The normal or expected changes and the abnormal or unexpected changes observed in each type of bypass conduit is discussed. The three major changes seen in saphenous vein grafts in the aortocoronary position are: (1) medial fibrous replacement; (2) adventitial fibrous proliferation; and (3) intimal fibrous proliferation. Medial fibrous replacement is the result of vein wall ischemia and necrosis and ultimately replacement of smooth muscle cells; adventitial fibrosis is the result of organization of fibrin and red cell clot and repair of ischemic damage. The cause of intimal fibrous proliferation is unclear but appears to be the result of chronic repair of injured intima and endothelium. That the severity of the changes varies along the length of one graft or among grafts in the same patient suggests that other factors contribute to the development of the changes observed. Although some structural changes have been observed, internal mammary arteries are relatively resistant to the changes seen in saphenous veins. Radial arterial grafts have shown severe structural changes with time, to a degree greater than that seen in the saphenous vein grafts. Heterograft conduits so far have been unsuccessful in the aortocoronary position in humans. The severe changes seen in radial artery and heterograft conduits indicate that they are inadequate for use as substitutes for saphenous vein and mammary artery as bypass conduits from aorta to coronary artery.