Methodological variation and agreement in assessing mitral valve orifice area by echo-Doppler methods in mitral stenosis.

Two-dimensional echocardiographic planimetry of the directly observed mitral valve orifice, pressure-half-time methods, continuity equation and the Gorlin formula are commonly used to calculate the mitral valve area. However, there have been few comparisons of the four methods. In this study, the mitral valve orifice area was determined by the above four methods using echo-Doppler data in 49 consecutive patients in sinus rhythm (mean area 0.87 to 1.26 cm2). The valve area estimated by these methods correlated well (r = 0.7 to 0.97) with excellent agreement between the continuity equation and the Gorlin formula (mean difference 0.4 cm2, r = 0.97, SEE = 0.26) and between the planimetric area and the pressure-half-time method (mean difference = 0.06 cm2, r = 0.87, SEE = 0.23). However, the limits of agreement were wide and exceeded 1 cm2 in planimetry versus the Gorlin, planimetry versus the continuity equation and pressure-half-time method versus the Gorlin formula. The standard error of estimate varied from 0.23 to 0.51 cm2 for various comparisons. Use of an empirical constant of 51.6 instead of 37.7 in the Gorlin formula provided excellent correlation between the valve area determined by the continuity equation and the modified hydraulic formula (mean difference 0.07 cm2, r = 0.95, SEE = 0.08). Estimates of the valve orifice area by any of the equations tested should be seen as a guide rather than a precise measure of actual orifice area.