Sleep related bradyarrhythmic events and heart rate variability in apparently healthy individuals

OBJECTIVE It is thought that abnormal cardiac impulses of the autonomic nervous system during sleep are responsible for sleep-related bradyarrhythmias. Despite a proposed common etiopathogenesis and having common name of "sleep-related bradyarrhythmias," precise importance of sinoatrial or atrioventricular (AV) node involvement remains elusive. This study aimed to determine whether there is a difference in sleeprelated bradyarrhythmias from the point of view of heart rate variability (HRV). METHODS Patients were evaluated using 24-hour Holter electrocardiogram monitor. After careful medical evaluation, apparently healthy individuals with sleep-related sinus pauses ≥2 seconds on at least 1 occasion or those in whom Mobitz type I AV block occurred were included. Frequency and time domain analyses were conducted for daytime, nighttime, and 24-hour period. RESULTS Total of 37 patients with sinus pause(s), 40 patients with Mobitz type I AV block(s), and 40 healthy controls were included. On HRV analyses, all time and frequency domain parameters were better in sinus pause group for daytime, nighttime, and 24-hour average (p<0.05 for all). Results of heart rate-corrected HRV analyses still showed significantly better total power (TP) and very low frequency (VLF) in the sinus pause group compared with AV block group (TP: 7.1x10-3 vs. 5.4x10-3, p=0.011; VLF: 4.9x10-3 vs. 3.7x10-3, p=0.007). CONCLUSION Despite proposed common autonomic mechanisms, sleep-related sinus pause cases demonstrated better HRV profile in comparison with Mobitz type I AV block.