Mechanisms of arterial graft healing. Rapid transmural capillary ingrowth provides a source of intimal endothelium and smooth muscle in porous PTFE prostheses

Abstract

Endothelial coverage of an exposed synthetic vascular graft surface limits thrombosis and may improve long-term graft performance. In most types of synthetic graft, luminal endothelium is derived from the cut edges of adjacent artery. In this study the authors investigated the possibility that endothelial coverage could also be obtained by ingrowth of capillaries from the outside of the graft. Porous 4-mm polytetrafluorethylene (PTFE; 60 mu internodal distance) grafts were inserted into the aortoiliac circulation of baboons and were retrieved at intervals of up to 12 weeks. Between 1 and 2 weeks after surgery a continuous sheet of cells began to appear on the surface along the entire graft. These cells stained for Factor VIII related antigen, exhibited endothelial morphology by scanning electron microscopy, were associated with capillary orifices at the luminal surface, and covered the entire graft by 4 weeks. Transmural capillaries were observed to connect the graft lumen to extravascular granulation tissue. Despite full coverage of the graft, endothelial cells continued to exhibit increased proliferation (thymidine labeling) at 12 weeks. Smooth muscle cells (pericytes) accompanied capillary endothelium into the graft lumen, exhibited vascular smooth-muscle-specific immunostaining, and proliferated under the luminal endothelium to form intima. These results indicate that under some circumstances capillary endothelium and smooth muscle cells can function in the same manner as large vessel endothelium and smooth muscle and can provide rapid coverage of porous synthetic graft surfaces in contact with the arterial circulation.