What is truncus arteriosus and why does it cause heart failure? 

Truncus arteriosus is a congenital (present at birth) heart condition where only one main blood vessel leaves the heart instead of the usual two. Before birth, the truncus arteriosus normally splits into two separate vessels– the pulmonary, which carries oxygen-poor blood to the lungs, and the aorta, which carries oxygen-rich blood to the rest of the body. However, in truncus arteriosus, the walls between the lower heart chambers (ventricles) may fail to close completely, a condition known as a ventricular septal defect.. This means that there is a fusion of the systemic and pulmonary circulation, and oxygen-deficient and oxygen-rich blood may mix, reducing the overall oxygen availability for the rest of the organs.¹ 

In some cases, defects in the valves can cause blood flow backwards into the ventricles, further disrupting circulation.¹ 

The exact cause of truncus arteriosus is unknown, but research suggests it may be linked to both genetic and environmental factors. Babies may be at a higher risk if they were exposed to certain factors during pregnancy, including viral infections, alcohol, or specific medications taken by the mother. Genetic mutations that result in abnormal chromosome numbers may also increase the risk.¹ In the United States, approximately 230 babies are born with this condition each year. Truncus arteriosus is often associated with genetic disorders and can lead to a range of complications caused by abnormal blood flow, these will be explored in later sections.²

How does truncus arteriosus lead to heart failure? 

Heart failure is the most prominent symptom of truncus arteriosus and occurs due to abnormal mixing and direction of blood flow. If a patient has a defect or leakage in the valves of the blood vessels, blood can pool in the heart chambers. As a result, early symptoms of heart failure, such as irregular heart rhythm, may occur.³ This leads to pulmonary over-circulation and causes both the right and left ventricles to become overloaded. Based on Starling's law, an increase in preload (the volume of blood entering the left ventricle) stimulates a stronger contraction of the heart muscle to pump blood out more forcefully.⁴ The heart must work harder to pump blood to both the lungs and the rest of the body through a single vessel. Over time, this increased workload may lead to progressive ventricular failure and dysfunction.⁵

Infants with this condition often experience sepsis, which is a leading cause of death among those with heart failure. When the heart cannot pump enough blood to the organs, the body’s immune response to infection becomes weaker, increasing the risk of sepsis. As a result, the body cannot respond effectively to infections, which may lead to progressive organ damage if septic shock develops.⁵ 

Furthermore, having a single large arterial vessel causes the lungs to receive an increased volume of blood from the heart. In response, the heart pumps harder to deliver blood to the rest of the body. However, because the blood is mixed, the organs receive less oxygen. This forces the heart to work harder, creating a vicious cycle of strain caused by hemodynamic disturbances.⁶

What are the signs and symptoms of heart failure in truncus arteriosus? 

Since mixed circulation prevents enough oxygen from reaching the body, patients often develop a bluish skin colour (cyanosis), particularly visible on the lips and skin. A lack of oxygen to meet the body’s needs can also cause exercise intolerance. Patients may experience fatigue and shortness of breath during physical activity. Poor feeding is another common symptom. Furthermore, as a response to the abnormal blood flow in truncus arteriosus, the heart must work harder to pump blood, often resulting in a faster heart rate (tachycardia). If left untreated, the condition may lead to progressive heart failure, pulmonary hypertension (high blood pressure), and long-term complications like arrhythmias (abnormal heart rhythms).^7,8

How is truncus arteriosus diagnosed?

How does echocardiography help in diagnosis?

To diagnose truncus arteriosus in infants, a non-invasive prenatal ultrasound can be performed during pregnancy to detect any defects in the structure of the heart. If the condition is suspected, echocardiography can be performed to assess the heart’s structure and function in greater detail before confirming a diagnosis.⁷ It helps doctors examine the heart’s walls, valves and chambers to determine whether they are structurally normal and working properly, using both imaging and sound waves to assess blood flow. In addition to congenital heart conditions, this type of ultrasound is also used to diagnose cardiomyopathy, endocarditis and other conditions that damage the heart.⁹

What is the role of cardiac catheterisation?

Cardiac catheterisation is a detailed assessment used to examine the heart’s internal structures. After sedation, a thin tube (catheter) is inserted into a blood vessel, usually in the groin or arm, and guided to the heart to measure the oxygen levels and blood pressure. Patients with truncus arteriosus often have high blood pressure in the lungs, known as pulmonary hypertension. To assess structures such as the aorta and pulmonary artery, a contrast dye is injected to provide clearer visualisation. This diagnostic method can detect features of the condition, such as a large single arterial trunk or a ventricular septal defect.¹⁰

When are MRI and CT imaging used?

MRI and CT imaging offer a more detailed view of the heart’s anatomy using 3D imaging techniques. They are particularly useful for diagnosing complex cases like truncus arteriosus, where echocardiography alone may not provide sufficient detail. CT scans allow clinicians to see defects in the blood vessels in greater detail. MRI helps assess abnormalities in the heart tissue and track blood flow in and out of the heart. CT scans are often preferred for diagnosing congenital heart diseases in infants and young children, as they require minimal sedation and use a low dose of ionising radiation. In addition, they produce high-quality images in a short period of time.¹¹

Can laboratory tests confirm the diagnosis?

BNP (B-type natriuretic peptide) and its precursor, NT-proBNP, are biomarkers that can be used to help diagnose patients with truncus arteriosus, a type of congenital heart disease. BNP is released by the ventricular heart muscle in response to volume or pressure overload, which may occur due to a truncus arteriosus. This release is a response to stress on the heart walls. Patients with heart failure will have higher BNP levels, and these levels increase as the condition progresses. Thus, BNP levels have proven to be a valuable biomarker for identifying ventricular dysfunction in diagnostic settings. Recent studies have shown that BNP is expressed in both the pediatric and adult populations, with chronic heart failure associated with congenital heart disease. BNP levels can also help distinguish whether respiratory distress is caused by lung (pulmonary) or heart (cardiac) conditions.¹²

What are the treatment options for truncus arteriosus-related heart failure?

How do diuretics help manage symptoms? 

Diuretics, also known as water pills, are often given to patients with truncus arteriosus to help manage fluid buildup. Diuretics like furosemide reduce water reabsorption in the kidney tubules and increase urine excretion. This decreases the volume of blood returning to the heart after circulating through the body. This helps reduce fluid overload, a common symptom of heart failure. Diuretics are often given to infants with truncus arteriosus heart failure before undergoing corrective surgery.¹³ 

What is the role of ACE Inhibitors in treatment? 

ACE inhibitors work by blocking the action of ACE, which converts angiotensin I to angiotensin II, a substance that causes vasoconstriction (narrowing of blood vessels due to muscle contraction). This leads to vasodilation, which lowers systemic resistance by widening the vessels. A reduced afterload means the heart does not have to work as hard to pump blood, easing its workload. Ventricular function and cardiac output can be improved to manage the symptoms of heart failure.¹⁴

When are beta-blockers used? 

Beta-blockers prevent the body’s natural neurotransmitters, adrenaline and noradrenaline, from binding to beta-adrenoreceptors, particularly the B1 subtype, which is found in high amounts in the heart muscle.¹⁵ This inhibition affects both heart rate and the strength of contraction, which reduces the heart’s workload. Blocking the B1-adrenoreceptor also reduces the release of renin, a hormone involved in blood pressure control. Overall, blood pressure will fall. If the B2-adrenoreceptor subtype is blocked instead, then there will be vasodilation, which also reduces blood pressure and the heart’s workload.¹⁶ Common beta-blockers include atenolol, metoprolol and propranolol, each targeting different beta-adrenoreceptor subtypes.¹⁵

Why are inotropes used temporarily? 

Inotropes are short-term medications used to stabilise patients with heart failure before other treatments, such as surgery, are provided. They work by increasing the cardiac output of the heart, as there is a low cardiac output associated with heart failure. They achieve this by increasing the strength of the heart muscle’s contractions (contractility). However, they are only effective temporarily. They can increase the heart’s oxygen demand and may cause arrhythmias, potentially worsening heart failure over time. Common inotropes administered to patients with acute heart failure include dobutamine, which is a beta-adrenoreceptor agonist that increases cardiac contractility and output. Another example would be milrinone, a drug that increases calcium entry into heart and blood vessel muscle cells. This helps strengthen heart contractions and widen blood vessels at the same time. This is beneficial to increase cardiac output and reduce vascular resistance.¹⁷

What does surgical repair involve?

Corrective surgery reconstructs the circulatory system to separate the pulmonary and systemic circulation. This involves dividing the large vessel into the pulmonary artery and the aorta, and patching any ventricular septal defect to separate the left and right ventricles. If there is a defect in the truncal valve that regulates the blood flow out of the heart through the single vessel, truncal valve repair is done. The timing of the surgery depends on the severity of the defect and the age at diagnosis, but it is usually performed as early as possible due to the life-threatening nature of truncus arteriosus. The surgical technique used will depend on the defect in the heart structure of the patient. Surgical correction can significantly improve the quality of life and reduce mortality in young patients.¹⁸

What long-term care is needed after surgery or treatment?

Equally important as the management strategies of truncus arteriosus, long-term follow-up is necessary to monitor patients’ symptoms, as well as their response to treatment. For instance, although surgery addresses the root cause of heart failure in truncus arteriosus, follow-up procedures may still be needed.. These can include conduit or valve replacements due to progressive valve dysfunction, which often requires intervention over time.¹⁸ A study showed a median follow-up duration of 23.4 years for patients who underwent truncus arteriosus repair.¹⁹ Furthermore, routine cardiac monitoring and regular check-ups with a cardiologist are essential to assess how well medications are working and to identify complications such as pulmonary hypertension or ventricular dysfunction. These issues may arise from long-term changes in the heart caused by factors such as medication use. This ongoing monitoring includes echocardiograms and clinical evaluations at regular intervals, to assess the heart’s structure and function. This helps ensure timely intervention and prevents any worsening of heart function. Medication plans can be adjusted based on the patient’s needs and response to current treatment.⁷ Together, these steps help improve the patient’s long-term quality of life. 

Summary

Heart failure is a major complication associated with truncus arteriosus, because cardiac output is reduced, restricting the heart’s ability to pump blood effectively around the body. Effective management strategies, including pharmacological interventions and surgical repair, such as truncal valve repair, are important for stabilising the patient by improving cardiac output and restoring heart structure for normal function. Long-term follow-up is also important to monitor for complications such as pulmonary hypertension and ventricular dysfunction, which can occur in patients with this congenital heart disease after treatment. This allows clinicians to modify treatment plans and achieve early intervention to prevent the patient’s condition from worsening. Ongoing advancements in surgical techniques, pharmacological agents, and therapies are necessary to ensure more effective management of heart failure.