Sonography of the Fetal Heart: Findings on the Four-Chamber View

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1 547 Sonography of the Fetal Heart: Findings on the Four-Chamber View John P. McGahan1 The normal and pathologic sonographic appearances of the fetal heart on four-chamber views are reviewed. Performed correctly, the four-chamber view is the best method of examining the complex cardiac anatomy of the small fetal heart and of detecting major congenital heart disease. Congenital heart disease is the most common severe congenital anomaly found in neonates [1]. It has been estimated that more than eight in i 000 live births have structural abnormalities of the heart or great vessels [2]. These anomalies may be associated with serious morbidity and mortality in the fetus and the neonate. While a number of noncardiac fetal malformations have been diagnosed routinely for over a decade, it is only recently with advances in sonographic instrumentation that imaging of the fetal heart has improved [3]. However, because of the complexities of cardiac anatomy and the small size of the fetal heart, optimal examination requires special professional expertise in prenatal sonogmaphy combined with detailed knowledge of cardiac anatomy. This sophisticated examination of the fetal heart requires the use of high-resolution meal-time equipment, with detailed examination of the heart in several anatomic planes, and the use of M-mode sonography, pulsed Doppler sonogmaphy, and color flow mapping. Most persons performing routine fetal obstetric sonography do not have such instrumentation or expertise to examine the fetal heart in great detail. However, many major structural defects of the heart, especially those causing the most serious morbidity and mortality, should be well recognized by obtaining a routine four-chamber view. This article Review Article reviews the normal and abnormal appearances of the fetal four-chamber view of the heart. Indications A four-chamber view of the heart has been proposed as a routine portion of the sonographic examination of the fetus to be obtained from 1 8 weeks to term [1, 4, 5]. It has been proposed that a satisfactory four-chamber view of the heart may be obtained in 95% of pregnancies after i 8 weeks [4]. Difficulty in performing a satisfactory examination of the fetal heart may be due to maternal body habitus, fetal position, or markedly increased or decreased amniotic fluid volume. A number of fetuses are at high risk for congenital heart disease. Risk factors can be divided into fetal risk factors and maternal risk factors (Table 1). For instance, the risk of congenital heart disease has been reported at 0.8% [2], but this risk increases to up to 4% if a sibling has a heart defect and i 2% risk if a parent has a heart defect [6]. If a noncardiac structural abnormality is detected on prenatal sonogmaphy, there is a very high risk of associated cardiac malformations in these cases, therefore requiring a careful examination of the fetal heart [7, 8]. However, in most cases, congenital heart disease is a spontaneous event without associated high-risk factors. Even in a referral-based practice, the majority of prenatally diagnosed cases of congenital heart disease fall into a low-risk group [9]. Therefore, for routine obstetric sonography, the four-chamber view has been proposed as Received July 23, 1 990; accepted after revision October 8, I Department of Radiology, University of California Davis Medical Center, Stockton Blvd., TICON II, Sacramento, CA AJR 156: , March X/91/ American Roentgen Ray Society

2 548 McGAHAN AJR:156, March 1991 the simplest, and yet a highly accurate, method of detecting significant congenital heart disease [4]. is considered, and (6) eliminates delay in definitive diagnosis and treatment [1 1]. Importance of Prenatal Diagnosis It is important to diagnose some of the more severe cases of congenital heart disease because of the high morbidity and mortality rates if untreated [2]. However, in the past 5 years, survival rates for major cardiac anomalies are much improved. Simplification of surgical techniques, improvement of other operations, and development of new operations have allowed the surgical repair of many complex congenital defects. Technical advances in intmaopemative and postoperative came such as extracompomeal membrane oxygenation, deep hypothermia, cardioplegia, and intmaaortic balloons have helped facilitate performance of complex operations and have improved infant survival [1 0]. Therefore, it is important to recognize a possible abnormality on a four-chamber view of the heart because it (1 ) allows time for a second look at fetal echocardiography for a more precise diagnosis, (2) allows prenatal counseling for the parents, (3) allows time for planned delivery, (4) allows time for relocation of family to centers equipped to handle such cases, (5) allows search time when heart transplantation TABLE 1: Risk Factors for Congenital Heart Disease Fetal Extracardiac abnormality Chromosomal abnormality Fetal cardiac arrythmia Nonimmune hydrops Risk Factors Question of cardiac anomaly on prior sonogram Intrauterine growth retardation Maternal Family history of congenital heart disease (parent or sibling) Teratogenic exposure (e.g., alcohol, amphetamines, anticonvulsives, lithium) Maternal disorders (diabetes mellitus, collagen vascular disease, phenylketonuria) Maternal infection (e.g., rubella) Familial syndromes a Adapted from Copel et al. 14]. Technique and Normal Anatomy When evaluating the fetal heart, the fetal position should be documented. The site of the stomach and the relationship of the suprahepatic portion of the inferior vena cava to the right atrium are noted to determine the situs. The fourchamber view is obtained in a horizontal section, just above the region of the diaphragm. The fetal spine is identified and the chest is scanned in the transverse axis to obtain a fourchamber view. Regardless of the fetal position, the apex of the heart should point at approximately a 45#{176} angle to the left anterior chest wall on the same side as the fetal stomach. A line drawn through the intmaventriculam septum will traverse a plane approximately 45#{176} with a line drawn between the spine and the sternum (Fig. i) [i2]. It is important to note if the heart is deviated from this position, as this may indicate a situs abnormality or result from fetal cardiac malpositioning or a noncardiac thoracic mass. In general, the two ventricles are of approximately equal size when studied on a four-chamber view of the heart. DeVome et al. [i 3] have made precise measurements of the internal dimensions of the left and right ventricles on M-mode sonograms obtained during diastole at the atrioventricular valve region. Although there is almost a one-to-one ratio, later in pregnancy the right ventricle assumes more of the cardiac output and is slightly larger than the left ventricle [1 3]. While M mode is much more precise than meal-time examination, the use of meal-time sonogmaphy should enable one to mecognize that the right ventricle and the left ventricle are almost the same size (Fig. 1). The might atrium can be identified sonographically by following the suprahepatic portion of the inferior vena cava into that chamber. The flap of the fomamen ovale can be identified opening into the left atrial cavity. This recognition can help separate the might from the left atrium. The left atrium is the most posteriorly situated structure within the thoracic cavity. Once the atrium is identified, the atrioventmiculam connections require recognition of certain morphologic features of Fig. 1.-A, Schematic drawing through normal fetal thorax shows four cardiac chambers. A line drawn through intraventricular septum will trayerse a plane approximately 45#{176} with a line drawn between fetal spine and sternum. (Modified and reprinted with permission from Comstock [12].) B, Magnified sonogram of fetal heart and thorax shows four chambers. Note trabeculated appearance of muscles of right ventricle (arrowhead) and atrioventricular valves (arrows). L = left, R = right, LV = left ventricle, R I = right ventricle, RA = right atrium, LA left atrium, 5 = spine.

3 AJR:156, March 1991 FOUR-CHAMBER VIEW OF FETAL HEART 549 the might and left ventricles. For instance, the right ventricle appears more trabeculated within the ventricular cavity than the left ventricle does because of the more prominent moderator band near the apex of the might ventricle (Fig. 1). Often within the left ventricle, a very bright reflection from the papillary muscles may be seen within that chamber (Fig. 2) [i4]. This should not be misinterpreted as a mass or tumor within the ventricle. The atrioventmiculam valves are then identified separating the atria from the ventricle. The leaflets of the tricuspid valve are usually inserted slightly lower in the ventricular septum than is the mitral valve. The relationship of the aorta and the pulmonary artery to the ventricular chambers cannot be assessed on this fourchamber view. The relationship of the pulmonary artery and aorta to the ventricular chamber is better assessed by other views. For instance, the relationship of the aorta to the left ventricle is best evaluated by a left ventricular long-axis view of the fetal heart (Fig. 3). This view is obtained by turning the transducer from the transverse plane used for the foum-chamber view, so the ultrasound plane is directed between the right shoulder of the fetus and the fetal stomach. However, many anomalies are initially recognized by noting associated septal defects, or ventricular disproportion, on the foum-cham- Fig. 2.-Normal papillary muscle on four-chamber view of heart. Bright echogenic focus (arrow) within left ventricle corresponds to a papillary musdc and is a normal finding. LA = left atrium, RA = right atrium, R = right ventricle, S = spine. (Courtesy of D. Nyberg, Seattle, WA.) Fig. 3.-Long-axis view of heart. Sonogram shows normal left-ventricular long-axis view of heart with aorta (A) originating from left ventricle (Lv). LA = left atrium, RV = right ventricle, S = spine. Fig. 4.-Pentalogy of Cantrel. Four-chamber view of heart shows an ectopic thoracic cordis (curved arrow), which was associated with an omphalocele. Straight arrows indicate margins of anterior thoracic cavity. S = spine. bem view [4]. In fact, in a recent review of over pregnancies with 74 structurally abnormal fetal hearts, an abnormality was identified on the four-chamber view in 71 (96%) [4]. Abnormal Four-Chamber View of the Heart A systematic approach to the four-chamber view of the heart will allow detection of both intracardiac as well as intrathoracic abnormalities. Six questions should be asked whenever evaluating the four-chamber view of the heart: Is the Heart in Its Normal Position? When evaluating the four-chamber view of the heart for normal position, cardiac situs should be evaluated. Situs abnormalities may be associated with specific syndromes such as asplenia or polysplenia. These specific abnormalities, including asplenia (bilateral might-sidedness) and polysplenia (bilateral left-sidedness), are also characterized by complex congenital heart disease. These abnormalities initially may be identified prenatally on sonography by recognition of the discordance between the location of the fetal stomach, which is normally located on the left, and the fetal heart, with the Fig. 5.-Type Ill cystic adenomatoid malformation. Transverse sonogram through fetal thorax shows large echogenic mass within left thorax displacing heart to right (arrows). LT = left, S = spine, R = right. p I..-..

4 McGAHAN AJR:156, March 1991 apex normally to the left [1 5]. Positional abnormalities of the heart also may occur in such anomalies as pentalogy of Cantrel, that is, thomacic ectopic cordis, which is associated with an abdominal wall defect (Fig. 4). More commonly, the four-chamber view of the heart may be used as a normal anatomic marker for extracamdiac abnormalities of the fetal thorax. For instance, if theme is a large mass within one side of the fetal thorax, this mass may first be appreciated by noting the abnormal position and orientation of the four-chamber view of the heart. For instance, in type III cystic adenomatoid malformation, a large pulmonary mass will cause cardiac displacement into the contralateral thoracic cavity (Fig. 5) [1 6]. By noting the abnormal position of the four-chamber heart, one can better ascertain if there is a mass lesion within the thorax. Is the Heart Normal in Size in Comparison with the Fetal Thorax? A four-chamber view of the heart can be used to assess cardiothoracic disproportion or a disproportionately small fetal BVOD (MM) i#{176}i!tti!!1r ventricle. Hypoplasia of the left ventricle is usually termed the, : e a io i6 ie CHEST CIRCUMFERENCE (CM) Fig. 6.-Confidence-limit (Cl) graph for M-mode biventncular outer dimension (BVOD). Mean, 95%, and 5% confidence limits for individual predictions of the biventricular outer dimensions regressed against chest circumference. (Reprinted with permission from Devore et al. [13].) thorax. Such measurements may be obtained from meal-time images but are more accurately obtained from M mode. Wellstandardized tables are available that compare the chest circumference with other routine measurements, including the biparietal diameter, femomal length, and head circumference. Standardized measurements of the ratio of the cardiac biventricular outer dimensions compared with the chest circumfemence obtained by meal-time and M-mode measurements have been tabulated throughout pregnancy (Fig. 6) [17]. These ratios may be helpful in predicting cardiomegaly or pulmonary hypoplasia. More detailed information concerning M-mode measurements may be obtained from other references [3, 5, 13, 17]. Are the Ventricular Chambers Approximately Equal in Size? If ventricles are not the same size, theme may be a complex cardiac abnormality. For instance, coamctation of the aorta may be indirectly diagnosed by noting that the left ventricle is smaller than the right ventricle on the four-chamber view [6]. It is unusual to identify the coarctation itself, but noting that the left ventricle appears smaller than the might on the fourchamber view provides indirect evidence of the possibility of a coarctation. More common abnormalities easily detected by noting discrepancies in the sizes of the ventricles are cardiac abnormalities associated with hypoplasia of either the left or right hypoplastic left heart syndrome [i 8]. This is a severe anomaly usually consisting of underdevelopment of the aorta, aortic valve, left ventricle, or mitral valve with an intact ventricular septum. In hypoplastic left ventricle, the left ventricle varies in size from essentially slitlike to smaller than normal, depending on the degree of hypoplasia of the mitral valve (Fig. 7) [19]. There is considerably more confusion concerning hypoplasia of the right ventricle. Most authors do not consider this a separate syndrome. However, this may be considered one of two anomalies, either pulmonary atmesia with an intact yentricular septum or a tricuspid atmesia with an associated ventricular septal defect (VSD). There is usually severe hy- Fig. 7.-Hypoplastic left ventricle. Four-chamber view of heart shows a hypoplastic left ventricle (LV) and a small remnant of atrial septum (arrow). Note size discrepancy between right ventricle (RV) and small left ventricle. Fig. 8.-Two-chamber heart. Four-chamber view of heart shows a single atrium or an atrial septal defect with a common atrium (A) that empties into a single ventricle (v). Note thickening of wall of ventricular chamber (arrow). S spine. 7 8

5 AJR:156, March 1991 FOUR-CHAMBER VIEW OF FETAL HEART 551 poplasia of the might ventricle associated with abnormalities of the pulmonary outflow tract in pulmonary atmesia with an intact ventricular septum [20]. In tricuspid atmesia with a VSD there may be a hypoplastic right ventricle. The amount of hypoplasia of the right ventricle depends on the size of the VSD. Another anomaly that may be embryologically different from severe hypoplastic right ventricle or severe hypoplastic left ventricle is the anomaly in which theme is a single ventricle [21]. This anomaly usually is associated with two atmia emptying into a single ventricular cavity, which may have the appearance of a right or left ventricle or may be an intermediate cavity. Such an anomaly should be easily recognized on a four-chamber view of the heart. Figure 8 shows a case of a single ventricle associated with a single atrium (i.e., twochamber heart) that was detected prenatally. Is There a Septal Defect? Other abnormalities that may be detected on the fourchamber view of the heart include defects in the atrial, atnoventricular, or ventricular septum. The most common prenatal Fig. 9.-ventricular septal defect. A, Complete scanning of ventricular septum is needed to exclude ventricular septal defects. For instance, in this four-chamber view of the heart in a fetus with an omphalocele (0) and transposition of the great vessels, ventricular septum appears intact (arrow). S = spine, V = ventricle. B, By obtaining a different scan plane through Intraventricular septum, however, a large ventricular septaldefect(arrow) is identified between the two ventricles. Fig. 10.-Transposition of great arteries. A, Diagram shows transposition of great yeseels with aorta originating from right ventricle (RV) and pulmonary artery (PA) originating from left ventricle (LV). There may be an accompanying septal defect. B, Four-chamber view demonstrated a large atrial septal defect. This more cephalic view shows the parallel course of aorta (A) and pulmonary artery rather than normal perpendicular course of these vessels. P = posterior. (Reprinted with permission from Nyberg and Emerson [7].) cardiac abnormality detected on a four-chamber view of the heart in one series was complete atrioventricular septal defect (endocardial cushion defect). This defect was detected in i6 (1 00%) of 1 6 cases on a four-chamber view of the heart [4]. Likewise, large VSDs may be detected by a four-chamber view of the heart. VSDs that are moderate to large in size are often associated with complex cardiac abnormalities. Therefore, initial detection of a VSD will necessitate a more careful search of the fetal heart for a more complex cardiac abnormality. Small and even moderate-sized VSDs may be overlooked [4, 9]. Even moderate to large VSDs may not be visualized if careful scanning is not performed. When evaluating the atrial or ventricular septum, a careful search of the entire septum is needed to exclude a VSD as illustrated in Figure 9. By obtaining only a single four-chamber view, a septal defect can easily be overlooked. It is possible that use of color flow imaging, in combination with routine scanning, will allow more easy recognition of these small VSDs. In any case, detection of an atrial septal defect, VSD, or endocardial cushion defect on a four-chamber view should prompt a complete fetal cardiac examination (Fig. 10).

6 552 McGAHAN AJR:156, March 1991 Fig. 11.-Ebstein anomaly. Attempted fourchamber view of heart shows marked dilatation of right atrium (RA) and inferior displacement of tricuspid leaflet (open arrow) into right ventricle (RV). There is also pleural effusion (solid arrow). LT = left, LV = left ventricle, LA = left atrium, S = spine. (Courtesy of D. Nyberg, Seattle, WA.) Are the Atrioventricular Valves in a Normal Position? Abnormal position of the atrioventriculam valves is easily detected on a four-chamber view [4]. Usually this abnormality is right-sided and is associated with malformations of the tricuspid valve, in which the septal leaflet of this valve is displaced into the cavity of the right ventricle-ebstein anomaly (Fig. 1 1). This produces a grossly enlarged dilatation of the right atrium that may be recognized prenatally on the fourchamber view of the heart [4]. Similar enlargement of the right atrium can result from tricuspid dysplasia and regurgitation without inferior displacement of the tricuspid valve [7]. Is There Any Abnormality of the Endocardium, Myocardium, or Pericardium? A four-chamber view of the heart also may be helpful to identify such problems as increased thickness and abnormal echogenicity of the heart muscle, as occurring with cardiomyopathies including endocardial fibroelastosis. This anomaly is characterized by gross thickening of the endocardium. Sonographically, the four-chamber view shows a large heart with poor contractility and a diffusely echogenic endocardium [22]. Focally increased echogenicity may be identified within the ventricles as a mass lesion associated with congenital heart tumors such as rhabdomyomas. Most rhabdomyomas are associated with syndromes such as tubemous sclerosis (Fig. 12) [23]. Normally a small amount of fluid is present within the pericardial sac. The four-chamber view may be helpful in detecting pencardial effusions appreciated as an anechoic region separating the two layers of the pericardium. Recognition of pericardial effusions may be a clue to systemic disorders such as fetal hydrops (Fig. 13). Fig. 12.-Cardiac rhabdomyomas. Fourchamber view of fetal heart shows echogenic masses (arrows) corresponding to cardiac rhabdomyomas in a fetus later documented to have tuberous sclerosis. LV = left ventricle, RV = right ventricle, LA = left atrium, RA = right atrium. Pitfalls of Four-Chamber Views Fig. 13.-Pericardial effusion. In a twin pregnancy, this four-chamber view of heart is associated with a small pericardial effusion (arrow) in a fetus with hydrops. Lv = left ventricle, Rv = right ventricle, LA = left atrium, RA = right atrium, S = spine. Several anomalies may be difficult to diagnose with a fourchamber view of the heart. These include tetmalogy of Fallot, transposition of the great arteries, simple VSDs, and coarctation of the aorta. However, there is some discrepancy within the literature concerning the prenatal diagnoses of these abnormalities. For instance, Copel et al. [4] diagnosed all cases of tetralogy of Fallot with a four-chamber view, while DeVore et al. [24] have stressed that the VSD in tetmalogy of Fallot usually is not visible on a four-chamber view, and recognition of the aortic dilatation is the key to correct diagnosis (Fig. 1 4). This abnormality is characterized by a VSD, an overriding aorta, stenosis of the might ventricular outflow tract, and right ventricle hypertrophy (Fig. 1 4). Therefore, in addition to the four-chamber view of the heart it may be important to assess the relationship of the aorta and the pulmonary arteries to the ventricular cavity. This may be performed easily by obtaining a left-ventricular long-axis view (Fig. 3). This view can assess the aortic root dilatation and the overriding aorta associated with tetralogy of Fallot. Similarly, transposition of the great vessels without a VSD may be missed with the four-chamber view of the heart [6]. Again, a long-axis view of the heart may be helpful in assessing the abnormal relationship of the aorta and the pulmonary arteries to the ventricular chambers. Normally, the pulmonary artery lies anterior to the aorta. The pulmonary artery bifurcates into the might and left pulmonary arteries. The aorta and the pulmonary artery usually cross perpendicular to each other while in transposition they have a more parallel course (Fig. io). Other anomalies such as very small VSDs are typically missed with the four-chamber view of the heart. Similarly, coamctation of the aorta may be missed, but there may be indirect evidence of this anomaly by an enlarged right ventricle as compared with the left ventricle. Encouraging is the fact

7 AJA:156, March 1991 FOUR-CHAMBER VIEW OF FETAL HEART 553 Fig. 14.-Tetralogy of Fallot. A, Four-chamber view of heart shows right yentricular hypertrophy (open arrow) and slightly increased size of ventricle (RV) as compared with left ventricle (LV). However, ventricular septum appears intact (solid arrow). RA = right atrium, LA = left atrium. B, Long-axis view of heart shows a dilated aortic root (AO) overriding intraventricular septum (arrow). ventricular septal defect was not appreciated. that, in one report, 96% of structural abnormalities of the heart were identifiable on a four-chamber view of the heart. In another report, cardiac lesions were not identified in 17 of 74 cases examined by prenatal sonography [25]. However, most of these missed anomalies were VSDs, many of which closed spontaneously and were associated with good neonatal outcomes [25]. A review of the data presented in the literature seems to indicate that a technically adequate four-chamber view of the heart is an important anatomic marker to exclude major structural abnormalities of the fetal heart and thorax. It is important to recognize these abnormalities because of the high associated morbidity and mortality, which affect perinatal management and decisions. Therefore, it is important for those practicing routine obstetric sonography to be familiar with the normal appearance of the four-chamber view of the heart as a marker for both intra- and extracardiac thoracic abnormalities. ACKNOWLEDGMENTS I thank Karen Anderson and Edie Johnson for manuscript preparation. REFERENCES 1. Allan LD, Crawford DC, Chita 5K, Tynan MJ. Prenatal screening for congenital heart disease. BMJ 1986:292: Moller JH, Neal WA. Heart disease in infancy. New York: Appleton- Century-Crofts, DeVore G. Fetal echocardiography: state of the art. 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