What is Truncus Arteriosus?
Truncus arteriosus is a congenital heart defect characterized by the improper development of the embryonic heart during fetal growth. In a normal heart, the aorta and pulmonary artery are separate vessels that carry oxygenated and deoxygenated blood, respectively. However, in individuals with truncus arteriosus, there is a single large blood vessel (truncus) that arises from the heart, overriding both ventricles. This leads to a mixing of oxygenated and deoxygenated blood, resulting in inadequate oxygen supply to the body.
Patients with truncus arteriosus often experience symptoms such as cyanosis (bluish discoloration of the skin), difficulty breathing, and poor growth. Surgical intervention is typically necessary to correct the defect, involving the separation of the common truncal vessel into the aorta and pulmonary artery, and the placement of a conduit to redirect blood flow appropriately. Early diagnosis and intervention are crucial for a better prognosis and improved quality of life for individuals with truncus arteriosus.
Types of Truncus Arteriosus
Truncus arteriosus is classified into four types. Each type involves a single trunk vessel exiting the heart. The types of truncus arteriosus are categorized according to how and where the pulmonary arteries (right and left) separate to carry blood to each lung. Surgery differs for each type depending on where the split of the pulmonary arteries occurs.
The four types are:
- Truncus arteriosus type 1 – This is the most common form of truncus arteriosus encompassing 60% of the cases. Both the right and left pulmonary arteries share a common arterial trunk.
- Truncus arteriosus type 2 – The right and left pulmonary arteries branch off separately from the common trunk.
- Truncus arteriosus type 3 – One pulmonary artery branch off the common trunk while the other artery branches off the aorta.
- Truncus arteriosus type 4 – The right and left pulmonary arteries do not branch off the main artery; instead, they branch off the aorta (the section that descends into the chest).
Epidemiology
Truncus arteriosus (TA) manifests with an annual occurrence of seven cases per 100,000 live births. Although it constitutes less than 1% of all congenital heart abnormalities, it represents 4% of critical congenital heart defects.
Pathophysiology of Truncus Arteriosus
In patients with truncus arteriosus (TA), a ventricular septal defect (VSD) allows the mixing of oxygenated and deoxygenated blood before ejection through a common truncal valve to a single great artery, supplying the coronary, pulmonary, and systemic circulations. The common semilunar valve may have 1 to 4 cusps, with tricuspid being most common. Various cardiac and vascular abnormalities may accompany a single arterial trunk, such as interrupted aortic arches, abnormal coronary artery origins, pulmonary artery stenosis, and patent ductus arteriosus. Collett and Edwards and Van Praagh classifications are based on the origins of the pulmonary vascular system, with Van Praagh also considering aortic abnormalities.
During fetal development, high pulmonary vascular resistance (PVR) leads to shunting of mixed blood into the systemic circuit, causing mild cyanosis. As PVR decreases and pulmonary blood flow (PBF) increases, congestive heart failure (CHF) occurs due to pulmonary over-circulation. Without treatment, this can progress to severe irreversible pulmonary vascular disease and death. Worsening pulmonary vascular disease results in increased PVR, leading to worsening cyanosis or a right-to-left shunt (Eisenmenger syndrome). The pathophysiology and clinical picture of TA are influenced by the mixing of pulmonary and systemic blood, PBF, and PVR.
Symptoms of Truncus Arteriosus
The symptoms of this disease generally develop in the initial days of life after the birth, and they include:
- Palpitations.
- Restlessness and irritability.
- Breathlessness, which is also called dyspnea.
- Breathing rapidly, which is also called tachypnea.
- Poor physical growth.
- Sleepiness.
Discolouration of the skin (cyanosis). - Poor feeding.
- Fatigue.
Causes of Truncus Arteriosus
The exact cause of truncus arteriosus is not always known, but it is believed to involve a combination of genetic and environmental factors. Here are some potential contributing factors:
- Genetic Factors: There may be a genetic predisposition to certain congenital heart defects, including truncus arteriosus. Mutations in genes responsible for heart development can be inherited from parents or occur spontaneously.
- Environmental Factors: Exsposure to certain environmental factors during pregnancy may increase the risk of congenital heart defects. These factors can include maternal infections, exposure to certain medications, or maternal health conditions such as diabetes.
- Chromosomal Abnormalities: Truncus arteriosus is sometimes associated with chromosomal abnormalities, such as DiGeorge syndrome, which is caused by a deletion of a portion of chromosome 22. Chromosomal abnormalities can disrupt normal heart development.
- Multifactorial Causes: In many cases, the development of truncus arteriosus is likely influenced by a combination of genetic and environmental factors. The interplay between these factors can vary, making it challenging to pinpoint a single cause.
It’s important to note that while certain risk factors may increase the likelihood of congenital heart defects, in many cases the specific cause remains unknown. Genetic counseling and prenatal care are crucial for identifying and managing potential risk factors, and early detection through ultrasound and other diagnostic tests can aid in planning appropriate medical interventions and treatments.
Risk factors of Truncus Arteriosus
While the exact cause of congenital heart defects, such as truncus arteriosus, is unknown, several factors might increase the risk of a baby being born with a heart condition. These include:
- Viral illness during pregnancy. If a woman contracts rubella (German measles) or another viral illness during early pregnancy, the risk of congenital heart defects in her baby is increased.
- Poorly controlled diabetes during pregnancy. Diabetes that isn’t well-managed can increase the risk of birth defects, including heart defects.
- Certain medications taken during pregnancy. Many medications aren’t recommended for use during pregnancy because of potential risks to the foetus.
- Certain chromosomal disorders. Children with DiGeorge’s syndrome or velocardiofacial syndrome have an increased risk of truncus arteriosus. These conditions are caused by an extra or defective chromosome.
- Smoking during pregnancy. Continuing to smoke while pregnant increases the risk that the baby will be born with a heart defect.
- Alcohol use. Women who drink alcohol during the first trimester of pregnancy increase their risk of having a baby with a congenital heart defect. Men who drink alcohol also contribute to their baby’s congenital heart defect risk.
- Obesity. Women who are obese can have an increased risk of having babies with congenital heart defects
Complications
If not treated, truncus arteriosus may cause complications such as:
- Lung damage
- Heart failure
- Infection of the lining of the heart and heart valves (bacterial endocarditis)
- Poor growth and development
- Diminished ability to function
- Easily tired
- Death
How to diagnosis Truncus Arteriosus?
A prenatal ultrasound may show truncus arteriosus. Your child’s healthcare provider will check your child after birth. They may find signs like a pounding heart and weak pulse. They may hear an abnormal heart sound (heart murmur) when listening to your baby’s chest with a stethoscope. If they do, you may have been referred to a pediatric cardiologist for a diagnosis. This is a healthcare provider with special training to diagnose and treat heart problems in babies and children.
These specialists will also examine your baby. They will listen to their heart and lungs with a stethoscope. Your baby may have other tests, including:
- Pulse oximetry. A probe placed on your child’s finger or toe can measure the oxygen level. Low levels may mean a diagnosis of truncus arteriosus.
- Chest X-ray. This shows the overall size and shape of the heart and lungs. It may show signs typical of truncus arteriosus.
- Electrocardiogram (ECG). An ECG records the electrical activity of the heart. It shows abnormal rhythms, and finds heart muscle stress.
- Echocardiogram (echo). An echo uses sound waves (ultrasound) to make a moving picture of the heart and heart valves. An echo shows the truncus arteriosus.
- Cardiac catheterization. This gives very detailed information about the structures inside the heart. Your baby will be given medicine to relax (sedation). The healthcare provider will put a thin, flexible tube (catheter) into a blood vessel in the groin. It is then moved to the heart. They will take measurements of blood pressure and oxygen in the heart chambers. The pulmonary artery and aorta will also be checked. Contrast dye is also injected to let the provider more clearly see the structures inside the heart.
Treatment of Truncus Arteriosus
The main treatment for truncus arteriosus is surgical repair.
- Surgical Repair: The primary treatment for truncus arteriosus is surgical correction. This typically involves separating the pulmonary arteries from the common trunk and creating a connection between the right ventricle and the pulmonary arteries. Additionally, a conduit or tube graft may be used to redirect blood flow from the right ventricle to the pulmonary arteries.
- Medications: Prior to surgery or as part of the postoperative care, medications may be used to manage symptoms and improve heart function. Medications might include diuretics to reduce fluid buildup and workload on the heart, as well as medications to support heart function.
- Ongoing Monitoring and Follow-up: Individuals with truncus arteriosus require ongoing medical care and monitoring. Regular follow-up visits with a pediatric cardiologist or a congenital heart disease specialist are essential to assess the individual’s heart function, growth, and development.
- Lifestyle Modifications: Individuals with truncus arteriosus may need to make certain lifestyle modifications to manage their condition. This could include dietary adjustments, activity restrictions, and other recommendations based on the specific needs of the patient.
- Heart Transplant: In some severe cases or if complications arise, a heart transplant may be considered. However, heart transplants are typically reserved for cases where other treatments have not been successful, and a suitable donor heart becomes available.
It’s important to note that the specific treatment plan for truncus arteriosus may vary depending on the individual case and the overall health of the patient. The timing of surgical intervention, the choice of surgical techniques, and the postoperative care plan are determined based on the severity of the condition and the individual patient’s circumstances. The goal of treatment is to improve the individual’s quality of life and long-term prognosis.
Prevention
preventing the specific occurrence of truncus arteriosus is challenging. However, there are some general recommendations that can help reduce the risk of congenital heart defects, including truncus arteriosus:
Prenatal Care: Early and regular prenatal care is crucial for monitoring the health of both the mother and the developing fetus. Regular prenatal check-ups can help identify and manage factors that may contribute to congenital heart defects.
Avoiding Teratogenic Substances: Pregnant women should avoid exposure to substances known to increase the risk of birth defects. This includes certain medications, alcohol, tobacco, and recreational drugs.
Managing Chronic Conditions: Women with pre-existing medical conditions such as diabetes should work closely with their healthcare providers to manage these conditions before and during pregnancy.
Genetic Counseling: Couples with a family history of congenital heart defects or other genetic disorders may consider genetic counseling before conception. Genetic counseling can help assess the risk of having a child with a congenital heart defect and provide information about potential genetic factors.
Folic Acid Supplementation: Adequate intake of folic acid before and during early pregnancy is known to reduce the risk of certain congenital heart defects. Women planning to become pregnant are often advised to take a prenatal vitamin containing folic acid.
Early detection through prenatal screening and appropriate medical care during pregnancy can also help manage and address congenital heart defects to improve outcomes for both the mother and the baby.