Cardiac autonomic function score: a novel risk stratification tool in the cardiac intensive care unit based on periodic repolarization dynamics and deceleration capacity of heart rate (LMU-eICU study).

Aims: Treatment capacities on intensive care units (ICUs) are a limited resource reserved for high-risk patients. To facilitate risk stratification of ICU patients, several scoring systems have been developed over time. Among them, the Simplified Acute Physiology Score 3 (SAPS3) is the gold standard, but lacks specificity for cardiac ICU patients. Here, we propose a novel, fully automated, electrocardiogram-based cardiac autonomic risk stratification score (CAF_ICU) that substantially adds to current risk stratification strategies.

Methods and results: CAF_ICU is based on periodic repolarization dynamics, a marker of sympathetic overactivity and deceleration capacity of heart rate, a parameter of vagal imbalance. We developed CAF_ICU in a retrospective cohort of 355 ICU patients and subsequently validated the score in a cohort of 702 ICU patients, enrolled between February-November 2018 and December 2018-April 2020 at a large cardiac ICU in a tertiary hospital. The primary endpoint of the study was 30-day intrahospital mortality. Thirty (8.5%) and 100 (14.2%) patients reached the primary endpoint in the training and validation cohorts, respectively. CAF_ICU was significantly higher in non-survivors than survivors (2.58 ± 1.34 vs. 1.76 ± 0.97 units; P = 0.003 in the training cohort and 2.20 ± 1.05 vs. 1.70 ± 0.83 units; P < 0.001 in the validation cohort) and was a strong predictor of mortality in both the training [hazard ratio (HR) 25.67; 95% confidence interval (CI) 3.50-188.40; P = 0.001] and validation cohorts (HR 4.70; 95% CI 2.79-7.92; P < 0.001). In the pooled cohort, CAF_ICU significantly improved risk stratification based on SAPS3 (IDI-increase 0.033; 95% CI 0.010-0.061; P < 0.001).

Conclusion: ECG-based automatic autonomic risk stratification by means of PRD and DC is highly predictive of short-term mortality in the ICU and can be combined with the SAPS3-Score to identify patients with increased risk for intrahospital mortality. This method can be integrated in conventional monitors and may improve risk stratification strategies in cardiac ICUs.