What is subclavian steal syndrome, and how is it diagnosed and treated?

Subclavian Steal Syndrome: Diagnosis and Management

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

Definition and Pathophysiology

• SSS is primarily caused by atherosclerotic stenosis or occlusion of the proximal subclavian artery, resulting in reversed flow in the ipsilateral vertebral artery to maintain blood supply to the arm 2, 1
• While atherosclerosis is the most common cause, other etiologies include Takayasu arteritis, giant cell arteritis, fibromuscular dysplasia, and radiation-induced arteriopathy 1
• The subclavian artery and brachiocephalic trunk are the most common locations for atherosclerotic lesions in the upper extremities 2

Clinical Presentation

• Symptoms of vertebrobasilar insufficiency include dizziness, vertigo, blurred vision, alternating hemiparesis, dysphasia, dysarthria, confusion, loss of consciousness, drop attacks, ataxia, and sensory disturbances 2, 1
• Upper limb claudication manifests as muscular fatigue and crampy pain on exercise in the affected arm 2, 1
• Symptoms typically worsen with arm exercise due to increased demand for blood flow 1
• Coronary-subclavian steal can occur in patients with coronary bypass using the internal mammary artery, presenting as myocardial ischemia 2

Diagnostic Approach

Clinical Examination

• Blood pressure asymmetry between arms (difference ≥15 mmHg) is highly suspicious for subclavian stenosis 2, 1
• Detection of a periclavicular or infraclavicular bruit may indicate subclavian stenosis 1
• Assessment of axillary, brachial, radial, and ulnar artery pulses should be performed bilaterally 2

Diagnostic Imaging

• Duplex ultrasound is the recommended initial screening tool that can detect:

  • High-velocity flows indicating >50% stenosis 2
  • Monophasic post-stenotic flow and altered flow in the ipsilateral vertebral artery (common in >70% proximal subclavian stenosis) 2
  • Flow reversal in the ipsilateral extracranial vertebral artery (can be assessed by hyperemia testing) 2, 1

• Abnormal or doubtful duplex ultrasound findings should lead to anatomic imaging 2

• Computed Tomography Angiography (CTA):

  • Excellent imaging tool for supra-aortic lesions 2
  • Provides extravascular information, especially when thoracic outlet syndrome is a differential diagnosis 2

• Magnetic Resonance Angiography (MRA):

  • Provides both functional and morphological information 2
  • Useful to distinguish anterograde from retrograde perfusion and estimate stenosis severity 2, 3

• Digital Subtraction Angiography (DSA):

  • Considered the gold standard imaging method but increasingly replaced by other modalities 2
  • Mainly used in combination with endovascular therapy 2

Treatment

Medical Management

• Risk factor control and best medical therapy are recommended in all patients with symptomatic upper extremity artery disease to reduce cardiovascular risk 2
• This includes antiplatelet therapy, lipid-lowering medications, blood pressure control, and smoking cessation 2

Revascularization Indications

• Revascularization is indicated in symptomatic patients with:

  • TIA/stroke
  • Coronary subclavian steal syndrome
  • Ipsilateral hemodialysis access dysfunction
  • Impaired quality of life 2

• Revascularization should be considered in asymptomatic patients with:

  • Planned coronary artery bypass grafting using the internal mammary artery
  • Ipsilateral hemodialysis access
  • Significant bilateral subclavian stenosis/occlusion for adequate BP surveillance 2

Revascularization Options

• Both endovascular and surgical procedures are available, with the choice depending on lesion characteristics and patient risk factors 2, 1

• Endovascular Treatment:

  • Percutaneous angioplasty with stenting is often preferred 2
  • Technical success is 100% when treating stenosis and 80-95% when treating occlusions 2
  • Balloon-expandable stents provide more radial force than nitinol stents in heavily calcified ostial lesions 2
  • Mid-term patency (>24 months) is 70-85% 2
  • Post-procedural stroke rate is approximately 2.6% 2

• Surgical Options:

  • Carotid-subclavian bypass with prosthetic grafting
  • Subclavian-subclavian or axilloaxillary bypass
  • Post-procedural stroke rate is 0.9-2.4% 2
  • Higher long-term patency rates compared to endovascular procedures 1

Prognosis and Follow-up

• The natural history of subclavian stenosis appears relatively benign in most cases 2
• Life-threatening conditions include subclavian steal with myocardial ischemia in patients with internal mammary artery coronary bypass and symptomatic brachiocephalic atherosclerosis with stroke episodes 2
• Vertebrobasilar insufficiency related to subclavian artery stenosis can recur even after revascularization procedures 2
• Regular follow-up with non-invasive vascular studies is recommended to monitor disease progression and treatment efficacy 4

Important Considerations and Pitfalls

• SSS is often asymptomatic and discovered incidentally 5
• The presence of SSS should prompt evaluation for coexisting coronary, carotid, or peripheral artery disease 6
• Patients with SSS are more likely to experience TIA or stroke involving the carotid circulation than the vertebrobasilar circulation 4
• Differentiate SSS from other causes of vertebrobasilar insufficiency such as cardiac arrhythmias or intracerebral small vessel disease 2