Cardiac variability in critically ill adults:: Influence of sepsis

Objective: To evaluate, in critically ill adults, factors associated with impaired sympathovagal balance. Design: One-month inception cohort study. Setting: Twenty-six-bed medical intensive care unit of a teaching hospital. Patients: critically ill adults with an expected duration of intensive care unit stay of greater than or equal to 48 hrs were enrolled. Patients with permanent arrhythmia or cardiac pacing were not included. Interventions: None. Measurement and Main Results: Sympathovagal balance was assessed on the day after intensive care unit admission by the low-frequency/high-frequency ratio obtained from spectral components of heart rate signal: overall variability, low frequency, and high frequency. Results: Forty-one patients, 13 with sepsis and 28 without sepsis, were assessed. Predictors of low-frequency/high-frequency ratio with the automatic interaction detection method were sepsis and age. Binary logit analysis adjusted for age showed that sepsis remained a strong and independent factor of a low-frequency/high-frequency ratio of < 1.50, with an odds ratio of 3.63 (95% confidence interval, 1.47-9.01, p = .005). Use of mechanical ventilation, catecholamines, or sedation did not add any information. The use of the low-frequency/high-frequency ratio in diagnosing sepsis may be supported by a likelihood ratio for low frequency/high frequency < 1 at 6.47. Conclusions: This work suggests that impaired cardiac variability and notably sympathovagal balance (i.e., a low-frequency/high-frequency ratio < 1.0) may be a diagnostic test for sepsis.