Parametric Computational Assessment of Valvular Dysfunction in Discrete Subaortic Stenosis and Aortoseptal Angle Abnormalities

Abstract

Objective: Discrete subaortic stenosis (DSS) is a left-ventricular outflow tract (LVOT) obstruction caused by a membranous lesion. DSS is commonly associated with steep aortoseptal angles (AoSAs) and is a major risk factor for aortic regurgitation (AR). However, the etiology of AR secondary to DSS remains poorly understood. This study aimed at quantifying computationally the mechanistic impact of AoSA steepening and DSS on aortic valve (AV) hemodynamics and AR development. Methods: A 2D LV geometry reconstructed from cine-MRI data was connected to an AV geometry to generate a unified 2D LV-AV model (Figure 1A). Six geometrical variants were considered: unobstructed (CTRL) and DSS-obstructed LVOT (DSS), each reflecting three AoSA variations (110°, 120°, 130°). (Figure 1B). Fluid-structure interaction simulations were run to compute LV blood flow, AV leaflet dynamics, and regurgitant fraction (RF). Results: AoSA steepening and DSS generated vortex dynamics alterations and stenotic flow conditions (Figure 1D). While the CTRL-110° generated the highest degree of leaflet opening asymmetry, DSS preferentially altered superior leaflet kinematics, and caused leaflet-dependent alterations in systolic fluttering. LVOT steepening and DSS subjected the leaflets to increasing WSS overloads (up to 94% increase in temporal shear magnitude), while DSS also increased WSS bidirectionality on the inferior leaflet belly (+0.30-point in oscillatory shear index) (Figure 1E). Although AoSA steepening and DSS increased diastolic transvalvular backflow, regurgitant fractions (RF<7%) remained below the threshold defining clinical mild AR. Conclusions: The mechanical interactions between AV leaflets and LVOT steepening/DSS hemodynamic derangements do not cause AR. However, the leaflet WSS abnormalities predicted in those anatomies provide new support to a mechanobiological etiology of AR secondary to DSS. Figure 1. Unified 2D LV-AV FSI simulations in unobstructed (CTRL) and obstructed (DSS) LVOT anatomies: A) schematic showing the LV-AV assembly, B) LVOT geometries in considered in this study, C) AV geometry with WSS characterization sites, D) snapshots of velocity vector and vorticity contour fields taken at peak systole, E) 3D surface plots regional showing time-averaged WSS characteristics for all models