A 66-year-old man reports dizziness and visual dimming in both eyes whenever he works with his left arm raised, relieved immediately by lowering it. The left radial pulse is weaker than the right, and there is a 25 mmHg systolic blood pressure difference between the arms. Duplex ultrasound shows retrograde flow in the left vertebral artery. Where is the causative lesion?

• A Left vertebral artery origin itself
• B Ostium of the left subclavian artery, proximal to the vertebral origin ✓
• C Intracranial portion of the basilar artery
• D Brachiocephalic trunk bifurcation

Explanation

Subclavian steal requires a proximal subclavian stenosis upstream of the vertebral take-off so that arm exercise lowers distal resistance and siphons blood retrogradely from the vertebrobasilar circulation into the arm, producing posterior circulation symptoms. The haemodynamic signature includes an inter-arm systolic pressure difference exceeding 20 mmHg and reversed ipsilateral vertebral flow on Doppler. B stenosis at the vertebral origin would reduce arm perfusion but cannot reverse vertebral flow direction toward the limb.

Reference: Rutherford's Vascular Surgery and Endovascular Therapy, 9th ed.

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Written and medically reviewed by the StethoPrep medical team.