Association between nighttime heart rate and cardiovascular mortality in patients with implantable cardioverter-defibrillator: A cohort study

BACKGROUND Although studies have shown that an increased resting heart rate measured randomly at a single point of the day has been associated with adverse cardiovascular outcomes, the utility of continuous monitoring of nighttime heart rate (NTHR) has remained largely uninvestigated. OBJECTIVE This study aimed to explore the association between NTHR and cardiovascular mortality.METHODS The Study of Home Monitoring System Safety and Efficacy in Cardiac Implantable Electronic Device-implanted Patients, which isa prospective cohort study, enrolled patients with implantable cardioverter-defibrillator (ICD) or cardiac resynchronization therapy defibrillator between 2010 and 2015. Baseline NTHR was measured during the programmed sleep period from 30 to 60 days after implantation. The primary outcome was cardiovascular mortality, fitted by a restricted cubic spline function.RESULTS A total of 534 implantable cardioverter-defibrillator recipients with sinus rhythm during the detection window were included in the study. The mean baseline NTHR was 59.6 +/- 8.0beats/min. During the follow-up period of 60.4 +/- 21.8 months, 88 (16.5%) patients experienced cardiovascular mortality. After considering potential confounders, a linear association was observed. Each 1 beat/min increase in NTHR was associated with a 7.8%, 10.1%, and 5.7% increase in the risk of cardiovascular mortality in the total population, patients with heart failure, and patients without heart failure, respectively.CONCLUSION Continuous monitoring of NTHR may identify patients at high risk of cardiovascular mortality in a timely manner, with the potential for "preemptive" action.TRIAL REGISTRATION No. ChiCTR-ONRC-13003695.