D2I2.
vascular

Subclavian steal syndrome

Subclavian steal (SSS), also called subclavian steal steno-occlusive disease, is a medical condition characterized by retrograde (reversed) blood flow in the vertebral or the internal thoracic artery. This reversal occurs due to (narrowing) or occlusion of the subclavian artery.

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Plain-language summary adapted from Wikipedia. Not medical advice.