Coarctation of the aorta

Coarctation is a fancy way of saying “narrowing,” so a coarctation of the aorta means a narrowing of the aorta. If we look at the heart, we’ve got the right and left atria, the right and left ventricles, the pulmonary artery leaving the right ventricle to go to the lungs, and the aorta leaving the left ventricle to go to the body.

There are two forms of aortic coarctation to be familiar with: an “infant” form and an “adult” form. With the infant form, which accounts for about 70% of cases, the coarctation comes after the aortic arch, which branches off to the upper extremities and to the head, and before the ductus arteriosus. Now, you might be thinking, “Hey, what’s this ductus arteriosus thing doing here?” Well, typically this guy only exists during fetal development and closes after birth, but with infantile coarctation, the ductus arteriosus is usually still open, or patent, so there’s a patent ductus arteriosus. In fact, sometimes this form is also called preductal coarctation.

So, if we draw out a more simplified version of the heart, we’ve got deoxygenated blood coming into the right atrium that flows into the right ventricle. Now, as it’s pumped out of the pulmonary artery, it’s got two choices, right? One option is to go through the patent ductus arteriosus and continue down the aorta; the other option is to continue down the way it’s going. Well, since it’s higher pressure over here on the left side, you might think that the blood would say “thanks, but no thanks,” and keep going down the lower pressure pulmonary artery. Instead, this aortic coarctation adds a little twist. Since the spot right before the ductus arteriosus is narrower, blood flowing from the left side has a harder time going through, so actually there’s high pressure upstream of the coarctation, but low pressure downstream. So, what happens is that blood decides to go this way, through the patent ductus arteriosus and into the lower pressure area in the systemic circulation, and then continues down to the lower extremities, rather than the slightly higher pressure pulmonary artery. This gives you a real sense of exactly how much this coarctation reduces the pressure over on the systemic side.

Since deoxygenated blood is going to the lower extremities, infants typically present with lower extremity cyanosis, meaning a bluish or purplish discoloration of the lower limbs, which is often present even at birth. This is a really important thing to catch, because without intervention, these infants often don’t survive past the neonatal period. Infantile coarctation is something that happens during fetal development, and can occur on its own or can be associated with other congenital changes. It’s worth mentioning that it’s highly associated with Turner syndrome, a genetic abnormality where females only have one X chromosome instead of two.

All right, this brings us to adult coarctation, which accounts for the other 30% of cases, and typically develops, well, as an adult. Compared to infantile coarctation, in this type there usually isn’t a patent ductus arteriosus; instead, it’s been long since closed off and is now known as the ligamentum arteriosum. The coarctation usually happens in adults just distal to this ligament. So, now there’s no mixing of deoxygenated and oxygenated blood, but just like in infantile coarctation, the pressure is increased before the coarctation, because blood has a harder time squeezing through this narrowed artery, and it’s going to be lower downstream from the coarctation.

This causes both upstream and downstream issues. Upstream issues include blood flow increases into the aortic branches, and thus blood pressure increases in the upper extremities and the head. Increased cerebral blood flow means an increased risk of berry aneurysms, which happen when weak spots along blood vessels in the brain balloon out from the high pressures and become tiny sacs filled with blood. This increased pressure also tends to cause the aorta and aortic valve to dilate, or get larger, and the increased pressure means the aorta is at risk of aortic dissection, or tearing of the inner layer of the aorta.