Bicuspid Aortic Valve Flow Helicity Generates Wall Shear Stress Magnitude And Directionality Abnormalities In Ascending Aortas
Janet Liu, Philippe Sucosky.
Wright State University, Dayton, OH, USA.
OBJECTIVE: The bicuspid aortic valve (BAV) is a major risk factor for aortic dilation. While hemodynamics is presumed to play a role in BAV aortopathy, the characterization of the mechanical interactions between BAV flow and the aortic wall remains incomplete. While previous studies have isolated abnormalities in wall shear stress (WSS) magnitude and pulsatility by quantifying the local temporal shear magnitude (TSM) and oscillatory shear index (OSI) in BAV aortic wall regions prone to dilation, they have typically focused on the streamwise stress component and have ignored the multidirectionality of the flow field, which could be of pathobiological importance. The objective of this study was to compare computationally the multidirectional characteristics of the WSS in tricuspid aortic valve (TAV) and BAV aortas.
METHODS: 3D valve-aorta geometries were created using CT images of an AA and idealized TAV and left-right (LR-) BAV geometries. Fluid-structure simulations were performed to simulate the flow over one cardiac cycle in each model. The WSS vector was captured in the proximal AA convexity and concavity and was quantified in terms of TSM, OSI and a new transverse WSS (transWSS) index.
RESULTS: During systole, the LR-BAV subjected the aortic wall to WSS overloads (44% and 60% increase in convexity and concavity TSM, respectively, relative to the TAV) and decreased WSS oscillation (0.11 and 0.29 decrease in OSI convexity and concavity, respectively, relative to TAV). While both valves generated highly multidirectional WSS environments in the concavity (0.89<transWSS<0.91 Pa), the TAV resulted in a WSS vector more consistently aligned along the longitudinal direction (37% decrease in transWSS vs. LR-BAV).
CONCLUSIONS: This study demonstrates that LR-BAVs subject the aortic wall to increased WSS magnitude and the only substantial difference between the TAV and LR-BAV WSS environments in the disease-prone aortic wall convexity is the larger WSS multidirectionality imposed by the LR-BAV. The results suggest that the transWSS metric might be a better predictor of aortopathy than the typical WSS magnitude and pulsatility metrics considered thus far.
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