Subclavian steal syndrome is a compilation of symptoms that occur from a retrograde blood flow in vertebral arteries. This also includes retrograde blood flow of thoracic arteries, which can both be attributed to a nearby Subclavian artery stenosis, the occlusion or narrowing of subclavian arteries.
Symptoms of Subclavian steal syndrome can include any decreased neurological ability, any signs of fainting, presyncope (feeling that one is going to faint), or syncope (actually fainting).
Ways that Subclavian steal syndrome is diagnosed is testing to see any change or decrease in neurological activity, caused by cerebral ischemia, or the lack of blood flow to the brain. This is usually determined by a simple ipsilateral exercise of the arms. Another form of diagnosis of Subclavian steal syndrome is measuring the differential of blood pressure and flow between arms, and then determine if there is any difference. If so, it is then needed to be tested to see if this is due to pressure of any kind to the artery, stenosis, or any occlusion within the artery.
Synonym : - Harrison and Smyth's syndrome, Subclavian Steal Syndrome, SSS
The subclavian steal phenomenon (SSP) occurs when there is stenosis or occlusion of the subclavian artery proximal to the origin of the vertebral artery. This may cause flow reversal in the ipsilateral vertebral artery as blood is 'stolen' from the circular vertebro-basilar system, to supply the distal territory of the occluded or stenosed artery. Retrograde flow in the vertebral artery, associated with a subclavian or innominate (brachiocephalic) artery stenosis, can be an incidental finding during doppler US examination of the cerebral supply.
The term 'subclavian steal syndrome' should strictly be applied only to cases where this aberrant blood flow causes neurological symptoms. These are related to reduced cerebral perfusion when the arm ipsilateral to the subclavian stenosis is exercised.
Anatomy and blood flow in SSP
See image of normal anatomy of aortic arch and its branches.1
Subclavian steal phenomenon affects the left side much more commonly than the right, with relative incidence about 3-4:1.2,3 This is due to anatomical differences that means the left subclavian artery is much more commonly affected by atherosclerosis.
See diagrams of aberrant flow patterns in left and right subclavian steal phenomena.1
Note, if the left vertebral artery arises directly from the aortic arch (as it does in 2% of population), stenosis of the proximal left subclavian artery cannot cause the syndrome because there is no communication between the vertebral and subclavian arteries.
Risk factors4
As the majority of cases are due to atherosclerosis, risk factors for SSP are as for cardiovascular disease (CVD) in general :
-
Family history of vascular disease
Smoking
Hypertension
Diabetes
Hyperlipidaemia
In Asia, a significant proportion of SSP (36%) is caused by Takayasu's arteritis. These tend to present at a much earlier age (< 30 years) and have a female predominance.2 Takayasu's arteritis is a very rare disease in Europe.5
Symptoms
Seek a history of a provoking event that is clearly linked to symptoms. These may be reproducible. Symptoms are usually related to vertebrobasilar and posterior cerebral circulation ischaemia.
On exercising the upper limb on the affected side, the patient may experience any of the following : -
Vertigo
Visual loss ranging from unilateral visual field loss (amaurosis fugax) to bilateral total blindness
Transient periods of ataxia, diplopia, dysphagia and dysarthria
Tingling or numbness of the face, sensory hemianaesthesia affecting body or transient hemiparesis
Hand ischaemia causing arm claudication and rest pain (not a usual feature, consider atheroembolism as a cause)
Drop attacks (syncope) - fall to the ground without warning, ± temporary loss of consciousness with immediate recovery6
Pulsatile tinnitus7
Neck movements may also cause symptoms.
Signs
BP is decreased (>20 mm Hg) in the affected arm distal to the steno-occlusive disease. Check radial and ulnar pulses and elevate the arm, where they may be felt to diminish. It is unusual for a case of genuine subclavian steal syndrome to have no difference in blood pressure between the two arms.
Look for a subclavian bruit.
Differential diagnosis
Aortic dissection
Giant cell (temporal) arteritis
Takayasu's arteritis
Atherosclerosis/thromboembolism
Cerebral/cerebellar pathology e.g. MS, tumour
Investigations
Doppler ultrasound or angiography shows retrograde flow down vertebral artery (often an asymptomatic, incidental finding).
CT or MRI to exclude intracerebral lesion and show any infarcts.
Management
Angioplasty or surgery can both be used to bypass the stenosis of the subclavian artery. Both carry a risk of stroke and death - angioplasty 3.6%, surgery 0.4-2.4% (death only) and recurrent attacks follow surgical treatment in 10-24% of patients. Where symptoms are not severe, conservative management is usually recommended.2
Prognosis
Symptoms may spontaneously resolve due to the establishment of extracranial collaterals to the subclavian circulation. This makes the decision to treat a symptomatic patient not clear cut: treatment is usually reserved for patients with debilitating vertebrobasilar transient ischaemic attacks.
More generally, subclavian stenosis is significantly associated with increased total and CVD-related death, independent of CVD risk factors and existent CVD at diagnosis.8
Associated steal syndromes
Coronary-subclavian steal syndrome : - usually iatrogenic and follows coronary artery bypass grafting utilising the internal mammary artery.9 Subclavian stenosis causes 'stealing' of coronary blood flow via the arterial anastomosis, causing angina.
Spinal artery steal syndrome : - this very rare condition occurs due to vertebral artery flow reversal, to supply blood to the spinal cord, caused by proximal vertebral artery occlusion.
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Subclavian steal syndrome is a compilation of symptoms that occur from a retrograde blood flow in vertebral arteries. This also includes retrograde blood flow of thoracic arteries, which can both be attributed to a nearby Subclavian artery stenosis, the occlusion or narrowing of subclavian arteries. 
