From the Guidelines
A 20 mmHg variation in systolic blood pressure from the right to the left arm is clinically significant and warrants further evaluation. This finding suggests possible peripheral vascular disease, particularly subclavian artery stenosis, which can indicate broader cardiovascular disease 1. Patients with this blood pressure difference have an increased risk of cardiovascular events and mortality compared to those without such a difference. The variation may also indicate aortic dissection in acute settings, especially when accompanied by chest pain or other concerning symptoms.
When detected, patients should undergo a comprehensive cardiovascular risk assessment including imaging studies of the subclavian arteries and aortic arch. Blood pressure measurements should always be taken in both arms during initial evaluation, with subsequent measurements taken in the arm with the higher reading, as recommended by the 2020 International Society of Hypertension global hypertension practice guidelines 1. This approach ensures accurate hypertension diagnosis and management, as treating based on the lower reading could lead to inadequate blood pressure control. The underlying mechanism involves atherosclerotic narrowing of the subclavian artery, reducing blood flow and pressure to the affected arm.
Key considerations in managing such patients include:
- Measuring blood pressure in both arms at the initial visit to detect any inter-arm difference 1
- Using the arm with the higher blood pressure value for subsequent measurements if a difference is detected 1
- Considering further investigation if the inter-arm difference is >20 mmHg 1
- Being aware of the potential for aortic dissection or other serious conditions in the presence of a significant inter-arm blood pressure difference, especially with accompanying symptoms.
From the Research
Significance of 20 mmHg Variation in Systolic Blood Pressure
- A 20 mmHg variation in systolic blood pressure (SBP) from the right (RT) to the left (LT) arm is considered significant and may indicate underlying pathology 2, 3, 4.
- Studies have shown that inter-arm differences in blood pressure are common, with 20% of participants having a difference of > 10 mmHg and 3.5% having a difference of > 20 mmHg in systolic blood pressure 2.
- A difference of > 20 mmHg in systolic blood pressure between arms has been associated with acute aortic dissection (AAD) 3 and peripheral vascular disease (PVD) 4.
Clinical Implications
- Measuring blood pressure in both arms initially is important to prevent misdiagnosis of hypertension due to normal differences in blood pressure between the arms 2, 5.
- The normal range for inter-arm differences in blood pressure is -9 mmHg to 11 mmHg for systolic blood pressure and -10 mmHg to 10 mmHg for diastolic blood pressure 5.
- A difference of > 10 mmHg in systolic blood pressure between arms is frequent in asymptomatic hypertensive individuals and does not necessarily indicate a pathologic condition 6.
Associations with Underlying Conditions
- A systolic blood pressure difference of > 20 mmHg between arms has been associated with non-traumatic AAD 3 and PVD 4.
- Age was the only significant predictor of clinically significant variations in inter-arm blood pressures and mean absolute blood pressure differences 2.
- The incidence of systolic pressure difference ≥ 20 mmHg between arms was greater in patients with PVD (21%) compared to those with coronary artery disease (CAD) (3%) or control subjects (0%) 4.