Congenital Heart Disease USMLE Step 1 Practice Question
A full-term newborn boy presents with severe cyanosis and respiratory distress within 6 hours of birth. Vital signs show HR 165/min, RR 58/min, BP 55/35 mmHg, SpO2 72% on room air, and temperature 37.2°C. Chest radiograph demonstrates an "egg on string" appearance with decreased pulmonary vascularity. Echocardiography reveals the aorta arising from the right ventricle and pulmonary artery from the left ventricle. Patent ductus arteriosus is present. No associated chromosomal abnormalities are noted. Which embryologic error accounts for this defect?
Answer choices
- AFailure of truncal cushions to fuse completely resulting in a single outflow tract
- BFailure of endocardial cushion fusion
- CExcess apoptosis of the interventricular septum
- DAbnormal neural crest migration causing failure of aorticopulmonary septum spiralingCorrect answer
- EAbnormal left to right shunting through the ductus arteriosus
- FFailure of the bulbus cordis to properly septate from the conus arteriosus
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