An inter-arm difference in systolic BP can predict cardiovascular morbidity and all-cause mortality after 10 years in patients with hypertension, a UK study in the BMJ has found.

This cohort study was carried out in a rural general practice setting in Devon. It analysed 230 patients receiving treatment for hypertension; 47 of whom had cardiovascular disease at recruitment. BP was measured using a standard mercury sphygmomanometer on both arms at three successive surgery visits.

Follow-up visits were planned every six months if the BP was controlled or at shorter intervals if not. A mean reading was obtained for each arm to calculate a mean inter-arm difference.

The primary outcome was cardiovascular events and death from all causes during a median follow-up of 9.8 years.

A total of 52 cardiovascular and 27 cerebrovascular events occurred in 76 participants over the study period. A hundred (44%) patients had an event or died and there were 59 deaths overall.

An inter-arm difference in systolic BP ≥ 10 mmHg and ≥ 15 mmHg were both associated with increases in the hazard of cardiovascular events, cardiovascular mortality, all-cause mortality and combined non-fatal events or all-cause mortality.

Almost a quarter, 24% (55/230) of patients had a mean inter-arm difference in systolic BP ≥ 10 mmHg and 9% (21/230) ≥ 15 mmHg.

This equated to an increased risk of all-cause mortality, hazard ratio (HR) 3.6 (95% CI: 2.0-6.5) and HR 3.1 (95% CI: 1.6-6.0) respectively.

A subgroup analysis revealed that the risk of death was also increased in the 183 patients without pre-existing cardiovascular disease at recruitment. An inter-arm difference in systolic BP ≥ 10 mmHg or ≥ 15 mmHg conferring risks of HR 2.6 (95% CI: 1.4-4.8) and HR 2.7 (95% CI: 1.3-5.4) respectively.

An inter-arm difference in diastolic BP ≥ 10 mmHg or more was weakly associated with an increased risk of cardiovascular events or death.

It is not routine practice for clinicians to measure BP in both arms. This is usually undertaken during a search for secondary causes of hypertension such as coarctation of the aorta or other aortic pathology such as chronic dissection. Current practice is to consider an inter-arm difference in systolic BP of < 10 mmHg as normal and to refer those with a difference >20 mmHg.

The authors conclude that differences in systolic BP between arms can predict an increased risk of cardiovascular events and all-cause mortality over 10 years in patients with hypertension. They suggest that this could be used as another indicator of increased cardiovascular risk and furthermore that BP measurement on both arms should be performed as a matter of routine in primary care.

‘Assessment of BP in both arms is recommended by guidelines and should become a core component of initial BP measurement in primary care,’ the authors state.

Dr Peter Savill

• Clark CE, Taylor RS, Shore AC, Campbell JL. The difference in blood pressure readings between arms and survival: primary care cohort study. BMJ 2012; 344:e1327