The epidemiology of congenital heart disease.

Abstract During the past 30 years the mortality rates for congenital malformations of the circulatory system in the white population of the United States have declined in those under 1 year and increased slightly in those aged 1–14 years. In the nonwhites there has been an increase in both groups. The incidence of congenital heart disease in the United States, United Kingdom and Sweden is about 5 per 1000 births. At least 20,000 babies with congenital heart disease will probably be born each year in the United States. Genetic factors explain some cases of congenital heart disease. A few cases have been known to occur in association with arachnodactyly, Ellis' and van Creveld's syndrome and mongolism. Apart from mongolism, congenital heart disease has sometimes been found to be associated with chromosomal abnormalities. The incidence of the disease in relatives of patients with congenital heart disease is higher than the incidence in the general population. The degree of familial aggregation appears to vary with the particular type of malformation, being higher in pulmonary valvular stenosis and patent ductus arteriosus than in Fallot's tetralogy or interventricular septal defect. Malformation in systems other than the cardiovascular are more common in propositi with congenital heart disease and in their relatives. These malformations are more often found in association with cyanotic types of congenital heart disease than with acyanotic types. Certain types of congenital heart disease may be due to recessive inheritance, but consanguinity is clearly unimportant in the etiology of the majority of cases. Twin studies have usually shown a lack of concordance of congenital heart disease in monozygous pairs, another indication that genetic factors cannot be wholly responsible in the majority of cases. Environmental factors explain some of the cases. The original Australian studies linking congenital malformations with rubella frequently noted congenital heart disease. Women who have developed rubella in pregnancy have shown an increased risk of congenital heart disease, mainly from the 5th to the 9th week when the heart is rapidly developing. Patent ductus arteriosus is the most common defect; septal defects, pulmonary valvular stenosis, and Fallet's tetralogy occur less often. Congenital heart disease occurred with undue frequency, usually in association with other abnormalities, in children of women treated with thalidomide during pregnancy. High frequencies of certain forms of congenital heart disease have been found in people living at high altitudes; this has supported the suggestion that anoxia is an important factor in this disease. Radiation also appears to be a possible factor in the production of congenital heart disease. Certain types of congenital heart disease appear to be more common in children born at certain times of the year. Most studies have failed to support this hypothesis and other explanations have been advanced, for example, hours of daylight, amount of sunshine and temperature. No consistent associations have been shown between congenital heart disease and parental age, birth order or social class. In the majority of cases of congenital heart disease neither genetic nor environmental factors can as yet be implicated. The search for environmental factors would appear to offer the most promising line of epidemiological research. Studies of pregnant women and women who have already borne a malformed child should prove fruitful. Variation in frequency of congenital heart disease in relation to race, geography, altitude, background irradiation, and epidemic patterns are relevant to current etiological patterns.