Synonyms: Single outlet of the heart.

Definition: A congenital anomaly in which a single common artery arises from the heart and supplies the coronary, pulmonary, and systemic circulations.

Prevalence: 0.3:10,000 live births, may be slightly less common in males than females (M0.72:F1)¹.

Etiology: Multifactorial inheritance.

Pathogenesis: Failure of the aorticopulmonary septum to develop and separate the truncus arteriosus into the aorta and the pulmonary artery.

Associated anomalies: Truncus arteriosus is frequently associated with other cardiac anomalies including: ventricular septal defects, aortic arch abnormalities, single ventricle, atrioventricular valve abnormalities, absent ductus arteriosus, and abnormal pulmonary venous return.  Extracardiac anomalies occur in up to 50% of the cases and include: situs inversus, asplenia, bony defects, cleft lip/palate, urinary tract abnormalities (absent or aplastic kidney), absent gallbladder, hypoplastic lung, and neural tube defects.

Differential diagnosis: Tetralogy of Fallot, atresia of pulmonary artery.

Prognosis: Poor prognosis without treatment. Approximately 65% of untreated patient die before 6 months, and early surgical repair (prior to 6 months of age) significantly improves outcome.

Recurrence risk: 1.2-7.7%^2,3.

Management: Includes careful evaluation for associated anomalies, karyotype analysis, and serial ultrasound examinations to detect signs of congestive heart failure. If there is no evidence of heart failure, standard obstetrical management is recommended with  delivery at a tertiary care center.

MESH Truncus arteriosus, cardiovascular anomalies, congenital BDE 0972 ID9 745.0 CDC 745.000

Address correspondence to Daniel Gauthier, MD, Dept. of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, University of Illinois College of Medicine, 840 South Wood Street, M/C 808, Chicago, IL 60612-4324 Ph: 312-996-7300; Fax: 312-996-4238

Introduction

Persistent truncus arteriosus is a rare congenital cardiac malformation in which there is only a single common artery arising from the heart.  This single artery supplies the systemic, pulmonary, and coronary circulations. Prenatal diagnosis of truncus arteriosus can be challenging, and only a few cases have been reported^4-7.  We present a case of truncus arteriosus detected prenatally and the ultrasonic findings that led to this diagnosis.

Case report

A 22-year-old black patient, G₁P₀ was referred at 34 weeks gestational age for lagging fundal height measurements. The patient was dated by both last menstrual periods and a 14-week ultrasound examination. No anomalies were detected at the early ultrasound examination, and the patient"s prenatal course was unremarkable except for mild iron deficiency anemia. Our ultrasound examination revealed biometry measurements consistent with 33 weeks gestational age. No extracardiac anomalies were visualized. Fetal cardiac examination revealed a normal apical four-chamber view and aortic arch (figs. 1 and 2).

Fig. 1: Normal appearing 4-chamber view.

Fig. 2: Aortic arch (A) with brachiocephalic vessels (arrows).

A long axis view of the left ventricle revealed a dilated outflow tract (fig. 3).

Fig 3: Long axis view of the left ventricle (LV) with dilated outflow tract (LVOT). The distance between the calipers was 13 millimeters.

On further examination, a more subcostal four-chamber view revealed a single large outflow tract equally overriding the ventricular septum (fig. 4).

Fig. 4: Subcostal 4-chamber view with single large outflow tract (T) equally overriding the ventricular septum. A small VSD (arrow) is present. LV, left ventricle; RV, right ventricle.

A ventricular septal defect was also present. On color Doppler imaging, blood flow from both ventricles could be seen entering the single outflow tract (fig. 5).

Fig. 5: Color Doppler imaging of figure 4 revealing blood flow from both ventricles entering the single outflow tract.

The ductus arteriosus was not visualized. M-mode examination revealed normal end-diastolic ventricular dimensions as well as normal end-diastolic ventricular wall measurements. Pulsed Doppler examination and color flow imaging of the single outflow tract revealed no evidence of regurgitation across the valve. A diagnosis of truncus arteriosus versus tetralogy of Fallot with pulmonary atresia was made.

A detailed genetic history was negative for congenital heart disease, birth defects, or mental retardation. The patient denied any exposure to medications, drugs, X-rays, or chemicals. Prenatal chromosomal analysis was offered and the patient elected to have percutaneous umbilical blood sampling. This procedure was performed without complication and revealed a normal 46, XX, karyotype.

The patient was then followed with serial ultrasound examinations which failed to show any signs of congestive heart failure. The patient went into spontaneous labor at 39 weeks gestational age. The labor was complicated by meconium-stained amniotic fluid as well as multiple variable and late decelerations. A cesarean section was performed and the patient delivered a female infant with a birthweight of 3013g and Apgar scores of 7 and 9.

Immediate neonatal course was unremarkable with no extracardiac anomalies identified. A type 2 truncus arteriosus (see below) was diagnosed by an echocardiogram obtained soon after birth (fig. 6).

Fig. 6: Neonatal echocardiogram demonstrating the origin of the pulmonary arteries (P) from the dorsal wall of the truncus (Tr).

At one month of age, the infant began to show signs of congestive heart failure and was begun on digitalis and furosemide. She is currently awaiting corrective surgery.

Discussion

Persistent truncus arteriosus is a rare congenital anomaly with an estimated incidence of 3 per 100,000 live births and may show a slight predilection for females (58:42)¹. Other reports, however, have shown an equal sex distribution^8,9. Truncus arteriosus accounts for approximately 1.0% of congenital heart disease in live-born infants¹⁰.

Pathology

Two classification systems have been suggested for truncus arteriosus. According to Van Praagh and Van Praagh¹² (fig. 7), truncus arteriosus is classified into two types based on the presence (type A) or absence (type B) of a ventricular septal defect with the latter type being more rare.

Fig. 7: Van Praagh classification¹². Truncus arteriosus is classified into two types, based on the presence (type A) or absence (type B) of a ventricular septal defect. The 2 types are further subclassified into 4 subtypes, depending on the orientation of the great arteries.  In subtype 1 (Left), the aorticopulmonary septum is incompletely formed, resulting in a partially separate main pulmonary artery. In subtype 2 (Middle left), the aorticopulmonary septum is entirely absent with both pulmonary arteries arising directly from the truncus. In subtype 3 (Middle right), one pulmonary artery is absent and that lung is supplied by collateral arteries from the descending aorta. In subtype 4 (Right), hypoplasia, coarctation, atresia, or absence of the aortic arch is associated with a large patent ductus arteriosus.

The 2 types are further subclassified into 4 subtypes, depending on the orientation of the great arteries: subtype 1 - the aorticopulmonary septum is incompletely formed, resulting in a partially separate main pulmonary artery; subtype 2 - the AP septum is entirely absent with both pulmonary arteries arising directly from the truncus; subtype 3 -absence of one pulmonary artery, with that lung being supplied by collateral arteries from the descending aorta; and subtype 4 - Hypoplasia, coarctation, atresia, or absence of the aortic arch associated with a large patent ductus arteriosus.

In the classification outlined by Collett and Edwards¹³, four types of truncus arteriosus are described (fig. 8): type 1 - a single pulmonary trunk and ascending aorta arise from the truncus arteriosus; type 2 - the two pulmonary arteries originate close together from the dorsal wall of the truncus arteriosus; type 3 - one or both pulmonary arteries arise independently from the side of the truncus arteriosus; and type 4 - an absence of the pulmonary arteries with the pulmonary circulation being supplied from collateral arteries arising from the descending aorta.

Fig. 8: Collett and Edwards classification¹³: type 1 (Left): a single pulmonary trunk and ascending aorta arise from the truncus arteriosus; type 2 (Middle left): both pulmonary arteries originate close together from the dorsal wall of the truncus arteriosus; type 3 (Middle right): one or both pulmonary arteries arise independently from the side of the truncus arteriosus; and type 4 (Right): absence of the pulmonary arteries with the pulmonary circulation being supplied from collateral arteries arising from the descending aorta.

In both classification systems, truncus arteriosus type 1 and type 2 are most common. Also common to both classification systems is the presence of a single arterial or truncal valve. The truncal valve usually is tricuspid but may have up to six leaflets and is frequently abnormal and/or incompetent.

Embryology

During the fifth week of embryologic development, opposing ridges of subendocardial tissue appear in the bulbus cordis and truncus arteriosus. These ridges are continuous with each other and normally develop in spiral fashion. Fusion of these ridges then occurs, forming the aortico­pulmonary septum (see fig. 9).

Fig. 9: Early stage in the division of the truncus arteriosus into the aorta and pulmonary trunk. The formation of the aortico-pulmonary septum results from the fusion of the subendocardial bulbar and truncal ridges. This normally occurs in a spiral fashion.

Pathogenesis

Persistent truncus arteriosus is thought to result from failure of the aorticopulmonary septum to develop and subsequently divide the truncus into the aorta and the pulmonary trunk¹¹.

Associated anomalies

Truncus arteriosus is frequently associated with other cardiac

anomalies (Table 1). Extracardiac anomalies also occur in 20% to 50% of cases^1,12 (Table 1).

Table 1. Anomalies associated with truncus arteriosus^8,12-14

Fetal hydrops and cardiac arrhythmias have been described in those cases of truncus arteriosus diagnosed prenatally^5,7.

The incidence of chromosomal abnormalities in association with truncus arteriosus has been reported to be approximately 5% (1 in 22)¹⁵. Chromosomal abnormalities reported include partial trisomy 4q, abnormal banding pattern in chromosome 8, and a C-G translocation^8,14. Trisomy 13 translocation has been detected in a case of truncus arteriosus diagnosed prenatally⁶.

Differential diagnosis

The diagnosis is made by observing a single common arterial outflow tract overriding the ventricular septum. This finding, however, may be indistinguishable from that which is seen in cases of tetralogy of Fallot or pulmonary atresia with a ventricular septal defect. In our case, a normal 4-chamber view and ventricular measurements, in addition to the inability to identify either a right outflow tract or ductus arteriosus, suggested the diagnosis of truncus arteriosus over that of tetralogy of Fallot. Demonstration of the pulmonary arteries originating from the arterial trunk or a truncal valve with 4 or more leaflets may also help differentiate truncus arteriosus from other anomalies. The former finding has been described in a case of truncus arteriosus diagnosed prenatally⁶.

Prognosis

Persistent truncus arteriosus is associated with a high mortality rate. Approximately 65% of untreated patients do not survive more than 6 months, and up to 90% die before one year of age^8,9,12,13,16.

Infants with truncus arteriosus usually develop progressive congestive heart failure. This is due to a large left-to-right shunt that develops postnatally secondary to the decrease in pulmonary vascular resistance. This shunt may eventually result in pulmonary hypertension. Truncal valve incompetence, when present, usually worsens the progressive congestive heart failure and is associated with a poorer prognosis. Aortic diastolic pressures are frequently low and lead to an increase in pulse pressure and a decrease in coronary blood flow. The decrease in coronary perfusion along with increased myocardial oxygen demand that occurs with congestive heart failure is thought to make these patients more prone to subendocardial ischemia¹⁷.

The treatment of choice for truncus arteriosus is early surgical repair¹⁷. In the past, pulmonary artery banding was used as a palliative procedure, but results were poor, with operative mortality rates being, at best, 50%^18,19. Recently, a more physiologic surgical repair, done prior to 6 months of age, has resulted in much improved outcome^20,21. This procedure entails the placement of an extracardiac valved or valveless conduit and closure of the ventricular septal defect. Operative mortality rate from this procedure has ranged from 10 to 20%, with increased risk in patients with significant truncal regurgitation¹⁷. Most patients, however, require replacement of the conduit, either because they outgrow the conduit or as a result of conduit stenosis. The use of adult size allografts may decrease the need for reoperation^17,20.

Management

When prenatal diagnosis of truncus arteriosus is made before viability, termination of pregnancy can be offered. A meticulous search for associated anomalies should be performed. Chromosomal analysis is advised, especially in the presence of associated anomalies. Serial ultrasonic evaluation is recommended to follow fetal growth, amniotic fluid volume, and to detect signs of fetal hydrops. Truncal valve competence can be assessed with pulsed Doppler or with color flow imaging. If incompetence of the truncal valve is detected, the fetus may be at increased risk of developing hydrops.

If there are no other complicating factors, standard obstetrical management for labor and delivery is recommended. However, it is essential for delivery to occur in a tertiary care center where a pediatric cardiologist is available to assist in the neonatal management of these patients.

References

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21. Spicer RL, Behrendt D, Crowly DC, et al.: Repair of truncus arteriosus in neonates with the use of a valveless conduit. Circulation 70(suppl):26-29. 1984.