BP variability link to stroke risk reinforced

By Eleanor McDermid

Analysis of data from the Women's Health Initiative (WHI) supports the contention that variability in a person's blood pressure (BP) affects their risk for stroke.

The possible link between BP variability and stroke risk was first highlighted 2 years ago by Peter Rothwell (John Radcliffe Hospital, Oxford, UK) in several articles in The Lancet and The Lancet Neurology.

Speaking to MedWire News, Rothwell said of the current study: "I think one of the encouraging things is that it's not a clinical trial population… It's good to see that in a large study of people not taking blood-pressure-lowering drugs [BP] variability is still predictive."

He remarked that BP variability is something that could add to existing scores, rather than being a risk factor in itself. "There are lots of things that are risk factors but don't really add much when you put them in the context of everything else."

The analysis, which appears in Hypertension, included 58,228 postmenopausal women who had 997 strokes during a median 5.4 years of follow up. The annual stroke rate rose in line with the variability in the women's visit-to-visit BP (ie, the standard deviation [SD] of their average BP during follow up), from 0.20% for a SD of less than 6 mmHg to 0.49% for a SD of 13 mmHg or more.

After accounting for a raft of baseline variables, and average BP, heart rate, and antihypertensive medication use during follow up, this equated to a 16% increase in stroke risk for each 5 mmHg rise in BP variability.

The association remained significant after Daichi Shimbo (Columbia University Medical Center, New York, USA) and team further adjusted for increases in average BP over time (by calculating the SD about the regression line), at a 12% increased risk per 5 mmHg rise.

Consistent with Rothwell's previous findings, Shimbo et al found the strongest effect of BP variability to be among women with relatively low average systolic BP - below 120 mmHg.

"As mean blood pressure rises, then other factors will be proportionally less important," explained Rothwell. "If your mean blood pressure is 160 or 170 [mmHg] systolic then you've got a problem, probably irrespective of whether you're variable."

In another study published this week, in Circulation, Giuseppe Mancia (University of Milano-Bicocca, Italy) and colleagues found no association between BP variability and cardiovascular events (including stroke, myocardial infarction, and all-cause death) in 1521 patients in the European Lacidipine Study on Atherosclerosis.

However, Rothwell said: "The only claims we've made for blood pressure variability was that it's important for stroke and I think that the evidence that it's important for MI [myocardial infarction] or for heart failure or for sudden death is less good."

He added: "Blood flow in the coronary arteries only occurs in diastole so you wouldn't expect necessarily fluctuations in systolic blood pressure to do much to the heart, whereas they might do a lot more to the kidneys and the brain."

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