Discrepancies between doppler and catheter gradients in aortic prosthetic valves in vitro: A manifestation of localized gradients and pressure recovery

Abstract

To evaluate possible causes of discrepancy between Doppler and catheter gradients across prosthetic valves, five sizes (19-27 mm) of St. Jude and Hancock valves were studied in an aortic pulsatile flow model. Catheter gradients at multiple sites distal to the valve were compared with simultaneously obtained Doppler gradients. In the St. Jude valve, significant differences between Doppler and catheter gradients measured 30 mm downstream from the valve were found: Doppler gradients exceeded peak catheter gradients of 10 mm Hg or more by 81±35% (15±3.6 mm Hg), and mean catheter gradients by 71±11% (10.3±2.5 mm Hg). When the catheter was pulled back through the tunnel-like central orifice of the valve, high localized gradients at the valve plane and significant early pressure recovery were found. When the catheter was pulled back through the large side orifices, gradients at the same level were only 46±6% of the central orifice gradients (mean difference, 7.6±4.5 mm Hg). Doppler peak and mean gradients showed excellent agreement with the highest central orifice catheter gradients (mean difference, 1.0±3.1 and 0.9±1.5 mm Hg, respectively). A significantly better agreement between Doppler and catheter gradients at 30 mm was found for the Hancock valve, although Doppler peak and mean gradients were still slightly greater than catheter gradients. Doppler gradients exceeded catheter gradients by 18±10% (3.4±1.9 mm Hg) and 13±11% (2.1±0.9 mm Hg), respectively. When the catheter was pulled back through the valve, the highest gradients were found approximately 20 mm distal to the valve ring. Doppler peak and mean gradients showed excellent agreement with these catheter gradients (mean difference, -0.6±2.1 and -1.2±0.9 mm Hg, respectively). Therefore, Doppler gradients accurately reflect the highest obtainable catheter gradients, which occur between the two leaflets (but not in the side orifices) of St. Jude valves and 20 mm distal to the prosthesis in the Hancock valves. However, Doppler gradients may be significantly higher than catheter gradients measured further downstream due to localized gradients and pressure recovery. The difference between Doppler and catheter gradients is, therefore, not due to overestimation by Doppler, but to the fact that the two techniques measure gradients in different locations. Doppler measurements reflect the maximum gradient along the interrogation line, whereas catheterization measures the recovered pressure distal to the valve. The magnitude of this discrepancy is not clinically significant in Hancock valves but may be substantial in St. Jude valves, particularly in smaller valve sizes at high flow rates. These findings suggest the importance of considering valve type, valve size, flow rate, and catheter position when using continuous wave Doppler to predict clinical catheter-ization gradients in prosthetic valves.