Unfortunately, blood pressure is still too rarely measured in both arms. Yet a new study shows that even a small difference in systolic blood pressure of 5 mmHg between the left and right arm significantly increases the risk of cardiovascular and all-cause mortality.
Hypertension is an important cardiovascular risk factor that can be diagnosed quite easily by repeated blood pressure measurements. However, many physicians neglect a small but crucial issue: Ideally, blood pressure should be measured at least once in both arms to detect a possible difference in blood pressure between them. Not only can this diagnose unilateral arterial stenosis (e.g. of the subclavian artery); a relevant blood pressure difference is also an independent cardiovascular risk factor. The European and US guidelines currently set the cut-off at ≥ 15 mmHg difference. However, the data basis for this recommendation is rather thin. Moreover, it is still unclear whether even a lower blood pressure difference is associated with a higher cardiovascular risk.
A team led by Dr. Christopher Clark from the University of Exeter in England has conducted a new meta-analysis. In contrast to earlier studies, individual patient data from more than 57,000 subjects from 24 longitudinal studies (14 from Western Europe) were collected for this analysis. All included studies fulfilled the authors' conditions: measurement of blood pressure in both arms, no blood pressure-lowering intervention and reliable determination of other cardiovascular risk factors.
The mean age of the study participants was 60 years, about 48% of the subjects were female and 76% were of European descent. Baseline blood pressure averaged 138/81 mmHg. Cardiovascular disease was known in 18% of the participants, diabetes in 15% and hypertension in 56%. The researchers' hypothesis was that a systolic blood pressure difference between the two arms at baseline could predict mortality and the risk of cardiovascular events over a 10-year period. Possible confounders such as systolic blood pressure, age, sex, ancestry, nicotine abuse, total cholesterol levels, diabetes, and obesity were included in the calculations.
Within the observation period, 9.2% of the study participants died. The study showed a dose-response relationship between the blood pressure difference of both arms and the risk of death. A blood pressure difference of 5 mmHg between the two arms increased the risk of death by 5% in each case, regardless of other risk factors. The same was true for cardiovascular death, which occurred in 3% of the subjects. Here, too, the risk was gradually increased by 6% for each blood pressure difference of 5 mmHg. For cardiovascular events (fatal and non-fatal), there was no significant association (p = 0.17).
In a further step, the researchers tested in a subgroup of participants without cardiovascular disease whether the blood pressure difference of both arms could predict cardiovascular risk independently of known cardiovascular scores. In the case of the atherosclerotic cardiovascular disease (ASCVD), Framingham and QRISK2 scores, which are mainly used in the USA, the blood pressure difference between the two arms actually had an additional informative value.
Thus, an arm-to-arm difference of ≥ 10 mmHg increased the risk of cardiovascular death by an additional 4 to 12% within 10 years. However, in the SCORE chart of the European Society of Cardiology (ESC), the blood pressure difference of both arms had no additional significance (p = 0.18). The researchers argue that with 0.9%, only relatively few subjects with a complete SCORE data set died of a cardiovascular event, which may have distorted the statistical significance.
The authors conclude from the data of their meta-analysis that the systolic blood pressure difference of both arms is an important measure for determining cardiovascular risk. Although a few analyses are not significant, the results on cardiovascular and all-cause mortality (about 5% risk increase per 5 mmHg blood pressure difference) are clear. The authors recommend an adjustment of the US and European guidelines so that a difference ≥ 10 mmHg (instead of ≥ 15 mmHg) is already defined as a cardiovascular risk factor.
After all, about 11% of all hypertensive patients have a corresponding difference of ≥ 10 mmHg between both arms and would thus have a higher cardiovascular risk. They could therefore benefit from an intensification of therapy. Patients with a borderline elevated cardiovascular risk who are considering drug therapy (e.g. lipid-lowering therapy) could also benefit. The measurement of blood pressure difference between both arms could be an additional factor here to help with therapy decisions.
It would be easy to implement the recommendation, because practically every physician has a blood pressure monitor and only needs about one minute more time to measure the blood pressure in both arms.
Sources:
Clark et al. Associations Between Systolic Interarm Differences in Blood Pressure and Cardiovascular Disease Outcomes and Mortality. Hypertension. Originally published 21 Dec 2020.