It’s normal for babies to have a ductus arteriosus. Before they’re born, this vessel shifts blood away from their lungs into their aorta. This works fine because babies don’t breathe on their own until after they’re born, so they don’t need blood going to their lungs to get oxygen.
Normally, the ductus arteriosus closes soon after birth. In babies with a normal aorta, this closure does not cause problems. In babies with interrupted aortic arch, however, the closure means there’s no way for blood to get to the descending aorta.
Before the ductus arteriosus closes, babies born with this defect do get blood to their lower body. But it’s not oxygen-rich blood coming from their left ventricle. For most babies, it’s a mix of oxygen-poor (blue) and oxygen-rich (red) blood.
This happens because most babies with interrupted aortic arch also have a hole in the septum between the right and left ventricles called a ventricular septal defect or VSD. This hole allows some oxygen-rich blood to flow from the left ventricle to the right ventricle and then to the ductus arteriosus.
About 2 in every 100,000 babies have interrupted aortic arch.