Subclavian steal syndrome !

A blocked artery near the shoulder makes the arm borrow blood from an artery that feeds the brain, causing dizziness when the arm is used.

Updated 2026-11-01

Structures involved

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Why it happens

What it is

A narrowing or blockage of the subclavian artery before the origin of the vertebral artery makes blood flow backwards down the vertebral artery to supply the arm. The flow reversal itself is the 'steal phenomenon'; it becomes a syndrome when it causes symptoms of brainstem or arm ischaemia.

Who gets it

Flow reversal is found in a small percentage of people on vascular imaging, but most are asymptomatic. The left side is affected in most cases. It is commoner in older smokers with atherosclerosis; in young women in Latin America, Takayasu arteritis is an important cause.

Causes

Atherosclerosis of the proximal subclavian artery (most common)
Takayasu arteritis and giant cell arteritis
Thoracic outlet compression or a cervical rib
Congenital aortic arch anomalies and complications of coarctation repair
Aortic dissection or radiation arteritis

Risk factors

Smoking
Arterial hypertension
Dyslipidaemia
Diabetes mellitus
Atherosclerosis in other territories
Internal thoracic artery coronary bypass graft (coronary-subclavian steal)

Pathophysiology

With a proximal subclavian stenosis, pressure in the distal subclavian falls below that of the basilar system. Blood then flows from the opposite vertebral artery into the basilar junction and down the ipsilateral vertebral artery to the arm. Arm exercise lowers resistance in the arm and increases this steal, which can reduce posterior circulation flow. After an internal thoracic artery bypass, the same mechanism can steal blood from the heart and cause angina.

Classification

Grade I: reduced antegrade flow in the vertebral artery
Grade II: alternating (to-and-fro) flow
Grade III: permanently reversed flow
Variant: coronary-subclavian steal after internal thoracic artery bypass

Symptoms and signs

Dizziness or vertigo, especially with arm exercise
Blurred or double vision
Unsteadiness (ataxia) or fainting
Arm pain, fatigue, coldness or tingling with use (arm claudication)
Often no symptoms at all

Diagnosis

Clinical: Blood pressure in both arms: a difference of 15 mmHg or more points to subclavian stenosis. Weak or delayed radial pulse on the affected side and a supraclavicular bruit support the diagnosis.
Tests: Laboratory tests help find causes and risk factors (lipids, glucose, inflammatory markers when vasculitis is suspected).
Imaging: Duplex ultrasound shows reversed or alternating vertebral artery flow and is the first test. CT or MR angiography maps the stenosis and the aortic arch; catheter angiography is used for treatment.

Differential diagnosis

Vertebrobasilar transient ischaemic attack from other causes
Benign paroxysmal positional vertigo and other vestibular disorders
Cardiac arrhythmia causing syncope
Thoracic outlet syndrome
Orthostatic hypotension

Goal of treatment

Relieve symptoms by restoring forward flow in the subclavian artery when needed, and reduce cardiovascular risk from the underlying atherosclerosis or vasculitis.

Treatment

Medical: Antiplatelet agents, statins and control of blood pressure and diabetes for all patients; immunosuppressive treatment when the cause is vasculitis.
Lifestyle: Stopping smoking, regular exercise and a heart-healthy diet.
Procedure: Endovascular angioplasty and stenting of the subclavian artery for symptomatic patients, and before or after an internal thoracic artery coronary bypass.
Surgical: Open surgery (carotid-subclavian bypass or subclavian transposition) for occlusions unsuitable for stenting or failed endovascular treatment.
Follow-up: Nursing priorities: measure blood pressure in the unaffected arm (or both arms), check radial pulses, and avoid blood pressure cuffs and venous lines on the affected arm when possible; teach to report neurological symptoms.

Complications

Vertebrobasilar transient ischaemic attack or stroke
Arm ischaemia and digital embolism
Angina or myocardial ischaemia in coronary-subclavian steal
Restenosis after stenting

Prognosis

Most people with the steal phenomenon remain asymptomatic and do well with risk-factor control. Revascularisation relieves symptoms in most symptomatic patients, with good long-term patency. Overall prognosis depends on the extent of atherosclerosis elsewhere.

Prevention

Not smoking
Control of blood pressure, cholesterol and diabetes
Regular physical activity

Test yourself

Think of the answer, then tap the question to see it.

Where must the subclavian lesion lie to cause subclavian steal?

Proximal to the origin of the vertebral artery, so the distal subclavian pressure falls and vertebral flow reverses.

Which side is most often affected in subclavian steal syndrome?

The left subclavian artery.

What simple bedside finding suggests subclavian stenosis?

A systolic blood pressure difference of 15 mmHg or more between the arms, with a weaker radial pulse on the affected side.

Why do symptoms worsen with arm exercise?

Exercise lowers resistance in the arm and increases reversed vertebral flow, diverting blood from the posterior circulation.

What is coronary-subclavian steal?

Reversed flow in an internal thoracic artery coronary bypass graft caused by proximal subclavian stenosis, producing myocardial ischaemia.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Subclavian Steal Syndrome (SSS): Symptoms & Causes (Cleveland Clinic, 2024).

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Representative model, for educational purposes only.

Subclavian artery highlighted on the Durgical 3D model