Velocities, shear stresses and blood damage potential of the leakage jets of the Medtronic Parallel bileaflet valve.

Even nowadays, the essential problem of mechanical heart valve prostheses is the risk of thromboembolic events mainly caused by unnatural hemodynamics, e.g. just a few years ago the Medtronic Parallel (MP) showed unsatisfactory clinical results caused by thrombi. 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 channel laser Doppler anemometer. From the measured data, mean velocity profiles and the distribution of Reynolds shear stresses, as a function of the location within the jet, were calculated. From this data the potential of blood damage is evaluated computing a Blood Damage Index (BDI) of hemolysis and platelet damage. Four regurgitant free jets right above the hinges were observed during systole 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 turbulent shear stresses around 100 N/m2 within this area. The BDI for platelets of the MP is around ten times higher than the BDI of the St.-Jude-Medical. The study shows that besides the flow structure within the hinges of a mechanical heart valve, the whole regurgitant jet has a large blood damage potential. This potential is measurable, respectively calculable and seems to be (on account of it's support of the clinical outcome) one piece of the puzzle that explains the negative trials of the MP.