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This New Study Changes Decades of Assumption About Interpreting Blood Pressure Readings

For decades, medical experts believed the “upper” systolic blood-pressure reading was a more important predictor of cardiovascular outcomes than the “lower” diastolic number. Cardiology guidelines have focused primarily on the former, and some experts have even recommended discounting the diastolic reading entirely. But new research disrupts this school of thought.

What Did the Study Find?

Published in the New England Journal of Medicine, the Kaiser Permanente study included more than 36 million blood-pressure readings from more than 1 million people — the largest of its kind. It found that both diastolic and systolic data can independently predict a patient’s risk of heart attack or stroke.

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For the study, researchers reviewed blood-pressure readings taken during outpatient visits between 2007 and 2016 from adult Kaiser Permanente members in Northern California. They learned that while systolic blood-pressure elevation had a greater impact on risk of heart attack or stroke, diastolic pressure also “influenced the risk of adverse cardiovascular events, regardless of the definition used for high blood pressure (≥140/90 mm Hg or ≥130/80 mm Hg),” according to research article.

(Recent changes in the American College of Cardiology and American Heart Association guidelines recommended tighter blood-pressure control in higher risk patients with hypertension.)

The authors also pointed out that this research relied on standardized oscillometric blood-pressure measurement at a near population-level scale. This is a strength, they note, because automated oscillometric measurements obtained by medical assistants have a lower risk of “white-coat hypertension” — or when being in a clinical setting raises a patient’s blood pressure.

“Because our data came from a comprehensive electronic medical record, rather than a billing and administrative database, we used rigorously identified covariates and outcomes,” the study explains. “We included every routine outpatient blood-pressure reading for every participant in the cohort, which allowed for a granular estimate of hypertension burden.”

What Does the Study Mean for Clinicians?

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“We should not ignore the diastolic number. This applies to everyone involved in the management of hypertension,” says Alexander C. Flint, MD, study co-author and Kaiser Permanente stroke specialist. “It’s important that doctors and nurses work to control both these numbers [diastolic and systolic], and it’s critical to bring this into everyone’s consciousness so it becomes routine clinical practice. If we only pay attention to the top number, we will be leaving some people behind in terms of blood pressure.”

Effect of Systolic and Diastolic Blood Pressure on Cardiovascular Outcomes, New England Journal of Medicine.

Last updated on 10/9/19.

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