Nighttime, 24-Hour BP Readings Have Strongest Link to Poor Outcomes

When using blood pressure values to assess a patient’s long-term risk of dying or having a cardiovascular event, nighttime and 24-hour readings from ambulatory blood-pressure monitoring (ABPM) appear to have the best predictive value, a population-based study shows.

All BP indexes—both in the office and on ABPM—were significantly associated with mortality and CV events through a median 13.8 years of follow-up, but the magnitudes of the relationships were greatest for the nighttime and 24-hour readings. And even after adjusting for other measures, these two remained predictive of poor outcomes, according to findings published in the August 6, 2019, issue of JAMA.

Senior author Jan Staessen, MD, PhD (University of Leuven, Belgium), told TCTMD the implications are clear—ABPM should be more broadly used. “We should always use ambulatory pressure to diagnose hypertension and to manage hypertension,” he said.

Study co-author Gladys Maestre, MD, PhD (University of Texas Rio Grande Valley School of Medicine, Brownsville), argued that the findings support expanding the indications for which ABPM is reimbursed in the United States under a Centers for Medicare & Medicaid Services (CMS) coverage decision updated just last month. ABPM will now be covered when used in patients with suspected white coat or masked hypertension; previously, it was covered only for the assessment of suspected white coat hypertension.

These new data also support adding other clinical scenarios to the mix, such as assessment of whether a patient is controlled on antihypertensive therapy, Maestre indicated. Expanding the criteria for reimbursement “will enhance the care of everybody that is at risk for hypertension,” she said, adding that paying for ABPM out of pocket is not an option for many patients.

But Philip Greenland, MD (Northwestern University Feinberg School of Medicine, Chicago, IL), senior editor of JAMA, took a more cautious view of the results, noting that there were strong correlations between all of the BP measures—both office and ABPM. He said it’s not surprising that there would be an improvement in risk prediction using ambulatory measures “because the more measures of blood pressure you have, the more accurate the characterization of the patient.”

That doesn’t necessarily mean, however, that ABPM should be used more widely outside of the indication currently covered by CMS, Greenland told TCTMD. He indicated that the paper was accepted for publication because it contained information that would be useful for clinicians trying to make sense of all of the information coming from ABPM.

“If you stand back and look at the data, it gives you a sense of what to do with ambulatory blood pressure readings if you choose to get them,” Greenland said. But as to whether ABPM should be used routinely in a larger proportion of patients, “I don’t think that’s what the data show,” he added.

Small Improvement in Predictive Value

ABPM is considered the preferred approach for measuring BP in guidelines from around the world, but it had not been clear which specific measure is most predictive of adverse outcomes.

To find out, the investigators, with lead author Wen-Yi Yang, MD, PhD (University of Leuven), dug into the International Database on Ambulatory Blood Pressure in Relation to Cardiovascular Outcomes (IDACO). The analysis incorporated data from 13 longitudinal, population-based cohorts that included a total of 11,135 adults (median age 54.7 years; 49.3% women) from Europe, Asia, and South America. Using a cutoff of 140/90 mm Hg, 43.7% had hypertension; of that group, only 46.5% were taking antihypertensive drugs.

The researchers determined the relationships between various BP measurements—conventional and automated office readings and 24-hour, daytime, and nighttime ambulatory readings—taken at baseline and rates of mortality and CV events (CV mortality, nonfatal coronary events, heart failure, or stroke) over long-term follow-up.

Both endpoints were most strongly tied to nighttime and 24-hour readings. For example, for every 20/10-mm Hg rise in nighttime systolic pressure, total mortality was increased by a relative 23% (HR 1.23; 95% CI 1.17-1.28) and CV events were increased by a relative 36% (HR 1.36; 95% CI 1.30-1.43). Findings were similar when using diastolic readings.

Predictive models that included single systolic BP indexes provided area under the curve (AUC) values of 0.83 for mortality and 0.84 for CV events. Adding nighttime or 24-hour measurements to those models resulted in slight improvements in predictive value (AUC gains ranging from 0.0013 to 0.0075).

“Thus, 24-hour and nighttime blood pressure may be considered optimal measurements for estimating CV risk, although statistically, model improvement compared with other blood pressure indexes was small,” the authors say.

This study confirms prior research and indicates “that ambulatory BP monitoring over and beyond measures taken in clinicians’ offices improved risk stratification among patients with or those suspected of having hypertension,” they write.

In particular, Maestre said, the results show that nighttime BP “gives us a tremendous power to do risk stratification.” She speculated that nighttime readings may be better than others because they’re taken without interference from physical activity and diet and while participants are lying still.

Staessen said the researchers are now planning to conduct cost-effectiveness analyses in this data set, pointing out, however, that prior studies have already shown that ABPM is cost-effective.