INACCURATE NONINVASIVE MITRAL-VALVE AREA CALCULATION DURING PREGNANCY

Objective: To compare two different Doppler echocardiographic techniqu es for the assessment of the transmittal area in pregnant patients wit h native mitral valve stenosis or prosthetic mitral valves. Methods: E ight consecutive gravid women with prosthetic mitral valves or obstruc tive native mitral valve disease were evaluated using both the pressur e half-time and the continuity equation Doppler echocardiographic meth ods. Heart rate, cardiac output, and transmitral valve gradient and ar ea were calculated. These studies were repeated postpartum in five wom en. Differences between the two methods were assessed by characterizin g the absolute differences between the mean and standard deviation and by paired t tests. Linear regression analysis was also applied. Resul ts: For the five women who also had postpartum studies, antepartum dat a 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 y ielded comparable antepartum and postpartum estimates of transmitral a reas (1.31 +/- 0.41 versus 1.32 +/- 0.44 cm(2) respectively, r = 0.96) . These estimates were also consistent with the initial clinical prese ntation. In contrast, antepartum transmitral valve areas calculated us ing the pressure halftime technique (2.67 +/- 0.61 cm(2)) were markedl y higher than postpartum (1.94 +/- 0.58 cm(2)). The correlation betwee n the estimates of antepartum valve area given by the two methods was not statistically significant (r = 0.02). In contrast, there was excel lent postpartum correlation of transmittal area between the methods (r = 0.99), despite a significant difference (P < .001) in the transmitr al area calculated with each technique. Conclusions: The results indic ate that Doppler echocardiographic estimates of the transvalvular area using the continuity equation technique during pregnancy are valid. I n contrast, estimates of area using the pressure half-time technique i n pregnant patients are dubious and could result in life-threatening c onsequences.