Computational Assessment of Valvular Dysfunction in Discrete Subaortic Stenosis: A Parametric Study.

Area of Science:

• Cardiovascular Physiology
• Biomechanical Engineering
• Medical Imaging

Background:

• Discrete subaortic stenosis (DSS) obstructs left-ventricular outflow tract (LVOT) and is linked to aortic regurgitation (AR).
• The precise mechanism by which DSS and associated aortoseptal angle (AoSA) steepening contribute to AR remains unclear.
• Understanding these hemodynamic alterations is crucial for managing DSS and preventing AR.

Purpose of the Study:

• To computationally quantify the impact of AoSA steepening and DSS on aortic valve (AV) hemodynamics.
• To investigate the role of these factors in the development of AR.
• To explore the mechanobiological underpinnings of AR secondary to DSS.

Main Methods:

• A 2D LV-AV model was created using cine-MRI data, incorporating six geometric variants (unobstructed and DSS-obstructed LVOT with varying AoSAs).
• Fluid-structure interaction simulations were performed to analyze LVOT flow, AV leaflet dynamics, and regurgitant fraction (RF).
• Wall shear stress (WSS) and oscillatory shear index (OSI) were computed to assess leaflet loading.

Main Results:

• DSS and AoSA steepening induced vortex alterations and stenotic flow patterns.
• DSS preferentially affected superior leaflet kinematics and caused leaflet-dependent systolic fluttering.
• While diastolic backflow increased, RF remained below the clinical threshold for mild AR (<7%).
• Significant increases in leaflet WSS magnitude (up to 94%) and OSI were observed.

Conclusions:

• Hemodynamic derangements from DSS and AoSA steepening alone do not cause AR.
• Predicted leaflet WSS abnormalities offer support for a mechanobiological etiology of AR secondary to DSS.
• Further research into mechanobiology is warranted to fully elucidate AR development in DSS patients.