BILEAFLET MECHANICAL HEART-VALVES AT LOW CARDIAC-OUTPUT

Several earlier studies have indicated that bileaflet mechanical heart valves behave irregularly at low cardiac output and low pulse rate co nditions, and that their hydrodynamic performances are generally inade quate. The authors conducted in vitro experiments in a pulsatile mock circulatory loop to compare the performance of the St. Jude Medical (S JM) valve and a long body bileaflet prosthesis recently introduced by Medical Carbon Research Institute (MCRI) (Austin, TX). The new MCRI me chanical heart valve model was designed with emphasis on improved hydr odynamic efficacy by introducing a long body with parallel leaflets an d by leaflets increasing the flow area. Experimental studies were cond ucted on five test valves (MCRI 19 mm, MCRI 25 mm, SJM 19 mm, SJM 23 m m, and SJM 29 mm) with cardiac outputs of 2.0, 2.5, 3.0, and 3.5 L/min at a pulse rate of 40 beats/min, and 3.5, 4.0, 4.5, and 5.0 L/min at a pulse rate of 70 beats/min. Transvalvular pressure drop and closure volume were assessed by measuring the instantaneous ventricular and ao rtic pressures and aortic flow. The leaflet motions of the tested valv es were observed by direct video recording using a charge coupled devi ce camera while the flow measurements were being conducted. Testing un der simulated physiologic ventricular and aortic pressure waveforms, t he results of this study show that the MCRI bileaflets remained fully open during the entire ejection phase, even at very low cardiac output conditions (2.0 L/min). The closure volume (defined as percentage of forward flow volume) increased with decreasing cardiac output, as repo rted earlier by others. Comparative results also indicate that the MCR I design has nearly a two size pressure drop advantage over the SJM, w ith significantly smaller closure volume.