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EPIDEMIOLOGY OF THE HYPOPLASTIC LEFT HEART SYNDROME IN ONTARIO, 1971–73

This study had as its purposes the description of hypoplastic left heart syndrome (HLH) in Ontario and the testing of a specific hypothesis about geographic clustering of the defect in the vicinity of Toronto. A series of 52 cases of HLH born in Ontario during 1971 to 1973 was studied, and its characteristics contrasted to those of all other infants born during those years. Cases were ascertained from death certificate information made available by the Registrar-General of Ontario. There were no false-negatives among infants known to us to have died from any congenital heart defect. False-positives among the death certificates were distributed as was the pattern of infant deaths. Autopsy rates for infant deaths in different regions of the Province are comparable. The cases clustered beyond chance expectation in the populous southern part of Ontario (p < .02), but also seem to be associated with some characteriatic(s) of the more ‘rural’ parts of the Province. Birthweight in full-term infants who had HLH tended to be depressed from that of normal full-term infants (p < .02) when the overall distribution is considered. This series contradicted previous suggestions in that we could not demonstrate either elevated parental age or any significant seasonal pattern in dates of conception or of birth.