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Summary Table

Category	Details
Risk Factors	Turner syndrome (45,XO), bicuspid aortic valve, male sex (2:1 ratio), family history of left-sided obstructive heart lesions
Etiology	Congenital narrowing of the aorta, typically just distal to the left subclavian artery at or near the ligamentum arteriosum (juxtaductal region)
Patient Presentation	Neonates: cardiovascular collapse, shock, poor feeding when the ductus arteriosus closes. Older children/young adults: hypertension detected incidentally, headache, epistaxis, leg claudication during exercise
Classic Physical Exam	Upper extremity hypertension with diminished or absent femoral pulses, blood pressure differential >20 mmHg between upper and lower extremities, systolic murmur heard best over the left interscapular area, visible pulsatile collaterals in older patients
Key Diagnostic Results	Chest X-ray: "3 sign" (indentation at coarctation site) and rib notching (bilateral, involving ribs 3 through 8). Echocardiography confirms the site and severity. CT angiography or MR angiography for anatomic detail
Management	Neonate (ductus-dependent): IV prostaglandin E1 to reopen the ductus arteriosus, followed by surgical repair. Older children/adults: surgical repair or catheter-based balloon angioplasty with stenting
Keywords	"Upper vs. lower extremity BP gradient," "absent femoral pulses," "rib notching," "Turner syndrome with hypertension," "radio-femoral delay," "3 sign on CXR"

1. Pathophysiology

Coarctation of the aorta is a discrete narrowing of the aortic lumen, almost always located in the region where the ductus arteriosus inserts into the aorta (the juxtaductal segment), just distal to the origin of the left subclavian artery. This location is key to understanding every downstream consequence.

The narrowing creates a mechanical obstruction to forward blood flow from the aortic arch to the descending aorta. Proximal to the coarctation, pressure rises. Distal to it, pressure and perfusion drop. This is why the hallmark finding is hypertension in the upper extremities (supplied by branches arising proximal to the obstruction) and hypotension in the lower extremities (supplied by the descending aorta beyond the obstruction). The blood pressure gradient between the arms and the legs is therefore the hemodynamic signature of this lesion.

In neonates, the ductus arteriosus initially allows blood to bypass the narrowed segment by shunting flow from the pulmonary artery into the descending aorta. The infant may appear well as long as the ductus remains open. However, when the ductus closes physiologically in the first days of life, the full impact of the obstruction is unmasked. This results in acute left ventricular pressure overload, decreased cardiac output to the lower body, metabolic acidosis, and cardiovascular collapse. This is why neonatal coarctation is classified as a ductus-dependent lesion.

In older children and adults who have milder or gradually progressing coarctation, the body compensates by developing extensive collateral circulation through intercostal arteries, internal mammary arteries, and other thoracic wall vessels. These dilated, tortuous intercostal arteries erode the undersurface of the ribs over time, producing the classic radiographic finding of rib notching. The chronic pressure overload on the left ventricle also leads to concentric left ventricular hypertrophy and sustained systemic hypertension.

The association with bicuspid aortic valve (present in up to 85% of patients) and Turner syndrome is extremely high-yield. Any vignette describing a young female with short stature, webbed neck, and hypertension should immediately trigger consideration of coarctation.

2. Classification and Clinical Manifestation

Coarctation is broadly divided by presentation timing and hemodynamic behavior:

Classification	Age Group	Ductus Status	Presentation	Key Findings
Critical / Infantile (preductal tendency)	Neonate (first 1 to 2 weeks of life)	Closing or recently closed	Acute heart failure, shock, poor feeding, tachypnea, oliguria, metabolic acidosis	Differential cyanosis possible (lower body cyanotic, upper body pink if right-to-left PDA shunt), absent femoral pulses, single S2
Adult / Non-critical (juxtaductal)	Older child, adolescent, young adult	Closed (long-standing)	Often asymptomatic, found on routine BP screening, headache, epistaxis, exertional leg fatigue or claudication	Upper extremity hypertension, BP gradient >20 mmHg arms vs. legs, radio-femoral delay, interscapular systolic murmur, visible collaterals

An additional clinical nuance involves differential cyanosis. In neonates where the ductus remains partially patent and a right-to-left shunt exists through the PDA, deoxygenated blood from the pulmonary artery enters the descending aorta. The result is cyanosis of the lower extremities while the upper body remains pink (pre-ductal oxygen saturation is higher than post-ductal saturation). This finding, when present, strongly localizes the problem to the aortic isthmus region.

3. Diagnostic Workup

Test	Role	Key Findings
Four-extremity blood pressure measurement	Best initial screening step	Systolic BP in arms >20 mmHg higher than in legs (normally legs are equal to or slightly higher than arms)
Chest X-ray	Initial imaging	"3 sign" or "reverse E sign" (pre-stenotic dilation, the coarctation itself, and post-stenotic dilation), bilateral rib notching on ribs 3 through 8
Echocardiography	Confirmatory test in neonates and children	Visualizes the coarctation site and severity, assesses gradient by Doppler, evaluates for bicuspid aortic valve and LV function
CT angiography or MR angiography	Confirmatory and surgical planning in older patients	Provides detailed anatomy of the narrowing, collateral vessels, and associated arch anomalies
Cardiac catheterization	Gold standard for hemodynamic assessment	Measures the pressure gradient directly across the coarctation, also allows intervention (balloon angioplasty and stenting)

The diagnostic approach begins with a clinical suspicion based on physical exam. In any patient (of any age) with upper extremity hypertension and weak or absent femoral pulses, the very first step is to measure blood pressure in all four extremities. A systolic gradient exceeding 20 mmHg between the upper and lower limbs is highly suggestive.

Chest X-ray is often the next study and provides two classic findings. The "3 sign" is seen on the frontal film as an indentation at the level of the coarctation flanked by a dilated left subclavian artery above and post-stenotic aortic dilation below. Rib notching is caused by dilated intercostal collateral arteries eroding the inferior rib margins. It typically appears on ribs 3 through 8 bilaterally. Importantly, rib notching is not present in neonates or young infants because collateral development requires time (usually years).

Echocardiography is the best initial confirmatory imaging modality. It can visualize the narrowing, estimate the pressure gradient via Doppler, and evaluate the aortic valve morphology and left ventricular function.

For older patients and for preoperative planning, CT angiography or MR angiography provides excellent anatomic detail. MRA is often preferred in younger patients to avoid radiation. Cardiac catheterization is reserved for cases where intervention (balloon dilation with stent placement) is planned or when noninvasive imaging is inconclusive.

4. Management and Treatment

Clinical Scenario	Management	Details
Critical neonatal coarctation (ductus-dependent shock)	Prostaglandin E1 (PGE1) IV infusion	Starting dose 0.05 to 0.1 mcg/kg/min to reopen and maintain ductus arteriosus patency. Monitor for apnea (be prepared to intubate). Followed by definitive surgical repair once stabilized
Neonatal surgical repair	End-to-end anastomosis or extended end-to-end anastomosis	Gold standard repair in neonates and young infants. Resects the coarctation segment and reconnects the aorta
Older children (typically >25 kg)	Balloon angioplasty with stent placement or surgical repair	Catheter-based approach increasingly preferred if anatomy is favorable. Surgical options include resection with end-to-end anastomosis or subclavian flap aortoplasty
Adolescents and adults	Catheter-based stenting (preferred) or surgical repair	Stenting is the first-line approach in native and recurrent coarctation for older patients
Hypertension management (pre- and post-repair)	Beta-blockers (e.g., atenolol, metoprolol)	Many patients retain hypertension even after successful repair, requiring long-term antihypertensive therapy
Endocarditis prophylaxis	Per current guidelines	Recommended for 6 months after surgical or catheter-based repair with prosthetic material

In a critically ill neonate presenting with shock, the very first intervention is IV prostaglandin E1. This is the single most important emergency step. PGE1 reopens the closing ductus arteriosus, restoring blood flow to the descending aorta and lower body. The dose is typically 0.05 to 0.1 mcg/kg/min as continuous infusion. The major side effect to anticipate is apnea, so airway equipment and readiness for intubation must be available. Additional acute stabilization includes volume resuscitation, correction of metabolic acidosis, and inotropic support if needed.

Once hemodynamically stabilized, the neonate proceeds to surgical repair. The most common technique is resection of the coarctation segment with end-to-end anastomosis. This is preferred over patch or balloon approaches in neonates because the abnormal ductal tissue is completely removed, lowering the risk of re-coarctation.

For older children, adolescents, and adults, the approach depends on anatomy and clinical context. Catheter-based balloon angioplasty with stent placement has become the preferred approach for native discrete coarctation in patients who are large enough. It is also the treatment of choice for re-coarctation after prior surgical repair.

A critical long-term consideration is that hypertension often persists after repair, particularly in patients who underwent repair later in life. The proposed mechanism involves residual vascular remodeling and altered baroreceptor function. These patients require lifelong cardiovascular follow-up and often need antihypertensive medications (beta-blockers or ACE inhibitors).

All patients with coarctation, whether repaired or unrepaired, are at risk for several long-term complications: re-coarctation, aortic aneurysm formation at the repair site, persistent hypertension, premature coronary artery disease, and cerebrovascular events (berry aneurysms of the circle of Willis are an important association).

5. Differential Diagnosis and Distractors

Differential Diagnosis	Why It Looks Similar	Key Discriminator
Interrupted aortic arch	Also presents as neonatal shock with ductus-dependent circulation and absent femoral pulses	Interrupted arch shows complete discontinuity of the aortic arch on imaging (no lumen at all), more commonly associated with DiGeorge syndrome (22q11.2 deletion), whereas coarctation has a narrowed but still present lumen
Takayasu arteritis	Young patient with upper extremity hypertension, weak pulses, and aortic narrowing	Takayasu affects multiple arterial segments (aorta and branches diffusely), presents with systemic inflammatory symptoms (fever, elevated ESR, weight loss), and occurs in young women of Asian descent typically between ages 15 and 40
Mid-aortic syndrome (abdominal coarctation)	Hypertension in children with aortic narrowing	The narrowing is in the abdominal aorta (suprarenal or infrarenal), not at the isthmus. Associated with neurofibromatosis type 1 or Williams syndrome. No rib notching on chest X-ray
Essential hypertension	Hypertension in a young adult	Femoral pulses are normal and symmetric, no arm-to-leg BP gradient, no murmur over the back. Coarctation should always be excluded in any young patient with hypertension
Aortic stenosis (valvular)	Systolic murmur and left ventricular hypertrophy in a young patient, may coexist with bicuspid aortic valve	Aortic stenosis produces a crescendo-decrescendo murmur at the right upper sternal border radiating to the carotids, with equal upper and lower extremity pulses. No arm-to-leg gradient

6. Traps and High-Yield Pearls

The most common way students lose points on coarctation questions is by failing to check femoral pulses or four-extremity blood pressures when presented with a young hypertensive patient. Vignettes are often written to mimic essential hypertension in a young adult or to focus on headache and epistaxis without making the diagnosis obvious. The test-writer expects you to recognize that hypertension in a patient under 30 always warrants evaluation for secondary causes, and the fastest screening maneuver for coarctation is comparing arm and leg blood pressures.

A second common trap involves the neonatal presentation. The vignette will describe an infant who was well at birth but develops acute shock, poor feeding, and metabolic acidosis at 5 to 10 days of life. Students may fixate on sepsis or inborn errors of metabolism. The key clue is absent or diminished femoral pulses alongside the shock presentation. The expected answer is to start PGE1 immediately, not antibiotics as the primary intervention (though empiric antibiotics are often given simultaneously while ruling out sepsis).

A third trap targets the chest X-ray findings. Rib notching is tested frequently, but students sometimes select it for neonates. Rib notching does not appear in infants; it requires years of collateral vessel development and is only seen in older children and adults. Similarly, the "3 sign" on CXR is an older-patient finding.

Finally, remember the Turner syndrome connection. Any vignette describing a short-statured female with a webbed neck, shield chest, and hypertension is a classic lead-in for coarctation. The association with bicuspid aortic valve is equally high-yield, and examiners love to combine both in a single question stem.

The core competency being tested is the ability to connect physical exam findings (pulse and blood pressure discrepancy) to an anatomic lesion, to recognize ductus-dependent physiology in neonates, and to initiate the correct emergency treatment without delay.

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