A practical guideline for performing a comprehensive transthoracic echocardiogram in the congenital heart disease patient: consensus recommendations from the British Society of Echocardiography

Abstract

Transthoracic echocardiography is an essential tool in the diagnosis, assessment, and management of paediatric and adult populations with suspected or confirmed congenital heart disease. Congenital echocardiography is highly operator-dependent, requiring advanced technical acquisition and interpretative skill levels. This document is designed to complement previous congenital echocardiography literature by providing detailed practical echocardiography imaging guidance on sequential segmental analysis, and is intended for implementation predominantly, but not exclusively, within adult congenital heart disease settings. It encompasses the recommended dataset to be performed and is structured in the preferred order for a complete anatomical and functional sequential segmental congenital echocardiogram. It is recommended that this level of study be performed at least once on all patients being assessed by a specialist congenital cardiology service. This document will be supplemented by a series of practical pathology specific congenital echocardiography guidelines. Collectively, these will provide structure and standardisation to image acquisition and reporting, to ensure that all important information is collected and interpreted appropriately.

Introduction

Advances in medical, surgical, and interventional congenital heart disease (CHD) management have led to marked improvements in paediatric CHD survival; with the number of adult congenital heart disease (ACHD) patients now exceeding that of their paediatric counterparts [1, 2]. Consequently, there is an increasing worldwide recognition for more specialised ACHD services. Life-long expert multi-modality imaging surveillance is of paramount importance for many CHD patients [3, 4], as they continue to experience CHD related cardiovascular sequalae [5]. Transthoracic echocardiography (TTE) has the ability to provide detailed information on cardiac morphology and haemodynamic physiology, and is largely accessible, non-invasive, and portable. Therefore, TTE remains the first line imaging tool in the diagnosis, assessment, and management of paediatric and adult populations with suspected or confirmed CHD [3,4,5,6].

Congenital TTE is a highly operator-dependent imaging practice that requires advanced technical acquisition and interpretative skill levels. Specialist training is required to ensure accurate assessment and reporting of cardiovascular malformations and outcomes of surgical/interventional procedures. Whilst thorough knowledge and understanding of cardiac morphology is central to paediatric congenital cardiology practice, it is somewhat a less familiar territory within adult cardiology practice [6]. Given most children with CHD now survive into adulthood, the ability to understand and perform congenital TTE in adult settings is of paramount importance. Standard adult TTE practices are largely designed to provide systematic guidance on performing a TTE study to detect and quantify acquired diseases in the structurally “normal” heart [7]. In CHD TTE, normal connections (i.e. cardiac morphology) cannot be assumed, and a knowledge of specific congenital lesions, their haemodynamic impact, and the surgical repair techniques is warranted. The British Society of Echocardiography (BSE) recognise that there is a need for more specialist CHD echocardiography practitioners and appreciate that there is limited opportunity to formally educate and practically train within CHD TTE nationwide. It is strongly recommended that any staff independently performing, and reporting CHD TTE studies are suitably qualified, i.e. BSE CHD, European Association for Cardiovascular Imaging (EACVI) CHD certified. This position will ensure all practitioners in CHD TTE are theoretically and practicably competent in understanding cardiac morphology, CHD nomenclature, the CHD pathology spectrum, and their associated repair/palliation methods. Importantly, this will enable practitioners to undertake a sequential segmental TTE approach to cardiac structure, avoiding interpretation based on assumed ‘normal’ cardiac morphology [6].

This document is designed to complement previous CHD TTE literature by providing detailed practical TTE imaging guidance on sequential segmental analysis [6,7,8,9], and is intended for implementation predominantly, but not exclusively, within ACHD settings. In contrast to a paediatric cardiology environment, anatomical diagnosis in ACHD settings is typically already established, aiding the TTE assessment. However, sometimes a patient’s historical TTE examination reflects very focused imaging. Therefore, it is recommended that a complete CHD TTE be performed at least once on all patients being assessed by a specialist congenital cardiology service, with subsequent CHD TTE studies being based on the patient’s anatomical and functional complexities, alongside patient amenability. It is therefore acceptable, within reason, that not all follow-up CHD TTE studies repeat a full sequential segmental anatomical evaluation, with the emphasis on pathology specific assessment.

This document will form the basis for a series of structured and practical pathology specific CHD TTE guidelines that will complement the BSE CHD accreditation curriculum. Collectively, these will help ensure important information is not missed or misinterpreted and aims to improve CHD TTE imaging quality by becoming an easy-to-use reference. It is anticipated that they will aid CHD TTE imaging and reporting standardisation, whilst also benefit future nationwide CHD TTE training and multicentre research.

Principles of sequential segmental analysis by echocardiography

Whilst it is appreciated that CHD imaging protocols will to some extent vary from centre to centre, sequential segmental analysis within CHD TTE is essential for detailing cardiovascular anatomy and ensuring important pathology is not missed [6]. Concomitant with the advent of TTE, sequential segmental analysis was standardised by Anderson and colleagues and is well established within paediatric imaging practices [8, 16,17,18]. Principally, this approach removes speculative assumption and permits cardiac morphology to be described into cardiac segments (atriums, ventricles, great arteries) and connections (atrioventricular and ventriculoarterial junctions) in a logical narrative, through identifying salient morphological features. It is recognised that complete segmental and functional assessment is not always feasible by TTE and that there is a need for complimentary multi-modality imaging.

Situs

Subcostal imaging should be initially conducted in order to infer atrial arrangement from the abdominal visceral situs (lateralised body arrangement), since direct visualization of atrial morphology by TTE, such as the appendages (right atrium: triangular and broad-based versus left atrium: narrow finger-like) is largely not possible [6]. By TTE, atrial arrangement is principally inferred from the position of the inferior vena cava (compressible and non-pulsatile) and aorta (round, non-compressible and pulsatile) relative to the spine (Fig. 1). If a ipsilateral vein is seen posterior to the aorta, interruption of the inferior vena cava should be suspected and equally if an ipsilateral vein is seen anterior to the aorta, right atrial isomerism should be suspected [19, 20]. It is important to note that veno-atrial drainage and the side in which the atrium is positioned do not define atrial morphology [19]. Alongside atrial arrangement, subcostal imaging can permit gross anatomy (cardiac segments and connections) understanding, if attainable. Although, latter imaging is additive for further detailed assessment, the preferred imaging order of TTE sequential segmental analysis discourages starting from the parasternal window in the CHD patient without an established diagnosis, where the standard adult TTE study commences.

Fig. 1

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Inferred atrial arrangement from the abdominal visceral situs. A Situs solitus: Normal atrial arrangement with right-sided right atrium (RA) and left-sided left atrium (LA). B Situs inversus: Mirror-image atrial arrangement with left-sided RA and right-sided LA. C Left atrial isomerism (LAI) with azygous continuation. D Left atrial isomerism with hemi-azygous continuation. In LAI, venous blood can return to the atria via the right superior vena cava (SVC), direct left SVC insertion or left SVC to coronary sinus (CS). There is direct hepatic drainage to the atriums, the CS is a left-sided structure and is often present, and whilst pulmonary veins often connect normally, they can drain abnormally (i.e. septal malposition or symmetrically to either side of the atrial septum). E Right atrial isomerism: cardiac anomalies are often more complex with inherent total anomalous pulmonary venous return, bilateral SVCs, absent CS and typically a common atrium. The concept of two morphologically identical atria/appendages is adopted for diagrammatic educational purposes only. Illustrations modified with permission from Geva L (2021) segmental approach to congenital heart disease. In Echocardiography in Pediatric and Congenital Heart Disease: From Fetus to Adult, 3rd edn, ch 3. Eds WW Lai, LL Mertons, MS Cohen, T Geva.

Cardiac position and cardiac apex

Cardiac position should then be defined in reference to which side of the chest the heart lies and the relative position of the apex (Fig. 2). In order to avoid confusing nomenclature such as ‘dextroposition with dextrocardia apex orientation and/or dextroversion’, we advocate a simpler descriptive approach whereby cardiac position is characterised as left-sided, right-sided or midline alongside a leftward, rightward or midline apex. Cardiac position and orientation can be different if the heart is pushed or pulled from an extracardiac abnormality.

Fig. 2

Cardiac position in reference to the thorax and relative position of the apex

Cardiac chambers and connections

The atrioventricular connection and the respective valve morphology should then be examined (Fig. 3). In the normally connected heart, the left and right atriums will connect via individual atrioventricular valves to their respective left and right ventricles, which is described as concordant atrioventricular connections. However, atriums can also connect to an opposing ventricle (discordant atrioventricular connections), not connect at all (absent), or both to the same ventricle (double inlet) [19]. In most biventricular anatomies, unless the atrioventricular junction is guarded by a common valve, the type of atrioventricular valve (i.e. tricuspid or mitral valve) directly aligns with the expected morphological ventricle (i.e. right or left ventricle, respectively). A tricuspid valve is typically more apically inserted with a trileaflet triangular orifice and septal leaflet/chordal insertion into the ventricular septal mass. Whereas a mitral valve typically has a more basal insertion, a bileaflet elliptical orifice with two distinct papillary muscles inserting away from the ventricular septal mass. Confirmation of ventricular morphology can be supported by an awareness that the right ventricle comprises a moderator band, courser trabeculations and three components: inlet, apical and outlet portions (crescentic shape) versus a more cone-like, smooth walled left ventricle morphology. However, caution should be adopted with respect to identifiable TTE features of ventricular morphology, due to the impact abnormal connections or loading conditions can have on their appearance.

Fig. 3

Potential atrioventricular (AV) connections examples. A Concordant AV connections. B Discordant AV connections. The right ventricle is more trabeculated to the LV and there is a distinct moderator band (*). The arrows in A and B highlight the apical offset of the tricuspid valve, which helps identify the morphological right ventricle. C Absent left AV valve/mitral valve. D Absent right AV valve/tricuspid valve. The dashed arrows in C and D identify the hypoplastic/rudimentary ventricle. E Double inlet left ventricle connection. The arrows in E exhibit the inflow nature of both AV valves to a single left ventricle. F Common AV valve (CAVV) connection. All images are examples from usual atrial arrangement (situs solitus) anatomies for convenience. Further variability can exist, which demonstrates the importance of sequential segmental analysis. * = moderator band

The ventriculoarterial connection and the respective great artery morphology should then be examined (Fig. 4). In the normally connected heart, the left ventricle connects to the aorta, which typically gives rise to the coronary ostia then head and neck vessels. Whilst the right ventricle connects to the pulmonary artery, which typically exhibits bifurcation into respective left and right pulmonary artery branches. These are concordant ventriculoarterial connections with normal spatial orientation, whereby the pulmonary outflow is anterior and leftward relative to the aorta and in short-axis views the aorta is seen enface and pulmonary outflow along its length [6, 19]. However, unless this junction is guarded by a common trunk, great arteries can also connect to opposing ventricles (discordant ventriculoarterial connections), not connect at all (absent/atretic), or arise both completely or mostly from the same ventricle, in which spatial orientation can be highly variable (double outlet) [19].

Fig. 4

Potential ventriculoarterial (VA) connections examples. A Concordant VA connection (pulmonary outflow is anterior and leftward relative to the aorta (outflow roots cannot be viewed simultaneously, arrows identify respective outflow direction). B Discordant VA connection— transposition of the great arteries (aorta is anterior and rightward relative to the pulmonary valve in a parallel arrangement). C Discordant VA connection— congenitally corrected transposition of the great arteries (aorta is anterior and leftward relative to the pulmonary valve in a parallel arrangement). D Absent right VA valve/atretic pulmonary valve connection (*).From the parasternal window, differential diagnosis must be considered when a single overriding outlet is observed, for example pulmonary atresia, tetralogy of Fallot or truncus arteriosus. E Double outlet right ventricle. All images are examples from usual atrial arrangement (situs solitus) anatomies for convenience. Further variability can exist, which demonstrates the importance of sequential segmental analysis.

In the normal heart, the connection between the right ventricle and the pulmonary artery includes a complete ring of muscle (infundibulum). In contrast, the normal left ventricular outflow tract is characterised by partial absence of an infundibulum with fibrous continuity of the mitral valve and the aorta [19]. In the abnormal heart, outlet septum morphology may change. The outlet septum (muscle between the outlets of the heart), which is also referred to as the conal septum, may be deviated into either the subpulmonary or subaortic region to cause obstruction to either outlet of the heart. For example, tetralogy of Fallot is characterised by anterior deviation of muscle (the outlet septum) into the right ventricular outflow tract, causing a variable degree of obstruction. In other types of abnormal ventriculoarterial connection, for example, simple transposition of the great arteries, there is a subaortic infundibulum and fibrous continuity between the mitral and pulmonary valve. In more complex forms of transposition of the great arteries or double outlet right ventricle there may be both subaortic and sub-pulmonary infundibulum with associated loss of continuity between the corresponding atrioventricular valve and great artery. In rare instances of double outlet left ventricle, an outlet septum may exhibit bilaterally absent sub-aortic and sub-pulmonary infundibulum with associated fibrous continuity between the corresponding atrioventricular valve and great artery.

Image optimisation

It is essential that all TTE studies are optimised. Within CHD, there are particular imaging challenges to consider. An appreciation of these challenges and an awareness of how they can sometimes be overcome will facilitate a comprehensive assessment of the congenital anatomy. Common encounters include variable patient size, chest shape malformations, bespoke positioning of surgical baffles/conduits and/or significant surgical scarring, because of multiple surgeries. These can often be overcome through utilising non-orthodox “off-axis” imaging planes and/or “sweeps” (i.e. using timed captured storage), if deemed necessary, to display and quantify anatomy or pathology. Although the adoption of cardiac “sweeps” within CHD TTE can be advantageous, they should not be over utilised. They are most beneficial with respect to greater appreciation of complex CHD anatomies and relationships.

Detailed guidance on frequency selection, focus, harmonics, gain, compression, colour Doppler, zoom, alongside the adoption of more novel TTE technologies (i.e. 3D and speckle tracking) and general TTE lab set-up (i.e. identifying information, chaperones, etc.) have been addressed in detail in the most recent BSE adult minimum dataset [10]. When low velocity flow is being assessed (e.g. venous flow in Fontan palliated circuits or coronary flow), velocity ranges should reflect this with a low Nyquist limit (i.e. 15–20 cm/s) and decreased wall filters to capture spectral Doppler information. In instances where it is not always possible to attain complete sequential segmental imaging studies in CHD populations (i.e. inadequate imaging “window” and/or un-cooperation), reports should detail this fact, as well as whether this is a follow-up serial surveillance imaging study, which itself can negate the need to perform a “full CHD TTE study” as long as the clinical question remains answered.

Imaging interpretation, time and reporting

It is strongly recommended to record height, weight (body surface area), heart rate/electrocardiogram, oxygen saturation and blood pressure details in order to maximise sizing, function and haemodynamic quantification. Careful consideration should be given when adopting normative adult reference datasets [15], as these are not directly applicable to the entire spectrum of the CHD cohort. Typically, more emphasis should be placed on the patient’s baseline and/or serial comparative TTE studies, which often act as their own normative/acceptable range data. Furthermore, whilst Z-scoring is routine in paediatric TTE practices in order to appreciate cardiovascular allometric scaling, it is accepted that it is not routine within ACHD TTE environments.

Sufficient time should be allocated to each CHD TTE study. Additional time may be required to study a complex anatomy, pathology, haemodynamic or functional state. Consideration should also be given to the potential amenability of a patient. Conversely, an uncomplicated CHD lesion or follow-up surveillance CHD TTE exam may require less time. Additional post-processing time for advanced imaging techniques, such as 3D and speckle tracking, that have been shown to benefit assessment of cardiac morphology, physiology, pathophysiology, and function, should be permitted [7, 21,22,23]. Incorporation of advanced imaging techniques into departmental practices is of growing importance in order to develop echocardiography expertise and to aid future research and normative dataset development.

The reporting of a patient’s first CHD TTE and/or pre-admission TTE study, when a “full CHD TTE study” is typically performed, should mirror that of the adopted sequential segmental imaging approach (Table 4) [6, 7]. A follow-up report is typically more focused, reflecting the nature of CHD TTE surveillance imaging; this being based on the patient’s specific anatomical and functional complexities. Within ACHD settings, TTE reports are typically pre-formatted to reflect standard adult cardiology practice [10]. Whilst this reporting style is adequate for most biventricular anatomies, if all cardiac segments and connections remain described, it is not advisable for complex/unrepaired congenital pathologies, systemic right ventricles, or Fontan palliated populations.

Specific considerations when interpreting the congenital echocardiogram

It is important to recognise the situations where normative values and practices of standard adult TTE are not applicable in the CHD patient. When the size, morphology, haemodynamic loading condition and/or position of the cardiac ventricles are abnormal, assumptive interpretations of standard adult TTE are invalid [7]. Common examples encountered include:

The systemic right ventricle i.e. congenitally corrected transposition of the great arteries and post Mustard’s or Senning’s atrial-switch repair

Besides serial comparison, TTE assessment remains largely qualitative. Tricuspid regurgitation cannot be implemented in pulmonary pressure probability (i.e. use sub-pulmonic mitral regurgitation, if present) and the use of geometric Simpson’s ejection fraction method on the systemic right ventricle is invalid [24]. Careful assessment for tricuspid valve regurgitation is needed in the systemic right ventricle as this carries prognostic and clinical significance. The usual indicators of severity remain carefully adopted as detailed in the BSE valvular guidelines as they are not directly applicable [11]. The primary mechanisms that make systemic tricuspid valve regurgitation a common feature include irregular interventricular septal confirmation, leaflet tethering from right ventricular dilation and/or dysplastic leaflet displacement resembling ‘Ebstein-like’ malformation that is often exhibited in congenitally corrected transposition of the great arteries. With respect to diastology in atrial-switch repair anatomies, baffle compliance (i.e. often stiff and non-contractile) will abnormally impact inflow characteristics. Thus, although important, standard inflow diastolic parameters generally remain non-applicable [25, 26].

Unrepaired univentricular physiology and Fontan palliations

These offer further complexities with respect to geometry and contractility compared to the structurally normal heart and although TTE assessment remains the mainstay, TTE functional assessment is essentially qualitative with standard measurement parameters only serving to aid serial comparisons, rather than permitting graded quantification. Consequently, there remains an important role for the visual assessment (‘eyeballing’) of the single /uni- ventricle function. Diastolic assessment is also erroneous in Fontan patients due to being pre-load deprived [27]. There is additionally a lack of any reliable normative data given the morphological heterogeneity of this group.

Cardiac surgery

Where cardiac surgery has taken place, abnormally reduced myocardial motion may be misleading to overall function. For example, basal septal parameters in those with ventricular septal defect patch repair will be reduced, but overall function may remain normal as there isn’t necessarily a primary issue with the myocardium.

Atrioventricular anomalies i.e. atrioventricular septal defects

Valvular quantitative methods are often invalid. For example, linear areas of regurgitation do not apply in cleft anatomy, whilst residual shunting (including left ventricle to right atrium), which are recognised sequalae, alter the haemodynamic conditions for valid quantification.

Shunts

Many CHD patients possess intracardiac shunts, which must be considered with respect to functional and haemodynamic TTE quantification. For example, underestimation of valve obstruction will occur if a chamber is enabled to “blow-off” through a shunt, and hence chamber pressure will not increase to generate high gradients (i.e. ventricular septal defects and aortic stenosis or atrial septal defects and mitral stenosis). Similarly, it should be understood that in the presence of an isolated shunt defect, inflow gradients may be falsely elevated in the context of increased veno-atrial flow (i.e. ventricular septal defect and mitral inflow).

Image orientation

There is a wide spectrum of adopted practices in relation to the orientation of the CHD TTE study. A CHD TTE study may be performed displaying superior and anterior structures at the top of the imaging screen, the apex at the bottom and rightward structures on the left side of the imaging screen. This demonstrates cardiac structures in their ‘anatomical’ orientation (does not apply to the parasternal long axis). Alternatively, CHD TTE may reflect working practices purely from an ‘adult’ orientation, with the apex positioned at the top of the imaging screen. It should be noted that “adult” orientated TTE is now a relative outlier compared to other cross-sectional imaging modalities, with the reason for its adoption being somewhat historic due to the inability of early ultrasound technologies to modify the image screen. Irrespective of the study orientation, the CHD TTE study should be presented in a way that allows the operator and reviewing clinicians to correctly interpret them. This may reflect a combination of both orientations, particularly when trying to better understand complex congenital anatomies, in which it is recognised that ‘anatomical’ orientated TTE imaging can aid sequential segmental cardiac morphology interpretation. This is especially apparent with the initial subcostal window. It is recognised that many subcostal CHD TTE views are not routinely performed in the adult TTE study, thus this will present new learning for those in CHD TTE training, when attainable. We therefore recommend, particularly within ACHD services, that CHD TTE should seek to offer training in the acquisition and interpretation of both orientations. The TTE imaging within the CHD TTE BSE guidelines will reflect ‘anatomical’ orientation for the subcostal views and ‘adult’ orientation for the apical views.

The practical sequential segmental transthoracic imaging congenital heart disease guideline

Table 1 outlines a proposed sequential segmental TTE practical guideline in the CHD patient. It encompasses the recommended dataset to be undertaken (in bold) and is structured in the preferred order for a complete anatomical and functional sequential segmental CHD TTE study. It outlines the specific view, modality of assessment, anatomy to assess and measurements to be taken alongside example TTE imaging. Abbreviations used within Table 1 are outlined in Table 2. The CHD TTE imaging guideline is summarised in Table 3 (one-page). An example sequential segmental TTE report is also provided (Table 4). This guideline will not duplicate functional guidance already detailed within BSE adult TTE guidelines but will detail the areas where these guidelines may have limitations or are not directly applicable in the CHD setting [10,11,12,13,14,15].

Table 1 The practical guideline for performing a comprehensive sequential segmental TTE in the CHD patient

Table 2 Abbreviations

Table 3 Summarised guideline for performing a comprehensive sequential segmental TTE in the CHD patient

Table 4 Sample sequential segmental CHD TTE report (normal)