Abstract

BACKGROUND
An acceleration or deceleration of the heart rate (HR), which reflects autonomic effects, is observed before the onset of paroxysmal atrial fibrillation (PAF). The purpose of this study was to assess the discrepancy in the autonomic interactions before the onset of PAF for different patterns of change in the HR. MATERIALS AND METHODS: From 105 Holter tapes with the PAF recorded, 55 episodes (42 patients, 34 men, 58+/-12 years) of PAF (>5 min), preceded by a sinus rhythm for more than 1 hour, were selected and submitted to time-domain and frequency-domain HR variability analyses. Fifty-five episodes were divided into 2 groups: group A PAF (n=30) with acceleration of the HR during the last 2 minutes before the PAF and group B (n=25) with deceleration of the HR. RESULTS: A significant linear decrease in the mean R-R interval was observed in group A (924+/-30 to 835+/-28 ms, P=0.001) and an increase from 831+/-32 to 866+/-31 ms in group B PAF episodes (P=0.046). In the frequency-domain analyses, the LF/HF ratio exhibited a progressive linear increase before the PAF in group A (P=0.005). The HF normalized units (HFnu) and natural logarithm-transformed HF (lnHF) values decreased from 30.8+/-4.0 to 16.1+/-1.8 (P=0.003) and 4.49+/-0.25 to 4.07+/-0.22 (P=0.001), respectively. Contrary to the results in group A, a significant increase in the HF components (HFnu and lnHF) (from 22.6+/-3.2 to 30.2+/-4.0, P=0.005, and 4.27+/-0.27 to 4.75 0.33, P=0.001, respectively) and a resultant decrease in the LF/HF ratio were observed in group B PAF episodes. No significant changes were observed in the LF components in either PAF group. CONCLUSION: Autonomic stimuli leading to an acceleration or deceleration of the HR before the onset of AF are due to parasympathetic modulation. Parasympathetic modulation plays a key role in the initiation of PAF

• Keywords: Atrial Fibrillation;Autonomic Nervous System;Heart Rate;Variability;