Occasional High Blood Pressure Risky, Too?

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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