Truncus arteriosus is a complex congenital heart defect involving a common channel for the LVOT and RVOT. This particular case shows a parasternal long axis with a common outflow tract in 2D and in colour for the ventricular output. More information on truncus arteriosus here.

Frequency: about 2% of all congenital heart defect. Conotruncal heart defect (think of DiGeorge syndrome). Left to right shunt by steal effect in the pulmonary vasculature. Bounding pulses. Rapid evolution towards fixation of pulmonary vascular resistances. Requires early surgical repair. Prognosis dictated often by the truncal valve who will become the systemic valve. The truncal valve has between 2 to 6 cusps. The valve may be insufficient, stenotic or both - this dictates the overall prognosis.

As the pulmonary vascular resistance drop, the overcirculation leads to pulmonary vascular congestion, increased pulmonary edema, which leads to tachypnea, increased work of breathing and a "congested" chest radiography. There is progressive diastolic steal effect from the systemic compartment, which puts these infants at risk of end-organ damage by ischemia / poor perfusion.  These patients are at risk for necrotizing enterocolitis. These patients may be desaturated because of the mixing within the same compartment. However, due to the increasing left to right shunt (and increased Qp:Qs), these patients may not appeart desaturated. 

Auscultation may have a benign systolic ejection murmur at left sternal border (often from the flow through the pulmonary artery). There may be a single second heart sound and ejection click. Truncal valve stenosis may be associated with systolic ejection murmur. Truncal valve insufficiency may be associated with a diastolic murmur. 

Collett and Edwards classification

Type I: Main pulmonary artery from common arterial trunk. It then divides in the branch pulmonary arteries (RPA and LPA).

Type II: RPA and LPA arise from posterior part of the common arterial trunk. 

Type III: RPA and LPA arise from lateral part of truncal root. 

Type IV: RPA and LPA supplied by collaterals from descending aorta. (Tetralogy of Fallot with pulmonary atresia and MAPCAs.)

Van Praagh classification

Type A (truncus arteriosus with ventricular septal defect) 

• A1: MPA from truncal vessel and divides into RPA and LPA

• A2: RPA and LPA arise separately from posterior part of truncal vessel 

• A3: One lung supplied by branch PA from the truncal vessel. The other lung (commonly the left) supplied by a ductus-like collateral. There is absence of a PA branch from truncal vessel supplying that other lung.  

• A4: Truncal vessel is a large PA. There is interruption of the aortic arch or presence of a coarctation.

Type B (truncus arteriosus without ventricular septal defect). 

Case 1

Parasternal long axis view showing the common arterial trunk. There is some mild truncal valve insufficiency. 

Case 2

Common arterial trunk (Truncus Arteriosus). Common origin of pulmonary arteries (type 1 - A1). Dysplastic (thick) truncal valve leaflets. The branch pulmonary artery are small / hypoplastic. There is some truncal valve insufficiency.