Pathophysiology: An occlusion in an artery prior to the origin of a vertebral artery causes a post-stenotic drop in blood pressure. This relative vacuum results in retrograde blood flow from that vertebral artery, causing a reduction of cerebral blood flow. If collateral blood flow is adequate then there may be no reduction in blood pressure and no steal.
Causes of the subclavian steal syndrome:
(1) atherosclerosis (most common)
(1a) proximal left subclavian artery before the origin of the left vertebral artery
(1b) right subclavian artery between the origins of the right carotid and right vertebral arteries
(1c) proximal right brachiocephalic (innominate) artery before the origin of the right carotid artery
(2) congenital aplasia or atresia in the aortic arch, right brachiocephalic, right subclavian or left subclavian artery (refer to Embryology for Surgeons by Skandalakis JE and Gray SW)
(3) traumatic stenosis
(4) operative (Blalock-Tuassig, Claget, others)
(5) arterial thrombosis
Factors affecting the magnitude of the "steal":
(1) exercise vs rest of the affected arm
(2) presence and severity of occlusion in the vertebral artery
(3) collateral circulation in the intra- and extra-cerebral arteries
Clinical groups:
(1) cerebral symptoms only
(2) arm symptoms only
(3) cerebral and arm symptoms occurring simultaneously
(4) asymptomatic
Clinical findings:
(1) The systolic blood pressure in the upper extremity of the affected side will be lower than that of the opposite side. The gradient is usually >= 20 mm Hg.
(2) The pulse will be reduced or absent in the affected upper extremity.
(3) A bruit may heard over the affected artery.
(4) In some patients symptoms become more pronounced or may be precipitated with exercise or physical work using the arm on the affected side.
(5) Cerebral symptoms are usually transient and may include headache, vertigo, syncope, unconsciousness, sudden disturbance in vision, paralysis in the muscles for half of the face, paresis (hemi- or tetra-), ataxia, dysarthria, aphasia, and/or a hearing disorder.
(6) Arm symptoms include sudden onset in the affected arm of weakness, paresthesias, fatigue, pallor, livid color, pain at rest, pain during activity, or a feeling of coldness.
(7) Symptoms may be progressive and sometimes may be followed by residual findings.
