FLOW INDUCED PLATELET ACTIVATION IN BILEAFLET AND MONOLEAFLET MECHANICAL HEART VALVES

Abstract

The procoagulant properties of platelets induced by circulation through bileaflet and monoleaflet mechanical heart valves (MHVs) were measured in vitro in a left ventricular assist device (LVAD). Platelet activation state (PAS), measured by a modified prothrombinase assay, was determined for platelets circulated through the LVAD with (i) a St. Jude bileaflet MHV; (ii) a Bjork-Shiley monoleaflet MHV; and (iii) a St. Jude MHV mounted in a tilted position (12.5°). To determine possible sources of activating stress, turbulent, transient, non-Newtonian blood flow patterns generated by the monoleaflet and bileaflet designs were simulated by computational fluid dynamics (CFD) using the Wilcox k-o turbulence model. Platelet shear stress histories (cumulative effect of shear stress and time) were calculated in pertinent turbulent flow trajectories using a stochastic model, and compared with the PAS measurements. The PAS measurement indicated that the bileaflet MHV activated platelets at a rate of more than twice of that of the monoleaflet MHV (P <0.05). The tilted bileaflet MHV activated platelets at a higher rate than that of the untilted valve. Turbulent flow patterns were observed in CFD simulations in both the monoleaflet and the bileaflet valves, and the computed shear-stress histories indicated that the bileaflet MHV causes more shear-stress exposure than the monoleaflet MHV. CFD simulations also confirmed that the tilted bileaflet MHV induces higher shear stress than the untilted. The CFD simulations correlated well with the in vitro PAS measurements.