Indian J Pediatr 1991; 58 : 493-503 i

Fetal Echocardiography : A Review Mien D. W i l s o n

Department of Pediatrics, Division of Pediatric Cardiology, Universityof Wisconsin Medical School, Madison, Wisconsin, U.S.A.

Since 1972 when the first report of M-mode studies in the human fetus appearcd, ~ there have been dramatic and steady improvements in ultrasound technology which improve our ability to image and resolve smaller structures at greater depth. At the same time steady advances in premature and newborn intensive care have made the choice of early delivery a more viable one for many babies. Fetal ultrasound studies have allowed much more objective decisions regarding which pregnancies should be carried longer, and which delivered sooner. It is important to know what information cardiac ultrasound can and cannot provide. This review summarizes and updates several excellent earlier reviews)"4

congenital heart disease (especially previous child with left heart obstructionS), diabetes, collagen and vascular disease (risk of heart block in the fetus), drug exposures (especially Lithium, Phenytoin or steroids), or polyhydramnios (see Table). METHODS OF

The fetal heart has finished most of its development by 13 weeks of gestation, but is best imaged with transabdominal ultrasound later between 18 and 24 weeks of gestation when fetal cardiac structures are larger and easier to see. The main goals of a fetal heart study are to image the atrial and ventricular septae and examine all four valves and both great vessels with imaging and with pulsed DopINDICATIONS FOR STUDY pler recording. On a routine screening Fetal risk factors which call for ultrasound study, Doppler recording with its higher study of the heart include arrhythmia, hy- energy output may not be needed and twodrops (ascites, pleural fluid or pericardial dimensional imaging may be adequate. For fluid), abnormal genetic screen, growth ab- a thorough high risk cardiac study however, normalities, decreased fetal movement, or at least selected pulsed Doppler is more abnormalities in other systems on screening important with sampling across all four ultrasound study (especially gastrointestinal valves and sampling in the descending aorta or genitourinary abnorrrlalities). 2 Maternal and across the foramen ovale. risk factors include family history of First, the position of the baby is identified and the long axis determined for referReprint requests : Dr. Allen D. Wilson, ence. The first view obtained is the four Department of Pediatrics, University of chamber view (Figure 1), which is perpenWisconsin Children's Hospital, 600 Highland dicular to the long axis of the baby. This Avenue, Madison, WI 53792, U.S.A. 493

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Fig. 1. Four chamber fetal heart view with apex toward transducer. LV = left ventricle, RV -- right ventricle, ao = descending aorta. view is best for imaging the atrial septum, size and motion of mitral and tricuspid valves, relative size and thickness of the two ventricles, the integrity of the inflow ventricular septum. The flap of the foramcn ovale moves in to the left atrium. The right ventricle is more anterior than the left ventricle, and the tricuspid valve ring and leaflets ride lower in the right ventricle than the mitral valve in the left ventricle. Common atrioventricular canal, Ebstein's disease and other AV valve abnormalities are best seen from this view. This is the best view also for Doppler sampling of velocity in line with blood flow across mitral and tricuspid valves, and also in the ascending aorta with slight angulation of the transducer. It is the best view for assessing relative sizes of the two ventricles. During the 2nd trimester of pregnancy the two sidcs of the heart are equal in size, though during the third trimester the right ventricle and pulmonary

artery may be slightly larger than the left ventricle and the aorta. Wall thickness should be equal on both sides of the heart. By rotating the transducer 90~ the long axis views are found which show the 3 fetal great vessel arches. The aortic arch, pulmonary-ductus arteriosus arch, and inferior vena cava right atrium-superior vena cava arch (Figure 2) can all be identified. These views clarify the outflow pathways from both ventriclcs. The pulmonary arch gives the best site for Doppler sampling of the main pulmonary artery flow, and ductus arteriosus flow. Most of the study can be done with twodimensional imaging, whereas M-mode is used for making measurements of chamber and great vessel size. M-mode measurement can also be used in making the diagnosis of specific type of fetal arrhythmia. In this case views are chosen which show simultaneous atrial and ventricular wall

WILSON : FERALECHOCARDIOGRAPHY T~LE 1. Indications for Fetal Echocardiogram

Fetal factors

Arrhythmia Hydrops Abnormal genetic screen Growth abnormalities Decreased fetal movement Gastrointestinal anomaly Genitourinary anomaly

Matemal factors Family history of congenital heart disease Diabetes Collagen/vascular disease Drug exposure (lithium, phenytoin, steroids) Polyhydramnois motion and the sequence of activation is then determined allowing diagnosis of the arrhythmia. Pulsed Doppler measurement of simultaneous mitral and aortic outflow velocities has also been extremely useful in the diagnosis of arrhythmias. A slightly larger than usual pulsed sample volume is placed in the left ventricular outflow tract and then every

495 atrial contraction shows velocity through the mitral valve in one direction, and every ventricular contraction shows velocity in opposite direction out of the left ventricular outflow tract. 6 SAFETY Several experimental studies have been performed and more are underway testing various "doses" of ultrasound energy on animals, and also following outcome of baby's exposed and not exposed to ultrasound during pregnancy. So far, there are no confirmed reports of any deleterious effects of ultrasound at levels in use clinically in this country. Certainly, exposure to very high intensity ultrasound or very prolonged exposure can cause heat injury to animal cells and this has prompted the Federal Government to place arbitrary limits on the ultrasound "doses" of machines in the U.S.A. They have placed especially stringent arbitrary limits on ultrasound doses for fetal work.

Fig. 2a. Aortic arch view showing tight curve of the aortic arch (Ao) with head vessels arising from it. 2b. Pulmonary arch view showing fight ventricle out flow tract (RV) giving rise to main pulmonary artery (PA) which divides into pulmonary artery branch and patent ductus which leads to descending aorta (DAo). 2c. Systemic venous return arch showing superior vena cava(s) and inferior vena cava (i) entering fight atriun (RA). Hepatic vein (h) enters IVC just before right atrium.

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Fig. 3. Truncus arteriosus. The echocardiogram demonstrates an enlarged aorta which is really the truncus arteriosus (TR) which overrides the ventricular septum with large ventricular septal defect (arrow points from right ventricle across the ventricular defect.) LV = left ventricle. The truncal valve is thickened and there was no separate pulmonary valve identified. Most ultrasound imaging work in the human fetus can be accomplished while remaining under these arbitrary "dose" levels. In fetal cardiac also, the imaging and regular Doppler studies can be performed staying under the arbitrary ultrasound dose levels. By using color Doppler for only the very briefest periods of time needed and only after 18 weeks of gestation, we believe the dose is still extremely safe and not of risk to the developing baby. IDENTIFICATION OF STRUCTURAL ABNORMALITIES Investigators have reported the successful

diagnosis of most forms of congenital heart disease using fetal ultrasound study.4 Examples of fetal heart defects are shown in Figure 3-6. In most cases diagnosis of a congenital heart problem does not change management of pregnancy but allows for the planning of newborn cardiac care after the baby is born. This was the case in Figure 3 in which the diagnosis of truncus arteriosus was made. Finding of fetal hydrops (Figure 4) however, is a sign of severe fetal difficulty and often indicates a fetal heart problem (arrhythmia alone or structural abnormality or both). This patient with fetal hydrops had asplenia syndrome with pulmonary

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Fig. 4. Fetal hydrops. The heart is enlarged within the chest cavity, (RV = right ventricle, LV = left ventricle), and there is significant pleural effusion (small arrows, L --- lung). ,~ atresia (Figure 5a), transpoition of the great vessels (Figure 5b), and common atrioventricular canal (Figure 5c). In addition she had heart block and did not survive, which is usually the case with the combination of fetal heart block and structural heart disease. Another congenital heart defect which may be associated with severe interuterine problems is Ebsteins disease, 1~ especially when associated with significant tricuspid insufficiency and right atrial enlargement. The patient in Figure 6 had typical features of Ebstein's disease with downward displacement of the septal leaflet of the tricuspid valve and severe tricuspid insufficiency and right atrial enlargement. She also had severe pulmonary stenosis and died in the newborn period. Serial echocardiogram did

not show atrial flutter or hydrops, but there is not any way currently to improve on her outcome. Lesions which cause atrioventricular valve insufficiency such as Ebstein's disease and common atrioventricular canal seem to be the most dangerous for the fetal circulation. Severe congenitalheart defects such as hypoplastic right left or hypoplastic heart usually do not cause problems for the fetus but it is after birth when the patent ductus doses, that symptoms of low-output state or severe cyanosis develop. Fetal cardiac ultrasound studies are gradually providing a better idea of the true spectrum of structural congenital heart disease. 11 Some defects, for example small ventricular septal defects and coarctation, remain very difficult to image. Coarctation may be suspected when RV enlargement is

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Fig. 5a. Pulmonary valve atresia. The large arrow points from ventricle (V) to obstructecl pulmOnary valve. The main pulmonary artery is small and bifurcates (small arrow). One pulmonary artery branch is seen entering the lung (lng) which is collapsed and surrounded by pleural fluid (p!).

noted and confirmed by finding flow disturbance in the early descending aorta. A norreal fetal echocardiogram study does not rule out coarctation however. Every fetus normally has a patent foramen ovale and patent ductus arteriosus, and it is not possible to diagnose secundum atrial septai defeet in the fetus. Echocardiography can be used to detect signs of premature constriction of these vital fetal channels. 7,s.9 Some medicines such as prostaglandin inhibitors may cause ductal constriction and this remains to be proven with more clinical studies. 7 DIAGNOSIS AND TREATMENT OF FETAL ARRHYTHMIAS Fetal arrhythmias may be evident as either

irregular fetal heart beats or heart rate greater than 220 or less than 100 beats per minute. The specific arrhythmia can usually be diagnosed by using the methods described above. Occasional ectopic beats are common as are brief episodes of sinus bradycardia? Sustained tachycardia or tachycardia associated with fetal hydrops can usually be successfully treated by giving mother anti-arrhythmic agents such as, digoxin or verapamil. An example of supraventricular tachycardia is shown in Figure 7. This patient had intermittent episodes of tachycardia at 250 beats per minute. Normally this would be watched and observed for any sign of either signs of hydrops or sustained tachycardia which would prompt digoxin or

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Fig. 5b. q'~heaorta tAo) is ~oentmea as me great vesse~ glwng o~I me oracnJocephalicvessels. In this case it arises from the anterior ventricle (RV), and is therefore transposed. verapamil treatment per mother. This patient was treated right away however because of coexistent complex single ventricle anatomy. Digoxin controlled the tachycardia for two weeks, but then it returned in sustained form associated with hydrops. The baby had premature caesarean section and unsuccessful heart surgery, dying with resistant tachycardia in the post operative period. This case demonstrates however the importance of ultrasound in the diagnosis of the specific arrhythmia, in assessing its severity, and in monitoring its treatment. Sustained bradycardia often is associated with either structural heart disease or heart block. The association of heart block with maternal Lupus or other connective tissue disorders is well documented. Congenital

heart block alone may not require treatment. Bradycardia with structural heart disease carries a poor prognosis.12 Figure 8 is illustrative of another case in which ultrasound played a significant role in diagnosis and treatment monitoring. On routine screening obstetrical study the baby's heart was noted to skip beats. Detailed fetal cardiac ultrasound study showed findings of a common atrium with cleft mitral valve, and second degree atrioventricular block. (Heart rate was 100 beats per minute.) There was no hydrops. Mother was hospitalized for the last months of pregnancy and ultrasound monitoring studies were performed which showed no worsening of conduction or signs of hydrops. The baby had normal delivery and newborn

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Fig. 5c. Common atrioventricular canal. A large ventricular septal defect is seen in the posterior ventricular septum on the same plane as the mitral and tricuspid valves, which "bridge" the defect. This patient had very little atrial septal tissue, and in effect a common atrium

(CA). course only to develop complete heart block at 6 weeks of age requiring pacemaker placement at that time. She then had correction of her common atrium at one year of age and is doing well. Fetal cardiac ultrasound studies allowed us to delay her delivery and not intervene prematurely. FUTURE At present the most important uses for fetal echocardiography are in identification of structural fetal heart disease and in the diagnosis and management of fetal arrhythmia and fetal hydrops. More and more work now however is being done in using

ultrasound methods to provide more sensitive measures of fetal circulatory status) a which will help obstetricians in their management of high risk babies, with and without primary heart disease. Not so far away also, is the possibility of fetal heart surgery, I~ and fetal ultrasound studies will then be pushed to their extreme limits in providing precise diagnosis before surgery, and then monitoring during and after surgery. What now seems like a technique very limited in use will become an extremely important tool in pediatric cardiology care, serving both in initial screening and in definitive diagnostic study of the fetus with heart disease.

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Fig. 6a. Fetal Ebstein's disease. Short axis view shows enlarged right atrium (RA) with downward displacement of septal tricuspid valve leaflet and redundant anterior leaflet (arrows). RV = right ventricle. This patient had severe tricuspid insufficiency. Fig. 6b. Tricuspid insufficiency is evident with wide speckled jet reaching back to posterior wall of right atrium. (arrows).

Fig. 7. Supraventricular trachycardia. The Doppler sample volume is placed in the right ventricular outflow tract, and velocity recordings at the lower part of the figure shows smooth regular flow pulses at 250 beats per minute (small arrows) preceeded by atrial in flow pulse for each beat. Larger outline arrows indicate 1 second in time.

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Fig. 8a. Four chamber view shows normal sized vent..~cles equal in thickness. Small arrows indicate bidirectional blood flow across the region of the missing atrial septum. (LV = left ventricle, RV = right ventricle).

Fig. 8b. Four chamber view with pulsed Doppler sample volume placed in left ventricular outflow tract. Doppler velocity recordings at bottom of figure show regular atrial flow pulse towards transducer through the mitral valve at rate of 120 beats per minute (solid arrows). Every fourth beat is not conducted to ventricles as evidenced by missing ventricular outflow pulse (outlined arrows) and ventricular Doppler pulse rate of 100 beats per minute.

WILSON : FETAl, ECHOCARDIOGRAPHY RrrE~r~ci~s 1. Winsberg F. Echocardiography of the fetal and n e~vborn heart. Invest Radiol 1972; 3 : 152-158. 2. Kleinman CS. Assessment of cardiac function in (human) fetus. J Am Coil Cardiol 1985; 5: 84S-94S. 3. Allan LD. A review of fetal echocardiography. Echocardiography 1985; 2 : 351376. 4. Snider AR. Two-dimensional and Doppler echocardiographic evaluation-of heart disease in the neonate and fetus. Clin Petinatol 1988; 15 : 523-565. 5. Brenner JI, Berg KA, Schnieder DS et al. Cardiac malformations in relatives of infants with hypoplastic left-heart syndrome. Am JDis Child 1989; 143 : 1491-1494. 6. Strasburger IF. Doppler echocardiography in the diagnosis and management of persistant fetal arrhythmias. J Am Coil Cardiol 1986; 7 : 1386-1391. 7. Huhta JC, Mosie KJ, Fisher DJ et al. Detection and quantiation of constriction of the fetal ductus arteriosus by Doppler eehocardiography. Circulation 1987; 75 : 406412.

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