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Echocardiography and the neonatologist
SYMPOSIUM: NEONATOLOGY
Echocardiography and the neonatologist
European Paediatric and Congenital Cardiology (AEPC), discussing the importance of targeted neonatal echocardiography. fEcho should be performed as an adjunct to existing clinical parameters, for example: lactate; capillary refill time (CRT); heart rate and blood pressure, which are open to observer variability. fEcho is employed to make serial measurements and to answer specific clinical questions. In particular, it provides a direct measure of myocardial function, pulmonary and systemic blood flow and intra/extra cardiac shunting. Traditionally the diagnosis and management of significant and complex congenital heart disease has been the realm of the paediatric cardiologist and this continues to be international practice. Neonatologists must be are aware of their limitations when assessing the structure of the neonatal heart as even in the hands of experience echocardiographers certain diagnoses can be challenging and devastating if missed, for example: coarctation of the aorta and total anomalous pulmonary venous drainage (TAPVD). For this reason the initial neonatal echocardiogram must involve a comprehensive assessment of the cardiac anatomy, in addition to a full functional assessment. As per international guidelines this initial echocardiogram should be reviewed by a paediatric cardiologist within a mutually agreed time frame. A clear distinction must be made between an echocardiogram undertaken in infants with CHD, and fEcho to assess haemodynamics and myocardial function in a structurally normal heart. Once structural CHD has been excluded, subsequent echocardiograms can focus on the functional cardiac status. fEcho performed by the attending neonatologist allows for frequent assessment and therapeutic adjustment, without the immediate input of a paediatric cardiologist. To ensure neonatologists are adequately trained and supported, open and easily accessible lines of communication between the paediatric cardiologist and the neonatologist is desirable. We recommend a model of support at ward level, by continuing medical education (CME), echocardiography courses, training materials and ongoing positive feedback. Official accreditation for neonatologists undertaking targeted neonatal echocardiography is not consistent internationally. In the UK, Paediatricians with Expertise in Cardiology Specialist Interest Group (PECSIG) has been recognized by the Royal College of Paediatric and Child Health (RCPCH) since 2008, which aims to improve the care children with cardiac conditions receive, by supporting and enhancing the training of paediatricians with expertise in cardiology. Within Europe, the European Association for Cardiovascular Imaging (EACVI) in conjunction with the Association for European Paediatric and Congenital Cardiology (AEPC) provide accreditation in congenital heart echocardiography, but this is comprehensive and not entirely suitable for neonatologists undertaking targeted neonatal echocardiography. However, in Australasia an accreditation process specifically for neonatologists has been available since 2008: ‘The Neonatal Certificate in Clinician Performed Ultrasound’ (CCPU in neonatal ultrasound) which was developed by the Australasian Society for Ultrasound in Medicine.
Lindsey Hunter Neil Patel
Abstract Neonatal echocardiographic assessment is a component of neonatal point of care ultrasound and can be broadly divided into structural and functional cardiac 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 haemodynamic parameters including ventricular outputs and superior vena cava (SVC) flow, ventricular function, pulmonary arterial pressures, arterial ducts 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 arterial duct; 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 a useful and accessible modality within the neonatal intensive care unit (NICU). It is an effective tool in the hands of an appropriately trained operator, particularly when used as an adjunct to clinical assessment. Echocardiography is a fundamental component of ‘neonatal point of care ultrasound’ also known as ‘targeted neonatal echocardiography’ and can be broadly divided into functional cardiac assessment and structural cardiac assessment. There is a distinct overlap between the two assessment categories, as each informs and complements the other. Structural assessment is essential to delineate the cardiac anatomy, in particular to identify or exclude congenital heart disease (CHD). In contrast functional echocardiography (fEcho) assessment is used to evaluate myocardial function and the haemodynamic stability of sick term or preterm neonates. Although introduced primarily as a research tool, fEcho is increasingly employed at the bedside by neonatologists. International guidelines have been published by the American Society of Echocardiography (ASE) in conjunction with the European Association of Echocardiography (EAE) and the Association for
Lindsey Hunter MBChB MRCPCH is a Consultant Paediatric & Fetal Cardiologist, Cardiology Department, Royal Hospital for Sick Children, Glasgow, UK. Conflicts of interest: no conflicts of interest have been declared.
Part 2
Neil Patel BA MBChB MRCPCH MD is a Consultant Neonatologist, Neonatal Intensive Care Unit, Royal Hospital for Sick Children, Glasgow, UK. Conflicts of interest: no conflicts of interest have been declared.
PAEDIATRICS AND CHILD HEALTH --:-
The second part of this article focuses on some of the specific functional echocardiographic measurements which are
1
Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Hunter L, Patel N, Echocardiography and the neonatologist, Paediatrics and Child Health (2015), http:// dx.doi.org/10.1016/j.paed.2015.02.006
SYMPOSIUM: NEONATOLOGY
frequently utilized in the NICU. As discussed in Part 1, initial echocardiographic assessment should include a comprehensive assessment of the cardiac anatomy. Whilst we hope to provide some practical insights into some of these functional assessments, it is beyond the scope of this article to discuss all available techniques or to teach these techniques.
The shunt flow through an arterial duct may also be indirectly quantified by measuring 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, with a subsequent increase in the LA: Ao ratio. Both the LA and Ao diameters are obtained from an M Mode measurement in the parasternal long axis view. The aortic valve diameter is measured in end diastole and the maximal LA diameter in end systole. A ratio greater than 1.5:1 is associated with an HSDA. Management of the HSDA remains controversial and variable within NICUs. Early targeted treatment using NSAIDs for example ibuprofen or indomethacin, is advocated by some authors to achieve greater rates of arterial duct 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 side effects.
Assessment of the patent arterial duct (PDA) Assessment of the arterial duct is most frequently performed in preterm infants, in whom consideration may be given to closure by surgical intervention or medical therapy. Ductal assessment is important in the management of duct-dependent CHD and also aids in the assessment of pulmonary artery pressures within a structurally normal heart. The arterial duct is visualized from either a high left parasternal or suprasternal view. From this position the entire length of the arterial duct can be demonstrated extending from the proximal descending aorta to the main pulmonary artery (MPA). These views allow for assessment of the ductal diameter, shunt direction and flow velocities by pulse wave (PW) Doppler and colour Doppler assessment. (Figure 1) The diameter of the arterial duct can be measured at its insertion into the MPA by 2dimensional imaging and primary constriction usually occurs at the pulmonary artery insertion point. The diameter of the duct and evidence of constriction may indicate a potential for spontaneous ductal closure. There is increasing interest in defining a haemodynamically significant ductus arteriosus (HSDA). Clinically there may be evidence of systemic hypoperfusion or increased pulmonary blood flow, which can impact on longer term morbidity. Deciding whether an arterial duct is haemodynamically significant depends on combined echocardiographic and clinical assessments, and may be assisted by a scoring system, such as that proposed by McNamara et al. Echocardiographic findings in HSDA include a moderate to large sized duct with unrestricted left to right flow, with a high Doppler velocity. Colour flow and PW Doppler may demonstrate diastolic flow reversal in the proximal descending aorta, indicating diastolic left to right shunting at the arterial duct. Clinically this may be accompanied by evidence of impaired abdominal end organ perfusion.
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 deemed too risky or may be technically challenging. Calculation of flow requires measurement of a valve diameter, 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 mls/kg/minutes. Cardiac output ¼Velocity 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 association with respiratory distress syndrome (RDS), arterial ducts and high cardiac output states. In the absence of any shunts right ventricular output (RVO) and left ventricular output (LVO) are equal to each other and therefore systemic blood flow (SBF), and are normally between 220 and 250 mls/kg/minutes. However, atrial and ductal shunts are common in preterm infants 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 right atrium (RA) is obtained and combined with SVC diameter measurements from long axis views to calculate SVC flows, which are normally around 80 mLs/kg/minutes. SVC Flow ¼Velocity time integer SVC cross sectional area
Figure 1 Echocardiographic image of the arterial duct demonstrating position for Doppler of arterial ductal flow.
PAEDIATRICS AND CHILD HEALTH --:-
heart rate
2
Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Hunter L, Patel N, Echocardiography and the neonatologist, Paediatrics and Child Health (2015), http:// dx.doi.org/10.1016/j.paed.2015.02.006
SYMPOSIUM: NEONATOLOGY
Pulmonary artery pressure Pulmonary hypertension (PHT) is common in sick newborn infants and leads to impaired pulmonary blood flow and ventricular dysfunction due to increased afterload, and pulmonarysystemic shunting leading to hypoxaemia. There are two principal echo methods of measuring pulmonary artery pressure (PAP) in newborns: peak velocity of the tricuspid regurgitation jet (TR) and direction/velocity of ductal shunts. In the TR jet technique, in the absence of right ventricle (RV) outflow tract obstruction, the peak TR velocity is inserted into a modified Bernouilli equation, to calculate the gradient between the RV and right atrium (RA):
SVC flows appear to be lower in a proportion of preterm infants (newborn low output state) who may be at risk of hypotension, intraventricular haemorrhage (IVH) and neurodevelopmental abnormality. Although the technique is not widely used by all clinicians, appropriately trained and equipped neonatal units may routinely measure ventricular outputs and SVC flows. It should be appreciated that the error in any flow measurement may be as high as 25%, due to the numerous measurements involved. Ventricular function Ventricular function assessment is complicated by the complex nature of the cardiac cycle, 3-dimensional geometry of the ventricles and the faster heart rate of a term or preterm infant. 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. These techniques have the significant limitation of being subjective, observer dependent and non-quantitative. Quantitative volumetric measures of LV function include ejection fraction and fractional shortening, calculated from long or short-axis parasternal M-mode images. Although widely employed this technique measures systolic function only, is prone to measurement error and is not independent of changes in loading conditions. LV ejection fraction can also be calculated by the Simpson’s biplane method. Three-dimensional volume assessment is widely utilized in the paediatric population but has not yet been validated in haemodynamically compromised neonates. An alternative measure of LV systolic function is the relationship between LV mean velocity of circumferential fibre shortening (LV MVCF). This technique has the advantage of being preload independent and takes afterload into account. However, LV MVCF requires measurements of the 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. Although easily performed in neonates, the MPI does not differentiate between systolic and diastolic function, is variable with faster heart rates, is affected by changes in preload or afterload, and is independent of the myocardial function. Other techniques include the mitral valve inflow pattern and velocities, but these are also affected by loading conditions and the velocities are often fused due to high neonatal heart rates. Tissue Doppler imaging (TDI) is a more recently developed technique involving measurement of regional myocardial velocities allowing separate, quantitative assessment of systolic and diastolic function. Normative TDI velocities have been reported in term and preterm infants and increasing use has been reported in neonatal disease states including pulmonary hypertension where diastolic dysfunction has been identified. However, there are newer modalities in the form of speckle tracking which allows assessment of strain (myocardial deformation), strain rate (the rate of deformation) and the velocity and vector of myocardial motion. Initial studies have shown the feasibility of these techniques and their potential for future clinical use in neonates.
PAEDIATRICS AND CHILD HEALTH --:-
Pressure gradient ¼ 4ðvelocityÞ2 RV peak systolic pressure (RVp) is obtained by adding this pressure gradient to an estimate of RA pressure (usually around 5 mmHg in the absence of RA dilatation). The RVp should be equal to the 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 can be obtained from the apical 4-chamber view (Figure 2) or parasternal short axis view, ensuring a minimal angle of insonation. The extent of the TR jet often increases with increasing PAP, even when the tricuspid valve is morphologically normal. In some infants, 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 arterial duct. This will be 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 the aortic pressure (Aop) exceeds PAP. As PAP increases, flow in the arterial duct may reverse, becoming bidirectional. If PAP is above aortic pressure throughout the cardiac cycle, as in severe pulmonary hypertension, then arterial duct flow will be exclusively right-to-left. The velocity of the arterial duct flow can be inserted into the Bernouilli 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
Figure 2 Apical 4 chamber view demonstrating position of the Doppler beam for measurement of tricuspid regurgitation velocity.
3
Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Hunter L, Patel N, Echocardiography and the neonatologist, Paediatrics and Child Health (2015), http:// dx.doi.org/10.1016/j.paed.2015.02.006
SYMPOSIUM: NEONATOLOGY
10 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. 11 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. 12 Mori K, Nakagawa R, Nii M, et al. Pulsed wave Doppler tissue echocardiography assessment of the long axis function of the right and left ventricles during the early neonatal period. Heart 2004; 90: 175e80. 13 Patel N, Mills JF, Cheung MM. Assessment of right ventricular function using Tissue Doppler Imaging in Infants with Pulmonary Hypertension. Neonatology 2009; 96: 193e9. 14 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. 15 Patel N, Mills JF, Cheung MM. Use of the myocardial performance index to assess right ventricular function in infants with pulmonary hypertension. Pediatr Cardiol 2009; 30: 133e7.
because RV and LV ejection do not necessarily coincide, and therefore peak PAP and peak Aop are not simultaneous. PAP is not linearly related to RV function, and therefore any assessment of pulmonary pressures should include an assessment of ventricular function.
Summary The role of targeted neonatal echocardiography within the NICU setting with particular attention to fEcho, by appropriately trained neonatologists, is internationally accepted. Neonatologists must work in conjunction with, and be supported by, their Paediatric Cardiology colleagues, in particular to exclude congenital heart disease. Neonatal functional echocardiography remains an area of evolving research with the potential to reduce morbidity and improve the outcomes for all sick preterm and term infants. A FURTHER READING 1 Ward CJ, Purdie J. Diagnostic accuracy of paediatric echocardiograms interpreted by individuals other than paediatric cardiologists. J Paediatr Child Health 2001; 37: 3316. 2 Mertens L, Seri I, Marek J, et al. Targeted neonatal echocardiography in the neonatal intensive care unit: practice guidelines and recommendations for training. Eur J Echocardiogr 2011; 12: 715e36. 3 Evans N, Kluckow M. Neonatology concerns about the TNE consensus statement. J Am Soc Echocardiogr 2012; 25: 242. 4 Point-of-care ultrasound in the neonatal intensive care unit: international perspectives. Semin Fetal Neonatal Med 2011; 16: 61e8. 5 Sehgal A, McNamara PJ. Does point of care functional echocardiography enhance cardiovascular care in the NICU? J Perinatol 2008; 28: 729e35. 6 Evans N. Echocardiography on neonatal intensive care units in Australia and New Zealand. J Paediatr Child Health 2000; 36: 169e71. 7 de Waal K, Lakkundi A, Othman F. Speckle tracking echocardiography in very preterm infants: feasibility and reference values. Early Hum Dev 2014 Jun; 90: 275e9. 8 Kluckow M, Seri I, Evans N. Functional echocardiography an emerging tool for the neonatologist. J Pediatr 2007; 150: 125e30. 9 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: F424e7.
PAEDIATRICS AND CHILD HEALTH --:-
Practice points C
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Echocardiography is a convenient and increasingly important tool in the assessment and management of newborn infants in the neonatal intensive care unit. A comprehensive understanding is required of the haemodynamic transition that occurs in the preterm and term neonate. Neonatologists performing echocardiography must be appropriately trained, and should work collaboratively with a supportive local Paediatric Cardiology team. Neonatal echocardiography includes structural and functional assessment. Complete structural assessment is imperative to detect congenital heart disease which should be managed in conjunction with the Paediatric Cardiology Team. Functional assessment (fEcho) allows improved understanding of the mechanisms of cardiovascular compromise in preterm and term neonates. Functional echocardiography includes an assessment of ventricular function, relative pulmonary and systemic pressures, and shunt flow at the level of the atria and arterial duct.
Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Hunter L, Patel N, Echocardiography and the neonatologist, Paediatrics and Child Health (2015), http:// dx.doi.org/10.1016/j.paed.2015.02.006
Echocardiography and the neonatologist
European Paediatric and Congenital Cardiology (AEPC), discussing the importance of targeted neonatal echocardiography. fEcho should be performed as an adjunct to existing clinical parameters, for example: lactate; capillary refill time (CRT); heart rate and blood pressure, which are open to observer variability. fEcho is employed to make serial measurements and to answer specific clinical questions. In particular, it provides a direct measure of myocardial function, pulmonary and systemic blood flow and intra/extra cardiac shunting. Traditionally the diagnosis and management of significant and complex congenital heart disease has been the realm of the paediatric cardiologist and this continues to be international practice. Neonatologists must be are aware of their limitations when assessing the structure of the neonatal heart as even in the hands of experience echocardiographers certain diagnoses can be challenging and devastating if missed, for example: coarctation of the aorta and total anomalous pulmonary venous drainage (TAPVD). For this reason the initial neonatal echocardiogram must involve a comprehensive assessment of the cardiac anatomy, in addition to a full functional assessment. As per international guidelines this initial echocardiogram should be reviewed by a paediatric cardiologist within a mutually agreed time frame. A clear distinction must be made between an echocardiogram undertaken in infants with CHD, and fEcho to assess haemodynamics and myocardial function in a structurally normal heart. Once structural CHD has been excluded, subsequent echocardiograms can focus on the functional cardiac status. fEcho performed by the attending neonatologist allows for frequent assessment and therapeutic adjustment, without the immediate input of a paediatric cardiologist. To ensure neonatologists are adequately trained and supported, open and easily accessible lines of communication between the paediatric cardiologist and the neonatologist is desirable. We recommend a model of support at ward level, by continuing medical education (CME), echocardiography courses, training materials and ongoing positive feedback. Official accreditation for neonatologists undertaking targeted neonatal echocardiography is not consistent internationally. In the UK, Paediatricians with Expertise in Cardiology Specialist Interest Group (PECSIG) has been recognized by the Royal College of Paediatric and Child Health (RCPCH) since 2008, which aims to improve the care children with cardiac conditions receive, by supporting and enhancing the training of paediatricians with expertise in cardiology. Within Europe, the European Association for Cardiovascular Imaging (EACVI) in conjunction with the Association for European Paediatric and Congenital Cardiology (AEPC) provide accreditation in congenital heart echocardiography, but this is comprehensive and not entirely suitable for neonatologists undertaking targeted neonatal echocardiography. However, in Australasia an accreditation process specifically for neonatologists has been available since 2008: ‘The Neonatal Certificate in Clinician Performed Ultrasound’ (CCPU in neonatal ultrasound) which was developed by the Australasian Society for Ultrasound in Medicine.
Lindsey Hunter Neil Patel
Abstract Neonatal echocardiographic assessment is a component of neonatal point of care ultrasound and can be broadly divided into structural and functional cardiac 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 haemodynamic parameters including ventricular outputs and superior vena cava (SVC) flow, ventricular function, pulmonary arterial pressures, arterial ducts 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 arterial duct; 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 a useful and accessible modality within the neonatal intensive care unit (NICU). It is an effective tool in the hands of an appropriately trained operator, particularly when used as an adjunct to clinical assessment. Echocardiography is a fundamental component of ‘neonatal point of care ultrasound’ also known as ‘targeted neonatal echocardiography’ and can be broadly divided into functional cardiac assessment and structural cardiac assessment. There is a distinct overlap between the two assessment categories, as each informs and complements the other. Structural assessment is essential to delineate the cardiac anatomy, in particular to identify or exclude congenital heart disease (CHD). In contrast functional echocardiography (fEcho) assessment is used to evaluate myocardial function and the haemodynamic stability of sick term or preterm neonates. Although introduced primarily as a research tool, fEcho is increasingly employed at the bedside by neonatologists. International guidelines have been published by the American Society of Echocardiography (ASE) in conjunction with the European Association of Echocardiography (EAE) and the Association for
Lindsey Hunter MBChB MRCPCH is a Consultant Paediatric & Fetal Cardiologist, Cardiology Department, Royal Hospital for Sick Children, Glasgow, UK. Conflicts of interest: no conflicts of interest have been declared.
Part 2
Neil Patel BA MBChB MRCPCH MD is a Consultant Neonatologist, Neonatal Intensive Care Unit, Royal Hospital for Sick Children, Glasgow, UK. Conflicts of interest: no conflicts of interest have been declared.
PAEDIATRICS AND CHILD HEALTH --:-
The second part of this article focuses on some of the specific functional echocardiographic measurements which are
1
Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Hunter L, Patel N, Echocardiography and the neonatologist, Paediatrics and Child Health (2015), http:// dx.doi.org/10.1016/j.paed.2015.02.006
SYMPOSIUM: NEONATOLOGY
frequently utilized in the NICU. As discussed in Part 1, initial echocardiographic assessment should include a comprehensive assessment of the cardiac anatomy. Whilst we hope to provide some practical insights into some of these functional assessments, it is beyond the scope of this article to discuss all available techniques or to teach these techniques.
The shunt flow through an arterial duct may also be indirectly quantified by measuring 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, with a subsequent increase in the LA: Ao ratio. Both the LA and Ao diameters are obtained from an M Mode measurement in the parasternal long axis view. The aortic valve diameter is measured in end diastole and the maximal LA diameter in end systole. A ratio greater than 1.5:1 is associated with an HSDA. Management of the HSDA remains controversial and variable within NICUs. Early targeted treatment using NSAIDs for example ibuprofen or indomethacin, is advocated by some authors to achieve greater rates of arterial duct 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 side effects.
Assessment of the patent arterial duct (PDA) Assessment of the arterial duct is most frequently performed in preterm infants, in whom consideration may be given to closure by surgical intervention or medical therapy. Ductal assessment is important in the management of duct-dependent CHD and also aids in the assessment of pulmonary artery pressures within a structurally normal heart. The arterial duct is visualized from either a high left parasternal or suprasternal view. From this position the entire length of the arterial duct can be demonstrated extending from the proximal descending aorta to the main pulmonary artery (MPA). These views allow for assessment of the ductal diameter, shunt direction and flow velocities by pulse wave (PW) Doppler and colour Doppler assessment. (Figure 1) The diameter of the arterial duct can be measured at its insertion into the MPA by 2dimensional imaging and primary constriction usually occurs at the pulmonary artery insertion point. The diameter of the duct and evidence of constriction may indicate a potential for spontaneous ductal closure. There is increasing interest in defining a haemodynamically significant ductus arteriosus (HSDA). Clinically there may be evidence of systemic hypoperfusion or increased pulmonary blood flow, which can impact on longer term morbidity. Deciding whether an arterial duct is haemodynamically significant depends on combined echocardiographic and clinical assessments, and may be assisted by a scoring system, such as that proposed by McNamara et al. Echocardiographic findings in HSDA include a moderate to large sized duct with unrestricted left to right flow, with a high Doppler velocity. Colour flow and PW Doppler may demonstrate diastolic flow reversal in the proximal descending aorta, indicating diastolic left to right shunting at the arterial duct. Clinically this may be accompanied by evidence of impaired abdominal end organ perfusion.
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 deemed too risky or may be technically challenging. Calculation of flow requires measurement of a valve diameter, 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 mls/kg/minutes. Cardiac output ¼Velocity 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 association with respiratory distress syndrome (RDS), arterial ducts and high cardiac output states. In the absence of any shunts right ventricular output (RVO) and left ventricular output (LVO) are equal to each other and therefore systemic blood flow (SBF), and are normally between 220 and 250 mls/kg/minutes. However, atrial and ductal shunts are common in preterm infants 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 right atrium (RA) is obtained and combined with SVC diameter measurements from long axis views to calculate SVC flows, which are normally around 80 mLs/kg/minutes. SVC Flow ¼Velocity time integer SVC cross sectional area
Figure 1 Echocardiographic image of the arterial duct demonstrating position for Doppler of arterial ductal flow.
PAEDIATRICS AND CHILD HEALTH --:-
heart rate
2
Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Hunter L, Patel N, Echocardiography and the neonatologist, Paediatrics and Child Health (2015), http:// dx.doi.org/10.1016/j.paed.2015.02.006
SYMPOSIUM: NEONATOLOGY
Pulmonary artery pressure Pulmonary hypertension (PHT) is common in sick newborn infants and leads to impaired pulmonary blood flow and ventricular dysfunction due to increased afterload, and pulmonarysystemic shunting leading to hypoxaemia. There are two principal echo methods of measuring pulmonary artery pressure (PAP) in newborns: peak velocity of the tricuspid regurgitation jet (TR) and direction/velocity of ductal shunts. In the TR jet technique, in the absence of right ventricle (RV) outflow tract obstruction, the peak TR velocity is inserted into a modified Bernouilli equation, to calculate the gradient between the RV and right atrium (RA):
SVC flows appear to be lower in a proportion of preterm infants (newborn low output state) who may be at risk of hypotension, intraventricular haemorrhage (IVH) and neurodevelopmental abnormality. Although the technique is not widely used by all clinicians, appropriately trained and equipped neonatal units may routinely measure ventricular outputs and SVC flows. It should be appreciated that the error in any flow measurement may be as high as 25%, due to the numerous measurements involved. Ventricular function Ventricular function assessment is complicated by the complex nature of the cardiac cycle, 3-dimensional geometry of the ventricles and the faster heart rate of a term or preterm infant. 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. These techniques have the significant limitation of being subjective, observer dependent and non-quantitative. Quantitative volumetric measures of LV function include ejection fraction and fractional shortening, calculated from long or short-axis parasternal M-mode images. Although widely employed this technique measures systolic function only, is prone to measurement error and is not independent of changes in loading conditions. LV ejection fraction can also be calculated by the Simpson’s biplane method. Three-dimensional volume assessment is widely utilized in the paediatric population but has not yet been validated in haemodynamically compromised neonates. An alternative measure of LV systolic function is the relationship between LV mean velocity of circumferential fibre shortening (LV MVCF). This technique has the advantage of being preload independent and takes afterload into account. However, LV MVCF requires measurements of the 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. Although easily performed in neonates, the MPI does not differentiate between systolic and diastolic function, is variable with faster heart rates, is affected by changes in preload or afterload, and is independent of the myocardial function. Other techniques include the mitral valve inflow pattern and velocities, but these are also affected by loading conditions and the velocities are often fused due to high neonatal heart rates. Tissue Doppler imaging (TDI) is a more recently developed technique involving measurement of regional myocardial velocities allowing separate, quantitative assessment of systolic and diastolic function. Normative TDI velocities have been reported in term and preterm infants and increasing use has been reported in neonatal disease states including pulmonary hypertension where diastolic dysfunction has been identified. However, there are newer modalities in the form of speckle tracking which allows assessment of strain (myocardial deformation), strain rate (the rate of deformation) and the velocity and vector of myocardial motion. Initial studies have shown the feasibility of these techniques and their potential for future clinical use in neonates.
PAEDIATRICS AND CHILD HEALTH --:-
Pressure gradient ¼ 4ðvelocityÞ2 RV peak systolic pressure (RVp) is obtained by adding this pressure gradient to an estimate of RA pressure (usually around 5 mmHg in the absence of RA dilatation). The RVp should be equal to the 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 can be obtained from the apical 4-chamber view (Figure 2) or parasternal short axis view, ensuring a minimal angle of insonation. The extent of the TR jet often increases with increasing PAP, even when the tricuspid valve is morphologically normal. In some infants, 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 arterial duct. This will be 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 the aortic pressure (Aop) exceeds PAP. As PAP increases, flow in the arterial duct may reverse, becoming bidirectional. If PAP is above aortic pressure throughout the cardiac cycle, as in severe pulmonary hypertension, then arterial duct flow will be exclusively right-to-left. The velocity of the arterial duct flow can be inserted into the Bernouilli 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
Figure 2 Apical 4 chamber view demonstrating position of the Doppler beam for measurement of tricuspid regurgitation velocity.
3
Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Hunter L, Patel N, Echocardiography and the neonatologist, Paediatrics and Child Health (2015), http:// dx.doi.org/10.1016/j.paed.2015.02.006
SYMPOSIUM: NEONATOLOGY
10 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. 11 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. 12 Mori K, Nakagawa R, Nii M, et al. Pulsed wave Doppler tissue echocardiography assessment of the long axis function of the right and left ventricles during the early neonatal period. Heart 2004; 90: 175e80. 13 Patel N, Mills JF, Cheung MM. Assessment of right ventricular function using Tissue Doppler Imaging in Infants with Pulmonary Hypertension. Neonatology 2009; 96: 193e9. 14 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. 15 Patel N, Mills JF, Cheung MM. Use of the myocardial performance index to assess right ventricular function in infants with pulmonary hypertension. Pediatr Cardiol 2009; 30: 133e7.
because RV and LV ejection do not necessarily coincide, and therefore peak PAP and peak Aop are not simultaneous. PAP is not linearly related to RV function, and therefore any assessment of pulmonary pressures should include an assessment of ventricular function.
Summary The role of targeted neonatal echocardiography within the NICU setting with particular attention to fEcho, by appropriately trained neonatologists, is internationally accepted. Neonatologists must work in conjunction with, and be supported by, their Paediatric Cardiology colleagues, in particular to exclude congenital heart disease. Neonatal functional echocardiography remains an area of evolving research with the potential to reduce morbidity and improve the outcomes for all sick preterm and term infants. A FURTHER READING 1 Ward CJ, Purdie J. Diagnostic accuracy of paediatric echocardiograms interpreted by individuals other than paediatric cardiologists. J Paediatr Child Health 2001; 37: 3316. 2 Mertens L, Seri I, Marek J, et al. Targeted neonatal echocardiography in the neonatal intensive care unit: practice guidelines and recommendations for training. Eur J Echocardiogr 2011; 12: 715e36. 3 Evans N, Kluckow M. Neonatology concerns about the TNE consensus statement. J Am Soc Echocardiogr 2012; 25: 242. 4 Point-of-care ultrasound in the neonatal intensive care unit: international perspectives. Semin Fetal Neonatal Med 2011; 16: 61e8. 5 Sehgal A, McNamara PJ. Does point of care functional echocardiography enhance cardiovascular care in the NICU? J Perinatol 2008; 28: 729e35. 6 Evans N. Echocardiography on neonatal intensive care units in Australia and New Zealand. J Paediatr Child Health 2000; 36: 169e71. 7 de Waal K, Lakkundi A, Othman F. Speckle tracking echocardiography in very preterm infants: feasibility and reference values. Early Hum Dev 2014 Jun; 90: 275e9. 8 Kluckow M, Seri I, Evans N. Functional echocardiography an emerging tool for the neonatologist. J Pediatr 2007; 150: 125e30. 9 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: F424e7.
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Echocardiography is a convenient and increasingly important tool in the assessment and management of newborn infants in the neonatal intensive care unit. A comprehensive understanding is required of the haemodynamic transition that occurs in the preterm and term neonate. Neonatologists performing echocardiography must be appropriately trained, and should work collaboratively with a supportive local Paediatric Cardiology team. Neonatal echocardiography includes structural and functional assessment. Complete structural assessment is imperative to detect congenital heart disease which should be managed in conjunction with the Paediatric Cardiology Team. Functional assessment (fEcho) allows improved understanding of the mechanisms of cardiovascular compromise in preterm and term neonates. Functional echocardiography includes an assessment of ventricular function, relative pulmonary and systemic pressures, and shunt flow at the level of the atria and arterial duct.
Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Hunter L, Patel N, Echocardiography and the neonatologist, Paediatrics and Child Health (2015), http:// dx.doi.org/10.1016/j.paed.2015.02.006