Derivation and validation of diagnostic thresholds for central blood pressure measurements based on long-term cardiovascular risks

Abstract

Objectives: This study sought to derive and validate outcome-driven thresholds of central blood pressure (CBP) for diagnosing hypertension.

Background: Current guidelines for managing patients with hypertension mainly rely on blood pressure (BP) measured at brachial arteries (cuff BP). However, BP measured at the central aorta (central BP [CBP]) may be a better prognostic factor for predicting future cardiovascular events than cuff BP.

Methods: In a derivation cohort (1,272 individuals and a median follow-up of 15 years), we determined diagnostic thresholds for CBP by using current guideline-endorsed cutoffs for cuff BP with a bootstrapping (resampling by drawing randomly with replacement) and an approximation method. To evaluate the discriminatory power in predicting cardiovascular outcomes, the derived thresholds were tested in a validation cohort (2,501 individuals with median follow-up of 10 years).

Results: The 2 analyses yielded similar diagnostic thresholds for CBP. After rounding, systolic/diastolic threshold was 110/80 mm Hg for optimal BP and 130/90 mm Hg for hypertension. Compared with optimal BP, the risk of cardiovascular mortality increased significantly in subjects with hypertension (hazard ratio: 3.08, 95% confidence interval: 1.05 to 9.05). Of the multivariate Cox proportional hazards model, incorporation of a dichotomous variable by defining hypertension as CBP ≥ 130/90 mm Hg was associated with the largest contribution to the predictive power.

Conclusions: CBP of 130/90 mm Hg was determined to be the cutoff limit for normality and was characterized by a greater discriminatory power for long-term events in our validation cohort. This report represents an important step toward the application of the CBP concept in clinical practice.

Keywords: BP; CBP; CI; DBP; PP; SBP; blood pressure; central blood pressure; confidence interval; cuff BP; diagnostic thresholds; diastolic blood pressure; high blood pressure; hypertension; peripheral blood pressure; pulse pressure; systolic blood pressure.

Copyright © 2013 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1. The Sensitivity and Specificity of Cuff SBP and Central SBP for Predicting Cardiovascular Mortality in the Derivation Cohort

With increasing systolic blood pressure (SBP) cutoff values, specificity (SPE) improved at the expense of decreasing sensitivity (SEN). Reasonable cutoff limits for central SBP can then be determined by approximating based on the sensitivity or specificity of the guideline-endorsed cuff SBP cutoff points as demonstrated in Table 3. cuff BP = peripheral blood pressure.

Figure 2. Performance of the CBP Diagnostic Thresholds in the Validation Cohort

Incorporating the dichotomous variable of defined hypertension based on different central blood pressure (CBP) Levels (x-axis) and the resulting contribution (Wald Chi-square and model R2) to the predictive power of the Cox proportional hazards model are shown. A CBP cutoff limit of 130/90 mm Hg was associated with a higher Wald chi-square and model R2 than other thresholds.