An Experimental Study of Replacement of the Vena Cavawith Expanded Polytetrafluoroethylene Grafts

The long patency of vascular prosthesis in venous reconstruction has not been acceptable. The purpose of this study was to evaluate the expanded polytetrafluoroethylene (EPTFE) grafts when used as a large vein replacement in the dogs. Three different fibril length (FL) of the EPTFE grafts (10, 20 and 30μFL), 5cm length with 7 to 10mm diameter were implanted in the infrarenal vena cava (IVC) in 60 dogs and the same kinds of grafts, 3.5cm length were implanted in the superior vena cava (SVC) in 16 dogs. All the grafts were harvested from two to 461 days after vena caval reconstruction. These dogs were devided into three groups in the IVC replacement with urokinase (UK), and with dipyridamole (DP) and without anticoagulant agents. In the SVC replacement group, the anticoagulant agents were not given. UK was given 6000 units/day intravenously for two days after implantation. DP was administrated 20mg/kg/day orally for one month after implantation. The patency was recognized by venogram. Following results were obtained. The over all early patency rate (less two weeks) in the 10μFL groups was 85% in the IVC replacement, but the late patency rate (two weeks to 10 months) was decreased to 50% . In the DP administrated groups, the over all early patency rate was 78.3% but the late patency rate was decreased to 39.1% . In the SVC replacement, the over all early patency rate was 81.3% and the late patency rate was same. The effect of UK was not so significant on the coagulation systems for the IVC replacement. However, in the DP administrated groups with high patency rate at two weeks after implantation, fibrinogen level, platelet adhesiveness and platelet aggregation reduced significantly. The r level of thromboelastogram was also prolonged significantly. All of the grafts were more or less deformed and shortened. On the gross section, neointimal hyperplasia was showed at the anastomosis and midportion of grafts showed immature neointima and thrombus. Microscopically, at the anastomosis, the neointima was well organized, but at the mid portion of the graft, the neointima showed coagulation necrosis (59% ). Fibrin or fibrinoid materials, red cells, white cells and hemosiderin were seen in the necrosis. In the SVC replacement, neointima was thiner than the IVC replacement graft and coagulation necrosis was seen only in one graft. The inner layer of the SVC graft was covered with the thin fibrin network or the thin epitherial cells. The rate of calcium deposit was 65% in the IVC replacement and 100% in the SVC replacement, especially calcium deposit was showed on the inside of the grafts. In the 30μFL group, the rate of the calcium deposit was 100% . Cell arrangement was investigated with a scanning electron microscope. The inner surface of the almost all grafts were covered with the endothelial cells and the cells arranged in parallel to the direction of the blood flow. The endothelial cells also covered the portion of calcium deposit and coagulation necrosis. But the origin of endothelial cells were not established. In the SVC replacement, the matrix of the EPTFE graft was occasionally seen right under the epithelial cells or thin layered fibrin network. It is concluded from these results that a 10μFL EPTFE graft may be superior to other materials for vena caval replacement with administrating anticoagulant agents at present time. However, additional studies should be necessary to obtain the more useful graft and the long term patency for vena caval replacement