SummaryTwenty 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 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 (QT, = Q T /~) 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. SpeculationSleep 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.Prolongation of the QT interval has been implicated in the genesis of ventricular fibrillation and sudden death (17,20,24). Such prolongation of the QT interval has been postulated to occur in REM sleep (20), which occupies a greater proportion of sleep in very young infants. This might, therefore, predispose to sudden death during sleep (sudden infant death syndrome or SIDS). Before being able to evaluate the QT interval during sleep in the infant at risk for SIDS, it is necessary to examine the effect of sleep state on the QT interval in normal infants. In this study, we measured the QT interval in both quiet and REM sleep in order to determine the relation of the sleep state to the repolarization process of the ventricles in normal infants during the first 4 months of life. MATERIALS AND METHODS PATIENT POPULATIONThirty-seven studies were performed in 12 normal infants during sleep. Pregnancy, delivery, and neonatal course were uneventful. Birth weight ranged from 2900 to 4560 g and gestational age from 38 to 42 weeks. There were seven males and five females. Written informed consent was obtained from the parents of all infants. Infants were studied for 2 to 3 hr after the midmorning feed at 2 weeks and 1,2,3 and 4 months of age. Ten infants were studied three to five times; two infants were studied only once.None of the infants was on any medication and none had any clinical evidence of electrolyte imbalance. There was no history of SIDS in their siblings nor was there a family history of deafness, an abnormality that has been associated in many instances with prolongation of the QT interval (14). Eight infants are now over I year old; all have normal neurologic and developmental examinations. Conventional 12-lead electrocardiograms performed at the time of each study were normal in all infants. NEUROPHYSIOLOGIC AND ELECTROCARDIOGRAPHIC SIGNALSStandard surface electrodes were ...
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