Change of autonomic influence on the heart immediately before the onset of spontaneous idiopathic ventricular tachycardia.

OBJECTIVES: This study aimed to assess heart rate variability immediately before the onset of episodes of spontaneous ventricular tachycardia.
BACKGROUND: It has been shown that decreased heart rate variability may be associated with a propensity to ventricular tachyarrhythmias. However, it is still disputed whether there is an abrupt change in heart rate variability immediately before the onset of these arrhythmias.
METHODS: Twenty-three patients with idiopathic ventricular tachycardia underwent two-channel 24-h Holter monitoring in a drug-free state. Spectral heart rate variability was computed as low (0.04 to 0.15 Hz) and high (0.15 to 0.40 Hz) frequency components at 2-min intervals over a 1-h period immediately before the onset of ventricular tachycardia. Average values of heart rate variability were also computed for the entire 24-h recordings. The low/high frequency component ratio was calculated as an index of the autonomic balance of the heart.
RESULTS: Seventy-one episodes of ventricular tachycardia from the 23 recordings formed this study. There was an increased low/high ratio during 6- to 8-min periods immediately before the onset of ventricular tachycardia episodes compared with the average values for the entire 24 h. This increase in the low/high ratio resulted largely from a decrease in the high frequency component value (4.70 +/- 1.15 vs. 5.10 +/- 1.06 ln[ms2] [mean +/- SD], p = 0.001) because there was no significant change in the low frequency component value (6.37 +/- 1.20 vs. 6.34 +/- 0.91 ln[ms2], p = 0.786, 95% confidence interval -0.25 to 0.19 ln[ms2], type II error < 0.0001 for change of 7.8%). In contrast, there were no significant differences in the low or high frequency components or low/high ratio between 6-min salvo-free periods 40 min before the onset of ventricular tachycardia and the average 24-h values (type II error < 0.0001, < 0.038 and < 0.1841, respectively, for change of 7.8%). The low/high ratio was also significantly higher during the 6 min immediately before the onset of ventricular tachycardia compared with that during the 6-min salvo-free periods 40 min before the onset of ventricular tachycardia. A significant increase in mean heart rate immediately before the onset of ventricular tachycardia was also noted.
CONCLUSIONS: There is a significant change in autonomic influence on the heart during the last few minutes preceding the onset of episodes of idiopathic ventricular tachycardia. This seems to result mainly from decreased vagal activity rather than enhanced sympathetic input to the heart.