Truncus arteriosus (also termed common arterial trunk) is an unusual^1–4 developmental anomaly, characterized by incomplete conotruncal septation, leading to a common aortopulmonary trunk and ventricular septal defect. The disorder was first described by Wilson in 1798.⁵ Initial surgical management consisted of palliative pulmonary artery (PA) banding; however, long-term survival associated with this treatment was poor. The first surgical repair was performed in 1962, when Behrendt and colleagues closed the ventricular septal defect and used a valveless conduit to establish continuity between the right ventricle (RV) and the PA.⁶ Complete repair of truncus arteriosus with a valved conduit was first reported by McGoon in 1967⁷ and remains the procedure of choice for the majority of patients.

A recent prospective population-based study estimated the prevalence of truncus arteriosus to be approximately 0.07 per 1000 live births, representing 1.09 percent of all congenital cardiac malformations.^3,8 The incidence may be more than 3-fold higher in infants of diabetic mothers.⁹ Twenty years ago, the 1-year mortality rate for corrected truncus arteriosus was estimated at 2.6 per 100,000 live births, representing 3.7 percent of all deaths due to congenital heart disease during that period.¹⁰ Median 1-month mortality was 23 percent. With contemporary advancements in surgical technique and perioperative management, survival is likely higher. Without surgical correction, approximately 70 percent of infants die within the first 3 months of life,¹¹ whereas some individuals who are diagnosed later in life may survive for years without surgical intervention.^12–15 This subset likely represents those individuals with relatively balanced pulmonary-systemic circulations during infancy, and in whom severe pulmonary vascular obstructive disease inevitably develops.

The heart and great vessels develop from primitive mesoderm and neural crest cells. At approximately 20 days’ gestation, blood islands of the cardiogenic plate coalesce to form the left and right endocardial tubes within the intraembryonic coelom (early pericardial cavity). The endocardial tubes fuse to become the bulbus cordis at approximately 23 days. The most cephalad portions of the bulbus cordis become the truncus arteriosus and conus cordis. During this period, the bulboventricular structures begin to rotate anteriorly and to the right to form the heart loop. At approximately 29 days, cono-truncal swellings begin to develop into distinct ridges. As these ridges grow, they fuse to form the truncal septum, which divides the aorta from the PA and the conal septum, becoming the supraventricular crest and the subpulmonic infundibulum. Spiral rotation along an axis similar to the heart loop separates the posterolateral aortic root from the more antero-medial PA root at approximately 37 days. Fusion of the conal septum with the endocardial cushions during this period establishes ventricular separation, with resultant left ventricle–aorta and RV–PA concordance.

Persistent truncus arteriosus results from incomplete or altered septation and rotation of components of the bulbus cordis. Morphogenetic patterning of the conotruncus, and eventual septation into a PA and aorta, involves initial migration of the dorsal and ventral neural crest cells followed by differentiation of these cells into vascular smooth muscle cells, in response to poorly characterized developmental cues.^16–18 Experimental ablation of these regions of the neural crest is associated with hypoplasia or aplasia of the thymus, thyroid, and parathyroid glands and persistent truncus arteriosus. Although the mechanisms by which neural crest cells regulate cono-truncal development have not been clearly elucidated, it is believed that alterations in neural crest cell migration may explain the association between cono-truncal malformations and cranio-facial defects such as those observed in patients with the DiGeorge syndrome. Recent experimental studies have implicated abnormalities in the family of GATA zinc-finger transcription factors, particularly GATA-6, which play critical roles in regulating morphogenetic patterning of the cardiac outflow tract and aortic arch during development.^19,20

The genetic basis for persistent truncus arteriosus is likely multifactorial. An association between persistent truncus arteriosus and chromosome 22q11 deletion is well established. Chromosome 22q11 deletion affects approximately 700 infants annually in the United States and is present in 1.5 percent of patients with congenital heart defects²¹ and in up to 40 percent of patients with truncus arteriosus.^22,23 Moreover, truncus arteriosus is present in approximately 10 percent of patients with chromosome 22q11 deletion.²⁴ In addition to cardiovascular malformations, chromosome 22q11 deletion has also been clearly linked to aplasia and hypoplasia of the thymus.^21,25,26 It is now recognized that 22q11 deletion syndrome encompasses the phenotypes previously described as DiGeorge syndrome and velocardiofacial syndrome. Because of these strong associations, genetic testing for chromosome 22q11 deletion in patients diagnosed with truncus arteriosus or thymic aplasia or hypoplasia is warranted. Recent evidence suggests that conditional inactivation of GATA-6 within neural crest cell derived smooth muscle cells results in cono-truncal defects including truncus arteriosus, interrupted aortic arch (IAA), and double-outlet RV.^19,27 Additional potential etiologic genetic alterations linked to truncus arteriosus include chromosomal duplication of 8p and 8q^28,29 and mutations in transcription factors NKX2.5³⁰ and Pitx2.³¹ Evidence supporting rare autosomal recessive inheritance of truncus arteriosus in the absence of 22q11.2 deletion has been reported.³²

Truncus arteriosus is characterized by a single aortopulmonary trunk arising from the base of the heart, which gives rise to the coronary, systemic, and pulmonary arteries. An obligatory ventricular septal defect is present. The origin of the PAs varies considerably and forms the basis of the two major classification systems. Collett and Edwards¹⁴ proposed the first widely accepted classification scheme in 1949. In their system, the spectrum of truncal variations is divided into four general categories based on the origin of the PAs. In type I truncus arteriosus, the left and right branch PAs arise from a single short main pulmonary trunk. The main pulmonary trunk commonly arises from the posterior aspect of the truncus, just above the truncal valve. In type II truncus arteriosus, the origins of the left and right PAs are in close proximity to one another along the posterior aspect of the truncus. In type III truncus arteriosus, the origins of the left and right PAs arise more laterally and separate from one another. In type IV truncus arteriosus, the PAs arise from the descending aorta rather than the truncus (extrapericardial origin of the branch PAs). Although this configuration has historically been referred to as “pseudotruncus,” it is now generally believed to represent a form of pulmonary atresia with aortopulmonary collateral vessels and should not be classified as a variation of truncus arteriosus.

An additional classification system was developed by Van Praagh and Van Praagh in 1965.³³ Like the Collett and Edwards classification systems, this system also divides truncus arteriosus into four categories. Type A1 is characterized by a main PA segment arising from the truncus due to a partially formed aorticopulmonary septum. Type A2 is characterized by the presence of left and right PAs arising independently from the truncus, irrespective of the proximity of their origins. Type A3 is characterized by the presence of a single PA arising from the truncus. In this form, often referred to as “hemitruncus,” the contralateral lung is supplied by a pulmonary collateral vessel arising from either the distal aorta or the ductus arteriosus. Type A4 is characterized by a hypoplastic or IAA with PAs arising from a large ductus arteriosus. In this classification scheme the designation of type B indicates absence of a ventricular septal defect. However, because the presence of a true truncus arteriosus in these patients is questionable, the Van Praagh B classification is seldom used. These classification schemes share overlapping features and are schematically represented in Figure 72-1. Collett and Edwards type I and Van Praagh type A1 are essentially the same. Van Praagh type A2 encompasses the Collett and Edwards types II and III.

In 2000, a new classification system was developed by the STS Congenital Heart Surgery Database Committee and representatives of the European Association for Cardiothoracic Surgery.³⁴ This system, based on the Van Praagh scheme, divides truncus arteriosus into three main categories: truncus arteriosus with confluent or near confluent PAs, truncus arteriosus with absence of one PA, and truncus arteriosus with IAA or coarctation. In this system, modifiers are used to denote the number of truncal valve leaflets, the presence and degree of truncal valve stenosis or insufficiency and the presence of ventricular hypoplasia, coronary artery anomaly, overriding truncal valve, transposition, or thymic aplasia. A similar nomenclature scheme to describe various methods of repairing or palliating truncus arteriosus has also been proposed. Although these classification systems may be very useful for risk-stratification analysis, the Van Praagh and Collett and Edward’s classification systems continue to be widely used.

The truncal valve is most commonly tricuspid (about 50 percent), quadricuspid (about 30 percent), or bicuspid (about 5 percent). More than four cusps and, rarely, a single cusp may also be seen. Valve leaflets may be thickened and dysplastic, contributing to valvular insufficiency or stenosis. Despite these functional and morphologic variations, fibrous continuity between the truncal valve and the mitral valve is preserved. The tricuspid valve may be in fibrous continuity or may be separated from the truncal valve by a thin muscular band. The truncal valve typically overrides the interventricular septum and the subarterial ventricular septal defect in a balanced manner or may be more committed to the RV. Less frequently, the truncus arises predominantly from the left ventricle. The ventricular septal defect is normally located in the subarterial portion of the infundibular septum. The ventriculoinfundibular fold typically forms the posterior margin of the defect and separates it from the anterior leaflet of the tricuspid valve. Less commonly, the ventricular septal defect may extend posteriorly to the tricuspid valve annulus in the perimembranous outlet portion of the septum. The inferior margin of the ventricular septal defect is made up by the trabecula septomarginalis, and the superior margin typically extends to the truncal valve.

Coronary artery anatomy in truncus arteriosus may exhibit significant variability.³⁵ Two coronary ostia are generally present. The left coronary artery typically originates from the left portion of the truncus. It may originate high in the sinus of Valsalva or above the sinus in proximity to the takeoff of the PA. The right coronary artery typically originates from the right anterior portion of the truncus. However, an anterior descending coronary artery may originate from the right coronary artery and cross the RV near the infundibulum. In up to 18 percent of cases, a single coronary ostium originating from either the left or right is present. Additional coronary anomalies that have been reported include the circumflex artery originating from the right coronary artery, ostial stenosis due to structural deformation related to the adjacent commissure, right coronary artery originating from the anterior descending coronary artery, and major coronary branches of the right coronary artery crossing the RV outflow tract to supply antero-basal surfaces of both ventricles and the upper portion of the interventricular septum.³⁶ Abnormal coronary anatomy must be carefully considered in planning surgical correction, because failure to recognize variations in coronary anatomy may cause or contribute to perioperative morbidity or mortality.³⁷

Truncus arteriosus is generally associated with a left aortic arch, but a right aortic arch is present in approximately 30 percent of cases. Association with double aortic arch³⁸ and persistent embryonic fifth aortic arch^39,40 has also been reported. In approximately 15 percent of cases, the aortic arch is either interrupted or severely hypoplastic.⁴¹ The interruption usually occurs distal to the origin of the left common carotid artery (type B aortic arch interruption; see Chapter 76) and is accompanied by ductal continuity with the descending thoracic aorta. In this morphologic variant, the PAs arise from the ductus arteriosus. Other associated abnormalities of the great vessels include IAA with postductal origin of all brachiocephalic vessels⁴² and the absence of one PA.⁴³ Absence of one PA occurs most frequently on the same side as the aortic arch. Truncus arteriosus is also commonly associated with patent foramen ovale/secundum atrial septal defect and tricuspid insufficiency or stenosis.⁴⁴

The physiologic features of truncus arteriosus are typical of those seen in other forms of cyanotic congenital heart disease with increased pulmonary blood flow. The single aorto-pulmonary trunk results in parallel pulmonary–systemic circulations, making intracardiac mixing of systemic and pulmonary blood at the level of the ventricular septum obligatory to maintain adequate systemic oxygenation. Additional mixing occurs at the level of the atrial septal defect when present (Fig. 72-2). During fetal development pulmonary blood flow represents less than 10 percent of the cardiac output due to increased pulmonary vascular resistance. At birth, the combined cardiac output traverses the truncal valve and the amount of pulmonary blood flow is determined by the change in pulmonary vascular resistance and the presence of any PA narrowing. Because the pulmonary vascular resistance initially falls below the systemic vascular resistance, severe hypoxia rarely occurs. When it does, proximal or distal PA narrowing must be suspected. As the pulmonary vascular resistance continues to fall during early postnatal life, pulmonary blood flow increases. Increased pulmonary venous return leads to volume overload of the RV, cardiopulmonary inefficiency, and congestive heart failure. Any degree of truncal valve incompetence can further increase the volume load on the ventricle, as well as compromise coronary perfusion due to diastolic flow reversal in the common trunk. The large, nonrestrictive ventricular septal defect enables pressure equilibration between the LV and RV, which leads to RV hypertrophy. Increased pulmonary blood flow, combined with systemic level arterial pressures within the pulmonary circulation, ultimately brings about pulmonary vascular changes that, in turn, increase pulmonary vascular resistance. Because the PAs originate above the truncal valve, the pulmonary circulation is exposed to systemic-level pressures during both systole and diastole. It is believed that this accelerates the abnormal pulmonary vascular changes leading to increased pulmonary vascular resistance and pulmonary hypertension. Although increased pulmonary vascular resistance and pressure generally occur several months later in life, there is evidence that early molecular and cellular changes occur within a few weeks in the presence of increased pulmonary blood flow⁴⁵ and that observed vascular changes are related to alterations in nitric oxide and endothelin activity.⁴⁶ These findings may explain the improved outcomes associated with early surgical repair.

The clinical findings associated with truncus arteriosus depend on the degree of truncal valve competence, pulmonary vascular resistance, and coexisting cardiac defects. Shortly after birth, infants will generally exhibit mild cyanosis, tachycardia, tachypnea, costo-sternal retractions, and diaphoresis, which may worsen during feeding. The second heart sound is single and a harsh systolic ejection murmur may be audible at the left lower sternal border. A precordial thrill may be present. Pulmonary runoff produces a low diastolic pressure and widened pulse pressure. Truncal valve stenosis and insufficiency may produce a more pronounced ejection murmur or a diastolic decrescendo murmur, respectively. Cyanosis may improve as pulmonary vascular resistance continues to fall over the first few weeks. Increasing pulmonary overcirculation leads to progressive worsening symptoms of congestive heart failure, including pulmonary edema, hepatomegaly, and failure to thrive. These findings may develop at an accelerated rate or may be more pronounced in the setting of truncal valve insufficiency. Neonates not undergoing repair may exhibit improvement in heart failure symptoms but worsening of cyanosis as maladaptive pulmonary vascular changes progress and pulmonary blood flow decreases. Infants with Van Praagh type A4 truncus arteriosus (IAA, ductal origin of PAs) may exhibit symptoms of systemic hypoperfusion and ischemia as well as hypoxia as the ductus arteriosus begins to close shortly after birth. Features such as micrognathia, choanal atresia, and cleft palate may be found in patients with coexisting chromosome 22q11 deletion syndromes (Fig. 72-3).

Diagnostic Studies

Truncus arteriosus is most commonly diagnosed shortly after birth; however, prenatal diagnosis is becoming increasingly common as prenatal care becomes more accessible. All cyanotic infants should undergo careful diagnostic testing, including blood gas analysis, pulse oximetry, electrocardiography, chest radiography, and transthoracic or transesophageal echocardiography. Early pulse oximetric screening may detect evidence of truncus arteriosus before symptoms develop.⁴⁷ Biventricular hypertrophy is generally evident on the electrocardiogram and may become more pronounced over time. Although initial chest radiographs may appear normal, subsequent studies typically demonstrate cardiomegaly and increased pulmonary vascular markings. Absence of the thymic shadow may be observed in patients with coexisting neural crest disorders such as DiGeorge syndrome. A right-sided aortic arch may be apparent in approximately 30 percent of cases. Two-dimensional and Doppler echocardiography accurately detect truncus arteriosus and characterize important anatomic and hemodynamic features, including type of truncus, truncal valve morphology and function, presence of PA stenosis, size and location of the ventricular septal defect, location of coronary ostia, pulmonary blood flow and resistance, and presence of associated lesions.⁴⁸ Although the echocardiographic distinction between different cono-truncal abnormalities is challenging in the fetus, truncus arteriosus may be accurately diagnosed by fetal echocardiography.⁴⁹ Accurate in utero diagnostic studies are invaluable in counseling parents. Cardiac catheterization and coronary angiography are useful for accurate anatomic and physiologic assessment of the PAs and to determine the precise orientation and course of the coronary arteries. This is especially important in older infants who may exhibit pulmonary vascular hypertrophic changes and in infants with echocardiographic evidence of coronary artery abnormalities. Computed tomography and resonance magnetic imaging with three-dimensional reconstruction are gaining wide acceptance as additional diagnostic tools.

The initial medical management of these patients should focus on the treatment of congestive heart failure and ensuring adequate oxygen delivery. Initial hypoxia may necessitate endotracheal intubation and mechanical ventilation. As pulmonary vascular resistance falls, decreased diastolic coronary perfusion may lead to worsening of heart failure symptoms, especially during feeding and crying. Diuretics, digoxin, and occasionally more powerful inotropic agents are useful in managing heart failure. Hypocalcemia must be corrected in patients with coexisting syndromes involving the deletion of chromosome 22q11. The findings of progressive tachycardia, hypotension, acidosis, and hypoxemia during early postnatal life suggest truncus arteriosus with IAA (Van Praagh type A4). Intravenous prostaglandin therapy must be initiated to arrest closure of the ductus arteriosus. Genetic screening for chromosome 22q11 deletion should be undertaken in all patients with truncus arteriosus. Patients presenting later in life with evidence of advanced pulmonary vascular obstructive disease and pulmonary hypertension, may benefit from inhaled nitric oxide therapy. However, the prognosis for these children remains poor.

Surgical Therapy

Initial surgical management of truncus arteriosus was limited to palliative PA banding, which resulted in survival rates similar to those observed in untreated patients. The first reported surgical repair utilizing a nonvalved Teflon conduit was performed in 1962.⁶ Following this, McGoon and colleagues performed the first successful repair with a valved conduit in an older child in 1967.⁷ Reports of successful repair and improved outcomes in younger infants⁵⁰ subsequently led to earlier repair and avoidance of maladaptive pulmonary vascular changes. Currently, banding of the PAs should be considered only when coexisting conditions such as sepsis, shock, or intracranial hemorrhage prevent surgical repair. Rarely, in cases where truncus arteriosus coexists with IAA, banding may be considered as initial palliation.⁵¹

The timing of surgical intervention in these patients has received considerable attention. Overall, the trend has been toward earlier repair in infants and neonates. Repair of truncus arteriosus during the first few weeks of life may be safely accomplished in the majority of patients⁵² and appears to improve survival.⁵³ Early repair ameliorates congestive heart failure and failure to thrive and prevents irreversible pulmonary vascular disease. However, the overall operative mortality associated with neonatal correction of truncus arteriosus, estimated at 15.4 percent based on a recent large multi-institutional sample, remains relatively high compared with repair of other forms of complex congenital cardiac disease.^54–56 The reason for this discrepancy is unclear. A review of the strategy for management of truncus arteriosus by Brizard and colleagues⁵⁷ found that weight less than 3 kg is an independent risk factor for early perioperative mortality and that deferring surgery until 2 to 3 months of age decreases surgical risks. Although such a policy results in surgical intervention on infants of greater body weight and the use of larger valved conduits with associated longer freedom from reoperation, improved results may represent exclusion of neonates with otherwise unfavorable characteristics or risk factors. We prefer initial complete correction in infancy, except in unusual circumstances (extremely low-birth weight or prematurity, severe truncal valve dysfunction, arch anomalies), where we have used an initial palliative approach consisting of removal of the PAs from the truncus and subsequent connection to a 6-mm RV-to-PA (Sano-type) shunt. This procedure is then followed by complete intracardiac repair at a more favorable time.

Operative Technique

We routinely employ intraoperative transesophageal echocardiography to evaluate valve function, intracardiac shunting, and wall motion before and after repair. Repair of a type 1 truncus arteriosus is depicted in Figure 72-4. Following median sternotomy, a generous portion of pericardium is harvested and treated with glutaraldehyde. The origin and course of the coronary arteries are carefully evaluated. The common arterial trunk, complete aortic arch, and great vessels are extensively mobilized. The PAs are mobilized well into the hilum and snares are placed. When a ductus arteriosus is present, care must be taken to avoid injuring it. In the presence of an IAA, snares are also placed around the great vessels. Arterial cannulation should be performed in the most distal ascending aorta or the transverse arch. Bicaval cannulae and a left ventricular vent are used to adequately decompress the heart. Snares are tightened to occlude the PAs upon initiation of cardiopulmonary bypass. If a ductus arteriosus is present, it is ligated. After distal aortic cross-clamping, cold blood cardioplegia is administered via an ascending aortic cannula and readministered intermittently throughout the procedure. In the setting of significant truncal valve insufficiency, retrograde cardioplegia may be delivered via the coronary sinus. Alternatively, the common trunk may be opened just distal to the origin of the PAs and cardioplegia given directly into the coronary ostia. Topical iced slush is applied and the patient is cooled to 32°C.