**6. Diagnostic studies**

#### **6.1 Echocardiogram**

Echocardiography remains the mainstay in the diagnosis of patients with Ebstein's anomaly and guides management decisions regarding surgical strategy. Each patient with the Ebstein anomaly should undergo a comprehensive transthoracic echocardiogram that allows evaluation of the right atrial size, right ventricular size, and function, the accurate anatomy of the tricuspid valve, the right ventricular outflow tract, the pulmonary valve, the atrial and ventricular septum, and left ventricle. This evaluation


#### **Table 1.**

*Checklist for echocardiography in Ebstein anomaly.*

is crucial for decision-making before surgical repair [20]. **Table 1** summarizes the important details elucidated by echocardiogram that need to be evaluated in patients with Ebstein's anomaly.

The most sensitive and specific echocardiographic finding to diagnose Ebstein's anomaly is the apical displacement of the septal leaflet of the tricuspid valve. This can be best seen in apical four-chamber views by echocardiography. When indexed to the body surface area, the distance between the hinge point of the septal leaflet of the tricuspid valve and the anterior leaflet of the mitral valve is called the displacement index. A displacement index above 8 mm/m<sup>2</sup> is considered diagnostic of Ebstein's anomaly (**Figure 8**) [21]. However, it is important to note that there are rare cases of "atypical Ebstein" anomaly with normal displacement index [22]. Additionally, there are some cases with a displacement of the anterior leaflet of the tricuspid valve [23]. The evaluation of the tricuspid valve leaflets and attachments can be best performed from an apical view with sweeps posteriorly toward the coronary sinus and anteriorly toward the ventricular outflow tracts. In addition to the displacement, this will clarify septal attachments. It is common to have tethering attachments of the septal and posterior/inferior leaflets of the tricuspid valve to the right ventricular wall. In some cases, the posterior/inferior leaflet is muscularized with muscular attachments to the right ventricular free wall (**Figure 9**). These attachments are called the linear attachments of the tricuspid valve and they have implications for surgical repair [24]. As the anterior leaflet is usually the larger leaflet and is often sail-like, describing this leaflet's

#### **Figure 8.**

*Apical four-chamber view measuring the displacement of the tricuspid valve which is mild in the left panel and severe in the right panel.*

#### **Figure 9.**

*Muscularization and abnormal attachments of the posterior/inferior leaflet of the tricuspid valve by 2D echocardiography and 3D echocardiography showing the muscular "linear" attachments.*

size and attachments is important to help surgical planning. The parasternal long-axis views allow for an accurate description of the anterior and posterior/inferior leaflets (**Figure 10**). It is important to note that often, there is a fusion of the anterior and posterior/inferior leaflets creating a bileaflet tricuspid valve, as discussed above. Three-dimensional echocardiography can give important insights into the valve anatomy in many patients and should be used when possible. The tricuspid valve is also often severely rotated toward the right ventricular outflow tract, and this can be seen by parasternal long and short axis views (**Figure 11**). Additional important features include the annular size, which is often dilated. Also, muscularization and dysplasia of the tricuspid valve leaflets should be evaluated.

After evaluating the anatomical features of the tricuspid valve, it is important to evaluate the tricuspid valve function using multiple views. Grading of the tricuspid

#### **Figure 10.**

*Parasternal long-axis view with a focus on the tricuspid valve showing the anterior and septal leaflet on the left panel and the posterior/inferior and anterior leaflet on the right panel.*

#### **Figure 11.**

*Parasternal short axis view showing the anatomy of the tricuspid valve leaflets and the rotation of the tricuspid valve orifice toward the right ventricular outflow tract. LV: left ventricle, RVOT: right ventricular outflow tract, TV: tricuspid valve.*

regurgitation depends on the width of the vena contracta and can be challenging in the malformed valve. Using multiple views helps to clarify the severity of tricuspid regurgitation. The classification can be graded as trivial, mild, moderate, or severe. A width below 3 mm in multiple views is considered mild, while a width of more than 7 mm is considered severe (**Figure 12**). It is important to note that these criteria are derived from older patients and may not apply to the infant. Furthermore, the evaluation can be challenging when multiple jets exist. In infants, the percentage of the vena contract width to the tricuspid valve annulus is used with a width below 10% considered as mild while above 30% considered as severe [25]. It is also important to note that the orientation of the regurgitant jet can be unusual due to the rotation of the valve and thus using multiple views and sweeps will be essential to clarify the inflow and regurgitation jets. By continuous wave doppler, the tricuspid regurgitation jet velocity is reported as a measure of the ability of the right ventricle to generate pressure. Also, evaluation by Doppler to assess the degree of tricuspid stenosis is

#### **Figure 12.**

*Apical four chamber and parasternal short-axis views showing a patient with Ebstein anomaly and severe tricuspid regurgitation.*

important, as some patients may have a significant degree of narrowing of the tricuspid valve orifice. Post tricuspid valve repair or replacement, a mild gradient <6 mmHg is common and should be followed.

An echocardiographic grading system for determining the severity of neonatal Ebstein, The Great Ormond Street score (Celermajer index), is calculated by dividing the combined area of the right atrium and atrialized right ventricle by the combined area of the functioning right ventricle and left heart. At the end of diastole, the measures are taken in the apical four-chamber view. Patients with a ratio of <1 had a 92% survival rate and those with a ratio of >1.5 had a 100% mortality rate [26].

For a variety of reasons, quantifying RV function in the Ebstein anomaly is difficult by two-dimensional echocardiography. Although evaluation of RV volume and function is always challenging by 2D echocardiogram, it is even more difficult to assess in Ebstein's anomaly. The RV is frequently enlarged (both the atrialized and functional portions) to the point where imaging it totally in one plane is challenging. Although experienced observers may classify right ventricular activity based on qualitative evidence, intraobserver and interobserver variability is very common. To assess ventricular function, the fractional area change (FAC) of the RV can be calculated. This can be determined by tracing the systolic and diastolic areas in the apical four-chamber view or from the systolic and diastolic areas in the apical four-chamber image. This is limited by the inability to visualize the dilated RV in one image in Ebstein patients [25, 27]. Tricuspid Annular Plane Systolic Excursion (TAPSE) has also been used to evaluate the right ventricular function and poses a challenge in Ebstein's anomaly given the abnormal tricuspid valve annulus and morphology. Tissue Doppler systolic wave S<sup>0</sup> of the tricuspid valve has similar challenges [28].

The atrial septum should also be evaluated. Atrial septal defect or patent foramen ovale is very common. Evaluating the size and direction of shunting should be performed. This can be best seen from subcostal coronal and sagittal views. Right to left flow across the atrial septum may result in desaturation at rest or with exercise [29].

The right ventricular outflow tract should also be carefully evaluated. In severe Ebstein cases, the RV outflow tract can become a large part of the functional right ventricle. The function of the pulmonary valve should be evaluated for pulmonary
