Persistent truncus arteriosus
|Persistent truncus arteriosus|
|Other names: Patent truncus arteriosus, common arterial trunk|
|Illustration of truncus arteriosus|
|Symptoms||First few days: Mild bluish skin|
Later: Poor activity, poor feeding, fast breathing
|Complications||Heart failure, Eisenmenger syndrome|
|Usual onset||Present at birth|
|Risk factors||DiGeorge syndrome|
|Diagnostic method||Ultrasound of the heart|
|Differential diagnosis||Tetralogy of Fallot, tricuspid atresia, total anomalous pulmonary venous return, hypoplastic left heart syndrome, coarctation of the aorta|
|Treatment||Prostaglandin E1, breathing support, furosemide, surgery|
|Prognosis||20 year survival >80% with treatment|
|Frequency||7 per 100,000 live births|
Persistent truncus arteriosus (PTA) is a congenital heart disease that presents with a common ventricular outflow tract, ventricular septal defect (VSD), and single truncal valve. In the first few days of life bluish skin is generally mild. Without treatment, this is followed by heart failure with poor activity, poor feeding, and fast breathing. Complications may include Eisenmenger syndrome.
The cause is generally unknown, though the condition may be associated with DiGeorge syndrome. The underlying mechanism involves failure of the truncus arteriosus to divide into the pulmonary trunk and aorta during early development. This results in blood from both sides of the heart mixing before it enters the coronary arteries, pulmonary arteries, and systemic circulation. The condition may be suspected based on an ECG showing enlargement of both ventricles, a chest X-ray showing a large heart, and a systolic heart murmur. Confirmation is by ultrasound of the heart.
Initial treatment may include prostaglandin E1 and breathing support. If pulmonary edema is present furosemide, CPAP, and avoiding extra oxygen may be recommended. Surgery correction is generally recommended within the first month of life. About 75% of people require a further operation in their next 10 years of life.
PTA is rare, affecting about 7 per 100,000 live births. It makes up less than 1% of cases of congenital heart disease. Without treatment, death generally occurs within a year of birth. With surgery; however, more than 80% live more than 20 years. The work "truncus arteriosus" is Latin for single artery. It was first described by Wilson in 1798.
Signs and symptoms
In the first few days of life bluish skin is generally mild. Without treatment, this is followed by heart failure with poor activity, poor feeding, and fast breathing. Complications may include Eisenmenger syndrome.
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 (DiGeorge syndrome). The neural crest, specifically a population known as the cardiac neural crest, directly contributes to the aorticopulmonary septum.
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 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
- right-to-left shunting of blood
- Cyanosis presents at birth
- Heart failure may occur within weeks
- Systolic ejection murmur is heard at the left sternal border
- Widened pulse pressure
- Bounding arterial pulses
- Loud second heart sound
- Biventricular hypertrophy
- Increased pulmonary vascularity
- Hypocalcemia (if associated with DiGeorge syndrome)
The most well-known classification was the fourfold system developed by Collett and Edwards in 1949. Collett/Edwards Types I, II, and III are distinguished by the branching pattern of the pulmonary arteries:
- 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.
Treatment is with neonatal surgical repair, with the objective of restoring a normal pattern of blood flow. The surgery is open heart, and the patient will be placed on cardiopulmonary bypass to allow the surgeon to work on a still heart. The heart is opened and 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). The common artery, now separated from the pulmonary circulation, functions as the aorta with the truncal valve operating as the aortic valve. Most babies survive this surgical repair, but may require further surgery as they grow up. For example, the conduit does not grow with the child and may need to be replaced as the child grows. Furthermore, the truncal valve is often abnormal and may require future surgery to improve its function. There have been cases where the condition has been diagnosed at birth and surgical intervention is an option. A number of these cases have survived well into adulthood.
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