Tricuspid Valve Dysplasia

Review of Tricuspid Valve Dysplasia

Tricuspid Valve Dysplasia (TVD) is recognized as a specific congenital anomaly of the heart valve apparatus, often discussed alongside Ebstein malformation (EM) due to shared functional consequences, despite distinct pathological differences. Pathologically, TVD is characterized by nondisplaced septal leaflets. In this condition, the valve is typically dysplastic, appearing nodular, irregular, or tethered, leading to limited mobility. The myocardium may also show abnormalities, a feature it shares with Ebstein anomaly. The anatomical distinction from EM is crucial: EM involves downward displacement of the valve leaflets resulting from a failure of delamination from the underlying myocardium. In contrast, TVD occurs when dysplasia is present, but the valve leaflets are fully delaminated and not apically displaced. However, given the rarity and tremendous morphological heterogeneity of both conditions, they are frequently grouped together for clinical studies and discussions, primarily because both lead to severe tricuspid regurgitation (TR).

Clinical Significance and Pathophysiology

Severe tricuspid regurgitation (TR) in the fetus, whether resulting from TVD or EM, is poorly tolerated because the right ventricle (RV) acts as the dominant ventricle in the fetal circulation, significantly impacting cardiac output and central venous pressures. This severe presentation is associated with a high perinatal mortality rate, noted historically to be around 45% when grouping TVD and EM. Risk factors for adverse perinatal outcome include an earlier gestational age at diagnosis, cardiac enlargement, pericardial effusion, and abnormal umbilical arterial Doppler findings.

A serious hemodynamic consequence that may develop, particularly in severe cases, is the circular shunt physiology, sometimes referred to as the "circle of death". This scenario is exacerbated by the evolution of pulmonary regurgitation (PR) alongside severe TR, creating a vicious cycle where blood shunts across the foramen ovale to the left side of the heart, then back across the ductus arteriosus into the weak RV, leading to a lack of systemic perfusion and unhealthy ventricular loading. TVD frequently occurs in conjunction with other lesions, notably pulmonary atresia with intact ventricular septum (PA/IVS). Post-mortem studies of PA/IVS cases have found the tricuspid valve to be both hypoplastic and dysplastic in the majority (69%) of cases. In severe PA/IVS, the TV leaflets are often abnormally thickened, and the chordae tendineae may be stiff and short. Tricuspid valve hypoplasia typically correlates proportionally with the size of the hypoplastic RV cavity. Structural abnormalities of the TV, such as redundant anterior leaflet tissue, may also cause or contribute to right ventricular outflow tract obstruction (RVOTO). Genetic evaluation is pertinent for major anomalies like TVD; Trisomy 21 (Down syndrome) is the most common associated genetic abnormality, occurring in up to 10% of cohorts studied.

Diagnosis and Assessment

Echocardiography is the primary diagnostic method. Assessment of the tricuspid valve involves describing the degree of dysplasia/morphology of the septal and posterior leaflets, any redundancy or tethering of the anterior leaflet to the RV, and measurement of the TV annulus size. The severity of TR is quantified, and the peak TR jet velocity can be measured as an indicator of the RV's ability to generate pressure. Doppler flow studies are crucial for determining the magnitude of TR and the direction and extent of shunting across any atrial communication. Quantification using metrics like the tricuspid valve annulus z-score is often used in research as a surrogate for overall disease severity.

Management Considerations

Management of TVD, especially when severe, requires a multidisciplinary team approach starting prenatally. For fetuses presenting with severe circular shunting, temporary stabilization in utero using non-steroidal anti-inflammatory drugs (NSAIDs) therapy, such as Indomethacin (often starting at 100 mg twice daily), may be considered, requiring very close fetal monitoring. 

In the neonatal period, the goal is stabilization. In cases of critical pulmonary stenosis (PS) associated with severe TR, interventions such as percutaneous balloon valvuloplasty might be used as initial treatment. However, neonates with critical PS and severe TR must be closely monitored for the development of circular shunt physiology following procedures that induce pulmonary insufficiency. If circular shunting occurs, prompt surgical ligation of the persistent ductus arteriosus (PDA) is warranted, sometimes accompanied by the creation of a systemic-to-pulmonary shunt if cyanosis persists. Surgical interruption of the circular shunt in the early neonatal period can provide stabilization and may not necessarily commit the patient to a single ventricle pathway long-term. Sometimes, they may present function pulmonary atresia, where the RV pumps backward its cardiac output, with inability to generate forward flow through the RV outflow tract. 

For patients with PA/IVS, management decisions regarding a biventricular versus single-ventricle repair are heavily influenced by TV and RV size. Tricuspid valve diameter may be a reliable index of the RV's capacity for development after obstruction relief. Values such as a TV diameter less than 8 mm in a newborn or a TV-to-mitral valve diameter ratio less than 0.7 have been considered inadequate to sustain full cardiac output. The ultimate therapeutic strategy is highly individualized based on the RV's capacity and overall cardiovascular status.

In some infants with tricuspid valve dysplasia, severe tricuspid regurgitation and markedly impaired right ventricular function can lead to functional pulmonary valve atresia (see echocardiography example below), where the pulmonary valve is anatomically present but fails to open because the right ventricle cannot generate sufficient forward pressure. This physiology indicates right-sided dysfunction, significant tricuspid regurgitation with minimal or absent antegrade pulmonary blood flow, placing the neonate at high risk for circular shunting, cyanosis, and/or systemic hypoperfusion. These patients may be quite blue and may initially depend on the ductus for pulmonary blood flow (although with time, the ductus may compete with the right ventricle by exposing the pulmonary vasculature to systemic pressures - and by proxy the recovering right ventricle to the aortic pressure/systemic vascular resistances). Management is focused on stabilizing hemodynamics by maintaining ductal patency with prostaglandin infusion while closely assessing the potential for right ventricular recovery. In some situation, iNO and oxygen can help relax the pulmonary vasculature and promote forward flow through the right ventricular outflow tract. Inotropes like dobutamine can help the struggling RV to recover. 

Neonatal Echocardiography

References