BACKGROUND: Heart rate (HR) was one of the risk factors for cardiovascular disease, but there was insufficient evidence to demonstrate a relationship between heart rate fluctuations and the prognosis of patients with acute myocardial infarction (AMI). The objective of this study is to investigate the relationship between 24-h heart rate fluctuations after admission to the Intensive Care Unit (ICU) and 30-day, 1-year, and 3-year mortality rates in patients with AMI in order to examine its implications for prognosis in AMI patients.
METHODS: All data were obtained from the Medical Information Mart for Intensive Care III Database (MIMIC III). We calculated heart rate fluctuations using the maximum and minimum values of the patient's heart rate during the first 24 h after ICU admission and divided them into three groups (< 23beats/min, 23-33beats/min, > 33beats/min) according to tertiles. The COX risk regression model was applied to the analysis, and subgroup analyses were performed for use in testing the robustness of the results. Curve fitting was performed to explore whether there was a nonlinear relationship between heart rate fluctuations and mortality. Outcome measures were 30-day, 1-year, and 3-year mortality in patients with AMI.
RESULTS: After strict confounding adjustment, COX multifactorial analysis showed that patients' heart rate fluctuations were positively associated with 30-day, 1-year, and 3-year mortality rates (HR = 1.17, 95%CI: 1.11 ~ 1.23; HR = 1.17, 95%CI: 1.12 ~ 1.22; HR = 1.17, 95%CI: 1.12 ~ 1.21). In addition, the high heart rate fluctuation group (> 33 beats/min) had a significantly increased risk of death (HR = 1.76, 95%CI: 1.28 ~ 2.42; HR = 1.59, 95%CI: 1.25 ~ 2.03; HR = 1.43, 95%CI: 1.15 ~ 1.77). In the curve-fitting analysis, a J-shaped curve relationship among heart rate fluctuations and 1- and 3-year mortality was found (p for non-linearity = 0.049; p for non-linearity = 0.004), with an inflection point of 28 beats/min. In subgroup analyses, there was an interaction between heart rate fluctuations and age (P for interaction = 0.041).
CONCLUSIONS: Heart rate fluctuations within 24 h after ICU admission of AMI patients were associated with 30-day, 1-year, and 3-year mortality, which is a simple and stable predictor of patients' short- and long-term prognosis. Furthermore, 24-h heart rate fluctuations showed a "J" curve relationship with 1- and 3-year mortality, with fluctuations of 28 beats/min predicting the best prognosis.
