Bileaflet, tilting disc and porcine aortic valve substitutes: in vitro hydrodynamic characteristics

The desire for a low profile mechanical valve with better fluid dynamic performance led to the design and development of the St. Jude Medical bileaflet prosthesis. Comparative in vitro flow studies indicate that it has better pressure drop characteristics than the Björk-Shiley (convexo-concave) and Carpentier-Edwards porcine valves in current clinical use, especially in the small sizes. In the 21 to 27 mm aortic valve size range the St. Jude valve has an average performance index of 0.66, compared with 0.46 and 0.32 for the Björk-Shiley and Carpentier-Edwards valves, respectively. In contrast, the St. Jude valve has larger regurgitant volumes than both the Björk-Shiley and Carpentier-Edwards valves. Velocity measurements with a laser-Doppler anemometer indicate relatively centralized flow with small amounts of turbulence downstream of the St. Jude valve. The flow is unevenly distributed between the central and side orifices. The turbulent shear stresses are, however, large enough to cause sublethal or lethal damage to blood elements. Wall shear stresses are smaller than those measured downstream of the Björk-Shiley valve. Regions of flow separation were observed just downstream from the sewing ring, which could lead to excess tissue growth along the sewing ring. The results of this study indicate that overall in vitro fluid dynamic performance of the St. Jude valve is superior to that of the two other commonly used prostheses.