Patent ductus arteriosus

Video summary

Patent ductus arteriosus (PDA) is a congenital heart defect in which the ductus arteriosus, a blood vessel that normally closes after birth, remains open. During fetal development, the ductus arteriosus connects and shunts blood from the pulmonary artery to the aorta, because the fetus doesn't use its lungs yet.

Initially, PDA causes a left-to-right shunt, resulting in pulmonary hypertension. Over time, as the pulmonary artery pressure increases, this is converted into a right-to-left shunt. This switch in the shunt is known as Eisenmenger's syndrome. PDA can be treated with the drug indomethacin, or by surgical ligation.

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Content Reviewers

Filip Vasiljević, MD,Christine Strunk, DO,Lisa Miklush PhD, RN, CNS,Conrad Krawiec, MD (Pediatrics)

With patent ductus arteriosus, or PDA, “patent” comes from the Latin word patere, meaning “to lie open”, while ductus arteriosus refers to a blood vessel that normally connects the pulmonary artery to the aorta. During fetal development, the ductus arteriosus allows blood to bypass the lungs, but normally it closes soon after birth. So, in patent ductus arteriosus, this blood vessel fails to close and remains open.

But before we proceed, first, let’s look at how fetal circulation works. During fetal development, the baby’s lungs are filled with fluid and not yet involved in breathing, so the fetus relies entirely on oxygen-rich blood from the mother. This oxygen-rich blood travels from the placenta through the umbilical vein and eventually reaches the right atrium of the heart. From here, most of it takes a shortcut through the opening between the right and left atria, called the foramen ovale. This allows oxygen-rich blood to completely bypass the lungs and enter the left atrium directly. From the left atrium, blood enters the left ventricle, and from there it’s pumped into the aorta and systemic circulation.

However, not all blood follows this path. A small amount still reaches the right ventricle and gets pumped into the pulmonary artery. However, since the fetal lungs are not yet functioning, the pulmonary vessels are squeezed, creating high resistance that makes it difficult for blood to flow into the lungs. As a result, most of the blood follows the path of least resistance and slips from the pulmonary artery through another fetal shunt called the ductus arteriosus into the aorta.

Anatomically, the ductus arteriosus sits right on the aortic arch, just after the arteries that branch off to supply the brain and upper extremities. This setup allows oxygen-rich blood from the left ventricle to reach the brain and upper extremities first, while blood from the right ventricle via the ductus arteriosus supplies the lower body. This arrangement helps prioritize oxygen delivery to the most important organs, like the brain and heart, while the ductus arteriosus sends the remaining oxygenated blood to the rest of the body.