Usefulness of the Prenatal Echocardiogram in Fetuses With Isolated Transposition of the Great Arteries to Predict the Need for Balloon Atrial Septostomy

Abstract

The outcome of the arterial switch operation for transposition of the great arteries (TGA) is excellent, but there is still associated preoperative mortality. Hypoxemia due to inadequate mixing of the pulmonary and systemic circulations may be implicated. Prediction of early hypoxemia by prenatal echocardiographic criteria has proved difficult. We aimed to identify prenatal echocardiographic features that may predict the need for emergency balloon atrial septostomy (BAS) in isolated TGA. Third trimester fetal echocardiograms of the last 40 cases of isolated TGA were reviewed without knowledge of the postnatal outcome. Measurements of the arterial valves, arterial duct, total septal length (TSL), and foramen ovale (FO) length were made, in addition to a subjective assessment of the atrial septum. The first postnatal echocardiogram and charts were reviewed. Comparison with 40 gestation-matched control fetuses was performed. The FO length in normal fetuses was not significantly different from those with TGA who did not require an emergency BAS but was significantly smaller in fetuses with TGA who required an emergency BAS (p= 0.01). An emergency BAS was required in 12 of 40 cases. All 3 cases with limited movement of the atrial septum required emergency BAS. A hypermobile atrial septum was observed in 10 cases and was not associated with emergency BAS (p= 0.8). The FO:TSL was significantly smaller in those who required an emergency BAS with good predictive value (area under the receiver operating characteristics curve: 0.80). The sensitivity for FO:TSL <0.5 was 99%. There was no significant difference in arterial duct, pulmonary valve, or branch pulmonary artery diameters between those cases requiring emergency BAS and those who did not. In conclusion, the likelihood of an emergency BAS is increased by FO:TSL <0.5 and a fixed appearance of the flap valve. Hypermobile and/or aneurysmal atrial septum did not indicate inadequate postnatal mixing in our group.