Prolonged elevated heart rate and 28-day in-hospital mortality in patients with asthma-related critical illness: a multicenter retrospective cohort study.

BACKGROUND: Prolonged elevated heart rate (PeHR) has been reported to be associated with adverse outcomes in several critical illnesses, but its prognostic significance in patients with asthma-related critical illness remains unclear. This study aimed to evaluate the association between PeHR and 28-day in-hospital mortality in this population. METHODS: We conducted a retrospective cohort study using two large intensive care unit (ICU) databases, the Medical Information Mart for Intensive Care IV (MIMIC-IV) and the eICU Collaborative Research Database (eICU-CRD). The MIMIC-IV cohort included 2,355 ICU patients with a recorded diagnosis of asthma or status asthmaticus, and the eICU-CRD cohort included 1,575 patients as an external validation cohort. PeHR was defined as an hourly mean heart rate >100 beats per minute (bpm) for at least 11 hours within any consecutive 12-hour window. Cox proportional hazards models were used to evaluate the association between PeHR and 28-day in-hospital mortality. A 24-hour landmark analysis, subgroup analyses, and multiple sensitivity analyses were further performed. As an exploratory supplementary analysis, elastic-net models based on routinely available variables from the first 24 hours after ICU admission were developed to stratify the risk of 28-day in-hospital mortality after the 24-hour landmark and to assess the incremental predictive value of PeHR. RESULTS: In the MIMIC-IV cohort, 589 patients (25.0%) met the PeHR definition. The 28-day in-hospital mortality rate was higher in the PeHR group than in the no-PeHR group (11.4% vs. 2.2%). In the fully adjusted Cox model, PeHR was independently associated with increased 28-day in-hospital mortality [hazard ratio (HR), 2.75; 95% confidence interval (CI): 1.76-4.28; P<0.001]. This association was also observed in the eICU-CRD external validation cohort (HR, 1.70; 95% CI: 1.10-2.90; P=0.041). In the 24-hour landmark analysis, the association was attenuated but remained statistically significant in both cohorts (MIMIC-IV: HR, 1.46; 95% CI: 1.11-1.93; P=0.009; eICU-CRD: HR, 1.34; 95% CI: 1.05-1.71; P=0.02). Sensitivity analyses generally supported the main findings. Exploratory elastic-net models showed good risk-stratification performance in both internal and external validation, but adding PeHR did not materially improve discrimination, precision-recall performance, or calibration. CONCLUSIONS: Among patients with asthma-related critical illness, PeHR was independently associated with higher 28-day in-hospital mortality, with a similar direction of association observed in the external validation cohort and in the 24-hour landmark analysis. PeHR may serve as an easily obtainable and interpretable marker of short-term mortality risk; however, its incremental predictive value in multivariable prediction models appears limited and requires further prospective validation.