A study published in the New England Journal of Medicine July 18 suggests it may be time for the medical community to rethink its perception of diastolic blood pressure, which has long been considered inferior to systolic BP as a measure of cardiovascular wellness.
While the systolic vs. diastolic debate has persisted since the 1960s, it was the long-running Framingham Heart Study that first made headlines with results suggesting systolic hypertension was a more important predictor of CV outcomes than its diastolic counterpart. It was a finding backed by other research, and by 2000 the National High Blood Pressure Education Program’s latest clinical advisory statement had all but ignored diastolic hypertension.
Alexander C. Flint, MD, PhD, and colleagues with Kaiser Permanente attempted to clarify the relationship between outpatient systolic and diastolic BP and CV outcomes in a study of 1.3 million adults. The authors said the roles of both measurements were muddied in recent years after national guidelines redefined hypertension as a reading of 130/80 mm Hg or up.
Flint et al. performed a multivariable Cox survival analysis to examine the effect of the burden of systolic and diastolic hypertension on a composite outcome of MI, ischemic stroke or hemorrhagic stroke over a period of eight years. The team’s analysis controlled for demographic characteristics and comorbidities.
They found the burdens of systolic and diastolic hypertension each independently predicted adverse cardiovascular outcomes in patients. A continuous burden of systolic hypertension, at 140 mm Hg and up with a hazard ratio per unit increase in z score of 1.18, independently predicted the composite outcome, as did a continuous burden of diastolic hypertension at 90 mm Hg and up with a hazard ratio per unit increase in z score of 1.06.
When the authors conducted the same tests using the newer, lower threshold for hypertension—130/80 mm Hg—their results persisted.
“We found that systolic and diastolic hypertension independently predicted adverse outcomes, despite a greater effect of systolic hypertension,” they wrote. “We observed that the relationship between systolic blood pressure, diastolic blood pressure and adverse cardiovascular outcomes was not altered by choice of threshold—a finding that supports recent guideline changes that tightened blood pressure targets for high-risk patients.”
Systolic BP indeed seemed to have a greater bearing on CV outcomes—a J-curve relationship between diastolic BP and outcomes was explained at least in part by age, other covariates and a higher effect of systolic hypertension among people in the lowest quartile of diastolic BP. But Flint and colleagues said that, based on this study, it would be “inappropriate” to focus solely on systolic values, noting diastolic BP “ought not to be ignored.”
“Both systolic and diastolic hypertension contribute significantly to cardiovascular risk, regardless of the threshold used for hypertension,” they wrote.