What is Truncus Arteriosus?
Truncus arteriosus is a rare heart defect that babies may be born with, often leading to a bluish tint to the skin (“cyanosis”) due to a lack of oxygen. It’s marked by a hole in the heart wall (or a “ventricular septal defect”), a single heart valve, and a common outflow tract which leads to mixed oxygen-rich and oxygen-poor blood. This condition causes the blood going out from the heart to have less oxygen than needed. Since the arteries running to the lungs come directly from this tract, the amount of oxygen-poor blood reaching the lungs is determined by their natural resistance. Babies with this condition very likely won’t survive their first year without surgery. However, with surgical treatment and careful ongoing monitoring by a heart doctor, the outlook is generally positive.
The main feature of truncus arteriosus is that the heart doesn’t have a typical artery-based separator (seen in 21% of cases). Most commonly though, 50% of cases have a partially formed separator. The heart’s half-moon-like valve might have 1 to 4 flaps, usually 3. This condition might also be linked with several heart, aortic, and pulmonary abnormalities. The aorta could be located on the right, interrupted, or underdeveloped, possibly with a narrowing (“coarctation”) of the aorta itself. The point of origin for the coronary arteries is typically irregular and doesn’t follow one specific pattern. The pulmonary arteries (that deliver blood to the lungs) may be unusual, ranging from a single small vessel to branching out from various places within the aortic root or a typically temporary extra vessel in newborns (“patent ductus arteriosus”). Other heart defects might exist along with truncus arteriosus like defects in the wall separating the top two heart chambers, irregular subclavian artery, a persistent left superior vena cava draining into a large vein on the heart’s back surface, and patent ductus arteriosus.
Over time, researchers created different ways to categorize truncus arteriosus. Both Collett and Edwards and Van Praagh created separate systems to classify the various forms of this condition. Collett and Edwards mainly focused on where the pulmonary blood vessels originated, while Van Praagh threw a wider net and also included aortic abnormalities.
Such categorizations help doctors tailor the treatment approach and educate families about the complexity of this congenital heart defect. At the end of the day, the goal remains saving the life of the infant and managing the condition in the long-term for a quality life.
What Causes Truncus Arteriosus?
Truncus arteriosus is a heart condition that happens if certain processes during the development of a baby in the womb fail to happen properly. Normally, a blood vessel structure in the heart separates into two pathways – one leading to the aorta, the other to the pulmonary artery. However, in the case of truncus arteriosus, this separation does not occur. This also prevents the formation of two separate heart valves – the aortic and pulmonary valves – and instead results in a single, shared valve.
While the exact reasons behind why this happens aren’t fully understood, it’s often found in people with a genetic condition known as 22q11.2 microdeletion syndrome, or Di George syndrome. This is seen in 12% to 35% of patients with truncus arteriosus. Additionally, abnormalities in certain parts of the heart during its formation in the womb are also thought to play a significant role.
Risk Factors and Frequency for Truncus Arteriosus
Truncus arteriosus is a heart condition seen in about 7 out of every 100,000 newborns. Although it makes up less than 1% of all heart issues present from birth, truncus arteriosus represents around 4% of the most serious of these defects.
Signs and Symptoms of Truncus Arteriosus
The symptoms a person with truncus arteriosus experiences are largely determined by several factors, including changes in blood flow to the lungs, abnormalities in the semilunar valves and issues with the aortic arch. Shortly after birth, the baby may show signs of breathing difficulties or a blue skin color, prompting further medical examination. A screen for critical congenital heart defects performed a few days after birth might expose mild to moderate desaturation. Infants who weren’t screened may display symptoms of heart failure due to increased pulmonary blood flow between the first 2 weeks of their life. These symptoms include trouble feeding, failure to thrive, sluggishness, rapid breathing, chest retractions, grunting, nostrils flaring up, increased heart rate, enlarged liver, and persistent blueness despite oxygen therapy.
Many with truncus arteriosus would have an antenatal history, with abnormal heart markers showing up on fetal ultrasound or echocardiography. There may also be a family history of heart disease or associated genetic syndromes. Any prior heart-related procedures or surgeries are also taken into account, and it’s important to check whether the child has any developmental or cognitive delays due to their heart condition.
During a medical examination, doctors may note signs of respiratory distress. An inspection of the neck could reveal swollen jugular veins, while an examination of the hands and feet might display clubbing and a bluish tint. The abdomen might be enlarged due to the liver’s swelling. If truncus arteriosus is part of a syndrome, other defects such as facial aberrations and muscoloskeletal problems might be noted.
The heart assessment itself could reveal a loud, rough heartbeat, a loud second heart sound, and a heartbeat during diastole if the truncal valve is leaking. The pulse in the peripheral areas might be excessively strong due to excess blood flowing into the pulmonary arteries. An increased amount of blood flowing to the lungs during diastole may cause higher pulse pressures. Issues with the heart valves such as regurgitation or narrowing are common. Specifically, valve leakage – reported in half of the patients – may exacerbate heart failure symptoms. Insufficiency in the aortic arch or coarctation, observed in about 10% of patients with truncus arteriosus, can lead to cardiovascular collapse, which may present as a medical emergency or, sadly, death.
Testing for Truncus Arteriosus
Baby heart check-ups, or fetal echocardiography, are usually done around the 22nd week of pregnancy but can be done as early as the 13th week. This type of ultrasound check-up is used to check if there’s only one main artery leading out of the heart, if there’s a significant hole between the heart’s main chambers (VSD), or if the main lung artery or its branches originate from the truncal root instead of the normal pulmonary valve. A genetic test is usually also done during pregnancy because this condition is often linked with a specific genetic issue (the 22q11.2 deletion). Knowing about these heart problems before birth allows for the baby to be born in a hospital that can immediately start necessary treatments.
After the baby is born, a test called a transthoracic echocardiogram is done to get a detailed look at the heart’s structure. Sometimes, more imaging tests, like a cardiac magnetic resonance imaging (MRI) or computed tomography angiography (CTA), are used to look especially at the heart arteries and the branches of the lung arteries. This can be important, especially in a specific kind of truncus arteriosus (Van Praagh Type A3), to determine if the aorta, the main artery leading out of the heart, is interrupted or narrowed (coarctation), which would affect how the doctors plan for surgery. After surgery, CTA can be used to check the lung homograft and lung artery structure for any recurrence or leftover narrowing (stenosis). Cardiac catheterization, a more invasive and targeted method, is usually only done for direct procedures like using a balloon or stent to open up narrowed lung arteries between surgeries.
Treatment Options for Truncus Arteriosus
When a patient is first diagnosed with a heart condition, the initial focus of treatment is to help the patient become stable and ensure that blood is flowing evenly around the body. This usually includes the interruption of the aortic arch, a part of the heart’s blood vessel, which is crucial for this balance. Healthcare providers typically monitor and treat these patients in a neonatal intensive care unit (NICU) or a cardiac intensive care unit (CICU), depending on the age and specific heart condition of the patient.
Treatment for congestive heart failure, specifically in the lungs, often involves medications known as loop and thiazide diuretics, which help maintain a proper balance of fluid in the body. These medicines aim to reduce the amount of fluid in your body to lower the pressure in your heart and help it pump blood more easily. They also play a role in improving failures in the right and left ventricles, which are the lower chambers of the heart.
If a patient is having difficulty breathing, additional support may be needed. This can include positive-pressure devices that assist with respiration, such as continuous positive airway pressure (CPAP) machines, or, in more severe cases, endotracheal intubation, which involves inserting a tube into the windpipe through the mouth or nose to allow for mechanical ventilation. However, supplementary oxygen should generally be avoided as it could worsen the condition by causing overcirculation of blood through the lungs. Additionally, addressing irregularities in the body’s metabolism, electrolytes, and glucose levels, as well as treating any anemia, is essential to avoid further heart complications.
For patients with a particular kind of heart anomaly known as an aortic arch anomaly, an infusion of a hormone-like substance called prostaglandins could be used as part of the treatment. This helps to keep the duct connecting the aorta and pulmonary artery open, which is crucial to ensure sufficient blood flow to the body.
A definite surgical correction is usually carried out within the first month of life. This surgery involves a single-stage repair that is specifically used for a rare heart defect called truncus arteriosus, provided there are no other complications related to the heart valve known as the truncal valve or the aortic arch. The procedure involves rerouting the pulmonary artery from the truncus to the right ventricle, creating a conduit-like structure to facilitate the outflow of blood from the right ventricle to the lungs, and closing the ventricular septal defect (a hole in the wall that separates the heart’s lower chambers).
In some cases, primary palliation with pulmonary arterial banding and delayed surgical repair may be required to allow the baby to grow. However, this two-stage method is not generally recommended because it comes with higher risks and a possibility of higher mortality rates.
After the operation, the patient will be closely monitored in the CICU. The healthcare providers will watch for many important health factors during this postoperative period, including balancing fluids and electrolytes, ensuring comfort, and controlling pain. They will also manage the patient’s breathing, heart health, kidney function, and neurological status, while also preventing infection and addressing nutritional needs. Monitoring methods in the CICU may be noninvasive, like using a device to measure heart rate, breathing rate, and oxygen saturation. However, in some cases, invasive techniques, such as inserting catheters into the heart or blood vessels, may be necessary to collect detailed information about the heart and lungs.
What else can Truncus Arteriosus be?
Thanks to the latest technology, over 90% of truncus arteriosus cases can now be diagnosed before birth. However, it may be wrongly identified as pulmonary atresia with a VSD if certain structures and aortopulmonary collaterals can’t be correctly spotted during the prenatal ultrasound scan.
Other conditions that could present a similar single outflow tract of the heart on an scan, and therefore might be confused with truncus arteriosus are:
- Double outlet right ventricle with both pulmonary and aortic atresia.
What to expect with Truncus Arteriosus
If the advised one-step repair surgery isn’t carried out, patients typically don’t survive past two months of age. For patients who don’t have the surgery, the chances of living past their first birthday are fewer than 20%. If left untreated until they reach four years old, the damage to the blood vessels in the lungs gets so bad that surgery can’t help, and these patients often don’t live past their teenage years due to heart failure.
On a brighter note, after the one-step repair, patients have a higher chance of living past 20 years, with over 80% making it. However, these patients often need more surgeries later in life, so it’s essential that they have regular medical check-ups.
Possible Complications When Diagnosed with Truncus Arteriosus
Truncus arteriosus is a health condition that can lead to complications before surgery. Often, patients with this condition may also have Di George syndrome’s 22q11.2 deletion – a genetic disorder. These patients may experience neonatal seizures caused by a drop in calcium (hypocalcemia) due to under-developed parathyroid glands. Also, decreased thymus function (thymic hypoplasia) in these patients may make them prone to viral, bacterial, and fungal infections.
After the operation, patients may experience complications within the first two days, including pulmonary hypertensive crisis and low cardiac output syndrome – conditions that can affect blood flow and oxygen distribution. To avoid pulmonary hypertensive crisis, patients should be handled carefully and not moved a lot immediately after the operation. They may also experience right bundle branch block and heart rhythm issues such as fast, irregular heartbeats (supraventricular tachycardia). Complications needing immediate corrective surgery include internal chest bleeding (mediastinal bleeding), fluid collection around the lungs (pleural effusion), air trapped in the chest cavity (pneumothorax), and pressure buildup around the heart due to fluid (cardiac tamponade).
Common complications following any surgery include seizures, other nervous system injuries, prolonged bleeding times, and kidney failure. As patients age, they might require additional procedures as they may outgrow their right ventricular pulmonary artery conduit, or the truncal valve insufficiency might worsen. By the 10th postoperative year, about 75% of patients may need a revisit to surgery, usually for procedures such as right ventricle outflow tract reconstruction and valve repair or replacement.
Post-Surgery Complications:
- Pulmonary hypertensive crisis
- Low cardiac output syndrome
- Right bundle branch block and supraventricular tachycardia
- Mediastinal bleeding, pleural effusion, and pneumothorax
- Cardiac tamponade
- Seizures and other nervous system injuries
- Prolonged bleeding times
- Kidney failure
Preventing Truncus Arteriosus
If your family has a member with a condition called truncus arteriosus, it’s recommended to seek advice from a genetic counselor. They can provide detailed information about the role of genetics in this condition, which can help in family planning. Genetic counselors can identify those in your family who may be at risk, and can arrange for tests during pregnancy to find out whether future babies might also be affected by this condition.
Anyone with truncus arteriosus should have regular check-ups with a doctor who specializes in heart conditions from birth. These check-ups should continue throughout their entire life. It’s important that both the patient and their doctor monitor any changes in how well the patient can exercise, whether they’re experiencing any strange heart rhythms, fainting episodes, swelling or shortness of breath. Additionally, they need to pay attention to a specific kind of heart sound that only a doctor can hear (a diastolic murmur), which might signal a heart valve not working properly. You should also look out for signs of heart failure, such as buildup of fluid in the lungs and swelling in the limbs. Certain physical signs like a swollen liver or a noticeable pulse in the neck might mean the pressure in the right side of the heart is too high.
To confirm these observations and monitor the condition, regular heart ultrasound scans (echocardiograms) are recommended. These scans assess the connection between the right side of the heart and the blood vessels going to the lungs, how well both sides of the heart are working, and whether the heart valve is too narrow or leaking. If the patient’s ability to exercise decreases, or if they experience symptoms of heart failure or irregular heartbeats, they will need more frequent checks including heart tracings (electrocardiograms), heart rate monitors, stress tests, and heart scans. More detailed imaging like a cardiac MRI or CT scan may also be needed to identify any blockages, heart valve leakage, evaluate the overall heart function and check for heart muscle scarring.
Adults with heart conditions from birth, like truncus arteriosus, might also face mental health issues. The severity of these issues often depends on how badly the heart condition affects the patient’s daily life. Specialists, including doctors and other healthcare providers, can work together to improve these patients’ quality of life – something that clinicians in heart disease from childhood to adulthood are actively supporting.
