[Replacement of small caliber arteries with synthetic transplants]

Under comparable biological and hemodynamical conditions two different types of arterial prostheses (USCI-Sauvage Filamentous Vascular Prostheses versus Gore-Tex expanded PTFE-prostheses) were implanted in 32 dogs in aorto-iliacal (14 animals) respectively in carotid position (18 animals). The graft length was 8--10 cm, the diameter 4 mm. Followed-up to 24 weeks the expanded PTFE-prostheses had a statistically higher failure rate than the filamentous Dacron-prostheses (67% respectively 52%). Light microscope and scanning electronmicroscope evaluations 2, 4, 8, 12, 20 and 24 weeks postoperatively showed a complete ingrowth of fibrous tissue through the wall of the filamentous Dacron-prostheses with a fibrous neo-intimal layer. At the same time the luminal surface of the expanded PTFE-prostheses was covered with fibrin. Tissue invasion was limited to the outer one third of the graft wall. With increasing time interval a thickening of the inner layer with consecutive narrowing of the lumen could be observed in the filamentous Dacron-prostheses. A neo-intimal thickening of more than 600 mu always leads to a thrombotic graft occlusion. The expanded PTFE-prostheses showed even after 24 weeks no complete ingrowth of fibrous tissue. A fibrous neo-intima with an endothelial lining had only developed near the anastomoses. The remaining surface of the graft was covered by a fibrin layer. Endothelial islands apart of the anastomoses could be observed only in some Dacron-prostheses. The presented results indicate that long term patency of synthetic grafts for reconstruction of small arteries (less than 6 mm) is in the first place limited by the quality of the neo-intimal layer. Further research should be directed therefore to the improvement of the inner surface (for instance by coating with an antithrombogenic layer) and to a better quality of the synthetic wall (compliance, flexibility, etc.).