In a 10‑day‑old neonate with a brief resolved unexplained event and four‑limb blood pressure readings showing markedly higher systolic pressure in the left arm than in the right arm and both legs, what is the most likely diagnosis and what immediate management should be initiated?

Coarctation of the Aorta with Aberrant Right Subclavian Artery

This 10-day-old neonate most likely has coarctation of the aorta with an aberrant right subclavian artery arising distal to the coarctation, and requires immediate echocardiography followed by urgent surgical repair given the neonatal age and risk of cardiovascular collapse.

Diagnosis

The blood pressure pattern is pathognomonic:

• Left arm markedly elevated (110-129 systolic) compared to right arm (87 systolic) and both legs (67-92 systolic)
• This indicates the left subclavian artery arises proximal to the coarctation (receiving pre-coarctation pressure)
• The right subclavian artery and descending aorta are distal to the coarctation (receiving post-coarctation pressure)

While normal neonates can show variable upper-to-lower limb gradients in the first week of life 1, 2, 3, a significant gradient between the two arms is never normal and indicates anatomic variation in the relationship of the subclavian arteries to a coarctation site.

Critical Context for Neonatal Coarctation

Coarctation accounts for 6-8% of congenital heart defects and typically occurs juxtaductally, just distal to the left subclavian artery 4. Neonates with coarctation present with signs and symptoms of low cardiac output and shock once the ductus arteriosus closes 4. The BRUE in this infant may represent early cardiovascular compromise.

Immediate Management Algorithm

Step 1: Urgent Echocardiography (Within Hours)

• Confirm coarctation location and severity
• Identify aberrant right subclavian anatomy
• Assess for bicuspid aortic valve (present in 30-40% of cases) 4
• Evaluate ventricular function and ductal patency

Step 2: Stabilization Measures

• Prostaglandin E1 infusion to maintain ductal patency and preserve lower body perfusion
• Continuous cardiorespiratory monitoring
• Assess for signs of shock or heart failure
• Avoid lower extremity arterial access (compromised perfusion)

Step 3: Surgical Consultation

Extended resection with end-to-end anastomosis remains the gold standard for neonatal coarctation 4. Transcatheter balloon angioplasty is not appropriate at 10 days of age due to:

• Higher recurrence rates in young infants (<1 month) 4
• Risk of aneurysm formation 4
• Frequent arch hypoplasia in neonates 4

Step 4: Additional Evaluation

• Four-extremity pulse examination (expect weak/absent femoral pulses)
• Assess for Turner syndrome features (increased coarctation prevalence) 4
• Consider future screening for intracranial aneurysms (present in 10% of coarctation cases) 4

Critical Pitfalls to Avoid

1. Do not dismiss arm-to-arm BP differences as normal variation - this always indicates pathology in neonates
2. Do not delay intervention - neonates can deteriorate rapidly with ductal closure
3. Do not attempt balloon angioplasty as first-line therapy at this age - surgical repair is indicated 4
4. Do not overlook the BRUE - this may represent early cardiovascular decompensation requiring immediate stabilization

Anatomic Considerations

The aberrant right subclavian artery likely arises from the descending aorta distal to the coarctation (or from a diverticulum of Kommerell), explaining why it receives post-coarctation pressure similar to the lower extremities. This anatomic variant will need to be addressed during surgical repair to ensure adequate perfusion to the right arm postoperatively.