Coarctation of the aorta

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Introduction0:00–0:23

. With coarctation of the aorta, the word coarctation is just a fancy way of saying narrowing.
So a coarctation of the aorta literally means a narrowing of the aorta. If we look at the heart, the right and left atria sit on top with the right and left ventricles below.
Next, the pulmonary artery exits the right ventricle to carry blood to the lungs, while the aorta exits the left ventricle to supply the rest of the body.

Infant Coarctation0:23–2:57

But during fetal development, the lungs are collapsed and filled with fluid, so the fetus relies entirely on oxygenated blood from the placenta.
Oxygenated blood from the placenta enters the fetus via the umbilical vein. And flows through the ductus sinosis into the inferior vena cava, where it mixes with deoxygenated blood from the rest of the body.
This mixed blood enters the right atrium. But instead of going to the right ventricle, some of this blood shunts through the opening in the atrial septum, known as the foraminal valley.
From the left atrium, the blood travels down the left ventricle, eventually entering the ascending aorta, which gives rise to several branches that supply the brain and upper parts of the body.
Meanwhile, the blood that remains in the right atrium enters the right ventricle, eventually reaching the pulmonary artery.
But here's the thing, since the fetal lungs are collapsed, this keeps pulmonary vascular resistance high. In other words, the pressure in the pulmonary artery is also high, so blood prefers to take a path of lower resistance.
That's where the ductus arteriosis comes to play. This shunt connects the pulmonary artery to the aorta just after the left subclavian artery branches off.
This allows the right ventricle to bypass the lungs and send blood through the ductus arteriosis into the descending aorta, supplying the lower parts of the body.
To make this detour possible, the placenta and the ductus arteriosis release prostaglandin E2 to keep it open. For most babies, the transition from fetal to newborn circulation goes smoothly as the lungs expand with the first breath.
The pulmonary vessels open up, causing pulmonary resistance to drop. This change in pressure causes the two fetal shunts to close first, as the left atrial pressure rises above the right atrial pressure, the foraminal valley seals.
Next, prostaglandin levels drop, and the lungs start releasing bradykinin, which constricts the smooth muscle cells of the ductus arteriosis.

Adult Coarctation2:57–3:38

Ultimately this causes the ductus arteriosis to close. Redirecting blood from the right ventricle into the lungs.
But sometimes the process of closure can go a little sideways. The tissue that allows the ductus arteriosis to constrict and seal can extend into the wall of the adjacent aorta.
So when the ductus begins to close after birth, that same tissue contracts and pulls in the surrounding aortic wall, eventually creating a localized narrowing known as a coarctation of the aorta.
Now coarctation of the aorta can occur as an isolated defect, but it's frequently seen in combination with other congenital anomalies.

Upstream complications3:38–4:12

One of the most common partners in crime is a bicuspid aortic valve, while on the genetic side, it has a strong association with Turner syndrome, which is a condition where females have one X chromosome instead of two.
Now coarctation of the aorta is divided into two main types, based on where the narrowing occurs in relation to the ductus arteriosis, called preductal and postductal.

Downstream complications4:12–4:46

In preductal coarctation, the narrowing lies before the ductus arteriosis. This type presents soon after birth, so it's also known as infantile coarctation.
In this scenario, the left ventricle pumps blood easily into the ascending aorta and its branches supplying the upper body, but the narrowed segment before the ductus limits blood flow to the lower body.
As a result, the lower body depends heavily on a patent ductus arteriosis to maintain adequate perfusion. However, unlike during fetal life, the blood crossing the ductus is deoxygenated.

Intercostal Arteries complications4:46–6:51

This is because deoxygenated blood returns from the body to the right atrium, flows into the right ventricle, and eventually enters the pulmonary artery.
Normally this blood would head straight to the lungs since pulmonary resistance is lower than systemic resistance after birth.
But in preductal coarctation, the narrowing just before the ductus arteriosis creates a pressure difference. The pressure before coarctation is high and the pressure beyond it is low.
At this crossroads, blood from the right ventricle can enter the lungs or shunt through the ductus arteriosis, but the pressure in the aorta after the narrowing is lower than the pressure in the pulmonary artery, so some blood takes the easier route through the ductus, bypassing the lungs and entering the descending aorta.
However, not all blood is diverted, some still reach the lungs for oxygenation, which is crucial for survival. In infants, this shunting of deoxygenated blood back to the aorta causes lower extremity cyanosis, which is a blue or purplish discoloration of the lower limbs, often present at birth.
Because the supply to the branches of the aortic arch is not affected, the upper half of the body is perfused normally with oxygenated blood.
This difference in profusion between the upper and lower body is known as differential cyanosis. Once the ductus arteriosis closes, blood can no longer reach the descending aorta, leaving the lower parts of the body with no blood supply.
As a result, newborns can deteriorate quickly, developing symptoms like lethargy, rapid breathing, poor feeding, and signs of shock as the left ventricle strains against the high resistance above the narrowing.

Treatment6:51–12:01

Recognizing these signs is really important because without intervention, infants often don't survive past the neonatal period.
On the other hand, in post-ductal coarctation, the narrowing occurs after the ductus arteriosis. This form usually presents later in life, which is why it's commonly referred to as adult type coarctation.
Unlike the preductal form, the descending aorta is not dependent on a patent ductus for blood flow, and there is no mixing of oxygenated and deoxygenated blood.
However, the core hemodynamic issue remains the same high pressure before the cooctation and low pressure beyond it. This pressure gradient leads to two distinct sets of problems, one upstream and one downstream.
Upstream, the elevated pressure affects arteries branching off before the narrowing, especially those supplying the head and upper limbs.
Chronically high pressure in the cerebral vessels increases the risk of Barry aneurysms, which can rupture and cause life-threatening subarachnoid hemorrhages.
The aortic valve and aortic wall also experience increased strain, increasing the risk of aortic root dilation and aortic dissection.
Downstream, the problem is reduced perfusion, less blood is reaching lower extremities, leading to weak femoral pulses. And lower leg BP when compared to the arms.
This is a hallmark finding on physical exam. Some may experience intermittent claudication, which refers to leg pain and cramping due to poor perfusion, and it doesn't stop there.
Reduced blood flow to the kidneys tricks the body into thinking there's not enough volume in circulation. In response, the kidneys activate the renin angiotensin aldosterone system, which increases sodium and water retention.
Ironically, this compensatory mechanism only makes things worse, driving up systemic BP, even in the upper body where it's already elevated.
Over time, the body adapts by developing collateral circulation to bypass the coarctation of the aorta and deliver more blood to the lower body.
One of the most important collateral pathways involves the intercostal arteries which run along the ribs. The anterior intercostal arteries, which branch off the internal thoracic artery before the coarctation, anastomos with the posterior intercostal arteries, some of which branch off the thoracic aorta after the narrowing.
Because of the pressure gradient, blood flows retrograde through the posterior intercostal arteries to help perfuse the descending aorta.
These posterior intercostal arteries become dilated and tortuous due to the increased flow. Over time, their pulsations erode the underside of the ribs, creating a classic finding on chest X-ray known as rib notching.
It most commonly affects ribs 3 to 9, particularly ribs 4 to 6, where the pressure gradient is most pronounced. Ribs 1 and 2 are typically spared since their intercostal arteries arise above the coarctation and are not part of the collateral circuit.
All right, moving on to diagnosis. Echocardiography is usually the go to diagnostic method in infants and children, since it clearly shows where the narrowing is and how severe it is.
Adults typically require cardiac MRI or CT angiography, which gives a better view of the aorta. Finally, treatment depends on the type of coarctation.
Preductal coarctations are not compatible with life, unless the ductus arteriosis stays open. So the first step is to keep the ductus open using prostaglandin E infusions.
This initial step is then followed by surgical repair. On the other hand, post ductal corructation involves several treatment options.
One common approach is balloon dilation with stenting, where a tiny balloon widens the narrowed part of the aorta and a stent keeps it open.
The second option includes surgical reparation of the narrowed segment. All right.
As a quick recap, coarctation of the aorta is a congenital narrowing of the aortic lumen often caused by the contraction of ductal tissue that extends into the adjacent aortic wall near the ductus arteriosis.
It can occur as an isolated defect or alongside other conditions, most notably bicuspid aortic valve and Turner syndrome.
Based on the location of the narrowing relative to the ductus arteriosis, it's classified as either preductal or postductal