Truncus Arteriosus: Symptoms, Types, Causes and Treatment

Truncus arteriosus is a rare but serious congenital heart defect present from birth. In this condition, a single common arterial trunk arises from the heart, instead of the normal separate pulmonary artery and aorta. Understanding the symptoms, different types, causes, and treatment options is vital for patients, families, and healthcare providers. This comprehensive article synthesizes current research to present a detailed, evidence-based overview of truncus arteriosus.

Symptoms of Truncus Arteriosus

When a baby is born with truncus arteriosus, the heart cannot efficiently separate oxygen-rich and oxygen-poor blood. This leads to a mixture of blood going to both the body and lungs, which can cause a range of symptoms soon after birth. Recognizing these symptoms early is crucial, as delays in diagnosis and treatment can lead to life-threatening complications.

Symptom	Description	Timing	Source(s)
Cyanosis	Bluish skin or lips due to low oxygen	Birth/Infancy	1 3 5
Rapid Breathing	Fast or labored breathing	Neonatal period	5 12
Poor Feeding	Difficulty feeding, tiring easily	Early infancy	1 5 12
Heart Murmur	Abnormal heart sounds	Detected early	5 12
Failure to Thrive	Poor weight gain	Progressive	1 12
Congestive Heart Failure	Fluid overload symptoms	Early weeks	1 12 13

Table 1: Key Symptoms

Overview of Symptoms

Truncus arteriosus typically presents within the first days or weeks of life. The body’s inability to deliver enough oxygen-rich blood leads to visible cyanosis—bluish discoloration of the skin, lips, or nail beds. Other hallmark symptoms include rapid or labored breathing and signs of heart failure such as poor feeding and inadequate weight gain 1 3 5 12 13.

Detailed Symptom Breakdown

Cyanosis and Oxygen Issues

• Cyanosis is often the most noticeable sign. Because both oxygenated and deoxygenated blood mix in the single arterial trunk, not enough oxygen reaches body tissues, making babies appear blue 1 5.
• The severity of cyanosis can vary depending on the anatomy, such as the size of the pulmonary arteries and the degree of pulmonary blood flow.

Breathing and Feeding Difficulties

• Infants with truncus arteriosus often breathe rapidly or struggle to breathe, a result of the heart’s inefficiency and extra fluid in the lungs 5 12.
• Feeding can be exhausting, and babies may tire quickly or sweat during feeds, leading to poor overall nutrition and growth 1 12.

Heart Murmur and Heart Failure

• A heart murmur, caused by turbulent blood flow across the abnormal valve and ventricular septal defect (VSD), is commonly detected during a routine newborn exam 5 12.
• Congestive heart failure can develop rapidly, with fluid retention, swelling, and further breathing difficulties 1 12 13.

Progression Without Treatment

• Without intervention, symptoms worsen quickly. Failure to thrive becomes evident, and there is a high risk of early mortality, often within weeks to months 1 12.
• Early detection is critical for improving survival and outcomes 13.

Types of Truncus Arteriosus

Truncus arteriosus is not a single uniform defect. Anatomical variations affect how the pulmonary arteries arise and how blood is distributed, influencing both symptoms and treatment. Over the years, several classification systems have been used, with Collett-Edwards and Van Praagh being the most widely referenced.

Type	Main Feature	Prevalence	Source(s)
Type I	Main pulmonary artery arises from trunk	Most common (50%)	1 2 4 5
Type II	Separate origins of pulmonary arteries	Common (20-26%)	2 4
Type III	One pulmonary artery from trunk, other collateral	Rare (8-10%)	1 3 4
Type IV	Interrupted aortic arch	11-12%	1 2 4

Table 2: Major Types of Truncus Arteriosus

Understanding the Main Types

Type I (Collett-Edwards and Van Praagh)

• Main pulmonary artery arises from the trunk and then divides into right and left pulmonary arteries.
• This is the most common form, representing about half of all cases 1 2 4 5.
• The trunk supplies all systemic, pulmonary, and coronary circulations.

Type II

• Right and left pulmonary arteries arise separately and directly from the posterior aspect of the truncal artery.
• Prevalence is about 20-26% 2 4.
• The main pulmonary trunk is absent.

Type III

• One pulmonary artery originates from the trunk; the other is supplied by a collateral vessel or arises from the aortic arch.
• This is a rarer variant (8–10%) 1 3 4.
• This can result in significant asymmetry in blood flow to the lungs.

Type IV (Sometimes Controversial)

• Characterized by an interrupted aortic arch or severe aortic arch anomaly.
• Accounts for around 11–12% of cases 1 2 4.
• Sometimes considered a separate entity due to its complexity.

Additional Classification Details

• Valve Anatomy: The truncal valve may have variable numbers of cusps—tricuspid, bicuspid, quadricuspid, or rarely unicommissural—and may be thickened or dysplastic, sometimes leading to stenosis or regurgitation 2 15.
• Associated Anomalies: Right aortic arch, coronary artery anomalies, and other congenital heart defects can coexist 2 5 15.
• Rare Variants: Some cases show hypoplastic or absent pulmonary arteries, or special circulatory patterns, such as pulmonary circulation maintained via the ductus arteriosus 3 4 5.

Causes of Truncus Arteriosus

While truncus arteriosus is a structural defect that develops during fetal heart formation, research has uncovered several genetic and environmental factors that contribute to its occurrence. Some causes remain unknown, but genetic studies are providing new insights.

Cause	Description	Prevalence/Notes	Source(s)
22q11.2 Deletion	Chromosomal microdeletion (DiGeorge syndrome)	12–35% of cases	10
Single-Gene Mutations	GATA6, TBX20, NKX2.6, PLXND1, NOTCH1, TMEM260	Rare, familial or sporadic	6 7 8 9 10
Unknown/Idiopathic	No identifiable cause	Many cases	9 10
Environmental Factors	Maternal diabetes, teratogens (unproven in most cases)	Possible, not confirmed	10

Table 3: Main Causes and Genetic Associations

Genetic Causes

22q11.2 Deletion (DiGeorge Syndrome)

• The most common identifiable cause, found in 12–35% of truncus arteriosus cases 10.
• Associated with other features: immune deficiency, cleft palate, facial anomalies.

Single-Gene Mutations

• GATA6: Mutations disrupt cardiac outflow tract development, leading to persistent truncus arteriosus 6 10.
• NKX2.6: Mutations in this transcription factor gene have been linked to common arterial trunk and truncus arteriosus in families 7.
• TBX20: Loss-of-function mutations can result in familial or sporadic truncus arteriosus and other congenital heart diseases 8.
• PLXND1: Mutations affect the semaphorin-plexin signaling pathway, critical for the separation of the outflow tract 9.
• TMEM260: Especially in certain populations (e.g., Japanese), biallelic loss-of-function variants have been identified as a significant cause 10.
• NOTCH1: Rare de novo mutations associated in some cases 10.

Other Genetic and Environmental Factors

• Many cases remain unexplained, but ongoing research is likely to identify more causative genes 9 10.
• Environmental factors are suspected but not well proven; maternal diabetes and teratogenic exposures are possible contributors 10.

Pathophysiology: How the Defect Arises

• In normal development, the heart’s outflow tract separates into the aorta and pulmonary artery.
• In truncus arteriosus, this septation fails, leaving a single arterial trunk 6 7 9.
• The defect is often accompanied by a large ventricular septal defect (VSD), allowing mixing of blood 1 4.

Treatment of Truncus Arteriosus

Prompt surgical intervention is the cornerstone of truncus arteriosus management. Without surgery, survival beyond infancy is rare. Advances in surgical techniques and perioperative care have significantly improved outcomes, though challenges and risks remain.

Treatment	Purpose	Timing/Outcome	Source(s)
Surgical Repair	Separate pulmonary/systemic circulations	Ideally in 1st 1–2 months	1 11 12 13 14 15
Valve/Conduit Replacement	Address conduit/valve dysfunction	As needed, often years later	11 12 15
Medical Management	Stabilize before surgery	Short-term, preoperative	12 14 15
Re-operations	Address complications or growth	20–40% need reoperation	11 12 15

Table 4: Treatment Approaches and Outcomes

Surgical Repair: The Mainstay

• Goal: Separate the pulmonary and systemic circulations by closing the VSD and creating a connection between the right ventricle and pulmonary arteries (often with a conduit) 1 12 13 14.
• Timing: Early surgery, preferably within the first 1–2 months of life, is recommended to prevent irreversible pulmonary vascular damage 1 11 12.
• Technique: Involves closure of the VSD, detachment of pulmonary arteries from the common trunk, and creation of a right ventricle-to-pulmonary artery conduit (can be homograft, synthetic, or containing a valve) 12 14.

Outcomes and Prognosis

• Survival: Surgical mortality has decreased over time—from nearly 50% in earlier eras to under 10% in contemporary series 11 12 13 15.
• Long-term Results: Most survivors enjoy good functional status, but many require reoperations for conduit replacement or repair of the truncal valve 11 12 15.
• Complications: Truncal valve regurgitation, conduit stenosis, and branch pulmonary artery stenosis are common reasons for further interventions 11 15.

Medical Management

• Short-term: Preoperative stabilization with medications for heart failure (diuretics, inotropes) and supportive care (oxygen, nutrition) 12 14.
• Long-term: Not a definitive treatment—surgery is necessary for survival 1 12.

Re-operations and Long-Term Care

• Conduit Replacements: As children grow, or if the conduit degenerates, replacements are needed (often every 5–10 years) 11 12 15.
• Valve Surgery: Some patients require repair or replacement of the truncal valve if it becomes dysfunctional 11 15.
• Follow-up: Lifelong cardiac follow-up is essential to monitor for complications and manage residual defects 11 15.
• Recent Advances: Improved surgical techniques, earlier diagnosis, and better perioperative care have all contributed to better outcomes 11 12 13 15.

Conclusion

Truncus arteriosus is a rare and complex congenital heart defect, but significant advances in diagnosis, genetics, and surgical treatment have transformed outcomes for affected children. Key points include:

• Symptoms: Early signs include cyanosis, rapid breathing, poor feeding, heart murmur, and failure to thrive. Early recognition is critical.
• Types: The anatomical classification (Types I-IV) is based on how the pulmonary arteries originate from the common trunk.
• Causes: Both genetic (notably 22q11.2 deletion and several single-gene mutations) and unknown factors contribute; ongoing gene discovery is improving our understanding.
• Treatment: Early surgical correction is essential for survival. Most patients require ongoing follow-up, and many need additional surgeries as they grow.

In summary:

• Early detection and surgery have dramatically improved survival.
• Lifelong cardiac care is necessary due to the risk of complications and need for reoperations.
• Genetic counseling and testing may be important in some families.

Ongoing research and innovations hold promise for even better outcomes in the future.