Coil-stent Tear Occlusion Device For Distal Entry Tears Of Aortic Dissection Located In Branched Area Of Abdominal Aorta

BackgroundWhether the distal entry tears should be treated after covering the proximal entry tear for aortic dissection has always been a concern for clinicians and patients.Clinically,distal aorta would be closely monitored and hypertension would be managed after treatment of the proximal entry tear for most Type B aortic dissection patients.However,there were many patients developed distal false lumen growth,and even aortic rupture.Then,more and more researchers suggest that treatment of proximal entry tear is far from enough.We divided the distal aortic into three parts,remaining thoracic descending aorta,branched area of abdominal aorta and infra-renal abdominal aorta.The descending thoracic aorta and infra-renal abdominal aorta can be easily covered by stents.According to the clinical experience and literature review,the remaining entry tears involving the branched area of abdominal aorta ranges from 49% to 88%.Treatment of this area will affect the blood supply of the important organs,which makes the treatment complicated and difficult.To cover the tears as well as to ensure the patency of branched vessels,it often involves high cost and risk.The contemporary treatment for dissected visceral branch area contains branched technique,fenestration,hybrid operation,occluder,multi-layer bare stents,bare stent combined with coil,and etc.However,because of the difficulty of technique and high morbidity rate,the aforementioned methods are difficult to be widely carried out.Objective1.To describe the occurrence of distal aortic expansion after TEVAR and to analyze the risk factors of distal aortic expansion,then provide some suggestions for treatment;2.To verify the feasibility of the coil-stent tear occlusion device via in vitro experiment,to optimize the structure design and to standardize the operation process;3.To assess the safety and effectiveness of the coil-stent tear occlusion device for distal entry tears located in branched area of abdominal aorta.Methods1.Retrospectively identify the risk factors for distal aortic expansion by investigating distal aortic remolding in patients with first-episode type B aortic dissection treated by endovascular or hybrid operation in this center from April 1999 to October 2016;2.Build in vitro model of abdominal aortic dissection for research.Complete the in vitro release of the coil-stent tear occlusion device,improve the structure and assembly mode of the delivery system,and to optimize the operational processes;3.Build animal model of abdominal aortic dissection with branched area affected.The coil-stent tear occlusion device was implanted in the animal model.After 1-month follow-up,the diameter of the dissected aorta,thrombosis of the false lumen and the patency of branch vessels were observed by CTA.Results1.Among 333 patients,a total of 70(21.02%)patients experienced distal aortic expansion at a mean time period of 51.18±15.05 months after treatment.Multivariate analysis reviewed independent risk factors of postoperative distal aortic expansion,including residual length of patent false lumen,postoperative number of dissection tears over thoracic aorta,maximum diameter of the proximal aorta and aortic arch type;as well as protective factors which involves non-smoking history,application of stent restrictive technique and increased number of postoperative dissection tears over abdominal aorta;2.Quartz and silica were applied to customize a set of proximal renal artery model and abdominal aortic dissection model,respectively.Through the design improvement of the coil-stent tear occlusion device and conveying system,we realized the linkage of the bare stent and coils and solved the winding problem in the process of assembling the coil-stent tear occlusion device,and eventually completed the coil-stent tear occlusion device in vitro release;3.The modeling experiment of abdominal aortic dissection was carried out in 18 animals,of which 2 cases had sudden cardiac arrest and died during the operation.16 cases were successfully modeled,among them,2 cases had complete thrombosis in the false lumen examined by CT angiography 3 days after operation and the other 14 cases kept patency in the false lumen.The coil-stent tear occlusion device was implanted into the remaining 14 cases of animal models.The coils were twined around the bare stent in one case during the procedure,which led to the deformation of the stent and teared the proximal entry tear.The operation was successful in 13 cases,and the success rate was 92.86%.After 1-month follow-up,it was found that the maximum diameter was decreased,the short diameter of the true lumen increased and the short diameter of the false lumen decreased.Formation rate of thrombus in the false lumen increased.The patency rate of renal artery was 100% and achieved the desired effect.ConclusionDistal aortic expansion in Stanford type B aortic dissection after TEVAR has a high morbidity and is dangerous.Timely and effective intervention should be carried out considering risk factors for distal expansion and the clinical experience.Due to the involvement of the important branch vessels in the abdominal aortic visceral branch area,the conventional endovascular strategies have limitations.The coil-stent tear occlusion device can accurately embolize the distal entry tears,promoting the process of thrombosis in the false lumen and maintaining the patency of the branch vessels.It provides a new strategy for endovascular treatment of aortic dissection involving abdominal aortic visceral branch area and is worth further research and spreading.