On the spatial velocity electrocardiogram. I. Apparatus

Heart rate variability after acute traumatic brain injury in children

OBJECTIVE

To evaluate heart rate variability (HRV) by power spectral analysis of heart rate and its relationship to intracranial pressure (ICP), cerebral perfusion pressure (CPP), and outcomes in children with acute traumatic head injury.

DESIGN

Prospective, case series.

SETTING

Pediatric intensive care unit in a level II trauma center/children's hospital.

SUBJECTS

Fifteen critically ill children with documented acute traumatic brain injury and four control subjects.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The normalized total power from 0.04 to 0.15 Hz was used to quantify low-frequency HRV and from 0.15 to 0.40 Hz to quantify high-frequency HRV. The ratio of low- to high-frequency (LF/HF) power was used as a measure of sympathetic modulation of heart rate. The power spectral data from the 5-min samples were averaged over each hour of data collection, and an hourly LF/HF ratio was obtained based on a 60-min electrocardiogram collection (twelve 5-min segments). The daily mean LF/HF ratio was calculated from the hourly LF/HF measurements. We found no linear correlation between the LF/HF ratio and either ICP or CPP (p = NS). There was a significant decrease in the LF/HF ratio when the intracranial pressure was >30 mm Hg (p < .001) or the cerebral perfusion pressure was <40 mm Hg (p < .001). Children with a Glasgow Coma Scale score of 3-4 had a lower LF/HF ratio compared with those who had a Glasgow Coma Scale score of 5-8 (p < .005). Patients who progressed to brain death had a markedly lower LF/HF ratio (p < .001), with a significant decrease after the first 4 hrs of hospitalization. Patients with more favorable outcomes had significantly higher LF/HF ratios.

CONCLUSIONS

Our findings suggest that an ICP of >30 mm Hg or a CPP of <40 mm Hg may be associated with marked autonomic dysfunction and poor outcome. We speculate that HRV power spectral analysis may be a useful adjunct in determining the severity of neurologic insult and the prognosis for recovery in children. The LF/HF ratio may be helpful not only in identifying those patients who will progress to brain death but also in predicting which patients will have favorable outcomes.

The normal values of spatial velocity in the second part of QRS (a cooperative study of 229 healthy individuals)

The Spatial Velocity (SV) represents the inscription velocity from spatial vectors of the QRS loop. According to Sano, this parameter has revealed a diagnostic capacity for some well defined pathologies. Using Hellerstein and Hamlin's formula, the SV has been determined from the orthogonal Frank leads in a 250 mm/sec recording. Using Simonson's criteria, 229 normal individuals, arranged in seven groups according to age and sex, were used in an attempt to get normal values for the second half of the QRS loop. SV was determined in six time intervals of 2.5 msec from the 25 msec vector before the end of QRS. We found significant difference between the values obtained from each time interval, except in the 35--37.5 msec and 37.5--40 msec vectors. On the other hand, no significant differences were found among the normal individual groups. The 96th percentile distribution was used to get the normal extreme values in the entire group of individuals.