The Development And In Vivo Study Of A Type Ⅱ Endoleak Preventable Stent-Graft

Objectives:1. To develop a prototype of stent-graft which can preclude the type II endoleak complicated by the endovascular repair of abdominal aortic aneurysms (EVAR).2. Create the abdominal aortic aneurysm (AAA) whose intrasac pressure can be monitored in a porcine model. After the implantation of stent-graft, type II endoleak can be replicated in the porcine model. To evaluate the feasibility of replicating type II endoleak in the porcine model and the effect of stent-graft in test group to treat type II endoleak.3. To evaluate the biocompatibility of the type II endoleak preventable stent-graft in the abdominal aortic aorta.Methods:1. Regarding the Hercules-T stent-graft as the prototype, the Dacron graft was covered with the coagulating drug to make the type II endoleak preventable stent-graft. Multiple drugs were compared to evaluate their coagulating effect with the pharmacological principle and the thrombelastograph. The coagulating drug covering Dacron graft was made with the hot-press method for the type II endoleak preventable stent-graft. The releasing rate of drug was tested in the coagulating drug covering Dacron graft by the chromatography.2. Twelve tamed porcine weighing between 60~80kg were selected to create the AAAs with the PTFE patch and the strain-gauge pressure transducer. The second and third pair of infrarenal lumber arteries were preserved for retrograde flow and contained in the AAA which formed the type II endoleak after the implantation of stent-graft in both the test and control groups. The intrasac pressure of the AAA in both groups were monitored with the strain-gauge pressure transducer and compared to evaluate the effect of type II endoleak preventable stent-graft.3. The porcines were euthanatized on the 10th day after EVAR and the specimens including AAA and stent-graft were retrieved after laparotomy. The microscopic and computed imaging analysis were carried out in the tissue of aortic wall of AAA's neckand the pseudo-membrane in the lumen of stent-graft with hematoxylin-eosin stain, Van Gieson stain, Weigert stain and immunohistochemical stain of a-SMA in order to discover how etamsylate and macromolecular material effected the aortic wall and the stent-graft.Results:1. The etamsylate can promote the platelet function and enhance the rigidity of clotting according to the pharmacological principle and the thrombelastograph, thus it was used to make the type II endoleak preventable stent-graft. The Dacron graft containing 100mg etamsylate was made successfully with hot press method and the stent-graft made of the graft could be accommodated by the 16F sheath. The etamsylate on the graft were all released in 10～30min and the releasing rate was qualified.2. AAAs whose intrasac pressure could be monitored were successfully created in 12 tamed porcine model. Type II endoleaks created succesfully in all 12 porcine model were demonstrated by computed tomographic aortogram (CTA) after EVAR. The intrasac average and pulse pressure precipitated in both groups and both the average pressure (p=0.000<0.001) and pulse pressure (p=0.004<0.01) in the test group decreased more rapidly than the control group according to the repeated measure analysis. The average pressure of 60.50±2.950mmHg in the test group were far more below that of 91.00±5.441mmHg in the control group (p=0.000< 0.001), at the same time, the pulse pressure of 6.83±2.483mmHg in the test group were far more below that of 20.83±3.656mmHg in the control group (p=0.000<0.001). Repeated CTA demonstrated the type II endoleaks in the control group which were absent in the test group.3. The AAA sac in the test group were fulfilled with old thrombus, however little fresh thrombus were discovered on the aneurysmal wall and surface of stent-graft in the control group. There was no difference in the constitution of tissue on the AAA neck in both groups according to the microscopic and computed imaging analysis. The thickness of pseudo-memebrane in the test group which was 845.25±64.428mm nearly doubled that in the control group which was 461.75±84.996mm (p=0.000< 0.001).Conclusion:1. The Dacron graft covered with etamsylate could be used to make the type II endoleak preventable stent-graft.2. It is feasible to establish the AAA whose intrasac pressure could be monitored and type II endoleak in the porcine model. The intrasac pressure monitoring experiment demonstrated that the stent-graft in the test group could treat type II endoleak effectively.3. The biocompatibility of the type II endoleak preventable stent-graft were qualified in short term however required further study.