False diagnosis of subpulmonary obstruction by echocardiography in d-transposition of the great arteries.

Twenty-one consecutive children (aged 3 to 14 months) with d-transposition of the great arteries were evaluated with standard M mode echocardiography at the time of hospital admission for routine preoperative cardiac catheterization. At catheterization, 6 of the 21 were found to have a systolic pressure gradient between the body of the left ventricle and the main pulmonary artery. Echocardiographic systolic anterior mitral valve motion was noted in nine patients, including five who did not have a left ventricular to pulmonary arterial systolic pressure gradient. Diastolic approximation of the anterior mitral leaflet to the septum was noted in 14 (9 without a gradient), pulmonary valve flutter was also present in 14 (9 without a gradient) and there was premature systolic pulmonary valve closure in 6 (3 without a gradient). Echographic left heart dimensions were not different in patients with a left ventricular outflow pressure gradient than in those without, but patients wit systolic anterior mitral valve motion and diastolic approximation of the mitral leaflet to the septum did have smaller left ventricular and pulmonary root dimensions than did those without these echocardiographic findings. Echocardiographic findings that have been described as suggesting left ventricular outflow obstruction in patients with d-transposition of the great arteries appear to be more related to size and configuration of the left ventricle than to the presence or absence of obstruction.