Tricuspid atresia (TA) is a congenital heart defect where the tricuspid valve, which normally separates the upper and lower chambers on the right side of the heart, is either absent or improperly formed. This means there is no direct path for blood to flow from the right atrium to the right ventricle. Because the heart cannot function with two separate pumping chambers, TA results in a single-ventricle circulation, a life-threatening condition requiring immediate intervention. Medical management and subsequent surgery aim to restructure the circulation to support the body’s needs with only one functional ventricle.
The Anatomy and Physiology of Tricuspid Atresia
The normal heart operates as two side-by-side pumps, with the right side receiving deoxygenated blood from the body and sending it to the lungs for oxygenation. In tricuspid atresia, the absence of the tricuspid valve prevents blood from the right atrium (RA) from entering the right ventricle (RV). Consequently, the right ventricle is underdeveloped, or hypoplastic, as it does not receive a normal volume of blood.
For the infant to survive, deoxygenated blood must find an alternate route out of the right atrium by flowing through an opening in the wall between the two upper chambers. This shunts the systemic blood into the left atrium (LA), where it mixes with the oxygenated blood returning from the lungs. This mixture then flows into the left ventricle (LV), which becomes the single functional pumping chamber supplying blood to both the body and the lungs.
Oxygen saturation depends heavily on the presence and size of other associated defects, particularly a ventricular septal defect (VSD). A VSD is a hole between the left and right ventricles, allowing the single pumping chamber (LV) to send mixed blood into the small right ventricle and on to the pulmonary artery and lungs. If pulmonary blood flow is too restricted, the baby will be severely cyanotic. If flow is too open, the baby risks heart failure from excessive flow to the lungs.
Identifying the Condition
Diagnosis of tricuspid atresia can begin before birth through a fetal echocardiogram. Prenatal diagnosis allows the medical team to prepare for immediate intervention upon delivery. Postnatal diagnosis is often prompted by clinical signs appearing shortly after birth.
One common early sign is cyanosis, a bluish or purplish tint to the skin, lips, and nail beds, indicating low blood oxygen levels. Newborns may also exhibit difficulty feeding, rapid or labored breathing, and general fatigue. A pulse oximetry screening, a routine test for newborns, will show lower-than-expected oxygen saturation, leading to further investigation.
The echocardiogram uses sound waves to visualize the heart’s structure and blood flow. This test clearly shows the absence of the tricuspid valve and the size discrepancy between the ventricles. An electrocardiogram (EKG) and chest X-ray may also be used to assess the heart’s electrical activity and size. In urgent cases, a balloon atrial septostomy may be performed via cardiac catheterization if the atrial communication is too small, restricting blood flow and worsening cyanosis.
The Staged Surgical Repair Strategy
The treatment for tricuspid atresia is a staged surgical repair strategy, which aims to create a functional circulation system using the single ventricle. This typically involves three open-heart procedures performed over several years, designed to separate the systemic and pulmonary circulations.
The first stage is an initial shunt procedure, such as the modified Blalock-Taussig (BT) shunt. This procedure creates an artificial connection between a systemic artery and the pulmonary artery. For babies with excessive blood flow to the lungs, an alternative is a pulmonary artery band, which restricts the artery to stabilize oxygen levels and control flow to the pulmonary circuit.
The second stage, known as the Bidirectional Glenn Procedure or Hemi-Fontan, is typically performed when the infant is between four and six months old. This operation disconnects the superior vena cava from the heart and connects it directly to the pulmonary artery. The original shunt is removed, and deoxygenated blood from the upper body now flows passively to the lungs, reducing the volume load on the single ventricle.
The third and final stage is the Fontan Procedure, usually carried out between 18 months and four years of age. This operation completes the single-ventricle circulation by redirecting the blood from the inferior vena cava directly to the pulmonary artery. The procedure creates a total cavopulmonary connection, meaning all deoxygenated blood bypasses the heart and flows straight into the lungs. The single ventricle is then left to pump only oxygenated blood to the body.
Long-Term Management and Follow-Up
Following the Fontan procedure, patients enter a phase of lifelong management under chronically elevated systemic venous pressures. These individuals require continuous care from specialists in Adult Congenital Heart Disease (ACHD). Regular follow-up is necessary to watch for specific long-term complications related to the passive blood flow.
One significant potential issue is Fontan-associated liver disease (FALD), which results from chronic venous congestion. Arrhythmias, or irregular heart rhythms, are also common and increase with age, often requiring medication or pacemaker implantation. The elevated pressure can also lead to Protein-Losing Enteropathy (PLE), resulting in chronic diarrhea and fluid retention.
Other potential complications include chronic fluid retention, plastic bronchitis, and a reduction in exercise tolerance. Patients must be monitored for signs of “Fontan failure,” which describes a deterioration of the circulation leading to multiorgan dysfunction. Long-term management focuses on mitigating these risks and preserving the health of the single ventricle and associated organs.