Cuff BP Readings Differ Significantly From Invasive Measures

Marlene Busko

August 03, 2017

TASMANIA, AUSTRALIA — A new study shows differences in noninvasive cuff-measured blood-pressure readings vs invasive intra-arterial brachial and aortic readings, suggesting more accurate noninvasive measures are needed[1].

Dr Dean S Picone (University of Tasmania, Hobart, Australia) and colleagues performed three meta-analyses of more than 70 studies dating back to the 1950s, and their results were published online July 24, 2017 in the Journal of the American College of Cardiology.

"The most important finding of the present study was the inaccuracy of cuff BP when compared with intra-arterial brachial BP and aortic BP," they write. "These deviations substantially influenced BP classification according to clinical guideline criteria."

They report that there is "reasonable confidence" that brachial cuff readings indicating normal blood pressure (<120/80 mm Hg) or stage 2 hypertension (>160/100 mm Hg) were accurate compared with intra-arterial measurements.

However, cuff readings indicating prehypertension (>120/80 mm Hg to <140/90 mm Hg) or stage 1 hypertension (>140/90 to <160/100 mm Hg) in some cases underestimated systolic BP and overestimated diastolic BP, correctly classifying patients only about half of the time.

Nevertheless, "our findings should not detract from the incredibly important role that cuff-measured blood pressure has played over many decades in identifying people with high blood pressure and reducing their risk of cardiovascular events," senior author Dr James E Sharman (University of Tasmania, Hobart, Australia) told theheart.org | Medscape Cardiology in an email.

"We are certainly not suggesting that people should have intra-arterial blood pressure measured as a routine procedure," he stressed. That would be "impractical, unethical, and unnecessary."

Despite the important methodological issues in arterial blood-pressure measurement that this study identified, "hypertension management in clinical practice has been a great success story in medicine," Dr George S Stergiou (University of Athens, Greece) and colleagues write in an accompanying editorial[2].

More research is needed. But in the meantime, "standardized office BP measurements (right posture of patient, standardized conditions, repeated measurements, validated device, appropriate cuff, etc) combined with the appropriate use of out-of-office BP monitoring methods" such as 24-hour ambulatory readings are very important to improve the accuracy of blood-pressure readings and optimize patient management, editorialist Dr Anastasios Kollias (University of Athens) told theheart.org | Medscape Cardiology in an email.

Cuff vs Intra-Arterial BP Readings

It is not clear whether cuff-measured blood pressure is as accurate as invasive intra-arterial blood-pressure measurements, Picone and colleagues write. Underestimating blood pressure could miss patients who would benefit from treatment to lower their cardiovascular risk, but overestimating blood pressure increases treatment costs and might expose a patient to potential adverse effects from unnecessary treatment.

The researchers performed three meta-analyses to determine the agreement between intra-arterial aortic vs brachial blood pressure; cuff blood pressure vs intra-arterial brachial blood pressure; and cuff blood pressure vs intra-arterial aortic blood pressure.

The team identified 74 studies with 3073 participants in 18 countries.

In the first meta-analysis, the mean intra-arterial brachial systolic BP was 8 mm Hg higher and the mean intra-arterial brachial diastolic BP was 1 mm Hg lower than aortic systolic and diastolic BPs (P<0.001 and P=0.038, respectively).

In the second meta-analysis, the mean cuff systolic BP was 6 mm Hg lower and the mean cuff diastolic BP was 6 mm Hg higher than corresponding intra-arterial brachial systolic and diastolic BPs (P<0.0001 for both).

The third meta-analysis showed no significant difference between the mean brachial cuff and the intra-arterial aortic systolic BP (P=0.77), but there was poor agreement (mean absolute difference 8 mm Hg); and the brachial cuff significantly overestimated diastolic BP compared with the aortic readings.

The differences between cuff and intra-arterial readings ranged from >5 mm Hg in 67% of patients to >15 mm Hg in 22% and 26% of patients.

When the patients were classified into hypertension categories based on the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7) criteria, cuff blood pressure correctly identified prehypertension and stage 1 hypertension in only about one-half of the participants.

True Implications

"The true implications of these findings with respect to identification of risk related to BP in clinical practice will require future studies," Picone and colleagues write.

"Some kind of misclassification of patients when using cuff vs invasive BP measurements might be expected," Kollias noted, and this "seems to be considerable in patients with BP close to the thresholds."

However, the clinical importance of this misclassification is not yet known.

"We might profit from more accurate brachial cuff-based measurement of the brachial blood pressure," he added, but "this possibility must be tested in clinical research studies."

Similarly, new devices that estimate aortic BP using simple brachial cuff-based noninvasive methods need to be validated in prospective clinical studies with hard end points.

On the other hand, guidelines based on a considerable amount of evidence show that brachial cuff BP estimation is still highly effective to diagnose hypertension, stratify risk, and determine appropriate treatment, Kollias said.

"Our data suggests that we can do better, and there is room to improve the accuracy standards of blood-pressure monitors," said Sharman.

In the meantime, the best available options to determine blood pressure are "using out-of-clinic measures such as 24-hour ambulatory or home blood-pressure monitoring, or automated, unobserved clinic blood pressure," where multiple measures are recorded and averaged, which may reduce measurement error, he said.

Picone and Sharman have no relevant financial relationships. Disclosures for the coauthors are listed in the paper. The editorialists have no relevant financial relationships.

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