Prenatal Imaging and Therapy of Congenital Heart Disease

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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.

Inflow/Outflow

Right-Sided Inflow Lesions

Right ventricular inflow lesions include Ebstein anomaly, tricuspid valve dysplasia, and tricuspid stenosis or atresia. The tricuspid valve orifice is displaced apically in Ebstein anomaly, with abnormal delamination of the septal leaflet and tricuspid valve regurgitation. (Fig. 71-10) Milder disease may not present until the first decade of life with arrhythmias and tricuspid regurgitation; severe forms can cause fetal hydrops, death, or neonatal cyanosis. Ebstein anomaly can be associated with pulmonary stenosis or atresia, causing cyanosis and requiring initiation of prostaglandin therapy to maintain ductus arteriosus patency. Tricuspid valve dysplasia has similar features but without apical displacement of the valve annulus. Tricuspid atresia or stenosis can be associated with hypoplasia of the right ventricle and pulmonary outflow obstruction; without a VSD, this lesion requires postnatal prostaglandin to maintain ductal patency prior to neonatal single-ventricle palliation surgery.

Right-Sided Outflow Lesions

Pulmonary outflow obstruction can be subvalvular, valvular, or supravalvular. The disease spectrum ranges from severe cyanosis and pulmonary atresia in newborns to normal oxygen saturation and a near normal pulmonary outflow tract in infants. Fetal echocardiography can predict the degree of subvalvular and valvular stenosis.

Isolated pulmonary valve stenosis is diagnosed by identifying domed and thickened pulmonary valve leaflets. The annulus may be hypoplastic. Fetal Doppler echocardiography may not accurately predict the postnatal pulmonary valve gradient. This lack of agreement between prenatal and postnatal gradients is attributed to in utero physiology, elevated pulmonary vascular resistance, and right-to-left shunting at the atrial level. Supravalvular pulmonic stenosis is associated with Williams syndrome. Subvalvular obstruction is usually seen in combination with other defects such as tetralogy of Fallot (Fig. 71-11).

Left-Sided Outflow Lesions

Left-sided outflow tract obstruction can occur at the subvalvular, valvular, or supravalvular levels. Infants of mothers with diabetes, especially of mothers with poor glucose control, are at risk for hypertrophic cardiomyopathy (with or without obstruction).17 Even in severe cases, the hypertrophy usually regresses by 3 months of age. Valvular aortic stenosis seen in utero can be associated with left ventricular dysfunction and progressive hydrops. Supravalvular stenosis is associated with Williams syndrome and can occur in combination with right-sided outflow tract obstruction. Left-sided obstructive lesions can be associated with Turner syndrome.18

Conotruncal Defects

Conotruncal defects include abnormalities of the connection between the ventricles and the great vessels, including tetralogy of Fallot, transposition of the great arteries, truncus arteriosus, and double-outlet right ventricle. The lesions can be associated with deletions in chromosome locus 22q11 (DiGeorge sequence, velocardiofacial syndrome, CATCH 22 [cardiac defects, abnormal facies, thymic hypoplasia, cleft palate, hypocalcemia]).19

Tetralogy of Fallot (right ventricular outflow obstruction, right ventricular hypertrophy, overriding aorta, and large anterior malaligned VSD) is the most common form of cyanotic congenital heart disease, with transposition of the great vessels being the second most common. In transposition, the aorta originates from the right ventricle, and the pulmonary artery arises from the left ventricle. Echocardiography shows parallel great vessels with aorta located anterior and rightward of the pulmonary artery (Fig. 71-12). A laterally branching vessel (left pulmonary artery) from the great artery is seen related to the left ventricle. Additional abnormalities such as VSDs (one third of cases) also are identified. The four-chamber view is normal, making diagnosis quite difficult.

In the double-outlet right ventricle, the presence of subaortic conus causes anterior displacement of the aorta. A VSD is present. The disease can encompass a spectrum of physiology from single ventricle lesions, to tetralogy of Fallot or transposition of the great arteries. In truncus arteriosus, a single outflow tract originates from the heart, with a malalignment-type VSD. Pulmonary arteries vary in size, and originate from the truncal outflow. The truncal valve can range from unicuspid to quadricuspid and often is stenotic or insufficient.

Ventricular Hypoplasia

Underdevelopment of either ventricle can result in a univentricular heart. After birth, patients require staged surgical palliation and possible heart transplantation later. Hypoplastic right heart syndrome can result from tricuspid atresia or pulmonary atresia with an intact interventricular septum (Fig. 71-13). Hypoplastic left heart syndrome may have severe aortic and mitral stenosis or atresia (Fig. 71-14) and requires intervention or surgery in the neonatal period. Double-inlet left ventricle with a right ventricular outlet chamber is another, more complex form of a single ventricle heart (see Fig. 71-14) and can be associated with a normal or hypoplastic outflow tract.

Fibroelastosis

Endocardial fibroelastosis is an abnormality of the endocardial surface. Prenatally, thickening and fibrosis of the endocardium due to inflammation or hypoxia result in an echobright appearance. These areas can be either focal or diffuse. It has been described in fetuses with maternal Sjogren’s antibody exposure; structural anomalies such as hypolastic left heart syndrome; anomalous coronaries; aortic stenosis; fetal infections such as parvovirus infection; metabolic diseases; and cardiomyopathy (Fig. 71-15).20 Once diagnosed, serial assessment of ventricular function, venous flow patterns, and valve regurgitation is warranted to evaluate for development of fetal hydrops fetalis.

Venous and Aortic Arch Anomalies

Systemic venous abnormalities often have no clinical consequences. A common abnormality, existing in 3% of the normal population, is bilateral superior vena cavae with the left superior vena cava draining into the coronary sinus. It may be suspected when an enlarged coronary sinus is seen and is more prevalent in patients with congenital heart disease.

Some or all of the pulmonary veins can drain anomalously to the systemic (right) circulation, entering supracardiac (through a vertical vein into the innominate vein), intracardiac (directly into the right atrium or coronary sinus), or infracardiac (through the liver or inferior vena cava). In obstructed total anomalous pulmonary venous drainage, neonates may be critically ill and require immediate surgery. This lesion is suspected when a small left atrium is seen in combination with dilated right heart. It is difficult to diagnose prenatally because of the decreased pulmonary venous return.

Aortic arch abnormalities include vascular rings, coarctation of the aorta, and interrupted aortic arch. Vascular rings can be associated with a right-sided aortic arch, aberrant left subclavian artery, and Kommerell’s diverticulum or ligamentum arteriosus. Depending on the type of ring, infants may be asymptomatic, have airway narrowing, or have feeding difficulties. Finding a right aortic arch warrants further evaluation for associated anomalies. Coarctation of the aorta may present in early infancy with cardiogenic shock after ductal closure or in later life with hypertension. Coarctation may be difficult to diagnose in the fetal period when the ductus arteriosus is still open. Interrupted aortic arch is a severe type of coarctation, in which the ascending and descending aorta are discontinuous, with the descending aorta supplied by the ductus arteriosus. When associated with a VSD, this form is considered a conotruncal abnormality. Patent ductus arteriosus is a normal fetal structure; its premature closure can lead to right-sided heart failure in utero (Fig. 71-16). Indomethacin and other nonsteroidal antiinflammatory drugs predispose to this condition. The heart normalizes at delivery.21

Heterotaxy Syndromes: Situs/Cardiac Masses/Arrhythmias

Situs abnormalities and complex congenital heart disease can be diagnosed by carefully evaluating abdominal and cardiac situs and intracardiac relationships (Fig. 71-17).22 Correct determination of abdominal and cardiac situs depends on the delineation of fetal position and right or left orientation. Double-outlet right ventricle, atrioventricular septal defects, and venous anomalies are frequently associated with abnormalities of abdominal situs resulting in asplenia (bilateral “right-sidedness”) or polysplenia (bilateral “left-sidedness”). Abnormal looping of the fetal heart may result in ventricular inversion (right-sided morphologic left ventricle and left-sided morphologic right ventricle) in these patients.

Cardiac Masses

Tiny echogenic objects in the left ventricular papillary muscles are frequently noted on fetal echocardiography (Fig. 71-18) and are considered normal variants.23 Larger, more numerous masses suggest the presence of cardiac tumors. The most common prenatal cardiac tumors are rhabdomyomas (Fig. 71-19). They usually are associated with tuberous sclerosis. Although benign and usually regressive after birth, these tumors can cause obstruction or arrhythmias.24

Fetal Arrhythmias

Echocardiography provides accurate diagnosis of fetal arrhythmias.25,26 Premature atrial contractions (Fig. 71-20) are common and usually benign. Supraventricular tachycardia and atrial flutter can be diagnosed with M-mode and Doppler ultrasound (Figs. 71-21 and 71-22). Bradycardia may be benign and is often caused by blocked premature atrial contractions. Complete heart block, a rare complication of maternal Sjögren antibody exposure, can be diagnosed by M-mode or Doppler ultrasound (Fig. 71-23).27 Serial Doppler assessment of the time between atrial and ventricular contractions is used in maternal Sjögren antibody carriers to follow the fetal conduction system (Fig. 71-24).

Fetal Management

Fetal echocardiography can provide crucial information that improves the outcomes of newborns with certain types of congenital heart disease. It is invaluable in counseling families and guiding prenatal and delivery room treatments of structural heart disease and arrhythmias.

The most common rhythm disturbances in the fetus do not require treatment. Persistent supraventricular tachycardia or atrial flutter can result in cardiac dysfunction and hydrops if left untreated. Administration of digoxin to the mother is often successful as first-line therapy for fetuses with supraventricular tachycardia, but it is less effective in fetuses with atrial flutter or those who are hydropic. Higher dosages of digoxin are required during pregnancy because of increased maternal volume of distribution. Sotalol can be considered as a first-line drug for atrial flutter. Second-line drugs for supraventricular tachycardia (other than atrial flutter) include sotalol, flecainide, or amiodarone. Close monitoring of the mother and fetus is required, and initiation of drug therapy may necessitate hospitalization. Administration of adenosine via the umbilical cord may be considered in severely compromised fetuses with supraventricular tachycardia. Complete heart block is difficult to manage. Maternal steroid and β-agonist treatment has been used with variable success in these patients. Early delivery may be required if hydrops and fetal compromise are present.

Fetuses with ductal-dependent systemic or pulmonary blood flow require prostaglandin treatment immediately after birth. If the diagnosis is unknown and the ductus closes, severe cyanosis, acidosis, and compromised cardiac output are likely to occur, resulting in potential multisystemic organ damage. Patients with hypoplastic left heart syndrome and transposition of the great arteries with intact atrial septum are at highest risk for compromise at birth. They may require immediate interventional cardiac catheterization to open the atrial communication for survival. Considerable planning is required to deliver these infants in a setting where a pediatric cardiac catheterization laboratory and intervention are available immediately or soon after delivery.

Although the heart develops by 8 weeks’ gestation, fetal flow patterns can affect development of the heart throughout gestation. Disproportionate flow to one side of the circulation may lead to underdevelopment of either side of the heart. Fetuses with aortic or pulmonary valve stenosis at 18 to 20 weeks’ gestation can progress to hypoplastic left or right heart by 30 weeks’ gestation (Fig. 71-25). Fetal catheter-based intervention to relieve aortic stenosis, pulmonary stenosis, or a restrictive atrial septum has been performed.2831 Technically successful fetal balloon aortic valvuloplasty in fetuses with critical aortic valve stenosis with likely evolving hypoplastic left heart syndrome was reported in 2004. Improved left heart growth and postnatal two-ventricular circulation was seen in some of the successful cases (Figs. 71-26 through 71-28).

Conclusion

Fetal echocardiography is an important adjunct to other prenatal evaluations, including ultrasound and genetic screening. Radiologists, cardiologists, perinatologists, neonataologists, and other pediatric subspecialists must work together to provide a multidisciplinary treatment and counseling approach to patients with complex diagnoses (Fig. 71-29). Newer imaging modalities of the fetal heart, including three-dimensional echocardiography and magnetic resonance imaging, will further contribute to fetal cardiac management. As technology and treatments evolve, fetal cardiology represents an area of tremendous potential for early diagnosis and in utero treatment of abnormalities. In the future, intervention during the fetal period may allow physicians to actually alter the evolution of structural cardiac disease, thus helping improve long-term outcome.

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