Blunted heart rate dip during sleep and all-cause mortality

Although it has been somewhat overlooked, resting heart rate is an established predictor of cardiovascular and noncardiovascular outcome. 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.

We studied a cohort of 3957 patients aged 55 +/- 16 (mean +/- SD) years (58% treated for hypertension) who were referred for ABPM during 1991 to 2005. Heart rate nondipping was defined as follows: (awake value - sleep value)/awake value < 0.1. Linear and logistic regression models assessed covariate associations with ambulatory heart rate indices. All-cause mortality was analyzed by Cox proportional hazards modeling.

Female sex, body mass index (calculated as weight in kilograms divided by height in meters squared), and treated diabetes were positively related to awake and sleep heart rate, whereas age and treated hypertension were inversely associated. All these variables were associated with lower sleep-related heart rate dipping magnitude. Multivariate-adjusted odds ratios (95% confidence intervals) for heart rate nondipping were 1.02 (1.02-1.03) per year of age; 1.05 (1.03-1.06) for body mass index; 1.39 (1.20-1.60) for women; 1.30 (1.12-1.51) for nappers; 2.19 (1.87-2.57) for treated hypertensive patients; and 1.38 (1.09-1.76) for treated diabetic patients. Mortality analysis according to deciles of the different heart rate variables showed a robust linear relationship only for heart rate dip and a hazard ratio of 2.67 (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. 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.