Sleep is known to modulate the activity of the autonomous nervous system and thereby heart rate variability (HRV). QT interval variability (QTV) is also affected by autonomous nervous system, but reports on its behavior during sleep are highly inconsistent. Both, physiological and technical influence factors, might contribute to existing inconsistencies. While many previous studies failed to prove an impact, we recently demonstrated a significant impact of sleep stages on ventricular repolarization variability. The objective of this study was to investigate the relationship between nocturnal repolarization variability and sex.
We analyzed polysomnographic recordings of 2,263 participants enrolled in the Sleep Heart Health Study. In addition to standard HRV parameters, we extracted beat-to-beat QT interval parameters from consecutive epochs of 5 minutes by employing two-dimensional signal warping. We used a general linear mixed model (GLMM) to investigate in the relationship between extracted parameters and sex under consideration of clinical and sleep characteristics.
The GLMM shows a significant impact (P < 0.001) of sex to QTV, T wave amplitude and standard HRV parameters. In addition, the GLMM shows significant effects on sleep stages and age. While standard deviation of QT intervals is significantly (P < 0.001) higher in females than males, T wave amplitude is about 30 % lower (P < 0.001) in females than in males. Applying T wave amplitude correction to QTV minimized within-group variability and removed sex-related differences (P = 0.587).
We demonstrated a significant sex difference in nocturnal QTV. This difference is likely due to lower T wave amplitudes in females. By applying a correction formula, we can account for T amplitude differences. Corrected QTV measures might yield improved characterization of autonomic nervous system activity during sleep.