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Occasional High Blood Pressure Risky, Too?

Study Finds Episodes of High Blood Pressure, Often Ignored, Boost Stroke Risk
WebMD Health News
Reviewed by Laura J. Martin, MD

March 11, 2010 -- Occasional high blood pressure readings are often dismissed as nothing to worry about, but a new study suggests this episodic high blood pressure is a strong predictor of strokes.

''We have shown that it is variations in people's blood pressure rather than the average level that predicts stroke most powerfully," says study lead author Peter Rothwell, MD, professor of clinical neurology at the Stroke Prevention Research Unit, John Radcliffe Hospital in Oxford, England.

The study, published in The Lancet, followed more than 2,000 patients who had a transient ischemic attack or TIA, a ''mini-stroke'' predictive of a larger stroke, and validated the results with results from three other studies, in finding the link between occasional high blood pressure and stroke risk.

The researchers focused on the systolic blood pressure reading, the top number in the measurement, reflecting the pressure when the heart contracts while pumping blood. Normal blood pressure readings are below 120/80 millimeters of mercury, or mmHg.

How much variability predicts stroke risk? ''One certainly sees an increased risk of stroke when the systolic blood pressure fluctuates 40 mmHg or more (say between 120 mmHg and 160 mmHg) even when mean [or average] blood pressure is very well controlled," Rothwell tells WebMD in an email interview.

Occasional High Blood Pressure and Stroke Risk: Study Details

Rothwell and his colleagues evaluated data from 2,435 patients who had been enrolled in the UK-TIA aspirin trial, which assigned patients with a recent TIA or ischemic stroke to take aspirin or a placebo. Rothwell's team evaluated only the 2,006 patients from this study who had TIAs but no strokes, to avoid compromising the results due to the effect of a recent stroke on blood pressure.

Blood pressure in these patients was measured once at every four-month follow-up visit during the study, which ran from 1979 to 1985.

The results from this study were validated by Rothwell's team with results from three other large studies, each involving more than 2,000 patients.

Occasional High Blood Pressure Predicts Stroke

Patients with the most variation in their systolic blood pressure over seven clinic visits were found six times more likely to have a stroke, Rothwell found.

The highest blood pressure readings were also associated with higher stroke risk. Those with the highest readings over the seven visits were 15 times more likely to have a stroke during the follow-up period.

Not all the patients were being treated for hypertension, Rothwell tells WebMD. "Variability was predictive of stroke in both groups," he says, treated and untreated. "Some had stable hypertension, some had episodic hypertension and some had stable normal blood pressure. The episodic hypertension group had the highest risk of stroke.''

In one of the studies, variability in blood pressure also predicted the risk of heart attacks.

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