Finite element modeling to predict procedural success of thoracic endovascular aortic repair in type A aortic dissection

Xun Yuan, Xiaoxin Kan, Xiao Yun Xu, Christoph A Nienaber, Xun Yuan, Xiaoxin Kan, Xiao Yun Xu, Christoph A Nienaber

Abstract

Objective: Thoracic endovascular aortic repair (TEVAR) is recommended for type B aortic dissection and recently has even been used in selected cases of proximal (Stanford type A) aortic dissections in scenarios of prohibitive surgical risk. However, mechanical interactions between the native aorta and stent-graft are poorly understood, as some cases ended in failure. The aim of this study is to explore and better understand biomechanical changes after TEVAR and predict the result via virtual stenting.

Methods: A case of type A aortic dissection was considered inoperable and selected for TEVAR. The procedure failed due to stent-graft migration even with precise deployment. A novel patient-specific virtual stent-graft deployment model based on finite element method was employed to analyze TEVAR-induced changes under such conditions. Two landing positions were simulated to investigate the reason for stent-graft migration immediately after TEVAR and explore options for optimization.

Results: Simulation of the actual procedure revealed that the proximal bare metal stent pushed the lamella into the false lumen and led to further stent-graft migration during the launch phase. An alternative landing position has reduced the local deformation of the dissection lamella and avoided stent-graft migration. Higher maximum principal stress (>20 KPa) was found on the lamella with deployment at the actual position, while the alternative strategy would have reduced the stress to <5 KPa.

Conclusions: Virtual stent-graft deployment simulation based on finite element model could be helpful to both predict outcomes of TEVAR and better plan future endovascular procedures.

Keywords: CT, computed tomography; ECG, electrocardiogram; TEVAR; TEVAR, thoracic endovascular aortic repair; finite element analysis; type A aortic dissection; virtual stent-graft deployment.

© 2020 The Authors.

Figures

https://www.ncbi.nlm.nih.gov/pmc/articles/instance/8307501/bin/fx1.jpg
Virtual stent-graft deployment simulation to predict outcome of TEVAR.
Figure 1
Figure 1
Electrocardiogram at admission shows rapid atrial fibrillation, right bundle branch block, and t-wave inversion on leads V2-V6, I, II, III, and aVF, reflecting left ventricular hypertrophy due to long standing hypertension.
Figure 2
Figure 2
Periprocedural images of an inoperable patient with type A aortic dissection managed by thoracic endovascular aortic repair. A, 3-dimentional reconstruction of a computed tomographic angiogram with type A aortic dissection showing a single large entry tear; B1, true and false lumens opacified using digital subtraction angiography; B2, transesophageal echocardiogram showing true and false lumen and the lamella (asterisk); C1, postintervention 3-dimentional computed tomographic angiogram showing stent-graft migration and the proximal part of stent-graft pushing into the false lumen best seen on the 2-dimentional image (C2).
Figure 3
Figure 3
Patient-specific finite element model analysis. A, Fluoroscopic view of stent-graft positioning in semi-open stage before launch. B, Simulated image of the stent-graft in the ascending aorta with virtual adaptation to the aortic curvature. The orange circle marks the proximal landing position in scenario I, which simulates the actual thoracic endovascular aortic repair procedure, whereas the green circle simulates the proximal position of stent-graft in scenario II, which assumed a more proximal positioning by 10 mm. C, The mathematical equation governed stent-graft geometry was created by following the design details of the stent-graft device. The blue wire represents the nitinol metallic skeleton, whereas the yellow tube represents the graft fabric. e-PTFE, Expanded polytetrafluoroethylene.
Video 1
Video 1
Computational virtual stent-graft deployment simulation performed by using finite element analysis. Scenario I was based on the pre-TEVAR images and the simulation accurately predicted the actual result. The proximal bare metal stent pushed the lamella into the false lumen and led to further stent-graft migration during the launching phase. Scenario II was based on the assumption that stent-graft would be deployed 10 mm proximally and close to the aortic root. In addition, the simulated tissue stress maps revealed differences in the lamella with lower focal stress in scenario II compared with scenario I. This might explain the failure in this case (high stress combined with localized deformation caused stent-graft migration during TEVAR). Video available at: https://www.jtcvs.org/article/S2666-2507(20)30575-7/fulltext.
Figure 4
Figure 4
Virtual stenting simulation results. A, Simulated description of various phases of stent-graft placement from left to right. B, Postinterventional digital subtraction angiogram showing stent-graft migration. C, Virtual stent-graft deployment simulation of the actual procedure (scenario I). D, Virtual stent-graft deployment simulation based on the assumption of stent-graft deployed 10 mm proximally (scenario II). The final configuration of stent-graft in both scenarios are projected onto the postinterventional digital subtraction angiogram.

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