Sudden Infant Death
QT or Not QT? That Is No Longer the Question
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The association between Long QT syndrome (LQTS) and sudden infant death syndrome (SIDS) remains highly topical and even polarizing.1 Because the landmark Italian study of the QT interval and SIDS2 triggered extensive controversy,3,4 there has been a substantial and commendable effort to establish LQTS as one of the true causes of SIDS.5 The motivation underlying this effort is based on the fact that true LQTS is a potentially preventable cause of sudden death.
Many questions, however, remain.6 Where and how does LQTS fit into the spectrum of SIDS? Have we reached the stage where we can describe a typical phenotype for SIDS because of LQTS? Is it conceivable that some SIDS victims die with contribution from a channelopathy genetic variant, rather than because of it in isolation? After SIDS, can we identify those cases that are more likely to have been LQTS and, therefore, warrant genetic testing? When should family clinical screening be undertaken?7 To facilitate clarity of academic discussion, research and clinical care, we suggest a paradigm shift in how to analytically view the LQTS–SIDS association.
Definition of SIDS
Over the years there have been multiple working definitions of SIDS including many contradictions.8–10 The definition includes the sudden unexpected death of an infant <1 year of age, with onset of the fatal episode apparently occurring during sleep, that remains unexplained after a thorough investigation, including performance of a complete autopsy and review of the circumstances of death and the clinical history. In the most widely accepted definition, there is a graded classification based predominantly on the thoroughness of the autopsy investigation in excluding potential causes, and the possibility of positional asphyxia.10,11 Type 1 occurs between the ages of 21 days and 9 months in otherwise healthy, normal infants, …