Truncus Arteriosus

Key Features

Essentials of Diagnosis

• Early heart failure (HF) with or without cyanosis

• Systolic ejection click

General Considerations

• Accounts for < 1% of congenital heart malformations

• A single great artery arises from the heart, giving rise to the systemic, pulmonary, and coronary circulations

• The number of truncal valve leaflets varies from two to six, and the valve may be insufficient or stenotic

• Divided into subtypes by the anatomy of the pulmonary circulation

  • A single main pulmonary artery may arise from the base of the trunk and gives rise to branch pulmonary arteries (type 1)

  • Alternatively, the pulmonary arteries may arise separately from the common trunk, either in close association with one another (type 2) or widely separated (type 3)

• The degree of systemic arterial oxygen saturation depends on the ratio of pulmonary to systemic blood flow

  • If pulmonary vascular resistance is normal, the pulmonary blood flow is greater than the systemic blood flow and the saturation is relatively high

  • If pulmonary vascular resistance is elevated because of pulmonary vascular obstructive disease or small pulmonary arteries, pulmonary blood flow is reduced and oxygen saturation is low

Clinical Findings

• Growth retardation, easy fatigability, and HF are most common manifestations

• High pulmonary blood flow is characteristic

• Cyanosis

  • Usually minimal

  • More profound in patients with decreased pulmonary blood flow

• Examination of the heart reveals a hyperactive precordium

• At the lower left sternal border

  • A systolic murmur is heard

  • A systolic thrill is common

  • A loud holosystolic murmur is audible

• A loud early systolic ejection click is commonly heard

• A diastolic flow murmur can often be heard at the apex due to increased pulmonary venous return crossing the mitral valve

• An additional diastolic murmur of truncal insufficiency may be present

• S₁ and S₂ are single and loud

• A VSD is always present

Diagnosis

Imaging

• Radiography

  • Shows cardiomegaly; absence of the main pulmonary artery segment; and a large aorta, which has a right arch 30% of the time

  • Pulmonary vascular markings vary with the degree of pulmonary blood flow

• Echocardiography

  • Shows override of a single great artery (similar to tetralogy of Fallot, but no second great artery arises directly from the heart)

  • Defines origin of the pulmonary arteries and the degree of truncal valve abnormality

  • Color-flow Doppler can aid in the description of pulmonary flow and the function of the truncal valve, both of which are critical to management

  • Identifies associated lesions that will impact surgical planning, such as the presence of an interrupted aortic arch

Diagnostic Procedures

• Electrocardiography

  • The axis is usually normal

  • Right ventricular hypertrophy or combined ventricular hypertrophy is commonly present

• Cardiac catheterization

  • Not routinely performed

  • May be of value in older infants in whom pulmonary vascular disease must be ruled out

• Angiocardiography

  • One injection demonstrates origin of ...