Transoesophageal echocardiography in adult congenital heart disease
- Dr Masani
The diagnosis of congenital heart disease de novo in adults is now uncommon. Increasing numbers of children with congenital heart disease are surviving to adulthood, leading to the development of adult congenital heart disease as a distinct subspecialty.1Nevertheless, adults with congenital heart disease still present to general cardiologists—as an initial presentation, for geographical or logistic reasons, during acute or concurrent illness, or through loss of regular follow up. Echocardiography is the mainstay of diagnostic imaging in adult congenital heart disease—its role in the spectrum of congenital heart disease most often encountered in adults has been reviewed comprehensively.2 However, precordial windows in these patients are often suboptimal because of previous surgery, chest deformity or lung disease. Multiplane transoesophageal echocardiography (TOE) has proven to be of great value in adult congenital heart disease because of its high resolution, clear acoustic windows, proximity to posterior cardiac structures, and comprehensive imaging planes.3
In the diagnosis of congenital heart disease, the echocardiographic examination is performed in a detailed, systematic manner. This requires a protocol and mindset that differs from the approach often used in TOE in the adult cardiology setting. The purpose of this paper is to describe an approach to TOE in adult congenital heart disease. Specific emphasis is placed on those conditions that present in adulthood and that involve detailed TOE views of structures rarely necessary in general cardiology. The echocardiographic approach to patients who have undergone palliative procedures (for example, Mustard or Senning repairs, Fontan operations) are touched upon briefly; the echocardiographic approach to them has been discussed previously.2 The use of TOE during interventional and surgical procedures is beyond the remit of this paper.
Clinical training and experience in congenital heart disease, as well as expertise in echocardiography, are invaluable. The former to recognise the morphologic patterns, variations, clinical associations, and complications of adult congenital heart disease, the latter to appreciate the complex echo-anatomic relations that may be encountered. The advice of a cardiologist specialising in congenital heart disease (paediatric or adult), to complement the skills of the TOE operator during the study, is helpful in complex cases. TOE should be regarded as part of an integrated imaging approach combined with other complementary techniques, in particular transthoracic echocardiography, cardiac magnetic resonance imaging, and angiography.4Detailed patient information should be sought; however, diagnoses made in childhood should not be assumed to be complete.
TOE protocol for adult congenital heart disease
For all cases, it is important to develop and follow a structured comprehensive protocol, utilising multiplane views and all of the available windows (upper and mid oesophageal, gastro-oesophageal junction, mid gastric, and deep gastric). We use a systematic approach adapted from that used in adult patients with acquired cardiac disease (table 1). It is important to understand the segmental approach to scanning in congenital heart disease.5 Although this is best suited to transthoracic echocardiography (TTE), the TOE study should also start by establishing (or confirming) cardiac situs and connections, as outlined in table 2. The high resolution of TOE confers an advantage over TTE in the identification of the defining characteristics of cardiac structures (table 3), particularly the atrial appendages.
ASSESSMENT OF THE RIGHT ATRIUM AND SYSTEMIC VEINS
Differentiation of the right atrium (RA) from the left atrium (LA) is based on identification of the appendages—the characteristic broad mouthed, blunt appearance of the RA appendage is best appreciated in the vertical plane (90°)—the “bicaval view” (fig 1). The christa terminalis may be seen as a linear structure seen extending from the RA wall close to the inferior vena cava (IVC) to the septum adjacent to the superior vena cava (SVC). This can be mistaken for the atrial septum, leading to a false diagnosis of atrial septal defect (ASD). Agitated saline contrast (injected into the left arm, see below) is used to identify the systemic venous connections to their respective atrium and detect intracardiac right-to-left shunts.
The SVC is scanned in its transverse plane at 0°, from the upper oesophageal window (fig 2) down to the SVC/RA junction. This manoeuvre is used to identify anomalous pulmonary venous drainage (PAPVD) into the SVC/RA junction and superior sinus venosus ASD. By rotating the imaging plane to 90° the distal SVC is seen in its long axis (fig 1). The course of the IVC is difficult to visualise in adults. In the transgastric view at 0°, the IVC may be seen in cross section—rotation of the image plane until it appears in its long axis allows visualisation of its drainage into the RA. From the transoesophageal views, only its junction with the RA is seen (note the variable appearance of the eustachian valve at this site). This is best done by advancing the probe slightly in the biatrial view (90°).
The coronary sinus is seen in the horizontal plane (0°) by advancing the probe from the mid oesophageal window to the gastro-oesophageal junction, where it is seen traversing the atrioventricular groove behind the LA before entering the RA. A communication between the coronary sinus and the left atrium may occur (“unroofed coronary sinus”). For depicting the relation between the coronary sinus and an ASD, an oblique (130°) mid oesophageal view is useful. Pronounced dilatation of the coronary sinus, in the presence of normal RA pressure, is suggestive of persistent left SVC—diagnosed by following the course of the coronary sinus back to a vertically orientated vein and/or observing the wash-in of contrast injected into a left upper limb vein.
ASSESSMENT OF THE LEFT ATRIUM AND PULMONARY VEINS
The narrow hook shaped LA appendage is best seen by flexion/withdrawal of the probe from the mid oesophageal (four chamber) position. The pulmonary veins are difficult to examine by TTE in the adult but can be well seen by TOE. All four pulmonary veins entering the LA should be seen during routine TOE examination. The orientation of the upper pulmonary veins is more vertical, while that of the lower pulmonary veins is more horizontal. The left upper pulmonary vein is identifiable running above and parallel to the appendage, with the typical venous flow pattern toward the LA. Alignment along its long axis may be improved by rotating the imaging plane up to approximately 60°. Slight advancement of the probe (at 0°) enables the origin of the left lower pulmonary vein to be seen. At the same level in the oesophagus, rotation of the probe to the right brings the right lower pulmonary vein into view (fig 2). Slight withdrawal of the probe reveals the right upper pulmonary vein. The probe should be withdrawn to interrogate the relation between the right upper pulmonary vein and SVC.
ABNORMALITIES OF THE ATRIA AND VENOUS DRAINAGE
Although this is a very rare condition, it may present in adulthood. It is characterised by a membrane in the left atrium, obstructing pulmonary venous return within the LA cavity. The appearance of a membrane within the left atrium associated with obstructive flow patterns on colour flow mapping and spectral Doppler gradients are typical.
Partial anomalous pulmonary venous drainage (PAPVD)
This often accompanies sinus venosus ASD. Most commonly, the right upper and/or right lower pulmonary vein(s) drain into the SVC or SVC/RA junction (fig 2). More complex forms of PAPVD (including supra and infracardiac types) are rarely seen de novo in adults and are better diagnosed by magnetic resonance imaging.
Surgically corrected partial or total anomalous pulmonary venous drainage may require reinvestigation to determine the patency of the venous connection. Visualisation of the distorted vessels may be difficult, exacerbated by the echodensity of surgical patch/baffle material. The presence of turbulence on colour flow mapping should be noted, and spectral Doppler is mandatory (an example of an obstructed pulmonary venous connection is seen in fig11).
ASSESSMENT OF THE ATRIAL SEPTUM AND ATRIAL SEPTAL DEFECT
It is important to interrogate the entire atrial septum to ensure that small defects at the margins of the septum are not missed. In the horizontal plane (0°) the entire septum is interrogated, from the SVC/RA superiorly to the coronary sinus/RA junction inferiorly. Rotation of the image plane to the bicaval view (90°) displays the septum in an orthogonal plane, from IVC to SVC, thereby ensuring that inferior and superior sinus venosus ASDs (fig 2) are not missed.
Ostium secundum ASD
The secundum septum may be mobile, aneurysmal, contain a patent foramen ovale or septal defect—the most common de novo adult congenital heart disease diagnosis (fig 3). The presence of an ASD is confirmed by the use of colour flow mapping. Care should be taken not to misdiagnose colour flow mapping jets entering the RA from the vena cavae or coronary sinus. TOE is valuable in confirming the diagnosis, identifying associated defects, and assessing suitability of the defect for percutaneous device closure (table 4).
Sinus venosus ASD
The superior form of this defect is more commonly encountered, often associated with PAPVD. The SVC overrides the atrial septum, seen best in the biatrial view (90°) (fig 2).
Ostium primum ASD, partial and intermediate atrioventricular septal defect (AVSD)
This defect may include abnormal development of the atrioventricular (AV) septal region and valves, all of which must be assessed in detail. Partial AVSD (ostium primum ASD) affects the inferior part of the atrial septum and the AV valves; it may present in adulthood. The left AV valve usually has three leaflets (the anterior leaflet divided into superior and inferior parts by a “cleft”). Both AV leaflets insert into the crest of the ventricular septum, thereby “sealing off” an interventricular connection, often giving the upper septum an aneurysmal appearance (fig 4).
These defects are readily visualised in the mid oesophageal views. The value of TOE lies in detailing the morphology of the left AV valve and identifying associated defects. The cleft in the “anterior” leaflet may appear as a fold (fig 4) or cleft between the superior and inferior leaflets. Regurgitation may occur through the “cleft” as well as the normal leaflet orifice and this is identified by colour flow mapping. This is best seen at 0°, flexing slightly to interrogate the superior part of the anterior leaflet and by scanning through the valve from 0° to 130° where it is seen lengthways (fig 4). The chordal arrangement of both AV valves should also be assessed and can be performed by scanning up and down the transverse plane. Short axis transgastric views of the AV valves are obtained by careful full flexion of the probe at 0°. This may show the position of each leaflet (fig 4) and the site of regurgitation.
Complete AVSD, comprising an additional inlet ventricular septal defect and a common AV valve with five leaflets, is rarely encountered in adults. However, intermediate forms occur, with only partial closure of the ventricular septum by the atrioventricular valve attachments. A separate interrogation of this region is required—in common with other unusual or variable findings, this can be done efficiently by keeping the region of interest in the centre of the scan sector and performing a careful 180° sweep, first with two dimensional echo and then colour flow mapping.
Repair of the left AV valve in childhood may restrict leaflet mobility, leading to stenosis and/or regurgitation through the cleft or the normal orifice. Left ventricular outflow tract obstruction may also be a late feature.
Congenital defects of the AV valves rarely present in adulthood. Only Ebstein's anomaly is considered here.
This condition covers a spectrum of disease in which there is apical displacement of the origin (hinge point) of one or more tricuspid valve leaflet, from the AV junction into the RV cavity. The septal leaflet is most commonly affected. The anterosuperior leaflet may not be displaced but is commonly abnormally large, with anomalous attachments to the RV wall and apex. The tricuspid valve leaflets are often dysplastic. The “atrialisation” of the RV, together with a variable degree of RV wall dysplasia, severe tricuspid regurgitation, and occasionally tricuspid stenosis, result in a small, restrictive RV. There is often an ASD and, depending on the RA pressure and degree of tricuspid regurgitation, shunt flow may be right-to-left.
The diagnosis is usually made in the four chamber view (often better by TTE than TOE) (fig 5). The image plane is rotated to the short axis view (30-50º) and further until a long axis image of the RA, tricuspid valve, and RV is obtained (the angle at which this plane is obtained is variable) in which the abnormal morphology and distal attachments of the anterosuperior leaflet can be seen. In view of the variable morphology of these valves and the frequent association with severe dilatation of the right atrium, it is helpful to complete a full 180° sweep of the tricuspid valve, first with two dimensional echo, then colour flow mapping. It is very important, in the surgical workup of these patients, to determine the presence of tricuspid stenosis and the severity, site and mechanism of tricuspid regurgitation. In the adult patient this may be caused by the defect itself, superimposed damage due to endocarditis, leaflet rupture or perforation. These details are useful in predicting those patients in whom repair of the tricuspid valve may be possible (in particular the degree of leaflet tethering and “atrialisation of the RV”).
Congenitally corrected transposition of the great arteries (TGA)
It is important to recognise this rare condition, in which there is atrioventricular and ventriculo-arterial discordance resulting in a circulation that may function normally well into adulthood. The echocardiographic features are those of RV morphology in the systemic ventricular position and left ventricular (LV) morphology in the subpulmonary ventricular position. A common feature of conditions in which there is malposition of the great arteries is a parallel arrangement rather than the normal arrangement in which they are perpendicular to each other (see fig 11F). There may be associated tricuspid regurgitation (either from dysplasia of the valve or annular dilatation). In complex forms of the condition, there may be coexistent ventricular septal defect (VSD) and pulmonary stenosis.
ASSESSMENT OF THE VENTRICULAR SEPTUM AND VENTRICULAR SEPTAL DEFECT
The ventricular septum is a complex structure that requires careful interrogation in multiple planes. From the mid oesophageal window (0°), flexion displays the left ventricular outflow tract (LVOT) and thin membranous part of the septum (see perimembranous VSD). Advancing the probe reveals the muscular/trabecular part of the septum (see muscular VSD) but it may be impossible to fully interrogate the apex in this view. Image plane rotation to 30–45° produces a short axis view of the heart analogous to an inverted parasternal short axis view. By rotating the probe to image in a plane passing below the level of the aortic valve, perimembraneous and doubly committed VSD can be seen and differentiated (fig 6). Further rotation of the image plane to 130° produces an approximation of the apical long axis view (fig 6) providing further imaging of the perimembranous septum, another imaging plane through the muscular septum, and an ideal view to identify an overriding septum (that is, tetralogy of Fallot). Having performed the two dimensional echo sweep, this is repeated using colour flow mapping. Although it may be difficult to align the Doppler beam parallel to VSD flow, it is important to look out for turbulence within the RV cavity and a flow convergence zone within the LV cavity (fig 6). In order to interrogate the muscular septum fully, a transgastric transverse (0°) image is obtained and swept from its highest point to its deepest, first by two dimensional echo. From the deep fundal view, a view analogous to the apical TTE views may be obtained and this provides excellent imaging of the apex.
In patients with perimembraneous VSD, TOE is valuable in identifying the mechanism of spontaneous closure and associated findings—for example, suction of the right aortic cusp into the defect resulting in aortic regurgitation or involvement of tricuspid subvalvar tissue.
ASSESSMENT OF LEFT VENTRICULAR OUTFLOW AND OBSTRUCTIVE LEFT HEART LESIONS
Although there are numerous mechanisms of LVOT obstruction, only valvar aortic stenosis and subaortic stenosis caused by discrete fibromuscular obstruction (subaortic membrane) or left ventricular hypertrophy are likely to be seen in unoperated adult patients. These will be discussed below. Multiplane TOE offers excellent imaging of the LVOT and rarely encountered causes of LVOT obstruction (for example supra aortic stenosis, accessory or anomalous mitral valve tissue, deviation or abnormality of the septum as part of complex congenital heart disease) should be identifiable by thorough examination.
From the mid oesophageal window, flexion at 0° produces a “five chamber” view in which the LVOT and base of the aortic valve leaflets are well visualised. Colour flow mapping in this view is useful for showing flow acceleration and turbulence at the site of obstruction. Rotating the image plane to 30° produces a short axis view at the base of the heart. Starting in an imaging plane below the aortic valve, gradual withdrawal of the probe produces transverse sections through the LVOT, the base, bodies and tips of the aortic valve leaflets, then the sinuses of Valsalva and coronary ostia. The plane is rotated to 130° where the subaortic region, aortic valve, and ascending aorta are examined in their long axis. Transgastric views of the LVOT, permitting satisfactory Doppler alignment (obtained by deep flexion at 0° or an oblique view between 110–140°) can be obtained in about 75% cases. Alternatively, the deep fundal view is used to obtain images analogous to TTE apical views.
These may present in adults de novo or as a recurrence after previous resection. The membrane is a crescentic fibromuscular protuberance, attached medially to the ventricular septum just below the aortic valve, and laterally to the aorto-mitral junction or anterior mitral valve leaflet. The morphology of these lesions in adults may be complex, perhaps reflecting progression over time, and it is important to determine further attachments or involvement with the aortic valve leaflets. The subaortic membrane is most easily visualised in the long axis and five chamber views described above (fig 7). It is often difficult to image the crescentic nature and extent of the lesion in short axis. Subaortic membrane in adults is often accompanied by greater degree of left ventricular hypertrophy than expected. Upper septal hypertrophy may contribute to LVOT obstruction. It is common for patients with subaortic stenosis to develop aortic regurgitation due to interference of leaflet closure by the membrane and/or premature degenerative disease. Thus, the aortic valve appearance, and the severity and mechanism of aortic regurgitation, must be studied carefully.
Congenital aortic valve disease
The valve leaflets may be thin and pliant or thickened, calcified, and restricted. In the short axis view, scanning at the leaflet tips reveals the number and arrangement of cusps—note that this is done with the leaflets open in systole (fig 8). Although unicuspid and quadricuspid valves have been reported in adults, the vast majority are bicuspid—either two symmetrical leaflets or fusion of two leaflets, with a midline raphe, often associated with asymmetric sinuses of Valsalva. In young patients in whom there is little aortic valve calcification, transverse section scanning at the aortic valve leaflet tips (usually 30–60°) is used to obtain an accurate measure of aortic valve area. In the long axis, the hallmark sign of doming is best seen. In addition, “post-stenotic” dilatation (a misnomer) should be identified and measured (at aortic valve annulus, sinuses of Valsalva, sinotubular ridge, and ascending aorta). We use serial magnetic resonance imaging for accurate and reproducible follow up of aortic dilatation (and follow up of coarctation after surgery).
ASSESSMENT OF THE RIGHT VENTRICLE AND PULMONARY VALVE: OBSTRUCTIVE RIGHT HEART LESIONS
Pulmonary or subpulmonary stenosis may present or recur in adulthood, or develop as a consequence of RV hypertrophy from any cause. Severe right ventricular outflow tract (RVOT) obstruction may be remarkably well tolerated. With recent advances in TTE imaging, the pulmonary valve can be often seen; haemodynamic assessment by colour flow mapping and spectral Doppler is usually sufficient to diagnose RVOT obstruction, pulmonary stenosis or regurgitation. Nevertheless, it is possible to obtain more detailed and better defined images of the right heart with TOE and, in patients with suboptimal TTE windows, TOE is very useful in determining the nature and severity of RVOT obstruction.
In the mid oesophageal four chamber view the RVOT cannot be seen, but the presence of RV hypertrophy and prominent trabeculations forming a muscle band across the cavity may be seen. Rotation of the imaging plane to the short axis view (30°) separates RV inflow and outflow. The pulmonary valve leaflets may be difficult to see in patients with aortic root calcification. Further rotation to 90–130°, with the probe rotated to the right, reveals long axis views of the pulmonary valve and main pulmonary artery. Views of the pulmonary bifurcation are obtained in transverse (0°) scans in the upper oesophagus, from where the right pulmonary artery can be followed for several centimetres. The left pulmonary can rarely be seen beyond its origin. TOE is not an ideal technique for investigating branch pulmonary artery disease—angiography and magnetic resonance imaging are much better. The transgastric window affords excellent images of the RV. It is possible to align the Doppler signal to flow in the RVOT using a transgastric long axis view (fig 9), although this is a considerable distance from the probe tip and low transducer frequencies may be required.
Double chamber right ventricle
Mid cavity obstruction may develop secondary to any cause of RV hypertrophy—sometimes despite correction of the original problem such as a VSD (fig 9).
Subvalvar (infundibular) and valvar pulmonary stenosis
It is possible to differentiate subpulmonary stenosis—caused by abnormal hypertrophy of the infundibulum of the RV—from valvar pulmonary stenosis in the short axis and outflow views. Transverse views of the pulmonary valve are much more difficult to obtain than of the aortic valve and precise delineation of the leaflets may be impossible. However, doming of the leaflets is readily apparent (fig10).
COMPLEX CONGENITAL HEART DISEASE: CORRECTIVE AND PALLIATIVE SURGERY
A detailed discussion of the follow up investigation of patients who have undergone corrective or palliative surgery for congenital heart disease is beyond the scope of this paper. Homografts and repaired tetralogy of Fallot are described briefly. TOE is valuable in the assessment of patients who have undergone “atrial switch” (Mustard or Senning) procedures for transposition of the great arteries, since the systemic venous baffle and pulmonary venous confluence are posterior structures. The echocardiographic approach has been described elsewhere2; the TOE appearance is illustrated and described briefly in fig 11. Complex congenital heart disease involving single ventricle systems (with or without a Fontan-type circuit) are not addressed here. An example of an adult patient with a single ventricle (and systemic-pulmonary arterial shunt) is shown in fig 12.
Homografts are used in young patients undergoing a variety of corrective surgical procedures, typically RVOT repairs (Rastelli conduits, repair of tetralogy of Fallot) and aortic root replacement. Over time, they are susceptible to calcific degeneration, causing homograft stenosis and/or regurgitation and endocarditis. These patients are often very difficult from the TTE approach, made worse by calcification of anterior structures. While TOE is better, detailed imaging is sometimes disappointing for the same reasons. The approach to scanning these patients is the same as described for RVOT and LVOT. In addition, attempts are made to image the upper and lower anastomoses of the grafts, where aneurysm, pseudoaneurysm or abscess formation can occur.
Repaired tetralogy of Fallot
Corrective surgery may involve resection of infundibular stenosis, pulmonary transannular patch, valveless or valved conduit, VSD closure and branch pulmonary artery dilatation. The long term sequelae of such radical repair are often right ventricular hypertrophy (RVH) and dilatation, pulmonary stenosis, and (severe) pulmonary regurgitation. In addition, there may be residual VSD leak. The aortic root is large and there may be aortic root dilatation. Branch pulmonary stenosis is common but is poorly assessed by TOE.
TOE is a valuable and challenging technique in adult congenital heart disease. Combined expertise in echocardiography and congenital heart disease is required. A detailed standardised scanning protocol should be used and this approach is unfamiliar for many adult cardiologists. This is the very worst scenario in which to “stick the probe down and have a look”.