Nocturnal and Sleep Heart Rates Linked to All-Cause Mortality

October 25, 2007 — Nocturnal heart rate measures from awake levels as well as heart rate during sleep are associated with all-cause mortality, according to the results of a study reported in the October 22 issue of the Archives of Internal Medicine.
"Although it has been somewhat overlooked, resting heart rate is an established predictor of cardiovascular and noncardiovascular outcome," write Iddo Z. Ben-Dov, MD, from the Hadassah–Hebrew University Medical Center in Jerusalem, Israel, and colleagues. "We assessed the determinants and mortality associations of heart rate measured during ambulatory blood pressure monitoring (ABPM) to evaluate its informativeness during activity and sleep."
The study cohort consisted of 3957 patients who were referred for ABPM from 1991 to 2005. Mean age was 55 ± 16 years; 58% of patients were treated for hypertension. Nondipping of heart rate was defined as (awake value − sleep value)/awake value < 0.1. Covariate associations with ambulatory heart rate indices were determined from linear and logistic regression models, and all-cause mortality was evaluated with Cox proportional hazards modeling.
Positive correlates of awake and sleep heart rates were female sex, body mass index, and treated diabetes. In contrast, age and treated hypertension were inversely associated with awake and sleep heart rates. All of these variables were associated with a lower magnitude of sleep-related dipping of heart rate.
Multivariate-adjusted odds ratios (ORs) for nondipping of heart rate during sleep were 1.02 (95% confidence interval [CI], 1.02 - 1.03) per year of age, 1.05 (95% CI, 1.03 - 1.06) for body mass index, 1.39 (95% CI, 1.20 - 1.60) for female sex, 1.30 (95% CI, 1.12 - 1.51) for daytime naps, 2.19 (95% CI, 1.87 - 2.57) for treated hypertension, and 1.38 (95% CI, 1.09 - 1.76) for treated diabetes.
Mortality analysis based on deciles of the different heart rate variables showed that only dip in heart rate had a robust linear relationship, with a hazard ratio (HR) of 2.67 (95% CI, 1.31 - 5.47) for the lowest vs the highest decile.
"In clinical practice, ambulatory heart rate adds prognostic information beyond that of other ABPM predictors," the study authors write. "Heart rate measures during sleep, and in particular the absence of dipping of heart rate to sleep levels, were independently associated with all-cause mortality.... We suggest that a sympathetic overactive state may be better represented by an elevated sleeping heart rate than by the clinic heart rate (owing in part to poor standardization of the latter and the white coat effect) or by the awake heart rate (owing to its dependence on physical activity and fitness as well as sympathetic drive)."
This study was supported in part by a research prize from the Israel Society of Hypertension. The study authors have disclosed no relevant financial relationships.
Arch Intern Med. 2007;167:2116-2121.