Blood Pressures Measured at Home Better Predict CAD Events Than Do Clinic Readings

Blood pressure (BP) recorded at home in the morning strongly predicts strokes and CAD events, an observational analysis suggests, and it appears to have an advantage over measurements in the clinic for predicting CAD events. Questions remain, however, about the potential use of home BP monitoring for managing antihypertensive treatment in everyday practice.

“Randomized controlled trials are needed to confirm the relationship between morning [home BP] readings and future ischemic events and to determine whether therapy specifically targeted to lowering morning BP reduces the frequency of these events,” lead author Kazuomi Kario, MD (Jichi Medical University School of Medicine, Tochigi, Japan), and colleagues write in the April 5, 2016, issue of the Journal of the American College of Cardiology.

They note that there has been uncertainty about whether clinic or out-of-office BP measurements—including home and ambulatory readings—are better at predicting adverse outcomes. To explore the issue, they turned to the HONEST (Home Blood Pressure Measurement with Olmesartan Naive Patients to Establish Standard Target Blood Pressure) study. The real-world study, which did not have a control group, enrolled hypertensive Japanese patients who initiated treatment with olmesartan (Benicar; Daiichi Sankyo) alone or in combination with other agents between October 2009 and September 2010. Individual BP targets were established by the treating physicians.

The current analysis included 21,591 patients followed for an average of about 2 years. At baseline, mean morning BP at home was 151.2/86.9 mm Hg and mean clinic BP was 153.6/87.1 mm Hg. During follow-up, average systolic BP was 135.2 mm Hg both at home in the morning and in the clinic.

Predicting Stroke, CAD Events

On-treatment morning home systolic BP and clinic systolic BP were comparable in terms of their ability to predict stroke events during follow-up. Patients with a morning home systolic BP reading of at least 155 mm Hg were more likely to have a stroke compared with those with a reading less than 125 mm Hg (HR 6.01; 95% CI 2.85-12.68). For clinic systolic BP, patients with a measurement of at least 160 mm Hg had a greater risk compared with those with a reading less than 130 mm Hg (HR 5.82; 95% CI 3.17-10.67).

In contrast to the stroke findings, morning home systolic BP edged clinic systolic BP for predicting risk of CAD events, which included MI and revascularization. For home readings, systolic BP of at least 155 mm Hg was associated with an elevated risk compared with measures below 125 mm Hg (HR 6.24; 95% CI 2.82-13.84). When comparing clinic readings of at least 160 mm Hg and less than 130 mm Hg, the hazard ratio for CAD events was just 3.51 (95% CI 1.71-7.20).

That indicates that clinic readings may underestimate CAD risk relative to morning home readings, the authors say. A goodness-of-fit analysis supported the stronger predictive value of morning home systolic BP.

“CAD events occur most frequently in the morning, and this phenomenon may be associated with an increase in BP and BP variability in the morning, resulting from increased activity of the renin-angiotensin system, as well as increased platelet function activity and a thrombotic tendency at this time of the day,” they write. “Therefore, morning [home BP] can be a useful predictor of CAD events, providing assessment of BP at the time when CAD events are most likely to occur.”

Kario and colleagues note, however, that home BP included four readings for every measurement point and clinic BP included just one. “Therefore, there is the possibility that fewer [home BP] measurements might not be more effective than [clinic BP],” they say.

Randomized Trial Needed

In an accompanying editorial, Rajiv Agarwal, MD (Indiana University School of Medicine, Indianapolis, IN), says that it has “unambiguously emerged that compared with BP measured in the clinic, BP measured at home has greater prognostic significance.”

The reason why home BP is linked more strongly than clinic BP to CAD events is unclear, he says, adding, however, that the association is probably causal. He points to the greater precision in measuring home versus clinic BP and evidence of greater titration of antihypertensive medications in the home BP group.

But there is the possibility that the observed relationship is not causal and could be the result of confounding by various factors, including adherence and response to treatment, potential differences in missing data based on where measurements are taken, and the use of a “soft” endpoint. To the latter point, Agarwal notes that the difference in CAD events seen here was driven mainly by revascularization and not MI. “Therefore, a larger study with more hard endpoints is required to confirm the findings,” he says.

Considering the results of SPRINT, which showed that outcomes are improved with a lower clinic systolic BP goal, “the question that emerges is whether lower BP goals can be achieved using home BP monitoring,” Agarwal concludes.

“Several randomized trials suggest that this is feasible, and the large pragmatic HONEST study suggests that it is time to design a randomized trial similar to SPRINT with treatment targets dictated by—not clinic BP—but home BP assessments,” he says. “If home BP can predict cardiovascular outcomes at least as well as clinic BP, it is time to test this strategy for cost-effectiveness, convenience, and, ultimately, its capability to relieve cardiovascular morbidity and mortality with the simple expedient of home BP monitoring.”

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