What is subclavian steal syndrome?

Subclavian Steal Syndrome: Pathophysiology, Diagnosis, and Management

Subclavian steal syndrome occurs when proximal subclavian artery stenosis or occlusion causes retrograde blood flow in the ipsilateral vertebral artery, potentially leading to posterior cerebral circulatory insufficiency and upper extremity claudication. 1

Pathophysiology

• When the proximal subclavian artery becomes stenotic or occluded, branches distal to the obstruction (particularly the vertebral artery and internal mammary arteries) become sources of collateral circulation to the arm through flow reversal 1
• This reversal of flow in the vertebral artery may reduce basilar artery perfusion, especially when the dominant vertebral artery is affected 1
• Symptoms are typically aggravated by exercising the ipsilateral arm, which amplifies the flow reversal by increasing demand for blood in the subclavian artery and its branches 1
• Atherosclerosis is the most common cause, but other etiologies include Takayasu arteritis, giant cell arteritis, fibromuscular dysplasia, and radiation-induced arteriopathy 1

Clinical Presentation

Common Symptoms

• Most cases are asymptomatic, with reversal of flow detected incidentally 1

• Vertebral ischemic form (more common):

  • Symptoms of posterior cerebral or cerebellar hypoperfusion including lightheadedness, syncope, vertigo, ataxia, diplopia, and motor deficits 1
  • Upper limb claudication (muscular fatigue in the affected arm) 1
  • Symptoms typically worsen with arm exercise 1

• Coronary ischemic form (less common):

  • Occurs in patients with internal mammary artery bypass grafts 1
  • Blood is diverted from coronary arteries to the upper limb during arm exercise, producing angina pectoris 1

Diagnostic Approach

• Detection of a periclavicular or infraclavicular bruit suggests subclavian stenosis 1

• Blood pressure asymmetry between arms (>10-15 mmHg difference) is a key diagnostic finding 1

  • The side with lower pressure indicates subclavian artery stenosis or occlusion 1
  • Blood pressure tends to fall further in the affected limb after arm exercise 1
  • Note: Blood pressure may be symmetrical in bilateral subclavian disease 1

• Imaging studies:

  • Duplex ultrasonography can identify reversal of flow in a vertebral artery 1
    • Intrastenotic high-velocity flows (50% stenosis: peak systolic velocity ≥230 cm/s, PSV ratio ≥2.2; 70% stenosis: PSV ≥340 cm/s and PSV ratio ≥3.0) 1
    • Monophasic post-stenotic waveforms 1
  • CT angiography (CTA) or MR angiography (MRA) of the aortic arch can identify stenosis of the subclavian artery 1, 2

Management

Asymptomatic Patients

• No specific intervention needed other than strategies for secondary prevention of ischemic events related to systemic atherosclerosis 1
• Exception: Intervention may be warranted if the ipsilateral internal mammary artery is required for myocardial revascularization 1

Symptomatic Patients

• Symptomatic patients should be considered for subclavian revascularization with either endovascular or surgical techniques 1

• Endovascular options:

  • Balloon angioplasty, atherectomy, and stenting 1
  • High initial success rates (93-98%) 1
  • Lower long-term patency compared to surgery (70% vs 96% at 5 years) 1
  • May be preferred over surgery due to lower complication rates despite similar long-term outcomes 1

• Surgical options:

  • Carotid-subclavian bypass with prosthetic grafting 1
  • Other methods: carotid-axillary or axilloaxillary bypass, subclavian-carotid arterial transposition 1
  • Excellent long-term patency (96-100% at 5 years) 1
  • Higher freedom from recurrent symptoms compared to endovascular therapy 1

Special Considerations

• Bilateral arm blood pressure measurement is recommended for all patients with peripheral arterial disease 1
• Routine revascularization is not recommended in asymptomatic patients with subclavian steal syndrome 1
• In patients requiring CABG using the ipsilateral internal mammary artery, revascularization should be considered even in asymptomatic cases 1
• Symptomatic subclavian steal syndrome due to arteriovenous fistulas (for dialysis) may require more frequent surgical intervention than atherosclerotic forms 3

Pitfalls and Caveats

• Blood pressure asymmetry may be absent in bilateral subclavian disease or aortic arch syndrome 1
• The majority of patients (>90%) with at least 50% proximal subclavian stenosis have flow reversal in the vertebral artery, but not all will be symptomatic 1
• No randomized trials comparing endovascular and surgical revascularization have been published 1
• Symptoms may resolve spontaneously in some patients as collateral circulation develops 1
• Consider subclavian steal syndrome in patients with posterior circulation TIAs or strokes, especially with risk factors for atherosclerosis 4, 5