Prenatal Imaging and Therapy of Congenital Heart Disease

Chapter 71

Prenatal Imaging and Therapy of Congenital Heart Disease

Congenital heart disease, the most common birth defect, occurs in 3 to 8 per 1000 newborns.13 The incidence is higher prenatally, affecting 5.8% to 16.9% of fetuses undergoing screening echocardiograms.46 Despite advances in imaging techniques, routine obstetric ultrasound is only 30% to 50% sensitive for detection of congenital heart defects.712 With the addition of careful delineation of outflow tracts, sensitivity improves significantly.13 The most difficult lesions to diagnose prenatally are transposition of the great arteries and outflow tract abnormalities. A complete fetal echocardiogram includes two-dimensional, M-mode, and color Doppler imaging to assess fetal cardiac structure, rhythm, and function. Novel techniques include tissue Doppler and strain analysis.

Fetal Physiology and Flow

The fetal cardiac circulation has been studied in human and animal models (Fig. 71-1). Fetal and postnatal cardiovascular physiology differs markedly. Key differences include the following:

Fetuses with congenital heart disease have additional alterations of fetal physiology. They can have restricted intrauterine growth, neurologic abnormalities, and poor neurodevelopmental outcome. Circulatory alterations that accompany specific cardiac defects may cause blood flow disturbances that affect normal development. Doppler ultrasound of the middle cerebral artery, umbilical artery, umbilical vein, and ductus venosus can provide clinically useful information when combined with an understanding of fetal physiology.

Cerebral Resistance

Fetal cerebral vessels can vasodilate during stress, which decreases resistance and increases diastolic flow in the middle cerebral artery. Peripheral vessels vasoconstrict to direct blood to the brain; this causes increased resistance and decreased diastolic flow in the descending aorta. This represents an autoregulatory mechanism (Fig. 71-2). This phenomenon of increasing cerebral blood flow has been described in growth-restricted fetuses as a predictor of poor perinatal outcome (Fig. 71-3). This phenomenon also occurs in fetuses with congenital heart disease (Table 71-1), although the clinical significance of this finding as a predictor of outcome is still in question.14

Fetal Anatomy

A complete fetal echocardiogram includes imaging of the atria, ventricles, atrioventricular (AV) and semilunar valves, foramen ovale, pulmonary veins (at least two), ductal and aortic arches, branch pulmonary arteries, and cardiac rhythm and function. Measurements vary by gestational age and should be compared with normative data. Doppler and color interrogation of each structure should be performed.

Prenatal Imaging: Timing and Indications

Fetal echocardiography has been in use since the late 1980s. The optimal time for transabdominal imaging of the fetal heart is between 20 and 28 weeks of gestation. Transvaginal imaging can be performed as early as 8 weeks, with successful diagnosis of heart defects possible as early as 11 weeks.1516 Third-trimester imaging, although possible, is limited by paucity of the amniotic fluid and limited variability in fetal position. Indications for fetal echocardiography include maternal and fetal risk factors (Box 71-1). The most common reasons are family history of congenital heart disease, fetal dysrhythmia, maternal diabetes, and extracardiac defects. Indications that are most predictive of cardiac disease are an abnormal four-chamber view on routine ultrasound (30% to 50%), fetal dysrhythmia (30%), hydrops (30%), and polyhydramnios (25%).

Cardiac Defects

Septation Defects

Atrial Septal Defects

The most common atrial septal defects (ASDs) are ostium secundum defects. Sinus venosus defects (superior or inferior type) are often associated with anomalous drainage of the right pulmonary veins. Ostium primum defects are an endocardial cushion defect, and often associated with Down syndrome. A patent foramen ovale is a normal structure of the fetus and newborn (Figs. 71-6 and 71-7); it may be difficult to distinguish a normal foramen ovale from a secundum ASD prenatally. Secundum defects are amenable to catheter closure; other defects require surgical correction.

Atrioventricular Canal defects

AV canal (endocardial cushion) defects are easily diagnosed prenatally (Fig. 71-9) and can be associated with Down syndrome. They include a primum ASD, inlet VSD, and common AV valve. VSDs can be isolated. The cross-sectional anatomy of the common valve is best determined from short-axis imaging. Partial AV septal defects have a primum ASD with a cleft mitral valve. Transitional AV septal defects have an atrial defect, common AV valve, and restrictive VSD.

Dec 20, 2015 | Posted by in PEDIATRIC IMAGING | Comments Off on Prenatal Imaging and Therapy of Congenital Heart Disease

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