Ebstein Malformation

Historical Aspects

In an 1866 report titled “Concerning a very rare case of insufficiency of the tricuspid valve caused by a congenital malformation,” Dr. Wilhelm Ebstein (1836-1912), a German physician, described the unusual cardiac findings of a 19-year-old laborer who died of cyanotic heart disease. He accurately described the characteristic anatomic and hemodynamic abnormalities of Ebstein malformation ( Fig. 130-1 ). By 1950, only three case reports of Ebstein malformation had been published.

Pathologic Anatomy

Ebstein malformation of the tricuspid valve (TV) is characterized by ( Fig. 130-2 ):

• 1

  Failure of delamination of the septal, inferior, and anterior leaflets of the TV with subsequent adherence of the leaflets to the underlying myocardium

• 2

  Apical displacement of the functional TV annulus (septal>inferior>anterior)

• 3

  Dilation of the atrialized portion of the right ventricle (RV)

• 4

  Anterior leaflet fenestrations, redundancy or tethering

• 5

  Dilation of the true anatomic TV annulus

Tricuspid Valve

There is a highly variable TV morphology; the valve is almost always incompetent, and rarely stenotic. The anterior leaflet is usually large and is attached to the annulus; however, it may contain several fenestrations ( Fig. 130-3 ) and have various points of incomplete delamination. The chordae tendinea may be short and poorly formed.

The inferior and septal leaflet development is variable and most often rudimentary and may even be absent due to failure of the delamination process. The leading edges may be freely mobile with chordal or papillary muscular support, or they may be tethered (adherent) to the endocardium (linear attachment). The point of maximal displacement is at the commissure between the inferior and septal leaflets. In normal hearts, the downward displacement of the septal and posterior leaflets in relation to the anterior mitral valve leaflet is less than 8 mm/m ² body surface area. The spectrum of abnormality in Ebstein malformation can range from only minimal displacement of the septal and inferior leaflets to an imperforate membrane or muscular shelf between the inlet and trabecular zones of the RV. The range of variability is infinite, and the most important pathologic finding is “failure of delamination” of the leaflets. There often is marked dilation of the true TV annulus, which is not displaced, and a large chamber separating the true annulus from the functional RV is the “atrialized” portion of the RV (aRV).

Classifications of Ebstein Malformation

Several classifications have been proposed for Ebstein malformation. In general, classification systems of Ebstein malformation are difficult since there are infinite variations in the anatomy and no two hearts are alike.

Carpentier in 1988 proposed the following :

• Type A: the volume of the true RV is adequate

• Type B: a large atrialized component of the RV exists, but the anterior leaflet of the TV moves freely

• Type C: severe restriction of the anterior leaflet movement that can cause significant RV outflow tract obstruction

• Type D: near complete atrialization of the ventricle except for a small infundibular component

Another classification proposed four types of Ebstein malformation based on valve analysis during surgery. This is our preferred approach, which is to describe the exact anatomy of each of the involved structures of the heart as visualized at the time of surgery ( Table 130-1 ). This includes comment about the extent of failure of delamination of each leaflet, status of the leading edges of the leaflets, degree of displacement of the septal leaflet, description of the aRV, and size of the RA and RV.

Genetic Factors

Genetic factors in Ebstein malformation are heterogeneous. Most cases are sporadic and familial Ebstein is rare. Rare cases of cardiac transcription factor NKX2.5 mutations, 10p13-p14 deletion, and 1p34.3-p36.11 deletion have been described in association with Ebstein malformation. The results of a mutational analysis in a cohort of 141 unrelated probands with Ebstein malformation has been reported; eight were found to have a mutation in the gene MYH7, and six of the eight patients also had LV noncompaction. This result may warrant genetic testing and family evaluation in this subset of patients.

Pathophysiology

The functional impairment of the RV and the incompetence of the deformed TV retard forward flow of blood through the right side of the heart into the lungs. Moreover, during contraction of the atrium, the atrialized portion of the RV (which is adjacent to and in continuity with the RA) balloons out (if very thin) or acts as a passive reservoir, thus decreasing the volume to be ejected. During ventricular systole, the atrialized RV contracts, creating a pressure wave that impedes venous filling of the RA, which is in the diastolic phase. In most cases, there is a communication between the left and right atria, resulting from either patency of the foramen ovale or a distinct secundum ASD. The shunt of blood through the septal opening is generally from right to left, but may be bidirectional in some patients. The overall effect of these structural abnormalities on the RA is to produce gross dilation, which may reach enormous proportions, even in infants. This dilation leads to further incompetence of the TV and further widening of the interatrial communication.

As a consequence of atrial dilation, atrial tachyarrhythmias are common and become more likely as time goes on. In addition, approximately 15% of patients will have one or more accessory conduction pathways associated with WPW syndrome, and 1% to 2% of patients will have atrioventricular nodal reentrant tachycardia (AVNRT). In end-stage heart failure, ventricular arrhythmias can be present.

Clinical Presentations

Clinical presentations vary widely, because they depend on the anatomic severity and can range from a severely symptomatic neonate to an asymptomatic octogenarian.

The most common presentation varies with age at presentation :

• Fetuses: an abnormal routine prenatal scan (86%)

• Neonates: cyanosis (74%)

• Infants: heart failure (43%)

• Children: an incidental murmur (63%)

• Adolescents and adults: arrhythmia (42%), decreased exercise tolerance, fatigue, or right-sided heart failure