PURPOSE: Heart Rate Variability (HRV) allows noninvasive assessment of sympathovagal balance and has been associated with prognosis in heart failure. HRV may be useful in sepsis; it is unknown which parameters may provide the most utility. We studied frequency domain characteristics of HRV in septic patients.
METHODS: We prospectively identified patients with severe sepsis or septic shock within 12 hours of ICU admission. Electrocardiographic signal was collected at 500 Hz sampling rate from the patient monitor. Using in-house developed software, band pass filtering was performed, and the QRS peak was identified from the filtered signal using an adaptive threshold algorithm. Ectopic and post-ectopic beats and uninterpretable data were removed. Power spectral density (PSD) was calculated for the first 15 minutes of R-R interval time series using parametric autoregressive estimation for each of the following frequency bands: very low-frequency (VLF, 0-0.04 Hz), low-frequency (LF, 0.04-0.15 Hz), and high-frequency (HF, 0.15-0.40 Hz). We normalized LF and HF power as a fraction of total LF and HF power. We evaluated the relationship between frequency domain measures and admission Sequential Organ Failure Assessment (SOFA) score using Pearson’s Correlation.
RESULTS: Of 23 patients (57% female, median age 60), normalized LF power was inversely associated with admission SOFA score (Pearson’s rho -0.615, p = 0.002). The correlation was better when using a larger sample window (15 minutes, p = 0.002) rather than a smaller window (5 minute, p = 0.004). The LF/HF ratio (Pearson’s rho -0.45, p = 0.0432) and normalized HF (Pearson’s rho 0.471, p = 0.027) had weaker correlation.
CONCLUSIONS: LF power, generally associated with sympathetic tone, appears to be inversely associated with organ dysfunction in patients with sepsis, while HF power, generally associated with parasympathetic tone, was directly associated with organ dysfunction. Stability of this measure may require collection of 15 minutes of data.
CLINICAL IMPLICATIONS: LF and HF power of HRV may represent a simple, non-invasive assessment of disease severity among septic patients.
DISCLOSURE: The following authors have nothing to disclose: Subhasis Behera, Samuel Brown, Jason Jones, Michael Lanspa, Kathryn Kuttler, V. Mathews
HRV is a research tool currently. We are not describing or proposing a commercial product.