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 immediat ely before the onset of episodes of spontaneous ventricular tachycardi a. 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 hea rt rate variability immediately before the onset of these arrhythmias. Methods. Twenty-three patients with idiopathic ventricular tachycardi a underwent two-channel 24-h Holter monitoring in a drug-free state. S pectral heart rate variability was computed as low (0.04 to 0.15 Hz) a nd 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 e ntire 24-h recordings. The low/high frequency component ratio was calc u lated as an index of the autonomic balance of the heart. Results. Se venty-one episodes of ventricular tachycardia from the 23 recordings f ormed this study. There was an increased low/high ratio during 6 to 8- min periods immediately before the onset of ventricular tachycardia ep isodes compared with the average values for the entire 24 h. This incr ease in the low/high ratio resulted largely from a decrease in the hig h frequency component value (4.70 +/- 1.15 vs. 5.10 +/- 1.06 ln[ms(2)] [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[ ms(2)], p = 0.786, 95% confidence interval -0.25 to 0.19 In[ms(2)], ty pe II error < 0.0001 for change of 7.8%). In contrast, there were no s ignificant differences in the low or high frequency components or low/ high ratio between 6-min salve-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 l ow/high ratio was also significantly higher during the 6 min immediate ly before the onset of ventricular tachycardia compared with that duri ng the 6-min salve-free periods 40 min before the onset of ventricular tachycardia. A significant increase in mean heart rate immediately be fore the onset of ventricular tachycardia was also noted. Conclusions. There is a significant change in autonomic influ ence on the heart du ring the last few minutes preceding the onset of episodes of idiopathi c ventricular tachycardia. This seems to result mainly from decreased vagal activity rather than enhanced sympathetic input to the heart.