In an adult presenting with acute tearing chest, back, or abdominal pain, how concerning is a systolic blood pressure difference of ≥20 mm Hg between the right and left arms, and what immediate diagnostic and therapeutic steps should be taken?

Blood Pressure Difference in Aortic Dissection: Clinical Significance and Management

A systolic blood pressure difference of ≥20 mm Hg between arms is a significant high-risk clinical marker for acute aortic dissection that warrants immediate advanced imaging with CT angiography, regardless of other clinical findings. 1, 2

Diagnostic Value and Clinical Significance

The inter-arm blood pressure differential is a critical physical examination finding that substantially increases the likelihood of aortic dissection:

• A systolic BP difference >20 mm Hg between arms has an odds ratio of 2.7 (95% CI 1.39-5.25) for acute aortic dissection, making it a statistically significant predictor 3
• This finding is part of the high-risk examination features in the ADD (Aortic Dissection Detection) risk score, along with pulse deficit, focal neurologic deficit with pain, new murmur of aortic insufficiency, and hypotension/shock 1, 4
• The blood pressure differential is particularly characteristic of Type A aortic dissection (involving the ascending aorta), where left arm pressure exceeding right arm pressure by >15 mm Hg with right arm <130 mm Hg has an odds ratio of 25.97 (95% CI 2.45-275.67) 5
• All patients with left-right BP difference >20 mm Hg in one study had Type A dissection with extension to the brachiocephalic artery 5

Measurement Technique

Proper measurement technique is essential to avoid false positives and ensure diagnostic accuracy:

• Blood pressure must be measured in both arms during the initial assessment of any patient with suspected acute aortic syndrome 1, 2
• Sequential arm measurement is sufficiently reliable for clinical practice, though simultaneous measurement devices exist 2
• Use appropriately sized cuffs and position both arms at heart level during measurement 2
• The arm with the higher systolic pressure should be used for all subsequent blood pressure monitoring 2

Context: Normal Inter-Arm Differences

Understanding baseline inter-arm BP variation helps interpret pathologic findings:

• In healthy ambulatory patients without cardiovascular disease, the mean absolute inter-arm difference in systolic BP is only 2.61-3.19 mm Hg 6
• Approximately 84-90% of healthy patients have inter-arm systolic BP differences ≤6 mm Hg, and 98% have differences ≤10 mm Hg 6
• A difference of ≥15-20 mm Hg is definitively abnormal and suggests subclavian or innominate artery stenosis in peripheral artery disease, or aortic dissection in the acute setting 1

Immediate Diagnostic Steps

When a significant inter-arm BP difference is detected in a patient with acute chest, back, or abdominal pain:

1. Calculate the ADD risk score by assessing three categories 1, 4:

   • High-risk conditions: Marfan syndrome, family history of aortic disease, known aortic valve disease, recent aortic manipulation, or known thoracic aneurysm
   • High-risk pain features: Abrupt onset, severe intensity, or ripping/tearing quality
   • High-risk examination features: Pulse deficit, systolic BP differential, focal neurologic deficit, new murmur of aortic regurgitation, or hypotension

2. Obtain D-dimer if immediately available (sensitivity 91-100% for dissection), but do not delay imaging if D-dimer is negative or unavailable 4

3. Proceed directly to CT angiography of the chest as the initial diagnostic imaging modality, given its wide availability, accuracy, speed, and anatomic detail 1

   • TEE and MRI are reasonable alternatives if CT is contraindicated or unavailable 1
   • Plain chest radiography is neither sensitive nor specific enough to exclude dissection 1, 4

4. Do not rely on clinical decision rules alone to exclude dissection - even patients with ADD score of 0 have a 4.3-5.9% prevalence of dissection, which is insufficient to safely exclude the diagnosis 1, 4

Critical Clinical Pitfalls

Several common errors can delay diagnosis and increase mortality:

• Atypical presentations occur frequently: Up to 6.4% of patients with acute aortic dissection present without pain, particularly older patients, those on steroids, and patients with Marfan syndrome 4
• The classic "tearing" or "ripping" pain quality is actually uncommon - patients more commonly describe "sharp" or "stabbing" pain (51-64% of cases) 4
• Physical examination findings may be subtle or absent: Unequal dorsalis pedis pulses and the BP differential may be the only physical findings, as demonstrated in a case where a patient presented primarily with heart failure symptoms 7
• Pulse deficit has better diagnostic accuracy than BP differential alone (diagnostic OR 28.9 vs 2.71), so assess both peripheral pulses and bilateral arm pressures 3

Immediate Therapeutic Steps

Once aortic dissection is suspected or confirmed, initiate aggressive blood pressure control immediately:

• Target systolic BP between 100-120 mm Hg to prevent dissection extension 2
• Beta-blockers are first-line agents due to their effect on reducing the force of left ventricular ejection (e.g., labetalol drip) 2, 7
• Place an arterial line in the right radial artery for invasive blood pressure monitoring in unstable patients 2
• Use the arm with the higher blood pressure reading for ongoing BP monitoring to avoid pseudo-hypotension from aortic arch branch obstruction 2
• Transfer immediately to a facility with cardiothoracic surgery capability for definitive management 7

Special Considerations by Dissection Type

The clinical significance of BP differential varies by dissection location:

• Type A dissection (ascending aorta): BP differential is highly characteristic, particularly when left arm pressure exceeds right arm pressure with low right arm pressure (<130 mm Hg) 5
• Type B dissection (descending aorta only): Inter-arm BP differences are not significantly associated with Type B dissection 5
• This distinction has important implications: a significant BP differential in the setting of acute symptoms should raise particular concern for Type A dissection, which requires emergency surgical intervention 5