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Prenatal Diagnosis of Congenital Heart Disease:
Its Impact in Pediatric Cardiology

Dr. Elizabeth Shaffer

Ultrasound has become a common diagnostic tool in the evaluation of the fetus. There is no uniformity in the recommendation for routine ultrasonography or in its usefulness in improving fetal outcome. In the United States, the routine fetal survey includes the four chamber view of the heart. When abnormalities are detected, the mother may be referred for a more detailed cardiac examination. If a complete cardiac evaluation is carefully performed by experienced operators, most serious congenital heart disease has the potential to be diagnosed in utero. Unfortunately, most serious congenital heart disease is not currently diagnosed in utero. There are many reasons for this. The standard practice of screening the fetal heart by viewing only the four chamber view will not allow the diagnosis of many common serious types of congenital heart disease that involve the outflow tracts such as transposition of the great vessels or tetralogy of Fallot. Abnormalities of the four chamber view may be very subtle and be difficult to recognize. Timing of the fetal echocardiogram is critical. Scans done early or in mid gestation may not be able to detect some types of congenital heart disease.

The prenatal evaluation of the fetal heart has impacted the practice of pediatric cardiology in several important ways including the daily counseling of families, clinical outcome, incidence of congenital cardiac malformations, and the natural history of cardiac defects during gestation.

Many of the families that we see in our pediatric cardiology practices have been traumatized by the diagnosis of congenital heart disease. It is devastating to find out that your baby or child has congenital heart disease and may require medical management or heart surgery. It is not uncommon for families to decide against future pregnancies because of the fear of having another child with congenital heart disease. The counseling of these families has changed with the availability of fetal echocardiography. In our routine practices, we can offer fetal echocardiography to families who have had a child with congenital heart disease. In a study by Bjorkhem, 64% of families who had lost a child to congenital heart disease were influenced in the decision to have another child because of the availability of fetal echocardiography. The anxiety decreased significantly after the fetal echocardiogram. Fortunately, more and more of our patients are reaching maturity and facing the possibility of reproducing. Fetal echocardiography may be offered to this group of patients where the incidence of congenital heart disease is known to be higher than the general population.

An area where our expectations of prenatal diagnosis of congenital heart disease has been very high is in the outcome of patients. The hope is that prenatal diagnosis will make a significant positive impact on the clinical outcome of patients. From a statistical point of view, this is very difficult to prove however, the impression is that the in utero diagnosis of significant congenital heart disease does improve the morbidity and mortality for an individual patient. In the Routine Antenatal Diagnostic Imaging with Ultrasound study (RADIUS) greater than 15,000 pregnant women were evaluated to assess the impact of ultrasonography in perinatal outcome. It was concluded that screening ultrasonography as compared with the selective use of ultrasonography on the basis of clinician judgment did not improve perinatal outcome. In this large clinical trial, the prevalence of major anomalies was 2.3%. The detection rate of major anomalies was 35% in the ultrasound-screening group and only 10% in the control group. Unfortunately, the detection of anomalies by ultrasound screening did not reduce the frequency of adverse perinatal outcomes. In other studies, investigators have concentrated on the outcome of fetuses that were diagnosed in utero with duct dependent congenital heart disease. In a study by Chang et al., fetuses with left ventricular outflow tract obstruction were assessed. In this group of 22 fetuses, the in utero diagnosis was correct in 21. The mothers were admitted and delivered at the institution to optimize the immediate perinatal management of the infant including confirmation of the fetal cardiac diagnosis and institution of prostaglandin therapy. Even with this aggressive management scheme, an improvement in the early mortality in the prenatal vs. postnatal diagnosis of duct dependent systemic circulation could not be .established. Many factors account for this finding, not the least of which is sample size. It is very difficult for an individual center to gather the numbers of pre- and postnatal diagnoses of duct dependent congenital heart disease to show a statistically significant difference between the groups. Caregivers in the community are becoming very adept at suspecting congenital heart disease early in a neonates course and our ability to successful resuscitate infants with congenital heart disease has improved. There is also considerable data to suggest that infants diagnosed with congenital heart disease in utero have an overall worse prognosis than infants diagnosed with the same heart disease after birth. In a study by Allan, et al. 30 fetuses with hypoplastic left heart syndrome (HLHS) were diagnosed in utero. Of this group, 4 underwent termination of pregnancy and 2 elected not to treat the infant after birth. In the remaining 24 fetuses, there was an intention to treat after delivery. In this group, chromosomal abnormalities, extracardiac anomalies, prematurity and additional cardiac abnormalities decreased the number of infants that were ultimately offered the first stage Norwood procedure to 18 with 9 operative survivors. This represents a 37.5% survival rate for infants with an intention to treat in contrast to the ideal newborn Norwood candidate which has a 70% survival rate for the first stage of the operation. The prenatal diagnosis of HLHS has the potential to favorably impact heart transplantation as a primary treatment option for HLHS. 23 fetuses have been listed in utero for heart transplantation after the prenatal diagnosis of HLHS. The listing of mature fetuses for heart transplantation offers the possibility of an immediate heart transplant eliminating the need for long term prostaglandin therapy while the infant waits for a suitable donor. Unfortunately, few fetuses are offered a heart in utero and must start accumulating time on the transplant list after birth. The wait time for a donor heart in this population of patients may be very long increasing the morbidity and mortality. Whether the prenatal listing of patients with HLHS for heart transplantation will have a positive impact on their outcome remains an unknown.

A very interesting and significant phenomenon may be occurring because of the prenatal diagnosis of severe heart defects. The incidence of pulmonary atresia with intact ventricular septum and HLHS may actually be declining in select areas. This has been attributed to the high rate of termination of pregnancies in some countries after the diagnosis of these conditions has been made. As our therapies for these severe types of congenital heart disease improve, we may see a decrease in the number of pregnancy terminations but it is important to recognize that prenatal diagnosis can have a very profound effect on the incidence of congenital heart disease.

As our experience with fetal echocardiography increases, our understanding of cardiac development has broadened. It now seems clear that certain cardiac lesions undergo progression in utero such that with our current technology they may be indistinguishable from the normal fetal heart early in gestation. A recent study by Yagel, et al. demonstrates this concept very nicely. They conclude that fetal cardiac anomalies vary at different stages of gestation and that 20% of detectable congenital heart disease may not be identified during the early second trimester. Scans done in the late second or third trimester may increase the detection rate. Past studies have laid the foundation for this work by describing the in utero progression of such abnormalities as HLHS, coarctation of the aorta, and pulmonary stenosis.

The prenatal diagnosis of congenital heart disease has had a widespread impact on pediatric cardiology. It has helped shape our thinking about the development and natural history of congenital heart disease. It has affected the clinical outcomes of our patients with congenital heart disease. It has influenced our counseling of families and has allowed us to develop a new type of bond with parents. The prenatal diagnosis of congenital heart disease has even allowed a new sub-specialty to develop, that of the fetal cardiologist.

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Bibliography

Bjorkhem G, Jorgensen C, Hanseus K. Parental reactions to fetal echocardiography. J Maternal-Fetal Med 1997;6:87-92.
Ewigman BG, Crane JP, Frigoletto FD, et al. Effect of prenatal ultrasound screening on perinatal outcome. N Engl J Med. 1993;329:821-827.
Chang AC, Huhta JC, Yoon GY, et al. Diagnosis, transport, and outcome in fetuses with left ventricular outflow tract obstruction. J Thorac Cardiovasc Surg 1991;102:841-848.
Allan LD, Apfel HD, Printz BF. Outcome after prenatal diagnosis of the hypoplastic left heart syndrome. Heart 1998;79:371-374.
Allan LD, Cook A, Sullivan I, et al. Hypoplastic left heart syndrome: effects of fetal echocardiography on birth prevalence. Lancet 1991;337:959-961.
Daubeney PE, Sharland GK, Cook AC, et al. Pulmonary atresia with intact ventricular septum impact of fetal echocardiography on incidence at birth and postnatal outcome. Circulation 1998;98:562-566.
Yagel S, Weissman A, Rotstein Z, et al. Congenital heart defects natural course and in utero development. Circulation 1997;96:550-555.

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Update
10/01/99