Subclavian steal phenomenon occurs due to proximal stenosis of the subclavian artery, causing reversal of vertebral artery flow. Which artery is affected by the obstruction?

• A. Carotid artery
• B. Subclavian artery
• C. Aorta
• D. Renal artery

Answer: (B)

Subclavian steal happens when there is a blockage in the proximal subclavian artery, near where it branches from the aorta (left) or brachiocephalic trunk (right). This stenosis lowers pressure in the arm’s artery, so blood is drawn in reverse from the vertebral artery to perfuse the arm. The vertebral artery normally feeds the brain via the basilar system, but in this setup its flow becomes retrograde to help supply the arm, hence the “steal.” So the obstruction is in the subclavian artery itself. Choices like the carotid (which supplies front brain circulation), the aorta (upstream), or the renal artery (unrelated to this mechanism) don’t explain the reversal of vertebral flow.