Objective: We hypothesized that analysis of heart rate variability (HRV) in VLBW neonates on the first day of life (DOL #1) could prospectively identify those who would develop severe intraventricular hemorrhage (IVH).

Design: We prospectively studied all newborns born weighing less than 1500 gr. On DOL #1, between 12 and 24 hours of age, we obtained a single 256 second heart rate trace and a cranial ultrasound for each neonate. These studies were repeated at one week of age. No recordings were obtained from neonates during dopamine infusion > 5 mcg or exposure to narcotics within the preceding four hour period. Power spectra for both low-frequency variability (LFP, 0.05 - 0.2 Hz) and high-frequency variability (HFP, 0.2 - 1.0 Hz) were calculated by Fast Fourier Transform. Only neonates who were mechanically ventilated the time of the DOL#1 heart rate recording are discussed here. We used the Mann-Whitney U-test to compare both HFP and LFP in neonates with severe IVH (grades III and IV) and without severe IVH (none, grade I, and grade II).

Results: On DOL #1, neonates who were subsequently found at one week of life to have severe IVH had less HFP than those neonates who did not(n= 7 and 34, respectively; p= 0.02). This result may be generalizable to LFP as the size of our study grows (p= 0.11). These groups were not different with respect to birthweight, narcotic or sedative exposure, or FiO2 requirement at the time of study. None of the neonates with severe IVH at one week (n= 7) on whom DOL#1 cranial ultrasounds were available (n= 5) had severe IVH at that time. Of 41 neonates studied on DOL#1, follow-up heart rate recordings were available for 31. We found no differences in either HFP or LFP between neonates with and without severe IVH at this time (n=7 and 24, respectively; p= 0.78 and 0.30, respectively).

Conclusion: Transient changes in autonomic tone may precede radiographic evidence of severe IVH. HRV analysis may be a functional index of autonomic tone and a reflection of CNS integrity with potential to predict poor outcomes in VLBW neonates.