Tricuspid Atresia

Definition

Tricuspid Atresia is a cyanotic congenital heart defect characterized by the complete agenesis (underdevelopment) of the tricuspid valve and or right ventricle. This prevents blood from flowing directly to the lungs to pick up oxygen, leading to low oxygen levels in the body. The right ventricle is often small or underdeveloped, and other heart defects, like holes between chambers, are usually present to allow some blood flow. Consequently, the absence of communication between the right atrium and the ventricle leads to cyanosis. The condition has several subtypes with varied clinical presentations determined by the extent of pulmonary blood flow (Minocha, 2024). The anatomical variations in tricuspid atresia, often involving pulmonary obstruction, prompt a thorough evaluation to assess the degree of the lesion and its impact on a patient’s hemodynamic status. Many babies born with tricuspid atresia also have a hole between the two lower chambers of the heart. This hole, called a ventricular septal defect (VSD) helps blood to reach the lungs since the normal pathway is blocked in TA.

Key Features:

• No tricuspid valve: Blocks blood flow from right atrium to right ventricle.
• Associated Defects:
  • Atrial septal defect (ASD): A hole between the right and left atria, essential for survival.
  • Ventricular septal defect (VSD): A hole between the ventricles, present in most cases.
  • Pulmonary stenosis or atresia: Narrowing or absence of the pulmonary valve.
  • Transposition of the great arteries (TGA): Aorta and pulmonary artery may be swapped (in 12–25% of cases).
  • Prevalence: Affects about 1 in 10,000–15,000 babies, accounting for 1–3% of congenital heart defects.

Causes of tricuspid atresia

The root cause of tricuspid atresia happens when the heart doesn’t develop properly before birth, and there’s no proven link to inherited genes. Without treatment in the first year of life, the condition can be life-threatening.

The anatomical variations in tricuspid atresia, often involving pulmonary obstruction, prompt a thorough evaluation to assess the degree of the lesion and its impact on a patient’s hemodynamic status. The lesion is further classified into several subtypes, with or without pulmonary obstruction, based on the anatomical changes. Implementing further procedural recommendations based on the evaluation aims to restore normal blood flow.

Many babies born with tricuspid atresia also have a hole between the two lower chambers of the heart. This hole is called a ventricular septal defect (VSD). Because the normal pathway is blocked in tricuspid atresia, blood uses this hole to reach the lungs.

If the hole (VSD) is large, too much blood can go to the lungs. This puts extra stress on the heart and can lead to heart failure.

Risk factors

It is not entirely clear why congenital heart defects such as tricuspid atresia occur.

TA develops during the first 8 weeks of pregnancy when the heart and its valves form. The tricuspid valve fails to develop, often leaving a solid tissue barrier, and the right ventricle remains small due to lack of blood flow. The exact cause is usually unknown, but possible factors include:

• Genetic Factors: Linked to syndromes like Down syndrome, DiGeorge syndrome (22q11 deletion), Alagille, or Ellis Van Creveld. Mutations in genes like ZFPM2, HEY2, NFATC1, NKX2.5, or MYH6 may contribute.
• Environmental Factors: Maternal exposure to certain medications, infections (e.g., rubella), or environmental toxins may increase risk. Use of certain medications during pregnancy, including some used to treat acne, bipolar disorder and seizures
• Other Risks: Maternal diabetes, smoking, or alcohol use during pregnancy may play a role.

Prompt treatment greatly improves the outcome for babies with tricuspid atresia. But complications may develop later in life. Complications of tricuspid atresia may include:

• Easy fatiguability during activity
• Irregular heart rhythms
• Kidney or liver disease
• Heart failure

Diagnosis

Diagnosis of Tricuspid Atresia:

1. Echocardiography remains the main tool used to diagnose tricuspid atresia. A 2D echo will show that the tricuspid valve is missing and the left ventricle is bigger than the right. Color Doppler confirms there’s no blood flow through the tricuspid valve.

2. Cardiac catheterization is usually not needed for diagnosis. However, if blood can’t flow well from the right to the left atrium, a catheter procedure called balloon atrial septostomy may be done. Genetic testing might also be considered, especially if the condition is linked to syndromes like trisomies or VACTERL association.

TREATMENT/MANAGEMENT.

Right after birth, prostaglandin should be given to keep the ductus arteriosus open in babies who rely on it for blood flow to the lungs. If the baby has signs of heart failure and too much blood going to the lungs, diuretics may be used.

Glenn surgery has very good outcomes, with a survival rate of 87% after 5 years and a low death rate during surgery. However, some long-term problems may include:

• Blood clots
• Heart rhythm issues
• Weak heart function
• Cyanosis (low oxygen levels)

Protein-losing enteropathy (PLE), a condition that causes the body to lose protein through the intestines

Treatment

TA requires urgent treatment to improve blood flow to the lungs and body. Treatment involves medications and a series of surgeries, as replacing the tricuspid valve is not possible due to the underdeveloped right ventricle.

1. Stabilizing Your Baby:
   • Prostaglandin E1: Keeps the ductus arteriosus (PDA) open to allow blood flow to the lungs, especially if oxygen levels are low. May cause breathing issues, requiring a ventilator.
   • Oxygen or Ventilator: Helps with breathing.
   • Balloon Atrial Septostomy: If the ASD is too small, a catheter procedure enlarges it to improve blood flow.
2. Surgeries (Staged Reconstruction):
   • Stage 1 (First Weeks):
     • Blalock-Taussig-Thomas (BTT) Shunt: A tube connects an artery to the pulmonary artery to increase lung blood flow if too low.
     • Pulmonary Artery Banding: If too much blood flows to the lungs, a band narrows the pulmonary artery to protect the lungs.
     • Ductal Stent: A stent keeps the PDA open instead of a shunt.
     • Norwood Procedure: Needed if TA is combined with transposition of the great arteries.
   • Stage 2 (4–12 Months): Bidirectional Glenn shunt connects the superior vena cava to the pulmonary artery.
   • Stage 3 (2–4 Years): Fontan procedure connects the inferior vena cava to the pulmonary artery, allowing oxygen-poor blood to flow directly to the lungs without a ventricle.

Surgical repair diagram.

diagram showing the Fontan, Norwood or Glen procedure.