Subclavian artery steal syndrome is a syndrome in which there is partial or complete occlusive damage in the subclavian artery or the proximal segment of the vertebral artery at the beginning of the cephalic trunk, causing retrograde flow in the affected vertebral artery into the distal end of the affected subclavian artery due to siphoning, resulting in ischemic episodes in the vertebrobasilar artery and ischemia in the affected upper extremity. There can be symptoms of cerebral ischemia or upper extremity ischemia. Subclavian artery steal is mainly typed according to the proportion of reverse flow in the vertebral artery, and the following types are often used in China: early steal (steal I) spectral manifestation: more literature describes it as “early systolic tangential wave” (most think it is early systolic, a few think it is mid-late systolic), that is, there is a transient blood flow plunge during systole. The first peak is high and sharp, the second is rounded and blunt, and a tangent is formed between the two peaks, the lowest point of which may be above or slightly below the baseline. This is often accompanied by a mild decrease in peak systolic flow rate. Clinical significance: Most often seen in mild to moderate stenosis of the proximal segment of the subclavian artery or the unnamed artery. Partial blood theft (stage II blood theft): Spectral manifestations: vertebral artery flow is partially or fully reversed in systole and positive in diastole in a bidirectional flow spectrum. Clinical significance: Most often seen in subclavian artery proximal segment or nameless artery with moderate or above stenosis. Complete blood theft (stage III blood theft) spectrum: the vertebral artery flow is completely reversed, showing the reverse flow of the whole cardiac cycle Clinical significance: Most often seen in severe stenosis or occlusion of the proximal segment of the subclavian artery or the unnamed artery.