Circadian Distribution and Autonomic Tone Modulation in Paroxysmal Atrial Fibrillation

Abstract

Understanding the role played by autonomic tone changes in the initiation of paroxysmal atrial fibrillation (PAF) may be helpful in preventing the occurrence of the arrhythmia. The purpose of this review article is to discuss the relationship between sympathovagal imbalance and the initiation of PAF from past literature and our data regarding circadian distribution and heart rate variability (HRV) analysis in PAF. PAF in non-structural heart disease (NHD) frequently occurs during evening and night hours with a longer duration of each episode, and its initiation is directly associated with an increase in vagal tone. According to our data of HRV analysis in NHD, HF power (indicator of vagal tone) showed a reduction 15 to 30 minutes before PAF, followed by a sharp increase immediately before the onset, suggesting a primary increase in sympathetic tone followed by a marked changes toward vagal predominance. Very few studies have been reported on PAF onset or the modulation of autonomic tone in structural heart disease (SHD). Some studies showed no significant differences in the circadian variation of the onset between NHD and SHD. However, we demonstrated a triphasic circadian pattern with maximum peaks in early morning, late afternoon, and night in SHD, suggesting an association with not only a vagally induced origin but also a sympathecally induced or stress triggered origin in PAF onset in SHD. The occurrence of PAF greatly depends on modulation of autonomic tone and is extremely complicated. Further studies are required to clarify the relationship between the occurrence of PAF and autonomic modulation. (J Arrhythmia 2008; 24: 122-132)