Limitations of Doppler echocardiography in the assessment of prosthetic valve hemodynamics.

The purpose of this study was to determine the relationship between effective orifice areas of mechanical valves in the aortic position assessed by Doppler echocardiography, and published data from in vitro studies. Eighty-six patients with a normally functioning Standard St. Jude Medical (n = 56) or Björk-Shiley (n = 30) prosthesis in the aortic position were studied. Valve sizes varied between 19 and 27 mm. Pressure gradient was calculated by the Bernoulli, and effective orifice area by the continuity equation. Published data on prosthetic orifice areas from in vitro pulsatile flow experiments using the Gorlin formula were used for comparison. A weak correlation was present between Doppler derived pressure gradient and in vitro estimated effective orifice area, which significantly decreased with increasing valve size (R = -0.61; p < 0.0001). There was only a moderate correlation between Doppler derived and in vitro estimated effective orifice areas whether sewing ring diameter or left ventricular outflow tract diameter was used in the Doppler studies (R = 0.75 and R = 0.71, p < 0.0001, respectively). The difference between in vitro measured and Doppler derived areas was greater with Standard St. Jude Medical than with Björk-Shiley valves, both using the sewing ring diameter (1.04 +/- 0.61 cm2 vs. 0.53 +/- 0.39 cm2, p < 0.0003) and the outflow tract diameter (1.20 +/- 0.68 vs. 0.68 +/- 0.46 cm2, p < 0.006). The presence of atrial fibrillation, concomitant mitral valve replacement, small prosthesis size (19 to 23 mm) or a postoperative interval of less than one year did not change the uniform underestimation of prosthetic orifice areas by Doppler echocardiography. These findings are attributable to pressure recovery and localized transprosthetic velocities, and should be taken into account in the case of a suspected prosthesis malfunction.