Embedded Computational Fluid Dynamics in Aortic Dissection: Validation, Hemodynamic Risk Assessment, and Surgical Scenario Exploration

Aortic dissection (AD) is a life-threatening cardiovascular condition characterized by a tear in the aortic wall, which creates a new duct for blood flow, called false lumen (FL). This channel is separated from the true lumen (TL) by the first layer of aortic wall, called intimal flap (IF). Computational fluid dynamics (CFD) has emerged as a useful tool for hemodynamic analysis, as it's very challenging to evaluate key flow parameters directly in-vivo. This study explores and validates the embedded formulation, an unfitted meshing process, for the CFD simulation of AD hemodynamics, by comparing results with fluid-structure interaction (FSI) simulations available in the literature. Using patient-specific MRI data from a type B AD phantom, 3D geometries of aorta and IF were reconstructed. The embedded formulation, implemented via the open-source framework Kratos Multiphysics, enabled an efficient representation of the IF within the background fluid mesh, avoiding complex body-fitted meshing. Key hemodynamic parameters, including pressure, wall shear stress (WSS), and flow patterns were analyzed and compared to FSI results from the literature. Results demonstrated that embedded CFD was able to "qualitatively" replicate FSI derived pressure trends and flow patterns, despite rigid-wall assumptions overestimated WSS magnitudes. The second aim of this work was to analyze how the “surface extraction process” required for the embedded methodology, could influence the simulation results. Surface extraction of the IF introduced minor geometric errors (≤4% pressure variability) but preserved clinical relevance. Once the embedded formulation was validated and an estimation of the potential range of error introduced during the extraction process was established, the third aim was to investigate the hemodynamic indices (WSS, TAWSS, OSI, RRT, ECAP, Pressure), to identify regions at risk of vascular remodeling, thrombus formation, rupture. Hemodynamic risk regions aligned with FSI predictions in the literature: elevated TAWSS in TL and FL proximal regions indicated remodeling susceptibility, while high OSI and ECAP in the entire FL highlighted thrombogenic zones. Finally, different modified IF geometries were created and tested to evaluate their possible influence on the hemodynamic parameters and to show the potential of the embedded formulation, since allow to run a new simulation without the need to re-mesh the whole artery but only the IF. Modifying IF geometry (reducing entry/exit tear areas, adding fenestrations) revealed that reducing exit tear area significantly pressurized the FL and increased rupture risk, while reducing entry tear area promoted FL depressurization. Instead, fenestration process only decreased pressure locally, leading to mal-perfusion mitigation. Embedded CFD offers a computationally efficient alternative to FSI for AD analysis and allows for rapid testing of surgical scenarios (tear closure, fenestration) without remeshing the whole geometry. Although, it's true that "quantitative" discrepancies were found, "qualitative" agreement with FSI and experimental data demonstrates its utility in clinical environment.