QT Interval Prolongation and The Sudden Infant Death Syndrome

Abstract □ 95

The incidence of Sudden Infant Death Syndrome (SIDS) appears to have recently declined after the identification of several behavioral risk factors and their subsequent modification through public campaigns. Nonetheless, SIDS remains the leading cause of mortality in the first year of life after the neonatal period and effective preventive measures are still lacking due to the poor understanding of the underlying mechanisms. There is a consensus that SIDS is multifactorial but, despite the many hypotheses proposed, none has yet been proven. In 1976 we proposed that a prolongation of the QT interval on the electrocardiogram (ECG), possibly resulting from a developmental abnormality in cardiac sympathetic innervation, may increase the risk for life-threatening arrhythmias and contribute to SIDS. In order to test that hypothesis we recorded the ECG on the 3^rd-4^th day of life in 34,442 newborns and followed them prospectively for one year. The QT interval was analyzed with (QTc) and without correction for heart rate. A one-year follow-up was obtained in 33,034 infants. There were 34 deaths, of which 24 were due to SIDS. The SIDS victims had a longer QTc compared to the one-year survivors (435 ± 26 vs 400 ± 20 ms, p < 0.01), and to the non-SIDS victims (392 ± 26 ms, p < 0.05). Moreover, 12 of 24 (50%) SIDS victims and none of the non-SIDS victims had a prolonged QTc (≥ 440 ms). When the absolute QT was determined for the same range of cycle lengths it was found that 12/24 (50%) of SIDS victims had a QT value exceeding the 97.5th percentile. The Odds ratio of SIDS for infants with a prolonged QTc (≥ 440 ms) is 41.3 (95% confidence interval 17.3-98.4). This large prospective study based on more than 33,000 infants provides the first demonstration that QT interval prolongation, on the standard ECG recorded on the 3^rd-4^th day of life, is a risk factor for SIDS. Neonatal ECG screening may allow early identification of a significant percentage of infants at risk for SIDS and the institution of preventive measures may be possible.