High BP and high risk of heart attack

Contrary to common belief, high systolic and high diastolic blood pressure (BP) are both strongly and independently linked to risks of heart attack and stroke, according to a new research study led by Kaiser Permanente. The findings have been published in a recent issue of the “New England Journal of Medicine”.

In a large study, which included more than 36 million BP readings from more than one million people, both the “upper” systolic and the “lower” diastolic BP readings independently predicted the risk of heart attack or stroke. The results run counter to decades of research indicating that high systolic BP is more likely than diastolic pressure to result in adverse outcomes.

“This research brings a large amount of data to bear on a basic question, and it gives such a clear answer,” said the lead author Alexander C. Flint, a Kaiser Permanente stroke specialist. “Every way you slice the data, the systolic and diastolic pressures are both important.” According to him, the current retrospective study is “the largest by far of its kind”, which analysed 36 million BP readings taken during outpatient visits between 2007 and 2016 from 1.3 million adult Kaiser Permanente members in Northern California.

Systolic pressure measures how hard the heart pumps blood into arteries. Diastolic pressure indicates the pressure on the arteries when the heart rests between beats. Decades of research have shown that high systolic blood pressure is more likely to result in adverse outcomes. As a result, cardiology guidelines and risk estimation tools focus on the upper number, with some experts arguing that the diastolic number might reasonably be ignored, Flint said.

After adjusting the data for possible confounding factors, the researchers found that while systolic pressure has a greater impact, both systolic and diastolic pressures strongly influenced the risk of heart attack or stroke, regardless of the definition used for high blood pressure (140/90 mm versus 130/80 mm mercury). The finding that systolic and diastolic hypertension have similar impacts on risk at the lower threshold of 130/80 provides independent support for recent changes that were made in the American College of Cardiology and American Heart Association guidelines, Flint said. It also conforms to the findings from the National Institutes of Health’s Systolic Blood Pressure Intervention Trial, known as SPRINT.

“Controversy has long persisted about whether systolic blood pressure, diastolic blood pressure, or both contribute to cardiovascular risk,” said the senior author Deepak L. Bhatt, executive director of Interventional Cardiovascular Services at Brigham and professor of medicine at Harvard Medical School. “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.”