Subclavian Artery Stenosis

Subclavian artery stenosis is narrowing of the subclavian artery, usually in its proximal segment before the vertebral origin. The left side is affected about three times as often as the right.

Atherosclerosis causes most cases. Others are Takayasu arteritis, giant cell arteritis, radiation injury, fibromuscular dysplasia, surgical injury and, distally, thoracic outlet compression.

It is found in about 2% of the general population and in up to 10 to 15% of patients with peripheral artery disease. Most are silent.

A systolic pressure difference of over 15 mm Hg between the arms suggests it. The affected arm reads lower.

Pathophysiology. Pressure distal to the stenosis falls, so flow to the arm drops, particularly with exercise. When the stenosis lies before the vertebral origin, blood can flow backwards in the vertebral artery to supply the arm (subclavian steal), taking flow from the posterior circulation.

A left internal mammary graft on a diseased subclavian artery can steal from the coronary bed (coronary subclavian steal).

• Arm claudication, fatigue, coolness, pallor and paraesthesia on use. Rest ischaemia is rare because of collaterals.
• Posterior circulation symptoms on arm exercise: vertigo, diplopia, ataxia, visual change, syncope or drop attacks.
• Angina after bypass grafting with an internal mammary artery.
• Reduced or delayed radial pulse, supraclavicular bruit, lower pressure in the affected arm.
• Impaired function of a dialysis access in the affected arm. Embolic digital ischaemia is uncommon.

Red flags.

• Posterior circulation stroke or transient ischaemic attack
• Angina or ischaemia with an internal mammary graft
• Planned bypass surgery using an internal mammary artery
• Rest ischaemia of the arm or digital embolisation
• Onset in a young woman or with fever and raised inflammatory markers (arteritis)

• Blood pressure in both arms, seated, repeated. A difference of over 15 mm Hg is significant, and over 20 mm Hg strongly suggests stenosis. Check four limb pressures.
• Duplex ultrasound. Elevated velocity at the stenosis, damped distal waveform, and vertebral flow that is reversed at rest or after arm exercise or cuff deflation. A peak systolic velocity ratio of 2.0 or more across the lesion suggests a stenosis of 50% or more.
• CT or MR angiography of the arch and neck vessels: site, length, calcification, ostial involvement, wall thickening in arteritis, and the vertebral and carotid arteries.
• Catheter angiography with pressure measurement. A mean gradient of 10 to 15 mm Hg or more is significant.
• Brain imaging for posterior circulation events. Inflammatory markers (ESR, CRP) and imaging for large vessel arteritis when features suggest it.
• Coronary assessment before bypass grafting.

Differential diagnosis.

• Aortic arch syndrome and Takayasu arteritis
• Aortic dissection involving the arch branches
• Brachiocephalic or innominate stenosis
• Thoracic outlet syndrome and cervical rib
• Vertebrobasilar atherosclerosis and cardioembolic stroke
• Benign positional vertigo and other causes of syncope
• Raynaud phenomenon and embolic disease of the arm

All patients.

• Measure and treat blood pressure on the arm with the higher reading. Avoid blood pressure checks, venous cannulation and arterial lines on the affected side where possible.
• Aspirin 75 to 100 mg orally once daily (usual maximum 325 mg daily), or clopidogrel 75 mg once daily if aspirin is not tolerated, with pantoprazole 40 mg once daily for gastric protection (avoid omeprazole and esomeprazole with clopidogrel).
• Atorvastatin 40 to 80 mg orally once daily with liver enzymes at baseline and 3 months, aiming for LDL cholesterol under 1.4 mmol/L (55 mg/dL). Avoid in pregnancy.
• Blood pressure under 130/80 mm Hg, smoking cessation, glucose control and exercise.

Asymptomatic stenosis. No revascularisation. Surveillance by symptoms and arm pressures.

Indications for revascularisation. Disabling arm claudication, posterior circulation symptoms with steal, angina from coronary subclavian steal, impaired dialysis access, and any stenosis that needs treatment before bypass using an internal mammary artery.

Options.

• Endovascular repair is usual first choice for focal stenosis and short occlusions. Balloon expandable stents suit ostial lesions and self-expanding stents suit non-ostial lesions. Technical success is about 95%, with 5-year primary patency of about 80 to 90%. Risks are stroke (about 1%), embolisation, dissection, vertebral flow disturbance and restenosis in about 10 to 20%.
• Open repair: carotid subclavian bypass, or subclavian carotid transposition, for long or calcified lesions and failed stenting. Patency is over 90% at 10 years, with a stroke rate of about 1%, and risks of phrenic nerve palsy, Horner syndrome and thoracic duct injury.
• After stenting: aspirin 75 to 100 mg plus clopidogrel 75 mg once daily for 1 month, then a single antiplatelet drug long term.
• Treat the stenosis before, or at the same time as, coronary bypass when an internal mammary artery is planned (or use a different conduit).

Arteritis. Prednisolone 0.5 to 1 mg/kg orally once daily (maximum 60 mg) with a taper and a steroid sparing drug chosen with rheumatology, after screening for tuberculosis and hepatitis B. Revascularise only when inflammation has been quiet for 3 to 6 months.

Special groups. Pregnancy: avoid statins and manage blood pressure with labetalol, modified release nifedipine or methyldopa, using the arm with the higher reading. Region: Takayasu arteritis and tuberculosis are important causes in sub-Saharan Africa and Asia in young women.

Monitoring. Arm pressures and symptoms every 3 to 6 months after treatment, duplex at 1, 6 and 12 months and then yearly, and ESR and CRP in arteritis every 4 to 8 weeks during induction.

Referral and escalation. Refer to vascular surgery or a centre with endovascular capability. Urgent for posterior circulation events, angina with an internal mammary graft, or limb threatening arm ischaemia.