The Biomechanical Study Of Stent Graft-induced Distal Re-entry After Endovascular Treatment Of Aortic Dissection

Background and Objective: Endovascular stent-graft repair was introduced as animportant alternative to conventional open surgery for the treatment of aorticdissections. But studies reported various complications caused by stent-grafts, amongwhich, stent graft-induced new entry is not a rare complication and with highmortality. Despite of its importance, investigation on this aspect has been least carriedout and the underlying mechanisms are still unknown. As an alien objective, theendograft is much stiffer than the host arterial tissues. Moreover, when it is deployed,it can induce high mechanical stress concentrations over the contact region. Thereforethe hypothesis of this study is that the high stress concentration induced by thedismatch between the endograft and the aortic wall, and the local hymodynamiceffects response for the onset of complications.Methods: This study was conducted in three aspects: First, retrospectively analyzethe clinical data to sieve out the targets for following biomechanical analysis; Second,accurately calculate and depict the stress concentration over the contact region oncases with complications, by computational hemodynamic simulation and themechanical analyses of the interaction between the endograft and the aortic wall.These analyses will explain the associations between morphological features and thesubsequent clinical events; Third, test and analyze the biomechanical effects on theaorta as a whole, as well as on the local artery tissue of different contact regions. Atlast, integrating these results into a hazard regression model will help to find out thehistologic evidence of the mechanical and hymodynamic effects, and to identify thebest stent-graft configuration for respective aortic dissection.Result: In the Meta analysis study, we searched all published studies from January1998through December2008on endovascular stent-graft placement treating acuteAD (type B-AD or retrograde type A-AD with an entry tear in the descending aorta)conducted by Chinese investigators. We found significantly higher post-operationcomplications in patients undergoing stent-graft placement with acute A than thosewith chronic AD. Patients with acute AD had significantly higher in-hospital mortalitythan patients with chronic AD. Then we study the single-center data of674Stanfordtype B aortic dissections treated by TEVAR, From April1997to March2010. Wefound that the preoperative mismatch rate and follow-up mismatch rate of the SIDRwere significantly higher than that of the non-SIDR. Compared with the standardTEVAR, TEVAR+RBS was with lower incidence of SIDR and less secondary intervention. The placement of RBS significantly expanded the true lumen at the levelof descending aorta with narrowest true lumen and at the level of distal end ofstent-graft. Through the computational fluid dynamics study, we demonstrated that theRBS could reduce the high wall shear stress on the stenosis part of the true lumen ofdescending aorta. This would further make the wall pressure of the abdominal truelumen higher than false lumen in the same level, which could improve themorphological remodeling in the long term. Besides, RBS could improve theperfusion of the abdominal visceral arteries. In the study of solid mechanics exertedby stent-graft, we found that the stent structure with thinner struts and more crownsimposed smaller stress on the aortic wall. And the RBS could further reduce the wallstress. Through the mechanical properties study of aortic wall, we found the normalaortic wall is stiffer than aortic dissection and aneurysm wall.Conclusions: The solid mechanics from stent-graft, the hemodynamic effect from theaortic flow, and the weakness of the aortic dissection wall all contribute theoccurrence of SIDR. This study provides important in-sight on the mechanism of stentgraft-related complications, and it will be essential for optimizing the stent-graftdesign to preferably match the aortic dissection configuration. As biomechanicalrationales of endovascular treatment of aortic dissection, the outcomes of this series ofstudy may have great clinical potential.