Differences in heart rate dynamics before the spontaneous onset of long and short episodes of paroxysmal atrial fibrillation.

BACKGROUND: Altered heart rate (HR) dynamics precede the spontaneous onset of atrial fibrillation (AF), but the factors related to the perpetuation and duration of paroxysmal AF episodes are not well established. This study was designed to test the hypothesis that HR dynamics preceding the onset of (AF) may influence the duration of AF.
METHODS: Traditional time and frequency domain HR variability indices, along with a short-term fractal scaling exponent (alpha(1)) and approximate entropy (ApEn), were analyzed in 20-minute intervals before 92 episodes of spontaneous paroxysmal AF in 22 patients without structural heart disease. AF episodes were divided into two groups according to the duration of the arrhythmia episodes.
RESULTS: The high-frequency (HF) spectral component in normalized units (nu) of heart rate variability was higher and low-frequency (LF) component lower before long (> 200 s, n = 41) compared to short (< 200 s, n = 51) AF episodes (HF nu; 40.1 +/- 14.8 vs 31.5 +/- 16.4, P < 0.0001 and LF nu; 59.9 +/- 14.8 vs 68.5 +/- 16.4, P < 0.0001). Short-term scaling exponent values also were lower before long compared to short AF episodes (e.g., alpha(1); 1.12 +/- 0.21 vs 1.24 +/- 0.23, P < 0.0001). Women had a larger number of long AF episodes than men, but the duration of AF was not related to any other clinical or demographic features or antiarrhythmic medication.
CONCLUSION: Increased HF oscillations and decreased short-term correlation properties of R-R intervals, reflecting altered sympathovagal balance before the onset of AF, predispose to perpetuation of spontaneous arrhythmia episodes in patients with vulnerability to paroxysmal AF and without structural heart disease.