Increased cardiac atrial-to-ventricular length ratio in the fetal four-chamber view: a new marker for atrioventricular septal defects.

OBJECTIVES

Atrioventricular septal defects (AVSDs) are the most common cardiac abnormality in fetuses with numerical chromosomal aberrations, in particular trisomy 21. The majority of AVSDs are not detected by routine ultrasound examination in pregnancy. We report two simple cardiac measurements that may substantially improve antenatal detection of AVSDs.

METHODS

Cross-sectional ultrasound images through the fetal thorax demonstrating the four-chamber plane of the heart were obtained in 123 normal fetuses between 10 and 38 weeks of gestation. Heart length was measured at the level of interventricular septum by placing the calipers on the epicardium at the apex of the heart and on the endocardium at the top of the atrium. Ventricular length was measured by shifting the atrial caliper to the crossing point of the ventricular septum and mitral valve. Atrial length was calculated as the difference between the heart length and ventricular length. Based on these measurements, the atrial-to-ventricular length (AVL) ratio was calculated. Data were compared to measurements from 29 consecutive fetuses with AVSD between 13 and 39 weeks of gestation.

RESULTS

In normal fetuses, the AVL ratio did not change with gestation and the mean AVL ratio was 0.47 (95% prediction interval 0.35 to 0.63). In the AVSD group, the mean AVL ratio was 0.77 (range, 0.59-0.99). If a cut-off value for the AVL ratio of 0.6 was chosen, the detection rate of AVSD was 86.2% at a 5.7% false-positive rate. For a 100% detection rate, the false-positive rate was 7.3%.

CONCLUSIONS

The AVL ratio can accurately discriminate between hearts with AVSDs and normal cardiac anatomy. Incorporation of the AVL ratio measurement into routine antenatal ultrasonography may substantially improve the ability to diagnose AVSDs antenatally.