Could heart rate variability analysis become an early predictor of imminent brain death? A pilot study

Physiology of brain death is characterized by major disturbances of autonom ic nervous system (ANS) activity which can lead to graft dysfunction. These findings exhibit the importance of early diagnosis of brain death to impro ve transplantation outcome. The aim of this prospective study was to assess whether heart rate variability (HRV) analysis, a noninvasive method to inv estigate ANS activity in comatose patients, could achieve this goal. A tota l of 14 brain-injured patients were included in the study as soon as they e xhibited the clinical signs of imminent brain death. The electrocardiogram was then recorded from two leads with a Holter digital monitor. The clinica l diagnosis of brain death was considered after an autonomic storm had occu rred. HRV was assessed from 6 h before to 6 h after brain death in both tim e domain and spectral analysis, estimating either global ANS activity tinde r of variability, total power), parasympathetic activity (percentage of del ta of R-R interval >50 ms, root mean square for successive interval differe nces, LnHF) or sympathetic activity (LnLF). Hourly averages of these variab les were compared by using one-way analysis of variance. To assess whether HRV could per se diagnose brain death, receiver operating characteristic cu rves were generated for total power, root mean square for successive interv al differences, and LnHF. We observed, for 6 h before brain death, a progre ssive extinction of the influence of the ANS on cardiovascular regulation. There was no activity in the two components of the ANS as soon as brain dea th occurred. HRV analysis appeared to be a very sensitive but a less specif ic method of diagnosing brain death.