Ill effects of blood pressure variability disputed

By Eleanor McDermid, Senior medwireNews Reporter

The effect of visit-to-visit blood pressure (BP) variability on mortality may be partly caused by changes in average values over time, say researchers.

Instead, Sujuan Gao (Indiana University School of Medicine, Indianapolis, USA) and colleagues found that people with the smallest BP change over time had the lowest risk for all-cause and cardiovascular mortality. This finding is “not surprising”, they say, given that both high and very low BP have been linked to vascular risk in previous studies.

The study included 2906 patients aged at least 60 years. During up to 15 years of follow-up (median 12.9 years), 1711 (59%) patients died, with 305 dying of coronary heart disease (CHD) and 123 of stroke.

Overall, patients’ average baseline systolic (S)BP did not predict mortality or death from CHD or stroke during follow-up, and neither did SBP variability, after accounting for age, gender, race, smoking status and body mass index.

The researchers defined BP variability as the variability around the slope of participants’ BP over time. They say that the standard deviation (SD) is often used as a proxy for BP variability, but this cannot distinguish between people with a large rise or fall in BP over time, and those whose BP fluctuates around an unchanging average value.

“Thus, previous reports of increased cardiovascular disease and mortality risk with higher BP SD could be attributable to BP change over time”, they write in Hypertension.

When divided into groups according to BP change over time, patients with marked declines in BP had an increased mortality risk, as did those with marked increases. Patients with marked increases in BP had a similar mortality risk regardless of whether they had small or large BP variability, and variability also had no effect on risk among those with little or no BP change over time.

Conversely, patients with declining SBP over time had a higher mortality risk if they had little SBP variability, at a hazard ratio of 1.67 relative to those with marked increases and high variability, than if they had large variability, at a nonsignificant hazard ratio of 0.95. This pattern did not appear for CHD and stroke mortality, however.

The researchers suggest that larger BP variability might reflect “an intact or healthier cardiovascular system to accommodate BP increases, for example, when one exercises.”

They conclude: “It will be interesting to re-evaluate previous studies to determine how much of the reported association between increased variability and disease risks was accounted for by BP changes over time.”

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