Uncovering masked hypertension: Is the blood pressure really normal?

A number of studies have documented the incremental predictive ability of 24 hour ambulatory blood pressure monitoring over traditional office or casual blood pressure monitoring for predicting adverse cardiovascular events. In this issue, Ohkubo and colleagues report their findings comparing ambulatory blood pressure monitoring and casual (office) blood pressure readings from a population-based study performed in Japan. There has been great interest in management of white coat hypertension; however, this study reports that “masked hypertension” was even more prevalent in this population and was associated with a significant risk for cardiovascular mortality and stroke compared with sustained normal blood pressure. Masked hypertension is defined as elevated blood pressure on 24-hour ambulatory blood pressure monitoring with normal blood pressure in the office.

This study has significant strengths, including that it is population based and includes 10 years of follow-up for events. The findings raise questions that need to be addressed in further studies. This study included patients already receiving antihypertensive medical therapy and also patients without medical therapy. As the authors discussed in the original version of this report, the risk associated with masked hypertension was most impressive in the untreated subgroup (relative hazard [RH] 2.56 [1.4-4.7]); however there were trends toward increased risk in the treated group as well (RH 1.62 [.86-3.07].¹ The authors state that there was no significant statistical interaction related to treatment; however, I suspect a larger study with more events would be needed to further clarify which group should be targeted most for more aggressive monitoring outside the physician’s office. The authors wisely suggest that those at high general cardiovascular risk would be most appropriate for more monitoring due to their greater absolute risk for an event.

It would have been helpful to know what antihypertensive medical therapies the subjects with masked hypertension were receiving, compared with the other groups of treated hypertensive subjects. Since this study was performed more than 10 years ago, in Japan, it might not be completely relevant to current medical care in the United States. For example, were patients receiving short-acting antihypertensive medications, which are no longer the US standard of care? Further studies are needed to define what currently used US antihypertensive therapies are most likely to be associated with masked hypertension. As most blood pressure medications are prescribed once daily and the majority of patients receive more than 1 antihypertensive medication, studies should be performed to see if administering medications both in the morning and at night would improve 24-hour control. Of course, multiple dosing may also lead to decreased compliance compared with once-daily dosing.

Ambulatory blood pressure monitoring is rarely used at this time in general clinic practice, except to document white-coat hypertension. Home blood pressure monitoring is quite common, simpler, and less costly. Further studies are needed to determine the predictive power of home blood pressure monitoring to identify patients at risk for masked hypertension and cardiovascular events. We also need to know which untreated patients with normal casual, office blood pressure readings are at risk for elevated home blood pressure readings. Since we generally do not pursue further monitoring in our patients who have “normal” blood pressure in the office, at this time, as stated by the authors, we should be especially vigilant in pursuing more aggressive monitoring in patients who have evidence of target organ damage and normal casual, office blood pressure readings.