A comparison of the cavitation potential of prosthetic heart valves based on valve closing dynamics

Background and aims of the study: This study compares the cavitation potent ial of prosthetic heart valves based on valve closing dynamics. Methods: A laser sweeping technique measured valve closing dynamics (averag e closing velocity and deceleration) immediately before valve closure. A hi gh-fidelity, piezoelectric pressure transducer was mounted proximal to the mitral valve and measured the high-frequency pressure fluctuations caused b y cavitation bubble formation and collapse after valve closure. The band-pa ss filtered root mean squared (RMS) value of the mitral pressure signal was used as a measure of cavitation intensity. The combination of these two te chniques allowed the direct correlation of valve dynamics and cavitation in tensity for each valve closure. The effects of three parameters on prosthet ic heart valve dynamics and cavitation were examined: valve geometry (Medtr onic Hall(TM) and Bjork-Shiley Monostrut(TM)), occluder material (pyrolytic carbon and Delrin), and gap width between the occluder and housing. A dime nsional analysis was also performed to investigate the general form of the relationship between valve dynamics and cavitation intensity. Results: For all of the valves investigated in this study, the RMS pressure increased (signifying an increase in cavitation) as the average closing ve locity and deceleration increased. In order to compare the cavitation poten tial of the valves, the RMS pressure was estimated at specific closing velo cities using the linear regression of RMS pressure versus average closing v elocity for each valve. The effects of valve geometry, occluder material an d gap width were then examined at high valve loading conditions (closing ve locity of 4.0 m/s). For both pyrolytic carbon and Delrin, the Medtronic Hal l valves had significantly higher RMS pressures than did the Bjork-Shiley M onostrut valves. For a given valve geometry, the pyrolytic carbon occluder had a significantly higher RMS pressure than the Delrin occluder. The valve gap width did not have a significant effect on RMS pressure. The dimension al analysis revealed the general relationship among average closing velocit y, occluder material properties and cavitation intensity. Conclusions: The results presented here contribute to our fundamental under standing of cavitation on mechanical heart valves.