Twenty-four-hour heart rate power spectrum for evaluation of autonomic dysfunction in Guillain-Barré syndrome.

Long-term fluctuations of the heart rate have an important prognostic impact after myocardial infarction, in patients with chronic heart failure and even in elderly subjects. Autonomic dysfunction is a common complication in patients with Guillain-Barré syndrome, and particularly vagally-mediated bradyarrhythmias require early recognition for immediate initiation of appropriate preventive therapy. This study aimed at investigating (1) whether the 24-h heart rate power spectrum (HRPS) could be used as a measure of autonomic dysfunction also in patients with GBS, and (2) whether the slope of the regression line of power on frequency of the 24-h HRPS could indicate potentially fatal bradyarrhythmias in these patients. In 13 patients with GBS, the heart rate was continuously recorded in the intensive care unit during the early stages of the disease, averaged at 1-min intervals and stored for 4 to 82 days. The HRPS (n = 76, 2 to 14 per patient, median 5) was calculated by Fourier analysis of 24-h recordings and logarithmically transformed. The slope was estimated by regression analysis of log(power) on log(frequency) between 10(-4) and 4x10(-3) Hz demonstrating an inverse power law behaviour in all 76 HRPS. The slope of the regression line ranged from -0.66 to -2.18, and was significantly steeper in patients with tachycardia (median -1.51, interquartile range -1.35 to -1.71) than in those with vagal overreactivity (median -1.14. -1.02 to -1.23) who are suspected to be at risk for fatal arrhythmias. Correlation analysis suggested that the slope was moderately associated with the spectral components of 5-min epochs, but not significantly to standard tests of autonomic hypofunction. Patients with and without vagal overreactivity were better discriminated by the 24-h HRPS than by conventional measures of autonomic function. Therefore, the 24-h HRPS may be a useful adjunct to autonomic nervous system testing, and might be a promising tool to predict serious bradyarrhythmias in patients with GBS.