Local hemodynamic disturbance accelerates early thrombosis of small-caliber expanded polytetrafluoroethylene grafts

Objective: Small-caliber expanded polytetrafluoroethylene (ePTFE) grafts cannot be used widely in the clinical situation because of early thrombosis and occlusion. This unsolved and under-recognized problem warrants further investigation. Methods: Grafts of uncoated ePTFE (n = 6) and anti-CD34-coated ePTFE (n = 6) were implanted unilaterally into the carotid artery in 12 domestic pigs. Ultrasonography was used to test the proximal and distal anastomotic stoma morphology, diameters and blood velocities. A thrombosis instrument was used to examine the blood coagulation state. After seven days, the pigs were sacrificed and the implanted grafts were excised for general and histological analysis. Computational fluid dynamics was used to investigate the blood flow fields of the implanted grafts and to calculate parameters that might be indicative of thrombosis. Results: Thrombosis was detected in 10 of 12 (83.3%) implanted ePTFE grafts, 5 in uncoated grafts and 5 in anti-CD34-coated grafts. Endothelial cell coverage was observed in both uncoated and anti-CD34-coated grafts. No obvious abnormalities in anastomotic stoma or blood coagulation state were observed. Computer-based local hemodynamic simulation showed the low flexibility of synthetic ePTFE grafts caused obvious coarctation. Local wall pressure, velocity and wall shear stress were much higher than in the contralateral normal vessel. Conclusions: The patency of small-caliber ePTFE grafts for clinical use is impaired by early thrombosis due to mixed causes. Local hemodynamic disturbance was the most powerful predictor of early thrombosis. Decreasing local hemodynamic disturbance, improving the quality of anastomotic stoma, selecting reasonable anticoagulation strategies and promoting rapid endothelialization may increase the long-term patency of small-caliber vascular grafts.