| BackgroudSince Dake and his colleagues firstly reported their experience of transluminal placement of stent-grafts to treat descending thoracic aortic aneurysms in 1994, thoracic endovascular aortic repair has been developed as an main treatment for a range of descending thoracic aortic pathologies including type B aortic dissection, descending thoracic aortic aneurysms, pesudoaneurysms and penetrating aortic ulcer, for its virtue of minimal invasiveness and conquently favorable results. Ascending aortic aneurysm has been defined as a dilatation of ascending aorta to more than 150% of the diameter expected for a normal one accounting for 50% of all thoracic aortic aneurysms, which can lead to dissection and even rupture. Without surgical intervention, the mortality can increase up to 90% within five years. At present, conventional open surgery has been used as standard therapeutic method, involving the procedure of aortic replacement with a tube graft, and sometimes combined with valve implantation. Despite the progress in surgical techniques and devices, postoperative mortality and rate of complications can be rather high, espeacially in the patients with advanced age and co-morbidities. As a result, endovascular procedure has been tentatively applied in treatment of ascending aortic pathologies recently. A few of centers published limited number of ascending aortic aneurysm cases receiving endovascular treatment with commercially avaliable stent-graft, but these cases were highly selected with favorable anatomic features. So for the special anatomic characteristics of ascending aorta and strict requirement of conventional stent graft, most patients were deemed unfit for endovascular procedure. To develop the endovascular treatment for ascending aortic aneurysm, the technique and devices should be promoted on the basis of well understanding of the anatomic feature of this kind of pathology. Therefore we studied and analysed the anatomic data of a group of patients and designed a new type of stent-graft system guided by the concept of “Sac-anchoring”, and consequentially conducted in vitro experiment to verify the feasibility of the stent graft system.Objective1.To measure and analyze the anatomic characteristics of ascending aorta with aneurismal pathology and to develop a kind of new type stent graft for the treatment of ascending aortic aneurysm with appropriate material on the basis of morphological parameter such as length, diameter, tortuosity and volume of aneurismal sac.2. To select one kind of high molecular material with the ability of changing from a liquid to a solid under certain condition, and then improve its properties for the purpose of filling the endobag of stent-graft during endovascular procedure.3. To develop a matched delivery system and fit the two constituent parts together, and then verify the feasibility of the whole stent-graft system with an in vitro experiment in a plastic model of ascending aorta.MethodsWe have conducted the research by four steps.1. According to the inclusive and exclusive criteria, 70 patients were involved in our study for measurement of morphology. The morphological parameters included length, diameter, tortuosity and volume of aneurismal sac.2. At the same time, we detected the properties of 4 different high molecular materials and one of them was chosen for the purpose of filling the endobag. With the help of Nusil corporation, we shortened the cure time and decreased the viscosity of the additional liquid silicone rubber, and then detected the mechanical properties to determine whether it was meet the requirements for clinical use.3. On the basis of morphological data of ascending aortic aneurysm, we designed and made a new stent graft which was composed of a coated stent and an endobag made of latex. We still made a matched delivery system, and then compressed the stent graft and fitted them together.4. We made an in vitro model and introduced the stent-graft system, released the stent-graft, filled the endobag with filling material, and finally withdraw the delivery system.Results1. The diameter at the level of Sinus-tube junction is 37.0±6.0mm, the maximal diameter of the aneurysm is 52.6±6.0mm; the length of the ascending aorta is 92.56±14.79 mm, the length of the aneurysm is 81.52±21.01mm; the tortuosity of the aorta is 0.23±0.10 and the tortuosity of the aneurysm is 0.20±0.10; the volume of aneurismal sac is 171.87±58.26 ml.2.Additional liquid silicone rubber(ALSR) was chosen as the candidate for filling the endobag, and after promotion, we got a product MED4420 with viscosity of 20000 cp, cure time lesser than 5min, and the cured rubber’s mechanical properties were favorable with longitudinal tensile strain of 157.48%, longitudinal tensile stress of 0.41 MPa, circumferential tensile strain of 99.15%, circumferential tensile stress of 0.52 MPa.3. A new type stent graft was successfully made. The endobag was made of latex with diameter of 70 mm, volume of 200 ml, inner lumen diameter of 32 mm and length of 75 mm. A matched delivery system was made with several function components including controlling wire and filling pipeline. All constituent parts were fitted together and formed a complete system.4. An in vitro aneurismal model was manufactured with length of 60 mm, diameter of 63 mm. Then the stent-graft was introduced into the model and released successfully at the right location. The procedure of filling the endobag was conducted smoothly under the mean pressure of 5 atm, with mean filling time of 1 min and mean filling volume of 110 ml. Completion imaging showed that the endobag fitted the wall of aneurysm well and the stent was patent.Conclusion1. The copolymer additional liquid silicone rubber can be used as filling material and the properties fulfilled the requirement of clinical use.2. The new type stent-graft system based on the concept of “Sac-anchoring” can be manufactured and the success of in vitro experiment primarily verified the feasibility of the stent-graft system. |
PDF Full Text Request