What is subclavian steal?

Subclavian Steal Syndrome

Subclavian steal syndrome is a condition characterized by reversal of blood flow in the vertebral artery due to proximal subclavian artery stenosis or occlusion, causing vertebrobasilar insufficiency symptoms that typically worsen with exercise of the affected arm. 1

Pathophysiology

Subclavian steal syndrome occurs when:

• The proximal subclavian artery becomes stenotic or occluded (most commonly due to atherosclerosis)
• Blood flow reverses in the ipsilateral vertebral artery to supply the arm distal to the obstruction
• This reversal can reduce basilar artery perfusion, especially when the dominant vertebral artery is affected 2

The condition develops as branches distal to the subclavian obstruction become sources of collateral circulation to the arm through flow reversal in the vertebral and internal mammary arteries 2.

Clinical Presentation

Symptoms typically manifest in two main forms:

1. Vertebral ischemic form:

   • Posterior cerebral circulatory insufficiency symptoms
   • Lightheadedness, syncope, vertigo
   • Ataxia, diplopia, motor deficits
   • Symptoms worsen with ipsilateral arm exercise 2

2. Coronary ischemic form (less common):

   • Blood diverts from coronary arteries to upper limb through internal mammary artery graft
   • Produces angina pectoris during arm exercise 2

3. Upper extremity symptoms:

   • Arm or hand claudication
   • Paresthesia
   • Rest pain 2

Diagnosis

Key diagnostic findings include:

• Physical examination:

  • Asymmetry between left and right arm blood pressure (difference ≥15 mmHg is suspicious)
  • Periclavicular or infraclavicular bruit
  • Blood pressure tends to fall further in affected limb after arm exercise 2, 1

• Imaging:

  • Duplex ultrasonography: Can identify reversal of flow in vertebral artery 2, 1
  • CT angiography (CTA) or MR angiography (MRA): Identifies and characterizes subclavian artery stenosis 1

Management

Treatment approach depends on symptom severity:

1. Asymptomatic patients:

   • Most require no specific intervention 1
   • Should not undergo revascularization unless the internal mammary artery is required for myocardial revascularization 2

2. Symptomatic patients:

   • Should be considered for subclavian revascularization using endovascular or surgical techniques 2
   • Indications include:
     • TIA/stroke
     • Coronary subclavian steal syndrome
     • Ipsilateral hemodialysis access dysfunction
     • Severe upper extremity ischemia 1

3. Secondary prevention:

   • Antiplatelet therapy (aspirin 75-325 mg daily)
   • Aggressive cardiovascular risk factor modification
   • Lipid-lowering therapy aiming at >50% LDL-C reduction 1

Revascularization Options

1. Endovascular approach:

   • Angioplasty with or without stenting
   • Primary patency rates: 93% at 1 year, 70% at 5 years
   • Lower complication rates compared to surgery 1

2. Surgical options:

   • Carotid-subclavian bypass (100% success rate, 96% patency at 5 years)
   • Subclavian-carotid arterial transposition
   • Carotid-axillary or axilloaxillary bypass 2, 1

Important Considerations

• Subclavian steal syndrome is generally associated with a favorable prognosis 2
• Some patients with high-grade stenosis and mild symptoms become asymptomatic as collateral blood supply develops 2
• The presence of subclavian steal, even if asymptomatic, should prompt thorough cardiovascular workup for coexisting coronary, carotid, or peripheral artery disease 3
• Regular follow-up with serial noninvasive imaging at 1 month, 6 months, and annually is recommended after intervention 1

Pitfalls to Avoid

• Don't miss bilateral subclavian disease or aortic arch syndrome, where blood pressure may be symmetrical in both arms despite significant disease 2
• Remember that subclavian steal due to atherosclerosis is often asymptomatic, while cases related to dialysis arteriovenous fistulas are more frequently symptomatic 3
• Avoid unnecessary intervention in asymptomatic patients unless the internal mammary artery is needed for coronary bypass 2