Systolic, Diastolic BP Both Contribute to Cardiovascular Risk

July 25, 2019

Both systolic and diastolic hypertension are significant contributors to cardiovascular risk, regardless of the threshold used for hypertension, a large study of more than 1.3 million people shows.

"Controversy has long persisted about whether systolic blood pressure, diastolic blood pressure, or both contribute to cardiovascular risk. This analysis convincingly demonstrates that both are important, and it shows that in people who are otherwise generally healthy, the lower the blood pressure, the better," senior author Deepak L. Bhatt, MD, Brigham and Women's Hospital, Boston, Massachusetts, told Medscape Medical News.

"These findings are supportive of the NIH-sponsored SPRINT trial [Systolic Blood Pressure Intervention Trial] results and are in keeping with the latest recommendations from the ACC/AHA guidelines," he added.

The study was published in the July 18 issue of the New England Journal of Medicine.

Independent CV Risk Factors

For the study, the researchers analyzed data on more than 36 million blood pressure measurements in 1.3 million outpatients from Kaiser Permanente Northern California (KPNC), a large integrated health care delivery system.

Cardiovascular outcomes — a composite of myocardial infarction, ischemic stroke, or hemorrhagic stroke — were recorded over an 8-year observation period. During that time 44,286 outcome events occurred.

Researchers calculated the prevalence of hypertension using two thresholds (≥140/90 mm Hg and ≥130/80 mm Hg) from the 2017 ACC/AHA guidelines.  For the threshold of 140/90 mm Hg, 18.9% of the measurements showed hypertension, whereas for the threshold of 130/80 mm Hg, 43.5% of the measurements showed hypertension.

Systolic blood pressure measurements indicating hypertension increased as a function of age, whereas diastolic blood pressure measurements indicating hypertension peaked in the fifth decade of life.

Results showed that after controlling for demographic characteristics and coexisting conditions, the burdens of systolic and diastolic hypertension each independently predicted adverse outcomes.

Systolic hypertension (≥140 mm Hg) was associated with a greater risk (hazard ratio per unit increase in z score, 1.18) than diastolic hypertension (≥90 mm Hg; hazard ratio per unit increase in z score, 1.06).  

The investigators found similar results with the lower threshold of hypertension (≥130/80 mm Hg).

Lower Is Better

The investigators found a 'J-curve' relationship between diastolic blood pressure and outcomes, which investigators note was explained, at least in part, by the relationship to age and other covariates. 

They also note "systolic hypertension had a greater effect in the group of participants with lower diastolic blood pressures, an observation that had been previously reported to explain the J-curve."

However, they note that the study's outpatient cohort had "a low prevalence of coronary artery disease and a direct J-curve relationship may be of greater importance in patients with active coronary artery disease or in those with conditions involving end-organ microcirculatory abnormalities."

"With respect to the 'J curve' for diastolic blood pressure issue," said Bhatt, "it is still wise to be cautious about excessively aggressive blood pressure lowering in patients who are of advanced age, frail, or with critical cerebrovascular or coronary artery disease.

"Our study was a relatively healthy cohort, but other studies in patients with CAD suggest that a diastolic of less than 70 mm Hg may be associated with unfavorable cardiovascular outcomes."

However, he said, controversy persists as to whether there is some degree of confounding that explains part of the J-curve.

"Perhaps the real issue," Bhatt explained, "is older people with stiff atherosclerotic arteries with elevated systolic blood pressure and lowish diastolic blood pressures are really at increased risk because of the stiff arteries, or a wide pulse pressure, or the elevated systolic blood pressure that is difficult to treat without creating side effects — more so than the low diastolic blood pressure per se. Blood pressure is actually very complex."

"But the message from our paper is simpler: in generally healthy people, lower blood pressure is better," he concluded.

Adopt ACC/AHA Guidelines

Commenting on the study for Medscape Medical News, Michael A. Weber, MD, professor of medicine at SUNY Downstate College of Medicine in New York City, noted these new data "are supportive of the recent ACC/AHA hypertension guidelines since they establish 130/80 mmHg as well as 140/90 mmHg as thresholds above which there are clear increases in myocardial infarction and stroke event rates." 

Weber, who was not involved with the current study, agreed with Bhatt on the interpretation of the J-shaped curve for diastolic pressure.  

"The diastolic J-curve has reported several times previously," Weber said. "However, in general, low diastolic BPs appear to predict risk mainly when they are associated with high systolic BPs. In other words, in patients with wide pulse pressures (difference between systolic and diastolic measurements), which in turn are indicative of arterial stiffness and disease."

The study, he said, confirms this understanding since high systolic BPs appeared to help explain the diastolic J-curve.

In addition, said Weber, the SPRINT trial showed "the best cardiovascular protection with low achieved systolic BP values (around 120 mm Hg), even though diastolic BPs were often reduced down to the low-to-mid 60s."

The findings from this new report, he added, should encourage practitioners to adopt the ACC/AHA guidelines to diagnose hypertension at BP levels of 130/80 mm Hg and above, and to treat patients to levels below 130/80 mm Hg.

This study was supported by a grant from the Kaiser Permanente Northern California Community Benefit Program. Bhatt has disclosed no relevant financial relationships.

N Engl J Med. Published online July 18, 2019. Abstract

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