Hydrodynamic Alterations Produced by Subaortic Membranes: An in Vitro Study

Background

Subaortic stenosis is an aortic disease characterised by the presence of a membrane located at the aortic valve inlet, that causes a sudden reduction of the inflow lumen. The membrane develops as a tissue growth of variable thickness that can cause a major increase in the pressure gradient. In this case, when diagnosed, it is removed by surgical resection.

Methods

To investigate the haemodynamic alteration introduced by subaortic membranes, an in vitro study was designed and performed. Stiff and flexible membranes were implanted at the inlet of a bioprosthetic control valve. These mock membranes had different radial and angular alignment, modelling concentric and eccentric orifice positions. For each configuration, a range of different membrane extensions was studied, progressively reducing the orifice area at the inlet of the control valve.

Results

Analysis of the hydrodynamic performances indicates that the detrimental effect of subaortic membranes becomes significant when the membrane orifice areas reduce below 75% of the unobstructed inflow lumen. Video analysis of the valve leaflets dynamics indicates that, together with a worsening in the systolic pressure gradient, the presence of subaortic membranes increases cusps fluttering. As the membrane orifice area reduces, leaflets experience faster oscillation frequencies at decreasing amplitudes.

Conclusions

The fibromuscular or thin nature of the membrane has a significant role on the severity of the pathology, with higher stiffnesses generally producing worse hydrodynamics. The orifice dimension and position are also important on the systolic performance and can determine potential structural degradation and haematic damage.