masked hypertension

A recent study compared clinic blood pressure (CBP) measurements and ambulatory blood pressure monitoring (ABP), finding much more masked hypertension than white-coat hypertension (see htn masked circ2016 in dropbox, or doi.org/10.1161/CIRCULATIONAHA.116.023404). White-coat hypertension is when the CBP is higher than the ABP; masked hypertension is the opposite.

Details:
-- 888 healthy, employed, middle-aged individuals not on antihypertensive medications, found in a workplace screening program to have a blood pressure of <160/105 mmHg, then had 24 hour ABP.
-- Mean age 45, 89% female, 7.4% black/12% Hispanic
-- They compared the awake ABP (aABP), the CBP, and the difference. CBP was an average of nine readings over three visits after being seated a minimum of five minutes, and the participants had not smoked, eaten or had caffeinated beverages in the prior 30 minutes. Two other blood pressures were recorded 1 to 2 minutes afterwards. Those with CBP >140/90 were defined as having clinic-based hypertension, those with aABP >135/85 were defined as hypertensive. Those with elevated CBP but nonelevated aABP were defined as whitecoat hypertension. Those with nonelevated CBP but elevated aABP were classified as having masked hypertension.

Results:
-- average systolic/diastolic aABP was 123/77 mmHg
-- average CBP was 116/75 mmHg => average CBP was 7/2 mmHg lower than aABP
-- 5.3% were hypertensive by CBP; 19.2% were hypertensive by aABP; 15.7% with nonelevated CBP had masked hypertension. specifically,
                -- for those with clinic blood pressure higher than ambulatory (white-coat), found overall in 17.8% by systolic pressure and 35.8% by diastolic:
                                -- difference of > 5mmHg: 6.9% of subjects by systolic, 14.2% by diastolic
                                -- difference of >10 mmHg: 2.5% systolic, 4.2% diastolic
                                -- difference of >15 mmHg: 1.1% systolic, 0.9% diastolic
                -- for those with ambulatory blood pressure higher than clinic blood pressure (masked), 82.2% of systolic and 64.2% diastolic
                                -- difference of >5 mmHg: 63.7% systolic, 32.4% diastolic
                                -- difference of >10 mmHg: 34.8% systolic, 9.2% diastolic
                                -- difference of >15 mmHg: 14.4% systolic, 1.7% diastolic
-- this difference was most pronounced in young adults and those with normal BMI, decreasing at older ages and higher BMIs but did not disappear
-- no difference between men and women, black patients vs nonblack, Hispanic vs non-Hispanic, cigarette smokers vs past smokers vs nonsmokers

Commentary:

--I had seen a few studies on masked hypertension with similar findings, but I must admit I assumed there was lots of hyperbole/biases to their conclusions, that white coat hypertension was undoubtedly much more common than masked hypertension.  But -- just goes to show you: for several patients their daily lives are even more stressful than the calm and relaxing clinician's office….

--this is clearly a flawed study in terms of drawing generalizable conclusions: 
    --CBP was not really checked in a "clinic", but at a workplace
    --as a workplace-based study, there is the "healthy worker bias" which not only selects people who tend to be healthier, but also selects people who may have somewhat higher social economic status (which itself seems to confer better health outcomes), as well as having few individuals over the age of 65. Of note only 5% of these people had elevated CBP, likely reflecting this healthier population. 
    --the study did not include many nonwhite patients. 
--these biases clearly undercut the generalizability of the study's results. Also, the high level of masked hypertension raises the question that more fit people (lower BMI) exercise more and have higher ambulatory pressures​.

--BUT, other studies have found masked hypertension in a wide array of patients (see htn masked metaanal jhtn2008 in dropbox, or Bobrie G. J Hypertension 2008, 26:1715) which found that the prevalence of masked hypertension was between 8 and 20%, and as high as 50% in treated hypertensive patients. A few studies mentioned in this meta-analysis found that masked hypertension was actually associated with 2 to 3 times the cardiovascular events than either white-coat hypertension or controlled hypertension in treated patients. In untreated patients, the data seems pretty mixed: studies varied between no increased cardiovascular risk to the same risk as untreated sustained hypertension.​ a couple of the studies:

    --The Jackson Heart Study (Diaz KM. American Journal of Hypertension 28(7) July 2015) looked specifically at African-Americans, finding that the prevalence of masked hypertension was 25.9% (34.4% in people with normal CBP) and that all of the surrogate markers of carotid artery intima-media thickening, left ventricular mass, and microalbuminuria were elevated (vs controls) in those with masked hypertension, and similar to those with sustained hypertension. They also found that male gender, smoking, diabetes, and antihypertensive medication use were independently associated with masked hypertension. 

    --And, another study, the Dallas Heart Study (Tientcheu D. JACC. 2015; 66: 2170) assessed masked versus whitecoat hypertension and sustained hypertension in a group with 54% being African-American. They found a 17.8% prevalence of masked hypertension and a 3.3% of whitecoat hypertension. The risk for cardiovascular events over nine years was significantly higher in both the masked hypertension and sustained hypertension groups, but was barely significant in the whitecoat hypertension group, assessing cardiovascular outcomes. Controlling for an array of risk factors including clinic blood pressure measurements, they found that higher 24-hour a ambulatory systolic and diastolic pressures were independent risk factors for new cardiovascular events. The adjusted relative risk for cardiovascular events was a 34% increase for each 1-SD increase in the 24 hour blood pressure, a 30% increase for ambulatory systolic blood pressure during the daytime and a 27% increase for ambulatory systolic blood pressure during the nighttime. For diastolic pressure the cardiovascular risk was 21% for each 1-SD increase for each, 24% for ambulatory diastolic pressure during the daytime and 18% for the nighttime. This graphs shows that there was essentially no relationship between clinic systolic pressures and cardiovascular events, that the correlation within each group of office-based blood systolics was only by ABP.

​

-- So, there are a number of questions that arise from these studies: 

    --there is no clear consensus on how to define masked hypertension/what are the cutpoints?​ They used an ABP cutpoint of 135/85 mmHg as their definition of hypertension.  A consensus guideline suggested a 24-h average of >130/80, a daytime average of >135/85, and a night-time average of >120/70 (see O'Brien E. Hypertension 2013; 62: 988) 
    --are the clinical effects of masked hypertension really just those of increased blood pressure variability (see http://gmodestmedblogs.blogspot.com/2016/09/blood-pressure-variability-increases.html  )?
    --is there any real clinical advantage to identifying and treating patients with masked hypertension, and how? 
    --how do we look practically for masked hypertension in our patients given that they have normal blood pressure in the office (assuming the studies suggest that identifying and treating these patients actually matters). 

So, why, you might ask, am i bringing up masked hypertension, when there are no studies showing that unmasking it and treating it does anything???

-- i think it is always useful to hear about different information/perspectives which challenge the predominant ideology. The early studies on "mild hypertension" focused exclusively on clinic-based diastolic blood pressure. Then a few epidemiologic studies documented that systolic blood pressure was an even better predictor of cardiovascular events, moving the clinical target pressures into clinic-based full blood pressures. Then several studies either supporting or debunking the role of white-coat hypertension as important, and now, per my reading, suggesting that it is a little important but much less so than the other forms of hypertension. Then lots of studies on ambulatory blood pressure finding it to be much more predictive of clinical events than clinic-based blood pressure, and other studies showing that blood-pressure variability (either from clinic visit to clinic visit, or over the course of a 24-hour period) as being important. Now, over the past few years, emerges masked hypertension. We still do not know what to do with this, but there are a constellation of studies suggesting that this may be as important as sustained hypertension.​ But i think the real positive of this evolution in our thinking is that we are now situating hypertension in the realm of a person's actual life instead of the artificial constructs of the clinic setting, and the data support this...
--masked hypertension fits in well with the increasing data on ABP as the predictor-of-choice for clinical events
--it probably makes sense to think about masked hypertension in certain people, esp those with highish clinical blood pressure, since as in the above study, they are more liklely to have masked hypertension. or in those with possible hypertension-related damage (eg retinal changes, LVH, renal dysfunction/microalbuminuria....) And, i think it makes sense to use the diagnosis of masked hypertension to reinforce the generally-useful-anyway lifestyle changes (diet, exercise, stress reduction...). i would be hesitant to prescribe meds for masked hypertension, lacking any real data on outcomes
--and, as to how to  measure it, it would be great to have ABP monitoring available and inexpensive. but, my completely untested hypothesis (though likely more practicable) is to use home-based or pharmacy-based measurements (which seems to be more accurate than CBP and approach that of ABP in the few studies done), with the clear prescription that the person should sit down/relax for several minutes, then check the numbers.

and, for the complete set of hypertension blogs, see http://gmodestmedblogs.blogspot.com/search/label/hypertension