988 HEART RATE AND HEART RATE VARIABILITY IN NORMAL AND ABORTED SIDS INFANTS DURING SLEEP

Abstract

Heart rate (HR) and HR variability were studied in 15 normal infants and 6 infants with aborted Sudden Infant Death Syndrome (SIDS) during sleep at monthly intervals through 4 months of age. The RR interval (inverse of heart rate) was measured to an accuracy of 0.2 msec. Sleep was staged using EEG, EOG, EMG and behavioral criteria. The median HR was 4 to 10% greater in the aborted SIDS infants at each age in both sleep states and this was significant at 2,3 and 4 months in quiet and at 3 months in REM sleep (p < 0.05, Wilcoxon Rank Sum test). The beat to beat variability of the HR (Δ RR) in the aborted SIDS infants was 6 to 40% smaller than in the normal infants in both REM and quiet sleep at each age studied. The interquartile range of the HR, a measure of overall variability in HR, was the same in the aborted SIDS and normal infants. In both groups, the HR and its interquartile range were greater in REM sleep. These studies indicate that the group of infants with aborted SIDS may be differentiated from the normal infants by their increased heart rate and decreased beat to beat variability, and that these findings may reflect abnormal autonomic regulation of the heart rate.