[Circadian structure of cardiac rhythm in tachyarrhythmia]

To determine clinical implication of changes in the structure of circadian cardiac rhythm in patients with tachyarrhythmia basing on estimation of the circadian index (CI).

24-h Holter monitoring was conducted in 154 patients aged 4 to 18 years: 125--with supraventricular paroxysmal tachycardia, 13--with long Q-T interval, 16--with idiopathic ventricular tachycardia. CI was calculated as mean day heart rate (from 7.00 to 22.00)/mean night heart rate (from 23.00 to 6.00).

Patients with long Q-T interval had less CI while those with supraventricular paroxysmal and idiopathic ventricular tachycardia had higher CI vs normal values. CI changes became more pronounced with growing disease severity.

Cardiac arrhythmia with low CI is associated with progressive vegetative denervation while that with high CI occurs in increased cardiac sensitivity to sympathetic impacts.