Indian J Pediatr 1988; 55 : 96-108

Fetal and neonatal echocardiography D.R. Naik

Consultant Radiologist, Northern General Hospital, SheffieM Technical developments in the field of ultrasound have made it possible to obtain high-quality images of the fetal heart in the second and third trimesters of pregnancy. In addition to the improvement in the real-time cross-sectional images, the introduction of range-gated pulsed Doppler techniques has greatly enhanced ultrasound's potential for early diagnosis of fetal cardiac anomalies. The high-resolution images have been made possible by the use of sector scanning with 5 mhz and 7 mhz transducers. The recent introduction of colour flow mapping will further improve the diagnostic capabilities available to us. These developments have had a profound effect on the diagnosis and treatment of cardiac lesions in the fetus and the newborn.

Fetal heart movement can be detected as early as the 42nd post-menstrual day. Evaluation of the anatomy of the heart can be achieved from 16 weeks. A satisfactory four-chamber view at this stage allows visualisation of both atria, both ventricles, the septa and major valves. The heart is located relatively close to the anterior chest wall on the left side with the apex directed downward and to the left (Fig 1). Adequate visualisation of the heart requires the ultrasound beam to enter the fetal chest in the anteroposterior direction. Otherwise, acoustic shadowing from the spine and the ribs will prevent adequate examination. Normal anatomy

With patience and proper plane selection normal cardiac anatomy can be demonstrated even with a linear scanner. The ideal equipment for fetal echocardiography requires a 5 mhz medium-focussed transducer and also a fast frame-rate as the fetal heartrate is over 120 per minute. The most useful view is the standard four chamber view (Fig. 2) which allows examination of the relative sizes and shapes of the two atria and the ventricles. This view also demonstrates the atrial septrum including the foramen ovale with its flap opening towards the left atrium in the fetus. The ventricular septum is also seen in its entire length. The mitral and

Fetal eehocardiography

High-resolution echocardiography which incorporates pulsed Doppler blood flow analysis into the cross-sectional image enables the examiner to monitor the anatomy and function of the fetal heart, diagnose cardiac malformations in-utero and evaluate the efficiency of fetal cardiotherapeutic measures. Physiology of fetal hemodynamics can also be studied. Reprint requests : Dr. D.R. Naik, Consultant Radiologist, Northern General Hospital, Sheffield, U.K.

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Fig. 1. Diagram of a cross-section of the chest showing the position of the heart in relation to the spine and the ribs.

the tricuspid valves are seen with the tricuspid valve lying slightly lower in ~he ventricle, nearer the apex. The features to note in a normal fetal heart are : 1. The heart occupies approximately one-third of the fetal thorax. 2. The right ventricle lies closer to the anterior chest wall than the left ventricle. 3. The atria are approximately equal in size as are the ventricles. 4. The interventricular septum and the ventricular walls are of similar thickness. 5. The septa and the atrioventricular valves meet at the crux of the heart in a crOSS.

Scanning for anomalies Whereas most severe congenital abnormalities of the fetal heart will be detected by the experienced obstetric ultrasonographer certain high-risk pregnancies require special attention and possible referral to centres experienced in fetal echocardiography. The high-risk pregnancies include those with a family history of congenital heart disease. Maternal diseases such as diabetes and systemic lupus erythematosus also require special attention. Maternal exposure to rubella, radiation and drugs such as phenytoin and lithium are also associated with higher risk of cardiac

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anomalies. Detection of fetal ascites, skin edema or arrythmia may also point to a closer examination of the fetal heart. Other fetal anomalies detected by ultrasound such as oxamphalas, renal and neural tube defects have a higher incidence of associated congenital heart disease. The four-chamber view will help in excluding most of the abnormalities. Experienced ultrasonographers will be able to follow the venous connections to the appropriate atrium. The major arteries arising from the ventricles with the ascending aorta and the pulmonary artery crossing each other can also be demonstrated. When abnormal connections are found at the first examination it is advisable to recall the patient at a later date to confirm the findings. Description of the various cardiac anomalies which can be confidently diagnosed by echocardiography cannot be accommodated in a short review article. It is fair to say the results are very dependent on the experience of the ultrasonographer. All major cardiac anomalies such as large septal defects, atresias and hypoplastic left heart should be diagnosed and false positive predictions should be few if any. Defects such as ventricular septal defect and atrial septal defect are often missed when small but this is probably unavoidable, and in any case such cases have a favonrable prognosis in the neonatal period and subsequently. Coarctation of the aorts is the other anomaly which is difficult to diagnose in the fetus. After accurate diagnosis, the prognosis and the possible options can be considered. These will depend on the gestational age, the severity of the abnormality and associated extra-cardiac anomalies. Early diagnosis of a severe cardiac defect will

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give the parents an opportunity to agree to a termination of pregnancy. With less severe conditions the obstetric care can be altered. Even when termination of pregnancy is not carried out, severe cardiac anomalies have a very high incidence of intra-uterine death or death during early infancy. Fetal arrythmias are common. Irregular rhythm from atrial or ventricular escape beats usually disappears spontaneously and is not associated with morbidity or mortality. Short periods ofbradycardia can also be ignored. Bradycardia that persists for several minutes or recorded repeatedly needs further investigation. Complete heart block is often associated with structural heart disease. Isolated complete heart block has a high incidence in fetuses whose mothers have positive serology for connective tissue disorders. Tachycardia in the fetus is important to recognise. Even short bursts oftachycardia of over 200 beats per minute should be treated. If tachycardia persists and failure develops, digoxin and verapamil, either individually or in combination can be used, as adequate placental transfer can be achieved. Fetal hydrops can be completely resolved with treatment. Fetal echocardiography is useful in monitoring treatment in such cases.

Neonatal Echocardiography The last ten years has seen a revolu. tionary change in the practice of neonatal cardiology. Real-time cross-sectional imaging has enabled visualisation of the structural and functional abnormalities found across the whole spectrum of congenital heart disease. It has become possible to take diagnostic and management decisions on ill neonates without resorting to

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invasive procedures which in themselves have high morbidity and mortality. The addition of pulsed and continuous wave Doppler and, now, colour flow mapping has given the eehocardiographer the capability of diagnosing haemodynamic abnormalities in and around the heart.

Examination technique In order to exclude the possibility of congenital heart disease it is essential that a meticulous examination technique is followed. It is also advisable to perform the examination under standard conditions i.e., in the department where the examination is normally performed. There is a temptation to regard the examination as so urgent and special that the equipment is taken to the ward or the special care unit. Mistakes are made under these conditions as the echographer has to cope with so many difficulties that both his/ her concentration and physical skills are strained to the limit. Some departments may routinely carry out their neonatal examinations on the ward. Our practice is to bring the baby, in an incubator if necessary, to the department. Precautions have to be taken to ensure that the infant is kept warm and not disturbed unduly. The examination should be performed as rapidly as possible. It is preferable to repeat an examination if it proves too difficult or if the abnormality is a very complex one than to prolong the examination and risk hypothermia. Echocardiography is not a substitute for a clinical examination. In fact, accurate clinical assessment will greatly assist the echographer in concentrating on the diagnostic possibilities. Cross-sectional examination is carried out with a 7.5 mhz mechanical sector transducer. Pulsed Doppler facilties are available on the

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same equipment. The first view used is the parasagittal

long-axis section. This gives an excellent 'eye-ball" impression of the relative sizes of the aortic root and the left atrium. ff there is any suspicion that the left atrium is enlarged, an M-Mode Cursor is placed at right angles to the long axis of both structures (Fig. 3). An M-Mode trace is obtained usually in the 3rd space. The left atrial size is compared with the diameter of the aortic root. The measurement of the aortic root is taken from the leading (anterior) surface of the anterior wall of the aorta to the leading edge of the posterior wall at the end of systole. The left atrial size is measured from the anterior surface of the posterior aortic wall to the anterior surface of the posterior left atrial wall also at the end of the systole. A suprasternal view may have to be used for these measurements if there is sternal depression. The ratio of the left atrial to aortic root dimension is usually less than 1.3 : 1. Several measurements should be taken if there is doubt. Allowing for errors of measurement we consider that a significant shunt is present if the ratio exceeds 1.4 : 1 and ratio greater than 2 : 1 indicates a large shunt that requires urgent treatment. Valdes-cruz & Duddell 1 have shown that the left atrial size is the strongest predictor of left to right shunting and our experience confirms this view. These measurements can also be obtained from a hard-copy of the cross-sectional image. These measurements have been stressed here as they can be obtained on any instrument inciuding a linear scanner and specialised equipment for echocardiography is not essential. An abnormal ratio of the left atrial/ aortic root requires a search for a ventri-

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Fig. 2. A four-chamber view of the fetal heart showing normal anatomy. Fig, 3. Long axis section of the left heart with an M-Mode tracing showing left atrial enlargement in a left to right shunt.

cular septal defect or a patent ductus arteriosus. The long axis view (Fig. 4) also shows the left ventricular cavity with interventricular septum lying between the ventricles. The examination is started with the plane extending obliquely from the right shoulder towards the left hip. The left sided structures i.e., the left atrium and the left ventricle together with the aortic and mitral valves are easily and accurately assessed on this view. Large ventricular septal defects and abnormal thickness

of the myocardium will be evident on this view. The ultrasound plane is then turned in the clock-wise direction to the vertical. The right ventrMe and its outflow tract are seen in this view. Sometimes, further movement of the transducerma plane extending from the right hip to the left shoulder--will show the outflow tract of the right ventricle, pulmonary valve and the whole of the pulmonary artery in a single view (Fig. 5). The transducer movement is continued in a clock-wise direction

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Fig, 4. Long axis section of tile heart showing the left atrium and left ventricle and mitral and aortic valves. Fig. 5. A high short axis view with a cross-section of the aorta in the middle. heart is clearly shown including tile pulmonary artery.

The right side of th,0

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until a transverse or short-axis view is obtained. A high short-axis view will show the pulmonary artery anteriorly "wrapped round" the circular aortic root. Again, the pulmonary valve and the pulmonary artery may be visible. The left atrium lies posterior to the aortic root. Angulation of the transducer downwards gives a cross-section of the left ventricle with mitral valve opening ("fish-mouth" view) in the middle. Without changing the angle, the transducer can now be moved down the chest, usually only one interspace, and pointed towards the neck. This gives a fourchamber view. This sequential approach starting with the parasternat ~ong-axis view and ending with four-chamber view has proved valuable in teaching neonatal echocardiography to beginners. Rotating the transducer in one direction only (clockwise) and obtaining most of the views from a single position avoids confusion and eases the learning process. The four-chamber view very quickly allows assessment of the relative sizes of the atria and the ventricles. The relative position of the mitral and tricuspid valves is easily assessed. The normally placed tricuspid valve lies lower in the ventricle i.e. closer to the apex of the right ventricle and therefore closer to the transducer also. If the valves lie at the same level there is a very high probability that a high perimembranous ventricular septal defect is present. These standard or routine views can be augmented by two further views. Firstly, the subcostal or subxyphoid view (Fig. 6) in which the transducer is placed in the hollow of the epigastrium and pointed towards the neck. This view is useful in outlining the atria and the atrial septum--within which the foramen ovale

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and its flap are easily seen. The suprasterhal view is obtained by placing the transducer in the suprasternal notch and pointing downwards (Fig. 7). This view allows assessment of the relative position and size of the two major arteries. The aortic arch and the descending aorta are visualised from this position.

The value of Doppler echoeardiography Improved image quality and greater resolution obtained with high-frequency transducers provided excellent anatomical detail but information on blood flow was lacking until the introduction of Duplex scanners in the early years of this decade. The combination of a cross-sectional image and a Doppler Sample volume which could be manipulated within a displayed image greatly enhanced the diagnostic information available from echocardiography. With computer-based spectral analysis and sophisticated software built into the modern equipment Doppler examination with pulsed arid continuous wave modality gives invaluable qualitative and quantitative data rapidly and non-invasively. More recently the Doppler information both in terms of direction of flow and velocity range has been colourcoded. This colour flow mapping is proving extremely valuable in detecting abnormal flow and also in quantification of this flow in septal defects and in valvular regurgitation. At present, the cost of such equipment is prohibitive but experience with all ultrasound developments shows that such facilities will become cheaper and therefore, widely available.

Ventrieular septal defect Isolated ventricular septal defect is the

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Fig. 6. A sub-costa! view showing the atria and the atrial, septum. section. Fig. 7. A view of the aortic arch with the main arteries arising from iL

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The liver is on the left of tim

104 THE INDIAN JOURNAL OF PEDIATRICS most common lesion seen in children with congenital heart disease accounting for approximately 20~o of cases. The natural history of such defects show that 400 of them will close spontaneously by five years of age. Small defects particularly in the muscular part of the septum are highly likely to close. Large defects have also been shown to reduce in size by serial eehocardiography. Clinical suspicion together with an enlarged left atrium observed on the parasternal long-axis view makes it imperative to carry out a thorough search for a ventricular septaI defect (VSD). The cross-sectional examination will show a defect in the ventricular septum if the VSD is larger than 3 ram. Visualisation will also depend on the position of the defect. Large perimembranous defects will appear as a gap between the aortic root and the muscular septum (Fig. 8). The majority of defects are too small to be resolved by the twodimensional examination. Perimembranous inlet defects, among the most common, can be suspected by noting the position of the tricuspid valve on the fourchamber view. If the mitral and the tricuspid valves are at the same level Doppler sampling is likely to show a high VSD (Fig. 9). In the long-axis view, the Doppler sample gate is placed along the right ventricular side of the septum and then moved slowly along the whole length of the septum. High-pitched sound in early systole combined with an upward short turbulent trace on the Doppler spectral analysis indicates a small VSD (Fig. 10). A similar search should also be carried out on the four-chamber view. Small perimembranous defects are best detected on this view when sampling posterior to the septal cusp of the tri-

Vol. 55, No. 1 cuspid valve proves positive. Small defects in the muscular and trabecular septum are the most difficult to detect. In our experience, colour-flow mapping is a sensitive and reliable method in such cases and its availability will greatly increase the speed and accuracy of neonatal examinations. Muscular defects sometimes reveal their presence by slight irregularity in the outline of the septal echoes. Patent ductus arteriosis

Delayed closure of the arterial duct is a common finding (20~o) in all pre-term infants. The incidence of persistent patency in the neonate varies in different reports but the occurrence is thought to be inversely related to gestational age. 2 Clinical assessment will usually point to the presence of PDA. The role of chocardiography is to confirm the diagnosis and to try and quantify the degree of left to right shunting. Enlargement of the left atrium on the long-axis view is a strong pointer to the correct diagnosis. If there is clinical suspicion o f a PDA we immediately resort to Doppler Sampling of the pulmonary artery. The sample gate is moved gradually down the pulmonary artery starting from the pulmonary valve. Detection of turbulent diastolic flow in the pulmonary artery is virtually pathognomonic of PDA. The presence of abnormal flow is evident both from the audio signal and the Doppler trace. Routine sampling of the pulmonary artery with a Doppler sample is advised as we have diagnosed a PDA in the presence of another malformation such as a VSD. Occasionally, a patent arterial duct is discovered when it has not been clinically suspected. Demonstration of the vessel itself can be achieved with effort

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Fig. 8. Long axis view showing a VSD. Fig. 9. A child with a ven/ricular and atrial septal defect.

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Fig. 10. Long axis view with a Doppler sample placed in the region of a VSD. shows a high velocity jet.

but is unnecessary as Doppler examination is sensitive and accurate.

Fallot's tetralogy Diagnosis of this condition should be possible in the neonatal period. Again, attention to detail aids early recognition. In the long-axis parasagittal view the normal heart shows continuity between the interventricular septum (IVS) and the anterior wall of the aorta. The anterior cusp of the mitral valve is continuous with posterior wall of the aorta. In FaUot's Tetralogy there is a gap between the IVS and the anterior aortic wall. The two walls of the aorta, in fact, straddle or over-ride the septum. It is useful to note the line of closure of the aortic valve cusps-in Fallot's Tetralogy their line of closure is at the same depth as the ventricular septum slightly cephalad to the upper margin of the septum. The ventricular septal defect may be visible between the upper margin of the septum and the aortic wall. Even if the cross-sectional image does not demonstrate this, a Doppler sample will readily show the presence of abnormal flow across the septum. Right ventricular hypertrophy will be evident on the four chamber view.

The Doppler trace

The most difficult part of the examination is the demonstration of the outflow tract of the right ventricle. Infundilbular stenosis in neonates with Fallot's Tetralogy seems notoriously difficult to diagnose accurately. This is often due to interventing lung which is common in these patients and may be related to a rightsided aorta.

Transposition of great arteries Complete transposition of the great vessels represents concordant atrioventricular and discordant ventriculo-arteriaI connections. Various confusing terms are used in describing this anomaly. Experienced echocardiographer will identify the ventricles from their morphology and follow the main artery arising from each ventricle. In my view, the hallmark of recognition lies in the parallel position of the two arteries which is maintained in the upper mediastinum. Normally, the pulmonary artery which arises from the (anterior) right ventricle crosses the aorta from right to left within 1-2 eros of their respective origins. At the same time, it is also seen to be "wrapped around" the aorta as it goes posteriorly

NAIK : ECHOCARDIOGRAPHY towards the lungs. If the two vessels do not cross i.e., remain parallel for 2-3 cms there is a very strong possibility that a transposition is present. If there is any doubt the infant should be referred to a specialist centre as the condition requires urgent attention. Coarctation of aorta

This is a difficult diagnosis as the aortic arch needs to be outlined completely either from the high parasagittal or suprasternal transducer position. Normally, the aortic arch and its branches can be identified and Doppler examination will show normal flow velocities in the arch and the descending aorta. Short-segment coarctation can be quite severe and may not be identified on the cross-sectional examination. Again referral to a specialist centre is advised. Nonstructnral heart disease

In the last few years we have learnt to recognise a group of neonates with cyanosis and/or heart failure who have no structural cardiac abnormality. There are two broad groups--those with severe pulmonary hypertension and central right to left shunting and labelled as Persistent fetal circulation (PFC) and those with cardiac failure and poor left ventricular function considered to be due to Transient myocardial ischaemia (TMI). Neonates with nonstructural heart disease are often hypoxic, hypotensive and haemodynamically unstable. Two-dimensional echocardiography spares them invasive catheterisrtion which they find difficult to tolerate. Persistent fetal circulation

The primary abnormality in this condition is failure of the lung vascular

107 resistance to fall after birth. This may be due to intrinsic abnormality of the pulmonary vasculature but more commonly it is due to perinatal hypoxia, acidosis etc. Resulting pulmonary hypertension leads to right to left shunting at the atrial and the ductal level. The clinical picture is one of central cyanosis with little respiratory distress. The babies are born at term or post-mature and there is a history of difficult delivery. The echogram shows a normal heart with some dilatation of the right atrium and the right ventricle. The atrial septum bulges towards the left atrium and Doppler Sample wiU demonstrate flow from right atrium to left atrium. The main problem is to exclude cyanotic congenital heart disease. Structural lesions with right to left shunting such as tricuspid and pulmonary atresia and also transposition of the great arteries are identifiable by echocardiography. Total anomalous pulmonary venous connection is a more difficult diagnosis to exclude but is a rare condition. Transient myocardial ischaemia

This is a condition characterised by congestive cardiac failure in the neonate with no structural abnormality of the heart. Ischaemic myocardial damage has been shown to be the underlying cause and the syndrome may range from short-lived tachypnoea to cardiogenic shock. The milder forms present with cyanosis, intercostal recession and tachypnoea. X-ray of the chest shows normal or slightly enlarged heart with increased perihilar markings. More severe cases present with congestive cardiac failure and there is history of perinatal hypoxia. Murmurs of mitral or tricuspid regurgitation may be present together with ECG abnormality suggesting

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myocardial ischaemia. The role of echocardiography is to exclude structural heart disease. The echo may also show dilated left ventricle with poor contraction. The differential diagnosis includes coarctation of the aorta and critical aortic stenosis. I-Iypoplastic left heart syndrome and total anomalous pulmonary venous drainage also need to be excluded. Good quality cross-sectional echocardiography with Doppler examination is usually able to exclude all the important cardiac lesions mentioned above.

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References I. Valdes-cruz LM, Duddell GG. Specificity and accuracy of echocardiographic and clinical criteria for diagnosis oF palent ductus arterio. sus in fluid restricted infants. Pediatrics 1981 ; 898 : 298-305 2. Siassi B, Blanco C, Cabal LA, Coran AG. Incidence and clinical features of PDA in low birth weight infants; a prospective analysis of 150 consequently born infants. Pediatrics 1976; 57 : 347-351 3. Clinical echoeardiography 1986 ed. Kent : Stewart Hunter and Roger Hall Castle House Publications Ltd, Tunbridge Wells. 4. Echocardiography (3986) Harvey Feigenbaum, 4th edition. Philadelphia : Lea & Febiger,

IMPA]I~ED SENSITIVITY OF A SINGLE EARLY LEUKOCYTE COUNT IN SCREENING FOR NEONATAL SEPSIS The common clinical practice of using a single, early white blood cell (WBC) count to screen for early onset neonatal sepsis was investigated in a population of 61 newborn infants with culture proven sepsis in the first 3 days of life. Thirteen patients (21~0) had a normal WBC screening test. The patients with true positive and falsely normal WBC counts did not differ by risks factors for sepsis, birth weight, age, outcome or severity of disease. However, there was significant delay between the screening test and the positive blood culture in the patients with false normal WBC counts and not in the patients with positive abnormal WBC counts (14-9, 5-9 hours vs. 2.8, 1-4 hr. mean se, P<0.001). A WBC count obtained soon after birth as currently utilised may not adequately screen for early onset neonatal sepsis. In a commentary Christensen showed that in experments in which animals are inoculated with bacteria adult animals display abnormalities in blood and marrow neutrophil populations within about 1 hr. Newborn animals reacted similarly if they possessed specific antibody towards antigens on the bacteria. However newborn animals lacking antibodies to the organisms with which they were infected, a latent period of 3-4 hours between bacterial inoculation and any change in neutrophils populations was observed. This delay may be due to poor opsonization of organisms with delay in activation of complement on the surface of organisms. Products of complement activation are among humoral substances suspected of releasing neutrophils from marrow. It is emphasized that antimicrobial therapy treatment should not be withheld from ill neonates on the basis of normal blood neutrophil concentrations and morphology.

Abstracted from :

Rozycki H J, Stahl GE, Baumgart S. Pediatr Infect Dis J 1987; 6 : 440-442 ; Christensen RD. ldem 1987; 6 : 429-430.