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Novel method to quantify loss of heart rate variability in pediatric multiple organ failure
Shane M Tibby1, Helena Frndova, Andrew Durward
1Department of Critical Care Medicine, Hospital for Sick Children, Toronto, Canada.
Insights
A new power-law model effectively measures heart rate variability (HRV) in children with organ failure (OF). This model shows declining HRV with increasing OF, outperforming traditional methods in sensitivity and discrimination.
Area of Science:
- Pediatric critical care medicine
- Biomedical engineering
- Physiology
Background:
- Heart rate variability (HRV) is a crucial indicator of autonomic nervous system function.
- Assessing HRV in critically ill children, particularly those with organ failure (OF), presents unique challenges.
- Established HRV measurement methods may have limitations in sensitivity and applicability in this population.
Purpose of the Study:
- To develop and validate a novel power-law model for quantifying HRV in pediatric patients.
- To compare the efficacy of the power-law model against traditional time-domain, frequency-domain, and nonlinear HRV analysis methods.
- To investigate the relationship between HRV, as measured by the power-law model, and the severity of organ failure in children.
Main Methods:
- A prospective, observational study was conducted in a pediatric intensive care unit.
- Heart rate was recorded for 5-minute intervals in 50 pediatric patients (0-16 years) with varying degrees of organ failure (OF).
- A power-law model was applied to HRV data, with comparisons made to standard HRV metrics including time-domain, frequency-domain, and detrended fluctuation analysis.
Main Results:
- The power-law model demonstrated consistent reliability (r2 ≈ 0.87, slope ≈ -1.80) across all patients, irrespective of organ failure severity.
- HRV, quantified by the power-law model's x-intercept, significantly decreased with increasing organ failure (p < 0.001), independent of age or heart rate.
- While all methods indicated reduced HRV with OF, the power-law model uniquely discriminated between different levels of organ failure and correlated with changes in patient status.
Conclusions:
- The power-law model provides a robust and sensitive measure of HRV in pediatric patients, unaffected by age or heart rate.
- Increasing organ failure is associated with a significant decline in HRV, a finding more accurately captured by the power-law model.
- This novel model offers a valuable tool for monitoring autonomic function and disease progression in critically ill children with organ failure.
Objective:
To develop a power-law model for measurement of heart rate variability (HRV) and to compare this model with established methods for measuring HRV in a group of children with organ failure (OF).
Design:
Prospective, observational study.
Setting:
Pediatric intensive care unit of a tertiary children's hospital.
Patients:
A total of 104 measurements were made on 50 patients (median age, 8 months; range, 2 days to 16 yrs) and categorized into three groups according to the number of simultaneous organs failing: 0-1 OF, 2 OF, and >/=3 OF.
Interventions:
Heart rate was recorded over a 5-min period when patients were hemodynamically stable. The power-law model represents a power function relating frequency distribution to magnitude of effect (in this case, squared deviation from the mean heart rate). Plotting the data on a bi-logarithmic scale produces a regression line for each measurement, described in terms of r2, slope, and x-intercept. Comparison with other HRV measures included two time-domain measures (sd of the normal R-R intervals and the square root of the mean squared differences of successive normal R-R intervals), one frequency-domain method (power spectral analysis), and one nonlinear method (detrended fluctuation analysis).
Measurements And Results:
For the power-law model, patients exhibited a similar r2 of.87 (.09) (mean [sd]) and slope of -1.80 (0.29), regardless of the degree of OF. HRV could thus be described purely in terms of x-intercept, which demonstrated a left shift with increasing OF (p <.001). This was independent of age and heart rate. Loss of HRV with increasing OF was demonstrated by all methods; however, only the power-law model was able to discriminate between each OF group. Using the model, change in HRV in individual patients over successive days often concurred qualitatively with the change in OF status.
Conclusion:
The power-law model is an appropriate measure of HRV in pediatric patients, being neither age nor heart rate sensitive. Loss of HRV occurs with increasing OF; this effect was better demonstrated by the model compared with other measures of HRV.
