Clinical And Biomechanical Study On The Treatment Of Aortic Arch Dissection By Chimney Thoracic Endovascular Aortic Repair

BackgroundThe incidence of aortic dissection,one of the most lethal disease in China,has been significantly increasing in recent years.China has become one of the countries with the highest incidence of this disease.Compared with open surgery,endovascular repair of aortic dissection has been developed for more than ten years with its advantages of simple,minimally invasive,and low complication rate.How to improve the safety and effectiveness of minimally invasive endovascular repair is the current clinical hot spot.Parallel stent technique(PST),also known as chimney techntique,is applied in the treatment of aortic arch dissection.It can adapt to various aortic arch shape,supra-arch branch opening position and angle without customized support.With great potential,chimney technique has been widely used.However,postoperative endoleak is the main problem that hinders its wide application.The endoleak brings many uncertainties to the prognosis of the chimney technique,which restricts the further improvement of the operation safety and effectiveness.At present,for special anatomical condition of aortic arch dissection,the spatial structure and mechanical coupling between the endograft,chimney stent and the vessel wall have not been further studied.ObjectiveAccording to the clinical comparative analysis,experimental and biomechanical study in vitro,optimized configuration of endograft and parallel stent scheme are put forward to different characteristics of anatomical morphology,so as to minimize the risk of endoleak after CTEVAR and simultaneously not to increase the risk of aortic dissection recurrence and stent occlusion.This study will provide scientific theoretical basis and experimental data for the optimization,standardization and promotion of chimney technique.MethodsThis study was conducted in two steps.1.Clinical retrospective analysis of endoleak after the CTEVAR was made to sieve out the risk factors on aortic morphology,the strategies and stent-graft configurations so as to put forward the optimized plan and the configuration of the stent grafts.2.Based on finite element analysis,in vitro simulation,mechanical test and computed tomography scan,the pressure stress of tube wall and imaging measurement were taken as the main indicators to further optimize the matching scheme and configuration of stent grafts.Results1.The median follow-up time was 27 months(8-56 months).All chimney grafts were successfully implanted and no migration or occlusion was observed during follow-up.Mortality of this cohort was 1.7%(4/234).3(3/234,1.3%)patients suffered from cerebral vascular events.75(75/234,32.1%)had intraoperative type I endoleak.27(27/75,36.0%)of them were found disappeared in the follow-up period.The false lumens of 33(33/75,44.0%)were found stable,and 15(15/75,20%)were found expanded and were successfully re-treated by endoleak embolization.When the proximal tear located in Zone I,there was higher instant endoleak rate than in Zone C,S and N2(77.8%vs 16.7%,p=0.041;77.8%vs 33.3%,p=0.042;77.8%vs 30.1%,p=0.009).TC were found to have more instant endoleak than SC(60.0%vs 26.9%,p<0.001)and DC(60.0%vs 31.3%,p=0.012).But there was no significant difference between them in the follow-up.2.The finite element calculation of the gutter area under stent configuration were45.58mm~2(P),16.46mm~2(P1),38.24 mm~2(P2),23.96mm~2(P3),42.08mm~2(P4).The risk evaluation of wall rupture from stress analysis of stent on vascular wall revealed that stent P1 and P2 are well attached to the vessel wall without increasing stress.It was found in vitro that P1 and P2 were well expanded and attached to the wall while folding and tilting of the stent were both found in stent P3 and P4.The results of CT scan were 47.49±1.44mm~2(P),19.55±0.98 mm~2(P1),40.05±1.05 mm~2(P2),27.77±0.90 mm~2(P3),50.99±1.47mm~2(P4).Conclusions1.Triple-chimneys and the proximal tear located in Zone I were found with higher endoleak rate and it may need more rigorous follow up.There was no significant difference of follow-up endoleak rate between other treating models and locations of entry tear.Larger sample and longer follow-up are required to evaluate durability and validity of this technique.2.Considering the finite element analysis of gutter area,stress analysis of the stent on vessel wall,the release in vitro,CT scan of gutter area and feasibility of stent fabrication,P1 structure was optimal.Feasibility of P1 has been primarily verified in vitro experiment.