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.
What is Truncus Arterisus
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.
Treatment
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.
After surgery
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.
