Truncus Arteriosus – the condition, its effects, and treatment
In a normal heart, the aorta (the body’s main systemic artery) arises from the left side, from where it is fed oxygenated blood from the left ventricle (pumping chamber). Similarly, the pulmonary artery, which supplies the lungs with de-oxygenated blood, arises from the right ventricle. In truncus arteriosus, the aorta and the pulmonary arteries are fused at their base into a single vessel. Thus, the heart contains one major artery rather than two.
Further up, the truncus feeds into the aortic arch and the pulmonary arteries.
A large VSD (hole in the wall dividing the left and right ventricles) is always present.
The truncus characteristically sits over the VSD. This is important because it means that both the pulmonary arteries and the aorta will recevive a mixture of oxygenated and deoxygenated blood rather than operating on two separate circuits. Moreover, the lungs will receive too much blood to process, and the body will receive too little.
The effects of truncus arteriosus
Children with this condition will typically present with severe symptoms (cyanosis – or appearing blue – signs of heart failure and collapse are all common) very early in life.
This is because there are not two arteries arising from the heart, so the supply of blood cannot be separated out into oxygenated and deoxygenated components (with oxygenated blood supplying the body, and deoxygenated blood being taken to the lungs). In truncus arteriosus the systemic circulation is supplied with only partially oxygenated blood. Meanwhile, the pulmonary circulation also receives a mixture of deoxygenated and oxygenated blood.
Blood pressure will also be a problem. The single arterial trunk pushes too much blood towards the pulmonary arteries and not enough towards the systemic circulation. Consequently, the lungs become congested by the extra blood flow. If this is not corrected then permanent damage to the lungs may occur. Meanwhile, the systemic circulation is quantitatively and qualitatively inadequate.
Diagnosis and treatment of truncus arteriosus
Diagnosis is usually by echocardiography (a form of ultrasound). It may be necessary to clarify this by other forms of diagnostic imaging (probably cardiac catheterisation). If truncus arteriosus is discovered, surgical treatment will always be necessary.
In the first instance, pulmonary artery banding may be offered. As the name suggests, in this procedure a band is placed around the main pulmonary artery. The aim of this procedure is to limit the volume of blood flowing into the lungs. This is not a permanent solution: the aim is to “hold” the patient until definitive corrective surgery can be offered.
Definitive surgery takes the form of a procedure called the Rastelli. This is an open-heart procedure (i.e. it is conducted on cardiopulmonary bypass, and the heart will be stopped during the procedure so that work within it can be carried out).
In the Rastelli, a prosthetic main pulmonary artery is inserted, and stitched into position. The truncus is then used as the aorta, and is relocated so that it. The associated VSD is closed and if necessary the atrioventricular valve is repaired too.
The Rastelli is not a perfect procedure. The main reason for this is as follows: the prosthetic pulmonary artery cannot grow with the body, and repair is always necessary very early in life. Accordingly, it is probable that a child who has undergone primary repair will then require follow-up operations in order to fit new grafts.
There can also be difficulties with the base of the truncus (now the new aorta), as the leaflets are not always viable in the longer term. That said, it is at present the procedure of choice for this condition.