History
Patients with retrograde blood flow in a vertebral artery are usually asymptomatic. In addition, with few exceptions, proximal subclavian stenosis or occlusion rarely causes symptoms of arm ischemia. Muscle cramping due to arm ischemia typically occurs in laborers performing vigorous work, often with arms elevated above the head. If the increased oxygen demand from arm exercise exceeds the ability of collateral vessels to provide sufficient blood flow, cerebral ischemia may occur as more blood is siphoned from the brain via the vertebrobasilar system.
Numerous symptoms are associated with posterior-circulation cerebral ischemia. Symptoms of dizziness or vertigo occur in more than 50% of patients, and syncope and dysarthria have been noted in 18% and 12.5%, respectively. Visual symptoms secondary to vestibular dysfunction or nystagmus include a sensation of objects moving and inability to focus, as well as monocular or binocular visual loss. Diplopia occurs in 19% of cases. Fortunately, these transient ischemic episodes seldom progress to cause cerebral infarction.
Physical Examination
True subclavian steal syndrome cannot occur without retrograde blood flow in a vertebral artery associated with proximal ipsilateral subclavian artery stenosis or occlusion. In a healthy individual, blood pressures in both arms should be similar. Without a significant difference in blood pressure between the patient’s arms, proximal subclavian stenosis or occlusion cannot be present.
An invariable finding in patients with symptoms of subclavian steal syndrome is a difference in upper-extremity pulses and brachial systolic blood pressures between the patient’s arms. Therefore, with a simple physical examination, the clinician can effectively eliminate significant subclavian arterial lesions without the need for angiography or duplex ultrasonography (US).
The internal mammary artery (IMA) arises from the inferior aspect of the proximal subclavian artery, opposing the origin of the vertebral artery. Recurrent symptoms of angina pectoris after otherwise successful coronary revascularization with a left IMA (LIMA) graft may also indicate a hemodynamically significant proximal left subclavian stenosis.
Atherosclerotic lesions (stenosis or occlusion) of the proximal vertebral artery may produce similar symptoms. Occlusive disease of the vertebral artery should be considered if posterior circulation symptoms occur with normal blood pressures in the affected arm.
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Irregular proximal subclavian stenosis.
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Retrograde blood flow from left vertebral artery into left subclavian artery in patient with subclavian steal syndrome.
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Successful stent treatment of subclavian stenosis, with restored antegrade flow into vertebral artery.
