Echocardiography in Pediatric and Adult Congenital Heart Disease, 2nd Ed.

18. Truncus Arteriosus

Persistent truncus arteriosus is a rare congenital heart defect in which the aortic arch, pulmonary arteries, and coronary arteries arise from a common great artery originating from the base of the heart. It occurs in 1% to 4% of all cases of congenital heart disease. Truncus arteriosus is typically fatal without intervention in early infancy; however, with current surgical therapy most children with truncus arteriosus survive. Most cases are sent to surgery based on echocardiographic imaging alone. Accurate noninvasive imaging is critical to defining the cardiac anatomy, guiding appropriate surgical management, and following these patients in the long term.

DEVELOPMENT AND ANATOMY

Truncus arteriosus occurs within the first 3 to 4 weeks of fetal life when there is failure of the aorticopulmonary septum to form and spiral within the embryonic truncus arteriosus, preventing a partition between the two great arteries. The anatomic description of truncus arteriosus consists of an outlet ventricular septal defect (VSD), a single semilunar valve, and a common great artery that overrides the VSD. Collett and Edwards first established four different anatomic classifications of truncus arteriosus based on the origin of the pulmonary arteries (Fig. 18.1). In type I, the main pulmonary artery arises from the truncal root and bifurcates into a right and a left pulmonary artery. In type II, each pulmonary artery originates from a separate origin off the posterior aspect of the truncal root. In type III, each pulmonary artery arises independently from the lateral aspects of the truncal root. In type IV, no true pulmonary arteries are present and pulmonary blood flow is supplied via aortopulmonary collateral vessels. This type of truncus arteriosus is considered to be a form of pulmonary atresia with VSD. Van Praagh later developed a classification based on truncus patients with a VSD (group A) and those without (group B [very rare]). Among both groups A and B, the four subgroups are the same (see Fig. 18.1). In the Van Praagh classification system, type III truncus arteriosus includes patients with origin of one pulmonary artery from the truncus. In this subset of patients, the other pulmonary artery is supplied via the ductus arteriosus or an aortopulmonary collateral vessel. In the Van Praagh classification system, type IV truncus arteriosus includes interruption of the aortic arch, with the descending aorta supplied by the patent ductus arteriosus. In cases of aortic arch interruption, type B is the most common form of interruption. A modified version of the Collett and Edwards classification was established by Konstantinov and colleagues. Figure 18.2 represents variations of truncus arteriosus with interrupted aortic arch based on a multi-institutional study of 50 neonates in an effort to better define the morphology and characteristics of this particular anomaly. A simplified classification based on pulmonary or aortic dominance has more recently been advocated (Fig. 18.3). This simplified approach emphasizes the principal morphologic determinant of surgical outcome, with patients in the more common aortic dominant category (Fig. 18.3B) having higher survival than the less common pulmonary dominant group (Fig. 18.3A).

Figure 18.1. Truncus arteriosus classifications. (From Frank L, Dillman JR, Parish V, et al. Cardiovascular MR imaging of conotruncal anomalies. Radiographics. 2010 Jul–Aug;30(4):1069–1094.)

Figure 18.2. Truncus arteriosus with interrupted aortic arch classification. Ao, aorta, LSA, left subclavian artery. (Reproduced with permission from Konstantinov IE, et al. Ann Thorac Surg. 2006;81:214–223.)

The truncal valve commonly overrides both ventricles, but may be more committed to one ventricle than the other. Isolated truncal root origin from a ventricle is more common from the right ventricle than from the left ventricle. The truncal valve has a variable number of leaflets (one to six), and they are often morphologically thickened and dysplastic. Approximately two-thirds of all truncal valves are trileaflet, whereas almost one-quarter are quadricuspid. Less than 10% are found to be bicuspid. The truncal valve may be competent, but is more commonly regurgitant and/or stenotic because of the valve’s abnormal morphology.

CLINICAL PRESENTATION

Truncus arteriosus may be diagnosed prenatally with fetal echocardiography, although it can be difficult to diagnose from traditional obstetrical screening ultrasound four-chamber views. One of the keys to fetal diagnosis of truncus arteriosus is correct identification of the origin of the pulmonary arteries from the posterior aspect of the aorta (Videos 18.1 and 18.2). Patients not diagnosed prenatally with truncus arteriosus typically present during early infancy with tachypnea, feeding difficulty, failure to thrive, or other symptoms and signs related to pulmonary overcirculation as pulmonary vascular resistance falls. Patients with truncus and interrupted aortic arch typically present earlier because of decreased perfusion. The cardiac examination in patients with truncus arteriosus typically demonstrates a hyperactive precordium and a widened pulse pressure. There is characteristically a loud single S2, with a loud systolic murmur. Patients often have a click from the truncal valve and may have a diastolic murmur if there is significant truncal valve regurgitation. The chest radiograph demonstrates cardiomegaly and increased pulmonary vascularity because of an increase in pulmonary blood flow. One-third of patients have a right-sided aortic arch. The electrocardiogram typically shows biventricular hypertrophy.

Figure 18.3. Truncus arteriosus: pulmonary versus aortic dominance. Ao, aorta; LPA, left pulmonary artery; LV, left ventricle; MV, mitral valve; RV, right ventricle; RPA right pulmonary artery; VSD, ventricular septal defect. (Reproduced with permission from Russell HM, et al. J Thorac Cardiovasc Surg 2011;141:645–53.)

ASSOCIATED CONDITIONS

Cardiac abnormalities commonly associated with truncus arteriosus include (a) coronary artery anomalies, with a single coronary artery and an intramural course having the most important surgical implications, (b) right aortic arch, (c) secundum atrial septal defect, (d) left superior vena cava to coronary sinus, and (e) interrupted aortic arch (Table 18.1). Absence or atresia of the ductus arteriosus is usually expected with truncus arteriosus, the exception being truncus arteriosus with an interrupted aortic arch. Extracardiac anomalies include renal, skeletal, intestinal, and systemic defects. The association of truncus arteriosus with DiGeorge syndrome and chromosome 22 deletion is well recognized, with up to 35% of patients with truncus arteriosus having DiGeorge syndrome.

ECHOCARDIOGRAPHIC FEATURES

Two-Dimensional Echocardiographic Examination

Echocardiography has evolved as the modality of choice for diagnosing the many anatomic variations of truncus arteriosus. The anatomic information obtained from two-dimensional and Doppler echocardiography is usually sufficient to send the patient for surgical repair without the need for further testing.

In the parasternal long-axis view, the diagnosis of truncus arteriosus is suggested by a dilated single great artery, in continuity with the mitral valve, arising from the base of the heart, overriding the interventricular septum concomitant with a malalignment type VSD (Fig. 18.4). In truncus arteriosus type I, the short main pulmonary artery segment can frequently be seen arising from the truncal vessel posteriorly and leftward. (Videos 18.3 through 18.7) In some cases of truncus arteriosus, sweeping from the right to the patient’s left in the long axis demonstrates the deficiency of a separate pulmonary valve and the pulmonary arteries arising from the truncal vessel.

The parasternal short-axis view at the base of the heart is the preferred view for determining truncal valve morphology and number of leaflets (Fig. 18.5). It is an excellent window to view the VSD in the outlet septum. The pulmonary valve, main pulmonary artery, and branches are absent from their usual location. Visualization of the pulmonary arteries arising from the common truncus is a key finding in differentiating this anomaly from pulmonary atresia with VSD. The coronary artery origins and proximal courses are usually best imaged from the parasternal short-axis views, with the right coronary artery originating from the anterolateral aspect of the truncal root and the left coronary artery originating from the left posterolateral aspect of the truncal root. In truncus arteriosus type I, the truncal vessel can be seen in cross section with a short main pulmonary artery segment originating from the lateral aspect and bifurcating into the right and left pulmonary arteries. In truncus arteriosus type II, the pulmonary artery branches can be seen emerging posteriorly from the truncal root, originating from close but separate orifices (Fig. 18.6) (Videos 18.8 through 18.15). In truncus arteriosus type III (Collett and Edwards), it is seldom possible to image both branch pulmonary arteries simultaneously in the parasternal short-axis view because both pulmonary arteries originate independently from widely separated origins off the truncal root.

Figure 18.4. Parasternal long-axis view. Note the truncus arteriosus (T) overriding the large ventricular septal defect (yellow asterisk). LA, left atrium; LV, left ventricle; RV, right ventricle.

Figure 18.5. Parasternal short-axis view of a quadricuspid truncal valve.

The apical and subcostal views allow evaluation of the VSD, the degree of truncal override, the ventricular sizes, and the origin of the main and/or branch pulmonary arteries (Fig. 18.7). In truncus arteriosus type I, tilting the scan plane anteriorly in the apical four-chamber view allows the main pulmonary artery and branch pulmonary arteries to be visualized originating from the posterior aspect of the truncal root. The degree of truncal valve dysplasia may also be assessed from the apical and subcostal views, and these views typically provide for excellent Doppler evaluation of the truncal valve. Defects in the atrial septum are commonly present with truncus arteriosus and are optimally seen from the subcostal windows.

Figure 18.6. High parasternal short-axis view of a type II truncus arteriosus. Note the separate origins of the branch pulmonary arteries. LPA, left pulmonary artery; RPA right pulmonary artery; T, truncus arteriosus.

The suprasternal notch views are valuable for determining aortic arch sidedness, along with branch pulmonary artery anatomy and distribution. Aortic arch anomalies are common in patients with truncus arteriosus, with a right aortic arch being the most common. Truncus arteriosus with an interrupted aortic arch occurs in up to 20% of patients and is best diagnosed from the suprasternal notch views. (Videos 18.16 through 18.22) From an echocardiographic standpoint, truncus arteriosus with interrupted aortic arch presents a unique challenge due to the anatomic complexity and potential surgical implications. Defining the aortic arch branching pattern and head and neck vessels is critical to correctly defining this anatomy (Fig. 18.8).

Figure 18.7. Subcostal coronal view demonstrating a type I truncus arteriosus. Note the main pulmonary artery (MPA) (yellow arrow) arising from the truncus arteriosus (T). LPA, left pulmonary artery; LV, left ventricle; RPA, right pulmonary artery.

Figure 18.8. Suprasternal notch view of truncus arteriosus with an interrupted aortic arch. AAo, ascending aorta; DAo, descending aorta; LSCA, left subclavian artery; T, truncus arteriosus; yellow asterisk, patent ductus arteriosus.

Doppler Echocardiographic Examination

The Doppler examination in truncus arteriosus should focus primarily on those factors that have the greatest influence on the patient’s hemodynamic state—truncal valve stenosis/regurgitation and pulmonary artery blood flow. Color flow Doppler can provide a qualitative estimation of truncal valve insufficiency as well as identifying aliased flow at the level of the truncal valve in cases of truncal valve stenosis (Fig. 18.9). The peak and mean gradients across the truncal valve can be estimated using continuous-wave Doppler and the Bernoulli equation. Color flow Doppler is useful in delineating pulmonary artery anatomy as well as complex sources of pulmonary blood flow, particularly when pulmonary blood flow is supplied via aortopulmonary collaterals. Spectral Doppler is useful when interrogating the pulmonary arteries for the presence of stenosis, which can occur at any level but is most commonly at the takeoff from the truncal root.

Figure 18.9. Parasternal long-axis view with truncal valve regurgitation (yellow arrow head) demonstrated by color Doppler. LV, left ventricle; T, truncus arteriosus.

In addition, color Doppler echocardiography can help to identify the origin and anatomic patterns of the coronary arteries. In cases of truncus arteriosus with interrupted aortic arch, color Doppler can greatly aid in the diagnosis and identification of the arch vessel anatomy. Additional VSDs, not easily seen by two-dimensional echocardiography alone, can be identified using color flow Doppler.

Preoperative Echocardiographic Evaluation of Truncus Arteriosus

The accurate preoperative assessment of truncus arteriosus can have a profound impact on clinical and surgical management. The preoperative two-dimensional and Doppler echocardiographic assessment should include an accurate description of the following:

1.Type of truncus arteriosus

2.Pulmonary artery anatomy and size

3.Ventricular septal defect, size, and location

4.Coronary artery anatomy and distribution

5.Truncal valve morphology and degree of truncal override

a.Severity of truncal valve stenosis—estimated by the peak and mean Doppler gradients

b.Severity of truncal valve regurgitation—estimated by the regurgitant jet characteristics and Doppler velocity pressure half-time

6.Associated cardiac anomalies

a.Right aortic arch

b.Atrial septal defect

c.Additional ventricular septal defects

d.Persistent left superior vena cava to the coronary sinus

e.Absence of the ductus arteriosus

f.Interrupted aortic arch

Postoperative Echocardiographic Evaluation of Truncus Arteriosus

The surgical repair of truncus arteriosus consists of removing the pulmonary arteries from the truncal root, patch closure of the VSD, and usually placement of a valved conduit between the right ventricle and the pulmonary arteries (Fig. 18.10). When the truncal valve is significantly regurgitant or stenotic, repair or replacement with a homograft valve is typically performed. Intraoperative transesophageal echocardiography is usually performed to evaluate the cardiac repair. Patients are followed longitudinally for evidence of right ventricle–to–pulmonary artery conduit stenosis and/or regurgitation, because these conduits typically require replacement over time and as the patient grows (Figs. 18.11 and 18.12). Patients may develop branch pulmonary artery stenosis, and some require intervention, such as pulmonary artery stenting (Figs. 18.13 to 18.15). Truncal (neoaortic) valve regurgitation should be monitored serially, and some patients may require valvuloplasty or valve replacement. When echocardiography alone does not provide adequate information, then other imaging modalities may be used such as cardiac magnetic resonance imaging, computed tomography, or cardiac catheterization with angiography.

Figure 18.10. Figure of truncus arteriosus following surgical repair with patch closure of the ventricular septal defect and right ventricle–to–pulmonary artery conduit. (Reproduced with permission from Slesnick TC, Kovalchin JP. Truncus arteriosus. In: McMilan JA, ed. Oski’s Pediatrics. 4th ed. Philadelphia: Lippincott Williams & Wilkins; 2006:1540–1543.)

Figure 18.11. Parasternal short-axis view of the right ventricle (RV) to pulmonary conduit (C) following surgical repair. Note the turbulent Doppler flow representing conduit stenosis. RPA, right pulmonary artery; T, truncus.

Figure 18.12. Continuous-wave Doppler demonstrating conduit stenosis.

The postoperative two-dimensional and Doppler echocardiographic assessment should include an accurate assessment of the following:

1.Residual shunting across the VSD patch

2.Stenosis across the right ventricle–to–pulmonary artery conduit, including the peak and mean Doppler velocity gradients

3.Degree of pulmonary regurgitation

4.Branch pulmonary artery size and the presence of any stenosis

5.Truncal valve stenosis and regurgitation

6.Left ventricular outflow tract patency

7.Right ventricular systolic pressure based on either the peak Doppler velocity of a residual VSD or tricuspid regurgitation jet, if available

8.Evaluation of the aortic arch

9.Right and left ventricular size and function

Figure 18.13. Parasternal short-axis view. Severe right pulmonary artery stenosis (RPA) (yellow arrow head) following truncus arteriosus repair demonstrated by color Doppler. C, conduit; RPA, right pulmonary artery.

Figure 18.14. Cardiac computed tomography three-dimensional reconstruction demonstrating diffusely small branch pulmonary arteries following surgical repair. C, conduit; LPA, left pulmonary artery; RPA, right pulmonary artery.

Figure 18.15. Cardiac computed tomography. Axial image demonstrating bilateral pulmonary artery stents for severe branch pulmonary artery stenosis following truncus arteriosus repair. AAo, ascending aorta; C, conduit; DAo, descending aorta; LPA, left pulmonary artery; RPA, right pulmonary artery.

SUMMARY

Truncus arteriosus is a rare form of congenital heart disease with several distinct variations. Echocardiography is the primary tool for preoperative assessment of cardiac anatomy and in determining the surgical approach. Postoperative patients are followed serially by echocardiography to monitor for potential problems that may develop over time. Additional forms of noninvasive cardiac imaging such as magnetic resonance imaging or computed tomography become more important as these patients become older and echocardiographic imaging alone may not be sufficient.

SUGGESTED READING

Cabalka AK, Edwards WD, Dearani JA. Truncus arteriosus. In: Allen HD, Driscoll DJ, Shaddy RE, Feltes TF, eds. Moss and Adams’ Heart Disease in Infants, Children and Adolescents: Including the Fetus and Young Adult. 7th ed. Philadelphia: Lippincott Williams & Wilkins; 2008.

Collett RW, Edwards JE. Persistent truncus arteriosus: a classification according to anatomic types. Surg Clin North Am. 1949;29:1245.

Konstantinov IE, Karamlou T, Blackstone EH, et al. Truncus arteriosus associated with interrupted aortic arch in 50 neonates: a Congenital Heart Surgeons Society study. Ann Thorac Surg. 2006 Jan;81(1):214–22.Nguyen T, John JB, Nardell K, et al. Echocardiography of common arterial trunk. Cardiol Young.2012;22:655–63.

Russell HM, Jacobs ML, Anderson RH, et al. A simplified categorization for common arterial trunk. J Thorac Cardiovasc Surg. 2011;141:645–653.

Slesnick TC, Kovalchin JP Truncus arteriosus. In: McMilan JA, ed. Oski’s Pediatrics. 4th ed. Philadelphia: Lippincott Williams & Wilkins; 2006:1540–1543.

Van Praagh R, Van Praagh S: The anatomy of common aorticopulmonary trunk (truncus arteriosus communis) and its embryological implications. Am J Cardiol. 1965;16:406.

Questions

1.What is the most common number of truncal valve leaflets?

A.1

B.2

C.3

D.4

E.6

2.What syndrome is most often associated with truncus arteriosus?

A.Turner

B.DiGeorge

C.Williams

D.Noonan

E.Marfan

3.What percentage of patients with truncus arterious will have an interrupted aortic arch?

A.Less than 5%

B.10-20%

C.25%

D.Over 50%

E.40-50%

4.Which of the following is the most common associated cardiac finding with truncus arteriosus?

A.Atrial septal defect

B.Left superior vena cava

C.Interrupted aortic arch

D.Patent ductus arteriosus

E.Coronary artery anomaly

5.Where do patients with truncus arteriosus and interrupted aortic arch most often have the interruption?

A.Before the right innominate artery

B.Between the right subclavian artery and right carotid artery

C.Between the right carotid artery and left carotid artery

D.Between the left carotid artery and the left subclavian artery

E.After the left subclavian artery

6.What percentage of patients with truncus arteriosus have a right aortic arch?

A.Less than 5%

B.10%

C.25%

D.30-40%

E.Over 50%

7.In Type I truncus arteriosus, where do the pulmonary arteries arise?

A.The main pulmonary artery arises from the truncal root and bifurcates into a right and a left pulmonary artery.

B.Each pulmonary artery originates from a separate origin off the posterior aspect of the truncal root.

C.Each pulmonary artery arises independently from the lateral aspects of the truncal root

D.No true pulmonary arteries are present and pulmonary blood flow is supplied via aortopulmonary collateral vessels.

E.One arises from the truncal root and the other is atretic.

8.What percentage of patients with truncus arteriosus have coronary artery anomalies?

A.30-50%

B.10%

C.Less than 5%

D.20%

E.Over 50%

9.What type of ventricular septal defect is typically found in truncus arteriosus?

A.Subpulmonary

B.Muscular

C.Perimembranous

D.Inlet

E.Outlet

10.The truncal valve shown in the video clip demonstrates how many cusps?

A.1

B.2

C.3

D.4

E.6

Answers

1.Answer: C. The truncal valve has a variable number of leaflets (one to six), and they are often morphologically thickened and dysplastic. Approximately two-thirds of all truncal valves are trileaflet, whereas almost one-quarter are quadricuspid. Less than 10% are found to be bicuspid.

2.Answer: B. The association of truncus arteriosus with DiGeorge syndrome and Chromosome 22 deletion is well recognized, with up to 35% of patients with truncus arteriosus having DiGeorge syndrome.

3.Answer: B. Approximately 10-20% of patients with truncus arteriosus have an interrupted aortic arch.

4.Answer: E. Coronary artery anomaly is the most commonly associated cardiac finding with truncus arteriosus, occurring in 30-50% of cases.

5.Answer: D. In cases of truncus arteriosus with aortic arch interruption, Type B (between the left carotid artery and the left subclavian artery) is the most common form of interruption.

6.Answer: D. Approximately 30-40% of patients with truncus arteriosus have a right aortic arch.

7.Answer: A. In Type I, the main pulmonary artery arises from the truncal root and bifurcates into a right and a left pulmonary artery.

8.Answer: A. Coronary artery anomalies are present in 30-50% of patients with truncus arteriosus, with a single coronary artery and an intramural course having the most important surgical implications.

9.Answer: E. The anatomic description of truncus arteriosus consists of an outlet ventricular septal defect (VSD), a single semilunar valve, and a common great artery that overrides the VSD.

10.Answer: D. The video demonstrates that the truncal valve is quadricuspid.