Investigation of altered heart rate variability, nonlinear properties of heart rate signals, and organ dysfunction longitudinally over time in intensive care unit patients

PurposeTo investigate longitudinally over time heart rate dynamics and relation with mortality and organ dysfunction alterations in patients admitted to a multidisciplinary intensive care unit.MethodsData from 53 patients were used, with heart rate recorded from monitors and analyzed on a daily basis (every morning) for 600 seconds and sampling rate at 250 Hz, from admission to the intensive care unit until final discharge from the unit. Variance, which is a measure of heart rate variability; exponent α2; and approximate entropy (ApEn), which assess long-range correlations and periodicity within a signal, respectively; were measured and compared with every day Sequential Organ Failure Assessment Score (SOFA) and mortality.ResultsNonsurvivors had lower ApEn mean (greater periodicity in their signals) and minimum values compared to survivors (0.53 ± 0.25 vs 0.62 ± 0.23, P = .04; 0.24 ± 0.23 vs 0.48 ± 0.23, P = .01, respectively). Patients in better conditions with SOFA of less than 7 (mean value) had higher variance and ApEn (more variable, less periodic signals) than those with SOFA of 7 or higher (0.47 ± 0.51 vs 0.10 ± 0.65, P < .001; 0.67 ± 0.28 vs 0.49 ± 0.24, P < .001, respectively). The α2 exponent and variance were correlated with length of stay (r = 0.55, P = .02, and r = 0.53, P = .02, respectively) and minimum ApEn with mortality (r = 0.41, P = .01).ConclusionsLoss of variability and increase in periodicity in heart rate of critically ill patients are linked with parallel deterioration of organ dysfunction and high mortality.