Maternal hyperoxygenation improves left heart filling in fetuses with atrial septal aneurysm causing impediment to left ventricular inflow

Objectives: Aneurysm of the atrial septum (AAS) with excessive excursion of septum primum into the left atrium is an uncommon and relatively benign fetal condition associated with impediment to left ventricular (LV) filling and the appearance of a slender, but apex-forming, LV on fetal echocardiography. Impediment to filling can be severe, creating the image of LV hypoplasia with retrograde aortic flow. We hypothesize that maternal hyperoxygenation alters atrial septal position, improves LV filling, and normalizes aortic flow in fetuses with AAS by increasing fetal pulmonary venous return.

Methods: Fetal echocardiography was performed prior to, and at 10 min of, maternal hyperoxygenation in 12 fetuses with AAS who were referred to our center because of LV hypoplasia. Atrial septal excursion (ASE), LV and right ventricular (RV) sphericity index (SI) and direction of flow in the aortic isthmus, as determined by Doppler, were measured.

Results: With maternal hyperoxygenation, mean ± SD ASE decreased (0.76 ± 0.17 before maternal hyperoxygenation vs 0.53 ± 0.23 after maternal hyperoxygenation; P < 0.01), consistent with increased pulmonary venous return, LV-SI increased (0.29 ± 0.06 vs 0.42 ± 0.06; P < 0.001), indicating increased LV filling, and the direction of aortic isthmus flow changed from retrograde in all cases prior to maternal hyperoxygenation to antegrade in 10 and to bidirectional in two. RV-SI remained unchanged (0.53 ± 0.13 vs 0.52 ± 0.10; P = 0.7).

Conclusions: In cases of AAS, short-term maternal hyperoxygenation increases fetal pulmonary venous return, substantially alters LV geometry and promotes antegrade flow in the aortic isthmus. This demonstrates proof-of-concept that maternal hyperoxygenation can improve filling of the left side of the fetal heart in AAS.