Measurement of disease occurrence is usually expressed as the incidence, defined as new cases in the at risk population in a specific time period.

• Some cardiovascular malformations are determined at the moment of fertilization while others originate at later stages of intrauterine life initiated by infection or toxic exposure. There may be throughout pregnancy : ongoing causation (incidence) , loss of severely affected embryos (mortality) and possibly the removal of cases by healing. True incidence would include cases with lethal anomalies never seen in liveborns.
• The term prevalence-at-live-birth refers to the cases found in the population at a specific point of time.

It is obvious that the kinds of cases recognized in the early decades of Pediatric Cardiology would be different from those recognized and treated after the following developments:

• the introduction of cardiac surgery in the 1950s
• the development of open heart surgery in the 1960s
• the improvement of infant transport systems in the 1970s
• the non-invasive ultrasound diagnostic methods for detecting defects in the 1980s.

This last diagnostic change occurred during the BWIS study period and resulted in a dramatic increase in cases of small ventricular septal defect and of cases of mild pulmonic stenosis (Wilson, 1993, Martin, 1989).The dramatic differences resulting from changes in diagnostic methodology were illustrated also in the detailed evaluation by of the EUROCAT subproject on congenital heart disease (Pexieder and Bloch, 1995) . A comparison to the BWIS data, gathered in the same time period, and using a similarly defined subset of diagnoses, revealed differences, which could be explained by knowledge of the different practices on the two continents.

Selected References

Congenital malformations of the heart represent a major cause of infant deaths in developed countries. In the United States about 20% of deaths under one year of age are due to congenital anomalies and about 1/3 of these are due to abnormalities of the heart. (National Vital Statistics Reports, 2001).

Deaths are not evenly distributed within the various population groups, infant characteristics or the nature of the cardiac anomaly. It is therefore very difficult to generalize the findings without information on the factors which increase or decrease the risk of survival for any of the subgroups.

National data reveal lower mortality rates for white than for non-white infants. In the BWIS among the total of 4390 cases, the all-cause one year mortality was 18.2 %. The BWIS demonstrated a strong effect of low birth weight : for infants with birth weights under 1500 grams the case fatality rate was four times that of infants who weighed over 4000 grams ( 35% vs 8%). A similar difference was present by time of diagnosis: infants diagnosed in the first week of life had the most severe defects and 38% did not survive the first year of life, while infants whose diagnosis was made after 12 weeks of life had the lowest mortality (4%). Other factors such as the asssociated non-cardiac defects, including chromosome abnormalities, also had an important effect. An important effect on infant mortality was that of maternal diabetes which was discovered in separate analyses of that subgroup: (39% vs17.8% ) (Loffredo, 2001)

In these considerations affecting infant survival many factors are evident which deserve greater societal and medical attention to enhance the possibility of preventive interventions.

Selected References