Subclavian Steal Syndrome

Subclavian steal syndrome occurs when narrowing/occlusion of the subclavian artery proximal to the origin of the vertebral artery causes a reversal of blood flow in the ipsilateral vertebral artery to continue perfusing the ipsilateral arm. The most common cause is atherosclerosis. Symptoms are rare, but when they occur are usually triggered by physical exertion of the arm and subsequent hypoperfusion of the arm or brain. Patients may present with claudication, pain, pallor, paresthesias, and weakened pulse in the affected extremity. Patients may also present with transient neurologic disturbances concerning for a stroke. Diagnosis is made by clinical findings and imaging (ultrasound, CT, MRI). In addition to appropriate management of atherosclerosis, symptomatic patients may need angioplasty/stenting or surgical revascularization.

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Subclavian steal syndrome is the reversal of blood flow in the vertebral artery on the side of a stenotic subclavian artery that produces symptoms of arterial insufficiency in the brain or upper extremity.


  • 30% of patients with peripheral artery disease have subclavian stenosis.
  • Only a minority of those patients develop clinical subclavian steal syndrome.
  • The left subclavian artery is more commonly affected (> 75% of cases).
  • Incidence increases with age.
  • More common in men


  • Atherosclerosis (most common cause)
  • Takayasu’s arteritis 
  • Thoracic outlet syndrome:
    • Extrinsic compression of the subclavian artery
    • True subclavian steal is rare, as the compression is usually distal to vertebral artery.
  • Surgery for coarctation of the aorta or tetralogy of Fallot with Blalock-Taussig shunt
  • Congenital anomalies of the vasculature (e.g., right aortic arch)

Pathophysiology and Clinical Presentation


  • The main blood supply to the upper extremities comes from axillary arteries.
  • Axillary artery is a continuation of a subclavian artery once it exits the thoracic outlet:
    • Left subclavian artery arises directly from the aorta.
    • Right subclavian artery arises from the brachiocephalic artery, which originates from the aorta.
  • In most individuals, the vertebral arteries originate from the subclavian arteries.
  • Internal mammary artery (IMA), thyrocervical and costocervical trunk also originate from the subclavian artery.

Pathophysiology of subclavian steal

  • Stenosis or occlusion of the subclavian artery proximal to the origin of the vertebral artery →  hypoperfusion of the ipsilateral subclavian and vertebral arteries 
  • The reversal of blood flow occurs in the vertebral artery from the basilar and contralateral vertebral artery.
  • The ipsilateral arm with the stenotic subclavian artery is usually supplied by collateral vessels around the shoulder.
  • Physical activity creates increased demands not met by collateral circulation and claudication may develop.
  • The subclavian artery then gets a reverse flow from the ipsilateral vertebral artery as a physiologic mechanism to increase perfusion to the affected arm.
  • Reversal of blood flow can result in hypoperfusion of the basilar artery going to the brainstem (usually triggered by exertion of the affected arm).
  • Patients with symptoms of vertebrobasilar ischemia tend to have:
    • Additional cerebrovascular atherosclerotic lesions 
    • Anomalies of the circle of Willis 
  • Coronary-subclavian steal:
    • Described in patients who underwent coronary artery bypass surgery using IMA
    • If subclavian artery is stenotic proximal to the origin of IMA, a reversal of flow may occur in IMA, “stealing” from the coronary circulation.
    • Usually happens during exercise/exertion
    • Simultaneous coronary and cerebrovascular steal may occur.
Subclavian steal

Pathophysiology of subclavian steal syndrome:
Note the reversed blood flow in the ipsilateral vertebral artery.

Image by Lecturio.

Clinical presentation

Most patients with subclavian stenosis/steal are asymptomatic.

Symptoms of (ipsilateral) limb ischemia/hypoperfusion:

  • Claudication (pain or discomfort in arm with activity that improves with rest)
  • Paleness
  • Cool skin
  • Paresthesias
  • Weakness
  • Weakened pulse in affected arm

Symptoms related to cerebral hypoperfusion/vertebrobasilar insufficiency:

  • Syncope/presyncope
  • Dizziness
  • Vertigo
  • Visual disturbances (e.g., blurring, double vision, hemianopia, nystagmus)
  • Transient hearing loss
  • Tinnitus
  • Disequilibrium
  • Ataxia



  • History of atherosclerosis/peripheral vascular disease
  • Unilateral arm paresthesias/claudication
  • Syncopal episodes
  • Vertigo, transient visual/hearing disturbances

Physical exam

  • Blood pressure difference > 15 mm Hg between arms indicates subclavian stenosis.
  • Blood pressure difference > 40 mm Hg typically seen in those who are symptomatic
  • Difference in radial pulses
  • Hand skin and nail beds:
    • Look for blue discoloration, ulcerations, and splinter hemorrhages, which may indicate emboli from subclavian atherosclerotic lesions.


  • Duplex ultrasound:
    • 1st-line imaging modality
    • Detects subclavian stenosis
    • Reversal of flow in ipsilateral vertebral artery
  • MRA or CT angiography:
    • Used to confirm and grade the disease
    • Used for detailed anatomic evaluation of subclavian and vertebral arteries
  • Transcranial doppler:
    • Can be performed if reversal of flow in vertebral artery is observed
    • Evaluates for reversal of flow in the basilar artery, which is more predictive of symptoms than vertebral flow alone
  • Percutaneous angiography:
    • Invasive procedure
    • Can be diagnostic and therapeutic (angioplasty/stenting)
Critical ostial subclavian artery stenosis

Percutaneous transradial catheter angiogram showing critical ostial subclavian artery stenosis that caused coronary subclavian steal syndrome

Image: “Critical ostial subclavian artery stenosis” by Section of Cardiology, Christiana Care Health System, Newark, DE 19718, USA. License: CC BY 3.0

Grading of subclavian steal syndrome

  • Grade I (pre-subclavian steal):
    •  Reduced antegrade vertebral flow
    • < 70% subclavian stenosis
  • Grade II (partial/latent): 
    • Antegrade vertebral flow in the diastolic and retrograde flow in the systolic phase
    • > 70% subclavian stenosis
  • Grade III (permanent/advanced): 
    • Permanent retrograde vertebral flow
    • 95%–100% subclavian stenosis



  • Asymptomatic cases do not require invasive intervention.
  • However, subclavian stenosis is a marker for:
    • Atherosclerotic disease
    • Increased risk of cardiovascular events
  • Patients may benefit from secondary prevention:
    • Control of hypertension, hyperlipidemia, and diabetes
    • Smoking cessation
    • Lifestyle modifications (weight loss, exercise)
    • Antithrombotic therapy/antiplatelet agents

Invasive treatment

  • Indicated for symptomatic patients
  • Endovascular treatment:
    • Angioplasty +/- stenting
    • For short proximal stenosis
  • Surgical revascularization:
    • Indicated for evidence of distal embolization from subclavian lesion
    • For anatomy unfavorable for endovascular intervention
    • Options include:
      • Carotid-subclavian bypass
      • Bypass from contralateral subclavian or axillary artery

Differential Diagnosis

  • Vertebrobasilar stroke: a less common type of cerebrovascular accident with a high mortality rate caused by occlusion, embolism, or dissection affecting the extracranial and intracranial vertebral arteries, basilar artery, or posterior cerebral arteries. Presentation varies depending on the site of infarction. Magnetic resonance and CT angiography are used to confirm the diagnosis. There are few effective treatments for this type of stroke but angioplasty or open surgical repair may be attempted depending on the lesion site. 
  • Upper extremity deep vein thrombosis (DVT): a rare condition primarily triggered by vigorous upper extremity activity, typically in a young, healthy individual. The axillary and subclavian veins are most often affected. Secondary causes include central venous cannulation and prothrombotic states. Symptoms include sudden onset of pain, swelling, and cyanosis in the extremity. Diagnosis is made via ultrasound imaging. Treatment includes anticoagulation, thrombolysis, and surgical interventions when needed. 
  • Takayasu arteritis: a large-vessel vasculitis that most commonly affects women. This condition is characterized by granulomatous inflammation of the aortic wall and its branches. Symptoms include fatigue, weight loss, fevers, chest pain, and high blood pressure. Blood tests, ultrasound, and angiography are used to confirm the diagnosis. Management involves corticosteroids, immunosuppressants, biologic agents, and surgical interventions when needed. 
  • Thoracic outlet syndrome (TOS): compression of nerves or blood vessels in an area between the lower neck and upper chest called the thoracic outlet. The syndrome may be caused by anatomical defects such as a cervical 1st rib, trauma, poor posture, bodybuilding, or repetitive motions involving the arm and shoulder. Provocative maneuvers on exam and imaging studies help confirm the diagnosis. Management of vascular TOS involves thrombolytics, anticoagulants, and surgical interventions.


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  2. Bayat I. (2019). Subclavian Steal Syndrome. Retrieved February 19, 2021, from
  3. Labropoulos N., Nandivada P., Bekelis K. (2010). Prevalence and impact of the subclavian steal syndrome. Ann Surg. 2010 Jul. 252 (1):166-70. 
  4. Potter B.J., Pinto D.S. (2014). Subclavian steal syndrome. Circulation. 2014 Jun 3. 129 (22):2320-3.
  5. Spittell P.C. (2019). Subclavian steal syndrome. UpToDate. Retrieved February 15, 2021, from

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