Echocardiography and the neonatologist

SYMPOSIUM: NEONATOLOGY

Echocardiography and theneonatologistLindsey Hunter

Neil Patel

AbstractEchocardiographic assessment can be broadly divided into functional and

structural assessment. Functional echocardiography in the hands of an

appropriately trained neonatologist is an accessible and useful modality

in the neonatal intensive care unit. This tool allows the neonatologist

to assess various parameters, e.g. ventricular outputs and SVC flow,

ventricular function, pulmonary pressures and ductus arteriosus and

implement immediate management as result. It is essential that there is

support from the paediatric cardiologist to prevent misdiagnosis of

congenital heart disease and implement further management.

Keywords ductus arteriosus; echocardiography; functional assessment;

neonatal intensive care; structural assessment; SVC flows; ventricular

function

Part 1: overview of practice

Over the past decade echocardiography has increasingly become

both a useful and accessible modality within neonatal units.

Echocardiography (echo) is a powerful tool in the hands of an

appropriately trained operator. Echo assessment can be broadly

divided into functional and structural assessments. There is

a distinct overlap between the two assessment categories, each

will inform the other and neither should be considered in

isolation.

Structural assessment of congenital heart disease is impera-

tive to delineate basic and complex cardiac anatomy including

identifying significant anomalies.

Functional assessment is an evaluation of myocardial function

and haemodynamics. Although introduced primarily a research

tool, functional echo is increasingly employed at the bedside by

neonatologists. Serial measurements are used to answer specific

and immediate clinical questions in the context of the rapidly

changing haemodynamics of a sick neonate.

Functional echo should be performed as an adjunct or in addi-

tion to existing clinical parameters; e.g. lactate, CRT, heart rate,

blood pressurewhich are of limited value and are open to observer

variability. Functional echocardiography provides a direct

Lindsey Hunter MBChB MRCPCH is a Paediatric Cardiology Specialist

Trainee in the Cardiology Department Royal Hospital for Sick Children,

Glasgow G3 8SJ, UK. Conflicts of interest: none.

Neil Patel BA MBChB MRCPCH MD is a Consultant Neonatologist in Neonatal

Intensive Care at the Royal Hospital for Sick Children, Glasgow G3 8SJ,

UK. Conflicts of interest: none.

PAEDIATRICS AND CHILD HEALTH 21:6 254

measure of myocardial function, pulmonary and systemic blood

flows and also intra/extra cardiac shunting.

Who should undertake echocardiograms within the neonatal

intensive care? Practicalities, location and politics can often delay

a cardiology assessment within neonatal units. Traditionally the

diagnosis and management of significant and complex congenital

heart disease has been the realm of the appropriately skilled and

experienced paediatric cardiologist. However, if functional

echocardiograms are performed by the attending neonatal team

frequent assessment and therapeutic adjustment can be made

without the immediate input of paediatric cardiologist.

The neonatology team must be aware that functional assess-

ment does not exclude structural heart defects. This also high-

lights a potential medico-legal debate surrounding neonatologists

undertaking echocardiograms routinely; the main concern being

the potential to misinterpret or even misdiagnose life threatening

congenital heart disease. Neonatologists must be are aware of

their limitations when structurally assessing the neonatal heart;

in particular there are diagnoses which even an experienced

cardiologist may find difficult to make or have the potential to

miss including coarctation of the aorta, total anomalous pulmo-

nary venous drainage (TAPVD), anomalous left coronary artery

(ALCAPA), congenitally corrected transposition of the great

arteries and atrial isomerisms.

To ensure neonatologists are adequately trained and that

echocardiography within the neonatal intensive care is safe, open

and easily accessible lines of communication between the

paediatric cardiologists and the neonatologists is desirable. We

recommend a model of support for neonatologists by paediatric

cardiologists at a ward level, continuing medical education

(CME), echocardiography courses, training materials and

ongoing positive feedback. There should be opportunities for the

neonatal trainees to work alongside the cardiologists in the form

of an official placement. In the UK and worldwide, including at

our centre, formally-accredited echocardiography courses are run

which are appropriate for neonatologists and allied professionals.

In our hospital there is a close working relationship between

the paediatric cardiologists and neonatologists with a specialist

interest in cardiology. This allows for prompt and timely

assessment of newborns with abnormal clinical examination

findings or clinical parameters. Both teams meet weekly to

discuss the ongoing care of those neonates with significant heart

disease in the NICU.

Part 2

The second part of this article focuses on the specific functional

echocardiographic measures which are used frequently in the

neonatal intensive care unit. It is important to stress that these

should always be accompanied by a complete assessment of

cardiac structure, as discussed above. Whilst we hope to provide

some practical insights into these assessments, it is beyond the

scope of this article to teach these techniques.

Assessment of the ductus arteriosus (DA)

Assessment of the DA is most frequently performed in pre-term

infants, in whom consideration may be given to closure by

surgical or medical therapies, but is also important in

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http://dx.doi.org/10.1016/j.paed.2010.12.001


duct-dependent congenital cardiac disease and for assessment of

pulmonary artery pressures.

The DA is typically directly visualized from a high left para-

sternal view. From this position the entire length of the DA can

be demonstrated between proximal descending aorta and

pulmonary artery, and a Doppler of flow velocities and directions

may be performed (Figure 1).

The diameter of the DA may be measured at its insertion into

the pulmonary artery from 2-dimensional and colour Doppler

images. Any constriction of the PDA usually occurs at this point.

Ductal diameters, and the presence of constriction, may assist

prediction of spontaneous duct closure.

There is increasing interest in defining a haemodynamically

significant ductus arteriosus (HSDA). This depends on combined

echocardiographic and clinical assessment, and may be assisted

by a scoring system such as that proposed by McNamara et al.

(Ref). Echocardiographic findings in HSDA are of moderate to

large sized ductuswith unrestricted left-to-right flowof reasonably

high velocity. The echo may also demonstrate reversed diastolic

flow in the proximal descending aorta which may accompany

evidence of impaired abdominal end organ perfusion.

The shunt size through a DA may also be assessed indirectly

by measurement of the left atrium:aortic diameter ratio (LA:Ao).

A left-to-right ductal shunt leads to increased pulmonary venous

return, leading to enlargement of the LA and an increase in the

ratio. Both LA and Ao diameters are obtained from a parasternal,

long-axis m-mode image, the aortic valve diameter is measured

at end diastole and the maximal LA diameter at end systole. A

ratio of greater >1.5:1 is associated with a HSDA.

Management of the HSDA remains controversial and variable.

Early targeted treatment using NSAIDs, ibuprofen or indometh-

acin, is advocated by some authors to achieve greater rates of DA

closure and minimize the pathological consequence of an HSDA.

Serial echocardiography allows more selective, targeted and

shorter courses of NSAID to be given, thereby minimizing the

risks of side effects.

RVOT

MPA

LPA

Descending

aorta

Patent

ductus

Pulse wave

Doppler sample

RPA

Figure 1 Schematic diagram of DA demonstrating position for Doppler of

DA flow.


Calculation of ventricular outputs and superior vena cava

(SVC) flows

Measurement of systemic blood flow, combined with blood

pressure allows more informed therapeutic decisions to be made

in the haemodynamically compromised infant. Echocardiography

allows non-invasive measurement of flows in infants where

invasive flow monitoring is too risky or technically challenging.

Calculation of flows requires measurement of a valve diam-

eter, or vessel, to calculate its cross sectional area (CSA). A pulse

wave Doppler flow of velocity against time is then obtained

across the valve, or within the vessel, and the area under this

traced for one cardiac cycle to generate the velocity time integer

(VTI). The flow (in volume/time) is equal to the product of CSA,

VTI and heart rate and is often divided by weight for expression

as ml/kg/min.

Cardiac output¼ Velocity time integer

� valve cross sectional area� heart rate

Right and left ventricular outputs may be measured this way and

have been shown to change in RDS, PDA and high output states.

In the absence of any shunts right (RVO) and left ventricular

outputs (LVO) are equal to each other and systemic blood flow

(SBF), and are normally between 220 and 250 ml/kg/min.

However, atrial and ductal shunts are common in pre-term

infants (refs) and will lead to differences between RVO and LVO,

such that ventricular outputs cannot be considered equal to SBF.

It has therefore been suggested that measurement of SVC

flow, i.e. blood flow returning to the heart, may provide a better

proportional measure of SBF, independent of shunts. A subcostal

Doppler of SVC flow entering the RA is obtained and combined

with SVC diameter measurements from long-axis views to

calculate SVC flows, which are normally around 80 ml/kg/min.

SVC Flow¼ Velocity time integer� SVC cross sectional area

� heart rate

SVC flows appear to be low in a proportion of pre-term infants

(newborn low output state) who may be at risk of hypotension,

IVH and neurodevelopmental abnormality (HUNT).

Although not in widespread clinical use, appropriately trained

and equipped neonatal units may routinely measure ventricular

outputs and SVC flows.

It should be appreciated that the error in any flow measure-

ment may be as high as 25%, due to the numerous measure-

ments involved.

Ventricular function

Ventricular function assessment is complicated by the complex

nature of the cardiac cycle and 3-dimensional geometry of the

ventricles.

Rapid clinical assessment of ventricular function is often

based on subjective opinion from 2-dimensional images obtained

in the long and short parasternal axes and apical 4-chamber

views. This technique has the significant limitations of being

subjective, observer dependent and non-quantitative.

Quantitative volumetric measures of LV function include

ejection fraction and fractional shortening, calculated from



LARA

LVRV

Doppler beam

Figure 2 Apical 4-chamber view demonstrating position of Doppler sample

for measurement of tricuspid regurgitation velocity.


long-axis parasternal m-mode images. Though widely employed

this technique measures systolic function only, is prone to

measurement error and is not independent of changes in loading

conditions. An alternative measure of LV systolic function is the

relationship between LV mean velocity of circumferential fibre

shortening (LV MVCF). This technique is said to have the

advantages of being pre-load independent and takes after-load

into account. However, LV MVCF requires measurements of LV

volume, LV wall thickness, ejection time and arterial pressure

and is arguably too cumbersome for routine clinical use.

An alternative global measure of ventricular function is the

Myocardial Performance Index (MPI), or Tei index. This is

derived from time intervals during the cardiac cycle. Though

easily performed in neonates MPI gives no indication of systolic

and diastolic functions, and is also load-dependent i.e. changes

Figure 3 Doppler waveform demonstrating bidirectional flow in patent ductus


in pre-load or after-load may alter MPI independent of changes in

myocardial function.

Tissue Doppler Imaging, strain and speckle strain imaging are

newer and promising techniques. These have the ability to

directly quantify global and regional systolic and diastolic func-

tion in multiple dimensions. Initial studies have shown the

feasibility of these techniques and their potential for future

clinical use in neonates.

Pulmonary artery pressure

Pulmonary hypertension (PHT) is common in sick newborn

infants and leads to impaired pulmonary blood flow, ventricular

dysfunction due to increased after-load, and pulmonary-systemic

shunting leading to hypoxaemia.

There are two principal echo methods of measuring pulmo-

nary artery pressure (PAP) in newborns; tricuspid regurgitation

jet velocity (TR) and direction and velocity of ductal shunts.

In the TR jet technique the peak TR velocity is inserted into

a modified Bernoulli equation, to calculate the gradient between

the RV and RA:

Pressure gradient¼ 4ðvelocityÞ2

RV peak pressure (RVp) is obtained by adding this pressure

gradient to an estimate of RA pressure (usually around 5 mmHg).

RVp should be equal to PAP, in the absence of RV outflow

obstruction. Previous studies have confirmed that PAP obtained

by the TR method correlates well with gold-standard catheter

measures of PAP.

The TR jet is usually obtained from the apical 4-chamber view,

ensuring a minimal angle of insonation. (Figure 2). The extent of

the TR jet often increases with increasing PAP, even when the

tricuspid valve is otherwise normal and competent. In some

infants, however, TR may be absent, even in the presence of PHT.

An alternative method of estimating PAP is using the direction

and velocity of the flow through a patent DA. These will be

arteriosus in an infant with pulmonary hypertension.



Practice points

C Echocardiography is a convenient and increasingly important

tool in the assessment and management of newborn infants in

the intensive care unit.

C Neonatologists performing echocardiography must be

appropriately trained, and should work collaboratively with

a supportive local Paediatric Cardiology team.

C Neonatal echocardiography includes structural and functional

assessments.

C Complete structural assessment is imperative to detect

complex cardiac anatomy, which should be managed in

conjunction with the Paediatric Cardiology Team.

C Functional assessment allows improved understanding of the

mechanisms of cardiovascular compromise infants with and

without structural anomalies.

C Functional assessment includes measures of ventricular

function, pressures (including pulmonary arterial pressures),

and blood flows in the heart and major vessels.


dependent on the pressure gradient between the pulmonary

artery and aorta at any point in the cardiac cycle. Ductal flow will

be left-to-right if aortic pressure (Aop) exceeds PAP. As PAP

increases flow in the DA may reverse, becoming bidirectional

(Figure 3). If PAP is above aortic pressure throughout the cardiac

cycle, as in severe pulmonary hypertension, then DA flow will be

exclusively right-to-left flow.

The velocity of the DA flow can be inserted into the Bernoulli

equation to calculate the peak pressure gradient between PA and

Aop. However, this peak gradient does not equal the true

difference between peak PA and peak Aop. This is because RV

and LV ejections do not necessarily coincide, and therefore peak

PAP and peak Aop are not simultaneous either.

PAP is not linearly related to RV function, and therefore any

assessment of pulmonary pressures should include an assess-

ment of ventricular function.

Summary

There is an expanding role for functional echocardiographywithin

the NICU, and for neonatologists performing echocardiograms.

However, neonatologistsmust beappropriately trainedand should

work in conjunction with, and supported by, their Paediatric

Cardiology colleagues. Neonatal functional cardiology remains an

area of evolving research and discovery with the aim of improving

outcomes for all infants with haemodynamic compromise. A

FURTHER READING

Carmo K, Evans N, Paradisis M. Duration of indomethacin treatment of the

preterm patent ductus arteriosus as directed by echocardiography.

J Pediatr 2009; 155: 819e22.

Evans N. Diagnosis of patent ductus arteriosus in the preterm newborn.

Arch Dis Child 1993; 68: 58e61.

Evans N. Echocardiography on neonatal intensive care units in Australia

and New Zealand. J Paediatr Child Health 2000; 36(2): 169e71.

Evans N, Kluckow M. Early determinants of right and left ventricular

output in ventilated preterm infants. Arch Dis Child Fetal Neonatal Ed

1996; 74: F88e94.

Hiraishi S, Horiguchi Y, Misawa H, et al. Noninvasive Doppler echocar-

diographic evaluation of shunt flow dynamics of the ductus arteriosus.

Circulation 1987; 75: 1146e53.

Iyer P, Evans N. Re-evaluation of the left atrial to aortic root ratio as

a marker of patent ductus arterious. Arch Dis Child Fetal Neonatal Ed

1994; 70: F112e7.

Kluckow M, Evans N. Superior vena cava flow in newborn infants: a novel

marker of systemic blood flow. Arch Dis Child Fetal Neonatal Ed 2000;

82: F182e7.

Kluckow M, Seri I, Evans N. Functional echocardiography an emerging tool

for the neonatologist. J Pediatr 2007; 150: 125e30.

McNamara PJ, Sehgal A. Towards rational management of the patent

ductus arteriosus: the need for disease staging. Arch Dis Child Fetal

Neonatal Ed 2007; 93(6): F424e7.


Mori K, Nakagawa R, Nii M, et al. Pulsed wave Doppler tissue echocar-

diography assessment of the long axis function of the right and left

ventricles during the early neonatal period. Heart 2004; 90: 175e80.

Osborn DA, Evans N, Kluckow M. Left ventricular contractility in extremely

premature infants in the first day and response to inotropes. Pediatr

Res 2007; 61: 335e40.

Patel N, Mills JF, Cheung MM. Assessment of right ventricular function

using tissue Doppler imaging in infants with pulmonary hypertension.

Neonatology 2009; 96: 193e9.

Patel N, Mills JF, Cheung MM. Use of the myocardial performance index to

assess right ventricular function in infants with pulmonary hyperten-

sion. Pediatr Cardiol 2009; 30: 133e7.

Sehgal A, McNamara PJ. Does point of care functional echocardiography

enhance cardiovascular care in the NICU? J Perinatol 2008; 28:

729e35.

Skinner J, Alverson D, Hunter S. Echocardiography for the neonatologist,

vol. 6. London: Churchill Livingstone, 2000: 133e150.

Skinner JR, Stuart AG, O’Sullivan J, Heads A, Boys RJ, Hunter S. Right

heart pressure determination by Doppler in infants with tricuspid

regurgitation. Arch Dis Child 1993; 69: 216e20.

Skinner JR, Hunter S, Hey EN. Haemodynamic features at presentation in

persistent pulmonary hypertension of the newborn and outcome. Arch

Dis Child Fetal Neonatal Ed 1996; 74: F26e32.

Tsutsumi T, Ishii M, Eto G, Hota M, Kato H. Serial evaluation for myocardial

performance in fetuses and neonates using a new Doppler index.

Pediatr Int 1999; 41: 722e7.

Ward CJ, Purdie J. Diagnostic accuracy of paediatric echocardiograms

interpreted by individuals other than paediatric cardiologists. J Pae-

diatr Child Health 2001; 37: 3316.



Echocardiography and the neonatologist

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