Abstract 1137 Poster Session I, Saturday, 5/1 (poster 2)

Sudden infant death syndrome has been associated, in separate investigations, with both prolonged QT interval and prone sleep position. We hypothesized that these factors may have an underlying relationship and that sleep position by influencing sympathetic tone may cause prolongation of the QT interval and malignant ventricular arrhythmias. We studied 8 premature infants at 1 month corrected age with a sleep study in both prone and supine position with continuous ECG recording. Average gestational age at birth was 33.8 ± 2.5 weeks. We measured QT, RR and JT intervals during active and quiet sleep for each position using time-lapsed videosomography. The JT interval was measured to account for any interventricular conduction delay. These measures were corrected for heart rate using Bazett's formula. An average QTC and JTC for each position and sleep state was obtained and compared using a repeated measure ANOVA.

Results: No difference in the RR intervals were seen in prone vs. supine sleep position (460 ± 30 msec. vs. 450 ± 20 msec., p=.23) or in quiet sleep vs. active sleep (450 ± 30 msec. vs. 460 ± 25 msec., p=.44). No difference in QTc intervals could be seen with prone vs. supine sleep position (450 ± 20 msec. vs. 460 ± 20 msec., p=0.28. The JTc interval also was unchanged with differing positions (prone vs. supine-380 ± 20 msec. vs. 390 ± 20 msec., p = .26) Sleep state did not influence QTc (450 ± 20 msec. vs 460 ± .20 msec., p=.38, quiet sleep vs. active) or JTc intervals (380 ± 20 msec. vs. 390 ± 20 msec., p=.12, quiet sleep vs. active).

Conclusions: These preliminary data in a small population of infants show that the QT interval is not dependent on sleep position or sleep state. Although both sleep position and QT intervals are risk factors for sudden infant death syndrome, they do not appear to be related. Further study of the relationship between sleep position and the autonomic nervous system is warranted.