Congenital Heart Disease USMLE Step 1 Practice Question
A 14-year-old girl collapses while swimming and regains consciousness spontaneously. Her maternal uncle died suddenly at age 22. Vital signs show BP 118/76 mmHg, HR 92 bpm, RR 16/min, temp 37°C, SpO2 98% on room air. ECG reveals a prolonged QT interval of 520 ms. Serum electrolytes, including potassium and magnesium, are normal. She denies palpitations or chest pain. Which of the following is the most likely underlying mechanism?
Answer choices
- ADefective desmosomal proteins in the right ventricle
- BAccessory AV pathway causing preexcitation
- CMutation causing delayed ventricular repolarizationCorrect answer
- DFibrofatty replacement of the interventricular septum
- EAutoimmune destruction of the AV node
- FAbnormal calcium handling leading to early afterdepolarizations
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