Sex Differences in Nocturnal Ventricular Repolarization Variability

The objective of this study was to investigate sex differences in nocturnal repolarization variability. We analyzed polysomnographic recordings of 2,263 participants enrolled in the Sleep Heart Health Study. In addition to standard heart rate variability (HRV) parameters, we extracted beat-to-beat QT interval variability (QTV) parameters from consecutive epochs of 5 minutes by employing two-dimensional signal warping. We used a general linear mixed model (GLMM) to investigate the relationship between extracted parameters and sex under consideration of clinical and sleep characteristics. The GLMM shows a significant differences (P < 0.001) of sex on QTV, T wave amplitude and standard HRV parameters. In addition, the GLMM shows significant effects of sleep stages and age. While standard deviation of QT intervals is significantly higher in females than males (P < 0.001), T wave amplitude is about 30 % lower (P < 0.001) in females than in males. Applying T wave amplitude correction to QTV to minimize within-group variability and removed sex-related differences (P = 0.581). A demonstrated difference in uncorrected QTV is 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.