Makindo Medical Notes

Related Subjects: |Causes of Stroke |Ischaemic Stroke

Note: Subclavian artery "steals" blood from the vertebral artery, leading to symptoms of posterior circulation ischaemia.

About

• Subclavian Steal Syndrome (SSS): A condition where blood flow is reversed in the vertebral artery to supply the subclavian artery distal to an obstruction, resulting in compromised blood flow to the posterior cerebral circulation.

Anatomy

• Subclavian Artery: Arises from the aortic arch on the left and the brachiocephalic trunk on the right, supplying blood to the upper limbs, neck, and brainstem.
• Vertebral Artery: Branches from the subclavian artery and supplies blood to the posterior brain. In SSS, it becomes a collateral pathway when the subclavian artery is obstructed proximally.
• Subclavian Vein: A continuation of the axillary vein, it joins with the internal jugular vein to form the brachiocephalic vein, eventually leading to the superior vena cava.

Aetiology

• Atherosclerosis: The most common cause, leading to stenosis or occlusion of the subclavian artery proximal to the vertebral artery.
• Other Causes:
  • Arteritis, such as Takayasu arteritis.
  • Trauma or surgical injury.
  • Congenital abnormalities, such as aortic coarctation or subclavian artery anomalies.
• Ischemia Trigger: During ipsilateral upper limb exercise or exertion, increased demand in the affected limb results in blood flow reversal in the vertebral artery, leading to reduced perfusion of the posterior circulation.

Clinical Presentation

• Neurological Symptoms:
  • Dizziness, vertigo, and syncope due to compromised blood flow to the brainstem and cerebellum.
  • Ataxia and unsteady gait.
  • Visual disturbances, including temporary vision loss or blurriness.
• Upper Limb Symptoms:
  • Claudication or fatigue in the affected arm, especially during exertion.
  • Weakness or numbness in the ipsilateral arm due to reduced blood flow.
  • Decreased or absent radial pulse in the affected arm.
• Exercise-Induced Angina: In patients with left internal mammary artery (LIMA) grafts (for coronary artery bypass), subclavian artery stenosis can lead to angina during left arm exercise due to "stealing" of blood from the coronary circulation.

Investigations

• Physical Examination: Blood pressure difference of >15 mmHg between the arms, weaker pulse in the affected arm.
• Doppler Ultrasound: Shows reversed flow in the vertebral artery, which is diagnostic of subclavian steal.
• CT Angiography (CTA) or MR Angiography (MRA): Non-invasive imaging modalities to visualize subclavian artery stenosis or occlusion and evaluate the extent of the disease.
• Aortic Angiography: Invasive imaging that provides detailed information on stenotic or occlusive lesions in the subclavian artery and the direction of vertebral artery flow.
• Transcranial Doppler: May be used to assess blood flow in the vertebral and basilar arteries, especially during provocative arm exercises.

Management

• Medical Management:
  • Antiplatelet Therapy: Aspirin or clopidogrel to reduce the risk of thromboembolic events.
  • Statins: To manage dyslipidemia and reduce progression of atherosclerosis.
  • Risk Factor Modification: Smoking cessation, control of hypertension, diabetes management, and lifestyle changes.
• Interventional Management: Considered for symptomatic patients or those with significant vascular compromise.
  • Angioplasty with Stenting: Minimally invasive option where a balloon is used to widen the stenotic area, followed by stent placement to maintain vessel patency.
  • Bypass Surgery: Subclavian artery bypass grafting is considered in cases where endovascular interventions are unsuitable. A graft may be placed from the carotid to the subclavian artery.
  • Endarterectomy: Surgical removal of atherosclerotic plaque from the subclavian artery, often performed if the stenosis is focal and accessible.

Prognosis and Follow-Up

• Prognosis: With appropriate treatment, symptoms can improve significantly, and the risk of stroke or severe ischemic events can be reduced.
• Long-term Follow-Up: Patients should be monitored for progression of atherosclerotic disease and control of risk factors. Regular follow-up with Doppler ultrasound may be indicated to assess blood flow in the vertebral artery and detect recurrent stenosis.

References

• Wolters Kluwer, "Subclavian Steal Syndrome". Available at UpToDate.
• Ferri FF, "Ferri's Clinical Advisor". Elsevier Health Sciences, 2020.