Platelet Activation and Free Emboli Formation 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 and in a model of left ventricular assist device (LVAD), using an innovative platelet activity state (PAS) assay. The platelet activation significantly increased as a function of the recirculation time past the valve, and as compared to controls. Transcranial Doppler (TCD) measurements were conducted in the carotid artery of sheep with implanted MHV, showing marked increase in the number of HITS (High Intensity Transient Signals) signifying the passage of free emboli generated by the valve. The HITS were analyzed to distinguish between gaseous and thrombi emboli. Finally, platelet activity state measurements were conducted with sheep platelets, showing marked increase of platelet activation after valve implantation.