Healing of Implanted Expanded Polytetrafluoroethylene Vascular Access Grafts with Different Internodal Distances: A Histologic Study in Dogs

Abstract

Objective. We assessed characteristics of healing, over time, of two types of expanded polytetrafluoroethylene grafts. Study design. An experimental histological study in dogs. Methods. The graft types studied had the same internal diameter (5 mm) but different internodal distances. In one, the internodal distance was 60 μm in the external surface and 20 μm in the luminal surface. In the other, the internodal distance was 30 μm throughout the material. Sixteen grafts of each type were implanted between the femoral artery and vein in 16 dogs; explanted 1, 2, 4 or 12 weeks later; and examined histologically. Results. In both graft types, infiltrating-cell density and maximum cell-penetration depth increased significantly between 1 and 2 weeks after implantation, but no significant increases occurred after 2 weeks. The number of inflammatory cells peaked 1 week after implantation and decreased significantly by 2 weeks. Subsequently, there were no significant changes in inflammatory cell numbers, suggesting that the inflammatory phase was over by 2 weeks after implantation and the grafts had become attached to surrounding tissue. There were no significant differences between the two graft types in cell density, cell-penetration depth, or number of inflammatory cells at any assessment time. Conclusion. Our results provide histologic support for guidelines recommending that synthetic vascular grafts for hemodialysis access should not be cannulated until 2 weeks after implantation. Since increasing the internodal distance to 60 μm in the external surface had no effect on graft healing, methods other than manipulation of internodal distance should be used in developing a graft suitable for early cannulation.