oa The Congenital Bicuspid Aortic Valve can Experience High Frequency Unsteady Shear Stresses on its Leaflet Surface

Bicuspid aortic valve (BAV) is a common congenital malformation affecting 1-2% of the population and is highly correlated to early calcification of the valve leaflets. Two widely held hypothesis for this correlation are (1) altered shape of the BAV results in altered fluid mechanical environment, leading to pro-calcification biology responses, and (2) inherent genetic defects results in pre-disposition of the tissues to calcify. In the current study, we tested the first hypothesis with porcine valve models in an in vitro flow loop. One BAV model and one tricuspid aortic valve (TAV) model were constructed using healthy porcine AV leaflets and tested in a physiological pulsatile flow loop. Fluid velocities near the center of the aortic surface of the valve leaflets were measured with Laser Doppler Velocimetry at a spatial resolution of 89 microns, and ensemble average shear stresses were calculated at various time points in the cardiac cycle. Unsteadiness of flow near the valve leaflets was quantified with variance analysis and power spectral analysis. Particle Image Velocimetry was used to visualize flow fields downstream of the valves and in the sinuses. The leaflets of the BAV model experienced shear stresses on the aortic surface with magnitudes similar to that of the TAV. However, flow near the BAV leaflets had high frequency unsteadiness components, especially during mid- to late- systole, and had high cycle-to-cycle magnitude variability, indicating that shear stresses will have similar unsteadiness and magnitude variability. These are most likely due to the stenosis in the BAV and the skewed forward flow, which collided with the aorta wall. In conclusion, our study indicated that some BAVs could experience high frequency unsteadiness and cycle-to-cycle magnitude variability on the valve leaflets because of its geometry. We speculate that, together with genetic factors, such adverse mechanical force environment could play a role in causing early calcification in the BAV leaflets.