Ambulatory BP monitoring predicts mortality better than in-clinic measurement

In a study of nearly 64,000 patients in Spain, researchers demonstrated that ambulatory monitoring of systolic blood pressure (BP) was a stronger predictor of all-cause mortality and cardiovascular mortality than systolic pressure measured in the clinic. Results of the study were published in The New England Journal of Medicine.

“This research is a clear game-changer, as for the first time, it definitively shows that blood pressure measured regularly during a 24-hour period predicts the risk of heart disease, stroke, and death much better than blood pressure measured in a doctor’s surgery or clinic,” said co-lead investigator Bryan Williams, MD, Chair of Medicine, University College London, London, UK.

“Quite simply, measuring blood pressure over 24 hours is what doctors and medics should be using to make clinical decisions about treatment,” Dr. Williams advised.

The results also showed that sustained hypertension and white-coat hypertension were associated with increased risk of death, but the strongest association was found with masked hypertension.

Researchers included 63,910 adult patients (mean age 58.4 years; 58% men) who were enrolled in the ongoing Spanish Ambulatory Blood Pressure Registry between March 2004 and December 2014. Blood pressures were first measured in the clinic using the average of two standard readings. Then patients were fitted with a validated, pocket-sized ambulatory blood pressure monitor (ABPM) programmed to record measurements at 20- to 30-minute intervals around the clock.

The mean in-clinic BP was 147.9/86.7 mm Hg, and the mean 24-hour ambulatory BP was 129.2/76.5 mm Hg.

During a median follow-up of 4.7 years, 3,808 patients died—1,295 from cardiovascular causes, including 440 from ischemic heart disease, 291 from stroke, and 123 from heart failure.

Results showed that 24-hour systolic pressure was more strongly associated with all-cause mortality (HR 1.58 per 1-SD increase in pressure, 95% CI 1.56-1.60, after adjustment for in-clinic BP) than in-clinic systolic pressure (HR 1.02, 95% CI 1.00-1.04, after adjustment for 24-hour BP). These results were similar across subgroups of age, sex, and status with respect to obesity, diabetes, cardiovascular disease, and antihypertensive treatment.

Regarding cardiovascular mortality, 24-hour systolic pressure showed a stronger association with ischemic heart disease, stroke, and heart failure than in-clinic systolic pressure.

Masked hypertension was associated with a higher risk of death (HR 2.83) than sustained hypertension (HR 1.80) or white-coat hypertension (HR 1.79).

“For decades doctors have known that blood pressure measured ‘in-clinic’ could be masked or elevated, simply because the patient was in a medical setting, and this could lead to the wrong or a missed diagnosis,” Dr. Williams said. “With a much more accurate assessment of a patient’s blood pressure, doctors will be able to provide the most effective treatments at the earliest opportunity, which will save many more lives.”

He added, “With 1 billion people around the world having high blood pressure, this study, the largest ever of its kind, should lead to changes in clinical practice across the world, with the use of ABPM becoming much more commonplace.”

This study was supported by the Spanish Society of Hypertension, Lacer Laboratories, and European
government agencies.