Knowledge of the occurrence and etiology of congenital defects is essential to improvements in diagnosis, management, and genetic counseling. Congenital cardiovascular disease refers to structural abnormalities of the heart or intrathoracic great vessels that impact the function of the cardiovascular system. This chapter summarizes current knowledge regarding epidemiology and etiology of congenital cardiovascular disease. Information regarding the etiology of inherited cardiomyopathies and arrhythmias is presented in Chapters 9 and 10, respectively.
Epidemiologic studies seek to measure disease frequency and to establish associations between disease states and a multitude of other variables, such as cardiovascular defects and maternal diabetes. These observational studies establish statistical associations—but not causality—that are useful for (1) developing diagnostic screening studies, (2) defining heritability and recurrence risk, (3) evaluating the contribution of candidate genes identified in high-risk families or experimental models to disease in the general population, (4) characterizing environmental risk factors, (5) developing testable hypotheses regarding etiology and pathogenesis, and (6) planning for effective delivery of health care services.
All epidemiologic studies begin with measures of disease frequency (ie, how often a disease is found). The two most common measures are prevalence and incidence:
Prevalence is the proportion of the population at risk affected by disease at a given point in time. Prevalence excludes those who have already died from the disease, those in whom the disease has been cured or has spontaneously resolved, and those with undetected disease. Prevalence answers the question, “How many people have this disease in this place, at this time?”
Incidence is expressed as a rate and is defined as the number of new cases among those at risk within a population over a certain period of time. Incidence answers the question, “How often does this disease occur?” For congenital cardiovascular disease, the total population at risk includes all embryos. However, even with advances in fetal echocardiography, the true incidence of congenital cardiovascular disease is difficult to measure. Cardiovascular defects are associated with spontaneous abortion, elective pregnancy termination, and stillbirth so that many of those embryos are never known to have cardiovascular disease. Congenital cardiovascular disease is estimated to occur in about 15% of fetuses that have been spontaneously aborted and in about 8% of stillborn infants. Based on these estimates, it is likely that the true incidence of congenital cardiovascular disease is much greater than that reported in studies of the incidence of congenital cardiovascular disease at birth. Although incidence at birth is most frequently reported and is probably the most useful concept for the clinician, this figure must be interpreted with caution because the entire population with congenital cardiovascular disease is not considered.
Counting congenital cardiovascular disease cases after birth depends on the accurate detection of persons with various cardiac defects, and the accuracy of detection depends on the method used. No one method is completely accurate. Some studies have relied on data from ...