Inaccurate noninvasive mitral valve area calculation during pregnancy

To compare two different Doppler echocardiographic techniques for the assessment of the transmitral area in pregnant patients with native mitral valve stenosis or prosthetic mitral valves.

Eight consecutive gravid women with prosthetic mitral valves or obstructive native mitral valve disease were evaluated using both the pressure half-time and the continuity equation Doppler echocardiographic methods. Heart rate, cardiac output, and transmitral valve gradient and area were calculated. These studies were repeated postpartum in five women. Differences between the two methods were assessed by characterizing the absolute differences between the mean and standard deviation and by paired t tests. Linear regression analysis was also applied.

For the five women who also had postpartum studies, antepartum data were similar to those of the full set of eight patients. Postpartum heart rate, cardiac output, and transvalvular gradient were lower than antepartum measurements. Calculations using the continuity equation yielded comparable antepartum and postpartum estimates of transmitral areas (1.31 +/- 0.41 versus 1.32 +/- 0.44 cm2, respectively, r = 0.96). These estimates were also consistent with the initial clinical presentation. In contrast, antepartum transmitral valve areas calculated using the pressure half-time technique (2.67 +/- 0.61 cm2) were markedly higher than postpartum (1.94 +/- 0.58 cm2). The correlation between the estimates of antepartum valve area given by the two methods was not statistically significant (r = 0.02). In contrast, there was excellent postpartum correlation of transmitral area between the methods (r = 0.99), despite a significant difference (P < .001) in the transmitral area calculated with each technique.

The results indicate that Doppler echocardiographic estimates of the transvalvular area using the continuity equation technique during pregnancy are valid. In contrast, estimates of area using the pressure half-time technique in pregnant patients are dubious and could result in life-threatening consequences.