A method for determining the reference effective flow areas for mechanicalheart valve prostheses - In vitro validation studies

Background-The anatomic opening area (AOA) is usually reported as the prima ry index of mechanical heart valve function. Because flow contracts immedia tely distal to an orifice as a result of the vena contracta effect, AOA may not be a good measure of true effective flow area. Methods and Results-Laser flow imaging was used to visualize the contractio n in the jet flow stream as it passed through bileaflet mechanical valves u nder steady and pulsatile conditions. Such visualization allowed clear meas urement of the individual vena contracta areas (VCAs) of the 3 valve orific es. VCAs for side orifices were larger (94+/-2% of AOA) than those through the central orifice (34+/-8%). Formation of large radial vortices around th e leaflet tips constricted the central orifice flow stream and appeared to be the main reason for smaller central VCA. Total VCA remained constant unt il approximate to 0.5 orifice diameters (approximate to 1.0 cm) downstream, beyond which cross-sectional area increased as a result of entrainment of receiving chamber flow. Total VCA was larger for steady flow (89.6+/-2.7% o f AOA) than for pulsatile flow (76.3+/-5.0% of AOA). Conclusions-This study further clarifies flow dynamics through bileaflet me chanical valves and provides previously unavailable reference information o n VCAs for these valves. Such information should aid clinicians in explaini ng Doppler-derived and catheter-measured pressure discrepancies, validating clinical techniques for quantifying effective flow areas, and optimizing v alve size for implantation. The method should also be useful for comparativ e studies of different valve designs.