Preliminary Study Of Low-porosity Stent Alone For Treatment Of Experimentally Induced Aneurysms In The Rabbit

Part I Establishment of Aneurysm Models and Study of Angiography in the RabbitPURPOSE:To introduce a method of elastase-induced saccular aneurysm of right common carotid artery in rabbits, and to evaluate the feasible of intra-venous digital subtraction angiography (IV-DSA) for the aneurysm models. METHODS: New Zealand white rabbits (n=12) with elastase-induced saccular aneurysm model were involved in this study. Every rabbit was performed intra-arterial digital subtraction angiography (IA-DSA) and IVDSA at same pose and machine point of view. Neck size,height of aneurysm and diameter of parent artery were measured. Comparison of these datas between IA-DSA and IV-DSA were performed by paired t-test. RESULTS:10 successful aneurysm model were established. Mean Neck size of aneurysm, height of aneurysm and diameter of parent artery by IA-DSA were 4.23±0.91mm, 4.55±1.45mm, 3.91±0.51mm respectively. Mean Neck size of aneurysm, height of aneurysm and diameter of parent artery by IV-DSA were 4.21±0.92mm, 4.66±1.40mm, 3.93±0.54mm respectively. There were no significant differences in these datas between two angiography methods (P>0.05 respectively). CONCLUSIONS:IV-DSA can clearly show saccular aneurysm of right common carotid artery and parent artery in rabbits imaging, and it is a well complementary method to IA-DSA.Part II Analysis of Angiography after the NEST Stent Implantation for Treatment of Aneurysms in the RabbitPURPOSE: To evaluate the feasible of the technique of the NEST stent implantation alone for treatment with RCCA aneurysm in rabbits, and to follow up the results of stent implantation for aneurysm. METHODS:20 RCCA aneurysm models in rabbits were created by by using elastase in this study. They are randomly divided into group A and B (nA=nB=10). The NEST stent implantation alone was performed to 10 rabbits of group A, and 10 rabbits of group B only were undergone IADSA as comparison. Angiography was performed to all rabbits at time of prior to procedure, right after procedure, 6w after procedure and 3m after procedure. RESULTS:10 aneurysms in group A were successfully treated by 11 NESTs,and all with delayed circulation, also 2 with reduced volume at right after procedure. 2 aneurysms occluded and 5 with thrombus formation and all with delayed circulation during consequent follow-up. Control angiograms demonstrated patency and unchanged flow of all stented branch arteries throughout the observation period, without any stenosis of parent artery. CONCLUSIONS:The NEST implantation was safe and simple. It could change the intraaneurysm hemodynamic state significantly in the aneurysms quickly.Part III Histopathologic Study of Aneurysms after Stenting in Rabbit ModelsPURPOSE: To investigate the mechanism of neointima growth on the aneurysm orifice after the treatment with NEST, and to assess the effectiveness of this endovascular treatment technique. METHODS:In group A ,1 rabbit died 3w after the treatment, 2 rabbits were sacrificed 6m after treatment, and other 7 after 3 months, while in group B 1 rabbit died 1w after the treatment, and 1 after 3w, 2 rabbits were sacrificed 6m after treatment, and other 6 after 3 months. All aneurysms and arteries stented were harvested for gross histological examined. The 3w-rabbit, one of 6w and one of 3m in group A were observed by scanning electron microscope (SEM) with one in group B as comprison. Other specimens were sent for histopathologic study. RESULTS:Gross histological examination of the 3w-rabbit showed newly-formed thrombus in the aneurysm with the NEST across its orifice. Specimen examination of 6w showed thrombus obliteration in one aneurysm and the other was little thrombosis in aneurysm. Specimens of 3m showed aneurysms were occluded in one, partial thrombosis in 5 and opened in 2. All specimens revealed neointima formation at the aneurysm orifice. The occluded ones showed intact neointimal covering and some aneurysm with too wide neck with partial covering for over-expanded strut intervals. Histopathologic examination revealed stretching of the media of the carotid by the strut and reactive smooth muscle cell proliferation around the strut. No intima hyperplasty was observed. SEM revealed neointima covering of luminal surface of stent, as well as strut across the orifice of aneurysm. The stent struts were covered by 2-3 membranous layers in specimens of 1m and 3m. The neointima was mainly composed of collagenous fibers, and some endothelium cells covered them in a typical cobblestone pattern arrangement near the struts. CONCLUSIONS :Implantation of NEST could promote the growth of neointimal even in the early stage of the implantation. The growth velocity was correlation with the porosity and the plane of the stent surface. The stent with the normal surface morphous would not induce intima hyperplasty.