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Researchers find lowering systolic blood pressure reduces incidence of stroke

Washington University In St Louis : 26 July, 2000  (Technical Article)
Researchers have found that many strokes can be prevented by medications that lower isolated systolic hypertension, a condition that appears after the age of 55 and increases with age. Historically, physicians have paid more attention to diastolic blood pressure, but this study found that lowering systolic pressure below 160 mm Hg (millimeters of mercury) lowered the stroke rate by one third. And decreasing systolic pressure to lower than 150 reduced stroke risk even more.
In the July 26, 2000 issue of the Journal of the American Medical Association, H. Mitchell Perry, M.D., professor emeritus of medicine at Washington University School of Medicine and Physician Coordinator for Hypertension for the U.S. Department of Veterans Affairs, and colleagues report that controlling systolic pressure helps prevent both hemorrhagic and ischemic strokes.

Hemorrhagic strokes are caused by the rupture of blood vessels in the brain. Ischemic strokes are the result of interrupting blood flow to the brain, either because of a clot or plaque buildup inside a vessel supplying blood to the brain.

'The decrease in the incidence of strokes in those who achieved systolic blood pressure goals of less than 160 or less than 150 mm Hg should encourage physicians and patients to strive for such goals,' Perry said. 'Our findings strongly suggest that the level of systolic blood pressure is the main factor in reducing the incidence of stroke.'

Perry and colleagues examined data from the Systolic Hypertension in the Elderly Program, a double-blind, randomized, placebo-controlled trial designed to learn whether drug treatment to lower blood pressure would reduce the frequency of strokes.

The SHEP study was conducted at 16 clinical centers around the United States. It followed more than 4,700 men and women who were 60 and older and had isolated systolic hypertension. The systolic number is the upper number in a blood pressure reading. Patients with isolated systolic hypertension have a systolic blood pressure of 140 mm Hg or higher and a diastolic pressure below 90 mm Hg.

In SHEP, patients were randomly assigned either to an inactive placebo or the antihypertensive diuretic drug, chlorthalidone. Those patients on active treatment whose blood pressure was not controlled received a second drug, the beta-blocker atenolol. Those participants unable to take beta-blockers received low doses of the drug reserpine.

At the end of the trial, 46 percent of those randomized to active treatment were receiving only the step one study drug and 23 percent were receiving the step one and step two study drugs. However, almost 90 percent of those in the active treatment group were receiving some blood pressure-lowering drug throughout the study.

Some of those enrolled in the studyís placebo group also took other drugs to lower blood pressure. The percentage increased steadily from only 13 percent at one year to 44 percent by year five.

When the study concluded, 65 percent of those in the active systolic treatment group and 40 percent in the placebo group were at the studyís systolic blood pressure goal: a decrease of 20 mm Hg to a systolic blood pressure below 160 mm Hg.

Perry and colleagues found that effectively lowering systolic blood pressure reduced the incidence of all strokes, both hemorrhagic and ischemic. There were significantly fewer ischemic strokes among those in the active treatment group than among those in the placebo group (85 vs. 132).

Due to the small number of hemorrhagic strokes that occurred during the study (9 vs. 19), the difference between treatment and placebo groups was not statistically significant. The decrease in hemorrhagic strokes seemed to occur during the first year of treatment, while the decrease in ischemic strokes did not occur until the second year of treatment.

There was no significant difference in the percentage of fatal strokes. 'Although there were 65 percent more fatal strokes among placebo participants than among active treatment participants, in both groups just under 10 percent of the strokes that did occur were fatal,' Perry said.

Perry notes that while the two groupsí nursing home admissions and Activities of Daily Living scores were similar, the consistently fewer days of reduced activity, including days in bed, suggests that participants in the active treatment group were less disabled when they had a stroke than were those in the placebo group.
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