In vitro assessment of prosthesis type and pressure recovery characteristics: Doppler echocardiography overestimation of bileaflet mechanical and bioprosthetic aortic valve gradients

Abstract

Pressure recovery results in Doppler gradients greater than catheter gradients and is well established in association with bileaflet mechanical aortic valves. Because pressure recovery is influenced by orifice geometry, it might manifest differently with various valve prostheses. If true, then the reliability of Doppler echocardiography for the estimation of aortic valve gradients might be different with different prostheses. The purpose of the present study was to test, in an invitro setting, the degree to which pressure recovery results in Doppler overestimation of gradients for three commonly used aortic valve prostheses. Carpentier Edwards Perimount, Medtronic Mosaic, and St. Jude Medical bileaflet prostheses were tested under various flow conditions in a pulsatile mock flow loop with a normal aorta size. Mean pressure gradient was assessed with transducers 1 cm and 10 cm distal to the valve and with Doppler echocardiography. Pressure recovery was defined as the difference between the Doppler gradient and a 10-cm gradient. The percentage of the maximum pressure gradient composed of pressure recovery and the percentage of pressure recovery complete 1 cm distal to the valve were calculated. There was substantial pressure recovery for all valves in all flow states. Pressure recovery was responsible for 50% or more of the Doppler gradients for almost all conditions and was more than 70% complete within 1 cm for almost all conditions. Multivariate analysis found that flow and valve area (but not valve type) were predictors of pressure recovery; that flow was the major predictor of the percentage of Doppler gradient composed of pressure recovery (with minor contributions from the aorta size and prosthesis type); and that valve type and aorta size were the major predictors of the percentage of pressure recovery complete at 1 cm. In an invitro model with a normal aorta size, substantial pressure recovery occurred with all three aortic valve prostheses. Although statistically significant differences were found between valve types in the percentage of pressure recovery and percentage of pressure recovery complete at 1 cm, the differences were small and clinically unimportant. Clinically, among patients with an ascending aorta diameter less than 3.0 cm, Doppler echocardiography likely substantially overestimates aortic valve mean gradient, regardless of prosthesis type.