Truncus Arteriosus
Truncus Arteriosus accounts for 1-4% of all CHD, is more frequent in males and is associated with extra-cardiac anomalies in 20-30 % of cases. It is characterized by a single arterial trunk arising from the heart supplying the systemic, pulmonary and coronary circulation, and results from a defect in cono-truncal septation. This accounts for the almost universally large ventricular septal defect. The truncal valve may have one, or as many as six cusps - but is most commonly tricuspid, quadricuspid or bicuspid. In addition, the truncal valve may be stenotic and is often insufficient, sometimes significantly.
NOTES: Truncus Arteriosus
Truncus Arteriosus can be classified into 3 types depending on the site of origin of the pulmonary arteries. Type I (50-68%): a short pulmonary trunk that gives rise to the pulmonary arteries. Type II ( 25-48%): the pulmonary artery branches arise separately, but very close to each other from the posterior aspect of the truncal vessel. Type III (5-10%): the pulmonary arteries arise separately from the lateral aspect of the truncal vessel. Historically, some authors referred to a 'Type IV Truncus Arteriosus'. In fact, this complex actually represents a form of Pulmonary Atresia-VSD with multiple arterial collaterals from the descending aorta.
Truncus Arteriosus accounts for 1-4% of all CHD, and is more frequent in males. It is associated with extra-cardiac anomalies in 20-30 % of cases and there is a strong association with Di-George Syndrome and microdeletions of the short arm of chromosome 22q11. Associated cardiac anomalies include: right aortic arch, interrupted aortic arch type B (between the left carotid artery and the left subclavian artery), coronary arteries anomalies, and absence of the ductus arteriosus.
Clinical features depend on the amount of pulmonary blood flow and degree of truncal valve insufficiency. The majority of the patients have adequate or increased pulmonary blood flow so they present with little or no cyanosis and signs of congestive heart failure. Physical findings in this clinical scenario consist of bounding pulses, wide pulse pressure, and hyperactive precordium. Auscultation is characterized by a normal S1, a systolic ejection sound, a loud and single S2, and typically a holosystolic murmur at the left lower sternal border. Diastolic murmurs occur when secondary to truncal valve insufficiency. Continuous murmurs are present if there is ostial stenosis. When the pulmonary blood flow is reduced, patients present with cyanosis.
ECG findings include left atrial enlargement, RVH or biventricular hypertrophy. Chest X-ray will reflect the pulmonary blood flow. When excessive, the chest radiograph shows moderate cardiomegaly with increased pulmonary vascular markings, and right aortic arch. When diminished because of pulmonary artery ostial stenosis, there is oligemia in the lung fields. Echocardiography allows complete diagnosis diagnosis, including the type of truncus, degree of pulmonary blood flow, truncal valve function and associated anomalies.
Differential diagnosis includes conditions that cause early heart failure and little or no cyanosis, including large volume VSD, AVSD, large PDA, aorto-pulmonary window, DORV without limitation to pulmonary blood flow, univentricular hearts without pulmonary stenosis, and total anomalous pulmonary venous connections without obstruction - among others. In neonates who present with cyanosis other lesions have to be considered among the differential diagnosis: e.g. tricuspid atresia, pulmonary atresia, tetralogy of Fallot, transposition of the great arteries, DORV or univentricular hearts with PS.
Treatment includes management of congestive heart failure and early corrective surgery by the Rastelli technique whereby the VSD is closed, the pulmonary arteries are separated from the Truncus and made confluent and a connection is established from the right ventricle to the pulmonary artery confluence.
Parasternal long axis view in motion.
Color doppler parasternal long axis view shows the flow across the VSD where there is the over-riding great vessel. The common great vessel valve is abnormal and
regurgitant.
Labelled short axis view at the level of the great vessel shows by the arrow the connection between the aorta (Ao) and pulmonary artery (PA).
Short axis echo view of the proximal common great vessel shows the right pulmonary artery arising from the vessel and swinging behind the aorta.
Post-op repair of the truncus anatomy was achieved in this patient with closure of the Ao-PA communication and insertion of a Rastelli conduit into the main pulmonary artery segment.
Xray of a young adult with truncus. Note the over-circulation of the pulmonary arteries and the broadening of the aortic knob.