Platelet activation in flow past mechanical heart valves

Numerical studies, in vitro, and in vivo measurements were conducted, aimed at quantifying free emboli formation and procoagulant properties of platelets induced by flow past mechanical heart valves (MHV). Pulsatile turbulent flow simulation was conducted past a St. Jude medical MHV in the aortic position, to study the effects of valve implantation technique on the thromboembolic potential of the valve. A misaligned valve with subannualarly sutured pledgets produced accelerating jet flow through the valve orifices and a wider wake of shed vortices. Shear stress histories of platelets along turbulent trajectories exposed the platelets to elevated shear stresses around the leaflets, leading them to entrapment within the shed vortices. In vitro platelet studies were conducted past the MHV mounted in a recirculation flow loop, by measuring the platelets ability to support the activation of acetylated human prothrombin by factor xa, which enables sequestering flow induced effects and quantification of the platelets activity state. The platelet activation state increased monotonically as a function of the recirculation time past the valve, as measured by the thrombin generation rates in the assay. Finally, platelet activity state measurements were conducted in vivo, from a sheep with an implanted MHV, showing marked increase of platelet activation after valve implantation.