The QT interval was measured in 12 normal and 7 aborted sudden infant death syndrome (SIDS) infants in rapid eye movement (REM) and quiet sleep at monthly intervals through the age of 4 months. An accuracy of better than 2 msec was assured by high resolution of the digitized signal and calibration of each QT measurement with an accurately generated time code. In contrast to current speculations, the QT index was significantly smaller in the infants with aborted SIDS than in the normal infants in both REM and quiet sleep (P < 0.05). In addition, as in normal infants, the QTC was smaller in REM than in quiet sleep (P < 0.01). Although these results offer no support for the hypothesis that SIDS results from prolongation of the QT interval, they suggest that aborted SIDS infants have a functional abnormality in the autonomic nervous system.Speculation
We suggest that 1) the shortening of the QT interval in the aborted SIDS infants results from a uniform increase in the sympathetic outflow to the cardiac ventricles or an increase in circulating levels of catecholamines; and 2) an imbalance between the left and the right sympathetic outflow to the ventricles of aborted SIDS infants, as has been previously hypothesized, is not likely since the QTc was not larger in REM sleep, a sleep state in which an increase in sympathetic activity occurs.