Leakage flow at mechanical heart valve prostheses: Improved washout or increased blood damage?

Background and aims of the study: An essential problem of mechanical heart valve (MHV) prostheses is the risk of thromboembolic events and consequent need of lifetime anticoagulation due to unnatural hemodynamics that results in traumatization of red blood cells and platelets. The precise spatial an d tidal localization of blood-damaging events within the flow is poorly und erstood. The present study addresses the question whether leakage flow at M HV, which is claimed to improve washout in the hinge areas of microthrombi and platelet-activating agents, is responsible for significant blood damage . Methods: This study investigated leakage flow in vitro, primarily within tu rbulent leakage jets of currently used mechanical valves. St. Jude Medical, Sorin Bicarbon, Duromedics-Edwards and CarboMedics valves were analyzed in the mitral position of a circulatory mock loop. Jet configuration was dete rmined by echocardiography; velocity and shear stress distributions within jets were measured using laser-Doppler anemometry (LDA). A blood damage ind ex (BDI) was developed in terms of lactate dehydrogenase release by platele ts and hemoglobin release by red blood cells (RBC), as a function of exposu re time and shear stresses within the flow field. BDIs were validated by di rect measurement of hemolysis caused by leakage flow, using porcine blood. Results: All valves showed characteristic and reproducible jet patterns, ma inly emerging from the hinge areas. Maximum velocities up to 1.7 m/s were m easured. Maximum turbulent shear stresses >80 Pa were found. The investigat ed MHV revealed significant differences in calculated BDIs. The Sorin Bicar bon had a significantly lower BDI for RBC damage, as well as for platelet d amage; this was validated by direct hemolysis measurements. Conclusions: The relevance of the leakage-induced blood damage was demonstr ated from a literature investigation of hemolysis as a function of valve ty pe and implant position.