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Predictions of Wall-shear Stress on the Aortic Valve Leaflets Using a Three-dimensional Fluid-structure Interaction Model
Kai Cao, Philippe Sucosky.
University of Notre Dame, Notre Dame, IN, USA.

BACKGROUND:While hemodynamic stresses have been shown to modulate valvular biology, the native valvular fluid shear stress environment remains largely unknown. The objective of the present study was to characterize the regional wall shear stress (WSS) on aortic valve leaflets using three-dimensional (3D) fluid-structure interaction (FSI) modeling.
METHODS:The idealized 3D model consisted of the aortic root, the aortic sinus and three identical compliant leaflets with physiologic dimensions and non-uniform thickness. Only 1/6 of the structure was considered due to the valve trileaflet symmetry. The fully coupled FSI simulations were run in ANSYS by imposing a physiologic transvalvular pressure at the inlet of the fluid domain. Local leaflet WSS was characterized in terms of temporal shear magnitude (TSM) and oscillatory shear index (OSI).
RESULTS:The model successfully predicted leaflet and blood flow dynamics at a mean physiologic cardiac output of 4.2 L/min. During systole, the positive transvalvular pressure gradient generates a central forward flow contributing to leaflet opening (Fig.1A-C). During diastole, inversion of the pressure gradient produces strong flow recirculation and vortical structures in the aortic sinus cavity, which promotes leaflet coaptation and valve closure (Fig. 1D-E). Regardless of the leaflet region (base, belly, tip), the leaflet WSS was shown to be dominated by the radial component (Fig. 1F). The WSS magnitude on the ventricularis (TSM: 10.30 dyn/cm2) was found to be significantly higher than on the fibrosa (TSM: 1.83 dyn/cm2). The radial WSS variations predicted on both leaflet surfaces indicated the existence of a unidirectional WSS on the ventricularis (OSI = 0.04) and a bidirectional WSS on the fibrosa (OSI = 0.49).

Figure 1.Snapshots of flow velocity field computed at different phases (A-E).WSS variations in the leaflet base, belly and tip (F).
CONCLUSION:This study is the first to implement a commercial FSI software to predict the regional WSS on aortic valve leaflets. The results provide new insights into the macro-scale valvular hemodynamics and are critical to the assessment of the hemodynamic theory of calcific aortic valve disease.

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