Patent ductus arteriosus

Patent — not in the sense of a patent for an invention — refers to some opening. A patent ductus arteriosus, or PDA for short, refers to a blood vessel, the ductus arteriosus, which connects the pulmonary artery to the aorta during fetal development. The ductus arteriosus is right on the aortic arch where vessels branch off to the brain and upper extremities. All right, so to help visualize this, let’s look at a super simplified version of the heart to show the relationship between the aorta, branches, pulmonary artery, and ductus arteriosus. We’ll still keep the more anatomical heart for reference. So, the ductus arteriosus usually closes after birth because the walls collapse down; this vessel becomes a ligament, the ligamentum arteriosum. When it stays open after birth, we call it a patent ductus arteriosus because it’s still passing blood through it; in other words, it’s still patent.

Now, during development, the fetus doesn’t use the lungs yet; instead, it relies on oxygenated blood from the placenta, which comes into the right atrium. Most of that blood actually flows through the foramen ovale, an opening between the atria. Blood that doesn’t make it through the foramen ovale is pumped out of the right ventricle into the pulmonary artery, at which point most of it gets sent through the ductus arteriosus to the aorta instead of to the lungs. Remember, the fetus isn’t using the lungs yet.

During fetal development, the ductus arteriosus is kept open by high levels of a vasodilator prostaglandin E2, which is made by the placenta and the ductus arteriosus. At birth, a bunch of things change. First, oxygen levels in the blood go up dramatically and the lungs become the main source of oxygenated blood. Soon after birth, the foramen ovale closes and prostaglandin E2 levels fall, causing the ductus arteriosus to close off. The lungs also start to release a small peptide called bradykinin, which constricts the smooth muscle wall of the ductus arteriosus and sort of helps the process along. Within the first day, the ductus arteriosus usually starts clamping shut; within three weeks, it’s completely closed off and turned into the ligamentum arteriosum. If the ductus arteriosus doesn’t close, then the baby is left with a patent ductus arteriosus. This condition accounts for about 10% of all congenital heart defects, of which the vast majority, about 90%, are isolated heart defects, meaning there aren’t any additional congenital defects. On the other hand, a PDA can be associated with other congenital problems, such as congenital rubella syndrome, which happens when the mother contracts rubella virus during her pregnancy.