Common Arterial Trunk

Common arterial trunk (CAT) is characterized by a single arterial trunk that arises from the base of the heart and gives origin to the systemic, coronary and pulmonary circulation. A large ventricular septal defect (VSD) is almost always present.

CAT results from a septation failure during development of the ventricular outlets and the proximal arterial segment of the heart tube. According to the Collett and Edwards classification, CAT can be divided into different anatomical subtypes based on the anatomic origin of the pulmonary arteries:

- Type I: the main pulmonary trunk arises from the truncal artery just distal to the truncal valve;

- Types II and III: the pulmonary trunk is absent and both pulmonary arteries arise separately, as individual branches, from the posterior aspect of the trunk but close to each other (type II) or originating at different distance from the truncal valve (type III).

- Type IV, characterized by absence of branch pulmonary arteries and presence of aortopulmonary collaterals,is now reclassified as pulmonary atresia with ventricular septal defect (PA-VSD).

The CAT root is large and has a biventricular origin in most cases. However, in up to the 30% of cases the roots appears to arise entirely from the right ventricle and in rare cases from the left ventricle. The CAT valve is abnormal and dysplastic in the vast majority of cases: it has three leaflets (tricuspid) in about 69% of cases, four leaflets (quadricuspid) in 22%, and two leaflets (biscuspid) in 9% of cases.

CAT occurs in about 1.07 of 10.000 births and it's found in 1.6% of all newborns with congenital heart disease.

The four-chamber view appears normal, unless the VSD is large and visible in this plane. The constant malalignment VSD with an overriding large vessel is best displayed on the long-axis view of the left ventricle ( or on five-chamber view), as well as an absence of a separate pulmonary artery and valve arising from the right ventricle. Confirmation of the diagnosis and differentiation from tetralogy of Fallot (TOF) and PA-VSD is usually made by identifying the pulmonary trunk (or arteries) directly arising from the overriding large vessel in the long-axis view of the left ventricle ( or in the five-chamber view). In type I CAT, the main pulmonary trunk arises from the postero-lateral aspect of the common trunk and bifurcates into two pulmonary arteries. In types II and III, the pulmonary arteries arise separately.

The three-vessel view shows a single large vessel, which represents the aortic arch.

The truncal valve is almost always dysplastic; it may be insufficient or stenotic, and it could be also demonstrated in short-axis view. Color Doppler may be used to evaluate the steno-insufficiency of the truncal valve and to trace the course and connection of the pulmonary trunk and arteries. Spectral Doppler may help to quantify the degree of truncal valve stenosis and insufficiency.

Two cardiac anomalies should be considered in the differential diagnosis: TOF and PA-VSD, since both have an associated VSD and an overriding aorta. The demonstration of a common origin of both the aorta and the pulmonary artery from a large overriding trunk is crucial for the correct diagnosis of CAT. The semilunar valve is always dysplastic and typically stenotic and/or insufficient in CAT, which is unfrequent in TOF and PAVSD.

Associated cardiac malformations are common in CAT, including absence of ductus arteriosus (50% of cases), aortic arch anomalies and atrio-ventricular valve atresia.

Extracardiac structural malformations are present in up to 40% of cases. Numerical chromosomal anomalies are found in about 4.5% and include trisomies 21, 18 and 13 and 22q11 microdeletion (20%–30% of cases).

A detailed fetal anomaly scan should be performed by an expert to exclude the presence of extracardiac and cardiac abnormalities. Fetal karyotyping should be offered in view of the high risk of associated chromosomal anomalies and it has to include FISH analysis for the 22q11 microdeletion.

Delivery should take place in a tertiary referral center to ensure confirmation of the diagnosis and adequate neonatal management.

Prognosis is related to the presence of associated anomalies and of unfavorable cardiac anatomy.

Survival beyond infancy is uncommon without corrective surgery which should be performed in the first two-three months of life. Surgery consists in three parts: closure of the VSD, detachment of the pulmonary arteries from the truncal root, and reattachment of the pulmonary arteries to the right ventricle with a conduit. In recent series, the overall operative mortality rate is as low as 5%, if no severe truncal valve abnormalities are present.

Volpe P, Fanelli T,  Common Arterial Trunk, VISUOG, September 2014

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