A 68-year-old man experiences dizziness and visual dimming when using his left arm after gardening. Left brachial blood pressure is 30 mmHg lower than the right, and the left radial pulse is weak. Duplex shows retrograde flow in the left vertebral artery during arm exercise. The most likely site of the causative lesion is:
- A Left common carotid artery origin
- B Left vertebral artery ostium
- C Proximal left subclavian artery ✓
- D Brachiocephalic trunk
Correct answer: C. Proximal left subclavian artery
Explanation
Subclavian steal syndrome results from a significant stenosis or occlusion of the proximal subclavian artery before the vertebral artery origin. Arm exercise lowers peripheral resistance and blood is siphoned retrogradely down the ipsilateral vertebral artery, producing posterior circulation symptoms. An ostial vertebral lesion reduces antegrade flow without producing steal, and brachiocephalic involvement would affect the right side and carotid circulation.
Reference: Rutherford's Vascular Surgery and Endovascular Therapy, 9th ed.
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Written and medically reviewed by the StethoPrep medical team.