Erroneous diagnosis of significant obstruction by Doppler in a patient with discrete subaortic membrane: correct diagnosis by 3D-transthoracic echocardiography.

We report an adult with a discrete subaortic membrane in whom two-dimensional transthoracic Doppler echocardiography demonstrated peak and mean gradients of 64 and 33 mmHg, respectively in the left ventricular outflow tract (LVOT) and a calculated orifice area by continuity equation of 1.14 cm(2) consistent with significant obstruction. However, by direct en face visualization of the LVOT at the level of the membrane by live/real time three-dimensional transthoracic echocardiography (3D TTE), a larger orifice measuring 2.29 cm(2) was seen and was indicative of no significant obstruction. This finding was confirmed at cardiac catheterization, which showed insignificant obstruction.