BP is a labile hemodynamic parameter; it varies from
heartbeat to heartbeat, from morning to evening, from winter to summer, from
sleeping to awake and from sitting to standing. The same holds true for any
other CV hemodynamic parameter such as heart rate, cardiac output, ejection
faction or pulmonary wedge pressure. However, the information that is based on
invasively obtained measurements is often considered more reliable than
information based on simple BP recording.
Numerous studies have documented that BP, when measured
carefully under standardized conditions in physicians’ offices, is a
powerful and reliable predictor of morbidity and mortality. Recent studies have
documented that 24-hour ambulatory BP monitoring is even a closer surrogate
endpoint for heart attack and stroke than is office BP. Because the correlation
between 24-hour ambulatory BP measurement and office BP measurement is moderate
at best, it’s not unexpected that there will be a significant number of
people who are truly hypertensive but in whom the diagnosis is missed by BP
measurement in the office setting (masked hypertension). Conversely, BP may be
elevated in the office but not on ambulatory BP monitoring — an entity
known to most clinicians as white-coat hypertension.
White-coat hypertension is a well-known clinical entity
familiar to most physicians. A variety of studies have shown that the risk in
patients with white-coat hypertension is somewhat elevated but distinctly lower
than in patients who have sustained hypertension. Despite its commonness,
little is known how to best manage white-coat hypertension. Out of fear of
over-treatment, some physicians are taking a “wait and see approach”
in patients with white-coat hypertension. Conversely, out of fear of
litigation, some physicians may take an over-aggressive therapeutic approach,
which may lead to hypotension and orthostatic symptoms.
In stark contrast, masked hypertension is a much less
well-known (but not necessarily a less common) entity, which seems to carry a
distinctly more serious prognosis. This was documented by Pickering and
colleagues, who were the group that proposed the term “masked
hypertension.” The same entity has been described occasionally as
“reversed white-coat hypertension.” It was initially regarded as rare
but was recently found to be present (to some extent) in about one-third of the
hypertensive population. Risk factors for masked hypertension include alcohol,
tobacco, caffeine and physical inactivity.
In the PAMELA population, patients with masked
hypertension have a prevalence of echocardiographic left ventricular
hypertrophy that was much greater than that of normotensive patients.
Inappropriate target organ disease (ie, inappropriate for office BP) should,
therefore, trigger suspicion of masked hypertension and motivate physicians to
expose a susceptible patient to 24-hour ambulatory BP monitoring.
Difficulties detecting masked hypertension
The clinician should remember that it’s much easier
to suspect the diagnosis of white-coat hypertension, as patients will usually
tell that the BP is normal at home. In contrast, masked hypertension needs to
be looked for, and there are few clinical hints as to its presence. Normal BP
in the clinical setting does not mean that a patient is not at risk for an
elevated BP, which can occur at other times of the day.
This is particularly true in patients who are treated
with antihypertensive drugs that are not covering a full 24-hour period such as
atenolol (Tenormin, AstraZeneca), losartan (Cozaar, Merck) and
hydrochlorothiazide. Because the patient takes the medication in the morning,
BP values in the physician’s office most often are normal but may be
substantially elevated at the end of the dosing interval (ie, during the night
and early morning hours). Thus, in many hypertensive patients, clinic BP is
seemingly well-controlled, but morning BP, before taking the medication, may be
elevated, thereby exposing the patient to a high risk of CV events.
Unfortunately, masked hypertension has become a blind spot in the current
management of this disease.
Although we certainly cannot make a sweeping
recommendation that all patients with high BP (or normal BP) should undergo
24-hour ambulatory BP monitoring, we think that the presence of inappropriate
target organ disease such as LV hypertrophy or microalburminuria should raise
suspicion of masked hypertension and motivate physicians to initiate a further
As to the therapeutic approach, we should remember that
white-coat hypertension has a benign prognosis and can only be over-treated;
therefore, a conservative approach is probably justified. Quite in contrast,
masked hypertension has a much more serious prognosis and can only be
undertreated; it deserves, therefore, a much more aggressive therapeutic
For more information:
- Clement D. N Engl J Med. 2003;348:2407-2415.
- Hansen T. Hypertension. 2005;45:499-504.
- Messerli F. J Am Coll Cardiol. 2002;40:2201-2203.
- Ohkubo T. J Am Coll Cardiol. 2005;46:508-515.
- The sixth report of the Joint National Committee on prevention,
detection, evaluation, and treatment of High blood pressure. Arch Intern
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