The developing fetal heart begins as a simple tube that gradually specializes over time. In a normal fetus, blood is pumped from a single lower chamber of the heart (ventricle) through a trunk of arteries called the truncus arteriosus. As the fetus develops, a wall (septum) normally forms, dividing the single ventricle into two (left ventricle and right ventricle) and separating the truncus arteriosus into the pulmonary artery and aorta. The pulmonary artery travels from the right side of the heart to the lungs, and the aorta travels from the left side of the heart to the rest of the body.

There are rare cases in which a baby is born with an opening still present between the two ventricles (a ventricular septal defect) and the truncus arteriosus still undivided, or only partially divided. In addition, the valves that normally regulate the flow of blood between the lower ventricles and the pulmonary artery and aorta may be partially or completed fused. As a result, oxygen–rich blood and oxygen–poor blood freely mixes after the baby begins to take its first breaths of oxygen. Some oxygen–rich blood needlessly travels back to the lungs, and some oxygen–poor blood uselessly travels to the rest of the oxygen–demanding body.

This condition is called persistent truncus arteriosus or simply “truncus arteriosus.” Symptoms usually occur in the first week of life. Truncus arteriosus causes abnormal blood flow and increased pressure in the lungs, which may lead to symptoms of congestive heart failure within the first week of life. Babies born with truncus arteriosus may also develop a mild bluish tint the skin, lips, fingernails and other areas of the body due to a lack of oxygen–rich blood, a condition often called blue baby or cyanosis.

Although the condition involves complicated abnormalities of the heart and its structures, modern surgical advances have made it possible for babies born with this condition to have an excellent outlook.

Truncus arteriosus is a rare congenital heart defect in which an opening is still present between the two ventricles (a ventricular septal defect), and the trunk of arteries, called the truncus arteriosus, is still undivided. As a result, the pulmonary arteries, which normally arise from the right ventricle and carry oxygen-poor blood to the lungs, arise from the truncus arteriosus. Also, the pulmonary valve and the aortic valve are usually fused to some degree into a single valve with up to six leaflets. Truncus arteriosus is generally categorized by where along the truncus the pulmonary arteries arise.

Symptoms associated with truncus arteriosus usually emerge in the first week of life. When an infant is born, there is a higher degree of pulmonary resistance, meaning it's more difficult to pump blood into the lungs, which have not been used in utero. However, over the first week of life, as the child breaths, the resistance in the lungs gradually drops, changing the pressure gradient across the heart's outflow. Because the aorta and the pulmonary arteries are connected, the blood will naturally flow to the area of least resistance, or the lungs. This results in elevated blood pressure in the lungs (pulmonary hypertension), a reduction in blood flow to the rest of the body, and the onset of symptoms.

Initially, symptoms in truncus arteriosus may resemble congestive heart failure because of the damage done to the lungs by the increased blood flow. Also, babies with truncus arteriosus may also suffer from a lack of oxygen in the rest of the body, resulting in a bluish tinge to nails, gums and other body areas (cyanosis or blue baby). However, this bluish tinge is usually not as pronounced as it may be with other congenital heart defects.

In the past, physicians would try to stabilize infants with this condition and treat the congestive heart failure with drugs and other approaches. This often led to complications caused by the heart failure. Today, physicians are more likely to recommend surgery within the first week of life, or as soon as feasible.

The main sign of truncus arteriosus is the gradual development of symptoms consistent with congestive heart failure, caused by pulmonary hypertension. These may include:

• Shortness of breath (dyspnea) and general breathing difficulties
• Fatigue
• Difficulty feeding
• Weakness
• Delayed (or total lack of) growth
• Failure to thrive
• Cyanosis

Symptoms typically develop in the first weeks of life. Infants may also have a bluish tint (cyanosis) to the patient’s skin, lips, fingernails and other areas of the body, a condition often called blue baby. This is an indication that the body is not getting enough oxygen–rich blood

In some cases, truncus arteriosus can be diagnosed in utero, during fetal ultrasounds. Once a child has been born, if symptoms consistent with truncus arteriosus appear, a physician will ask the parents what they have observed in the child and give the child a physical examination. The examination may indicate that the baby is not thriving. One or more of the following painless tests will also be ordered to determine the exact nature and severity of the condition:

More invasive tests may be necessary to confirm a diagnosis. These tests include a cardiac catheterization to determine the nature and appearance of the deformed blood vessels. During this test, a catheter is introduced into the body (usually in the femoral vein) and guided to the heart, where it can be used to inject contrast dye that is visible under x–ray, or perform other tests.

In past decades, physicians generally approached truncus arteriosus by attempting to manage the congestive heart failure and delaying surgery. This might have meant drug therapy with diuretics or other agents that reduced the workload on the heart and relived symptoms of heart failure. Also, a procedure known as pulmonary artery banding was commonly recommended. During the procedure, a surgeon places a narrow tape of fabric (or “band”) around the pulmonary artery as it branches off from the truncus arteriosus and travels to the lungs. The band is then tightened so that its pressure is exactly one–half of the pressure in the aorta (which branches off from the truncus arteriosus and travels to the rest of the body). This procedure reduces the pressure in the lungs (pulmonary hypertension) while raising pressure in the aorta, which increases blood flow to the body and helps prevent or manage right–sided heart failure.

However, both approaches – medical management and pulmonary banding – had somewhat poor results, often because of complications due to the heart failure. Because of this, most surgical centers recommend surgery as soon as possible, sometimes within the first week of life or as soon as feasible after the diagnosis is confirmed. This corrective surgery is considered one of the more extensive cardiac surgeries performed on babies. It is an open-heart surgery that will require the use of a heart-lung machine. The procedure involves three main steps:

First, the surgeon divides the pulmonary arteries from the truncus arteriosus. The hole left by the removed pulmonary arteries is closed with either sutures or a Dacron patch. After other corrections have been made, the truncus arteriosus will carry only oxygen–rich blood through the aorta and out to the rest of the body. At the same time, the single valve is repaired.

Second, the surgeon opens the right ventricle and closes the hole in the septum (ventricular septal defect) with a Dacron patch. In combination with the first step, this step prevents the mixing of oxygen–rich and oxygen–poor blood. The patch is positioned so that the oxygen-rich blood from the left ventricle will be directed out the aorta.

The third step is called the Rastelli procedure, in which the surgeon attaches the pulmonary artery to the right ventricle using a valved conduit. A valved conduit is a tube made of fabric, human tissue from a cadaver or part of the patient’s own pericardium (the fluid–filled sac that surrounds the heart). Within the tube is a valve made of other organic tissue (a biological valve) or man–made tissue (a mechanical valve) to function as the pulmonic valve. This new valve will alternately open and close in precise time with the heartbeat, to allow blood to flow in only one direction and at only the right time. Therefore, oxygen-poor blood can be pumped by the right ventricle through the valved conduit and pulmonary artery to the lungs.

Surgery for truncus arteriosus is generally well tolerated. Following surgery, most babies will remain in the hospital for 10 days to two weeks barring any complications. Potential complications could include narrowing of the pulmonary artery – a condition known as branch pulmonary artery stenosis. Repeat surgery or widening procedures using a catheter may be performed. Additionally, because the valved conduit will not grow along with the child, replacement may be necessary two or three times during childhood.

Following a successful surgical repair, lifelong medical management will be necessary. For example, patients will be at increased risk of contracting a bacterial infection that could lead to endocarditis. Therefore, they will need to take antibiotics before any dental, medical or surgical procedures for the rest of their lives to reduce the risk of a bacterial infection.

Over the longterm, the individual who underwent surgery for truncus arteriosus may find their heart muscle gradually losing the ability to contract. This condition may be treated with diuretics to help the heart pump easier.

Patients with truncus arteriosus have an elevated risk of developing heart rhythm disturbances (arrhythmias). Medication is often used to control this problem.

The cause of truncus arteriosus is unknown. However, research has uncovered certain risk factors that may increase the overall chance of congenital heart defects. Among them is diabetes. Compared to non–diabetic women, studies find that babies born to diabetic women are at increased risk of such conditions as truncus arteriosus, tricuspid atresia and transposition of the great arteries.

Depending on personal and family medical history, the physician may recommend fetal ultrasound testing to rule out (or confirm) the presence of heart defects.

Preparing questions in advance can help parents have more meaningful discussions with their physicians regarding their child's condition. Parents may wish to ask their doctor the following questions related to truncus arteriosus:

1. Does my child have truncus arteriosus?
   
   
2. How seriously does this affect my child's overall health?
   
   
3. Will my child require surgery to correct this problem? How soon?
   
   
4. Will my child require any additional surgeries or therapies to correct this problem?
   
   
5. How much of a recovery is my child expected to make? Will this condition affect my child for the rest of his or her life?
   
   
6. Will my child require lifelong medical management to control this condition?
   
   
7. Will my child be able to live an active and full life? Are there any activities that my child will not be able to participate in later in life?
   
   
8. Could I have passed this condition on to my child? Could my child pass this condition on to his or her own children?