Sudden unexpected death in infants. Evidence on a lethal cardiac arrhythmia.

THE incidence of sudden unexpected death of infants ('cot death' 'crib death' in USA 'sudden unexpected and unexplained death in infants', 'sudden infant death syndrome'), termed below cot death, is 2.0 3.0 per 1,000 live births in 'developed' countries of Europe and North America1, less than 1.0 in Israel2' while no data are available for underdeveloped countries. In Northern Ireland the 'corrected' figure is 2.8 and represents 10 per cent of total infant, and 33 per cent of postneonatal, mortality4. The condition is considered sufficiently homogeneous to constitute a distinctive syndrome and most cases are thought to have an identical -though unidentified-'final common pathway' of death5' 6. Despite intensive research the cause i(or causes) is unknown; but the consensus holds that victims, mostly healthy throughout life, die because while passing through a period of enhanced physiological vulnerability some critical combination of intrinsic and extrinsic factors proves 'suddenly' and 'unexpectedly' fatal yet produces at autopsy no identifiable abnormality acceptable as being a 'cause' of death. Though certain 'risk factors' have been identified-9 it is not known through what 'final common pathway' (or 'pathways') death occurs. Of the many theories adduced that which now commands the widest support and which the data are alleged to favour is that these infants die a respiratory death-in the sense that death is mediated through a respiratory (rather than a cardiac) primary mechanism-due possibly to asphyxia secondary to laryngospasm, to apnoea with or without laryngospasm and mediated through some aberrant or immature reflex possibly impeding recovery from 'normal' sleep apnoea, or to respiratory failure as part of an immunological collapse or hypersensitivity on challenge with an appropriate antigen presumed to be a virus. These explanations are reached mainly by inductive inference: lethal laryngospasm has not been demonstrated; aberrant or immature reflexes have been indicted'0 but their role (if any) in cot death is unknown; no basis for an immunological mechanism has been established. Where deductions as to respiratory death are made either from animal models1" or from study of selected infants ultimately