A new flow model for Doppler ultrasound study of prosthetic heart valves

Background and aim of the study: Steady and pulsatile flow models used to a ssess the hydrodynamic aspects of prosthetic heart valves are generally mad e of Plexiglas and Lucite tubing. They often allow continuous-wave and puls ed-wave Doppler ultrasound velocity measurements to be made parallel to the flow, but cannot be used as such for ultrasound scanning of valve inflow a nd outflow velocities because of ultrasonic reverberation and refraction by the tubing. The aim of the study was to develop a new flow model which all owed ultrasonic scanning of the prosthetic valve flow for three-dimensional (3D) reconstruction of color Doppler flow distributions. Methods: The flow model, designed with left ventricular and aortic chambers composed of agar gel which mimics the ultrasound characteristics of biolog ical tissues, was developed and tested for comparative in vitro hydrodynami c and Doppler ultrasonic studies of aortic prosthetic valves. An electromag netic flowmeter and a pressure monitor provided the flow and pressure signa ls for the hydrodynamic tests. The Doppler ultrasonic evaluation was perfor med with an Ultramark 9 HDI ultrasound system and a 3D ultrasound imaging s ystem. The model was designed to enable assessment of prosthetic valve perf ormance by pulsed-wave and continuous-wave Doppler velocity measurements, a s well as by 3D color Doppler velocity measurements obtained by ultrasonic scanning of the left ventricle or aortic chamber with an ultrasound probe m ounted on a motorized translation assembly. Results: The study results showed that this new flow model can provide 3D c olor Doppler velocity distributions as well as accurate comparisons of hydr odynamic parameters of mechanical and bioprosthetic heart valves derived fr om Doppler and catheter measurements, both under steady and pulsatile flow conditions. Conclusion: This new flow model can be used to evaluate the usefulness of h ydrodynamic parameters for the assessment of prosthetic heart valves using both conventional Doppler echocardiography, as currently used in patients, and 3D color Doppler ultrasonic imaging.