Heart rate variability as a prognostic marker in critically ill patients

Background: Heart rate variability (HRV) can be used to assess cardiac autonomic activity in critically ill patients. Heart rate variability is termed as fluctuation in the time interval between adjacent heartbeats. The equilibrium among the sympathetic and parasympathetic subgroups of the autonomic nervous system (ANS) is essential for the maintenance of systemic homeostasis and effective response to external stressors. Hence we aimed this study to determine whether heart rate variability can be used as a prognostic marker in critically ill patients. Methods: A cross-sectional study was conducted among 225 consecutive critically ill patients admitted to the medicine Intensive care unit (ICU) of AVBRH, Sawangi (Meghe) based on the inclusion and exclusion criteria. The selected participants were evaluated for 24 hours Heart Rate Variability (HRV) and APACHE 4 score. Outcomes like mortality and survival were corelated with 24 hours Heart Rate Variability and APACHE 4 score. Results: The variables were significantly associated (p<0.05) with Standard deviation of the average Normal-to normal HRV intervals (SDANN) and Standard deviation of the NN intervals (SDNN). The variables were also significantly associated (p<0.05) with the variable High frequency (HF), High frequency/Low frequency (LF/HF) ratio. LF/HF parameter was abnormal in 86% of patients who died as compared to 54% of the patients who survived (p-value <0.001). Conclusions: Out of the 225 participants, 20% died during the study period. APACHE 4, Glasgow coma scale (GCS) score, and LF were significantly and independently associated with mortality. Decrease in Low frequency parameter of 24 hours Heart Rate Variability identified mortality with accuracy of 74% with 81.2% specificity, and 46.7 % sensitivity