A difference of more than 20mmHg between brachial artery pressures indicates what?

• A. Aortic dissection
• B. Peripheral edema
• C. Subclavian steal or stenosis on the side with the lower pressure
• D. Normal variation

Answer: (C)

A large difference between the two brachial blood pressures points to a problem with arterial inflow to the arm, usually from stenosis or occlusion of the subclavian artery proximal to the measurement site on the side with the lower pressure. When the subclavian artery is narrowed, the arm on that side runs with a lower systolic pressure, and in some cases blood can be diverted from the vertebral (posterior brain) circulation to the arm (subclavian steal), which reinforces the gradient. The threshold of about 20 mmHg is a clinically meaningful abnormal gradient that prompts evaluation for subclavian stenosis or steal on the side with the lower reading. Peripheral edema isn’t caused by arterial pressure differences, and a simple normal variation wouldn’t typically exceed this magnitude.