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Table of Contents
Abbreviations 1058
- 1.
Targeted Neonatal Echocardiography: Background and Indications 1058
- 1.1.
Cardiovascular Adaptations in the Neonatal Period 1058
- 1.2.
Indications for TNE 1059
- 1.2.1.
Indications for TNE With Standard Imaging (Standard TNE) 1059
- 1.2.2.
Indications for TNE With Focused Imaging (Focused TNE) 1062
- 1.2.1.
- 1.1.
- 2.
Targeted Neonatal Echocardiography: Practical Aspects 1063
- 2.1.
General Aspects of TNE 1063
- 2.1.1.
Technical and Safety Requirements for Performing TNE 1063
- 2.1.2.
Guidelines for Image Acquisition in the NICU 1063
- 2.1.3.
Components of Standard TNE 1064
- 2.1.3a.
Evaluation of LV Systolic Function 1064
- 2.1.3b.
Assessment of LV Diastolic or Combined Function 1065
- 2.1.3c.
Evaluation of RV Function 1065
- 2.1.3d.
Assessment of Atrial-Level Shunt 1065
- 2.1.3e.
Assessment of PDA 1066
- 2.1.3f.
Assessment of RVSp and PA Pressures 1066
- 2.1.3g.
Assessment of Systemic Blood Flow 1066
- 2.1.3h.
Assessment of Pericardial Fluid 1067
- 2.1.3a.
- 2.1.1.
- 2.2.
TNE for Specific Neonatal Conditions 1067
- 2.2.1.
Suspected PDA 1067
- 2.2.2.
Perinatal Asphyxia 1068
- 2.2.3.
Neonatal Hypotension 1068
- 2.2.4.
Suspected Persistent Pulmonary Hypertension of the Newborn (PPHN) 1069
- 2.2.5.
CDH 1069
- 2.2.6.
Suspected Effusion 1070
- 2.2.7.
Central Line Placement 1070
- 2.2.8.
ECMO Cannulation 1071
- 2.2.1.
- 2.1.
- 3.
Training and Accreditation in Targeted Neonatal Echocardiography 1071
- 3.1.
Overview of Existing Training Guidelines 1072
- 3.1.1.
US Pediatric Echocardiographic Guidelines 1072
- 3.1.2.
European Pediatric Echocardiographic Guidelines 1072
- 3.1.1.
- 3.2.
Proposal for Training in TNE 1073
- 3.2.1.
Core Training in TNE 1073
- 3.2.2.
Advanced Training in TNE 1074
- 3.2.1.
- 3.3.
Supervision of Training 1074
- 3.4.
Evaluation 1074
- 3.5.
Maintenance of Competence and Quality Assurance for TNE 1074
- 3.1.
Table of Contents
Abbreviations 1058
- 1.
Targeted Neonatal Echocardiography: Background and Indications 1058
- 1.1.
Cardiovascular Adaptations in the Neonatal Period 1058
- 1.2.
Indications for TNE 1059
- 1.2.1.
Indications for TNE With Standard Imaging (Standard TNE) 1059
- 1.2.2.
Indications for TNE With Focused Imaging (Focused TNE) 1062
- 1.2.1.
- 1.1.
- 2.
Targeted Neonatal Echocardiography: Practical Aspects 1063
- 2.1.
General Aspects of TNE 1063
- 2.1.1.
Technical and Safety Requirements for Performing TNE 1063
- 2.1.2.
Guidelines for Image Acquisition in the NICU 1063
- 2.1.3.
Components of Standard TNE 1064
- 2.1.3a.
Evaluation of LV Systolic Function 1064
- 2.1.3b.
Assessment of LV Diastolic or Combined Function 1065
- 2.1.3c.
Evaluation of RV Function 1065
- 2.1.3d.
Assessment of Atrial-Level Shunt 1065
- 2.1.3e.
Assessment of PDA 1066
- 2.1.3f.
Assessment of RVSp and PA Pressures 1066
- 2.1.3g.
Assessment of Systemic Blood Flow 1066
- 2.1.3h.
Assessment of Pericardial Fluid 1067
- 2.1.3a.
- 2.1.1.
- 2.2.
TNE for Specific Neonatal Conditions 1067
- 2.2.1.
Suspected PDA 1067
- 2.2.2.
Perinatal Asphyxia 1068
- 2.2.3.
Neonatal Hypotension 1068
- 2.2.4.
Suspected Persistent Pulmonary Hypertension of the Newborn (PPHN) 1069
- 2.2.5.
CDH 1069
- 2.2.6.
Suspected Effusion 1070
- 2.2.7.
Central Line Placement 1070
- 2.2.8.
ECMO Cannulation 1071
- 2.2.1.
- 2.1.
- 3.
Training and Accreditation in Targeted Neonatal Echocardiography 1071
- 3.1.
Overview of Existing Training Guidelines 1072
- 3.1.1.
US Pediatric Echocardiographic Guidelines 1072
- 3.1.2.
European Pediatric Echocardiographic Guidelines 1072
- 3.1.1.
- 3.2.
Proposal for Training in TNE 1073
- 3.2.1.
Core Training in TNE 1073
- 3.2.2.
Advanced Training in TNE 1074
- 3.2.1.
- 3.3.
Supervision of Training 1074
- 3.4.
Evaluation 1074
- 3.5.
Maintenance of Competence and Quality Assurance for TNE 1074
- 3.1.
1. Targeted Neonatal Echocardiography: Background and Indications
The role of echocardiography in the neonatal intensive care unit (NICU) has changed over the past few years. Previously, nearly all echocardiographic studies in the NICU were performed by pediatric cardiologists to diagnose or monitor congenital heart disease (CHD) and to screen for patent ductus arteriosus (PDA). More recently, neonatologists have become interested in the echocardiographic assessment of hemodynamic instability in infants. The terms functional echocardiography and point-of-care echocardiography have been introduced to describe the use of echocardiography as an adjunct in the clinical assessment of the hemodynamic status in neonates. The increasing availability of echocardiography, with miniaturization of the technology, has resulted in more widespread use of echocardiography in NICUs around the world. Perhaps the most significant challenge for the application of so-called functional studies is that newborns in the NICU with hemodynamic instability are at a much higher risk for having underlying CHD. In addition, newborns in the NICU are unique in that they are in the process of transition from fetal to postnatal circulation.
In this document, we make clear distinctions between initial echocardiographic studies in neonates with the suspicion of CHD and studies performed on infants without any clinical suspicion of CHD. If CHD has been excluded, subsequent studies in children with structurally normal hearts can focus on hemodynamic or functional assessment. The initial echocardiographic examination should always be a comprehensive study of both anatomy and function that is to be interpreted by a pediatric cardiologist within a reasonable time frame. Some structural defects, such as anomalous pulmonary venous return or coarctation of the aorta, can be difficult to detect using echocardiography and require extensive training and continued practice. Once significant congenital defects have been ruled out, more focused studies can be performed and interpreted by a trained echocardiographer for specific indications, as defined later in this document. We propose to use the term targeted neonatal echocardiography (TNE) for the more focused studies. The aims of the current document are: (1) to review the current indications of TNE; (2) to define recommendations for the performance of TNE; and (3) to propose training requirements for the operators performing and interpreting TNE.
1.1. Cardiovascular Adaptations in the Neonatal Period
The neonatal cardiovascular system differs from those of fetal, pediatric, and adult patients. At term, a neonate must successfully transition through abrupt changes in the cardiorespiratory system, including changes in lung volume and compliance and changes in left and right heart preload and afterload. Intracardiac and extracardiac shunts via the foramen ovale and ductus arteriosus, physiologic in the fetus, have varying effects on immediate postnatal hemodynamics. The neonatal heart may also have to cope with structural heart disease and/or extracardiac congenital and acquired conditions, such as congenital diaphragmatic hernia (CDH), sepsis, or pulmonary hypertension, that are tolerated differently compared with an older child. In the setting of a preterm delivery, the immaturity of the cardiovascular system and other organ systems makes it more difficult for the neonate to appropriately respond to the challenges of postnatal transition and extrauterine existence. Detailed understanding of fetal, transitional, and neonatal cardiovascular physiology is necessary to enable understanding of echocardiographic information obtained during the perinatal period.
The Transition From Fetus to Neonate
It is important for those performing TNE to understand the normal development of the myocardium and cardiopulmonary circulation and how preterm delivery may disrupt this process. In the fetus, myocytes are smaller and typically have a single nucleus, compared with the multinucleated myocytes that are prevalent postnatally. Although the fetus has a higher indexed myocardial mass, the fetal myocardium is less organized at the cellular level, with fewer sarcomeres per unit mass, different isoforms of contractile proteins, a developing sarcoplasmic reticulum, an overall higher water content, and a decreased number of mitochondria. In addition, the heart is enclosed within a poorly compliant thorax. As a result of these factors, the fetal heart is less compliant and less contractile than a term newborn or adult heart. These differences are manifested in the developmentally regulated limited fetal cardiac response to changes in preload or afterload, with heart rate changes being the major mechanism to alter fetal cardiac output, although some response to preload occurs if afterload remains constant. The fetal right and left ventricles also differ in myofiber architecture throughout gestation, with the right ventricle less tolerant to increases in afterload, despite its contributing slightly more to the combined ventricular output than the left ventricle during fetal life. The fetal pulmonary vasculature also exhibits significant differences from the adult pulmonary circulation. In the fetus, the pulmonary arteries and larger preacinar vessels demonstrate significant elastin in their medial layer, with a relative paucity of pulmonary smooth muscle, in contrast to the more distal preacinar and acinar vessels, which have a predominance of pulmonary smooth muscle in the media, and the most distal intra-acinar vessels, with no smooth muscle medial layer. These differences all result in the fetal pulmonary vascular bed being characterized by high vascular resistance, limiting fetal pulmonary blood flow from 11% to 22% of the combined cardiac output from early to late gestation, respectively.
The fetus is ideally adapted to these differences, because the fetal circulatory system includes the low-resistance placental circuit; a ductus arteriosus, which permits the right ventricular (RV) output to bypass the high-resistance lungs; and a patent foramen ovale, which permits mixing of the ductus venosus, hepatic, portal, and ultimately inferior vena caval venous flow with left atrial blood. During normal gestation, a large increase in fetal cardiac output is facilitated, and a gradual increase in cardiac contractility, sympathetic innervation, growth of cardiac chambers, growth of the lungs and the pulmonary vasculature, and redistribution of flow to the various fetal organs take place. If this process is interrupted, as in the case of premature birth, further development occurs under very different and often adverse circumstances.
With delivery, there is an abrupt increase in systemic afterload, with removal of the low-resistance placenta and via peripheral vasoconstriction in response to the labor-induced endogenous hormone release and the cold stress encountered by moving to the extrauterine environment. Preload to the right heart decreases because of the cessation of umbilical venous return. Simultaneously, there is a decrease in pulmonary vascular resistance due to lung expansion and increased partial pressure of oxygen in the alveoli and the exposure of the pulmonary vascular bed to higher pulmonary artery (PA) partial pressure of oxygen and endocrine and paracrine pulmonary vasodilators. These changes lead to decreased RV pressures and a decreased constraining effect of the right ventricle within the pericardium. Intrapericardial pressure is also reduced with spontaneous ventilation producing intrathoracic pressures that are lower than atmospheric. These right-heart changes help the left ventricle adapt to the increased preload resulting from increased pulmonary venous return.
In the term infant, the ductus venosus is functionally closed almost immediately with cessation of umbilical venous flow. Similarly, the flap of the foramen ovale quickly covers the fossa ovalis in the setting of higher left atrial pressures produced by increased pulmonary venous return and increased left ventricular (LV) afterload. The ductus arteriosus closes slightly more slowly, over the first several hours or days, in response to a higher partial pressure of oxygen, decreased local and circulating prostaglandin E 2 and other vasoactive factors, and a fully developed muscular medial layer. Myocardial contractility is also affected by increased levels of thyroid hormone, corticosteroids, and the catecholamine surge that occurs with labor and delivery.
The transition from fetal to postnatal life is more complicated in the preterm infant. The preterm LV myocardium is exposed to an abrupt increase in afterload while still relatively immature and thus may be less tolerant of the concurrent changes in preload conditions brought on by the presence of now pathologic atrial and ductal shunts. The preterm infant is also faced with immaturity of all organ systems, the preexisting intrauterine milieu that led to preterm delivery, and the resultant need for surfactant administration, ventilatory support, and vasoactive medications.
TNE can be a useful clinical adjunct to the overall assessment of the cardiovascular status of preterm and term neonates during normal and abnormal transition to extrauterine life. Ventricular systolic function can be noninvasively assessed using qualitative and quantitative methods; the direction and magnitude of atrial and ductus arteriosus shunting can be determined; and pressure estimations, particularly of the right ventricle and PA, can be made.
Recommendations: Every echocardiographer performing and interpreting TNE should be familiar with the normal neonatal cardiovascular adaptations and the effect of prematurity and disease on the neonatal cardiovascular system. This is crucial to understanding the findings of TNE.
1.2. Indications for TNE
TNE is proposed to “describe the bedside use of echocardiography to longitudinally assess myocardial function, systemic and pulmonary blood flow, intracardiac and extracardiac shunts, organ blood flow and tissue perfusion.” The primary goals of TNE are to provide noninvasive information on the underlying cardiovascular pathophysiology causing hemodynamic instability and the response to treatment in an individual patient over time. We are aware that the current indications for TNE have been primarily established on the basis not of large clinical studies or trials but of clinical experience in a growing number of neonatal units and recent observational studies. Therefore, it is currently difficult to define the most appropriate use criteria for TNE, because it remains a constantly evolving ultrasound application. It is important to realize that TNE is not intended as a substitute for the evaluation of a neonate with suspected CHD by a qualified pediatric cardiologist. If structural CHD or significant arrhythmia is clinically suspected in a neonate , the infant should be clinically assessed by a pediatric cardiologist, and echocardiography should be performed by a person trained in pediatric echocardiography (at least core-level training, as defined later in this document) and reviewed by a pediatric cardiologist. Clinical suspicion includes the presence of cyanosis, signs of circulatory shock, clinical signs of heart failure, the presence of a murmur, arrhythmia, and abnormal pulses in upper and/or lower extremities. In infants without any clinical suspicion for CHD , the first echocardiographic study must be a comprehensive examination assessing both structure and function. This initial study can be performed by a person with at least core training in TNE or a core pediatric echocardiographer. The initial interpretation of this comprehensive study can be done by an advanced TNE-trained person, but it is recommended that the study be reviewed within a reasonable time period by a pediatric cardiologist. If this level of expertise is not readily available in the NICU, the use of telemedicine technology (either real-time or store-and-forward transmission of images in a timely manner) is strongly encouraged.
1.2.1. Indications for TNE With Standard Imaging (Standard TNE)
In this document, we distinguish between “TNE with standard imaging (standard TNE)” and “TNE with focused imaging (focused TNE).” Standard, or full, TNE is a study including the different components as defined in Table 1 and further discussed in the next section of this document. The indications are listed below:
- a.
Clinically suspected PDA, especially in very low birth weight (VLBW) neonates during the first 24 to 72 postnatal hours and beyond
- b.
Assessment of infants with perinatal asphyxia
- c.
Abnormal cardiovascular adaptation presenting with hypotension, lactic acidosis, or oliguria during the first 24 postnatal hours and beyond in VLBW infants to diagnose low systemic blood flow state
- d.
Suspected persistent pulmonary hypertension in neonates
- e.
CDH
| Component of TNE | Technique | View | Essential | Optional | Remarks | Normal reference data |
|---|---|---|---|---|---|---|
| LV systolic function | ||||||
| LV end-diastolic diameter | 2D or M-mode | Parasternal short-axis | Yes | No | M-mode higher temporal resolution | Nagasawa (2010) |
| 2D | Subxiphoid short-axis | Zecca et al. (2001) | ||||
| Skelton et al. (1998) | ||||||
| Kampmann et al. (2000) | ||||||
| LV end-systolic dimension | 2D or M-mode | Parasternal short-axis | Yes | No | Nagasawa (2010) | |
| 2D | Subxiphoid short-axis | Zecca et al. (2001) | ||||
| Skelton et al. (1998) | ||||||
| Kampmann et al. (2000) | ||||||
| LV end-diastolic posterior wall thickness | 2D or M-mode | Parasternal short-axis | Yes | No | Nagasawa (2010) | |
| 2D | Subxiphoid short-axis | Zecca et al. (2001) | ||||
| Skelton et al. (1998) | ||||||
| Kampmann et al. (2000) | ||||||
| LV end-diastolic septal wall thickness | 2D or M-mode | Parasternal short-axis | Yes | No | Nagasawa (2010) | |
| 2D | Subxiphoid short-axis | Zecca et al. (2001) | ||||
| Skelton et al. (1998) | ||||||
| Kampmann et al. (2000) | ||||||
| LV SF | 2D or M-mode | Parasternal short-axis | If normal LV shape/normal septal motion | No | ||
| 2D | Subxiphoid short-axis | |||||
| LV EF | Biplane Simpson | Apical four-chamber and two-chamber | If abnormal LV shape/septal motion | If normal LV shape/septal motion | ||
| 3D volumes | Apical views | No | Yes | Requires validation | ||
| mVCFc | 2D or M-mode | Parasternal short-axis | No | Yes | mVCFc is preload independent | Colan et al. (1992) |
| Rowland and Gutgesell (1995) | ||||||
| LV diastolic function | ||||||
| LA dimension | 2D or M-mode | Parasternal long-axis | No | Yes | Kampmann et al. (2000) | |
| LA major axis | 2D | Apical four-chamber | No | Yes | ||
| LA minor axis | 2D | Apical four-chamber | No | Yes | ||
| MV E-wave peak velocity | PW Doppler | Apical four-chamber | Yes | Yes | Riggs et al. (1989) | |
| Schmitz et al. (1998) | ||||||
| Schmitz et al. (2004) | ||||||
| Harada et al. (1994) | ||||||
| MV A-wave peak velocity | PW Doppler | Apical four-chamber | Yes | Yes | Riggs et al. (1989) | |
| Schmitz et al. (1998) | ||||||
| Schmitz et al. (2004) | ||||||
| Harada et al. (1994) | ||||||
| MV E/A ratio | Riggs et al. (1989) | |||||
| Schmitz et al. (1998) | ||||||
| Schmitz et al. (2004) | ||||||
| Harada et al. (1994) | ||||||
| Pulmonary venous flow pattern | PW Doppler | Apical four-chamber | No | Yes | Influenced by atrial shunt | Ito et al. (2002) |
| Peak MV annular velocity early diastolic E′ | Tissue Doppler | Apical four-chamber | No | Yes | Mori et al. (2004) | |
| Peak MV annular velocity late diastolic A′ | Tissue Doppler | Apical four-chamber | No | Yes | Mori et al. (2004) | |
| Assessment of pulmonary hypertension | ||||||
| TR peak velocity | CW Doppler | Apical four-chamber view | Yes | No | Depends on angulation | |
| Parasternal RV inflow view | Not reliable if TR jet is trivial | |||||
| Pulmonary regurgitation early diastolic velocity | PW/CW Doppler | Parasternal short-axis | Yes | No | Correlates well with mean PA pressure | |
| Parasternal long-axis RVOT | ||||||
| Pulmonary regurgitation late diastolic velocity | PW/CW Doppler | Apical four-chamber view | No | Yes | Correlates with end-diastolic PA pressure | |
| Parasternal RV inflow view | ||||||
| Assessment of RV function | ||||||
| Tricuspid annular plane systolic excursion | M-mode | Apical four-chamber view | No | Yes | Correlates with EF | Koestenberger et al. (2009) |
| Fractional area change | 2D | Apical four-chamber view | No | Yes | Moderate correlation with EF | |
| Assessment of PDA | ||||||
| Narrowest dimension of duct | 2D or color Doppler | Ductal/suprasternal | Yes | No | ||
| Shunt directionality | Color/CW/PW Doppler | Ductal/suprasternal | Yes | No | ||
| Peak and mean gradient of ductal flow | CW/PW Doppler | Ductal/suprasternal | Yes | No | Obtain arterial blood pressure at the same time | |
| Assessment of atrial-level shunt | ||||||
| Shunt directionality | Color Doppler | Subxiphoid long-axis/short-axis | Yes | No | ||
| Peak and mean gradient of intra-atrial shunt | PW/CW Doppler | Subxiphoid long-axis/short-axis | No | Yes | Provides information on LA pressures | |
| Assessment of cardiac index (LVOT method) | ||||||
| LVOT diameter measurement | 2D | Parasternal long axis | No | Yes | ||
| Velocity-time integral of PW in LVOT | PW Doppler | Apical five-chamber view | No | Yes | Dependent on alignment and correct point placement | |
| Assessment of pericardial effusion | ||||||
| Measurement of pericardial effusion in diastole | ||||||
| Respiratory variation on mitral/tricuspid inflow | 2D | Different views | No | Yes | ||
| PW Doppler | Apical four-chamber | Yes if effusion | No |
1.2.2. Indications for TNE With Focused Imaging (Focused TNE)
- a.
Suspected effusion, either pericardial or pleural
- b.
Central line
- c.
Extracorporeal membrane oxygenation (ECMO) cannulation
Outside of these limited indications for focused imaging, we recommend performing a standard TNE for the other indications. For any indication, the first study must always be a full comprehensive study, or if focused TNE is performed in emergency situations such as pericardial tamponade, this should be followed by a comprehensive study as soon as the patient has been hemodynamically stabilized. Standard TNE can be considered as a functional follow-up study for patients without structural heart disease. The frequency with which these studies can be performed in the NICU is outside the scope of the current writing group, as no good scientific data exist on its use.
Recommendations: If strong clinical suspicion of CHD or arrhythmia is present in a newborn, the infant should be clinically assessed by a pediatric cardiologist, and comprehensive echocardiography should be performed and interpreted by a pediatric cardiologist. In hemodynamically unstable newborns without any clinical suspicion of CHD, the initial echocardiographic examination should always be a comprehensive study that can be performed by a core TNE person and initially interpreted by an advanced TNE person. However, it is strongly recommended that this initial study be read by a pediatric cardiologist within a reasonable time period. In the follow-up of children in whom CHD has been excluded, standard TNE can be performed as a targeted functional study for certain indications. Performance of these studies requires core training in TNE, and they should be interpreted by a person with advanced training in TNE. Focused TNE may be indicated for the evaluation and follow-up for a limited number of specific indications (effusions and lines). TNE should not be used in the follow-up of structural heart disease. See Table 2 for a summary of these recommendations.
| Study type | Training of performer | Training of interpreter | Additional imaging required |
|---|---|---|---|
| Suspicion of CHD (cyanosis, shock, congestive heart failure, murmur, arrhythmia, or abnormal pulses) | |||
| Comprehensive | Core pediatric | Pediatric cardiologist | None |
| No suspicion of CHD | Minimum training of performer | Minimum training of interpreter | |
| Initial study | |||
| Comprehensive | Core TNE or core pediatric | Advanced TNE or pediatric cardiologist | If read by advanced TNE, interpretation by pediatric cardiologist is strongly recommended within reasonable time |
| Focused TNE | Core TNE or core pediatric | Advanced TNE or pediatric cardiologist | Must be followed by comprehensive study |
| No CHD: follow-up study | |||
| Standard TNE | Core TNE or core pediatric | Advanced TNE or pediatric cardiologist | |
| Focused TNE | Core TNE or core pediatric | Core TNE or pediatric cardiologist |
2. Targeted Neonatal Echocardiography: Practical Aspects
2.1. General Aspects of TNE
2.1.1. Technical and Safety Requirements for Performing TNE
All ultrasound systems used for imaging neonatal hearts should include two-dimensional (2D), M-mode, and full Doppler capabilities and should display a simultaneous electrocardiographic tracing. A range of multifrequency probes should be available so that the operator can select the best probe depending on the size of the infant, the available imaging windows, and the information that is to be obtained. High-frequency probes (8–12 MHz) should be available on the machines used in the NICU. System settings should be optimized to image neonates and VLBW infants. When performing examinations on unstable infants, special precautions may need to be taken not to cause further cardiorespiratory instability in this population. These include but are not limited to the following actions:
- 1.
Attention to skin integrity and prevention of infection: Infection prevention is of utmost importance, because preterm and term infants have an immature humoral immune system and a tendency toward poor skin integrity. Use of connecting cables from the monitoring equipment already in use to the ultrasound system, rather than placement of additional electrodes for electrocardiographic acquisition, should be considered whenever possible to minimize skin trauma. Infection prevention measures differ among neonatal units. Therefore, it is recommended that individualized practice guidelines for infection prevention during echocardiographic studies be developed and that practitioners of TNE be aware of and adhere to local guidelines.
- 2.
Attention to maintenance of body temperature and neutral thermal environment: During the scan, the infant should be kept warm, and body temperature should be monitored. Warmed gel should be used to minimize the effect of direct skin cooling on the patient’s body temperature. Opening of incubators should be kept at a minimum, with the use of portals designed for handling rather than unnecessary opening of the unit.
- 3.
Cardiorespiratory monitoring: Premature and sick term neonates may become increasingly unstable with stimulation, and even light pressure on the abdomen and chest can influence chest expansion and venous return to the heart in small infants. Because the sonographer is primarily focused on image acquisition, assistance by additional staff members for monitoring cardiorespiratory stability during the scan may be useful. The duration of scanning should be minimized, particularly in critically ill infants.
Recommendations: The ultrasound systems used for TNE should be optimized for imaging the neonatal heart. When imaging a potentially unstable neonate or VLBW infant, special attention is required for the prevention of infection, maintenance of body temperature, and monitoring of cardiorespiratory function.
2.1.2. Guidelines for Image Acquisition in the NICU
The first echocardiographic study performed in a neonate should include a full morphologic and hemodynamic assessment of cardiac anatomy and physiology using a segmental approach. American Society of Echocardiography (ASE) guidelines and standards for the performance of pediatric echocardiography have been published, and these guidelines should be applied to neonatal scanning to ensure that no congenital defects are missed and that a full functional evaluation is obtained. on the basis of these guidelines, standardized echocardiography protocols should be developed and applied. Initial studies should include the different imaging windows (subxiphoid, parasternal, apical, and suprasternal) to complete the segmental analysis. A full assessment of cardiac structure should include imaging of atrial situs and position of the heart in the chest; systemic venous return; biatrial size and morphology; presence of an atrial communication; atrioventricular connection and function; biventricular morphology, size, and function; ventricular septal anatomy; structure and function of the ventriculoarterial connection; presence of a PDA; coronary artery anatomy; aortic arch and PA anatomy; pulmonary venous return; and presence of pericardial effusion. Full, standardized image acquisition during the initial scan should allow the pediatric cardiologist reviewing the study to rule out CHD. After this initial assessment, more targeted studies can be performed. The ASE has also published guidelines on quantification methods used in pediatric echocardiography. We recommend following these quantification guidelines when performing TNE. For the quantification of chamber dimensions as well as the dimensions of cardiac structures, this implies reporting the measurements as Z scores when these are available.
2.1.3. Components of Standard TNE
Every standard targeted neonatal echocardiographic study should include
- 1.
Evaluation of LV systolic function
- 2.
Evaluation of LV diastolic function
- 3.
Evaluation of RV function
- 4.
Assessment of atrial-level shunt
- 5.
Assessment of PDA
- 6.
Evaluation of RV systolic pressure (RVSp) and PA pressures
- 7.
Assessment of systemic blood flow
- 8.
Assessment of pericardial fluid
The overall standard targeted neonatal echocardiographic examination and the suggested measurements are summarized in Table 1 .
2.1.3a. Evaluation of LV Systolic Function
Hemodynamic instability in the neonate can be caused by LV dysfunction, and assessment of LV systolic function is a key component of TNE. The pediatric quantification guidelines can be partially used in the neonatal population.
Several standard techniques for the evaluation of LV systolic function can be applied to neonates and preterm infants. Although subjective qualitative assessment of LV systolic function can easily be performed, it is prone to interobserver and intraobserver variability; therefore, quantitative measures are preferred. Most standard techniques for LV systolic functional assessment are based on the assessment of LV dimensions or LV size. LV dimensions should be measured on the basis of M-mode or 2D images obtained from the short-axis or long-axis views at the level just distal to the leaflet tips of the mitral valve at end-diastole. M-mode imaging has higher temporal resolution, which can be an advantage in cases of high heart rates but low spatial resolution. Two-dimensional echocardiography has higher spatial but lower temporal resolution. Normal values for LV dimensions in term and preterm infants have been published. Increased LV end-diastolic dimensions suggest either volume loading (in the case of shunt lesions or valve regurgitation) or can be a sign of LV dysfunction in the case of dilated cardiomyopathy. Increase in wall thickness can occur in the context of pressure loading or infiltrative disorders. Assessment of global LV systolic function is generally based on geometric quantification either linear by measuring percentage shortening fraction (SF) or volumetric by calculating ejection fraction (EF). The pediatric quantification recommendations suggest calculating SF from the measurement of LV dimensions obtained from 2D parasternal or subxiphoid short-axis views, with measurements averaged over three cardiac cycles. In neonates and especially in preterm infants with high heart rates and with concomitant respiratory disease or lung interference, there might be an advantage to using M-mode measurements. In neonates, the use of SF (on 2D or M-mode imaging) can be limited by septal flattening or paradoxical motion of the ventricular septum due to the interaction between the hypertrophied and relatively high-pressure right ventricle and the left ventricle. In case of abnormal septal motion or ventricular geometry, measurement of LV EF using the biplane Simpson’s and five-sixths area × length methods are accepted alternatives. Poor imaging windows due to lung interference can be an important limitation. Current three-dimensional techniques for volumetric quantification in newborns have not been validated. When interpreting the SF and EF measurements, the influence of preload and afterload should be taken into account. This may be especially important when comparing measurements before and immediately after ductal closure. Removal of the left-to-right shunt reduces LV preload, and removal of the low-resistance pulmonary circulation increases mean arterial pressure and LV afterload. Therefore it is not surprising that LV SF and EF are reduced immediately after surgical duct ligation.
To overcome the problem of load dependency, alternative measurements of LV function may be considered. LV heart rate–corrected mean velocity of circumferential fiber shortening (mVCFc; calculated as SF/LV ejection time corrected for heart rate [ejection time/√RR interval]) is less preload dependent than SF; as an ejection parameter, however, it is afterload dependent. This measurement is not recommended as a routine measurement in TNE but might provide additional information. If LV geometry is normal, there is a linear relationship between mVCFc and wall stress. This stress-velocity relationship can be used as a load-independent measure of myocardial contractility. The clinical applicability of the stress-velocity relationship is not well studied in neonates and infants, with only limited research data available on the feasibility and reliability in a preterm population. There is some evidence that mVCFc correlates with cardiac troponin levels in the early neonatal period, but further data are needed. Newer functional echocardiographic techniques, including tissue Doppler methods and deformation imaging (strain and strain rate imaging), have recently been studied in neonates, but further validation and methodologic improvements are needed before they can be recommended for use in routine clinical practice.
Recommendations: Quantitative assessment of LV systolic function is an essential component of TNE. It requires the estimation of LV dimensions on the basis of M-mode or 2D measurements. LV end-diastolic dimension and septal and posterior wall thickness should be measured. On the basis of M-mode or 2D imaging, SF can be measured if there are no regional wall motion abnormalities and if septal motion is normal. In the case of wall motion abnormalities or abnormal septal motion, EF should be calculated using a biplane volumetric measurement (biplane Simpson’s or five-sixths area × length method). Optional techniques include mVCFc and wall stress measurements.
2.1.3b. Assessment of LV Diastolic or Combined Function
In contrast to systolic dysfunction, the impact of diastolic dysfunction on neonatal hemodynamics is less clear and more difficult to define by echocardiography. In children and adults, evaluation of diastolic function relies on a combination of different measurements, including mitral inflow, pulmonary venous flow, and tissue velocity measurements of the mitral annulus. In infants, the available data on diastolic function assessment are limited and based mainly on analysis of mitral inflow patterns. In normal neonates, important changes in mitral inflow patterns are observed during the first days and weeks of life. During the first week of life, there is a gradual change from a fetal filling type with more dependence on filling during atrial contraction (A wave) toward a more mature filling pattern with higher early filling (E wave). This change is characterized by progressive increase in E-wave velocities, increase in the E/A ratio, and early filling fraction. In preterm infants, this change is more pronounced. The difficulty when using the mitral inflow pattern and velocities in infants is that often the E and A waves are fused related to high heart rates. E-wave velocities are also sensitive to changes in preload, as in patients with PDAs with left-to-right shunting, because increased pulmonary flow increases left atrial pressures, resulting in increased E-wave velocities across the mitral valve. The use of pulmonary venous inflow is less affected by heart rate, but residual shunts at the atrial, ductal, or ventricular level will influence the pulmonary venous flow patterns. Tissue Doppler velocities for the assessment of diastolic function have not been well explored in the neonatal population. Changes in myocardial velocities have been observed in both ventricles. Limited data are available on the effect of disease on tissue velocities, limiting its practical use in clinical practice. Further research is needed in the neonatal and infant populations.
Assessment of volume status and decisions on fluid replacement therapy are clinically challenging in term and preterm infants. However, preload is an important determinant of cardiac output in this population, and decreased preload can be an important reason for decreased cardiac output. Because of decreased myocardial compliance and the limited capacity of the neonatal heart to cope with increased preload, overaggressive fluid replacement therapy can be detrimental. Noninvasive assessment of filling status would be beneficial for neonatal management optimization. Because it is impossible to calculate circulatory volume, filling pressures are used as a substitute for preload. It is extremely difficult to noninvasively assess filling pressures and filling status in neonates using Doppler or tissue Doppler parameters. Inferior vena cava diameter or collapsibility and measurement of LV end-diastolic dimension have been suggested as surrogates of preload (volume status) in spontaneously breathing infants, but utility may be decreased in those maintained on positive-pressure ventilation. The use of measurements of chamber dimensions as an indicator of filling status must take into account additional factors, including cardiac function, heart rate, afterload, and RV-LV interaction. Therefore, although the assessment of intravascular volume status is considered to be integral part of the hemodynamic assessment, no clear recommendations for quantification can be made at present; qualitative assessment on the basis of inferior vena cava and cardiac chamber size by an experienced observer with knowledge of the clinical status of the neonate may be the most informative.
The myocardial performance index (MPI) has been proposed as a relatively simple way to assess combined systolic and diastolic performance of the heart simultaneously. MPI combines the isovolumic relaxation and contraction times, corrected for the ejection time (MPI = [isovolumic contraction time + isovolumic relaxation time]/ejection time). Normal values in healthy neonates range from 0.25 to 0.38, with higher values obtained in the presence of abnormal prolongation of isovolumic time with respect to ejection time. The disadvantages of MPI are that it is nonspecific with respect to abnormalities of systolic versus diastolic function and it is influenced by preload and afterload changes. This makes it of limited use in hemodynamically unstable infants. In addition, the reproducibility of MPI in infants with higher heart rates has not been well studied.
Recommendations: Although the assessment of diastolic function and filling pressures should ideally be part of TNE, currently data are inadequate to permit any recommendation regarding the use of echocardiographic data in the fluid management of neonates and infants. Thus, this should be considered an optional component of standard TNE until further data sustain its use.
2.1.3c. Evaluation of RV Function
The evaluation of RV function should be an integral part of TNE, especially in patients with pulmonary hypertension, but it is difficult to perform, because there is no good quantitative parameter for the assessment of RV function. For the estimation of RV size , the ASE pediatric quantification guidelines recommend the measurement of end-diastolic diameters at the basal and mid cavity levels, end-diastolic length, and end-diastolic and end-systolic planimetered areas in apical four-chamber views. For the assessment of RV function , the pediatric guidelines recommend quantitative measurements such as fractional area change and tricuspid annular plane systolic excursion, but these measurements require further validation in the neonatal population. Because tricuspid annular plane systolic excursion is dependent on heart size, the normal values change with growth. Tissue Doppler and RV strain measurements have great potential but need further validation. In daily practice, qualitative assessment of RV function is often used, but this requires expertise, especially in the newborn and infant populations.
Recommendations: The assessment of RV size and function should be part of TNE. Qualitative visual assessment remains the most commonly used technique in routine clinical practice. Two-dimensional measurements, including tricuspid annular plane systolic excursion and fractional area change, can be used for quantitative serial follow-up.
2.1.3d. Assessment of Atrial-Level Shunt
A key component of TNE is the assessment of intracardiac and extracardiac shunting and its contribution to hemodynamic or respiratory instability. Assessment of shunting across the atrial septum (patent foramen ovale or atrial septal defect) is therefore a required part of the TNE.
Atrial shunting can be best evaluated from subxiphoid long-axis or short-axis views of the atrial septum. Color Doppler imaging is used to view the atrial shunt and shunt direction. Because velocities can be low, it might be necessary to lower the color scale. For TNE, the most important aspect is shunt direction. Normally, left atrial pressures are higher compared with right atrial (RA) pressures and a left-to-right shunt is present, although a bidirectional shunt can still be normal in the neonatal period. Right-to-left shunting is abnormal and in the absence of structural heart disease suggests elevated right-sided filling pressures, often related to pulmonary hypertension and RV hypertrophy. Bidirectional and right-to-left shunting can contribute to reduced arterial oxygenation. Apart from shunt direction, pulsed-wave or continuous-wave Doppler can be used to assess the pressure gradient across the atrial septum. The calculation of the mean gradient gives information on the pressure difference between left and right atria and the difference in filling pressures.
Recommendations: TNE should include evaluation for the presence, size, and direction of atrial-level shunting.
2.1.3e. Assessment of PDA
Assessment of ductal patency, determination of ductal shunt direction, and measurement of ductal pressure gradients are an important part of every targeted neonatal echocardiographic study.
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Visualization of the PDA: The PDA can be visualized from the subxiphoid, modified left parasternal (“ductal”), and suprasternal windows in infants using standard high-frequency ultrasound probes. Keeping the head in the neutral position, or using a small shoulder roll to place the patient in a mildly extended and/or mildly left lateral decubitus position, may facilitate imaging of the PDA in its entirety. From the modified left parasternal and suprasternal windows, the distal aortic arch may be evaluated to exclude significant aortic coarctation. These views may be suboptimal in the presence of significant lung disease, pneumothorax, or pneumomediastinum. Accurate determination of aortic arch sidedness is very important, especially when surgical ligation is considered. Ductal size is usually measured by 2D imaging at the narrowest point, which usually is toward the pulmonary end of the duct, where it constricts first.
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Assessment of shunt direction and gradient: Color Doppler mapping facilitates visualization of the PDA and allows evaluation of the direction of flow through the duct. Shunt direction reflects the difference between aortic and PA pressures and the relative resistance of the pulmonary and systemic circulation. It is crucial to have a simultaneous electrocardiographic tracing to identify systole and diastole. Normally a left-to-right shunt is present, which can cause diastolic retrograde flow in the abdominal aorta. The degree of diastolic flow reversal in the descending aorta provides information on the amount of diastolic left-to-right shunting through the duct. If PA pressures are suprasystemic, right-to-left shunting will occur during systole and more rarely also in diastole if PA diastolic pressures exceed aortic diastolic pressures. Therefore, the duration of the right-to-left shunt and the presence or absence of holodiastolic retrograde flow by pulsed-wave Doppler in the descending aorta at the level of the diaphragm provide important information on the degree of pulmonary hypertension and can be assessed during follow-up and treatment. For gradient calculation, pulsed-wave or continuous-wave Doppler interrogation should be performed parallel to the direction of the ductal flow jet, as seen on color Doppler mapping. This Doppler gradient can then be used to assess PA pressures, by comparing the peak and mean Doppler gradients to simultaneous systemic arterial systolic and mean arterial blood pressures. The mean pressure is only relevant if there is no bidirectional shunt. Measurement of the peak instantaneous PDA gradients may require the use of continuous-wave Doppler, whereas information on the location of narrowing may be better evaluated by pulsed-wave Doppler.
Recommendations: TNE should determine the presence of a ductus arteriosus, the direction and characteristics of the shunt across the duct, and the pressure gradient between the aorta and the PA. The hemodynamic significance is further assessed by studying the degree of volume overload by measuring LV dimensions.
2.1.3f. Assessment of RVSp and PA Pressures
Changes in pulmonary vascular resistance occur during the first weeks of life, so the assessment of PA pressures is an important component of every targeted neonatal echocardiography study. The most consistent technique to assess RVSp is measurement of the peak velocity of a tricuspid regurgitant jet. In the absence of RV outflow tract obstruction, RVSp represents systolic PA pressure. An adequate spectral trace is necessary to avoid underestimation of the true gradient. To obtain the absolute value of RVSp, RA pressure should be added to the tricuspid regurgitant gradient measurement. RA pressure can be measured invasively in the NICU or can be estimated indirectly. For infants and children with no obvious RA dilatation, RA pressure of 5 mm Hg is assumed. On the basis of the velocity of the tricuspid regurgitant jet, RVSp can be calculated, using the simplified Bernoulli equation, as RVSp = 4(tricuspid regurgitant peak velocity [m/sec]) 2 + RA pressure.
The pulmonary regurgitation jet may also be used to assess end-diastolic PA pressure. This also requires technical optimization of the Doppler signal to avoid underestimation and also requires estimation of RA pressures. It has also been shown that a good correlation exists between the peak diastolic velocity of the pulmonary regurgitant jet and the mean PA pressure measured during cardiac catheterization. This is a useful relationship, because mean PA pressure is an important component in the estimation of pulmonary vascular resistance. As mentioned in the previous section, the shunt direction and Doppler-derived pressure gradient across a PDA can be used for assessment of PA pressures. It should be taken into account that for the assessment of pressure gradients across a PDA, application of the Bernoulli equation may be limited because of the long and sometimes tortuous nature of the duct.
Recommendations: Estimation of RVSp and PA pressures is an essential component of TNE and is based on Doppler measurements of tricuspid and pulmonary regurgitant jets. The Doppler-derived pressure gradient across a PDA can also be used for assessment of PA pressures.
2.1.3g. Assessment of Systemic Blood Flow
Noninvasive quantitative echocardiographic measurement of cardiac output would be a useful adjunct to the clinical assessment in infants with hemodynamic instability. Unfortunately, no straightforward echocardiographic technique is available. The most commonly used technique is Doppler estimation of LV stroke volume. This is performed by multiplying the time-velocity integral (TVI) on the basis of a pulsed Doppler tracing in the LV outflow tract just below the aortic valve by the cross-sectional area at the site, usually by measurement of diameter and calculation of area as π( D /2) 2 . LV output can then be calculated as
LV output ( mL / min ) = TVI ( cm ) × π × ( D / 2 ) 2 ( cm 2 ) × heart rate .
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