Persistent truncus arteriosus

Persistent truncus arteriosus (or Truncus arteriosus) is a rare form of congenital heart disease that presents at birth. In this condition, the embryological structure known as the truncus arteriosus never properly divides into the pulmonary artery and aorta.

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Classification

The most well-known classification was the fourfold system developed by Collett and Edwards in 1949.^[1] Collett/Edwards Types I, II, and III are distinguished by the branching pattern of the pulmonary arteries:^[2][3]

• Type I: truncus -> one pulmonary artery -> two lateral pulmonary arteries
• Type II: truncus -> two posterior/posterolateral pulmonary arteries
• Type III: truncus -> two lateral pulmonary arteries

The "Type IV" proposed in 1949 is no longer considered a form of PTA by most modern sources.^[3]

Another well-known classification was defined by Van Praaghs in 1965.^[4][3]

Causes

Most of the time, this defect occurs spontaneously. Genetic disorders, and teratogens (viruses, metabolic imbalance, and industrial or pharmacological agents) have been associated as possible causes. Up to 50% (varies in studies) of cases are associated with chromosome 22q11 deletions. The neural crest, specifically a population known as the cardiac neural crest, directly contributes to the aorticopulmonary septum.^{[5] [6]}

Microablation of the cardiac neural crest in developing chick embryos and genetic anomalies affecting this population of cells in rodents results in persistent truncus arteriosus.^{[7] [8] [9]}

Numerous perturbations affecting the cardiac neural crest have been associated with persistent truncus arteriosus, some of which include growth factors (fibroblast growth factor 8 and bone morphogenetic protein), transcription factors (T-box, Pax, Nkx2-5, GATA-6, and Forkhead), and gap junction proteins (Connexin). The cardiac neural crest also contributes the smooth muscle of the great arteries.

Anatomical changes

Anatomical changes associated with this disorder includes:

• single artery arising from the two ventricles which gives rise to both the aortic and pulmonary vessels
• abnormal truncal valve
• right sided aortic arch in about 30% of cases (not shown)
• large ventricular septal defect
• pulmonary hypertension
• complete mixing occurring at level of the great vessel

Clinical manifestations

• Cyanosis presents at birth
• Heart failure occurs within weeks
• Systolic ejection murmur is heard at the left sternal border
• Widened pulse pressure
• Bounding arterial pulses
• Loud second heart sound
• Biventricular hypertrophy
• Cardiomegaly
• Increased pulmonary vascularity
• Hypocalcemia (if associated with DiGeorge syndrome)

Treatment

Treatment is with neonatal surgical repair.^[10] The ventricular septal defect is closed with a patch. The pulmonary arteries are then detached from the common artery (truncus arteriosus) and connected to the right ventricle using a tube (a conduit or tunnel).

References