Velocities, sheer stresses and blood damage potential of the leakage jets of the Medtronic Parallel (TM) bileaflet valve

Even nowadays, the essential problem of mechanical heart valve prostheses i s the risk of thromboembolic events mainly caused by unnatural hemodynamics , e.g. just a few years ago the Medtronic Parallel(TM) (MP) showed unsatisf actory clinical results caused by thrombi (1). Therefore, in vitro investigations of the whole leakage jets were performed at the MP in mitral position by means of a pulse duplicator using a two ch annel laser Doppler anemometer. From the measured data, mean velocity profi les and the distribution of Reynolds shear stresses, as a function of the l ocation within the jet, were calculated. From this data the potential of bl ood damage is evaluated computing a Blood Damage Index (BDI) of hemolysis a nd platelet damage. Four regurgitant free jets right above the hinges were observed during syst ole at the inflow side of the MP. The peak velocities at the origin of the jets were in the order of 1.6 - 2.1 m/s. Two jets experienced maximum turbu lent shear stresses around 100 N/m(2) within this area. The BDI for platele ts of the MP is around ten times higher than the BDI of the St.-Jude-Medica l. The study shows that besides the flow structure within the hinges of a m echanical heart valve, the whole regurgitant jet has a large blood damage p otential. This potential is measurable, respectively calculable and seems t o be ton account of it's support of the clinical outcome) one piece of the puzzle that explains the negative trials of the MP.