Pulse duplicator hydrodynamics of four different bileaflet valves in the mitral position.

The hydrodynamic performance of four different types of bileaflet heart valve was tested both in steady flow conditions and in a newly designed computerized artificial left heart system. Four 29-mm valves, manufactured by either St. Jude Medical, CarboMedics, ATS Medical or Medtronic Parallel were studied under a steady state and in pulsatile conditions by pressure and flow recording and colour Doppler echocardiography in the 'mitral position' at rest and at exercise (cardiac output range 4-30 l/Min). In the steady state, significant differences were measured at peak flows of 30 l/min, with mean (s.d.) increasing pressure drops (mmHg) recorded at 3.48(0.13) (St. Jude Medical), 3.80(0.11) (Medtronic Parallel), 4.31(0.06) (ATS Medical) (P < 0.005), and 4.78(0.06) (Carbo Medics), (P < 0.005). The mean ratio of the closing volume to the stroke volume was comparable for all valves despite one faulty sample. In the pulsatile state the effective orifice area calculated by the Continuity and Gorlin equations decreased from 2.10(0.04) (ATS Medical), 1.95(0.05) (St. Jude Medical), 1.87(0.03) (Carbo Medics) to 1.67(0.02) (Medtronic Parallel) independently of method used. No significant difference was found in the mean ratio of the regurgitant volume to the stroke volume. The performance index, defined as the ratio of effective orifice area to geometric orifice area ranks the valves in the order ATS Medical (0.44), St. Jude Medical (0.43), Carbo Medics (0.41) and Medtronic Parallel (0.38). Regurgitation visible on colour Doppler echo was a mere consequence of the working principle of the bileaflet valves in the mitral position and was by no means hydrodynamically important nor representative of severe insufficiencies. Differences between the valve types were notable under severe conditions, such as high peak flow.