Advances in prosthetic heart valves: fluid mechanics of aortic valve designs

The in vitro hemodynamic characteristics of a variety of mechanical and tissue heart valve designs used during the past two decades were investigated in the aortic position under pulsatile flow conditions. The following valve designs were studied: Starr-Edwards ball and cage (model 1260), Björk-Shiley tilting disc (convexo-concave model), Medtronic-Hall tilting disc, St. Jude Medical bileaflet, Carpentier-Edwards porcine and pericardial (models 2625, 2650 and 2900), Hancock porcine (models 250 and 410) and Ionescu-Shiley standard pericardial. The Starr-Edward ball and cage, Björk-Shiley tilting disc, Carpentier-Edwards porcine (model 2625) and Ionescu-Shiley standard pericardial valves were designed prior to 1975, while the Medtronic-Hall tilting disc, St. Jude Medical bileaflet, Hancock porcine (model 250), Hancock II porcine (model 410), Carpentier-Edwards porcine (model 2650) and Carpentier-Edwards pericardial (model 2900) valves were designed after 1975. The pressure drop results indicated that the valves designed prior to 1975 had performance indices of 0.30 to 0.45, whereas the valves designed after 1975 had performance indices of 0.40 to 0.70. The regurgitant volumes were higher for the mechanical designs (5.0 to 11.0 cm3/beat) compared to the tissue bioprostheses (1.0 to 5.0 cm3/beat). Two-dimensional laser Doppler anemometry studies indicated that the valves designed after 1975 tended to create more centralized flow fields, with reduced levels of turbulent shear stresses. However, none of the current valve designs is ideal: they all create areas of stasis and/or regions of low velocity reverse flow; and regions of elevated turbulent shear stresses that are capable of causing sub-lethal and/or lethal damage to the formed elements of blood.