Baseline Diastolic BP and Effects of Intensive BP Control

Study Questions:

What is the impact of baseline diastolic blood pressure (DBP) on the effect of intensive systolic blood pressure (SBP) lowering on cardiovascular disease (CVD), kidney disease, and all-cause mortality rates?

Methods:

The investigators conducted this analysis in the SPRINT (Systolic Blood Pressure Intervention Trial) randomized controlled trial, which compared the effects of intensive (target <120 mm Hg) versus standard (target <140 mm Hg) SBP control in 9,361 older adults with high BP at increased risk of CVD. The primary outcome was a composite of CVD events. All-cause death and incident kidney disease were secondary outcomes. This post-hoc analysis examined whether the effects of the SBP intervention differed by baseline DBP. The association of baseline DBP with the primary and secondary outcomes was analyzed by fitting a Cox regression model with the randomized SBP intervention and cubic spline terms in baseline DBP as predictor variables, with covariable adjustment for age, sex, and race.

Results:

Mean baseline SBP and DBP were 139.7 ± 15.6 and 78.1 ± 11.9 mm Hg, respectively. Irrespective of the randomized treatment, baseline DBP had a U-shaped association with the hazard of the primary CVD outcome. However, the effects of the intensive SBP intervention on the primary outcome were not influenced by baseline DBP level (p for interaction 0.83). The primary outcome hazard ratio for intensive versus standard treatment was 0.78 (95% confidence interval [CI], 0.57-1.07) in the lowest DBP quintile (mean baseline DBP 61 ± 5 mm Hg) and 0.74 (95% CI, 0.61-0.90) in the upper four DBP quintiles (mean baseline DBP 82 ± 9 mm Hg), with an interaction p value = 0.78. Results were similar for all-cause death and kidney events.

Conclusions:

The authors concluded that low baseline DBP was associated with an increased risk of CVD events.

Perspective:

This post-hoc analysis suggests that while low baseline DBP was associated with an increased risk of the primary CVD outcome, an intervention that actively lowered SBP consistently reduced the risk of the primary CVD outcome across baseline quintiles of DBP. In this analysis, SBP lowering appears beneficial across the spectrum of baseline DBP, even among those in the lowest quintile of DBP at baseline. Given the post-hoc nature of this analysis, additional prospective studies to determine optimal DBP would be useful.


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