Autonomic nervous system and paroxysmal atrial fibrillation: a study based on the analysis of RR interval changes before, during and after paroxysmal atrial fibrillation

Aims To evaluate the presence of an abnormal autonomic modulation before, during and immediately after paroxysmal atrial fibrillation (PAF). Methods and results We analysed Holter recordings of 65 patients with 110 PAF episodes lasting more then 30 s. Mean RR interval, co-efficient of variation and short-term heart rate variability were measured before, during and after PAF episodes. We observed a significant correlation between the coupling interval and both the cycle length measured from 30 min up to few cycles before PAF onset, and ventricular response. When comparing the heart rate variability (HRV) before and after PAF we observed a significant reduction of the low frequency/high frequency components (LF/HF) ratio (from 6.2±7.4 to 3.2±4.1). A short-long-short cycle sequence was detectable in 37 PAF onsets associated with a greater incidence of atrial ectopic beats and a greater LF component (62±25 vs. 53±27 normalised units) in comparison to the remaining episodes. When onsets were divided for a LF/HF ratio cut-off value of ≥2 to separate episodes with a predominant sympathetic, as opposed to those with a prevailing vagal (LF/HF<2) modulation, we observed opposite changes (from 9.1±7.8 to 4±3.7 and from 0.8±0.5 to 2±3.6, respectively) consistent with a recovery of a more physiological sympatho-vagal balance immediately after recovery of sinus rhythm. No changes in co-efficient of variation of ventricular response were detectable before PAF termination. Conclusions A predominant sympathetic modulation characterises the majority of PAF onsets whereas a vagal predominance was detectable in about 30% of episodes. These patterns are no longer detectable after recovery of sinus rhythm.