Delayed thrombosis of synthetic microvascular bypass grafts.

A 3-mm-diameter synthetic polytetrafluoroethylene (PTFE) cervical carotid bypass graft 20 cm in length was implanted in 30 dogs for the evaluation of blood flow, tissue response, and patency at intervals of 1 to 120 days. Although 4 of 5 grafts removed after 5 to 8 days were patent (80%), long term patency was observed in only 1 graft (10%). Aspirin treatment did not influence patency. Scanning electron microscopy demonstrated the lack of a neoendothelial layer upon the luminal surfaces of patent grafts, which were covered with a fibrin-blood cell lining. Subintimal fibrosis resulted in stenosis at sites of anastomosis in thrombosed grafts. The graft length, its small caliber, and a 40% decrease in blood flow after implantation may have contributed to thrombosis of the bypass graft in this model. Synthetic PTFE microvascular grafts may not be suitable for clinical use in extracranial-intracranial arterial bypass surgery.