What is subclavian steal syndrome, how is it clinically diagnosed and investigated, and what are the treatment options?

Subclavian Steal Syndrome: Diagnosis and Management

Subclavian steal syndrome 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 symptoms, requiring prompt diagnosis and appropriate management based on symptom severity.

Definition and Pathophysiology

• Subclavian steal syndrome (SSS) is characterized by retrograde blood flow in the vertebral artery due to proximal subclavian artery stenosis or occlusion, resulting in posterior cerebral circulatory insufficiency 1
• Atherosclerosis is the most common cause, though other etiologies include Takayasu arteritis, giant cell arteritis, fibromuscular dysplasia, and radiation-induced arteriopathy 2
• The syndrome develops when blood "steals" from the vertebrobasilar circulation to supply the affected arm, particularly during increased demand (exercise) 3

Clinical Presentation

• Symptoms of vertebrobasilar insufficiency include dizziness, vertigo, blurred vision, diplopia, dysarthria, confusion, loss of consciousness, drop attacks, and ataxia 4, 3
• Upper extremity claudication presents as exercise-induced crampy pain and fatigue in the affected arm 2
• Patients with coronary bypass using the internal mammary artery may develop myocardial ischemia as a manifestation of subclavian steal 4
• Most patients with subclavian steal phenomenon remain asymptomatic, with symptoms typically triggered by arm exercise 5

Clinical Diagnosis

• Bilateral arm blood pressure measurement is essential, with a difference >15 mmHg highly suspicious for subclavian stenosis 4, 2
• Detection of a periclavicular or infraclavicular bruit during auscultation suggests subclavian stenosis 1, 3
• Clinical examination should include assessment of axillary, brachial, radial, and ulnar artery pulses 4
• Signs such as pulse deficit, arm pain, pallor, paresthesia, and coldness warrant further investigation 4
• The Allen test should be performed in patients in whom the radial artery is instrumented or harvested for coronary revascularization 4

Diagnostic Investigations

• Duplex ultrasonography can identify reversal of flow in the vertebral artery and is valuable for differentiating occlusion from stenosis 4, 2
• Dynamic examination with cuff compression of the upper arm and consecutive hyperemia after decompression can demonstrate changes in vertebral flow direction 4
• CT angiography (CTA) provides excellent detailed imaging of upper limb atherosclerosis 4, 3
• MR angiography (MRA) offers both functional and morphological information, particularly helpful in detecting antegrade versus retrograde flow 4, 6
• Digital subtraction angiography (DSA) remains the gold standard but is increasingly being replaced by CTA and MRA 4

Treatment Approach

• Control of atherosclerotic risk factors should be offered to all patients with upper extremity arterial disease, including asymptomatic subjects 4
• Asymptomatic patients generally do not require intervention, except in specific cases such as:
  • Patients with planned use of the internal mammary artery for coronary bypass grafting 4
  • Patients with bilateral upper limb lesions to enable accurate blood pressure measurement 4
• For symptomatic patients, both endovascular and surgical treatment options are available:
  • Endovascular options include balloon angioplasty, atherectomy, and stenting (93-98% initial success rate) 3
  • Surgical options include carotid-subclavian bypass with prosthetic grafting (96-100% patency at 5 years) 1, 3
• Endovascular revascularization may be preferred over surgery due to lower complication rates, despite similar long-term outcomes 2

Prognosis and Follow-up

• The natural history of subclavian stenosis appears relatively benign in most cases 4, 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 4
• Vertebrobasilar insufficiency related to subclavian artery stenosis can recur even after revascularization procedures due to other conditions such as cardiac arrhythmias or intracerebral small vessel disease 4
• Patients should be monitored for progression of disease and symptom recurrence 2

Clinical Pearls and Pitfalls

• Not all patients with flow reversal in the vertebral artery will be symptomatic 2
• Measuring blood pressure in both arms identifies the arm with the highest systolic pressure, which is required for accurate measurement of the ankle-brachial index 2
• Identification of unequal blood pressures in the arms allows for more accurate measurement of blood pressure in the treatment of hypertension 2
• The combination of proximal and distal arm occlusive disease presents a clinical challenge with poor prognosis for the extremity 4