Knowledge of the occurrence and etiology of congenital defects
is essential to improvements in diagnosis, management, and genetic
counseling. Congenital heart 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 heart 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 heart defects and maternal diabetes. These
observational studies establish statistical associations (but not cause and effect)
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.
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 heart disease, the total population
at risk includes all embryos. However, even with advances in fetal
echocardiography, the true incidence of congenital heart disease
is difficult to measure. Many cardiovascular defects are associated
with spontaneous abortion and stillbirth so that many of those embryos
are never known to have heart disease. The prevalence of congenital
heart disease is estimated to be about 15% in fetuses that
have been spontaneously aborted and about 8% in stillborn
infants. Based on these data, it is apparent that the true incidence
of congenital heart disease is much greater than that reported in
studies of the frequency of congenital heart 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 heart
disease is not considered. Consequently, the importance of chromosomal
and genetic factors which are associated with spontaneous abortion or
stillbirth will be underestimated.
Counting congenital heart 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 ...