Valvular Heart Disease USMLE Step 1 Practice Question
A 67-year-old man with a history of bicuspid aortic valve presents to the emergency department after experiencing syncope during his morning jog. He reports progressive dyspnea on exertion over the past 6 months. Vital signs show BP 138/82 mmHg, HR 78 bpm, RR 16/min. Physical examination reveals a harsh, crescendo-decrescendo systolic ejection murmur best heard at the right upper sternal border with radiation to bilateral carotids. The carotid upstroke is delayed and diminished bilaterally. Echocardiography confirms severe aortic stenosis with an aortic valve area of 0.6 cm² and normal left ventricular systolic function at rest. Which of the following best explains the pathophysiology of his exertional syncope?
Answer choices
- AVasovagal reflex triggered by a paradoxical rise in left ventricular pressure that activates left ventricular mechanoreceptors
- BAcute pulmonary edema causing severe hypoxemia and altered cerebral metabolism during exertion
- CFixed cardiac output that cannot increase appropriately with exercise, resulting in inadequate cerebral perfusion pressureCorrect answer
- DAtrial fibrillation with rapid ventricular response causing hemodynamic collapse
- ECoronary steal phenomenon from severe aortic stenosis reducing left anterior descending artery perfusion
- FLeft ventricular outflow tract obstruction causing dynamic subaortic narrowing with Valsalva maneuver
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