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Any definition is inadequate and defective, unless itdoes really define, or describe, the disease.— Elisha Bartlett (1804–1855), Philosophy of Medical Science
An elevated blood pressure can be a normal physiologic reaction, an abnormality of uncertain significance, a marker of cardiovascular risk, or the cardinal sign of a disease with potentially serious immediate or long-term complications. Depending on the clinical circumstances, therefore, the physician can ignore the finding, extend the scope of observation, engage the patient in a conversation on statistical risk, or initiate antihypertensive therapy. From our observations in the private practice and academic settings, most physicians facing these possibilities initiate therapy reflexively, on the spot. The “decision to treat” almost certainly stems from the current dogma that defines and classifies systemic hypertension solely on the basis of arbitrary cutoff numbers.1,2 Mindless adherence to these numbers prompts us to emphasize several points.
First, the blood pressure is inherently labile. When monitored indirectly by cuff devices in ambulatory patients, it varies substantially in response to changes in physical activity or the environment.3 This lability is strikingly evident during direct intra-arterial monitoring, wherein the highest pressures are often at least double the lowest pressures.4
Second, when the blood pressure is measured in the resting state as part of a screening procedure, the value obtained indicates a statistical risk of future cardiovascular events or death for that individual.5 This risk worsens in a graded manner with the systolic pressure: the higher the systolic pressure, the greater the risk.1 But no definitive threshold for risk has been identified to date.6,7 As for the diastolic pressure, regardless of the controversies concerning a “J-curve” phenomenon,8,9 cutoff numbers do not conform to any of the observed risk curves.10–12
Third, in addition to the normal lability of the blood pressure and the absence of a threshold value for risk, the phenomena of white-coat hypertension,13 masked hypertension,14 and pseudohypertension15 pose further difficulties in diagnosing hypertension by means of cutoff numbers alone. Moreover, defining hypertension on the basis of numbers alone makes it particularly difficult to differentiate a clinically important elevation in blood pressure from an incidental elevation. For instance, in many hospitalized patients, an elevated blood pressure simply represents a reaction to their concurrent illness or to the anxiety-provoking environment, or both. Such elevation rarely signals impending danger to those patients—yet physicians often rush to reduce the blood pressure, seemingly oblivious to the potential danger of doing so.16–20 This lack of perspective is widespread and is particularly evident in recent proposals that advocate screening for hypertension in the emergency department.21
Fourth, defining and classifying hypertension solely on the basis of cutoff numbers facilitates the treatment of populations but overlooks the individual patient. For example, because mild hypertension, however defined,11,22 is highly prevalent, it is a target for intervention to decrease the burden of cardiovascular risk to the community.23–25 But because this risk is minimal for the individual patient,26,27 the great majority of people so treated will not derive benefit, and some may actually be harmed.28 The harm results not only from the direct costs and side effects of therapy, but also from the psychosomatic sequelae associated with the diagnosis of hypertension—the so-called “labeling effect.”29–32
Fifth, experts do not always agree on the specific cutoff numbers.33–35 Furthermore, those numbers have enormous socioeconomic and public health implications.22,35,36 Millions of individuals worldwide who are deemed normal today can literally be turned into patients tomorrow, simply by selecting new numbers.22 And the recently defined category of “prehypertension”1 converts millions more.37–39 Sir George Pickering aptly warned of the “fallacy of the dividing line” throughout his distinguished career, but to no avail.40 Decades later, we are still treating patients by the numbers for their numbers.
Clinically important hypertension is sometimes called “the silent killer.” While it may be silent, it is not necessarily invisible. Early signs of its effect, if carefully sought, can be seen before the disease becomes clinically manifest. The funduscopic examination, for example, can identify early vascular abnormalities that might be reversed by treatment of hypertension.41,42 Many other noninvasive techniques are available to help determine the early impact of blood pressure elevation on different parts of the vascular tree.43–48 And comorbid conditions such as diabetes, hypercholesterolemia, and cigarette smoking can magnify the effect of hypertension on various organs.1,2,49
In 1957, William Evans published an observational study on patients with elevated blood pressure whom he had monitored for up to 10 years.50 He found that signs of target organ damage at the first visit indicated a high risk of future cardiovascular events, but the absence of such signs portended a generally benign prognosis. Consequently, he proposed the term “hypertonia” for an elevated blood pressure without signs of target organ damage, and “arterial hypertension” for an elevated blood pressure with such signs.
Almost 50 years after Evans's publication, the Hypertension Writing Group—a panel of experts from around the country—noted that the current threshold-based definition of hypertension fails to identify a large group of individuals who have subclinical cardiovascular disease before blood pressure elevation becomes chronic or manifest.51 Accordingly, the group proposed that target organ damage be incorporated into the definition and classification of hypertension. In a subsequent report published in 2009, the group made a distinction between high blood pressure (one manifestation of the disease—a biomarker) and hypertension (the disease).52
In conclusion, we join Evans and the Hypertension Writing Group in recommending that the definition of hypertension as a disease include a description of the associated pathologic manifestations. Such definition would spur the creation of new tools for detecting those manifestations53–58 and would foster a better understanding of the natural history of the disease. It would also promote a public-health approach that targets persons most likely to benefit from intervention. And for physicians who must deal with elevated blood pressures in the course of daily clinical work, the revised definition would encourage the circumspection and due diligence consistent with Mutton's Law of optimal patient care: “Know what to do and when to do it.”59
Address for reprints: Michel Accad, MD, 1800 Sullivan Ave., Suite 304, Daly City, CA 94015