Middle-aged adults with long-term fluctuations in blood pressure may face a higher risk for sudden cardiac death than their peers with more consistent blood pressure readings, a large new study suggests.

The findings, which showed people with the greatest variability in blood pressure faced up to a nearly 70% greater risk for sudden cardiac death than people with the least variability, were recently presented at the American Heart Association's Scientific Sessions in Chicago. They are considered preliminary until full results are published in a peer-reviewed journal.

"Blood pressure variability is not just numbers on a chart," said the study's lead researcher, Ritam Patel, a second-year medical student at Northwestern University Feinberg School of Medicine in Chicago. "It's telling us something powerful about this hidden risk that we haven't been able to quantify before. For the millions of people who are measuring their blood pressure, there is incentive to go beyond the numbers and try to maintain stability."

A large body of research has shown that uncontrolled high blood pressure greatly increases the risk for heart disease, stroke, dementia and other chronic illnesses. As people get older, they are more likely to develop the condition, which affects nearly half of adults in the U.S.

With many people monitoring their blood pressure, researchers have more recently begun to investigate what happens when blood pressure readings fluctuate over time and have found links between variability and the risk for cardiovascular disease, chronic kidney disease, cognitive decline and mental illnesses.

The new study looked at the association between fluctuations in blood pressure measurements and sudden cardiac deaths, regardless of whether initial blood pressure readings were high, low or in the normal range.

Researchers analyzed data from 23,499 people who were 53 years old on average at the start of the study. They had their blood pressure measured at least three times over an average 15 years. Then they were followed for up to 30 years to track sudden cardiac deaths.

On average, systolic blood pressure – the top number that measures the force against artery walls when the heart beats – varied by about 11 to 12 millimeters of mercury, or mmHg. Diastolic pressure – the bottom number that measures the same force between beats – fluctuated about 6 to 7 mmHg.

After adjusting for health factors that could have affected the results, researchers found that for every 1 mmHg greater systolic blood pressure variability, the risk for sudden cardiac death rose 3%. Compared to people with the most consistent blood pressure readings, people with the largest fluctuations faced about a 40% to 70% higher risk for sudden cardiac death. The findings on variability were independent of whether blood pressure was higher or lower to begin with, and how much it rose with aging.

Cardiologist Dr. Donald Lloyd-Jones, a professor of preventive medicine at Feinberg and the study's senior investigator, said the findings suggest tracking blood pressure variability "may help us understand who is at greatest risk for sudden cardiac death so that it can be prevented."

"We think of blood pressure as one number, but it varies across days, months, years," he said. "As people monitor their blood pressure over time, and as electronic health records give us access to variability data, it may help us better flag those people at risk for sudden cardiac death."

The findings suggest that blood pressure variability data could "add depth to our understanding of that patient's cardiovascular risk profile," Patel said. "It gives us a chance to save lives before the condition becomes too serious. It opens a whole new window for prevention."

Lloyd-Jones said the study did not look at how or why blood pressure variability affected heart health, but that one possible explanation might be the fluctuations created extra stress on the body.

"Our body is designed to respond to stimuli and the response often takes time to mobilize over hours and days," he said. "Yo-yoing in any form, whether related to weight or blood pressure, places extra stress on the system because it is responding constantly."

What's causing blood pressure to fluctuate should be the next focus for investigators, said Dr. Wanpen Vongpatanasin, a professor in the department of internal medicine at UT Southwestern Medical Center in Dallas and director of its hypertension section in the division of cardiology.

"It's so hard to say what might explain this association," said Vongpatanasin, who was not involved in the research. "It could be that adherence to medication is not good or it could be a lifestyle issue or weight loss cycling that's causing blood pressure to fluctuate and the heart might not be able to cope with the demands of this stress."

For now, it's something to pay more attention to, she said. "If we knew the actual mechanics for driving yo-yo blood pressure readings, we could have better tools to reduce the consequence on the heart."

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