Effects of Valve Design and Orientation on Flow Induced Platelet Activation in Mechanical Heart Valves

Abstract

A study was conducted to estimate the thromboembolic potential of different Mechanical Heart Valve (MHV) designs and the effect of valve orientation (valve axial misalignment during implantation) on it. CFD simulations of turbulent, transient, non-Newtonian blood flow patterns generated by two types of MHVs (monoleaflet and bileaflet) and the effect of valve orientation were conducted using the Wilcox k-ω turbulence model. Platelet shear stress histories (cumulative effect of shear stress and time) were calculated and averaged over a large number of platelet trajectories within the flow field, and compared with in vitro Platelet Activity State (PAS) measurements conducted in a left ventricular assist device (LVAD) model. Platelets were circulated in the LVAD with Carbomedics bileaflet and Bjork-Shiley monoleaflet MHVs correspondingly. The PAS measurement indicated that PAS induced by the tilted St. Jude bileaflet MHV and the untilted valve was very similar (P>0.1). The bileaflet MHV activated platelets at a rate of more than 2-fold than that observed with the monoleaflet MHV (P<0.05). This confirmed the CFD platelet shear stress histories, which clearly indicated a higher level of stimulation of platelets for the bileaflet MHV.