Ebstein Anomaly Imaging 

Ebstein anomaly accounts for less than 1% of congenital heart diseases and occurs in 1 in 210,000 live births.^[1] The condition occurs with equal frequency in males and females; severely affected neonates can present on their day of birth.

The condition may completely escape detection, or patients may not become symptomatic until late in life. In some individuals, Ebstein anomaly is not diagnosed until the eighth decade of life.^[2] As many as one half of patients have an atrial septal defect (ASD), and as many as one quarter have an accessory conduction pathway. Ebstein anomaly in an infant and in an adult is seen in the images below.

The tricuspid valve is composed of 3 leaflets, including the anterior, posterior, and septal (also termed mural or medial) leaflets. In Ebstein anomaly, the leaflets are affected to various degrees. The septal leaflet is affected more than the posterior leaflet, which is affected more than the anterior leaflet.^[3] The septal and posterior leaflets are often displaced inferiorly toward the apex of the heart.

The anterior tricuspid valve leaflet may be elongated,^[4] and it may adhere to the wall of the right ventricle.^{[3, 5]} The septal and posterior leaflets are displaced inferiorly at least 20 mm or 8 mm/m² in adults.^{[5, 4]} This degree of inferior displacement of the septal leaflet is regarded as definitive.^[6]

The leaflets may be tethered by muscular bands or by shortened chordae tendineae and shortened papillary muscles, or the leaflets may adhere directly to the ventricular wall.^[3] The valve annulus is not displaced; therefore, it is situated correctly between the atrium and ventricle. Similarly, the proximal attachment of the anterior leaflet to the annulus is normal.^[5] The mural leaflet always is present in Ebstein anomaly; if it is absent, the patient's condition is known as unguarded tricuspid orifice rather than as Ebstein anomaly.^[7]

Because the annulus is sited anatomically as usual but the septal and posterior valve attachments are displaced inferiorly, a region of upper right ventricle functionally becomes atrial; this is termed the atrialized portion of the right ventricle. As a result of its structural alteration, this region actually is thinned and hence prone to aneurysmal dilatation, particularly between the attachment of the posterior leaflet and the annulus.^[5] Furthermore, the right ventricle has a decreased number of myocardial fibers, which increases the risk of dilatation.^[7]

Pathophysiology

Numerous abnormalities are associated with Ebstein anomaly, including the following:

• Ventricular septal defect (VSD)^{[3, 8, 9]}
• Aortic coarctation^{[10, 11]}
• Interatrial communication - ASD, especially secundum ASD, and patent foramen ovale^{[3, 5, 9, 12]}
• Pulmonary atresia with an intact ventricular septum^{[9, 13]}
• Partial atrioventricular canal^[3]
• Hypoplastic pulmonary arteries^[3]
• Patent ductus arteriosus^[3]
• Pulmonary stenosis^{[9, 14]}
• Parachute mitral valve^[3]
• Cleft anterior leaflet of the mitral valve^[3]
• Mitral valve prolapse^{[9, 3]}
• Left ventricular outflow obstruction^[12]
• Hypertensive pulmonary vascular disease^[12]
• Congenital deaf-mutism^[15]
• Corrected transposition of the great arteries^{[16, 17, 18]}
• Subaortic stenosis^[19]
• Tetralogy of Fallot^[20]

Infants with severe Ebstein anomaly and marked cardiomegaly may have further compromise due to excessive bilateral, pulmonary compression from the enlarged heart.

Preferred examination

Traditional imaging modalities for Ebstein anomaly include chest radiography, echocardiography, and cardiac catheterization with right ventriculography. Chest radiography is the best initial study, although findings are often nonspecific.

Two-dimensional (2D) echocardiography (seen in the images below) is usually performed next and may be all that is required. Echocardiography can help to confirm the diagnosis, assess the severity of the anatomic lesion, and determine the effects on cardiac function.^[21]

When available and of high quality, fast cardiac magnetic resonance imaging (MRI) with contrast-enhanced, 3-dimensional (3D) magnetic resonance angiography (MRA) has the potential to replace cardiac catheterization for assessing pulmonary artery anatomy and for providing information that echocardiography cannot. MRI can depict anatomy and function with an unrestricted field of view; even the pulmonary arteries and tricuspid valve can be evaluated during a single study. Comprehensive imaging of this type provides a vehicle for surgical planning. A comparison between an MR angiogram and a conventional, contrast-enhanced ventriculogram is shown in the below.^{[22, 23]}

Limitations of techniques

Plain radiographic findings are nonspecific despite occasional pathognomonic appearances. Normal chest radiographic findings do not exclude the diagnosis.

Echocardiography is usually performed after chest radiography; however, if echocardiography is inadequate, MRI can be used to assess anatomy and function with an unrestricted field of view. Echocardiography can be limited by restricted acoustic access, especially in patients who are obese, who have undergone surgery, or who cannot lie still. Echocardiography cannot be used to measure the size of the left and right pulmonary arteries. Also note that 2D echocardiographic assessment of the right ventricular size and function may not correlate with the values determined by MRI assessment.^[24]

MRI is not routinely performed because of its limited availability and expense, the limited availability of qualified personnel to perform the protocol and/or interpret the study, the inability of some patients to cooperate (eg, because of claustrophobia), unsuitability or contraindications (eg, clinically unstable condition, pacemaker, metal objects in an anatomic location where MRI is dangerous and therefore contraindicated), and physicians' unawareness of the uses of MRI.

Classic radiographic features of Ebstein anomaly include a squared-off cardiac contour and pulmonary oligemia (demonstrated in the image below). Cyanosis occurs as a result of a right-to-left shunt, most often at the atrial level, with reduced pulmonary perfusion resulting from ineffective right ventricular ejection.

Normal chest radiographic findings with an unremarkable clinical presentation can occur with mild forms of Ebstein anomaly, but this manifestation is not typical.

Cardiomegaly may be seen on plain images of the chest (as in the first image below). Decreased pulmonary vascularity may be seen in patients with right-to-left shunts, usually through an ASD (see the second image below). A distinctly enlarged right atrium may be identified on chest radiographs. All of these findings can be nonspecific, although in some patients, chest radiographic findings are characteristic.

On the lateral chest radiograph, distortion of the right ventricular outflow (see the image below) or displacement by the atrialized segment of the right ventricle may cause abnormal filling of the retrosternal space. This finding is of use in older children and adults. The presence of the thymus makes this sign irrelevant for the diagnosis of Ebstein anomaly in infants.

Although Ebstein anomaly can be evaluated by means of computed tomography (CT) scanning, MRI has largely supplanted CT.

On a chest CT scan, the right atrium and ventricle appear dilated. A variable degree of apical displacement of the tricuspid valve attachments can be seen relative to the atrioventricular junction. The atrialized and functional portions of the right ventricle may be discerned. The conspicuity of the myocardium may be greater in the functional portion of the right ventricle than in the atrialized portion. Depending on the image reconstruction, the patient's heart rate, and the CT scanner, leaflet thickening may be seen.

MRI is a better noninvasive alternative to CT scanning in evaluating Ebstein anomaly when echocardiography provides incomplete information. By using a combination of anatomic (spin-echo sequences and MRA) and functional imaging techniques (cine MRA), anatomy and function can be assessed reliably by imaging with an area larger than that studied with echocardiography. Even the pulmonary arteries and valve can be evaluated during a single study.^{[25, 26]}

Comprehensive imaging of this type provides a vehicle for surgical planning. The presence of support devices or arrhythmias limits the use of this technique in sick patients.

All 4 types of Ebstein anomaly that Carpentier et al identified and classified can be imaged by using MRI. Young and old patients tolerate MRI well.^[27] Critically ill neonates can be imaged in as few as 15 minutes without adverse sequelae.^[28] Imaging can be accomplished with 0.5- to 2-T machines.

Axial spin-echo electrocardiogram (ECG)-gated images are excellent for assessing valvular anatomy, particularly the septal and anterior leaflets (as seen in the images below), right atrial size, and morphology of the atrialized right ventricle.^[25]

The posterior leaflet is imaged best in a coronal or oblique-coronal orientation. Coronal and oblique-coronal views can help in assessing the functional right ventricle. Coronal images can help in assessing the right atrial size (as in the image below) and conformation of the atrialized right ventricle.^[25]

Axial images help in identifying dilatation of the tricuspid valve annulus; this identification is achieved by calculating the ratio of the tricuspid ring to the mitral ring (normal ratio = 0.9-1.2).^[29]

The degree of tricuspid-valve regurgitation or stenosis can be demonstrated by using cine techniques (employed in the image below). In addition, right-to-left shunts through an ASD and right ventricular function can be analyzed using cine techniques.^[25]

Cine MRI can demonstrate right ventricular dysfunction and paradoxic motion of the ventricular septum. The abnormal septal motion can, in turn, cause abnormalities of left ventricular morphology and function.^[5]

Cine MRI can also reveal the presence of mitral-valve prolapse, which is known to result from left ventricular distortion.^[3]

Multilevel time-of-flight sequences can be used to demonstrate pulmonary artery anatomy.

With new sequences, images can be acquired with breath-hold, contrast-enhanced, 3D MRA (used in the image below) more rapidly and reliably than before. Results of a study by Tangcharoen et al showed that MR coronary angiography provides accurate detection of coronary abnormalities, even in patients as young as 4 months.^[30]

Degree of confidence

When used properly and in suitable patients, MRI can be regarded as the standard for detecting Ebstein anomaly and for assessing several aspects of the disease when echocardiography is unable to provide all required information. However, MRI has limitations in evaluating the detail of tricuspid valve morphology, which is best ascertained by using echocardiography. In addition, image quality may be impaired in some patients with arrhythmia or a large heart.

Echocardiography can demonstrate elongated tricuspid valve leaflets (especially the anterior leaflet) and leaflet thickening, although the leaflets also may demonstrate a whipping motion.^{[31, 32]}

The right ventricular cavity is dilated, abnormal septal motion may be observed, excursion of the anterior leaflet may be increased, and leaflet tethering may be seen (as in the image below).

Low-velocity tricuspid regurgitation, which reflects the usual inability to generate high pressure in the right ventricle, is common.

The severity of the lesion can be estimated from the degree of right atrial and ventricular dilatation and from marked apical displacement of the tricuspid valve leaflets. The valve can be displaced inferiorly; such displacement is usually to the left. (See the images below.)^[31]

Prenatal ultrasonography can be helpful in identifying fetal cardiomegaly. Ebstein anomaly with pulmonary atresia has been diagnosed with fetal echocardiography. Hydrops fetalis and Down syndrome have been associated. Postnatal echocardiography can be performed in neonates with cyanosis.^{[33, 34, 35, 36, 37, 38]}

Degree of confidence

Echocardiography is an excellent method for assessing Ebstein anomaly, and it may be the first and only cross-sectional imaging investigation that is required. If inadequate images are obtained, as in evaluating the pulmonary arteries before surgery, or if clinically significant chest deformity is present, MRI or transesophageal echocardiography can be used.

Traditional imaging of Ebstein anomaly has included cardiac catheterization with right ventriculography. This method is performed less frequently now, except as part of an ablation procedure for arrhythmias. Relatively noninvasive testing with echocardiography or MRI has reduced the need for diagnostic cardiac catheterization.

Findings are identical to those in MRI and echocardiography, although the images are obtained at increased risk and with a decreased amount of information concerning tricuspid valve anatomy. (See the image below.)

Contrast angiography demonstrates a large right atrium with a variable degree of tricuspid regurgitation (see the image below). The exact position of the abnormal tricuspid valve may be difficult to determine.

A catheter with a tip electrode (eg, Zukor catheter) can be used to show that atrial pressures are recorded when a right ventricular ECG is detected, indicating displacement of the tricuspid valve towards the cardiac apex.