Differences in local hemodynamics of bileaflet prosthetic heart valves: the effect of increased orifice area

Enlarging the orifice of a mechanical prosthetic heart valve reduces its resistance to flow, but could adversely affect local flow dynamics. Regions of high turbulent shear stress and flow stagnation have been correlated with thrombus initiation and hemolysis. This study used laser Doppler velocimetry to reveal the effects of an increase in valvular orifice area on the velocities and turbulent shear stresses just distal to bileaflet valves under similar flow conditions. A restricted central orifice jet adjacent to a relatively large region of flow stagnation was observed within three of the valves studied. Within all valves, turbulent shear stresses were largest along the edge of the central orifice jet and within the lateral orifice jet adjacent to the mating of the leaflet and valve housing. These stresses decreased with increasing valvular orifice area. These results indicate that while increasing valvular orifice area may decrease local turbulent stresses, this change may also result in regions of flow stagnation close to the valve