QT interval prolongation in future SIDS victims: a polysomnographic study.

SUDDEN INFANT DEATH SYNDROME (SIDS) IS DEFINED AS THE SUDDEN DEATH OF AN INFANT UNDER THE AGE OF 1 YEAR THAT REMAINS UNEXPLAINED after a complete postmortem examination, including an investigation of the death scene and a review of the case history. Such deaths occur during sleep, which may be a daytime nap or a night sleep.1 Despite extensive research, the etiology of SIDS is still unknown. Cardiac mechanisms, including life-threatening arrhythmias, have been suspected of causing a proportion of SIDS cases.2 A large prospective cohort study provided evidence of an association between neonatal QT prolongation recorded on electrocardiogram (ECG) during the first days of life and the subsequent occurrence of SIDS.3 Various mechanisms could be implicated in the association between SIDS and QT prolongation. In the late 1970s, Schwartz et al suggested that abnormal development of cardiac sympathetic innervation could occur with a difference in the timing of the maturation between left and right cardiac sympathetic innervation during the first months of life.2 Such QT prolongation could also be an early manifestation of congenital long QT syndrome.2,4 Long QT syndrome is a primary cardiac channelopathy with 7 cardiac ion-channel genes currently implicated: KCNQ1, KCNH2, SCN5A, KCNE1, KCNE2, KCNJ2, and CAV3.5 Potentially lethal cardiac ion-channel gene mutations have been found in 9.5% of SIDS infants, suggesting that de novo mutations in cardiac ion channels could provide a lethal arrhythmogenic substrate in some infants at risk for SIDS.5 Another possibility is that prolongation of the QTc intervals could be related to the autonomic dysfunction already reported in some of these patients.6–8 In a previous study, following analysis of night polygraphic recordings of 18 infants who died some weeks later of SIDS, compared with those of matched control infants, we reported a higher sympathetic activity in SIDS infants, especially at the end of the night when most cases of SIDS occur.9 In Schwartz' prospective study of QT values,3 an ECG was obtained in the first week of life—when transitional QT prolongation is a relatively common finding. The purpose of the present study was to determine if certain future SIDS victims recorded at 2 to 3 months of age could also present with prolongations of QTc intervals, compared with matched control infants, and if this QTc prolongation was related to sleep stages, time of night, and autonomic nervous system activity.