The Study Of Correlation Between Stent-induced Distal Re-entry And Stent-grafts After TEVAR For Type B Aortic Dissection

Background Compared to traditional surgery,endovascular repair of type B aortic dissection has obviously reduced the morbidity and mortality rate.However,with the wide deployment of endovascular repair,the complications caused by stent-grafts increase gradually.Among those complications,stent-induced distal re-entry(SIDR)appears more often with time passage in follow-up after endovascular repair,which can lead to bad outcomes or even death in the long term.As a result,it is necessary to find the risking factors for SIDR and to explore the mechanisms,which can provide ideas and advice to prevent SIDR.Purposes The purpose of the investigation is to explore the risking factors and the force related mechanisms of SIDR after endovascular repair for acute and sub-acute type B aortic dissection,which can be used to guide the choice of stents in endovascular repair and improvise the strategies of endovascular treatment.Methods(1)Patients primarily diagnosed type B aortic dissection in acute and sub-acute phases from Jan.2008 to Dec.2016 were selected to perform analysis.The information of history and interventional details was included into the study.And the examination graphs of patients before and after intervention were reconstructed and measured in order to evaluate the risking factors and possible mechanisms for SIDR,as well as the reconstructing effect of the aorta after intervention.(2)The evaluation of radial force of the commonly available commercial stent-grafts of different brands for type B aortic dissection,as well as the combination of restrictive bare stents(RBS),was performed with a radial force testing equipment.The ananlysis was meant to test the mechanical characteristics of force change under different levels of compression with different oversize rate.(3)The CTA scans before and after endovascular treatment of patients with and without SIDR were chosen to perform computer simulation.The softwares of 3D Mimics and ANASYS were used to choose graphs to reconstruct,smoothen and mesh the 3-dimentional models.All the models were simulated through the system of ACE,and the structure of dissected aorta,the mechanical force of inserted stents and the change of fluids were analyzed.The data were analyzed quantitatively and qualitatively through ACE to find the risking indicators of SIDR.Results(1)Through Cox regression models,the distal oversize rate(DOR)of stents had segmental correlations with SIDR;when DOR was over 0% after adjustment,the risk of SIDR increased 2% for unit increment.The relation between the taper ratio(TR)of the true lumen before TEVAR and SIDR also demonstrated segmental effect,and when it was over 23.61%,the risk of SIDR increased 2% for each percent change.Besides,diabetes,Marfan's Syndrome,the history of aortic distension and the diameter of stents' distal ends were risking factors for SIDR,while the usage of RBS was a protecting factor for SIDR.There was a difference of risk for SIDR between patients in different follow-up periods;after 35-months follow-up,patients with high DOR had 4-times higher risk of SIDR than the patients with low DOR,while the difference didn't show in the period of 35-months follow-up.(2)The correlation between chronic outward force(COF)and the oversize rate of stents showed segmental effect in differnet thoracic stents and combinations,and the cutoff values of oversize rate changed accordingly.The radial force of different stents for different brands varies,and in the analysis of single thoracic stent,Gore TAG had the highest level of radial force among all brands with COF and resistant radial force(RRF)both above the value of the others in different compressing status.And at the beginning of compression,the correlation lines of different stents partly overlapped.In the analysis of combination of thoracic stents and RBS,the radial force of the overlapping segment was obviously higher than the value of single thoracic stent.In different compressing status,the level of force change was much higher,which makes the combination more stable with high force yielded in small compressing change.RBSs have special characteristics of radial force different from the characteristics of thoracic stents.The diameter of stents determines the level of radial force with smaller stents having higher force values,and level of radial force of multiple restrictive bare stents is hierarchyally related to the number of overlapped stents.(3)In the group of patients mainly using thoracic stents,the tortuosity of the aorta from the branch of the left sub-clavian artery(LSUB)to 25 mm distal to the end of the inserted stents in patients with and without SIDR demonstrated significant difference with higher values in non-SIDR patients,p< 0.05.The time average wall shear stress(TAWSS)in the area 15 mm distal to the inserted stents showed no difference between patients with and without SIDR.However,the stent-induced wall deformation(SWD)between groups was well cordinated to the area of SIDR.Conclusion(1)DOR of thoracic stents is closely related to SIDR after endovascular treatment in the long term.The level of DOR should be carefully limited to 0%.However,the level of DOR under 0% is not recommended for the possibility of endoleaks and unstable seal after intervention.(2)Whether in the usage of a single stent or the combination of thoracic and restrictive stents,the oversize rate of stents should be lowered to reduce the difference of radial force caused by the different characteristics in order to avoid vascular damage.(3)The tortuosity of the thoracic aorta may be related to SIDR.And the high stent-induced wall deformation level may result in the occurrence of SIDR.