Prognostic Significance of Between-Arm Blood Pressure Differences: Between-Arm Blood Pressure Difference and Mortality
To the Editor:
With interest we read the recent article in Hypertension by Agarwal et al.1 The authors conclude that blood pressure differences between arms are reproducible and that this difference is related to mortality.
We have some concerns with the methods and conclusions of this study.1 First, is the blood pressure device that was used validated? Second, the conclusion about the reproducibility concerns a remeasurement after only 1 week. In a study that we performed regarding possible between-arm blood pressure differences in patients with type 2 diabetes, we found that an interarm blood pressure difference of ≥10 mm Hg was not reproducible in 79% of patients after 1 year.2 Third, we wonder whether it is the interarm blood pressure that is related to mortality or whether it is the variability of blood pressure readings induced by irregular heart rhythm. If so, these patients could have greater interarm blood pressure differences and a higher mortality risk attributable to heart rhythm disturbances.
Furthermore, in our study we found that, at baseline, 33% of patients had an interarm blood pressure difference of >10 mm Hg. However, 25% of patients also had an intra-arm blood pressure difference of >10 mm Hg (device used: Omron M5-1). The same phenomenon of blood pressure fall while sequentially measuring at 1 arm seems to occur when measuring sequentially first at 1 arm and then at the other. In our article we reviewed 10 studies about this subject and concluded that it depends a great deal on whether blood pressure is measured simultaneously on both arms or not and how many consecutive measurements are performed. Studies using simultaneous measurements found less interarm blood pressure differences; the more consecutive measurements performed, the less interarm blood pressure differences were found. One study comparing the means of 8 measurements found no interarm blood pressure difference at all.3 Therefore, it can be questioned whether, apart from patients with, eg, 1-sided artery stenosis, interarm blood pressure differences really exist.
We ask the authors to elucidate some of the questions raised. Furthermore, we ask them whether it would be possible to further analyze their data to investigate whether an intra-arm variability is also related to mortality. Finding such a relationship would imply that it is not interarm difference but blood pressure variability that is related to mortality.
Agarwal R, Bunaye Z, Bekele DM. Prognostic significance of between-arm blood pressure differences. Hypertension. 2008; 51: 657–662.
Kleefstra N, Houweling ST, Meyboom-de Jong B, Bilo HJ. Measuring the blood pressure in both arms is of little use; longitudinal study into blood pressure differences between both arms and its reproducibility in patients with diabetes mellitus type 2. Ned Tijdschr Geneeskd. 2007; 151: 1509–1514.