Association between circadian variation of heart rate and mortality among critically ill patients: a retrospective cohort study

Background Heart rate (HR) related parameters, such as HR variability, HR turbulence, resting HR, and nighttime mean HR have been recognized as independent predictors of mortality. However, the influence of circadian changes in HR on mortality remains unclear in intensive care units (ICU). The study is designed to evaluate the relationship between the circadian variation in HR and mortality risk among critically ill patients. Methods The present study included 4,760 patients extracted from the Multiparameter Intelligent Monitoring in Intensive Care II database. The nighttime mean HR/daytime mean HR ratio was adopted as the circadian variation in HR. According to the median value of the circadian variation in HR, participants were divided into two groups: group A (<= 1) and group B (> 1). The outcomes included ICU, hospital, 30-day, and 1-year mortalities. The prognostic value of HR circadian variation was investigated by multivariable logistic regression models and Cox proportional hazards models. Results Patients in group B (n = 2,471) had higher mortality than those in group A (n = 2,289). Multivariable models revealed that the higher circadian variation in HR was associated with ICU mortality (odds ratio [OR], 1.393; 95% confidence interval [CI], 1.112-1.745; P = 0.004), hospital mortality (OR, 1.393; 95% CI, 1.112-1.745; P = 0.004), 30-day mortality (hazard ratio, 1.260; 95% CI, 1.064-1.491; P = 0.007), and 1-year mortality (hazard ratio, 1.207; 95% CI, 1.057-1.378; P = 0.005), especially in patients with higher SOFA scores. Conclusions The circadian variation in HR might aid in the early identification of critically ill patients at high risk of associated with ICU, hospital, 30-day, and 1-year mortalities.