New hypertension definition expands beyond cut points

Experts hope this broader approach will allow clinicians to see the mercury threshold as one factor among many.

Measuring hypertension as a threshold of mercury is far too arbitrary, and experts want to move the definition beyond simple blood pressure and into all areas of cardiovascular disease risk.

Thomas Giles, MD, professor of medicine at the Louisiana State University Health Science Center and president of the American Society of Hypertension, said hypertension specialists needed a broader view.

“To date we have not really had a good definition of hypertension. If you look up hypertension in most medical textbooks you are going to find a lot of information about blood pressure cut points, but this is not going to suffice any longer because blood pressure is a continuous variable,” Giles said at the American Society of Hypertension 20th Annual Scientific Meeting and Exposition.

A progressive syndrome

Giles led a plenary session on a suggested new definition of hypertension and its implications. The new definition states: “Hypertension is a progressive cardiovascular syndrome arising from complex and interrelated variables. Early markers of the syndrome are omnipresent before blood pressure elevation is sustained; therefore, hypertension cannot be classified solely by blood pressure thresholds. Progression is strongly associated with function and structure of cardiac and vascular abnormalities that damage the heart, kidneys, brain and vasculature, and lead to premature morbidity and death.”

Michael Weber, MD, professor of medicine at State University New York Health Science Center in Brooklyn and editorial board member of Cardiology Today's Hypertension and Vascular Disease section, said the new definition of hypertension could help clinicians deal with the heterogeneity of the disorder.

“When we look at the heterogeneity of risk factors, we can divide patients in many different ways, bearing in mind that risk factors have multiplicative effects,” Weber said. “For example, it’s becoming increasingly obvious that it’s really not all that good to be old. A man in his 40s with a systolic blood pressure of 180 is at as much risk as a man in his 60s with a systolic blood pressure of 120,” Weber said. “It’s becoming increasingly obvious that age itself is a powerful risk factor. For instance, a man in his 40s with a systolic blood pressure of 180 is no more at risk than a man in his 60s with a systolic blood pressure of only 120.”

The new definition of hypertension does not incorporate the thresholds used in reports from the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC), and it refines the prehypertension category outlined in JNC-7.

Cardiovascular disease

Prehypertension had been defined as systolic blood pressure between 120 mm Hg and 139 mm Hg. “This created a very large category. It was called prehypertension because there was evidence of increased risk, but the committee stopped short of calling it hypertension because there was not evidence that treatment was uniformly beneficial,” Daniel Levy, MD, of the National Heart, Lung, and Blood Institute’s Framingham Heart Study, said.

According to the new definition of hypertension, normal individuals are those with blood pressures <115/75 mm Hg with no identifiable cardiovascular disease and few if any risk factors. Furthermore, these individuals do not have any early disease markers or apparent end-organ damage.

Stage 1 individuals are patients with occasional or intermittent blood pressure elevations or early cardiovascular disease. These patients have several risk factors and have displayed early markers of disease, but they have no target-organ damage.

“Stage 1 hypertension is not divided into blood pressure cut points, but the descriptive categories tell a broader story,” Giles said. “You should not wait for the first stroke or the first myocardial infarction to begin to treat this patient group. It could be pharmacologic treatment, but it may not be.”

Stage 2 hypertensive patients display sustained blood pressure elevations, progressive cardiovascular disease, many risk factors, overtly present markers of disease and early signs of target-organ disease.

Finally, Stage 3 hypertensive patients have marked and sustained blood pressure elevations, progressive cardiovascular disease, many risk factors, overtly present and progressive disease markers and overtly present end-organ disease.

End-organ damage

Bradford Berk, MD, PhD, of the University of Rochester School of Medicine and Dentistry and editorial board member of Cardiology Today’s Vascular Biology section, said the focus on end-organ damage could allow for more thinking about hypertension at the vascular level.

“Vascular dysfunction contributes to target-organ damage and hypertension. In every organ that’s damaged by hypertension, blood vessels, as a consequence of their dysfunction, augment underlying disease in the brain, kidneys, eyes and the heart,” Berk said. “It’s becoming very clear that we need to think about biomarkers for hypertension.”

Weber agreed, adding that the idea that clinicians can slow the aging process by reversing arterial disease is not an “impossible dream.”

“There are several clinical trials going on even as we speak — and in some cases that have already been published — that show we might be able to turn back the clock in our hypertensive patients,” Weber said.

Concomitant risk factors

In addition to age, there are many other risk factors that affect the predictive value of blood pressure markers. “I like to call this the hypertension syndrome because concomitant risk factors are very important,” Weber said.

Some of these risk factors can be counterintuitive, as in the case of obesity. “Most of us would have thought that an obese hypertensive patient, having multiple risk factors, would have a poor prognosis, but it turns out that lean hypertensive patients do even worse,” he said.

Weber said lean individuals are more likely to exhibit adverse vascular changes due to their higher norepinephrine levels and renin levels. In fact, obese people have reduced renin responsiveness during treadmill-induced stress.

“This is just one example about how we’re dealing with different groups of people within the hypertension diagnosis,” Weber said.

Control rates

Levy said the new definition of hypertension will continue to evolve as we gather more evidence, but before we make radical changes to current definitions clinicians would benefit from practicing “what we’ve been preaching for quite a long time.”

Hypertension control rates in the United States, while better than the rest of the world, are far too low, Levy said.

“Today only 58% of people with hypertension in the United States are receiving antihypertensive therapy, and only about 30% of them are controlled to levels of less than 140/90,” Levy said.

“This number would look far worse still if we included lower goals for diabetics and for people with kidney disease and established cardiovascular disease,” he said.

Control rates become worse as people age, Levy said. According to data from NHANES (National Health and Nutrition Examination Survey), approximately 47% of Americans have normal blood pressure, but the rate drops to 10% among elderly Americans.

“There’s a 10-fold increase in the likelihood of an event from the same level of blood pressure simply by being 30 years older,” Weber said. “Roughly speaking, for every eight to 10 years of increasing age, we double the risk of events and that’s surely something we can’t ignore.”

The case for change

Levy questioned whether a change in definition is necessary at this time. “We have existing guidelines, we just have not applied them. We have existing definitions, but we’re not listening to them,” Levy said.

Giles said the definition of hypertension has changed multiple times since JNC started issuing reports.

“I think JNC would like to take back the first two reports simply because they made no comment whatsoever on systolic blood pressure,” Giles said.

Weber stressed that the new definition of hypertension was a work in progress. “The title of this session was moving ‘toward’ a new definition of hypertension,” Weber said.

“I don’t think any of us in this room could pretend for one moment that we are yet in a position to fully define hypertension, but we need to describe a template, a paradigm, for us to look at hypertension more realistically.” – by Jeremy Moore

For more information:

• Giles TD. The new definition of hypertension.
• Levy D. Epidemiological considerations.
• Berk BC. Vascular biology of hypertension.
• Weber MA. Clinical implications of the new definition of hypertension.
• All presented at the American Society of Hypertension 20th Annual Scientific Meeting and Exposition. May 14-18, 2005. San Francisco.