IN-VITRO EVALUATION OF THE LONG-BODY ON-X(R) BILEAFLET HEART-VALVE

Background and aims of the study: In order to optimize the length-to-d iameter ratio, a series of circular aluminum rings with flared inlet a nd varying ring lengths, with internal diameters corresponding to that of 19 mm replacement prosthetic heart valve orifices, were tested in a steady-flow hydraulic system. The study aim was to determine the rin g length-to-internal diameter ratio that produces the best hydraulic e fficiency (i.e. lowest pressure gradient) within the physiologic flow rate range. Methods: Each ring was tested at flow rates of 10, 15, 20, 25 and 30 l/min and length-to-diameter ratio effect on hydraulic effi ciency determined experimentally. The hydraulic effect was most signif icant for a ratio of about 0.6, with an increase to 1.2 providing litt le additional benefit. Thus, a ratio of about 0.6 was considered optim um in terms of hydraulic efficiency and incorporated into the design o f the On-X-(R) bileaflet mechanical heart valve (BHV) series. An in vi tro hydrodynamic study of the smallest (19 mm) and largest (25 mm) cli nical On-X aortic valves was performed at two independent laboratories . Standard St. Jude Medical BHVs were used as the study controls. Resu lts: Steady-flow experiments showed that the pressure gradient in the On-X valve was about 50% less than that of the comparable size control . The pulsatile flow study demonstrated a similar pressure gradient ad vantage. Laser Doppler anemometer velocity profiles taken downstream o f the On-X valve at the aortic root showed typical characteristics of bileaflet valves, with three velocity peaks. The peak velocity reached 1.6 m/s for the On-X and 1.75 m/s for the control valve. A recirculat ing vortex was seen in the sinus cavity during the ejection period. Th is vortex, found in most aortic valves (including bioprostheses), is b elieved to provide a beneficial wash-out of the valve region and assis t in valve closure. Conclusions: These two independent studies clearly demonstrated that the elongated valve body and comparably larger flow area helped to improve the valve hydrodynamic performance, which is e specially beneficial in the smallest (19 mm) size valve.