Interrupted Aortic Arch (IAA)

Interrupted Aortic Arch (IAA) is a rare but extremely severe congenital heart defect characterized by complete discontinuity of the aortic arch, preventing normal systemic blood flow. In this condition, the patent ductus arteriosus initially provides the only route for peripheral organ perfusion; however, its physiological closure soon after birth leads to rapid cardiogenic shock and fatal outcome if untreated.

Embryologically, IAA results from an anomaly in the formation of the fourth aortic arch during fetal development. It is often associated with a ventricular septal defect (VSD) and, in about half of cases, with a 22q11 chromosomal microdeletion, as seen in DiGeorge syndrome. Early diagnosis and prompt surgical intervention are crucial for neonatal survival and long-term quality of life.

Etiology, Pathogenesis, and Pathophysiology

IAA is caused by failed fusion of the embryonic segments of the aortic arch. Genetic abnormalities, particularly the 22q11 deletion, appear to predispose to this defect.

Anatomical classification is based on the location of interruption relative to the major arterial branches:

• Type A: interruption distal to the left subclavian artery.
• Type B: interruption between the left common carotid artery and the left subclavian artery (most common form).
• Type C: interruption proximal to both common carotid arteries.

Pathophysiologically, as long as the ductus arteriosus remains patent, systemic flow is partially maintained via a right-to-left shunt. Once the duct closes physiologically, the neonate experiences a drastic reduction in systemic perfusion, rapid development of metabolic acidosis, multi-organ hypoperfusion, and death if untreated.

Risk Factors and Prevention

As a congenital heart disease, IAA does not have modifiable environmental risk factors but is strongly associated with genetic defects and malformation syndromes. Main predisposing factors include:

• 22q11.2 microdeletion (DiGeorge syndrome): found in about 50% of cases.
• Family history of complex congenital heart disease.
• Rare genetic mutations related to aortic arch development.
• Other chromosomal anomalies, such as trisomy 18.

Primary prevention is currently impossible, whereas secondary prevention relies on prenatal diagnosis through fetal echocardiography in at-risk pregnancies or when ultrasound findings suggest cardiovascular anomalies.

Clinical Manifestations

IAA symptoms typically develop within the first few days of life, coinciding with ductal closure. Main clinical signs include:

• Hypoperfusion shock: pallor, cold extremities, weak pulse, metabolic acidosis.
• Central or peripheral cyanosis, more evident in the lower limbs.
• Absent or diminished femoral pulses compared to brachial pulses.
• Oliguria or anuria due to renal hypoperfusion.
• Lethargy, poor feeding, worsening respiratory distress.

Progression is extremely rapid and, without prompt recognition and treatment, leads to irreversible shock and neonatal death.

Diagnosis

IAA diagnosis must be made urgently. Clinical suspicion arises from signs of shock in a neonate who appeared healthy at birth, especially noting the discrepancy between upper and lower limb pulses. A rational diagnostic pathway includes:

Echocardiography

First-line investigation to identify the aortic arch interruption, assess ductal patency, and detect associated anomalies such as VSD or ventricular hypoplasia.

CT Angiography or Cardiac MRI

Used to detail vascular anatomy preoperatively, especially in complex or atypical cases.

Genetic Testing

Screening for 22q11.2 deletion should be systematically performed in all IAA patients due to the high association with genetic syndromes.

Treatment

IAA treatment requires a highly specialized, integrated approach consisting of:

Neonatal Stabilization

• Intravenous infusion of prostaglandin E1 (PGE1) to maintain ductal patency and ensure systemic perfusion.
• Ventilatory support and correction of metabolic acidosis.
• Rapid preparation for transfer to a pediatric cardiac surgery center.

Corrective Surgery

Surgical repair must be performed within a few days of diagnosis. Surgical strategies include:

• Direct anastomosis of the interrupted aortic segments when anatomy allows.
• Use of prosthetic grafts or patches to reconstruct missing segments.
• Simultaneous correction of associated defects, such as VSD closure if present.

In more complex or unstable cases, staged or palliative initial surgery may be necessary.

Prognosis and Complications

Survival rates of neonates undergoing early surgery have steadily improved, reaching up to 90% in specialized centers. However, long-term follow-up is crucial to monitor:

• Re-stenosis of the reconstructed arch, which may require dilation or reoperation.
• Aortic valve insufficiency or residual intracardiac shunts.
• Neurocognitive complications linked to preoperative hypoperfusion periods.
• Associated syndromic conditions (such as developmental delays in DiGeorge syndrome).

References
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