PROLONGATION OF THE QT INTERVAL AND THE SUDDEN-INFANT-DEATH-SYNDROME

Background The sudden infant death syndrome (SIDS) is multifactorial i n origin, but its causes remain unknown. We previously proposed that p rolongation of the QT interval on the electrocardiogram, possibly resu lting from a developmental abnormality in cardiac sympathetic innervat ion, may increase the risk of life-threatening ventricular arrhythmias and contribute to this devastating disorder. We prospectively tested this hypothesis. Methods Between 1976 and 1994, we recorded electrocar diograms on the third or fourth day of life in 34,442 newborns and fol lowed them prospectively for one year. The QT interval was analyzed wi th and without correction for the heart rate. Results One-year follow- up data were available for 33,034 of the infants. There were 34 deaths , of which 24 were due to SIDS. The infants who died of SIDS had a lon ger corrected QT interval (QTc) than did the survivors (mean [+/- SD], 435 +/- 45 vs. 400 +/- 20 msec, P < 0.01) and the infants who died fr om causes other than SIDS (393 +/- 24 msec, P < 0.05). Moreover, 12 of the 24 SIDS victims but none of the other infants had a prolonged QTc (defined as a QTc greater than 440 msec). When the absolute QT interv al was determined for similar cardiac-cycle lengths, it was found that 12 of the 24 infants who died of SIDS had a QT value exceeding the 97 .5th percentile for the study group as a whole. The odds ratio for SID S in infants with a prolonged QTc was 41.3 (95 percent confidence inte rval, 17.3 to 98.4). Conclusions Prolongation of the QT interval in th e first week of life is strongly associated with SIDS. Neonatal electr ocardiographic screening may permit the early identification of a subs tantial percentage of infants at risk for SIDS, and the institution of preventive measures may therefore be possible. (C) 1998, Massachusett s Medical Society.