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Persistent Truncus Arteriosus

by Jeanne Marie Baffa, MD

Persistent truncus arteriosus occurs when, during fetal development, the primitive truncus does not divide into the pulmonary artery and aorta, resulting in a single, large, arterial trunk that overlies a large, malaligned, perimembranous ventricular septal defect. Consequently, a mixture of oxygenated and deoxygenated blood enters systemic, pulmonary, and coronary circulations. Symptoms include cyanosis and heart failure, with poor feeding, diaphoresis, and tachypnea. A normal 1st heart sound (S 1 ) and a loud, single 2nd heart sound (S 2 ) are common; murmurs may vary. Diagnosis is by echocardiography or cardiac catheterization. Medical treatment for heart failure is typically followed by early surgical repair.

Persistent truncus arteriosus (see Figure: Truncus arteriosus.) accounts for 1 to 2% of congenital heart anomalies. About 35% of patients have 22q11 deletion syndrome, which includes DiGeorge syndrome and velocardiofacial syndromes.

Truncus arteriosus.

The primitive truncus does not divide into the pulmonary artery and aorta, resulting in a single large arterial trunk that overlies a large ventricular septal defect.

IVC = inferior vena cava; LA = left atrium; LV = left ventricle; PA = pulmonary artery; PV = pulmonary veins; RA =right atrium; RV = right ventricle; SVC = superior vena cava.

Classification

There are several classification systems in use.

The first classification, by Collett and Edwards, is

  • Type I: The main pulmonary artery arises from the truncus and then divides into the right and left pulmonary arteries.

  • Type II: The right and left pulmonary arteries arise separately (but adjacent to each other) from the posterior aspect of the truncus.

  • Type III: The right and left pulmonary arteries arise from the lateral aspects of the truncal root reasonably distant from each other.

  • Type IV: Both pulmonary arteries are supplied by collateral vessels from the descending aorta. (Type IV is now reclassified as tetralogy of Fallot with pulmonary atresia.)

An updated classification by Van Praagh consists of type A (truncus arteriosus with ventricular septal defect [VSD]) and the very rare type B (truncus arteriosus without VSD). Type A is subdivided into 4 types:

  • Type A1: The main pulmonary artery arises from the truncus and then divides into right and left pulmonary arteries.

  • Type A2: The right and left pulmonary arteries arise separately from the posterior aspect of the truncus.

  • Type A3: One lung is supplied by a pulmonary artery branch that arises from the truncus and the other lung (usually the left) is supplied by a ductus-like collateral artery

  • Type A4: The truncus is a large pulmonary artery and the aortic arch is interrupted or coarctation is present.

The truncal valve may be quite abnormal and manifest with stenosis, insufficiency, or both. Other anomalies (eg, right aortic arch, interrupted aortic arch, coronary artery anomalies, atrioventricular septal defect) may be present and may contribute to the high surgical mortality rate.

Physiologic consequences of truncus arteriosus include mild cyanosis, significant pulmonary overcirculation, and heart failure (HF).

Symptoms and Signs

Infants usually present with mild cyanosis and symptoms and signs of HF (eg, tachypnea, poor feeding, diaphoresis) in the first few weeks of life. Physical examination may detect a hyperdynamic precordium, increased pulse pressure with bounding pulses, a loud and single 2nd heart sound (S 2 ), and an ejection click. A grade 2 to 4/6 systolic murmur is audible along the left sternal border. A mid-diastolic mitral flow murmur may be audible at the apex when pulmonary blood flow is increased. With truncal valve insufficiency, a high-pitched diastolic decrescendo murmur is audible over the mid left sternal border.

Diagnosis

  • Chest x-ray and ECG

  • Echocardiography

  • Occasionally cardiac catheterization, cardiac MRI, or CT angiography

Diagnosis is suspected clinically, supported by chest x-ray and ECG, and established by 2-dimensional echocardiography with color flow and Doppler studies. Cardiac catheterization is occasionally necessary to delineate associated anomalies before surgery, but cardiac MRI or CT angiography may supplant the need for catheterization.

Chest x-ray shows varying degrees of cardiomegaly with increased pulmonary vascular markings, right aortic arch (in about 30%), and relatively high position of pulmonary arteries. ECG commonly shows combined ventricular hypertrophy. Substantial pulmonary overcirculation may produce evidence of left atrial enlargement.

Treatment

  • Surgical repair

  • Medical treatment of HF (eg, diuretics, digoxin, ACE inhibitors) before surgery

HF is treated vigorously with diuretics, digoxin, and ACE inhibitors, followed by early surgical repair. Prostaglandin infusion is not beneficial.

Surgical management consists of complete repair. The VSD is closed so that the left ventricle ejects into the truncal root. A conduit with or without a valve is placed between the right ventricle and the confluence of the pulmonary arteries. Surgical mortality rates have decreased to as low as 10% in recent years. Because the conduit is placed during early infancy, its size becomes inadequate as children grow, and the conduit must be revised during childhood. Branch pulmonary artery stenosis is a common sequela.

Endocarditis prophylaxis is recommended preoperatively but is required only for the first 6 mo after repair unless there is a residual defect adjacent to a surgical patch or prosthetic material.

Key Points

  • In persistent truncus arteriosus, the primitive truncus does not divide into the pulmonary artery and aorta, resulting in a single large arterial trunk that overlies a large ventricular septal defect (VSD).

  • Different types are distinguished based on the origin of the pulmonary arteries and associated defects.

  • Patients present with mild cyanosis, significant pulmonary overcirculation, and heart failure (HF); a grade 2 to 4/6 systolic murmur is audible along the left sternal border and a mid-diastolic mitral flow murmur may be audible at the apex.

  • Treat HF with diuretics, digoxin, and ACE inhibitors; prostaglandin infusion is not beneficial.

  • Do surgical repair early; one or more revisions are usually needed as children grow.

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