Abstract 17366: Effects of Acute Maternal Supplemental Oxygen on the Fetal Circulation in Transposition of the Great Arteries

Abstract

Introduction: The presence of a restrictive atrial septum in the setting of transposition of the great arteries (TGA) is associated with a high risk of hypoxic ischemic injury upon transition to postnatal circulation. Fetal cardiovascular magnetic resonance (CMR) measures of vessel flow and oxygen saturation provide a unique opportunity to study fetal TGA hemodynamics at baseline and during acute maternal hyperoxygenation. Methods: Thirty-one pregnant mothers with fetuses diagnosed with TGA and an intact ventricular septum (n=23) or small ventricular septal defect (n=8) were recruited and underwent fetal CMR in room air and during administration of 10L/min of oxygen by face mask for up to 45 minutes. Blood flow and oxygen saturations were measured in the major fetal vessels using cine phase contrast MRI and MR relaxometry at baseline and during hyperoxygenation. Results: Two patients exhibited severe restriction at the atrial septum, one undergoing fetal atrial septostomy at 37 weeks and one requiring cannulation onto ECMO shortly after birth. Both revealed reversal of the usual relationship of oxygen saturation between the aorta and the main pulmonary artery at baseline and during hyperoxygenation, i.e. in TGA with restrictive atrial septum the saturations are higher in the aorta than pulmonary. Acute maternal supplemental oxygen was associated with increased pulmonary blood flow (p=0.008) and reduced foramen ovale (p=0.01) and ductus arteriosus shunting (p=0.01). There were no significant changes in umbilical vein, descending aorta and superior vena cava flow. Fetal oxygen saturations increased throughout fetal circulation (p<0.0001) with an associated increase in fetal oxygen delivery (p=0.007), but no increase in fetal cerebral oxygen delivery (p=0.58). Conclusions: This study characterized the effects of acute maternal supplemental oxygen on the fetal circulation in patients with TGA and confirmed the redistribution of flow toward the fetal pulmonary circulation. We observed higher oxygen saturations in the aorta than main pulmonary artery in fetuses with TGA with an intact or highly restrictive atrial septal communication. This finding could be helpful in selecting patients for prenatal or emergency neonatal balloon atrial septostomy.