Magnesium Alloy Covered Stent For A Lateral Aneurysm Model In Rabbit Common Carotid Artery: An In Vivo Study

Background and purpose:Cerebral aneurysms are the most common cerebrovascular diseases,with an incidence secondary to cerebral infarction and hypertensive cerebral hemorrhage.Nowdays,the study hot for cerebral aneurysm is separation of the aneurysm with stent,such Pipeline stent and Willis covered stent.Because of metallic stent,they are implanted forever,and can result in vessel stenosis easily,which become the worldwide problem and block the development of the stent placement.The biodegradable Magnesium alloy covered stent is considered as the fourth innovation secondary to expandable balloon dilation,metallic stent and drug-eluting stent in the domain of the intervention.The biodegradable Magnesium alloy covered stent can provide enough radical force for vascular remodeling prior to degradation,and is the idea vascular stent for substitution the conventional metallic stent due to no long-term irritation for blood vessel and no need for orally taking antiplatelet drug forever.Therefore,we studied the magnesium alloy covered stent in vivo from three parts.Part? Improvement of a lateral aneurysm model in common carotid artery in rabbitsObjective:To improve the lateral aneurysm model in common carotid artery(CCA)in rabbits and evaluate it successful rate and patency rate of the CCA.Methods:40 rabbits were randomly allocated for two groups: ligation of left CCA(n=20),group A,n=20;non-ligation of left CCA(n=20),group B.The weight,the middle diameter of the right CCA and bilateral vertebral arteries was measured at the initial and one month later MRA examination.The lateral aneurysm model in common carotid arteries were established with discontinue extroversion suture,which was applied for anastomosis of vein pouch with common carotid artery with 6-0microsuture line.The angiography was performed 2 weeks later.Results:The left common carotid arteries were successful ligated in all twenty New Zealand rabbits in group A.MRA one month after ligation showed thickening of the right CCAs and non-thickening of the bilateral vertebral arteries in 17 rabbits,and thickening of the bilateral vertebral arteries was exhibited in the remaining 3 rabbits.The right CCA and the bilateral vertebral arteries were slightly thickened.There were no significantly differences in weight,the middle diameter of the right CCA and bilateral vertebral arteries between group A and group B at initial MAR examination;however,the middle diameter of the right CCA and bilateral vertebral arteries in group A were significantly greater than those in group B at one month later MRA examination.The lateral aneurysm models in CCAs were made in 35 rabbits(17 in group A and 18 in group B),and all rabbits were alive after aneurysm making.DSA obtained 2 weeks later showed lateral aneurysm models in 17 rabbits with small amounts of thrombosis in 4 aneurysms and patency of the right CCAs in group A.DSA reviewed 14 lateral aneurysm models in right CCAs with spontaneously complete occlusion of right CCAs in four rabbits.In 14 lateral aneurysm models,different degree of thrombosis was shown in 10 aneurysms,in which distal right CCAs were become small in 4 rabbits.The successful rate for aneurysm making in group A was significantly higher than that in group B(P<0.05),and moreover,the incidence of thrombosis and the spontaneously complete occlusion rate of right CCAs were significantly lower than those in group B(P<0.05).Conclusions:The improvement of the lateral aneurysm model in common carotid artery in rabbits was a useful approach for enhancement of the model successful rate and decrease the incidence of thrombosis in aneurysm and the spontaneously complete occlusion rate of right CCAsPART ? The feasiblility and degradation of the magnesium alloy covered stent for lateral aneurysm model in rabbit common carotid artery(CCA)in vivoObjective:To evaluate the long-term feasiblility and degradation of the magnesium alloy covered stent(MACS)for lateral aneurysm model in rabbit common carotid artery(CCA)in vivo.Methods:In 8 New Zealand rabbits(2.5-3.5kg),a MACS(group A,n=4)or a Willis covered stent(group B,n=4)was inserted in a lateral aneurysm model in rabbit CCA under fluoroscopic guidance.Rabbit were followed up for 12 months after stent placement.The long-term feasibility for anrueysms occlusion is observed through follow-up angiograms;the in vivo degradation behaviour is invastagated with MRA and molybdenum target.All the angiographic follow-ups were obtained in posteroanterior and lateral projections with use of a calibrated ruler to measure the diameter of the stent and stenosis of the stented artery.The diameters of the stent and stenosis in diameter of the stented CCA at follow-up were measured on each angiography with digital measurement(Photoshop 8.0).Multiple measurements at three parts of the stented CCA(proximal,middle,and distal)were performed,and their average value was obtained.Analyses of the angiographic findings were performed based on the consensus of three observers.Results:Stent placement was technically successful in all rabbits,and complete aneurismal occlusion was achieved in all aneurysms during follow-ups.The diameter of stented CCA in group A was significantly bigger at 6 and 12 months follow-ups than that at immediately after stent placement(P <0.05),and no significantly difference was observed in diameter of stented CCA in group A between 6 and12 months follow-ups.Whereas,the diameter of stented CCA in group B was significantly smaller at 6 and 12 months follow-ups than that at immediately after stent placement(P <0.05);moreover,the diameter of stented CCA in group B was significantly smaller at 12 months follow-ups than that at 6 months after stent placement(P <0.05).In addition,there was no significantly difference in diameter of stented CCA at immediately after stent placement between group A and B,but the diameter of stented CCA in group A was significantly bigger at 6 and 12 months follow-ups than those in group B(P <0.05).The morphology of the stented CCA presented single loss just like severe stenosis at 1 day after stent placement due to the existence of Nd,and the morphology of the stented CCA gradually became normal at5-6 weeks after stent placement with the degradation of Nd.The morphology of the magnesium alloy stent was intact and clear within two weeks after stent placement under Molybdenum target.The magnesium alloy stent was gradually disintegrated,and the contour of the stent became vague with time until the stent could not be easily visible under Molybdenum target at oneyear follow-up.Conclusions:Placement of a MACS proved to be feasible approach for occlusion of a lateral aneurysm in rabbit CCA with degradation of the stent.The diameter of stented CCA in group A was significantly bigger at 6 and 12 months follow-ups than that at immediately after stent placement,which indicates that MACS conveys distinct advantages in the growth of the stented CCA,as compared with the results with Willis covered stent.The diameter of stented CCA treated with Willis covered stent was significantly smaller at 6 and 12 months follow-ups than that at immediately after stent placement,and the diameter of stented CCA would become smaller and smaller with the time went on.Degradation of the magnesium alloy stent could be observed by Molybdenum target provided.PART ? Magnesium alloy covered stent for a lateral aneurysm model in rabbit common carotid artery: An intravascular ultrasound studyObjective:To evaluate the changes and vascular remodeling of the stented common carotid artery(CCA)in rabbits after stent placement with use of intravascular ultrasound(IVUS).Methods:In 8 New Zealand rabbits(2.5-3.5kg),a magnesium alloy covered stent(group A)or a Willis covered stent(group B)was inserted in a lateral aneurysm model in rabbit CCA under fluoroscopic guidance.Rabbit were followed up for 12 months after stent placement.IVUS was performed at initial,6 and 12 months after stent placement.The changes in the mean vessel area,mean scaffold area,mean lumen area,and luminal area stenosis were observed with intravascular ultrasound(IVUS).Remodeling index= the stentd vessel area/ the mean proximal and distal normal reffered vessel area.Results:IVUS follow-ups at initial,6 and 12 months after stent placement were successful in all rabbits.The mean vessel area,the mean scaffold area and the mean lumen area in group A at 6 or 12 months follow-ups were significantly increased than that at initial stent placement(P <0.05).The mean vessel area in group B at 6 or12 months follow-ups were significantly increased than that at initial stent placement(P <0.05),but the mean lumen area in group A at 6 or 12 months follow-ups were significantly decreased than that at initial stent placement(P <0.05).In addition,the mean lumen area in group A at initial stent placement was significantly smaller than that in group B(P <0.05),but the mean lumen area in group A at 6 or 12 months follow-ups were significantly bigger than those in group B(P <0.05).Intermediate remodling was obtained in all stented CCA in group A with remodeling index(IR)1.024 ± 0.018(range: 1.01-1.05,95% CI: 0.994-1.053);while negative remodeling was observed in all stentd CCA in group B with remodeling index(IR)0.62 ± 0.083(range: 0.58-0.74,95% CI: 0.487-0.752).Conclusions:The vessel in the stented CCA after implantation with a magnesium alloy covered stent could grow with the growth of the CCA;while,the vessel in the stented CCA after implantation with a Willis covered stent would become small due to the limitation of the stent with the time went on.Intermediate remodling was obtained in all stented CCA in group A;while negative remodeling was observed in all stentd CCA in group B.