Prenatal detection of severe right ventricular outflow tract obstruction: Pulmonary stenosis and pulmonary atresia

We reviewed the prenatal echocardiograms and clinical outcomes of 12 fetuses with severe valvar pulmonary stenosis (six cases) or pulmonary atresia (six cases), to identify in utero echocardiographic features associated with severe right ventricular outflow tract obstruction. The mean age at initial prenatal study was 25 ± 6 weeks of gestation. The echocardiographic appearance of the four chamber view, the right ventricular outflow tract, and the pulmonary arteries were similar for severe pulmonary stenosis and pulmonary atresia. The four chamber view was abnormal in all 12 cases. Right atrial dilation, with or without tricuspid regurgitation, was a common feature of severe pulmonary stenosis (six patients) and pulmonary atresia (four patients). In two fetuses with pulmonary atresia and significant right ventricular hypoplasia, a large atrial septal defect and no obvious right atrial enlargement were seen. Right ventricular hypoplasia was a feature in five fetuses with pulmonary atresia and in five fetuses with a patent pulmonic valve. All six fetuses with severe pulmonary stenosis and four fetuses with pulmonary atresia had right ventricular hypertrophy. Tricuspid regurgitation was present in five fetuses with severe pulmonary stenosis and in two with pulmonary atresia. All of the fetuses with pulmonary atresia had retrograde blood flow in the ductus arteriosus by color flow mapping. Despite the presence of a patent pulmonary valve, three fetuses with severe pulmonary stenosis had no antegrade blood flow detected through the right ventricular outflow tract, and only retrograde ductal and pulmonary artery flow could be demonstrated. Ratios of the dimensions of right to left heart structures, including ventricular diameters and lengths, and diameters of the atrioventricular valve and great artery, were not statistically different between the fetuses with atresia and stenosis. Recognition of the echocardiographic features associated with severe right ventricular outflow tract obstruction, particularly abnormalities of the four chamber view, should facilitate detection of severe pulmonary stenosis and pulmonary atresia on routine fetal screening. However, differentiation between these two conditions antenatally in the absence of antegrade right ventricular outflow appears to be unreliable at present.