Hemodynamics through the congenitally bicuspid aortic valve: a computational fluid dynamics comparison of opening orifice area and leaflet orientation.

A computational fluid dynamics model of a bicuspid aortic valve has been developed using idealised three-dimensional geometry. The aim was to compare how the orifice area and leaflet orientation affect the hemodynamics of a pure bicuspid valve. By applying physiologic material properties and boundary conditions, blood flow shear stresses were predicted during peak systole. A reduced orifice area altered blood velocity, the pressure drop across the valve and the wall shear stress through the valve. Bicuspid models predicted impaired blood flow similar to a stenotic valve, but the flow patterns were specific to leaflet orientation. Flow patterns developed in bicuspid aortic valves, such as helical flow, were sensitive to cusp orientation. In conclusion, the reduced opening area of a bicuspid aortic valve amplifies any impaired hemodynamics, but cusp orientation determines subsequent flow patterns which may determine the specific regions downstream from the valve most at risk of clinical complications.

Systolic fluid-structure interaction model of the congenitally bicuspid aortic valve: assessment of modelling requirements.

A transient fluid-structure interaction (FSI) model of a congenitally bicuspid aortic valve has been developed which allows simultaneous calculation of fluid flow and structural deformation. The valve is modelled during the systolic phase (the stage when blood pressure is elevated within the heart to pump blood to the body). The geometry was simplified to represent the bicuspid aortic valve in two dimensions. A congenital bicuspid valve is compared within the aortic root only and within the aortic arch. Symmetric and asymmetric cusps were simulated, along with differences in mechanical properties. A moving arbitrary Lagrange-Euler mesh was used to allow FSI. The FSI model requires blood flow to induce valve opening and induced strains in the region of 10%. It was determined that bicuspid aortic valve simulations required the inclusion of the ascending aorta and aortic arch. The flow patterns developed were sensitive to cusp asymmetry and differences in mechanical properties. Stiffening of the valve amplified peak velocities, and recirculation which developed in the ascending aorta. Model predictions demonstrate the need to take into account the category, including any existing cusp asymmetry, of a congenital bicuspid aortic valve when simulating its fluid flow and mechanics.