Echocardiography for the neonatologist

Current Paediatrics (1999) 9, 128-131 © 1999 Harcourt Brace& Co. Ltd

Symposium: Cardiology

Echocardiography for the neonatologist

N. Rutter

Ultrasound is an ideal tool for the investigation of the newborn infant. It is safe, painless and portable, involving less handling and interference than a chest X-ray or ECG. Cardiac ultrasound, echocardiograplay, gives detailed important information about the structure and function of the heart. Depending on the machine, the quality of images obtained in the newborn is usually very high, superior to images obtained in children and adults. Most neonatal units have access to an ultrasound machine, often dedicated to the unit, and neonatologists are used to scanning the heads o f preterm infants - why not the heart too?

echocardiography and who would welcome the opportunity to scan babies. There are two aspects of echocardiography that have to be mastered - doing the scan and interpreting it. Cardiac centres run courses for interested neonatologists which cover both of these areas and these are strongly recommended. Such courses need to be backed up by practice in the neonatal unit with healthy infants and the local machine.

PERFORMING AN ECHOCARDIOGRAM Equipment: Most ultrasound machines used on neonatal units will give good two dimensional (2D) images of the heart. A high frequency (7.5 MHz) probe gives excellent resolution with clear detailed images even in the tiniest babies. The probe has to be small enough to make good contact with the small curved anterior chest wall of a preterm infant. 2D echocardiography gives important information about the size of the heart and its chambers, the structure and the myocardial function. It is vital in the diagnosis of congenital heart disease. Doppler echocardiography (pulsed, continuous wave and colour flow Doppler) give additional physiological information which is particularly useful in assessing a patent ductus or persistent pulmonary hypertension but is not essential. Doppler echocardiography is more difficult to perform and the technology is more complex - the beginner is advised to master 2D imaging first. Technique: the settings on the machine need to be adjusted so that the images are clear and crisp. A systematic approach then ensures that all aspects of the heart are imaged. Parasternal, suprasternal and subcostal views are all easily obtained in the newborn. Details of how to scan the heart and interpret the images are beyond the scope of this chapter.

W H O S H O U L D DO NEONATAL H E A R T SCANS? There is no reason why an interested neonatologist should not learn to do heart scans and know how to diagnose the commoner structural and functional lesions. Paediatric cardiologists work in centres which are usually isolated from neonatal units and therefore are not available to scan babies unless they are transferred. Often though, the baby does not have a structural heart defect so transfer is not only inconvenient but inappropriate. The ability to perform an echocardiogram is a useful skill which is likely to become more so. It is now possible to transmit images electronically to a distant site where they can be reviewed and reported on by an expert, a facility which should become more widely available in the next few years. Most hospitals with neonatal units have cardiac departments with technicians who are expert in adult

ProfessorNicholasRutter,Professorof Paediatric Medicine, Department of Child Health, Queen's Medical Centre, Nottingham, NG7 2UH, UK Correspondenceand requests for offprints to N R.

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Echocardiography for the neonatologist USES OF NEONATAL E C H O C A R D I O G R A P H Y

Diagnosis of congenital heart disease There are a number of circumstances where an echocardiogram is performed with the object of diagnosing a structural abnormality of the heart. Antenatal detection or suspicion of a cardiac defect. If a cardiac defect has been diagnosed antenatally, there should be a management plan for the investigation and treatment of the baby after delivery. This will always include an echocardiogram to confirm the diagnosis and to identify any additional cardiac lesions. The abnormalities which are most commonly detected antenatally are those in which the standard four chamber view of the heart is abnormal and therefore readily recognised on postnatal scans. They are: • hypoplastic left heart syndrome • hypoplastic right heart syndrome (tricuspid and/or pulmonary atresia) • atrioventricular septal defects • single ventricle. Sometimes an antenatal scan shows a non-specific cardiac finding which may need evaluation after birth by echocardiography or which can be ignored. They include: Echogenic foci within the myocardium, usually in the papillary muscle of the left ventricle ('golf balls'). There is a weak association with Down's syndrome but not with congenital heart disease - they have usually disappeared by full term and echocardiography is not necessary. Cardiac rhythm irregularity is a common finding in the third trimester. The overall heart rate is normal, cardiac function is normal but there are frequent supraventricular ectopic beats. There is no association with structural heart defects and the ectopic beats usually disappear in late pregnancy or early infancy. Echocardiography is unnecessary. Right heart dominance where the right atrium and right ventricle are larger than the left atrium and left ventricle is sometimes noted in the third trimester, in the absence of any structural abnormality. It may be a benign finding of no significance but it is sometimes a marker of a congenital heart defect which can be difficult to see antenatally. Neonatal echocardiography is therefore important. The two lesions to look for are total anomalous pulmonary venous drainage and coarctation of the aorta. Symptomatic infants This is the most important reason for neonatal echocardiography. The infant with central cyanosis or breathlessness may have a heart abnormality or may have lung disease. An echocardiogram will determine whether the heart is abnormal and if so, what the

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abnormality is. A diagnosis greatly simplifies the management. The cardiac causes of central cyanosis in the newborn are shown in Table 1. They are all diagnosed on 2D echocardiography using the standard views. The most difficult to diagnose on scan is also the lesion which is most difficult to diagnose clinically, total anomalous pulmonary venous drainage. Use of Doppler echocardiography to demonstrate the pulmonary veins is sometimes helpful. The cardiac causes of breathlessness in the newborn are shown in Table 2. All can be diagnosed on 2D echocardiography without the use of Doppler. Asymptomatic infants with a heart murmur Heart murmurs are often heard in newborn infants with normal hearts and often not heard in newborn infants with heart defects so auscultation is a poor screening test at this time. A loud, long or unusual murmur or an associated abnormality of the pulses, the cardiac impulse or the heart sounds make a cardiac abnormality more likely. A 2D echocardiogram in these cases will rule out a major heart defect which is reassuring for the parents and the doctor, but it will not diagnose or exclude the common mild or moderate lesions like aortic and pulmonary stenosis or ventricular septal defect. Doppler echocardiography is very useful in these lesions but needs expertise and time; it need not be used as a routine investigation in healthy infants with soft murmurs. By 6 weeks of age, a heart murmur is a more specific and sensitive indicator of congenital heart disease - a 2D and Doppler echocardiogram will detect most lesions at this stage. Infants with a cardiac arrhythmia Supraventricular tachycardia is uncommon in the neonatal period. It can occasionally be associated with a structural heart defect, particularly if it is resistant to treatment, so echocardiography is useful. Ebstein's anomaly of the tricuspid valve and cardiac Table 1 Cardiac causes of central cyanosis in the newborn

Reduced pulmonary blood flow with right to left shunting Pulmonary atresia with an intact ventricular septum Severe ("critical") pulmonary stenosis Severe Fallot's tetralogy Tricuspid atresia Ebstein's anomaly 2. Common mixing of pulmonary and systemic blood Total anomalous pulmonary venous drainage* Single atrium Single ventricle* Truncus arteriosus* Pulmonary atresia with aorto-pulmonary collateral vessels* 3. Pulmonary and systemic circulations in parallel rather than in series Transposition of the great arteries* * variable breathlessness too

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Current Paediatrics

Table 2 Cardiaccauses of breathlessness in the newborn

Assessment of a patent ductus arteriosus

I. Leftsided obstruction with pulmonary venouscongestion Coarctation of the aorta Interrupted aortic arch Hypoplasticleft heart syndrome* Severe("critical") aortic stenosis Mitral stenosis Cor triatriatum Total anomalous pulmonary venous drainage with obstruction*

This is a c o m m o n complication of prematurity, particularly in ventilated infants. The clinical findings appear relatively late even though the left to right ductal shunt may be considerable. Echocardiography will make the diagnosis before the signs appear as well as confirming the diagnosis when the signs are present. It will also show the degree of left to fight shunting and therefore the significance of the duct, particularly helpful when decisions about duct closure are being made. 2D echocardiography is o f limited use. If the duct is moderate or large in width, it may be possible to image it directly but this can be difficult, particularly in ventilator dependent infants where lung may obscure the view. If there is a significant left to right ductal shunt there is left sided cardiac enlargement, especially o f the left atrium. The size of the left atrium is compared to the aorta in the long axis view and expressed as a ratio (LA/aorta). A ratio greater than 1.5 suggests a significant shunt. Colour Doppler echocardiography is the best method of diagnosing duct patency and size. The width of the colour jet within the duct when it is viewed throughout its length is an excellent indicator of the size o f the duct. It can be used to make the diagnosis before signs appear, to assess the need for treatment and to monitor the effect of treatment.

2. Leftto fight shunt with pulmonary plethora Patent ductus iartefiosus(preterm infants only) Atfioventricularseptal defect Truncus artefiosus* Ventficularseptal defect with somethingelse (e.g. patent ductus artefiosus, transposition of the great arteries* or double outlet right ventricle) Single ventricle* Aortopulmonary window Systemicarteriovenousmalformation(brain, liver, subcutaneous) * variable central cyanosis too

rhabdomyomas (as part of tuberose sclerosis) should be looked for. Runs of supraventricular tachycardia may also occur as a complication of a long line within the right atrium; this can be identified by scan and the line withdrawn until the arrhythmia disappears.

Infants with other abnormalities There is a high incidence of congenital heart disease in infants with chromosomal abnormalities and routine echocardiography is often requested. Most parents of infants with Down's syndrome are keen for an early heart scan and this is an important reason for doing one. Echocardiography will detect the major lesions but not the minor ones. It should be repeated at a later date if symptoms or a heart murmur appear. A normal heart scan in the newborn period does not necessarily mean a normal heart. Small ventricular septal defects and most secundum atrial septal defects are missed. There is an increased incidence of heart defects in infants with other congenital abnormalities, particularly diaphragmatic hernia, oesophageal atresia, exomphalos and anal atresia. A heart scan is useful even if the infant has no cardiac symptoms or signs, to exclude an important heart defect before major surgery is carried out. Although the presence o f a heart defect would not usually affect decisions about surgery, it is helpful to know about it during the anaesthetic and in the post-operative period.

Family history There is an increased risk o f congenital heart disease in families where a first degree relative has been affected. Although a detailed antenatal scan may have excluded an important heart defect, parents find a normal postnatal scan very reassuring, particularly if a previous infant was severely affected.

Persistent pulmonary hypertension of the newborn ( P P H N ) Echocardiography is very helpful in the diagnosis of this physiological condition which may mimic cyanotic congenital heart disease. A structural lesion can be ruled out by demonstration o f a normal cardiac anatomy, bearing in mind that total anomalous pulmonary venous drainage (TAPVD) is the condition which is most likely to be confused with persistent pulmonary hypertension of the newborn (PPHN). The echocardiographic hallmarks of P P H N are right sided cardiac enlargement, a bi-directional but predominantly right to left atrial shunt on colour Doppler, a high pulmonary artery pressure as measured by the velocity o f the jet of tricuspid regurgitation on pulsed Doppler, normal drainage o f the pulmonary veins into the left atrium and a right to left ductal shunt. In TAPVD, right sided cardiac enlargement is usually very marked, often with an apparently small left heart, no pulmonary veins can be seen entering the left atrium, and a confluence of pulmonary veins can usually be identified behind the left atrium and then seen to reach the systemic venous circulation. There is an obligatory right to left atrial shunt with no left to right component. Echocardiography can also be used to assess the response of P P H N to drug treatment although monitoring o f paO 2 or SaO 2 is simpler and more sensitive.

Echocardiography for the neonatologist

Assessment of cardiovascular function Doppler echocardiography can be used as a non-invasive method o f cardiac output measurement although this is mainly a research tool. Flow velocity across the pulmonary valve or aortic valve is directly measured by pulsed Doppler and pulmonary or aortic root diameter are directly measured from the 2D image. Right or left ventricular output is calculated from the product of these two measurements and the heart rate, expressed per Kg body weight. Right ventricular output is a better measure of cardiac output than left ventricular output in the preterm newborn because a left to right ductal shunt is invariably present. Left ventricular output therefore is a combined measure o f systemic flow plus the ductal shunt. Cardiac output measurement in the newborn has demonstrated how weak current clinical methods of assessing cardiac function are. Systemic blood pressure, invariably used as a cardiac function test in neonatal intensive care for decisions on volume expansion and inotropic support, correlates poorly with cardiac output which it is assumed to measure. Significant impairment of myocardial contraction can occur occasionally in severely asphyxiated babies. This is manifest clinically as systemic hypotension, sometimes with an apical pansystolic murmur of mitral regurgitation. 2D echocardiography shows a dilated, poorly contracting left ventricle and indicates that inotropes rather than volume expansion are needed. Normal myocardial contractility in the presence of severe hypotension suggests hypovolaemia and a need for volume expansion rather than inotropes.

Diagnosis of myocardial hypertrophy Marked hypertrophy of the myocardium is seen in infants o f diabetic mothers. Its presence is a marker of poor diabetic control. It is also seen in preterm infants with chronic lung disease in association with dexamethasone therapy. The myocardium, particularly of the interventricular septum, is greatly thickened on echocardiography, but this regresses during infancy. Follow-up scans are therefore unnecessary. Hypertrophic cardiomyopathy is rare in isolation in the newborn, but may be seen in Noonan's syndrome.

Location of indwelling catheters Echocardiography is a useful tool for locating the position of umbilical venous and arterial catheters within the chest or abdomen, particularly if the X-ray is confusing. It is also useful for locating the tips o f central lines within or close to the heart.

Line infection and endocarditis If an infant with an indwelling line becomes febrile

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with an increase in the markers o f infection, an echocardiogram will identify any thrombus on the catheter tip which would point strongly to a line infection, although this is an uncommon finding. Infants with long lines who receive prolonged courses of broad spectrum antibiotics are prone to systemic candida infection - an important complication o f this is candida endocarditis which can be diagnosed on echocardiography in infants with a positive blood culture. The vegetation is seen as an irregular echodensity within the right heart, particularly attached to one o f the leaflets of the tricuspid valve.

Evaluation of cardiomegaly Sometimes a large heart is discovered on a neonatal chest X ray. Echocardiography is a useful method o f investigating this. If the cardiomegaly is apparent rather than real, a scan will show a normal sized heart and a mediastinal mass such as a large thymus or a tumour. A pericardial effusion is easily diagnosed by scan - if it has to be tapped for diagnostic or therapeutic reasons, this is best done under echocardiographic control. If the heart itself is enlarged, echocardiography will show which chambers are enlarged and will identify any structural lesion.

CONCLUSION Heart scanning is second only to head scanning in terms o f usefulness as a skill in the ultrasound investigation of the newborn. Its use is not simply confined to the diagnosis o f structural congenital heart disease, a major reason why it should interest the neonatologist and not be the sole preserve of the paediatric cardiologist.

Further reading Alverson DC, Eldridge M, Dillon T, YabekSM, Berman WJ. Noninvasivepulsed Doppler determination of cardiac output in neonates and children. Journal of Pediatrics 1982;

101:46-50. Evans N. The neonate and the ductus arteriosus; importance, diagnosis and practical management. Current Paediatrics 1995; 5:114-117. Evans N. Echocardiographicassessment of the newborn infant with suspected persistent pulmonary hypertension.Seminars in Neonatology 1997;2:37-48. Kluckow M, Evans N. Relationshipbetween blood pressure and cardiac output in preterm infants requiring mechanical ventilation. Journal of Pediatrics 1996; 129:506-512. Kluckow M, Evans N. Early echocardiographicprediction of symptomaticpatent ductus arteriosus in preterm infants requiring mechanical ventilation. Journal of Pediatrics 1995; 127:774-779. Mellander M, Sabel KG, Caidahl K, Solymar L, Eriksson B. Doppler determination of cardiac output in infants and children: comparison with simultaneous thermodilution. Pediatric Cardiology 1987;8:241-246. Skinner J R. Echocardiographyon the neonatal unit: a job for the neonatologist or the cardiologist?Archivesof Disease in Childhood 1998;78:401-402.