Investigation of subaortic membrane pathology by means of in vitro and in silico analysis

Subaortic stenosis is a congenital heart disease characterised by a narrowing of the left ventricular outflow tract. This is often caused by the presence of a fibrous subaortic membrane (SAM) at the aortic valve inlet. This anatomical obstruction leads to a significant increase in the pressure gradient across the valve/SAM complex inducing haemodynamic alterations, which are not yet fully understood. This research investigates SAM's haemodynamic impact through a combined approach of in vitro tests and computer simulations. Experiments involved placing both rigid and flexible membranes of varying sizes and orientations at the inlet of a bioprosthetic aortic valve. These experiments measured global hydrodynamic parameters and tracked valve dynamics as the SAM orifice area progressively decreased. Complementary particle-based computational modelling provided detailed insights into the resulting haemodynamic effects. The findings indicate that the presence of SAM significantly impairs blood flow when the membrane orifice area is reduced to below 75% of the unobstructed inflow. High-speed video revealed abnormal fluttering of the aortic valve leaflets caused by SAM. Numerical simulations corroborated this, demonstrating the formation and shedding of vortices above the membrane, leading to oscillatory leaflet motion. Stiffness, size and position of the SAM orifice membranes critically affect systolic function and fluttering, with the consequent potential for structural damage and blood complications. This study underscores the importance of considering membrane orifice area and morphology, in addition to the mean pressure gradient, when determining surgical interventions for patients with SAM.