Definition and Morphology
Truncus arteriosus (also known as persistent truncus arteriosus, truncus arteriosus communis, common arterial trunk, or common aorticopulmonary trunk) naturally involves a single arterial vessel exiting the base of the heart, which gives rise to the coronary, pulmonary, and systemic arteries. Embryologically, it is due to abnormal migration of the neural crest tissue, which results in failure of septation of the outflow tract into a separate aortic and pulmonary trunk. There is a single semilunar valve, the truncal valve, and beneath the truncal valve there is almost invariably a ventricular septal defect (VSD).
The condition was first described in 1798 by Wilson and confirmed in an autopsy report by Buchanan in 1864. The basic morphologic criteria defining the anomaly were proposed in 1942 by Lev and Saphir. A classification was proposed by Collett and Edwards in 1949 and by Van Praagh and Van Praagh in 1965. Subsequently, the Society of Thoracic Surgeons tried to establish a unified classification for the basis of surgical reporting, which is essentially a modification of the Van Praagh classification. These classifications are further detailed and illustrated in Table 41.1 and Fig. 41.1 . More recently, a simplified categorization for truncus arteriosus was proposed, which is based on the presence or absence of an interrupted or hypoplastic aortic arch (hearts with pulmonary or aortic dominance, respectively).
| Collett and Edwards—Based on the Anatomic Origin of the Pulmonary Arteries | |||
|---|---|---|---|
| Type I: A short main pulmonary truncus arising from the truncus arteriosus that gives rise to right and left pulmonary arteries (48%-68% of cases). | Type II: No main pulmonary truncus, but the right and left pulmonary arteries arise close to one another (29%- 48% of cases). | Type III: No main pulmonary truncus, and the right and left pulmonary arteries arise distant from one another (6%- 10% of cases). | Type IV: Absence of the pulmonary arteries; the lungs are supplied by large aortopulmonary collateral arteries. This last type is now thought to be a variation of pulmonary atresia with ventricular septal defect and is no longer considered as part of the spectrum of truncus arteriosus. |
| Van Praagh—Based on the Embryological Development and Also Specifies the Presence (Type A) or Absence (Type B) of a VSD. | |||
| Type 1 : There is a partially formed aorticopulmonary septum and hence a main pulmonary artery segment is present. This corresponds to Collett and Edwards type I. | Type 2 : There is absence of the aorticopulmonary septum, and thus no main pulmonary artery segment is present. The right and left branch pulmonary arteries arise from the truncus arteriosus, but their proximity to one another is not specified. This corresponds to Collett and Edwards types II and III. | Type 3 : There is absence of one branch pulmonary artery from the truncus arteriosus (ie, it arises either from the ductus arteriosus or from the aorta). | Type 4 : The aortic arch is either hypoplastic or interrupted, and there is a large patent ductus arteriosus. |
| Modified Van Praagh—Proposed by the Society of Thoracic Surgeons in an Attempt to Provide a Unified Reporting System That Reflects Both the Anatomy and the Features That Affect Surgical Outcome, Rather Than an Attempt to Understand the Embryology. | |||
| Type 1-2 : Truncus arteriosus with confluent or nearly confluent pulmonary arteries. | Type 3 : Truncus arteriosus with absence of one pulmonary artery. | Type 4 : Truncus arteriosus with interrupted aortic arch or severe coarctation. | |
Truncus Arteriosus
The truncus arteriosus is larger than the normal aorta and is the only vessel that exits the base of the heart. It is often dilated, and histopathologic studies have demonstrated medial wall abnormalities similar to, and sometimes as extreme as, those found in patients with Marfan syndrome. The sinuses of Valsalva are often poorly developed. In the majority of cases (68% to 83%) the truncus arteriosus overrides the ventricular septum and has a biventricular origin. Less commonly (11% to 29%) it arises solely from the right ventricle. It rarely (4% to 6%) arises from the left ventricle.
Truncal Valve
According to various studies, the truncal valve is tricuspid in 69% of cases, quadricuspid in 22%, and bicuspid in 9%. There is fibrous continuity between the posterior leaflets of the truncal valve and the anterior leaflet of the mitral valve (as between the aortic and mitral valves in the normal heart), but only very rarely is there fibrous continuity between the truncal valve and the tricuspid valve. How well the leaflets of the truncal valve are formed impacts on survival: severe myxomatous thickening is found in one-third of cases, is associated with significant truncal valve incompetence, and is more common in neonates and young infants who develop severe heart failure or die. Occasionally (18%) the truncal valve may be stenotic.
Ventricular Septal Defect
The VSD in truncus arteriosus is usually large and nonrestrictive. It results from a deficiency or absence of the infundibular septum. It is subarterial, lying between the two limbs of the septal band (the septomarginal trabeculation), which form the inferior and anterior boundaries. The superior boundary is formed by the truncal valve, and is bounded posteriorly by the ventriculo-infundibular fold. There is usually a muscle bridge between the tricuspid and truncal valves caused by fusion of the inferior limb and the parietal band. When this bridge is absent (rarely), there is fibrous continuity between the two valves. Under these circumstances, the bundle of His is at risk of damage during surgical repair. The VSD is rarely restrictive. This usually occurs when the truncus arteriosus arises exclusively from one ventricle. Very rarely, the VSD is absent. This may occur if the truncus arteriosus arises exclusively from the right ventricle.
Pulmonary Arteries
The pulmonary arteries usually arise from the left posterolateral aspect of the truncus arteriosus, just above the truncal valve. When there are separate pulmonary artery ostia, the left is usually higher than the right. Very rarely (in the setting of an interrupted aortic arch) the left pulmonary artery ostium may arise to the right of the right ostium, leading to crossing of the pulmonary arteries behind the truncus. Stenoses of the pulmonary artery ostia are uncommon.
Coronary Arteries
Although variations in coronary artery anatomy exist, the coronary arteries usually arise from the sinuses of Valsalva above the truncal leaflets. In two-thirds of cases, the left coronary artery arises from the left posterolateral truncal surface and the right coronary artery arises from the right anterolateral truncal surface, similar to the arrangement found in normal hearts. However, the left anterior descending artery is often relatively small and is displaced to the left and the conus branch of the right is consequently large and supplies branches to the right ventricular outflow tract and septum (which may be important at operation). The coronary circulation is left-dominant in about 27% of patients, about three times higher than the prevalence in the normal population.
Ductus Arteriosus
The ductus arteriosus is present in about 50% of cases of truncus arteriosus. When present, it tends to remain patent postnatally in approximately two-thirds of cases. There is usually an inverse relationship between the diameter of the ductus and that of the ascending aorta and transverse arch: when the ductus is widely patent, the transverse arch is either interrupted or there is severe narrowing or coarctation, including tubular hypoplasia of the aortic isthmus and arch. Under these circumstances the pulmonary arteries arise separately from the truncus arteriosus. When there is neither aortic interruption/coarctation nor discontinuous pulmonary arteries, it is exceedingly rare to find a patent ductus arteriosus.
Ventricles
In the right ventricular outflow tract, the infundibular septum is absent. The right ventricle is invariably hypertrophied and enlarged. The left ventricular outflow tract is relatively normal.
Associated Anomalies
The most common cardiovascular anomalies coexisting with truncus arteriosus include VSD in most patients and interrupted aortic arch or coarctation, occurring in 10% to 20% of cases, in association with a widely patent ductus arteriosus. An interrupted aortic arch is often associated with the velocardiofacial syndrome (or DiGeorge syndrome, 22q11.2 microdeletion syndrome). A right aortic arch with mirror-image brachiocephalic branching occurs in 21% to 36% of patients with truncus arteriosus. Other common associated anomalies include secundum atrial septal defect (9% to 20%), aberrant subclavian artery (4% to 10%), persistent left superior vena cava to coronary sinus (4% to 9%), and mild tricuspid stenosis (6%). In 21% to 30% of patients, extracardiac anomalies are present.
Epidemiology and Genetics
Truncus arteriosus is an uncommon congenital cardiac malformation that accounts for 1% to 4% of the cardiac malformations found in large autopsy series and 0.6 to 1.4 per 10,000 live births.
It has been reported in monozygotic and dizygotic twins, siblings, and relatives of children with the defect. There is a strong association with chromosome 22q11 abnormalities, especially in the setting of interrupted aortic arch. However, additional disease genes are likely involved since the 22q11.2 microdeletion syndrome is only observed in approximately 30% of patients with truncus arteriosus.
Early Presentation and Natural History
Although intrauterine diagnosis with fetal echocardiography is possible, truncus arteriosus usually presents in the neonatal period or early infancy. Initial presentation consists of signs of heart failure as the pulmonary vascular resistance falls (tachycardia, tachypnea, excessive sweating, and feeding difficulties), followed by more florid signs of pulmonary and hepatic congestion. Before the fall in pulmonary vascular resistance, mild cyanosis may be detected. The presence of truncal valve insufficiency, stenosis, and coexisting interrupted aortic arch or coarctation exacerbates the problem of heart failure, usually resulting in earlier presentation and negative impact on outcome. Survival is favorably affected by naturally occurring pulmonary stenosis. The unoperated natural history, however, demonstrates an appalling outlook, with 1-year mortality around 70% to 90% usually due to heart failure. Beyond early childhood, pulmonary vascular disease (or pulmonary arterial hypertension, which can lead to Eisenmenger syndrome) is the major cause of death, although endocarditis and cerebral abscess may be responsible. Survival into adult life without surgical intervention has been described; however, it is very uncommon. In Figs. 41.2A and B, multidetector computed tomography images are shown of unoperated persistent truncus arteriosus in an 11-year-old cyanotic boy (Van Praagh type A1) and a 33-year-old cyanotic woman (Van Praagh type A2), respectively.
Surgical Repair
In view of the poor natural history, early surgery is the main form of treatment for truncus arteriosus. Initially, surgery comprised banding of one or both pulmonary arteries. However, problems are numerous: the band may be inadequate with subsequent development of pulmonary vascular disease; the band may migrate in type I truncus (in which a short main pulmonary artery is present), leading to obstruction of one pulmonary artery and the development of pulmonary vascular disease in the other; or there may be failure of pulmonary artery growth distal to the band or distortion of the pulmonary arteries.
Therefore primary and complete operative repair in the neonatal period or infancy is preferred. This was successfully accomplished initially in 1967 by McGoon et al. using an aortic homograft and aortic valve. Repair of truncus arteriosus in association with interrupted aortic arch was first successfully accomplished in 1971 by Gomes and McGoon. The basic procedure for repair of truncus arteriosus is demonstrated in Fig. 41.3 . Numerous iterations have taken place subsequently to try to prolong the life of the right ventricle-to-pulmonary artery conduit, including a Dacron conduit with a porcine semilunar valve and frozen or fresh homografts. Attempts have been made to repair the truncus arteriosus using an extracardiac patch with a pericardial monocusp valve, instead of an extracardiac conduit. This approach was not very successful because the monocusp valve subsequently shrinks, resulting in free pulmonary incompetence. More recently, a glutaraldehyde-preserved bovine jugular venous valved conduit (Contegra) was used for the right ventricle-to-pulmonary artery conduit, which seems to offer a cost-effective and readily available solution. However, there is a limited range of larger calibers, and the homograft valved conduit remains the gold standard. Truncal valve repair may include bicuspidalization through the approximation of two leaflets associated with triangular resection of the opposite one, or tricuspidalization through excision of one leaflet and related sinus of Valsalva (in the case of a quadricuspid incompetent truncal valve).
