Pediatric “5 Ts” (Cyanotic CHD) #1: Truncus Arteriosus — “One Vessel”

1. Overview

Truncus arteriosus is a congenital conotruncal heart defect characterized by a single arterial trunk arising from the ventricular mass and supplying the systemic, pulmonary, and coronary circulations. Instead of separate aortic and pulmonary roots, there is one common arterial root guarded by a single truncal valve. The simplest conceptual description is therefore “one vessel.”

A large ventricular septal defect (VSD) is almost invariably present beneath the truncal root. Blood from both ventricles enters the common arterial trunk, creating substantial admixture before being distributed to the systemic and pulmonary vascular beds.

The physiology is determined not only by admixture but also by how this common ventricular output is divided between the pulmonary and systemic circulations. As pulmonary vascular resistance (PVR) falls after birth, pulmonary blood flow increases rapidly, producing the characteristic combination of cyanosis, pulmonary overcirculation, increased pulmonary venous return, left ventricular volume overload, and congestive heart failure. Because leaving the pulmonary vascular bed exposed to unrestricted high flow and pressure promotes early pulmonary vascular injury, repair during the neonatal period or early infancy has become the predominant strategy, particularly in symptomatic patients [1,2].

2. Surgical Anatomy: One Common Arterial Outlet

Normally, the ventricular outflow tracts are separated into an aorta connected predominantly to the left ventricle and a pulmonary artery connected to the right ventricle. In truncus arteriosus, this separation fails, leaving a single common arterial outlet.

The truncal root supplies three essential circulations:

• the coronary arteries,
• the systemic arterial circulation, and
• the pulmonary arteries.

The pulmonary arteries may arise from a short common pulmonary segment or separately from the posterior or lateral aspect of the truncus. The exact configuration is important surgically because the pulmonary arteries must ultimately be separated from the systemic arterial pathway and incorporated into the reconstructed right ventricular outflow tract.

The truncal root remains as the systemic outflow after repair. Therefore, the relationships among the truncal valve, coronary ostia, pulmonary artery origins, and VSD are central to operative planning.

3. The Ventricular Septal Defect

The VSD in truncus arteriosus is typically large and nonrestrictive and is located beneath the common truncal root, often in association with malalignment of the outlet septal structures. Consequently, right and left ventricular systolic pressures are nearly equal, and both ventricles eject into the common arterial trunk.

From a surgical perspective, this VSD is more than simply a septal communication. During complete repair, the VSD patch is constructed to commit the left ventricle to the truncal root, which subsequently functions as the systemic outflow tract. The right ventricle is excluded from this pathway and connected separately to the pulmonary arteries.

Thus, the geometry of the VSD and its relationship to the truncal valve determine the configuration of the reconstructed left ventricular outflow tract.

4. Complete Admixture Physiology

Systemic venous blood enters the right heart, while oxygenated pulmonary venous blood returns to the left heart. Because of the large VSD and single arterial outlet, the two ventricular outputs mix extensively before entering the common trunk.

The systemic and pulmonary circulations therefore receive blood of similar oxygen content from the same arterial source.

This creates the fundamental admixture physiology of truncus arteriosus. However, systemic oxygen saturation depends not only on mixing but also on the ratio of pulmonary to systemic blood flow. Increased pulmonary flow returns more oxygenated blood to the left heart, which may raise the oxygen content of the mixed truncal output.

Consequently, a relatively satisfactory arterial oxygen saturation does not necessarily indicate a satisfactory circulation. An infant may have only mild cyanosis while simultaneously developing severe pulmonary overcirculation and compromised effective systemic blood flow.

This distinction is critical: oxygen saturation and systemic perfusion are not interchangeable measures of physiologic stability in truncus arteriosus.

5. The Postnatal Fall in PVR

Immediately after birth, PVR remains relatively high. During this period, the distribution of common ventricular output between the pulmonary and systemic circulations may remain relatively balanced.

Over the following days and weeks, normal postnatal pulmonary vascular adaptation causes PVR to fall. Because both the systemic and pulmonary circulations arise from the same common arterial source, decreasing pulmonary resistance preferentially directs increasing amounts of blood toward the pulmonary vascular bed.

The fundamental sequence is:

↓ PVR → ↑ pulmonary blood flow (Qp) → pulmonary overcirculation

As Qp rises, pulmonary venous return to the left atrium and left ventricle increases. The left ventricle therefore becomes progressively volume loaded.

This produces the second physiologic sequence:

↑ Qp → ↑ pulmonary venous return → ↑ LA/LV preload → LV volume overload → pulmonary congestion

The unrestricted pulmonary circulation is also exposed to high pressure. Prolonged exposure to excessive pulmonary flow and pressure can produce pulmonary vascular remodeling and an enhanced pulmonary vasoconstrictor response, increasing the risk of perioperative pulmonary hypertensive instability if repair is substantially delayed [1].

6. Cyanosis Plus Heart Failure

Truncus arteriosus differs physiologically from cyanotic lesions characterized by severe limitation of pulmonary blood flow. In most patients, pulmonary blood flow is not inadequate; it becomes excessive as PVR falls.

The clinical phenotype therefore combines two processes.

First, systemic arterial desaturation results from admixture of systemic and pulmonary venous blood within the common ventricular–truncal pathway. Second, progressive pulmonary runoff produces excessive pulmonary blood flow, increased pulmonary venous return, ventricular volume loading, and heart failure.

As pulmonary overcirculation progresses, patients commonly develop tachypnea, increased work of breathing, feeding difficulty, diaphoresis, poor weight gain, hepatomegaly, and pulmonary congestion. Cyanosis may remain only moderate despite significant hemodynamic deterioration.

The major physiologic problem is therefore not simply low oxygen saturation. It is an unbalanced parallel circulation in which progressively more common ventricular output is directed toward the low-resistance pulmonary vascular bed.

7. Truncal Valve Anatomy

The truncal valve is the single semilunar valve governing the entire ventricular output. Valve morphology is variable and may be bicuspid, tricuspid, or quadricuspid. Either regurgitation or stenosis may complicate the lesion.

Truncal valve regurgitation is particularly important because it adds further ventricular volume loading to an already volume-overloaded circulation. Moderate or greater preoperative truncal valve insufficiency has been associated with increased mortality and a greater likelihood of subsequent truncal valve intervention [3].

When significant valve dysfunction requires intervention during primary repair, valve repair is generally favored over replacement when technically feasible, particularly in neonates [1,4]. However, long-term durability remains an important limitation. In a 180-patient series, concomitant truncal valve repair itself was not associated with increased mortality, but patients requiring truncal valve surgery experienced a substantial subsequent reoperation burden [3].

Therefore, preoperative assessment should define leaflet number, commissural arrangement, annular dimensions, mechanism and severity of regurgitation, stenosis, and the relationship of the coronary ostia to the valve and planned repair.

8. Other Anatomical Features That Modify Surgical Risk

Several associated anatomical abnormalities substantially influence operative complexity.

Coronary artery anatomy is especially important because the coronary arteries originate from the truncal root and may have unusual ostial positions or courses. Coronary anomalies have been associated with late mortality after repair and must be identified before and during reconstruction [2].

Interrupted aortic arch may coexist with truncus arteriosus and requires simultaneous reconstruction of the systemic outflow. Although historically considered a major risk factor, contemporary surgical series demonstrate that excellent neonatal outcomes can be achieved when arch reconstruction is incorporated into complete repair [4].

Pulmonary artery anatomy affects both the primary reconstruction and subsequent reintervention risk. Hypoplastic, stenotic, or otherwise unfavorable branch pulmonary arteries may require pulmonary arterioplasty at initial repair and may predispose to later catheter-based or surgical intervention.

These anatomical factors explain why two neonates with apparently similar “one-vessel” physiology may have markedly different operative complexity.

9. Clinical Evaluation

Echocardiography usually establishes the diagnosis and provides the principal information required for surgical planning. Evaluation should define the common truncal root and valve, VSD anatomy, ventricular size and function, pulmonary artery origins and dimensions, truncal valve function, and aortic arch anatomy.

Particular attention should be directed toward features that alter operative strategy: significant truncal valve regurgitation or stenosis, coronary anomalies, interrupted aortic arch, and abnormal pulmonary artery configuration.

Cross-sectional imaging or catheterization may be useful when coronary, branch pulmonary artery, arch, or pulmonary vascular anatomy cannot be adequately characterized noninvasively.

Associated extracardiac and genetic abnormalities should also be recognized because they may influence airway management, calcium homeostasis, infection risk, nutrition, and postoperative recovery.

10. Timing and Preoperative Management

For most symptomatic neonates and young infants, prompt complete repair is favored rather than waiting for somatic growth [1,2]. The rationale is physiologic: as PVR decreases, pulmonary overcirculation progressively worsens, while continued exposure of the pulmonary vascular bed to excessive flow and pressure may increase pulmonary vascular reactivity.

Preoperative management should therefore support systemic perfusion without unnecessarily promoting pulmonary runoff. Diuretics may be required for pulmonary congestion, and respiratory and nutritional support should be individualized.

Supplemental oxygen should be administered for a clinical indication rather than simply to normalize arterial saturation. Excessive pulmonary vasodilation can further reduce PVR, increase Qp, and aggravate systemic-to-pulmonary flow imbalance.

The therapeutic target is balanced systemic and pulmonary perfusion, not normalization of oxygen saturation alone.

11. Complete Surgical Repair

Complete repair converts the original common circulation into separate systemic and pulmonary pathways.

VSD Closure and LV-to-Truncus Commitment

A patch is placed across the VSD to direct left ventricular output into the truncal root. The truncal root and truncal valve therefore become the reconstructed systemic outflow and functional aortic root.

Separation of the Pulmonary Arteries

The pulmonary artery bifurcation or individual pulmonary artery origins are detached from the common arterial trunk. The resulting defect in the truncal wall is reconstructed to establish an unobstructed systemic arterial pathway.

RV-to-PA Reconstruction

Continuity is then created between the right ventricle and pulmonary arteries. A valved RV–PA conduit is commonly used; a cryopreserved pulmonary allograft represents a well-established option [1]. Conduit selection and size depend on patient anatomy, body size, institutional practice, and available materials.

Additional procedures may include truncal valvuloplasty, branch pulmonary artery reconstruction, or aortic arch reconstruction [1,4].

The operation can therefore be understood conceptually as the transformation of “one vessel” into two independent ventricular outflow pathways.

12. Primary Versus Staged Repair

Primary complete repair remains the predominant approach in many congenital heart programs. However, surgical strategy is not completely uniform.

A Japanese national database study of 286 patients demonstrated substantial use of a staged strategy incorporating bilateral pulmonary artery banding before definitive repair. Operative mortality did not differ significantly between primary and staged approaches in that cohort, although patient selection and institutional strategy strongly influence such comparisons [5].

Accordingly, staged palliation can be considered in selected circumstances, but the available evidence does not establish it as universally superior to early primary repair. The appropriate strategy depends on neonatal condition, weight, associated anatomy, truncal valve function, pulmonary artery anatomy, and institutional experience.

13. Postoperative Considerations

After complete repair, the preoperative problem of pulmonary overcirculation has been eliminated by separation of the systemic and pulmonary circulations. Postoperative assessment instead focuses on the reconstructed pathways.

Important concerns include RV–PA conduit obstruction or insufficiency, branch pulmonary artery obstruction, residual VSD, truncal valve dysfunction, ventricular dysfunction, coronary perfusion abnormalities, and pulmonary vascular reactivity.

Pulmonary hypertensive instability remains particularly important in patients who have experienced prolonged preoperative pulmonary overcirculation. In a series that included patients presenting substantially later than the neonatal period, pulmonary hypertensive crises accounted for two of three hospital deaths, illustrating the potential consequences of established pulmonary vascular disease [7].

14. Long-Term Outcomes and Reintervention

Contemporary repair can provide good long-term survival and functional status, but reintervention is an expected component of lifetime management rather than an unusual complication.

A 255-patient multicenter experience reported 20-year survival of approximately 77%; survivors beyond the early postoperative period were predominantly in excellent functional class. Nevertheless, 175 patients required at least one reoperation, emphasizing the long-term procedural burden [2].

A separate 20-year single-center experience demonstrated marked improvement in early results across surgical eras, with early mortality falling to 4.5% in the more contemporary period. Despite this improvement, conduit and truncal valve reoperations remained important late events [6].

The most frequent long-term problem is deterioration of the RV–PA pathway because the conduit does not grow with the child and may develop stenosis, regurgitation, or both. Branch pulmonary artery stenosis is another important target for catheter-based or surgical treatment.

Recent data similarly emphasize this burden. In a 34-patient contemporary cohort, nearly half required surgical reintervention and half underwent catheter-based reintervention during follow-up. RV–PA conduit dysfunction dominated surgical reoperations, while branch pulmonary artery interventions were common. Truncal valve stenosis and the need for pulmonary artery reconstruction or truncal valve replacement at the initial operation were associated with earlier surgical reintervention, while hypoplastic confluent pulmonary arteries were associated with catheter-based reintervention [8].

Thus, neonatal complete repair establishes separated circulations but does not eliminate congenital heart disease. Lifelong surveillance of the RV–PA conduit, branch pulmonary arteries, truncal valve, ventricular function, systemic outflow, and coronary circulation remains essential.

15. Key Physiologic Concept

Truncus arteriosus can be summarized by two linked sequences:

One arterial trunk + large VSD → complete admixture → systemic desaturation

and, after birth:

↓ PVR → ↑ Qp → ↑ pulmonary venous return → LV volume overload + pulmonary congestion → heart failure

The defining clinical lesson is that truncus arteriosus is not simply a cyanotic lesion. It is a lesion of admixture combined with unrestricted pulmonary blood flow.

As neonatal PVR falls, pulmonary runoff increasingly dominates the circulation. A patient may therefore have only moderate cyanosis while developing severe pulmonary overcirculation and heart failure. Understanding the interaction among PVR, Qp/Qs, systemic perfusion, ventricular loading, truncal valve function, and pulmonary vascular injury provides the physiologic foundation for timely surgical repair and long-term management.

References

[1] Austin EH. Repair of truncus arteriosus. Oper Tech Thorac Cardiovasc Surg. 2003;8(3):111-120.

[2] Naimo PS, Bell D, Fricke TA, d'Udekem Y, Brizard CP, Alphonso N, Konstantinov IE. Truncus arteriosus repair: A 40-year multicenter perspective. J Thorac Cardiovasc Surg. 2021;161(1):230-240.

[3] Naimo PS, Fricke TA, d'Udekem Y, Brink J, Weintraub RG, Brizard CP, Konstantinov IE. Impact of truncal valve surgery on the outcomes of the truncus arteriosus repair. Eur J Cardiothorac Surg. 2018;54(3):524-531.

[4] Jahangiri M, Zurakowski D, Mayer JE Jr, del Nido PJ, Jonas RA. Repair of the truncal valve and associated interrupted arch in neonates with truncus arteriosus. J Thorac Cardiovasc Surg. 2000;119(3):508-514.

[5] Ota N, Tachimori H, Hirata Y, Miyata H, Suzuki T, Uchita S, Takamoto S, Izutani H. Contemporary patterns of the management of truncus arteriosus (primary versus staged repair): outcomes from the Japanese National Cardiovascular Database. Eur J Cardiothorac Surg. 2022;61(4):787-794.

[6] Ivanov Y, Mykychak Y, Fedevych O, Motrechko O, Kurkevych A, Yemets I. Single-centre 20-year experience with repair of truncus arteriosus. Interact Cardiovasc Thorac Surg. 2019;29(1):93-100.

[7] Chen Q, Gao H, Hua Z, Yang K, Yan J, Zhang H, Ma K, Zhang S, Qi L, Li S. Outcomes of surgical repair for persistent truncus arteriosus from neonates to adults: a single center's experience. PLoS One. 2016;11(1):e0146800.

[8] Alsbhani WM, Ba-Atiyah WK, Arfi AM, Nijres BM, Ahmad Z. Short-to-long-term outcomes following truncus arteriosus repair: reintervention burden and risk factor analysis from a tertiary center. Cardiothorac Surg. 2026;34:27.