Impact of design parameters on bileaflet mechanical heart valve flow dynamics.

Background And Aim Of The Study: One significant problem encountered during surgery to implant mechanical heart valve prostheses is the propensity for thrombus formation near the valve leaflet and housing. This may be caused by the high shear stresses present in the leakage jet flows through small gaps between leaflets and the valve housing during the valve closure phase.

Methods: A two-dimensional (2D) study was undertaken to demonstrate that design changes in bileaflet mechanical valves result in notable changes in the flow-induced stresses and prediction of platelet activation. A Cartesian grid technique was used for the 2D simulation of blood flow through two models of bileaflet mechanical valves, and their flow patterns, closure characteristics and platelet activation potential were compared. A local mesh refinement algorithm allowed efficient and fast flow computations with mesh adaptation based on the gradients of the flow field in the gap between the leaflet and housing at the instant of valve closure. Leaflet motion was calculated dynamically, based on the fluid forces acting on it. Platelets were modeled and tracked as point particles by a Lagrangian particle tracking method which incorporated the hemodynamic forces on the particles.

Results: A comparison of results showed that the velocity, wall shear stress and simulated platelet activation parameter were lower in the valve model, with a smaller angle of leaflet traverse between the fully open to the fully closed position. The parameters were also affected to a lesser extent by local changes in the leaflet and housing geometry.

Conclusion: Computational simulations can be used to examine local design changes to help minimize the fluid-induced stresses that may play a key role in thrombus initiation with the implanted mechanical valves.