Intrauterine risk factors: infants born to mothers with diabetes
Pathophysiology
Failed spiraling of the aorticopulmonary septum → RV emptying into the aorta and LV into the pulmonary artery → complete isolation of the pulmonary and systemic circuits → ↓ oxygenated blood entering the systemic circulation
Fatal, unless mixing occurs via an intracardiac shunt (e.g., PFO, VSD, ASD) or via an extracardiac connection (e.g., PDA)
Clinical features
Diagnostics
Chest x-ray: narrow mediastinum ± cardiomegaly ("egg on a string")
The enlarged, globular heart resembles an egg lying on its side.
The string represents the narrow superior mediastinum due to stress-induced thymic atrophy and hyperinflated lungs.
Hyperoxia test: little to no ↑ in arterial oxygenation with 100% O2
