Factors affecting the patency of small-caliber prostheses: Observations in a suitable canine model.

Lack of an endothelial surface is most often blamed for the relatively poor patency of polytetrafluoroethylene grafts used in infrageniculate bypass when compared to autogenous saphenous vein. Length, caliber, flow, and ability to withstand flexion are also acknowledged but have not been systematically examined. We report the results of our attempts to discriminate between the relative contributions of these factors and to develop a suitable canine model for evaluating small-caliber prostheses (4 mm x 10 cm thin-walled polytetrafluoroethylene). ASA/dipyridamole were given 1 week before and 4 weeks after operation. Patency was assessed by directional Doppler at frequent intervals (less than or equal to 3 days). The following were observed: (1) Iliac placement provided a useful patency reference point (40% to 50% patency at 60 days). (2) Carotid patency was not better than iliac patency. (3) Crossing a flexion crease decreased patency. (4) The low patencies were not technical but intrinsic to the graft. Iliofemoral vein grafts achieved 100% patency at 60 days. (5) External rings did not improve iliofemoral patency (equal in paired comparisons). (6) Neither baseline platelet aggregation nor platelet aggregation after ASA administration correlated with patency. This canine model is an excellent test for small caliber-low flow prostheses. It allows paired-site comparisons, which are essential, and meaningful patency data with reasonable numbers of subjects within 2 months' observation. Directional Doppler evaluation avoids need for angiography or serial postmortem analysis sacrifice.