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 vertebral artery origin causing reversed flow in the ipsilateral vertebral artery. Blood is 'stolen' from the circular vertebrobasilar 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 ultrasound examination of the cerebral supply.

The term 'subclavian steal syndrome' should only be used in 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 subclavian steal phenomenon

See image of normal anatomy of aortic arch and its branches.¹
Subclavian steal phenomenon (SSP) 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 put the left subclavian artery at greater risk of atherosclerosis.
See diagrams of aberrant flow patterns in left and right SSP.¹

Note: if the left vertebral artery arises directly from the aortic arch (as it does in 2% of the population), stenosis of the proximal left subclavian artery cannot cause the syndrome because there is no communication between the vertebral and subclavian arteries.

Epidemiology

Prevalence

This is a relatively uncommon disorder: subclavian stenosis affects about 2% of the general population and 7% of the clinical population.⁴ Subclavian steal phenomenon (SSP) is seen as an incidental finding on sonography of the vertebral system in about 2-5% of those examined. Of these, only about 5% of these patients suffer symptoms.²

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

Presentation

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 the body or transient hemiparesis.
• Intermittent arm claudication (note, rest pain is not a usual feature; consider atheroembolism as a cause).
• Drop attacks (syncope) - fall to the ground without warning, ± temporary loss of consciousness with immediate recovery.⁶
• Pulsatile tinnitus.⁷

Neck movements may also cause symptoms.

Signs

• Blood pressure 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. multiple sclerosis, tumour.

Investigations

• Doppler ultrasound or angiography shows retrograde flow down vertebral artery (often an asymptomatic, incidental finding).
• CT or MRI scanning to exclude intracerebral lesion and show any infarcts.

Investigations

May include:

• Colour Doppler ultrasound.
• CT angiography.
• CXR - to exclude external compression by, for example, cervical rib.
• ECG.

Management

Percutaneous transluminal angioplasty (+/- stenting) or surgery (carotid-subclavian bypass with either synthetic graft or saphenous vein graft or carotid-subclavian transposition) can both be used to bypass the stenosis of the subclavian artery. Endovascular methods are increasingly popular, particularly in high-risk patients, due to their minimally invasive approach under local anaesthetic, but bypass grafting is possibly more durable. ⁸ Complication rates of about 4% occur with angioplasty. 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.⁹

Associated steal syndromes

1. Coronary-subclavian steal syndrome: usually iatrogenic and follows coronary artery bypass grafting utilising the internal mammary artery.¹⁰ Subclavian stenosis causes 'stealing' of coronary blood flow via the arterial anastomosis, causing angina.
2. 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.

Document references

1. Horrow MM, Stassi J; Sonography of the vertebral arteries: a window to disease of the proximal great vessels. AJR Am J Roentgenol. 2001 Jul;177(1):53-9.; Good images/diagrams of aberrant flow in neck vessels.
2. Brophy P; Subclavian Steal Syndrome, eMedicine, Jul 2009
3. McIntyre K; Subclavian Steal Syndrome, eMedicine, Oct 2009
4. Shadman R, Criqui MH, Bundens WP, et al; Subclavian artery stenosis: prevalence, risk factors, and association with cardiovascular diseases. J Am Coll Cardiol. 2004 Aug 4;44(3):618-23. [abstract]
5. Ringleb PA, Strittmatter EI, Loewer M, et al; Cerebrovascular manifestations of Takayasu arteritis in Europe. Rheumatology (Oxford). 2005 Aug;44(8):1012-5. Epub 2005 Apr 19. [abstract]
6. Brignole M, Alboni P, Benditt D, et al; Guidelines on management (diagnosis and treatment) of syncope. Eur Heart J. 2001 Aug;22(15):1256-306.
7. Lehmann MF, Mounayer C, Benndorf G, et al; Pulsatile tinnitus: a symptom of chronic subclavian artery occlusion. AJNR Am J Neuroradiol. 2005 Sep;26(8):1960-3. [abstract]
8. AbuRahma AF, Bates MC, Stone PA, et al; Angioplasty and stenting versus carotid-subclavian bypass for the treatment of J Endovasc Ther. 2007 Oct;14(5):698-704. [abstract]
9. Aboyans V, Criqui MH, McDermott MM, et al; The vital prognosis of subclavian stenosis. J Am Coll Cardiol. 2007 Apr 10;49(14):1540-5. Epub 2007 Mar 26. [abstract]
10. Costa SM, Fitzsimmons PJ, Terry E, et al; Coronary-subclavian steal: case series and review of diagnostic and therapeutic strategies: three case reports. Angiology. 2007 Apr-May;58(2):242-8. [abstract]

Internet and further reading

• Taylor CL, Selman WR, Ratcheson RA; Steal affecting the central nervous system. Neurosurgery. 2002 Apr;50(4):679-88; discussion 688-9. [abstract]

Acknowledgements