Morphological studies of cellular responses to experimental arterial grafts

Cross-carotid microvascular bypass grafts 2-3 mm in diameter were implanted using microsurgical techniques for end-to-end anastomosis in four dogs. One autograft control and one of three denatured human umbilical artery xenografts (HUAG) were patent at 5 weeks. One of the other two denatured HUAGs had thrombosed at 1 week, and the other was occluded at 5 weeks. Host and graft vessel specimens were evaluated histologically as well as with transmission electron microscopy after sacrifice. Results indicate that failure of reconstitution of a true endothelial layer, presence of a subintimal myofibroblast population, increased collagen deposition of the muscularis, and occlusion of the adventitial and mural microcirculation were observed in both the early and late nonpatent vessels but not in the patent specimens. Evidence for myointimal cell proliferation was present in both patent and occluded grafts. A cohesive intimal layer was observed in both patent cases. Microvascular occlusion, due to an excess of endothelial cells, of new vasa vasorum in one case seems related to increased fibrosis, which could have resulted in graft stenosis. The surgical procedures and subsequent morphological analyses were adequate and sufficient for use in a long-term study of the possible causes of graft failure.