From Case Studies to Cohort of Patients: Automating FSI Simulations to Uncover Downstream Effects of Ascending Aortic Grafts

Abstract

Purpose Open surgical repair with replacement of the diseased segment by a synthetic Dacron graft remains the standard treatment for ascending thoracic aortic aneurysms and dissections. However, post-operative sequelae, including dissection of the descending aorta (DA), have been reported and are often attributed to the mechanical compliance mismatch between the rigid graft and native aortic tissue. This mismatch can significantly alter downstream hemodynamics, potentially promoting adverse vascular remodeling and accelerating disease progression. Methods A fully automated patient-specific fluid–structure interaction (FSI) pipeline was developed to evaluate hemodynamic changes following graft implantation based on cardiac imaging: aortic 3D anatomy is reconstructed from Magnetic Resonance Angiography; aortic wall mechanics are described as anisotropic hyperelastic, with region-specific parameters calibrated from Cine-MRI-derived wall thickness and compliance data; blood flow is modeled using inlet velocity profiles derived from 4D flow MRI and Windkessel outlet conditions tuned to in vivo pressures. The computational workflow, implemented in the open-source software SimVascular, comprised three stages: (i) computational fluid dynamics simulation to determine blood pressures, (ii) structural analysis for prestress estimation, and (iii) FSI simulation coupling fluid and solid responses. It was applied to five patients whose images were collected pre-operatively, and post-operatively. Pre-operative and post-operative scenarios were then compared to assess whether the compliance mismatch due to the presence of the ascending graft alters the hemodynamic and biomechanics in the DA. Results The proposed framework successfully performed standardized, automated FSI simulations for all patients. Comparison between pre- and post-operative states revealed preliminary evidence of graft-associated flow remodeling, with consistent increases in flow-induced wall shear stress (WSS), oscillatory shear index, and Time Averaged WSS (TAWSS) in the aortic isthmus, which is commonly associated with post-operative dilation. Additionally, a topological analysis of WSS manifolds demonstrated a redistribution of fixed points from the ascending to the isthmus region after graft implantation, suggesting localized hemodynamic disturbances which may correlate with adverse biological responses. Conclusion This automated framework enables large-scale patient-specific FSI analyses and highlights preliminary biomechanical changes induced by aortic grafts. The high values of WSS observed in the isthmus region suggest that next-generation compliant grafts should be designed to mitigate downstream disease progression by lowering WSSs.

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