Tricuspid atresia is a congenital heart defect in which the tricuspid valve, the gateway between the heart’s upper right chamber and lower right chamber, never forms. Without this valve, blood returning from the body cannot follow its normal path into the right ventricle and onward to the lungs for oxygen. It is one of the cyanotic heart defects, meaning it causes a bluish tint to the skin because oxygen levels in the blood are too low.
How Blood Flows Without the Tricuspid Valve
In a typical heart, oxygen-poor blood enters the right atrium, passes through the tricuspid valve into the right ventricle, and gets pumped to the lungs. In tricuspid atresia, that passage is completely blocked by a wall of tissue instead of a functioning valve. Because the right ventricle receives little or no blood, it stays underdeveloped, a condition called a hypoplastic right ventricle.
For the baby to survive at all, blood has to find an alternate route. An opening between the two upper chambers (an atrial septal defect or a patent foramen ovale) allows oxygen-poor blood from the right atrium to cross into the left atrium, where it mixes with oxygen-rich blood returning from the lungs. This mixed blood then flows into the left ventricle and out to the body. The result is that every organ receives blood with less oxygen than normal.
Some babies also have an opening between the two lower chambers (a ventricular septal defect), which lets a portion of blood reach the lungs through the underdeveloped right ventricle. How much blood actually gets to the lungs, and therefore how much oxygen reaches the body, depends on the size of these openings and the arrangement of the major blood vessels leaving the heart.
Types of Tricuspid Atresia
Not every case looks the same inside the heart. The standard classification divides tricuspid atresia into three types based on how the two great arteries (the aorta and the pulmonary artery) are positioned. In about 56% of cases, these arteries are in their normal positions (Type I). In roughly 42%, they are transposed, meaning the aorta and pulmonary artery have switched places (Type II). A rare third type involves a single shared vessel leaving the heart.
Within each type, doctors further categorize cases based on whether blood flow to the lungs is restricted, normal, or excessive. This distinction matters because it shapes which symptoms appear first and how urgently surgery is needed.
Symptoms in Newborns
Babies with tricuspid atresia show symptoms at birth or within the first hours of life. The hallmark sign is cyanosis, a bluish or ashen color most visible on the lips, fingernails, and skin. Other common signs include difficulty breathing, poor feeding, and unusual sleepiness. The severity depends on how much blood is reaching the lungs. Babies with very limited lung blood flow become deeply blue quickly, while those with larger internal openings may appear less cyanotic initially but can develop heart failure from too much blood flowing to the lungs.
How It Is Diagnosed
An echocardiogram (heart ultrasound) is the primary tool for confirming tricuspid atresia. It shows the missing valve, the underdeveloped right ventricle, and abnormal blood flow patterns. It also reveals any associated defects like holes between chambers or transposed arteries. An electrocardiogram (EKG) is typically done alongside it and can pick up irregular heart rhythms or unusual electrical patterns that suggest the right ventricle is smaller than it should be. In some cases, the defect is detected before birth on a routine prenatal ultrasound.
Staged Surgical Repair
Tricuspid atresia cannot be corrected with a single operation. Instead, children undergo a series of two or three surgeries over their first few years of life, each one gradually rerouting blood flow so the single functioning ventricle can do the work of two.
First Stage: Establishing Lung Blood Flow
If a newborn’s oxygen levels are dangerously low, the first surgery happens within days of birth. A small tube is placed to connect one of the arteries branching off the aorta to the pulmonary artery, creating a reliable pathway for blood to reach the lungs. This is a palliative procedure, not a fix. It buys time by improving oxygen levels while the baby grows large enough for the next stage. Babies who have too much blood flowing to the lungs may instead need a procedure to restrict that flow and protect the lung vessels from damage.
Second Stage: The Glenn Procedure
At around 4 to 6 months of age, the large vein carrying blood from the upper body (the superior vena cava) is disconnected from the heart and sewn directly to the pulmonary artery. This allows blood from the head and arms to flow passively into the lungs without being pumped, which significantly reduces the workload on the single ventricle. After this surgery, oxygen saturation levels typically sit in the mid-80s (percent), compared to the high 90s in a child with a normal heart. The child will still appear mildly blue, but the improvement over the previous circulation is substantial.
Timing matters. Data from large registries shows the lowest surgical mortality when this procedure is performed 3 to 6 months after the first-stage repair. Doing it before 4 months carries higher risk, partly because the blood vessels in the lungs are not yet ready to accept passive blood flow. Waiting past about 5 months of age also increases risk.
Third Stage: The Fontan Procedure
The final surgery, usually performed between ages 2 and 4, completes the rerouting. The remaining large vein carrying blood from the lower body (the inferior vena cava) is also connected to the pulmonary artery, typically through a tunnel or an external conduit running along the outside of the heart. After the Fontan, all oxygen-poor blood flows passively to the lungs without passing through the heart at all. The single ventricle is now dedicated entirely to pumping oxygen-rich blood to the body.
This arrangement is not a cure. It is the best possible circulation a single-ventricle heart can achieve, and it allows most children to grow, attend school, and be active. But it is fundamentally different from a normal two-ventricle circulation, and it comes with long-term trade-offs.
Long-Term Outlook
Survival after completion of the Fontan has improved considerably over the decades. In a recent study tracking adults with Fontan circulations (about a quarter of whom had tricuspid atresia as their underlying defect), transplant-free survival was 99% at 20 years after the Fontan, 87% at 30 years, and 63% at 40 years. These numbers reflect the reality that most children who complete the staged repairs live well into adulthood, but the Fontan circulation does take a toll on the body over time.
Long-Term Complications After the Fontan
The Fontan circulation works by maintaining higher-than-normal pressure in the veins to push blood through the lungs without a pump. This elevated venous pressure, sustained over years and decades, gradually affects multiple organs.
The liver is especially vulnerable. Chronically elevated pressure in the veins draining the liver can lead to progressive scarring (cirrhosis), and the risk of liver problems correlates with how many years a person has been living with Fontan circulation. In severe cases, this can progress to liver failure or increase the risk of liver cancer. Regular liver monitoring is a standard part of follow-up care for Fontan patients.
Other complications include heart rhythm abnormalities (arrhythmias), gradual weakening of the single ventricle’s pumping ability, blood clots due to sluggish flow in the venous system, and a condition called protein-losing enteropathy, where the gut loses protein into the digestive tract because of high venous pressure. Not every Fontan patient develops these problems, but the likelihood increases with time, which is why lifelong follow-up with a cardiologist specializing in congenital heart disease is essential.