Experimental Study Of A Vena Cava Stent-filter On Prevention From Pulmonary Embolism

Objective:①To evaluate the efficacy and safety of a vena cava stent-filter in the prevention from pulmonary embolism.②To evaluate the feasibility of turning into permanent venous stent and suitable dwelling periods in inferior vena cava of dogs.Methods:①Fusiform double basket-like vena cava filter was made of Nitinol wires and stainless steel metal pole.②Twelve mongrel dogs with iliofemaral deep venous thrombus were divided into 2 groups at random, with 6 dogs in each group.The deep venous thrombus was made to fall off directly in control group,and fall off with a self-made filter in the vena cava implanted via the opposite femoral vein in experimental group. The thrombi-trapping efficiency of the filters was evaluated by angiography and enhancement CT scanning of pulmonary artery,and inferior vena-cavography before and after the deep venous thrombus falling off.③The filter was placed in inferior vena cava via the right femoral vein in 14 dogs.The blood flow of inferior vena cava and the position of the filters were inspected by inferior vena-cavography at 2w, 3w,4w,5w,6w,7w and 8w after the filter insertion(2 dogs at each point).Then laparotomy was performed to remove the inferior vena cava from dogs for gross examination of filter thrombosis and the burnish degree of the filters,and for electron microscopic examination of the inferior vena cava intimal change of the involved segment.④The metal pole of the filter was retrieved via the femoral vein at 2 weeks after the filter was placed so that the filter became the permanent venous stent in 4 dogs.Angiography and pathological examination were performed at 3 months and 6 months(2 dogs each point)after the filter became stent.Results:①All 24 filters were placed in right position of the dogs successfully.②Six filters could successfully capture clot coming from the deep vein of lower limb and no detectable pulmonary artery embolism was observed,while pulmonary artery embolism occurred in all dogs of control group.③Angiography showed patent inferior vena cava without filter thrombosis at 2～8 weeks.There was no tilting and migration of the filter.Postmortem displayed no retroperitoneal hemorrhage and caval thrombosis.The barbs of the filters penetrated over the caval adventitial coat.Under electron microscope,a thin layer of neointima already covered the braiding net of the filters at 2 weeks after the deployment. The tunica intima became no thick at 3～5 weeks and with slightly endothelial proliferation at 6～8 weeks.④All 4 metal poles were successfully retrieved and the superior and inferior extremities of filter nets could be set free with all the filters turning into venous stents.The tunica intima wholly covered the braiding net of the venous stents with slightly endothelial proliferation at 3～6 months after the deployment. Conclusions:①The vena cava stent-filter can effectively prevent from the pulmonary embolism due to falling off of the emboli from deep venous thrombosis.The filter can keep long indwelling period according to the necessity of treatment with simultaneously keeping patent caval flow and stability of the position.②The vena cava stent-filter possesses little stimulus to blood vessel of dog.The filter is easy for placement and retrieval and can completely turn into permanent venous stent.