Fetal echocardiography: Congenital heart disease





Objectives


On completion of this chapter, you should be able to:




  • List the three factors that contribute to congenital heart disease



  • Describe why the four-chamber view cannot rule out all forms of congenital heart disease



  • Discuss the pathologic conditions covered in this chapter



  • Discuss the echocardiographic findings for septal defects, ventricular inflow and outflow tract disturbances, great vessel abnormalities, cardiac tumors, complex cardiac abnormalities, and dysrhythmias





This chapter presents the sonographer’s approach to evaluating congenital heart disease with examples of the more common fetal heart abnormalities. As presented in Chapter 35 , the development of the fetal heart is completed by the eighth week of embryonic life. The presence of congenital heart disease is a result of an interrupted or abnormal cardiac development during this time period.


The most common types of congenital heart disease are the ventricular septal defect, atrial septal defects, and pulmonary stenosis. The development of congenital heart disease is multifaceted. Environmental factors, chromosomal factors, and hereditary factors may influence the development of congenital heart disease in the fetus. Fetal echocardiography can help to establish the presence and severity of the cardiac abnormality. A simple acronym (CHRISTMAS) will assist the sonographer in prenatal detection of congenital heart disease:




  • C = Concordance and contractility



  • H = Hydrops



  • R = Risk factors and rhythm



  • I = Incorrect size (large or small for gestational age)



  • S = Symmetry



  • T = Tetralogy of Fallot, total anomalous pulmonary venous return, transposition, tricuspid atresia, truncus arteriosus



  • M = Masses and mobility



  • A = Aneuploidy



  • S = Situs





Relationship of genetics to congenital heart disease


Chromosomal abnormalities


The frequency of chromosomal abnormalities in infants with congenital heart disease is estimated as 5% to 10% from postnatal data. In a control study of 2100 live-born infants with cardiovascular malformations, chromosomal abnormalities were found in 13%. In this study, Down syndrome occurred in more than 10% of the infants, with the other trisomies each constituting the remaining 3%.


The frequency of abnormal karyotypes in fetuses with cardiac defects has been commonly found at 30% to 40%. Of these fetuses, most have trisomy 21, followed by trisomy 13, trisomy 18, and Turner’s syndrome. The association of congenital heart defects and chromosomal abnormalities is lower in live-born infants than in fetuses because of the high in utero mortality of the fetus with trisomy 18, trisomy 13, and Turner’s syndrome (trisomy 45,X).


The occurrence of associated extracardiac abnormalities in fetuses with cardiac defects and chromosomal abnormalities is on the order of 50% to 70%. In the fetus with a single cardiac abnormality, the incidence of chromosomal abnormalities is still increased (15% to 30%). The most common single cardiac abnormality is the ventricular septal defect.


Certain cardiac abnormalities are more likely associated with chromosomal defects. In general, malformations of the right side of the heart are rarely associated with karyotypic abnormalities (e.g., pulmonic stenosis and tricuspid atresia). On the other hand, abnormalities such as atrioventricular septal defect, perimembranous ventricular septal defect, tetralogy of Fallot, double-outlet right ventricle, coarctation of the aorta, and hypoplastic left heart are often associated with chromosomal abnormalities.


The incidence of cardiac defects in the fetus with trisomy is increased, with trisomy 21 showing the highest rate at 40% to 50%, Turner’s syndrome (45,X) showing 25% to 40%, and more than 90% having cardiac defects with trisomies 13 and 18 ( Table 36-1 ).



TABLE 36-1

Congenital Heart Disease and Chromosomal Abnormality





























Chromosomal Abnormality Incidence at Live Birth Associated Cardiac Abnormality Common Cardiac Abnormalities
Trisomy 21 1:800 40%–50% Atrioventricular septal defect
Ventricular septal defect
Cleft mitral valve
Heart block
Trisomy 18 1:8000 >90% Ventricular septal defect
Double-outlet right ventricle
Trisomy 13 1:20,000 >80% Ventricular septal defect
Atrial septal defect
Turner’s syndrome (trisomy 45,X) 1:10,000 25%–45% Coarctation of the aorta
Bicuspid aortic valve


Familial risks of congenital heart disease


Most congenital heart defects have more than one cause, with genetic and environmental factors both playing a role. Only about 10% to 15% of all congenital heart defects have been attributed to known chromosomal abnormalities, genetic syndromes, and teratogenic embryopathies.


The recurrence risk for an isolated congenital cardiovascular malformation is modified for each family based on the number of affected relatives and the severity of the abnormality. In general, a recurrence risk of 1% to 5% is estimated for the majority of congenital cardiac abnormalities.


Studies have shown that the contribution of genetic factors increases the risk of congenital heart disease significantly. For example, a mother who has had a child with an abnormality of the left side of the heart (mitral atresia or aortic atresia) has a significantly higher risk (13%) of delivering another child with a form of left-sided heart disease. This risk increases significantly with each pregnancy.




Incidence of congenital heart disease


Congenital heart disease is the most common severe congenital abnormality, with an incidence of 8% in live births. Approximately half of these defects are minor and may be corrected easily with surgery; the other half are responsible for more than 50% of the deaths from congenital abnormalities in childhood. Cardiac defects may account for as much as 4% of congenital heart disease in live births. Common cardiac defects include the bicuspid aortic valve, patent ductus arteriosus (common in premature infants), and ventricular septal defects. The incidence of the bicuspid aortic valve defect is 10 in 10,000 births; it may lead to aortic stenosis in adulthood.




Prenatal evaluation of congenital heart disease


The four-chamber view


All sonographers should be familiar with the routine four-chamber view that is part of the normal obstetric examination. This view is easily obtainable after 16 weeks of gestation, although the anatomy becomes more distinctly imaged with ultrasound between 18 and 22 weeks of gestation. The four-chamber view is normal when the following conditions are seen:



  • 1.

    The fetal situs is normal. (The heart is in the left side of the chest and its apex points to the left, the stomach is to the left, the aorta is anterior and to the left of the spine, and the inferior vena cava is anterior and to the right of the spine; Figure 36-1 , A. )




    FIGURE 36-1


    A, The fetal situs is normal. (Heart position is in the left chest and the apex of heart points to the left; stomach is to the left; aorta is anterior and to the left of the spine; and inferior vena cava is anterior and to the right of the spine.) B, The size of the heart in relation to the chest is normal. (Ratio of heart to thorax = 1:3.) C, The two atria are equal in size and the flap of the foramen ovale is seen to move toward the left atrium. (The atrium should comprise about one third the size of the heart.) D, The two ventricles are equal in size and contractility. (The ventricles should comprise about two thirds the size of the heart.) E, The interatrial and interventricular septa are completely formed and normal in thickness. F, The atrioventricular valves are normal in thickness, position, and opening.


  • 2.

    The size of the heart in relation to the chest is normal (ratio of heart to thorax = 1:3) ( Figure 36-1 , B ).


  • 3.

    The two atria are equal in size, and the flap of the foramen ovale is seen to move toward the left atrium. (The atria should constitute about one third of the size of the heart; Figure 36-1 , C. )


  • 4.

    The two ventricles are equal in size and contractility. (The ventricles should constitute about two thirds of the size of the heart; Figure 36-1 , D. )


  • 5.

    The interatrial and interventricular septa are completely formed and normal in thickness ( Figure 36-1 , E ).


  • 6.

    The atrioventricular valves are normal in thickness, position, and opening ( Figure 36-1 , F ).



Several cardiac abnormalities may be recognized with the four-chamber view alone, such as a large ventricular septal defect, atrioventricular septal defect, hypoplastic left or right heart, mitral or tricuspid atresia, Ebstein’s anomaly, and total anomalous pulmonary venous return (TAPVR; discussed later in this chapter). However, many cardiac abnormalities may be missed with only the four-chamber view. Abnormalities of the cardiac structure (especially the great vessels) that are not located in the four-chamber plane may show a normal four-chamber view, but the specific abnormality will be missed if a complete fetal echocardiogram with multiple “sweep cine loop images” is not conducted (e.g., transposition of the great arteries, truncus arteriosus, coarctation of the aorta, small outlet ventricular septal defect, and tetralogy of Fallot). Chapter 35 covers the normal fetal echocardiographic examination.




Cardiac malposition


When the heart is out of its normal position, several terms may be used to describe the exact position of the heart relative to location and position of the cardiac apex ( Figures 36-2 and 36-3 ). Dextrocardia means the heart is in the right side of the chest with the apex pointed to the right of the thorax ( Figure 36-4 , A ). Dextrocardia can be associated with a normal visceral situs, situs inversus, or situs ambiguous. Dextroposition of the heart refers to a condition in which the heart is located in the right side of the chest and the cardiac apex points medially or to the left. This condition is usually found when extrinsic factors, such as a space-occupying large diaphragmatic hernia or hypoplasia of the right lung, are present ( Figure 36-4 , B and C ).




FIGURE 36-2


The anatomic relationship of the descending aorta, left atrium, apex, and stomach in the four cardiac positions. A, Normal position, situs solitus. B, Situs inversus. C, Dextrocardia. D, Levocardia. LV, Left ventricle; RA, right atrium; RV, right ventricle.



FIGURE 36-3


The alignment of the descending aorta, apex, and stomach in the four basic cardiac positions from the frontal projection. A, In situs solitus, the descending aorta, apex, and stomach are all on the left. B, In situs inversus, the descending aorta, apex, and stomach are all on the right. C, In dextroversion, the descending aorta and stomach are on the left, but the apex is on the right. D, In levoversion, the descending aorta and stomach are on the right, but the apex is on the left.



FIGURE 36-4


Abnormal cardiac axis and position. A, True dextrocardia. B, Dextroposition secondary to a large left-sided cystic adenomatous malformation that pushes the heart into the right chest. C, Dextroposition caused by the presence of right lung hypoplasia. The heart shifts into the space lacking lung tissue but maintains a near-normal axis. D, Mesocardia.


Levocardia is the term used to denote the normal position of the heart in the left side of the chest (with the cardiac apex pointed to the left) and is often used when visceral situs abnormalities are present. Levocardia can be associated with normal situs, situs inversus (abdominal organs are located on the opposite side of normal), or situs ambiguous. Levoposition of the heart refers to the condition in which the heart is displaced further toward the left side of the chest, usually in association with a space-occupying lesion (see Figure 36-4 ).


Mesocardia indicates an atypical location of the heart, with the cardiac apex pointing toward the midline of the chest. Usually the heart is located more toward the midline. This may be found with the presence of an extracardiac mass or lung abnormalities ( Figure 36-4 , D ).




Cardiac enlargement


Cardiomyopathy


Cardiomyopathy is a condition of the myocardial tissue in the heart. This disease process may be caused by exposure to a virus (Coxsackie or mumps) or to bacteria, which leads to an infection that causes cardiomyopathy. Errors of metabolism may also cause cardiomyopathy. Endocardial fibroelastosis has also been associated with cardiomyopathies and hypoplastic left heart syndrome. Asymmetric septal hypertrophy (as seen in patients with hereditary idiopathic subaortic stenosis) and concentric hypertrophy (as seen in some uncontrolled diabetic mothers) have been reported.


Myocarditis is characterized by necrosis and destruction of myocardial cells and an inflammatory infiltrate. In a viral cardiomyopathy, all four chambers are dilated, with thinning of the myocardial walls. Gross valvular regurgitation may be present, resulting from the stretched mitral and tricuspid annulus ( Figure 36-5 ). Cardiac function is decreased severely, leading to congestive heart failure with pericardial effusion, bradycardia, and death. The general prognosis for a fetus with evidence for a cardiomyopathy is poor. Serial fetal echoes are performed to monitor chamber size, regurgitation, and contractility.






FIGURE 36-5


Four-chamber view of the heart shows dilation of all four chambers. B, Regurgitation was present in the mitral and tricuspid valves. Pericardial effusion (arrow). LA, Left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.


Pericardial effusion


Pericardial effusion is an abnormal collection of fluid surrounding the epicardial layer of the heart. In the four-chamber view, a hypoechoic area in the peripheral part of the epicardial/pericardial interface of 2 mm or less is considered within normal limits and does not represent a pericardial effusion. The separation must be seen on the M-mode to separate both in systole and in diastole and be greater than 2 mm. A separation that surrounds the heart (from the atrioventricular junction around the apex of the heart) may be associated with hydrops fetalis ( Figure 36-6 ).




FIGURE 36-6


A, Apical view of a small pericardial effusion. B, Apical view of a large pericardial effusion involving the right ventricle, apex, and left ventricle. LA, Left atrium; LV, left ventricle; MV, mitral valve; RA right atrium; RV, right ventricle; SVC, superior vena cava; TV, tricuspid valve.


With a small pericardial effusion, the separation of the pericardium from the epicardium may localize toward the posterolateral and apical walls of the heart. The larger effusion will extend to the atrioventricular groove posteriorly and around the anterior right ventricular wall.


Pericardial effusion may be seen secondary to indomethacin therapy with premature closure of the patent ductus arteriosus. Pericardial effusion has also been associated with coxsackievirus, cytomegalovirus, parvovirus, human immunodeficiency virus, intrauterine growth restriction, and aneuploidy.




Septal defects


Atrial septal defect


An Atrial septal defect allows communication between the left atrium and right atrium. The locations of three common atrial septal defects are shown in Figure 36-7 . There are three common forms of atrial septal defects: ostium secundum, ostium primum, and sinus venosus. The ostium secundum defect is the defect in the central atrial septum near the foramen ovale and is the most difficult to see in utero, as the flap of the foramen ovale is mobile at this period of development. The ostium primum defect is usually associated with the chromosomal abnormality of trisomy 21 and often will have a cleft mitral valve and abnormalities of the atrioventricular septum. The least common septal defect is the sinus venosus defect that is seen near the entrance of the superior vena cava into the right atrium. This may be associated with a partial anomalous pulmonary venous return.




FIGURE 36-7


Atrial septal defects: ostium secundum, ostium primum, and sinus venosus defects viewed from the right atrium.


The atrial septal defect is not always recognized during fetal life unless part of the intra-atrial septum is missing. The foramen ovale remains open in the fetal heart until after birth, and the pressures change between the right and left sides of the heart to force the foramen to close completely. Failure of the foramen to close may result in atrial septal defect, secundum type. An atrial septal defect provides communication between the right and left atrium. The defect must be quite large in the fetus to be identified by ultrasound.


The area of the foramen ovale is thinner in the fetus than the surrounding atrial tissue; therefore, with echocardiography, the area is prone to signal dropout, particularly in the apical four-chamber view when the transducer is parallel to the septum. Any break in the atrial septum in this view must be confirmed by the short-axis or “subcostal” view (the transducer is inferior to the heart and angled cephalad in a transverse or short-axis plane), in which the septum is more perpendicular to the transducer. Because of beam-width artifacts, the edges of the defect may be slightly blunted and appear brighter than the remaining septum.


In utero the natural flow in the atrium is right to left across the foramen (as the pressures are slightly higher on the right). A small reversal flow may be present. The foramen should flap into the left atrial cavity. The flap should not be so large as to touch the lateral wall of the atrium; when this redundancy of the foramen occurs, the sinoatrial node may become agitated in the right atrium and cause fetal arrhythmias. The sonographer should be sure to sweep inferior to superior along the atrial septum to identify the three parts of the septum: the primum septum, fossa ovalis, and septum secundum.


Ostium secundum atrial septal defect.


The most common atrial defect is the secundum atrial septal defect, which occurs in the area of the fossa ovalis ( Figure 36-8 ). Usually an absence of the foramen ovale flap is noted, with the fossa ovalis opening larger than normal.




FIGURE 36-8


Four-chamber view of the heart illustrating the absence of the flap of the foramen ovale. ASD, Atrial septal defect; LA, left atrium; LPV, left pulmonary vein; LV, left ventricle; RA, right atrium; RPV, right pulmonary vein; RV, right ventricle.


Sonographic findings.


Doppler tracings of the septal defect with the sample volume placed at the site of the defect show a right-to-left flow with a velocity of 20 to 30 cm/sec. Color flow Doppler is performed in the apical four-chamber and subcostal views and may be useful to outline the size and direction of flow as it crosses the foramen ovale ( Figure 36-9 ). The flow patterns of the mitral and tricuspid valves are slightly increased with the elevated shunt flow.




FIGURE 36-9


A, The most common type of atrial septal defects occurs in the area of the fossa ovalis, known as the secundum defect. Ao, Aorta; IVC, inferior vena cava; LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle. B, In the fetus, normal flow should occur at the level of the foramen ovale (FO). PV, Pulmonary vein.


Ostium primum septal defect.


The primum septal defect is deficient in the lower (inferior) portion of the septum, near the crux of the heart ( Figure 36-10 ). It may be seen in atrioventricular septal defect malformation in which there is malalignment of the atrioventricular valves secondary to the defect. In addition, a cleft of the mitral valve is present, causing mitral regurgitation into the left atrial cavity.






FIGURE 36-10


A, The ostium primum atrial septal defect in the four-chamber view. B, Atrioventricular defect with a primum and membranous septal defect. ASD, Atrial septal defect; LA, left atrium; LPV, left pulmonary vein; LV, left ventricle; RA, right atrium; RPV, right pulmonary vein; RV, right ventricle.


Sonographic findings.


The primum septal defect is best imaged in the four-chamber plane that is parallel to the transducer beam. The gain should be reduced to clearly identify the atrial septum. Look for the flap of the foramen ovale. This defect may be part of an atrioventricular septal defect or it may be a primary defect with or without a cleft mitral valve.


Sinus venosus septal defect.


The sinus venosus atrial septal defect is technically more difficult to visualize with echocardiography. This defect lies in the superior portion of the atrial septum, close to the inflow pattern of the superior vena cava ( Figure 36-11 ).




FIGURE 36-11


The sinus venosus atrial septal defect near the entrance of the superior vena cava and right upper pulmonary vein (RPV). ASD, Atrial septal defect; LA, left atrium; LPV, left pulmonary vein; LV, left ventricle; RA, right atrium; RPV, right pulmonary vein; RV, Right ventricle; SVC, superior vena cava.


Sonographic findings.


Sinus venosus septal defects are best visualized with the subxiphoid four-chamber view. If signs of right ventricular volume overload are present, with no atrial septal defect obvious, care should be taken to study the septum in search of a sinus venosus type of defect. Partial anomalous pulmonary venous drainage of the right pulmonary vein is usually associated with this type of defect; thus it is important to identify the entry site of the pulmonary veins into the left atrial cavity. Color flow mapping is useful in this type of problem because it allows the sonographer to visualize the venous return to the left atrium and a flow pattern crossing into the right atrial cavity.


Ventricular septal defect


Ventricular septal defect is the most common congenital lesion of the heart, accounting for 30% of all structural heart defects. The septum is divided into two basic segments: the membranous and muscular areas ( Figure 36-12 ). The septum lies in a curvilinear plane and has different areas of thickness. There are a number of sites where ventricular septal defects may occur within the septum. Muscular defects occur more inferior in the septum, usually are very small, and may be multiple ( Figure 36-13 ). Often, smaller defects will close spontaneously shortly after birth. This type of muscular defect is more difficult to image with echocardiography.




FIGURE 36-12


Ventricular septal defect. Portions of the ventricular septum showing the infundibular (outlet septum), membranous septum, inlet septum, and muscular septa.



FIGURE 36-13


Ventricular septal defects. A, Membranous or perimembranous ventricular septal defect may be difficult to visualize on 2D alone, but it can be recognized when associated with redundant atrioventricular valve tissue or aneurysm of membranous septum (arrow). B, Color flow Doppler confirms the membranous ventricular septal defect. The direction of flow (arrow) is typically from left ventricle (LV) to right ventricle (RV). RA, Right atrium. C, Muscular ventricular septal defect, particularly when small or moderate in size, may not be well seen by 2D alone, but it requires color Doppler set so there is no aliasing by changing the pulse repetition frequency with the depth setting, as shown in this anterior muscular defect. D, Outlet defects (arrow) when associated with malalignment of the outlet or conal septum are usually readily demonstrated by 2D alone because of their typical large size and overriding of one of the semilunar valves. PA, Pulmonary artery.


Membranous septal defect.


The (perimembranous) ventricular septal defect may be classified as membranous, aneurysmal, or supracristal ( Figure 36-14 ). The significant anatomic landmark is the crista supraventricularis ridge. The defect lies either above or below this ridge. Defects that lie above are called supracristal. Supracristal defects are located just beneath the pulmonary orifice so that the pulmonary valve forms part of the superior margin of the interventricular communication. Defects that lie below the crista are called infracristal and may be found in the membranous or muscular part of the septum. Infracristal defects are the most common.




FIGURE 36-14


The membranous septal defect is shown in this four-chamber view. This is located in the inflow of the ventricles. The muscular defect in this four-chamber view may be large, small, or multiple along the thicker part of the septum. FO, Foramen ovale; LA, left atrium; LV, left ventricle; MV, mitral valve; PV, pulmonary vein; RA, right atrium; RV, right ventricle; SVC, superior vena cava; TV, tricuspid valve; VSD, ventricular septal defect.


Sonographic findings.


The lesion may be partially covered by the tricuspid septal leaflet, and care must be taken to carefully evaluate this area with Doppler and color flow tracings. The membranous defect is found just below the aortic leaflets; sometimes the aortic leaflet is sucked into this defect ( Figure 36-15 ).




FIGURE 36-15


Ventricular septal defect. A, An isolated membranous septal defect shown in this four-chamber view. The edges of the defect are slightly brighter than the rest of the septum. LV, Left ventricle; RV, right ventricle. B, Color Doppler is helpful when the ventricular septal defect (VSD) is large enough to allow crossover of flow from the higher-pressure right side of the heart into the left side of the heart.


The presence of an isolated ventricular septal defect in utero usually does not change the hemodynamics of the fetus. Defects smaller than 2 mm are not detected by fetal echocardiography as these are beyond the limits of resolution. Care must be taken in the four-chamber view to carefully sweep the probe posterior to record the inlet part of the septum to anterior to record the outlet part of the septum.


Ventricular septal defects may close with the formation of aneurysm tissue, which is commonly found along the right side of the septal defect ( Figure 36-16 ). These aneurysms generally protrude into the right heart in one of the following three directions: (1) above the tricuspid valve and into the right atrium, (2) directly into the septal leaflet of the tricuspid valve, or (3) below the tricuspid leaflets and into the right ventricular cavity. Usually these aneurysms are small, but when they become large, obstruction may occur in the right ventricular outflow tract.




FIGURE 36-16


Five-chamber view of the heart illustrating the presence of a ventricular septal aneurysm inferior to the aortic cusps near the septal leaflet of the tricuspid valve. A, Atrium; Ao, aorta; LA, left atrium; LV, left ventricle; MV, mitral valve; RA, right atrium; RV, right ventricle; TV, tricuspid valve.


Muscular defect.


A less common infracristal defect is located in the muscular septum. These defects may be large or small, or they may be multiple fenestrated holes. The multiple defects are more difficult to repair, and their combination may have the same ventricular overload effect as a single large communication. Small muscular defects are usually found in the neonatal stage and often close spontaneously.


The prognosis is good for a patient with a single ventricular septal defect. However, the association with other cardiac anomalies, such as tetralogy of Fallot, single ventricle, transposition of the great arteries, and endocardial cushion defect, is increased when a ventricular septal defect is found.


Silverman and Schmidt reported that 40% of ventricular septal defects are closed within 2 years of life and that 60% close by 5 years. The incidence of closure for membranous defects is 25% by 5 years and 65% for muscular defects by 5 years.


Sonographic findings.


The best echocardiographic views to image the septal defect in the outflow tract are the long-axis, short-axis, and five-chamber views. The septal defect in the inflow tract is best seen on the four-chamber view.


Evaluation of shunt flow and direction is made with color flow mapping. Remember that pressures between the right and left heart are almost the same in utero, so a small defect will probably not show a velocity change. If the defect is large, the sample volume should be placed directly in the defect to see the jet flow direction and velocity.


Atrioventricular septal defect


The endocardial cushion defect is also called ostium primum atrial septal defect, atrioventricular canal malformation, endocardial cushion defect, and atrioventricular septal defect (AVSD) ( Figure 36-17 ). These defects are subdivided into complete, incomplete, and partial forms.




FIGURE 36-17


Atrioventricular septal defect. A, Long-axis view shows the discontinuity of the anterior leaflet of the mitral valve with the posterior wall of the aorta. The membranous septal defect is seen. Ao, Aorta; LA, left atrium; LV, left ventricle; MV, mitral valve; RV, right ventricle; TV, tricuspid valve. B, Short-axis through the atrioventricular valves shows the cleft in the anterior leaflet of the mitral valve (MV). The primum septal defect is seen. IAS, Interarterial septum. C, Four-chamber view showing the Rastelli type A large defect in the center (crux) of the heart. The membranous and primum septal defects are seen with the cleft mitral valve. There is a common leaflet from the anterior mitral leaflet to the septal tricuspid leaflet. ASD, Atrial septal defect; SVC, superior vena cava. D, Rastelli type B defect shows the chordal attachments from the medial portion of the cleft mitral leaflet related to the papillary muscle on the right side of the septal defect. E, Rastelli type C defect shows a free-floating common atrioventricular leaflet (C).


Incomplete atrioventricular septal defect.


The failure of the endocardial cushion to fuse is termed an incomplete atrioventricular septal defect. This condition results in a membranous ventricular septal defect, abnormal tricuspid valve, primum atrial septal defect, and cleft mitral valve ( Figure 36-18 ). A cleft mitral valve means that the anterior part of the leaflet is divided into two parts (medial and lateral). When the leaflet closes, blood leaks through this hole into the left atrial cavity. The leaflet is usually somewhat malformed, further causing regurgitation into the atrium. In addition, there is a communication between the left ventricle and right atrium (left ventricular to right atrial shunt) because of the absent primum atrial septum and membranous interventricular septum. The ventricular septal defect occurs just below the mitral ring and is continuous with the primum atrial septal defect.




FIGURE 36-18


Atrioventricular septal defect. A, A patient with trisomy 21 had 2:1 heart block secondary to the complete atrioventricular septal defect, which included the membranous and atrial septa. B, A patient with trisomy 21 had a huge atrioventricular defect. The membranous and part of the muscular septum is not present (VSD); the primum septum is also absent (ASD).


Complete atrioventricular septal defect.


The endocardial defect is characterized by the insertion of the chordae from the cleft mitral and tricuspid valve into the crest of the ventricular septum or a right ventricular papillary muscle ( Figure 36-19 ). The most primitive form is called a complete atrioventricular septal defect. This defect has a single, undivided, free-floating leaflet stretching across both ventricles. A two-dimensional (2D) sweep from the mitral to the aortic valves would show the anterior mitral leaflet swinging through the ventricular septal defect in continuity with the tricuspid valve. The tricuspid valve is said to cap the mitral valve. The anterior and posterior leaflets are on both sides of the interventricular septum, causing the valve to override or straddle the septum. This is a more complex abnormality to repair because the defect is larger and the single atrioventricular valve is more difficult to manage clinically, depending on the amount of regurgitation present. The regurgitant jet may extend from the right ventricle to left atrium secondary to the valve deformity and increased right heart pressures. Complete AVSDs are frequently associated with malpositions of the heart (mesocardia and dextrocardia) and atrioventricular block (abnormal rhythm secondary to distortion of the conduction tissues).




FIGURE 36-19


Atrioventricular septal defect. A, Prominent inflow velocities are seen across the mitral valve. There is a small regurgitant flow into the left atrium seen as flow reversal at the end of diastole below the baseline. B, Color flow imaging is helpful to map the flow across the defect and to track regurgitation into the atria. LA, Left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.


AVSDs are frequently associated with other cardiac defects, including truncoconal abnormalities, coarctation of the aorta, and pulmonary stenosis or atresia. There is an increased incidence of Down syndrome (50% of trisomy 21 babies have congenital heart disease) and asplenia and polysplenia syndromes.


Occasionally, complete absence of the interatrial septum is noted in the fetal four-chamber view. With color flow, the entire atria are completely filled throughout systole and diastole. This is termed common atria.


With a partial AVSD, the fetus has only some of the previously described findings, usually an absent primum atrial septum and a cleft mitral valve.


Sonographic findings.


Echocardiographically the ideal views are the long-axis, short-axis (to search for abnormalities in the atrioventricular valves, such as presence of cleft), and four-chamber views (to search for chordal attachment, overriding, or straddling of the valves). The atrioventricular valves share a superior and inferior bridging leaflet that results in a functional single large valve. This may be well demonstrated in the short-axis view of the ventricle as the single large valve appears as a wide circle “8” sign. The crux of the heart is carefully analyzed by slowly sweeping the transducer anterior (toward the aorta outlet) to posterior (toward the atrioventricular valve inlet) to record the outlet and inlet portions of the membranous septum.


Doppler and color flow techniques are extremely useful in determining the direction and degree of regurgitation present in the atrioventricular valves and the direction of shunt flow (increased right-sided heart pressure causes a right ventricular to left atrial shunt in the fetus).




Right ventricular inflow disturbance


Abnormalities that affect primarily the right side of the heart are listed as inflow or outflow tract disturbances. Each lesion is presented, along with technical advice on how to obtain the ideal fetal cardiac image.


Tricuspid atresia/stenosis


Tricuspid atresia is the interruption of the growth of the tricuspid leaflet that begins early in cardiac embryology. This interruption involves the growth of the tricuspid apparatus, causing the valve to be hypoplastic or atretic.


In tricuspid atresia, the inflow portion of the right ventricle has failed to form, and a membrane or dimple in the floor of the right atrium represents the position where the tricuspid valve should have originated ( Figure 36-20 ). A ventricular septal defect may be present to help shunt blood into the hypertrophied right ventricle. The right ventricular outflow tract and pulmonary artery are generally diminished in size.




FIGURE 36-20


The hypoplastic right ventricle and immobile echogenic tricuspid valve apparatus are key factors in the four-chamber view in the patient with tricuspid atresia. The right atrium (RA) is enlarged. ASD, Atrial septal defect; LA, left atrium; LV, left ventricle; MV, mitral valve; RV, right ventricle; SVC, superior vena cava.


Sonographic findings.


Echocardiographically the tricuspid valve is best visualized on the four-chamber view ( Figure 36-21 ). The findings in tricuspid atresia are a large dilated left ventricular cavity with a small, underdeveloped right ventricular cavity. The echogenic tricuspid annulus is seen with no valvular movement. The mitral valve is clearly the dominant atrioventricular valve. On the long- and short-axis views, the right ventricle is seen as a slitlike cavity just anterior to the interventricular septum.


May 29, 2019 | Posted by in ULTRASONOGRAPHY | Comments Off on Fetal echocardiography: Congenital heart disease
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