Tricuspid Atresia: Causes, Pathophysiology, Diagnosis, Management and Prevention

Tricuspid Atresia: Causes, Pathophysiology, Diagnosis and Management

~Introduction

Tricuspid atresia is a rare but serious congenital heart defect characterized by the absence or imperforation of the tricuspid valve — the valve that normally allows blood flow from the right atrium to the right ventricle. In this condition, the right atrium lacks a direct outlet to the right ventricle, leading to underdevelopment (hypoplasia) of the right ventricle and disruption of normal blood circulation through the heart and lungs.

This defect accounts for approximately 1–3% of all congenital heart diseases, with an incidence of about 1 in 10,000 live births. Without appropriate surgical intervention, tricuspid atresia is incompatible with long-term survival. However, advances in neonatal care and surgical techniques have dramatically improved the prognosis and life expectancy of affected children.

~Normal Cardiac Anatomy and Circulation

In a healthy heart, there are four chambers: two atria (right and left) and two ventricles (right and left). The tricuspid valve lies between the right atrium and right ventricle and allows deoxygenated blood to flow into the right ventricle during diastole. From there, blood is pumped through the pulmonary valve into the pulmonary artery and to the lungs for oxygenation.

After oxygenation, blood returns to the left atrium via pulmonary veins, passes through the mitral valve into the left ventricle, and is finally pumped through the aorta to the systemic circulation.

In tricuspid atresia, the absence of the tricuspid valve blocks this pathway entirely, severely altering the normal hemodynamics of the heart.

~Anatomy and Pathophysiology of Tricuspid Atresia

Anatomical Features

In tricuspid atresia:

• The tricuspid valve is either completely absent or replaced by a solid membrane.

• The right ventricle is typically small or hypoplastic due to the lack of inflow.

• Blood cannot flow directly from the right atrium to the right ventricle.

• The atrial septum usually has an opening — an atrial septal defect (ASD) or patent foramen ovale (PFO) — which allows systemic venous blood from the right atrium to pass into the left atrium.

• The ventricular septum may have a ventricular septal defect (VSD) that allows blood to reach the pulmonary artery.

• The pulmonary outflow tract may be normal, narrowed (stenotic), or completely absent (atresia).

Hemodynamic Consequences

The circulatory pattern depends on the presence or absence of a VSD and the degree of pulmonary stenosis:

1. If pulmonary blood flow is decreased (due to pulmonary stenosis or atresia):

   • Cyanosis appears early.

   • Pulmonary blood flow depends on a patent ductus arteriosus (PDA).

2. If pulmonary blood flow is increased (due to a large VSD and no stenosis):

   • Pulmonary overcirculation leads to heart failure, tachypnea, and hepatomegaly.

3. Systemic circulation is maintained through the left ventricle, which pumps mixed (oxygenated and deoxygenated) blood to both systemic and pulmonary circulations.

Thus, the entire cardiac output depends on the left ventricle, making it function as a single ventricle system.

~Classification of Tricuspid Atresia

Tricuspid atresia is classified based on the great artery relationship and pulmonary outflow status:

I. According to Great Artery Relationship

1. Type I: Normally related great arteries (aorta arises from left ventricle, pulmonary artery from right ventricle).

2. Type II: Transposed great arteries (aorta from right ventricle, pulmonary artery from left ventricle).

3. Type III: Other or complex great artery relationships.

II. According to Pulmonary Outflow Tract

Each of the above types is further divided into:

• a: Pulmonary atresia

• b: Pulmonary stenosis

• c: Normal pulmonary valve and arteries

• d: Pulmonary atresia with transposed arteries or other complex lesions

Simplified Clinical Classification

1. Decreased pulmonary blood flow — due to pulmonary stenosis or atresia (cyanotic type)

2. Increased pulmonary blood flow — due to large VSD and no obstruction (acyanotic or congestive type)

~Etiology and Risk Factors

The exact cause of tricuspid atresia remains unknown, but several genetic and environmental factors are associated:

• Genetic associations:

  • Chromosomal abnormalities such as trisomy 21 (Down syndrome) and DiGeorge syndrome.

  • Familial recurrence in congenital heart diseases.

• Maternal factors:

  • Rubella or viral infections during early pregnancy.

  • Diabetes mellitus in the mother.

  • Exposure to teratogens such as retinoic acid or lithium.

  • Alcohol consumption and smoking during pregnancy.

There is no clear evidence of inheritance, but recurrence risk in subsequent pregnancies is slightly higher than in the general population.

~Clinical Features

Symptoms

The clinical presentation varies depending on the pulmonary blood flow and presence of associated defects.

1. Cyanotic Type (Decreased Pulmonary Blood Flow)

• Cyanosis soon after birth

• Breathlessness or tachypnea

• Poor feeding and failure to thrive

• Clubbing (in older infants)

• Fatigue and exercise intolerance

2. Acyanotic or Congestive Type (Increased Pulmonary Blood Flow)

• Mild or no cyanosis initially

• Symptoms of congestive heart failure:

  • Rapid breathing

  • Sweating

  • Hepatomegaly

  • Feeding difficulties

Physical Findings

• Central cyanosis and clubbing (depending on severity)

• Single second heart sound (S2)

• Murmur due to associated VSD or PDA

• Systolic murmur over left sternal border

• Hepatomegaly in heart failure cases

~Diagnosis

Diagnosis relies on a combination of clinical findings, imaging studies, and cardiac catheterization when required.

1. Electrocardiogram (ECG)

• Left axis deviation (common finding)

• Left ventricular hypertrophy

• Right atrial enlargement

• Absence of right ventricular forces

2. Chest X-ray

• Normal or mildly increased cardiac silhouette

• Decreased pulmonary vascularity in cyanotic types

• Increased vascularity in cases with excessive pulmonary blood flow

• “Boot-shaped” heart in some forms

3. Echocardiography (2D and Doppler)

Echocardiography is the gold standard for diagnosis.
It can reveal:

• Absence of tricuspid valve

• Hypoplastic right ventricle

• Interatrial communication (ASD or PFO)

• VSD and great vessel relationships

• Pulmonary artery anatomy

• Direction of blood flow via Doppler imaging

4. Cardiac Catheterization and Angiography

Used mainly to assess pulmonary vascular resistance and anatomy prior to surgical intervention. It can define:

• Oxygen saturation levels

• Pressure gradients

• Shunt presence and size

5. Pulse Oximetry

Demonstrates reduced oxygen saturation, typically between 70–85%, depending on shunt size and pulmonary flow.

~Differential Diagnosis

Tricuspid atresia must be differentiated from other cyanotic congenital heart diseases such as:

• Tetralogy of Fallot

• Pulmonary atresia with intact ventricular septum

• Transposition of the great arteries

• Single ventricle physiology

• Ebstein’s anomaly of the tricuspid valve

~Natural History

Without intervention, most infants with tricuspid atresia die within the first year of life due to severe hypoxemia or heart failure. Survival beyond early childhood is rare without surgical palliation.

Those with balanced pulmonary blood flow may survive into childhood but eventually develop cyanosis, exercise intolerance, and complications such as polycythemia, stroke, or infective endocarditis.

~Management

Management of tricuspid atresia requires a stepwise surgical approach aimed at establishing adequate pulmonary and systemic circulation while maintaining balanced oxygenation.

1. Medical Management (Initial Stabilization)

In neonates with duct-dependent pulmonary blood flow:

• Prostaglandin E₁ infusion is administered to keep the ductus arteriosus patent, allowing pulmonary perfusion.

• Oxygen supplementation and diuretics for heart failure.

• Inotropic support if low cardiac output is present.

• Anticoagulation or aspirin in later stages to prevent thromboembolic events.

2. Palliative Surgical Procedures

These are performed in stages to balance circulation before definitive surgery.

a. Systemic-to-Pulmonary Shunt (Modified Blalock–Taussig Shunt)

• Indicated in patients with decreased pulmonary blood flow.

• Connects subclavian artery to pulmonary artery to increase blood flow to lungs and improve oxygenation.

b. Pulmonary Artery Banding

• Used when pulmonary blood flow is excessive (no pulmonary stenosis).

• Reduces pulmonary hypertension and prevents heart failure.

c. Atrial Septectomy (Balloon Atrial Septostomy)

• Performed if interatrial communication is restrictive, allowing better mixing of blood.

3. Definitive Surgical Procedures (Fontan Pathway)

The Fontan procedure and its modifications represent the definitive palliation for tricuspid atresia.

a. Glenn Shunt (Bidirectional Cavopulmonary Anastomosis)

• Performed at 3–6 months of age.

• The superior vena cava is connected directly to the right pulmonary artery, directing venous blood from the upper body to the lungs.

b. Fontan Procedure

• Usually done between 2–5 years of age.

• The inferior vena cava is connected to the pulmonary arteries, completing separation of systemic and pulmonary circulations.

• The entire systemic venous return flows passively to the lungs without passing through a ventricle.

Types of Fontan Procedures

1. Atriopulmonary Connection (Classic Fontan)

2. Lateral Tunnel Fontan

3. Extracardiac Conduit Fontan

The extracardiac conduit Fontan is most commonly used today, reducing arrhythmias and improving long-term outcomes.

~Complications and Long-term Outcomes

Early Postoperative Complications

• Low cardiac output

• Pleural effusions

• Arrhythmias

• Thrombosis or embolism

• Protein-losing enteropathy

Late Complications

• Chronic heart failure

• Atrial arrhythmias (especially after classic Fontan)

• Thromboembolism

• Cyanosis due to shunt obstruction

• Liver congestion and fibrosis (Fontan-associated liver disease)

• Plastic bronchitis (rare but serious)

Prognosis

With modern surgical techniques:

• Early survival after staged repair exceeds 85–90%.

• 10-year survival is around 80%.

• 20-year survival may reach 70% with good quality of life.

Patients require lifelong cardiology follow-up for rhythm monitoring, anticoagulation management, and surveillance for late Fontan complications.

~Recent Advances

• Fetal echocardiography enables prenatal diagnosis and perinatal planning.

• Hybrid procedures combining catheter-based and surgical techniques reduce morbidity.

• Fontan revisions and heart transplantation are options for end-stage Fontan failure.

• Stem cell therapies and ventricular assist devices (VADs) are under research to improve single-ventricle outcomes.

~Prevention and Genetic Counseling

While most cases are sporadic, genetic counseling is essential for families with a history of congenital heart disease.

• Prenatal screening using high-resolution ultrasound and fetal echocardiography helps early detection.

• Avoidance of teratogens, good maternal health, and rubella vaccination before pregnancy may reduce risk.

~Conclusion

Tricuspid atresia represents a complex but surgically manageable congenital heart defect. The absence of the tricuspid valve disrupts normal right-sided heart function, forcing the left ventricle to serve as the single pumping chamber. Early diagnosis, staged surgical repair (culminating in the Fontan circulation), and comprehensive long-term care have transformed the prognosis from uniformly fatal in infancy to one compatible with adulthood and an active life.

Continued innovations in pediatric cardiology, surgical techniques, and postoperative management hold promise for even better outcomes in the future.