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Left subclavian steal

Simplified schematic of the aortic arch and great vessels, showing the most common collateral pathway to supply the left arm in the face of severe steno-occlusive disease of the proximal left subclavian artery (light green box). Flow is reversed in the left vertebral artery, and consequently blood is “stolen” from the vertebrobasilar circulation. Generally, this is compensated by increased antegrade flow in the right vertebral artery. Flow generally remains antegrade in the basilar artery (top), but if there is steno-occlusive disease of the right vertebral artery, flow may be reversed in the basilar artery. (Contributed and modified by Dr. Douglas Lanska. Greatly modified from original sketch in Owen E. A Manual of Anatomy for Senior Students. London and New York: Longmans, Green, and Co., 1890.)