Fluid-Structure Interaction Simulations of Repaired Type A Aortic Dissection: a Comprehensive Comparison With Rigid Wall Models

Abstract

This study aimed to evaluate the effect of aortic wall compliance on intraluminal hemodynamics within surgically repaired type A aortic dissection (TAAD). Fully coupled two-way fluid-structure interaction (FSI) simulations were performed on two patient-specific post-surgery TAAD models reconstructed from computed tomography angiography images. Our FSI model incorporated prestress and different material properties for the aorta and graft. Computational results, including velocity, wall shear stress (WSS) and pressure difference between the true and false lumen, were compared between the FSI and rigid wall simulations. It was found that the FSI model predicted lower blood velocities and WSS along the dissected aorta. In particular, the area exposed to low time-averaged WSS (≤0.2 Pa) was increased from 21 cm2 (rigid) to 38 cm2 (FSI) in patient 1 and from 35 cm2 (rigid) to 144 cm2 (FSI) in patient 2. FSI models also produced more disturbed flow where much larger regions presented with higher turbulence intensity as compared to the rigid wall models. The effect of wall compliance on pressure difference between the true and false lumen was insignificant, with the maximum difference between FSI and rigid models being less than 0.25 mmHg for the two patient-specific models. Comparisons of simulation results for models with different Young’s moduli revealed that a more compliant wall resulted in further reduction in velocity and WSS magnitudes because of increased displacements. This study demonstrated the importance of FSI simulation for accurate prediction of low WSS regions in surgically repaired TAAD, but a rigid wall computational fluid dynamics simulation would be sufficient for prediction of luminal pressure difference.

The Influence of Minor Aortic Branches in Patient-Specific Flow Simulations of Type-B Aortic Dissection

“…Compared with compliant simulations, the assumption of a rigid wall in TBAD has been shown to reduce peak TAWSS, expand regions of high oscillatory shear and low TAWSS, and affect the distribution of flow through luminal tears. 4 , 41 However, the magnitude of these differences increased with flap compliance which is likely to be low due to the chronicity of this case of TBAD. Furthermore, time shifts in TL and FL pressure waves tend to zero in cases where large or numerous luminal communications are present; the assumption of a rigid flap has been previously justified on this basis.…”

The influence of minor aortic branches in Type-B Aortic Dissection: patient-specific flow simulations informed by 4D-Flow MRI

“…Furthermore, time shifts in TL and FL pressure waves tend to zero in cases where large or numerous luminal communications are present; the assumption of a rigid flap has been previously justified on this basis 6 . Even where flap compliance is large, TMP is minimally affected 4,37 . Finally, we have used a RANS turbulence model for computational efficiency which may affect the accuracy of WSS indices, however this is not yet well-documented 1 .…”

“…In terms of modelling assumptions, walls were assumed to be rigid. Compared with compliant simulations, the assumption of a rigid wall in TBAD has been shown to reduce peak TAWSS, expand regions of high oscillatory shear and low TAWSS, and affect the distribution of flow through luminal tears 37,4 . However, the magnitude of these differences increased with flap compliance which is likely to be low due to the chronicity of this case of TBAD.…”

A proposal of risk indicators for pathological development from hemodynamic simulation: application to aortic dissection

“…The role of hemodynamics in aortic dissection formation is well-recognized in the literature. Authors [12,25,26] have shown the existence of preferential sites for aortic dissection formation and have found that low and oscillating parietal stress favors dissection development by its impact on the shape and structure of endothelial cells. The improvement of medical imaging techniques [27][28][29][30][31] allow for providing more precise information on the rheological behavior of blood.…”

“…It is necessary to igure out the mechanical behavior of the aortic wall and the patient's hemodynamic characteristics to build a realistic bio-faithful model. Many researchers [12][13][14] have been interested in numerical simulations of hemodynamics for several years, allowing the location of dissections to be correlated with the area of regions where blood low is disturbed.…”