A study finds ultra-short heart rate variability recordings can reliably assess cardiac autonomic tone in patients with severe traumatic brain injury.
Published in Brain Medicine, the research shows time-domain heart rate variability (HRV) indices, particularly the root mean square of successive differences (rMSSD), exhibited high correlation and low variation between ultra-short (30-second and 1-minute) and standard 5-minute recordings.
The study analyzed electrocardiogram data from 48 patients one year after severe traumatic brain injury (TBI). Researchers compared HRV indices across 5-minute, 1-minute, and 30-second epochs using Pearson correlation analysis and ANOVA.
Key findings included:
- Time-domain indices showed higher correlation coefficients (r = 0.63 to 0.99, P < .05) compared to frequency-domain indices (r = 0.51 to 0.97, P < .05).
- rMSSD exhibited the highest reliability, with correlation coefficients of 0.99 (P < .05) for both 1-minute and 30-second epochs.
- Shorter recording times increased percentage variation for all indices, with rMSSD showing the lowest variation.
- No significant differences were found in mean HRV values between 5-minute and 1-minute epochs (P > .05), except for very low frequency (VLF) in some epochs.
- 30-second VLF epochs showed significant differences in mean values (F = 10.75, P = .0001).
The study included 39 men (81.25%) and 9 women (18.75%) with a mean age of 37.18 ± 15.56 years. Participants had a mean hospitalization duration of 30.60 ± 16.49 days and a mean intensive care unit stay of 15.00 ± 7.51 days.
Patient characteristics included:
- Glasgow Coma Scale (GCS) distribution: 29.79% had a score of 3, 8.51% had 4, 6.38% had 5, 12.77% had 6, 17.02% had 7, and 25.53% had 8.
- 82.98% of patients presented with isochoric pupils, while 17.02% had anisocoric pupils.
- Mean education level: 9.02 ± 2.99 years.
Injury characteristics were:
- Marshall CT classification: 10.64% Marshal I, 23.40% Marshal II, 44.68% Marshal III, 12.77% Marshal IV, 8.51% Marshal V.
- Subarachnoid hemorrhage (SAH) was present in 40.43% of patients.
- Associated trauma was observed in 61.70% of patients.
Lesion side predominance was:
- Right > Left: 37.5%
- Left > Right: 31.25%
- Not applicable: 31.25%
Glasgow Outcome Scale (GOS) at hospital discharge was:
- GOS 2: 2.08%
- GOS 3: 56.25%
- GOS 4: 35.42%
- GOS 5: 6.25%
Detailed HRV analysis results for 1-minute epochs showed:
- RR intervals: r = 0.981 to 0.991
- SDNN: r = 0.813 to 0.881
- HR: r = 0.986 to 0.991
- pNN50: r = 0.975 to 0.989
- LF: r = 0.796 to 0.891
- HF: r = 0.879 to 0.972
For 30-second epochs, results were:
- RR intervals: r = 0.971 to 0.989
- SDNN: r = 0.673 to 0.870
- HR: r = 0.976 to 0.990
- pNN50: r = 0.966 to 0.985
- LF: r = 0.418 to 0.818
- HF: r = 0.874 to 0.960
Percentage variation of mean HRV indices across 1-minute epochs was:
- RR: 0.32%
- HR: 0.47%
- SDNN: 11.43%
- rMSSD: 0.97%
- pNN50: 1.08%
- VLF: 42.38%
- LF: 7.34%
- HF: 6.29%
For 30-second epochs, percentage variation was:
- RR: 0.35%
- HR: 0.52%
- SDNN: 16.55%
- rMSSD: 0.46%
- pNN50: 1.30%
- VLF: 72.04%
- LF: 7.34%
- HF: 6.29%
ANOVA results showed a significant difference in mean VLF values for 30-second epochs (F = 10.75, P = .0001). Post hoc analysis revealed significant differences in some SDNN 30-second epochs (F = 1.17, P = .32 for ANOVA, but P < .05 for post hoc comparisons of the 1st and 4th epochs).
Methods:
Electrocardiographic recordings were performed using a Nihon Kohden amplifier sampled at 512 Hz. Patients were recorded in a supine position between 2 and 4 PM. The first 5 minutes of artifact-free recording were analyzed using Kubios v2.3 software. Ag/AgCl electrodes were placed in a triangular chest configuration. Muscle artifact epochs (<2%) were identified through visual inspection and excluded from analysis.
HRV indices calculated included mean RR intervals, mean heart rate, SDNN, rMSSD, pNN50, VLF, LF, and HF. Fast Fourier transform using a Hanning window of 256 seconds width with 50% overlap was used for frequency domain indices analysis.
Statistical analysis included Shapiro-Wilk tests for normality, ANOVA for comparing mean HRV values across epochs, and Pearson correlation with Bonferroni correction for multiple comparisons.
The researchers note that while SDNN and frequency domain indices showed significant correlations with 5-minute recordings, they exhibited greater variance in mean values compared to rMSSD. The results were obtained under controlled conditions and may not fully reflect typical hospital environments.
The authors declared having no competing interests.