The morphology of venovenous bypass graft endothelium

Venovenous bypass grafts are commonly used in the repair of vascular trauma to large- and small-caliber veins. This study examines the morphology of the venous wall in an experimental model of the venovenous bypass graft. The morphology of the venous endothelium from unmanipulated jugular veins and from jugular veins implanted as a venovenous bypass graft in the external jugular venous system for 10 min, 6 h, and 1, 3, 5, 7 and 28 days was examined. Veins and venovenous grafts were pressure fixed in situ at 80 mmHg and were examined by scanning and transmission electron microscopy. The endothelial cell lining remained confluent and intact over the 28-day period with evidence of endothelial cell contraction (spindle-shaped cells) for the first 72 h. Pinocytotic activity in endothelial cells and underlying smooth muscle cells was observed throughout the study, strongly indicating physiologically active cells. There was some accumulation of blood cells, predominantly polymorphonuclear leukocytes on the endothelial surface. Polymorphonuclear leukocytes were observed to infiltrate into the subendothelium through endothelial cell junctions within 6 h but by day 3, none was noted in the subendothelial space. There was no major disruption of the graft wall at any time point. By day 28, there was evidence of intimal thickening in the venovenous bypass grafts but no well-demarcated intimal hyperplasia. This study shows that there is no significant endothelial injury in the venovenous bypass grafts and that the endothelial cells remain physiologically active. Short-term failure of venovenous bypass grafts, therefore, appears not be due to significant endothelial cell damage in the graft.