Abstract
The bicuspid aortic valve (BAV) generates wall shear stress (WSS) abnormalities in the ascending aorta (AA) that may be responsible for the high prevalence of aortopathy in BAV patients. While previous studies have analyzed the magnitude and oscillatory characteristics of the total or streamwise WSS in BAV AAs, the assessment of the circumferential component is lacking despite its expected significance in this highly helical flow environment. This gap may have hampered the identification of a robust hemodynamic predictor of BAV aortopathy. The objective of this study was to perform a global and component-specific assessment of WSS magnitude, oscillatory and directional characteristics in BAV AAs. The WSS environments were computed in the proximal and middle convexity of tricuspid aortic valve (TAV) and BAV AAs using our previous valve-aorta fluid-structure interaction (FSI) models. Component-specific WSS characteristics were investigated in terms of temporal shear magnitude (TSM) and oscillatory shear index (OSI). WSS directionality was quantified in terms of mean WSS vector magnitude and angle, and angular dispersion index (Dα). Local WSS magnitude and multidirectionality were captured in a new shear magnitude and directionality index (SMDI) calculated as the product of the mean WSS magnitude and Dα. BAVs subjected the AA to circumferential TSM overloads (2.4-fold increase vs. TAV). TAV and BAV AAs exhibited a unidirectional circumferential WSS (OSI < 0.04) and an increasingly unidirectional longitudinal WSS between the proximal (OSI > 0.21) and middle (OSI < 0.07) sections. BAVs generated mean WSS vectors skewed toward the anterior wall and WSS angular distributions exhibiting decreased uniformity in the proximal AA (0.27-point increase in Dα vs. TAV). SMDI was elevated in all BAV AAs but peaked in the proximal LR-BAV AA (3.6-fold increase vs. TAV) and in the middle RN-BAV AA (1.6-fold increase vs. TAV). This analysis demonstrates the significance of the circumferential WSS component and the existence of substantial WSS directional abnormalities in BAV AAs. SMDI abnormality distributions in BAV AAs follow the morphotype-dependent occurrence of dilation in BAV AAs, suggesting the predictive potential of this metric for BAV aortopathy.
Highlights
The bicuspid aortic valve (BAV) is a congenital heart valve defect consisting of the formation of two functional leaflets instead of three
This could be due to the inability of those metrics to fully capture the impact of increased flow helicity on the wall shear stress (WSS) environment, which could be instrumental to the pathogenesis of BAV aortopathy
The comparison of the component-specific temporal shear magnitude (TSM) between all valves indicates the existence of large WSS overloads in BAV AAs (Figure 2A)
Summary
The bicuspid aortic valve (BAV) is a congenital heart valve defect consisting of the formation of two functional leaflets instead of three. Previous hemodynamic analyses performed in BAV AAs have focused on quantifying bulk flow shear magnitude (McNally et al, 2017), temporal shear magnitude (TSM) and oscillatory shear index (OSI) in the streamwise (Barker et al, 2010, 2012; Cao and Sucosky, 2015; Cao et al, 2017) and circumferential directions (Meierhofer et al, 2013; Piatti et al, 2017) While these WSS metrics have provided new insights into the morphotypedependent regional stress abnormalities in BAV aortas, they lack any predictive capability for BAV aortopathy. This could be due to the inability of those metrics to fully capture the impact of increased flow helicity on the WSS environment, which could be instrumental to the pathogenesis of BAV aortopathy
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