denominator Knowledge of the details and limitations of these data sources is important for critical appraisal The most complete data source would entail the active screening of a defined population-based cohort A sensitive and accurate method of identification would be universally applied to all subjects included in the denominator Clinical assessment by pediatric cardiologists has been shown to have sufficient though not perfect sensitivity and specificity for clinical detection, whereas assessments by other types of providers have fared less well.5,6 Echocardiography could then be applied more selectively for clinically suspected cases, to provide verification and specification Definition of Cases Regardless of the data source used for case ascertainment, it must be clearly defined which specific lesions were included and excluded from the numerator This predominately applies to lesions of minor or no functional consequence but which are very common, as discussed previously The inclusion or exclusion of these types of lesions can have an important impact on inflating the prevalence estimate In addition, the time period after live birth during which cases could be identified should be specified and reported It should be clearly stated whether cases identified as still births and cases diagnosed by fetal assessment but either spontaneously or electively aborted are included or excluded Relevance Estimates of incidence and prevalence, and the study of factors influencing them, have relevance to many aspects of congenital cardiac disease and its management This is summarized in Fig 13.1 FIG 13.1 Considerations related to relevance of knowledge of incidence and prevalence estimates of congenital heart disease Etiologic Associations Accepting the caveats discussed earlier, knowledge of factors that are associated with variations in the prevalence of specific lesions, or groups of lesions, may suggest etiologic influences These factors might then be used to target prenatal screening and counseling, or they might be amenable to intervention, resulting in the prevention of congenital cardiac disease Surveillance and Trends Over Time Related somewhat to etiology, there is an ongoing interest in discovering trends in the prevalence of congenital cardiac disease Ongoing surveillance is necessary to detect acute changes in prevalence that may be attributable to a specific etiology, such as occurred with the epidemic of birth defects associated with the use of thalidomide during pregnancy Likelihood of Diagnosis Knowledge of the relative frequency of specific lesions can aid somewhat in formulating differential diagnoses and informing an index of suspicion Burden of Disease and Requirements for Resources Disease involving the cardiovascular system continues to be the greatest contributor to infant mortality related to congenital malformations However, trends have shown significant decreases in mortality and an increasing age at which death might occur These factors increase the point prevalence of congenital cardiac disease at advancing ages and have created a growing population of adults with congenitally malformed hearts Indeed, the population of adults living with congenital heart disease has likely exceeded that for children