How important is the impact of pressure recovery on routine evaluation of aortic stenosis? A clinical study in 91 patients.

Background And Aim Of The Study: Experimental investigations and invasive studies conducted in small series of patients using specially designed high-fidelity micromanometer tip catheters have suggested that downstream pressure recovery (PR) within the aorta may significantly affect transvalvular pressure gradient (PG) measurement. The study aims were to evaluate in a large cohort of patients the extent of PR when transvalvular PGs are routinely measured by fluid-filled pigtail side-hole catheters (FPC) using pullback from the left ventricle to the ascending aorta (AO), and to analyze factors influencing PR. The influence of PR on the correlation between catheter and Doppler PG measurements was also assessed in a subset of patients.

Methods: Transvalvular PG were measured in 91 patients with aortic stenosis using FPC pullback with the catheter positioned at different sites within the ascending aorta. In 71 patients, Doppler echocardiography was obtained within 24 h of catheterization.

Results: Mean PR ranged from 0 to 20 mmHg, corresponding to a PR index (percent of maximal PG) ranging from 0 to 31%. PG was < 50 mmHg in nine of 61 patients (15%) with a PG > 50 mmHg at the origin of the aorta when further measurements were conducted with the catheter positioned more distally in the ascending aorta. PR index better correlated with the ratio of valve area to ascending AO cross-sectional area (r = 0.61, p = 0.001) than with valve area (r = 0.37, p = 0.001) and ascending AO cross-sectional area (0.27, p = 0.02) alone. Differences between Doppler- and catheter-predicted PG were minimized when correcting Doppler by non-invasively calculated PR (p < 0.0001).

Conclusion: The magnitude of PR recorded in aortic stenosis by FPC, as used in most clinical catheterization laboratories, is low in the vast majority of patients. As predicted from fluid mechanics theory, the ratio of valve area to ascending AO cross-sectional area is the central determinant of PR. PR may affect the Doppler-catheter correlation in some patients.