Assessment of prosthetic valve hemodynamics by Doppler: lessons from in vitro studies of the St. Jude valve.

Although Doppler assessment of native heart valve hemodynamics is quite accurate, assessment of prosthetic mechanical valve hemodynamics presents more potential problems. These problems arise from the unique geometry of prosthetic valves. Two important prosthetic valve phenomena can violate the basic assumptions underlying Doppler calculations: pressure recovery and localized gradients. When pressure recovery is present, Doppler systematically overestimates the actual net catheter gradient across the valve. In contrast, the presence of localized gradients may cause Doppler to measure differing gradients depending on which part of the valve is interrogated. These phenomena can also affect the calculation of prosthetic valve areas using the continuity equation. When assessing prosthetic valves with Doppler echocardiography, it must be remembered that Doppler measures velocity, not pressure gradients and that the echocardiographer must exercise great care when interpreting Doppler velocities as either pressure gradients or in calculating valve areas for prosthetic valves.