What is the appropriate evaluation and management for a patient with a persistent systolic blood pressure that is about 20 mm Hg higher in the left arm than the right arm?

Evaluation and Management of 20 mmHg Inter-Arm Blood Pressure Difference

A persistent 20 mmHg systolic blood pressure difference between arms is definitively abnormal and requires urgent vascular evaluation within 1-2 weeks, as this strongly suggests subclavian artery stenosis or other significant arterial pathology, and all future blood pressure measurements must be taken from the left (higher-reading) arm to avoid systematic undertreatment of hypertension. 1, 2

Immediate Confirmation Steps

Before proceeding with evaluation, confirm this finding is reproducible and not due to measurement error:

• Repeat bilateral measurements using proper technique: both arms positioned at heart level (mid-sternum), fully supported, after 5 minutes of seated rest in a quiet environment 1
• Use appropriately sized cuffs for each arm (cuff width ≥40% of arm circumference), as mismatched cuffs can create artificial differences of ≥10 mmHg 1, 2
• Measure sequentially 2-3 times in each arm, 1-2 minutes apart, to confirm reproducibility 1, 2
• If the difference persists at ≥20 mmHg, this confirms clinically significant pathology requiring urgent evaluation 1, 2

The 20 mmHg threshold is critical: approximately 21% of patients with peripheral vascular disease demonstrate systolic differences ≥20 mmHg, compared to 0-3% of those without vascular disease 3. In the absence of acute symptoms (chest pain, back pain, syncope, neurological deficits), this represents chronic vascular pathology rather than acute aortic dissection 2.

Focused Vascular Examination

Perform a targeted assessment to identify the underlying pathology:

• Palpate bilateral pulses: brachial, radial, and ulnar in both arms; assess for diminished or delayed pulses in the left (higher-reading) arm, which paradoxically suggests stenosis proximal to the measurement site 2, 4
• Auscultate for bruits over the supraclavicular and infraclavicular regions bilaterally, particularly on the side with lower pressure, as bruits indicate subclavian artery stenosis 2, 4
• Check lower extremity pulses (dorsalis pedis, posterior tibial) to screen for generalized peripheral arterial disease 2
• Assess for symptoms of vertebrobasilar insufficiency (dizziness, vertigo, diplopia with arm use), which suggests subclavian steal syndrome 2, 4

Most Likely Underlying Cause

Subclavian artery stenosis is the most common cause of inter-arm differences ≥15-20 mmHg, creating a pressure gradient across the narrowed vessel that results in lower blood pressure distal to the obstruction 2, 4. The stenosis is typically on the side with the lower reading, not the higher one—a common source of confusion 2.

Other potential causes include:

• Aortic coarctation (particularly in younger patients) 1, 2
• Brachiocephalic (innominate) artery stenosis 4
• Takayasu arteritis or other large-vessel vasculitis 2

Diagnostic Imaging Strategy

Proceed with vascular imaging in a stepwise fashion:

• First-line: Duplex ultrasound of subclavian and axillary arteries to detect stenosis or occlusion 2, 4
• If ultrasound is equivocal or clinical suspicion is high: obtain CT angiography or MR angiography of the aortic arch and great vessels to delineate the level and extent of obstruction 2, 4
• Consider inflammatory markers (ESR, CRP) if large-vessel vasculitis is suspected based on age, systemic symptoms, or examination findings 2

Urgent Referral Pathway

Refer to vascular surgery or cardiology within 1-2 weeks for:

• Confirmation of vascular pathology 2
• Assessment for concomitant coronary artery disease (patients with subclavian stenosis have high prevalence of CAD) 2, 4
• Consideration of intervention if symptomatic (arm claudication, subclavian steal) or if stenosis >50% with hypertension 1, 2

The European Society of Cardiology guidelines for coarctation specify that intervention is indicated when hypertension is present with an increased gradient and >50% narrowing, even if the invasive peak-to-peak gradient is <20 mmHg 1.

Critical Management Principle

Always use the left arm (higher-reading side) for all future blood pressure measurements and hypertension management decisions. 1, 2 Using the lower-reading arm leads to systematic underestimation of true blood pressure and results in undertreatment of hypertension, increasing cardiovascular risk 2, 4.

Red Flags Requiring Emergency Evaluation

While a 20 mmHg difference without symptoms is not an emergency, immediate ED evaluation is warranted if any of the following develop:

• Acute chest pain or back pain (especially between shoulder blades) 2
• Syncope or near-syncope 2
• Acute neurological symptoms 2
• New pulse deficits or signs of limb ischemia 2

These symptoms raise concern for acute aortic dissection, which requires emergent imaging and management 2.

Common Pitfalls to Avoid

• Do not dismiss the finding as measurement error without proper confirmation with repeat measurements using correct technique 2, 5
• Do not use different cuff sizes or techniques between arms during confirmation, as this creates artificial differences 1, 2, 4
• Do not fail to refer for vascular evaluation even in asymptomatic patients, as the finding indicates significant arterial disease requiring assessment 2, 4
• Do not continue measuring blood pressure in the right (lower-reading) arm, as this will lead to inadequate hypertension treatment 1, 2