Twenty QT intervals selected at random from the middle periods of rapid eye movement (REM) and quiet sleep were measured in 12 normal infants studied at 2 weeks and 1, 2, 3, and 4 months of life. A digitizing system, consisting of a precision rotational potentiometer mounted on a pair of calipers and an A/D converter, was used for measurements. An accuracy of ±2 msec was achieved by high resolution of the digitized signal and calibration of each QT measurement with an accurately generated time code. Sleep staging was done visually using an electroencephalogram (EEG), an electrooculogram (EOG), a submental electromyogram (EMG), and behavioral criteria. Our results show that the QT index (QTc = QT/□RR was significantly greater during quiet sleep (mean = 0.439) than during REM sleep (mean = 0.433) (P < 0.01) and that this difference existed at all ages studied.Speculation
Sleep states are shown to have detectable effects on the duration of ventricular repolarization as measured by the QT interval. We speculate that this sleep state-related difference in the QT interval may be caused by an increased sympathetic activity in REM sleep.