Ambulatory BP Monitoring Reliability Questioned for HTN Diagnosis

Patrice Wendling

December 14, 2020

Although guidelines generally recommend ambulatory over home blood pressure (BP) monitoring for diagnosing hypertension, new research questions home BP monitoring's role as second fiddle.

One week of home BP monitoring (HBPM) was more reliable than one 24-hour ambulatory BP or nine mercury readings across three office visits among younger, untreated participants in the Improving the Detection of Hypertension study.

The reliability coefficients were 0.938, 0.846, and 0.894 for systolic BP and 0.918, 0.843, and 0.847 for diastolic BP, respectively.

Further, HBPM had the strongest association with left ventricular mass index (LVMI), a predictor of adverse cardiovascular events, according to researchers led by Joseph E. Schwartz, PhD, Renaissance School of Medicine at Stony Brook University, New York, and Columbia University Irving Medical Center, New York City.

The association with LVMI also remained after multivariate adjustment and after correcting for regression dilution bias, indicating the results were not a result of differences in the number of readings, they write in the study, published online today in the Journal of the American College of Cardiology.

Whenever patients have an elevated blood pressure for the first time or even borderline elevated BP, guidelines recommend clinicians request a 24-hour ambulatory recording or home monitoring, Schwartz told | Medscape Cardiology. "I think this has the potential, for that purpose, to put ambulatory blood pressure monitoring out of business, even though that's what I've done for 30 years.”

Previous studies have shown that home and ambulatory BP monitoring (ABPM) correlate more strongly with target-organ damage and cardiovascular outcomes than office BP, but head-to-head outcomes trials of the two techniques are lacking. A recent systematic review also found scant evidence supporting one approach over the other for predicting CV events or mortality.

An accompanying editorial notes that ABPM is largely unavailable to primary care physicians in the United States and poorly reimbursed. "Thus the demonstration that HBPM is more reliable and associates more closely with LVMI than ABPM, if confirmed, would carry the potential to change clinical practice, write Robert M. Carey, MD, University of Virginia Health System in Charlottesville, and Thomas H. Marwick, MBBS, PhD, MPH, Baker Heart and Diabetes Institute, Melbourne, Australia.

Commenting to Medscape Cardiology, ABPM proponent Raymond R. Townsend, MD, said, "Honestly, it may be that we'll need to act on this. I'm not quite ready to do that and change my practice patterns but, on the other hand, I can't sweep this under the rug.”

He noted that it's ironic the study is coauthored by the late Thomas Pickering, MD, a maven of ABPM who coined the term "white-coat hypertension" and pointed out masked hypertension.

That said, "it raised the bar on ambulatory blood pressure monitoring: is it really worth our public health dollars? So I think it's a very good call to arms,” said Townsend, who directs the hypertension program at the University of Pennsylvania Perelman School of Medicine in Philadelphia.

Ambulatory BP monitoring has long been considered the gold standard but from a cost standpoint, HBPM is more attractive because the devices can be used more than once and track more than one person in a household, he said. The Center for Medicare Management also has a code in the 2020 bundle to reimburse physicians $15 for training patients and has a monthly charge for communicating with those filing regularly. "You're not going to get rich doing monitoring of home BP, but at least the government is recognizing we are moving more and more to the home base in terms of our managing common conditions like blood pressure.”

One of the attractions of ABPM is the ability to do every half-hour to every hour nocturnal pressures, but at least one home monitor, manufactured by Microlife, has added a nocturnal feature, Townsend noted. "So that's just one more incoming against the ABPM defenses about why ABPMs are still better.”

The study enrolled a community based sample of 408 participants who had office BP assessed at three visits (three readings per visit) using a mercury sphygmomanometer, a BpTRU (VSM MedTech) automated oscillometric device, and a home-validated Omron oscillometric device (Omron Healthcare).

After 5 minutes of in-office training and receipt of a reference sheet, participants also completed 3 weeks of HBPM with the Omron device as well as two 24-hour ambulatory measurements (Spacelabs Healthcare, Model 90207). Cardiovascular evaluations, including two-dimensional echocardiograms, were performed during the fifth office visit.

The 400 participants who completed all five visits had a mean age of 41 years, mean LVMI of 79.3 g/m2, and mean office systolic BP ranging from 116.0 to 117.2 mm Hg and diastolic BP from 75.6 to 76.5 mm Hg.

Both before and after correction for regression dilution bias, home systolic and diastolic BP were more highly correlated with LVMI than 24-hour ambulatory or office mercury readings. The corrected correlations for systolic BP were 0.501, 0.430, and 0.389, respectively.

After multivariable adjustment including office and 24-hour ambulatory BP, 10 mm Hg higher systolic and diastolic home BP were associated with 5.07 g/m2 (P = .001) and 3.92 g/m2 (P = .07) higher LVMI, respectively. After adjustment for home BP, however, neither systolic or diastolic office BP nor ambulatory BP was associated with LVMI.

Townsend and editorialists Carey and Marwick pointed out the study included a younger population in whom just 30% to 50% would have been classified as having hypertension by the 2017 American College of Cardiology/American Heart Association guidelines, which Carey helped to pen.

"These people are young and older people have a different kind of blood pressure driven more by the stiffness in their circulation and less by the resistance to blood flow that you find more characteristic in younger people,” Townsend observed.

"I don't know that you can extrapolate the findings from this study in healthy, younger untreated people to older, perhaps sicker, and more diabetic people where the real action is and where the endpoints like heart attack, death, and stroke actually occur,” he said.

The results suggest measurement of resting daytime BP may be relatively more important than dynamic daytime and/or nocturnal parameters in predicting subclinical cardiac target organ damage, but this requires further study, Carey and Marwick noted.

Commenting further, they write that the results suggest "HBPM could be especially important for detecting elevated BP and hypertension early in life, when adults are relatively healthy, but those with hypertension have a high lifetime risk of CVD.”

Schwartz acknowledged the study didn't include the typical hypertensive patient but said it goes to the central question of whether the risk associated with blood pressure is because of the heart's cumulative exposure over its lifetime and, thus, best measured with multiple readings taken under a variety of circumstances or with readings taken only at rest. 

"I've been posing that question at a conceptual level for 15 years, never in print, and this paper is the first hint, at least with respect to the left ventricular mass index…that getting a better measure of resting blood pressure is more important for controlling risk than the heart's cumulative exposure to blood pressure, as measured by ambulatory," he said.

The Improving the Detection of Hypertension study was supported by a grant from the National Heart, Lung, and Blood Institute of the National Institutes of Health (NIH). The authors have disclosed no relevant financial relationships. Townsend reports royalties as a writer for UpToDate and serving as an unpaid reviewer for Carey is principal investigator and project director of a NIH R01 and P01 grant, respectively; vice-chair of the 2017 ACC/AHA Hypertension Guideline writing committee; and chair of the AHA Resistant Hypertension Scientific Statement writing committee. Marwick has disclosed no relevant financial relationships.

JACC. Published online December 14, 2020. Full text, Editorial

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