A new study has shown that both systolic and diastolic blood pressure readings can predict the risk of heart attack or stroke in patients. This 'flies in the face' of years of believing that only high systolic blood pressure was the key indicator.
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The study used data from millions of outpatients
A Kaiser Permanente study was conducted on 36 million blood pressure readings from more than 1 million patients. The study, which was published today in the New England Journal of Medicine, could overturn decades of assumptions regarding blood pressure readings and heart attack/stroke risk.
The Kaiser Permanente Northern California Community Benefit Program, who supported the study, is one of America's leading health care providers and not-for-profit health plans. It was founded in 1945 and currently provides health care to 12.3 million members in eight states in the District of Columbia.
Lead author Alexander C. Flint, MD, Kaiser Permanente stroke specialist and adjunct researcher with the Division of Research said, "This research brings a large amount of data to bear on a basic question, and it gives such a clear answer."
"Every way you slice the data, the systolic and diastolic pressures are both important," he added.
For quick reference these terms mean:
Systolic pressure - AKA the "upper number" in a blood pressure reading measures how hard the heart pumps blood into arteries.
Diastolic pressure - This is the "bottom number" that indicates the pressure on the arteries when the heart rests between beats.
The study used a very large data set
The study used a large data set of 36 million readings from over 1 million patients. Reading data was from outpatients between 2007 and 2016.
The current retrospective study is "the largest by far of its kind," Dr. Flint said.
Dr. Flint notes that prior to this study medical professionals had always assumed that high systolic blood pressure was more potentially dangerous for patients than diastolic pressure. Because of this many cardiology guidelines and risk estimators tended to focus on the upper number.
Many even believed the diastolic number could be ignored altogether. But, as their study has discovered, this appears to be something of a potential oversight.
The study team, after adjusting the data for possible confounding factors, found that while systolic pressure has a greater impact, both systolic and diastolic pressures strongly influenced the risk of heart attack or stroke.
This, they say, is regardless of the definition used for high blood pressure (140/90 mm Hg versus 130/80 mm Hg).
It's time for change
In light of this, Dr. Flint and his team found that systolic and diastolic hypertension have similar impacts on the risk at the lower threshold of 130/80.
In this sense, the study provides independent support for recent changes that were made in the American College of Cardiology and American Heart Association guidelines.
These guidelines recommended tighter blood pressure control in higher-risk patients with hypertension. The results are also in keeping with findings from the National Institutes of Health's Systolic Blood Pressure Intervention Trial, known as SPRINT.
Senior author Deepak L. Bhatt, MD, MPH, executive director of Interventional Cardiovascular Services at Brigham and Women's Hospital and professor of medicine at Harvard Medical School said, "controversy has long persisted about whether systolic blood pressure, diastolic blood pressure or both contribute to cardiovascular risk."
"This analysis using a very large amount of longitudinal data convincingly demonstrates that both are important, and it shows that in people who are otherwise generally healthy, lower blood pressure numbers are better," he added.
The original study was published in the New England Journal of Medicine.