High Prevalence of Cyclical Variation in Heart Rate before Nocturnal Episodes of Paroxysmal Atrial Fibrillation

OBJECTIVE: Nighttime onset of atrial fibrillation (AF) is sometimes associated with obstructive sleep apnea accompanied by a characteristic heart rate (HR) pattern known as cyclical variation of HR. The aim of this study was to evaluate whether cyclical variation of HR is prevalent in patients with nocturnal AF. METHODS: The subjects consisted of 34 patients (68±12 years) with paroxysmal AF, including 14 patients with daytime AF and 20 patients with nighttime AF. Holter electrocardiogram (ECGs) were examined for the presence of cyclical variation in HR and to quantify the HR variability within the 40-minute period preceding each AF episode using a fast Fourier transform (FFT) methods. RESULTS: Cyclical variation in HR was observed in 12 of 20 (60%) nighttime episodes and in only two of 14 (14%) daytime episodes. The prevalence of cyclical variation in HR was significantly greater in the nighttime AF episodes than in the daytime AF episodes (Chi=5.34, p<0.05). The mean frequency of cyclical variation in HR was 0.015±0.003 Hz. The mean power of the VLF (very low frequency) component (0.008-0.04 Hz) before the onset of AF was significantly greater in the nighttime AF episodes than in the daytime AF episodes. Among the nighttime AF episodes, the power of the HF (high frequency), LF (low frequency) and very low frequency (VLF) components increased significantly just before the onset of AF compared with that observed 40 minutes before onset. CONCLUSION: The high prevalence of cyclical variation in HR observed before nocturnal AF episodes suggests that sleep apnea may play a role in the onset of nighttime AF.