Prenatal diagnosis of left atrial isomerism

Objective: To describe the cardiac anomalies and outcome in the fetus with left atrial isomerism. Methods: All fetuses with a diagnosis of left atrial isomerism between 1998 and 2008 were identified. Gestational age at diagnosis, the nuchal translucency, the karyotype, the cardiac findings and outcome were noted. A literature search from 1990 identified four publications reporting 10 or more cases of fetal left atrial isomerism. The same data, where available, were collected from these papers for comparison. Results: There were 41 fetuses with this diagnosis seen in our centre. All cases had an interrupted inferior vena cava with azygous continuation. Associated cardiac defects were similar in our series and in the 129 cases reported in the literature and are therefore grouped together. They included complete atrioventricular septal defect (68%), complete heart block (38%), viscerocardiac heterotaxy (54%), double outlet right ventricle (23%), right ventricular outflow tract obstruction (35%), left ventricular outflow tract obstruction (21%) and total anomalous pulmonary vein drainage (5%). In our series, there were 22 pregnancy terminations, seven intrauterine deaths, one neonatal death, one infant death and one was lost to follow-up. Of the continuing pregnancies only 50% in our series and 60% in the reported series survived. Conclusion: Left atrial isomerism presents a varied spectrum of cardiac malformations when it is detected prenatally. Complete heart block, complex cardiac abnormalities and fetal hydrops are poor prognostic features. Those with only minor cardiac malformations are at risk postnatally for biliary atresia and for bowel obstruction due to malrotation.