Experts redefine hypertension

May 16 2005

Leading US hypertension experts unveiled a new definition of hypertension at the American Society of Hypertension Inc. (ASH) Twentieth Annual Scientific Meeting.

The group has expanded the definition of hypertension beyond the numbers obtained from a blood pressure reading, and instead, urge that blood pressure be viewed as a part of a patient’s overall risk for cardiovascular disease. The goal of the new definition of hypertension is to improve the way physicians conceptualize, diagnose and treat hypertension by encouraging them to think about the disease earlier than they commonly do now, with the ultimate goal of reducing the risk of cardiovascular disease linked to high blood pressure, such as heart attack and stroke.

“For many years we have defined hypertension primarily by blood pressure levels, but in many cases elevated blood pressure is an effect, and not the cause of hypertension,” said Dr. Thomas Giles, president of the American Society of Hypertension and professor of medicine at the Louisiana State University School of Medicine in New Orleans, LA. “Our new definition incorporates the presence or absence of risk factors, early disease markers and target-organ damage, and more accurately represents the different physiological abnormalities in the cardiovascular system and other organs caused by hypertension.”

The expanded classification criteria are intended to improve the identification of at-risk individuals at an earlier point in the progression of hypertension. It focuses greater attention on a patient’s overall, individual cardiovascular risk - blood pressure being an important part of this risk. Broader classification criteria should assist doctors in identifying patients who are at risk for cardiovascular problems, even when their blood pressure numbers fall in the ‘normal’ category.

The new definition of hypertension, developed by the Writing Group of the American Society of Hypertension (WG-ASH) characterizes the disease as a progressive cardiovascular syndrome with many causes that result in both functional and structural changes to the heart and vascular system. The authors of the new definition write that the early stages of hypertension can begin before an individual develops sustained elevated blood pressure, and can progress to damage in the heart, kidneys, brain, vasculature and other organs, often leading to premature morbidity and death. Cardiovascular disease is the number one cause of death in the US, followed by cancer and stroke, according to 2001 data released by the Centers for Disease Control and Prevention.

Federal guidelines published in 2003 classified hypertension by blood pressure measurements, establishing a systolic measurement, or the upper number, of 120 mm Hg, and a diastolic measurement, or the lower number, of 80 mm Hg as normal blood pressure. Higher blood pressure levels were graded in stages, with stage 2 hypertension – readings of 160/100 mm Hg and higher – being the most severe. The new WG-ASH definition of hypertension also includes staging of hypertension, but in addition to blood pressure measurements, takes into account other factors indicating cardiovascular risk. The new definition means that instead of relying on blood pressure numbers alone to predict each patient’s risk of developing cardiovascular disease, this risk must be assessed on an individual basis by taking several factors into account. Thus one person with a blood pressure of 130/80 mm Hg may have signs of damage to their heart, kidneys or eyes caused by high blood pressure – and thus be at high risk for cardiovascular disease – while another person with the same blood pressure reading may have no such organ damage, and therefore be at lower risk for a heart attack or stroke.

“As a physician, responding to a patient’s elevated blood pressure in isolation represents only a partial understanding of hypertension,” said Dr. Giles. “We now know that hypertension is associated with many measurable cardiovascular indicators beyond blood pressure measurements.”

The new definition also refines the concept of “prehypertension”, which was coined in the 2003 federal guidelines. The WG-ASH definition does not include “prehypertension” since the classification aims to identify some people with low blood pressure levels as actually hypertensive if they also exhibit early signs of vascular damage, thus prompting healthcare providers to offer treatment to this at-risk group. Alternately, under the WG-ASH definition, others with low blood pressure levels and no signs of vascular abnormalities are classified simply as normal, thus averting any stigma as their risk of cardiovascular disease is no different than that of the general population.

The WG-ASH definition is based on assessment of a patient’s global cardiovascular risk, including early markers of cardiovascular disease, and target-organ damage in addition to blood pressure levels. Cardiovascular risk factors include age, sex, lipid levels, body-mass index, smoking and family history of cardiovascular disease. Examples of early markers of cardiovascular disease are exaggerated blood pressure response to exercise or mental stress, small amounts of protein in the urine (microalbuminuria) or an impaired ability to process blood sugar. Hypertensive target-organ damage can occur in the heart, arteries, kidneys and eyes. Assessment of the presence of such damage is important in determining overall cardiovascular risk.

Hypertension experts speaking at the meeting noted that more research is needed to determine exactly how this new understanding of the disorder should be best translated into clinical practice. They predict that expanding the definition will lead to new approaches to hypertension research, and perhaps, to new ways to treat the disease. The WG-ASH hope that it will pave the way for further research aimed at investigating the early stages of hypertension and cardiovascular disease, and urge researchers and physicians to apply this new understanding of hypertension to the ultimate goal of reducing cardiovascular risk in patients.