The subclavian steal syndrome is a rare but important cause of syncope. Since recognition of this syndrome can lead to successful treatment, a review by Chan-Tack emphasizes the need for a high index of suspicion in patients with a suggestive history, risk factors and physical findings, such as symptoms of vertebrobasilar insufficiency.

The syndrome results from occlusion of the proximal subclavian artery and the development of retrograde flow to the subclavian artery from the vertebral artery. The decreased blood flow to the posterior brain and upper extremity on the affected side results in a range of symptoms. Vertebrobasilar insufficiency may produce light-headedness, dizziness, ataxia, vertigo, visual disturbances, motor deficits, confusion, focal seizures, aphasia, headaches or syncope. Reduced blood flow to the arm causes symptoms such as weakness, coldness, paresthesias or arm claudication after exercise. Arm symptoms are generally less frequent and occur later than the vertebrobasilar symptoms.

Although the incidence and prevalence of subclavian steal syndrome are unknown, it generally occurs in patients older than 55 years and has a 2:1 male-to-female ratio. Risk factors include hypertension, diabetes, hypercholesterolemia, tobacco use and vigorous exercise of the affected extremity. In more than 95 percent of cases, arteriosclerosis causes occlusion of the proximal subclavian artery, but other potential causes include dissecting aortic arch aneurysm, embolism and Takayasu's arteritis. Symptoms may be precipitated by vigorous exercise of the arm, especially if combined with sudden sharp turning of the head to the affected side.

Physical examination findings may include unilaterally decreased pulses on the affected side, a blood pressure difference of greater than 20 mm Hg between the arms, supraclavicular bruits and disappearance of the radial pulse on exercise or elevation of the arm. The diagnosis may be confirmed by carotid duplex ultrasonography and magnetic resonance angiography, or arch aortography.

Symptomatic patients require operative intervention such as axilloaxillary bypass, carotid-subclavian bypass or percutaneous transluminal angioplasty of the subclavian artery with stent placement. Aggressive management of risk factors such as hypertension, diabetes and tobacco use is also essential for successful treatment of this syndrome.