Estimation of mitral valve area in patients with mitral stenosis by the flow convergence region method: selection of aliasing velocity.

OBJECTIVES

We attempted to determine the most suitable aliasing velocity for applying the hemispheric flow convergence equation to calculate the mitral valve area in mitral stenosis using a continuity equation.

BACKGROUND

The flow convergence region method has been used for calculating mitral valve area in patients with mitral stenosis. However, the effect of varying aliasing velocity on the accuracy of this method has not been investigated fully.

METHODS

We studied 42 patients with mitral stenosis using imaging and Doppler echocardiography. Aliasing velocities of 17, 21, 28, 34, 40 and 45 cm/s were used. The transmitral maximal flow rate (Q [ml/s]) was calculated using the hemispheric flow convergence equation Q = 2 x pi x R2 x AV x alpha/180, where R (cm) is the maximal radius of the flow convergence region, AV is the aliasing velocity, and alpha/180 is a factor accounting for the inflow angle (alpha). Mitral valve area (A [cm2]) was calculated according to the continuity equation A = Q/V, where V (cm/s) is the peak transmitral velocity by the continuous wave Doppler method.

RESULTS

Mitral valve area was progressively underestimated with increasing aliasing velocity. The actual and percent differences noted between the mitral valve area by the flow convergence region method and that by two-dimensional echocardiographic planimetry were -0.06 +/- 0.23 cm2 (mean +/- SD) and 0.09 +/- 15.7% at an aliasing velocity of 21 cm/s, increasing gradually with increasing aliasing velocity, and were -1.24 +/- 0.9 cm2 and -72.56 +/- 16.4% at an aliasing velocity of 45 cm/s. Mitral valve areas estimated by the flow convergence region method at an aliasing velocity of 21 cm/s in 11 patients with associated > 2+ mitral regurgitation (2.12 +/- 1.17 cm2) and 8 with associated > 2+ aortic regurgitation (1.28 +/- 0.71 cm2) were not significantly different using planimetry (2.24 +/- 1.39 cm2, p > 0.05 and 1.27 +/- 0.74 cm2, p > 0.05, respectively) but were significantly different by the pressure half-time method (1.59 +/- 1.12 cm2, p < 0.001 and 1.63 +/- 0.93 cm2, p < 0.01, respectively).

CONCLUSIONS

This study indicated the most appropriate aliasing velocity for the accurate estimation of mitral valve area in patients with mitral stenosis.