Why coarctation of aorta in infants, causing blood flow from pulmonary artery to aorta?

To Survive!: Blood must get to the head & body; coarctation is an obstruction to this flow. So blood flows through a vessel called the PDA (normal in a fetus), to go from the pulmonary artery to aorta ( getting blood and nutrients to the head and body). The infant will become very ill if nothing is done and the PDA closes. For more info, visit: http://www.Ncbi.Nlm.Nih.Gov/pubmedhealth/pmh0001242/.

Types of Coarctation: There are 3 types of aortic coarctation. If there is blood flow from the pulmonary artery to the aorta, the infant has preductal coarctation. This can be associated with turner syndrome, and genetic problem that affects female infants. If there is ongoing blood flow from the pulmonary artery to the aorta, repair is likely needed, which could be surgical or, less likely, through catheters alone.

PDA : It would only do that if the coarctation was severe and there was a patent ductus arteriosus (pda) which is a connecting artery between the aorta and pulmonary artery, leading to blood flow from pa to the descending aorta.