Difference in blood pressure between arms might reflect peripheral vascular disease

EDITOR—I believe that McAlister and Straus underestimate the frequency and significance of a blood pressure difference between the arms.1 They quote 6% from the paper by Harrison et al, but this group reported a difference in 10/131 (that is, 7.6%) normotensive subjects for systolic or diastolic differences, 44/310 hypertensive patients (14%) for a systolic difference, and 31/310 hypertensive patients (10%) for a diastolic difference.2

I have reviewed the English language literature and identified 11 studies with comparable data on at least 100 subjects. These studies (table) reported prevalences ranging from 12% to 18.4% for a systolic difference ≥20 mm Hg and 13% to 33.7% for a diastolic difference ≥10 mm Hg in selected populations. No publications were identified from primary care.

I have been prospectively gathering pairs of readings from hypertensive patients. To date I have collected 435 pairs of recordings from 205 patients. The mean absolute systolic difference is ≥10 mm Hg in 64 (31%) patients and ≥20 mm Hg in eight (4%). The mean absolute diastolic difference is ≥10 mm Hg in 27 (13%) patients. These data suggest that identification of any difference in blood pressure between arms is a vital part of the assessment of hypertensive patients if their diagnosis is to be accurate and their response to treatment reliably monitored.

The causes of a pressure difference between arms are unclear. Harrison et al found fewer differences with intra-arterial measurements than with indirect techniques, suggesting that variations in the measurement techniques or the soft tissues may play a part.2 For some patients the difference is vascular in origin. This may be due to characteristics of flow in a normal arterial tree,3 but I suggest that vascular disease may also cause a difference. One study found an increased prevalence of differences in patients with coronary heart disease or peripheral vascular disease,4 and another showed that 83% of vascular surgical patients with differences had angiographic evidence of innominate or subclavian artery stenosis on the side of the lower pressure.5

The importance of a difference is already recognised between the arm and the leg, as measured by the ankle-brachial pressure index, which is reduced in the presence of asymptomatic peripheral vascular disease; a reduced index is associated with increased mortality. Why should the pathology, and prognostic implications, not be the same with differences between arms?

Until more work is done, hypertensive patients with a reproducible difference in blood pressure between arms should be investigated and managed intensively, on the assumption that they have asymptomatic peripheral vascular disease.