A neonate born at 41 weeks gestation remains cyanotic despite oxygen administration. A soft systolic murmur is heard at the upper left sternal border. A chest X-ray shows an enlarged heart with decreased pulmonary vascularity. These findings are most consistent with which congenital heart defect?

• A. Pulmonary atresia
• B. Tetralogy of Fallot
• C. Transposition of the great arteries
• D. Hypoplastic left heart syndrome

Answer: (A)

This scenario tests recognition of a ductus-dependent cyanotic congenital heart disease with very low pulmonary blood flow. When a newborn remains cyanotic despite oxygen, consider defects where the lungs aren’t getting adequate blood flow or where oxygen alone can’t fix the saturation because the problem is structural rather than just a lack of oxygen.

A soft systolic murmur at the upper left sternal border can occur with restricted flow through the pulmonary outflow tract, while the chest X-ray showing an enlarged heart with decreased pulmonary vascular markings points to undercirculation of the lungs and increased right-sided or systemic load. Pulmonary atresia fits this pattern most closely: the right ventricular outflow to the pulmonary arteries is obstructed, so pulmonary blood flow is severely reduced unless a patent ductus arteriosus provides a route to the lungs. In this condition, oxygen therapy often doesn’t dramatically improve saturation because the fundamental flow to the lungs is limited, and survival depends on maintaining ductal patency and planning surgical palliation.

Other cyanotic defects can show differences: tetralogy of Fallot often has a boot-shaped heart and a clearer murmur from right ventricular outflow tract obstruction with reduced pulmonary markings as well, but the classic boot shape is not described here. Transposition of the great arteries typically presents with a different radiographic silhouette and a brisk need for ductal-dependent mixing, while hypoplastic left heart syndrome has a markedly different ventricular anatomy and often a different murmur pattern. The combination described most consistently points to pulmonary atresia.