Subclavian Artery Steal With and Without Basilar Artery Pathology

In presence of subclavian artery (SCA) steno-occlusion proximal to the origin of the vertebral artery (VA), the most important natural by-pass is represented by the ipsilateral VA: the blood is stolen by the VA from the contralateral VA (SCA steal phenomenon). This is a compensatory mechanism to increase flow to the affected extremity.

The SCA steal is a graded system showing a progressive change in the ipsilateral VA waveform: in the grade I lesions the VA flow is antegrade (with a diminished peak systolic velocity), while in the grade II lesions the VA waveform is bidirectional, and in the grade III lesions the VA waveform is completely retrograde, regardless of cardiac contractility.

While the SCA steal without a pathologic flow in the basilar artery (BA) seems only a marker of generalized atherosclerosis, the SCA steal with pathologic flow in the BA (post-stenotic, bidirectional or reverse flow) may be associated with a high risk of developing cerebrovascular accidents.

In this lesson the ultrasound parameters of the SCA with and without BA pathology are presented.

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