Introduction

What is truncus arteriosus?

Truncus arteriosus (TA), also known as common arterial trunk (CAT), is a congenital heart anomaly (a heart defect present at birth). In TA, the large blood vessel (artery) leaving the heart fails to separate into the aorta and the pulmonary artery, and remains as a single trunk. This defect results in altered blood flow to the lungs and the body. As a result, oxygen-rich blood and oxygen-poor blood mix in the common artery^.

Consequently, there is a backflow of oxygen-rich blood to the lungs, and the circulation of oxygen-poor blood throughout the body brings about an inadequate supply of oxygen to the body's cells and organs.² A major impact of this is the return of excess blood to the lungs and an increase in the rate of the heart to supply blood to the rest of the body.³ In addition, the presence of a singular valve instead of the aortic and pulmonary valves presents a difficulty in the flow of blood out of the heart, and in some cases, blood leaks back to the heart due to the thickening and improper closure of valves.3 Truncus arteriosus is mainly characterised by symptoms such as cyanosis and results in various health complications if left unresolved.^2,3

What is cyanosis?

Cyanosis is derived from the word ‘cyan’, which means blue, and simply refers to the abnormal bluish colouration of the skin due to low oxygen levels in the blood (known as hypoxemia).² Cyanosis is a common symptom of truncus arteriosus observed in babies. It presents as a discolouration in several areas of the body, including lips, fingertips, earlobes, and toes, and remains persistent in most cases.²

Other symptoms of truncus arteriosus

• Rapid breathing (tachypnea)
• Shortness of breath³
• Difficulty in breathing
• Clubbing or widening of fingertips due to low oxygen level
• Presence of heart sounds or murmurs¹

Causes of truncus arteriosus

There is no known single cause of truncus arteriosus. However, an interplay of multiple genetic and environmental factors may be responsible for this defect during embryological development..  Almost one-third of all instances of truncus arteriosus are caused by abnormalities in the number of chromosomes, mostly in the form of a deletion.⁴

Occurrence of truncus arteriosus

Truncus arteriosus is a rare heart defect in babies. Recent data from the Centres for Disease Control and Prevention (CDC) suggests there is only one case of truncus arteriosus for every 15,984 live births, with about 230 cases occurring in the United States yearly. Also, it is estimated to account for about 4%of all congenital cardiac anomalies.¹ 

Risk factors of truncus arteriosus

Although there is no single known verifiable cause of truncus arteriosus, several factors have been linked with an increased risk of this congenital condition.

These include:

• High blood sugar during pregnancy: Gestational Diabetes is associated with a high risk of poorly formed heart structures. The chances of having a baby with truncus arteriosus increase if you have diabetes
• Infections such as rubella in pregnancy can negatively affect the normal development of your baby
• Chromosomal abnormalities: Abnormal changes in the structure and number of chromosomes, usually found in DiGeorge syndrome, may play a role in developing TA
• Family history of truncus arteriosus: A baby is likely to have TA if a family member, such as father, mother or siblings, already had it
• Alcohol consumption and smoking during pregnancy: People who smoke or consume alcohol during pregnancy have a high risk of birthing a baby with this heart anomaly

When to seek medical attention

It is important to see a doctor right away if you notice changes in your baby’s health regarding the following:

• Physical growth and development
• Feeding
• Sleeping habits
• Fast-paced breathing
• Blue discolouration on the body
• Difficulty in breathing
• Weak pulse

Diagnosis of truncus arteriosus

It is possible to diagnose TA before a child is born, by an ultrasound scan, which is a device that generates images of the unborn during pregnancy screening tests. A healthcare provider may also carry out a more thorough ultrasound known as a fetal echocardiogram to confirm the diagnosis of TA.^. When a diagnosis is made early and correctly, parents can receive information about the prognosis and treatment choices.⁵

Additionally, post-birth,  the doctor may carry out the following diagnostic procedures:

• Echocardiogram
• Catheterisation of the heart
• Computed tomographic angiography (CTA): A technique used to assess the structures of the heart and its blood vessels
• Magnetic resonance imaging (MRI) of the heart¹

Treatment and management of TA

The first line of treatment involves restoring adequate blood flow to the lungs and body. This applies both during pregnancy and after birth. Medications such as diuretics and prostaglandins are usually given to achieve the following:

• Low blood pressure
• Help their bodies eliminate excess fluid

Surgical correction of TA

Getting medical care early can help improve the outcome of TA, although the condition still carries certain risks and may cause health complications. A surgical procedure is usually done within the first few weeks after the baby is born to prevent permanent damage to the lungs and further complications.⁵

This is involves the following stages:

• Separating the aorta and pulmonary artery from the common trunk
• Creating a connection between the right heart chamber (ventricle) and the pulmonary artery
• Closing the hole in the heart known as a ventricular septal defect
• Banding of the pulmonary artery using a patch⁶

However, some babies cannot undergo the surgical correction of TA because they are weak. Alternative treatments in such cases include:

• Feeding them calorie-rich foods to gain weight
• Medicines to strengthen their heart muscles 
• Medicines to improve the blood-pumping function of the heart⁶

Complications of truncus arteriosus

Over the years, treatment and management methods for TA have worked well. However, if the defect is not corrected, it can lead to:

• Death
• Congestive heart failure (that is, when the heart is unable to pump blood around the body properly)
• Pulmonary hypertension^7,8

FAQs

Can you live with truncus arteriosus without surgery?

No, it is impossible to live a normal life with truncus arteriosus without undergoing surgery due to its life-threatening nature. Surgery is the definitive method to treat truncus arteriosus, and without it, serious complications, including death, are likely to occur.¹⁰

Can truncus arteriosus be avoided or prevented?

The actual cause of truncus arteriosus is unknown; hence, there are no preventive measures to avoid it. But if you decide to get pregnant, you should:

• Avoid smoking or consuming alcohol when you are pregnant
• Consult with your healthcare provider about medicines during pregnancy
• Take approved vaccines for infections such as rubella, as they can affect your baby’s development
• Monitor and control your blood sugar if you have diabetes

What happens after my child undergoes surgery?

After undergoing a corrective surgery for truncus arteriosus, most children go on to live normal lives, and they can also engage in certain physical activities. But it is necessary to confirm the limits of their engagements with your doctor to ensure their safety and well-being.

Summary

Truncus arteriosus is a very rare heart disease present at birth, where the large artery of the heart remains one instead of forming two separate blood vessels, namely the aorta and pulmonary artery. This then gives rise to only one valve and presents a difficulty for blood flow to the lungs and the rest of the body, straining the heart to pump more blood than usual. A major symptom of this condition is persistent cyanosis, a bluish discolouration of the skin due to low oxygen levels in the body. Common areas of the body where this occurs are the earlobes, lips, fingers and toe tips. This defect significantly hinders the lung and heart function, leading to symptoms such as difficulty in breathing and the presence of abnormal heart sounds called murmurs. 

There is a lack of data on how many people are affected by this defect; however, it is estimated that about 1 case of truncus arteriosus occurs in nearly 16,000 live births. Even though the actual cause of the disease remains unknown, genetic factors and disorders in chromosomes have been shown to play a huge role in its occurrence. The chances of a baby being born with this heart condition are higher if there is a family history of it. Certain health issues during pregnancy, like diabetes or infections such as rubella, also increase the risk of TA. Smoking or drinking alcohol in pregnancy can affect the baby's development and lead to poor development of the heart and blood vessels.

Truncus arteriosus is a serious condition that requires medical care to manage symptoms and prevent further health problems, including the risk of death. It can be diagnosed during pregnancy or after the baby is born. Your medical provider would usually determine the best treatment plans for better health outcomes after the diagnostic phase. Medications and a suitable diet can be offered to manage some symptoms of truncus arteriosus, but a surgical procedure is necessary to correct the defect. In recent times, the outcomes of surgery in babies with truncus arteriosus have greatly improved due to better techniques. Nevertheless, long-term monitoring and frequent check-ups are still required.