Pressure recovery distal to a stenosis: Potential cause of gradient “verestimation” by Doppler echocardiography

Abstract

Doppler ultrasound is currently being widely applied to measure intracardiac pressure gradients noninvasively. In comparative invasive studies, it is generally assumed that pressure is effectively uniform distal to the stenosis. As the poststenotic jet expands, however, its velocity decreases, and pressure is recovered to the extent permitted by turbulence, so that the measured gradient will be lower if the distal catheter is positioned downstream from the vena contracta. This can lead to apparent Doppler "overestimation" of the pressure gradient because of this phenomenon of pressure recovery. This study demonstrates that pressure recovery can be important in a variety of clinical settings studied by in vitro models. Although most prominent in streamlined tunnels modeled after the obstruction in patients with hypertrophic cardiomyopathy, these effects are important even for central stenoses at physiologic flow rates. Because precise catheter position is not always known or controlled, these findings suggest an important advantage for Doppler gradient estimation, because it provides the maximal gradient at the vena contracta, which determines the load on the proximal chamber.

Assessment of Small-Diameter Aortic Mechanical Prostheses

“…It follows that if there is significant pressure recovery, pressure gradients derived from continuous-wave Doppler flow velocity data are likely to exceed manometric measurements. 2,3 Our in vitro data confirm previous reports of significant pressure recovery during physiological systolic ejection across small-caliber St Jude valves. 1,3,[17][18][19] However, this phenomenon was also observed with 20-mm Medtronic Hall valves, a finding that has not been emphasized previously.…”

“…1,3,[17][18][19] However, this phenomenon was also observed with 20-mm Medtronic Hall valves, a finding that has not been emphasized previously. 2 For both types of prosthetic valve, pressure gradients detected by manometers positioned 17.9 cm distal to the prosthetic valve orifice were systematically lower than those detected by manometers positioned just distal to the orifice, as shown in Figure 2. Previous studies have shown excellent agreement between the Doppler-derived gradient and the orifice gradient detected by manometers positioned just distal to the prosthetic valve orifice for both the 19-mm St Jude and the 20-mm Medtronic Hall valves.…”

“…1 Assessment of these prostheses is complicated by physical constraints that preclude or inhibit direct measurement of transprosthetic pressure gradients as well as theoretical constraints relating to the application of the Bernoulli model to flow velocities that frequently are not uniformly distributed across the plane of the prosthetic valve orifice. [2][3][4] Specifically, the hemodynamic relevance of the Doppler-derived transprosthetic gradient (which frequently exceeds the catheter-derived manometric gradient) has been challenged, 5,6 and invasive verification by catheter in patients with elevated Doppler gradients is hampered by the requirement for transprosthetic catheter placement or septal puncture. Moreover, the sensitivity of conventional valve orifice area estimates for detection of small changes or differences in hemodynamics, such as might occur in the early stages of pannus formation (tissue ingrowth) and/or thrombotic occlusion, has not been meaningfully evaluated.…”

Congenital Aortic Stenosis in Childhood

“…This phenomenon is considered to play an important role while interpreting data derived from ultrasonography studies in this clinical context. To note, pressure recovery has been found to be more significant in mild to moderate aortic valve stenosis (Levine et al, 1989). Moreover, the mean Doppler gradient is a better estimate of the catheter-derived gradients (Fyler, 1992;Levine et al, 1989), although not consistent with the known fluid mechanics principles of left ventricular ejection.…”

“…Peak-to-peak gradients determined by cardiac catheterization have constituted the basis of natural history studies and clinical-decision making. Although early investigations suggested that peak Doppler gradient reliably estimated the peak-to-peak catheter gradient (Currie et al, 1985), it was later demonstrated that it consistently overerestimates it by 20-30%, with an exacerbation in presence of significant valvar regurgitation (Baumgartner et al, 1999;Levine et al, 1989;Villavicencio et al, 2003). This is explained by the fact that Doppler technique reflects the maximal instantaneous velocity while peak-to-peak catheter gradient refers to the maximal difference between pressures measured in the left ventricle and the aorta, and also due to the phenomenon of pressure recovery (Clark, 1976).…”