Discrepancy between doppler and catheter measurements of pressure gradients across small-size prosthetic valve

Objectives: The exact role of pressure gradient across the prosthetic valve estimated from Doppler flow velocity remains controversial. This in-vivo study was designed to assess the actual discrepancy between Doppler and catheter measurements of the pressure gradients for small bileaflet prosthetic valves in the aortic position. Methods: Bileaflet prosthetic valves (19 mm-ATS) were implanted into the aortic position in pigs, and pressure gradients across the valves were examined by volume loading under right heart bypass. The pressure gradient obtained by catheter was defined as the conventional peak-to-peak gradient between the left ventricle and aorta. The peak Doppler gradients were calculated from the maximal instantaneous Doppler velocity with the ultrasound probe positioned on the diaphragm at the level of the cardiac apex. Results: There were strong correlations between pressure gradients and cardiac output. The Doppler gradient was constantly higher than the catheter values, and the resultant discrepancy between Doppler and catheter measurements was directly dependent on cardiac output (y=9.9x+0.6, r2=0.55). For cardiac output ≧5.0 L/min, the difference between Doppler and catheter gradients reached 40 mmHg, and maximum differences of up to 80 mmHg were observed. Conclusions: In view of the presence of striking overestimation of catheter gradient by Doppler measurement, Doppler ultrasound should be used cautiously to assess small-size bileaflet prosthetic valve function with consideration of the patient’s hemodynamic state.