Association between long-term blood pressure variability and mortality among incident hemodialysis patients

Background: Blood pressure variability (BPV) is one putative risk factor for cardiovascular disease and mortality in hemodialysis patients. The purposes of this study are to identify a suitable metric of long-term BPV in this population and determine whether an association between BPV and all-cause mortality exists. Study Design: Retrospective cohort study. Settings & Participants: Patients from the Accelerated Mortality on Renal Replacement (ArMORR) cohort who were adult, incident to hemodialysis at any Fresenius Medical Care unit between June 2004 and August 2005, and had suitable blood pressure data were studied (n = 6,961). Predictor: Predialysis blood pressures measured between dialysis days 91 and 180 were used to determine each patient's absolute level of, trend in (slope over time), and variability in blood pressure. Outcome: All-cause mortality beginning immediately after day 180 and continuing through day 365 or until censoring (median follow-up, 185 days). Results: Of the 4 candidate BPV metrics, only average residual-intercept ratio adequately distinguished BPV from absolute blood pressure level and temporal blood pressure trend. In the primary analysis, each SD increase in systolic and diastolic BPV was associated with adjusted hazard ratios for all-cause mortality of 1.13 (95% confidence interval, 1.03 to 1.23) and 1.15 (95% confidence interval, 1.06 to 1.26), respectively. Results were consistent across multiple sensitivity analyses in which inclusion and exclusion criteria and timing of blood pressure measurements were varied. Limitations: Contingency of results on the validity of mathematic description of BPV; potential for misclassification bias and residual confounding. Conclusions: Provided the mathematical descriptions of BPV are valid, the data suggest that systolic and diastolic BPV is associated with all-cause mortality in incident hemodialysis patients. Additional study is necessary to confirm and generalize findings, assess the interplay between systolic and diastolic BPV, and assess causality.