Truncus Arteriosus

Excerpt

Truncus arteriosus is a rare, congenital, cyanotic cardiac anomaly characterized by a ventricular septal defect (VSD), a single truncal valve, and a common ventricular outflow tract. Systemic and pulmonary venous blood mix at the VSD and desaturated blood is ejected into the outflow tract. The pulmonary arteries arise directly from the truncus. Thus, pulmonary vascular resistance (PVR) determines the amount of pulmonary blood flow (PBF). Death in infancy is probable without surgical intervention. Long-term surgical outcomes are positive, but residual and potential complications require long-term cardiology follow-up.

Anatomy

The most salient pathologic finding in truncus arteriosus is the absence of an aorticopulmonary septum (21%). However, the most common truncus arteriosus type is a partially formed aorticopulmonary septum (50%). The typical semilunar valve may have 1 to 4 cusps, usually 3 (see Image. Truncus Arteriosus Embryologic Origin). The presence of a single arterial trunk may be associated with several cardiac, aortic, and pulmonary abnormalities. In order of frequency, aortic arch anomalies may include a right-sided, interrupted, or hypoplastic aortic arch with or without coarctation of the aorta.

Coronary origin is usually abnormal and follows no specific pattern. The pulmonary arteries are abnormal, ranging from a single small trunk to the left of the aortic root to originating at various locations from within the aortic root or a patent ductus arteriosus (PDA). Other cardiac defects that may coexist with a truncus arteriosus include secundum atrial septal defects, aberrant subclavian artery, persistent left superior vena cava with drainage into the coronary sinus, and PDA.

Classification

Collett and Edwards and Van Praagh each classified the various forms of truncus arteriosus. Collett and Edwards based their system solely on the origins of the pulmonary vascular system (see Image. Collett and Edwards' Truncus Arteriosus Classification), while Van Praagh also considered aortic abnormalities.

The Collett and Edwards classification includes the following subtypes of truncus arteriosus:

1. Type I: A main pulmonary trunk arising from the truncal root

2. Type II: Right and left branch pulmonary arteries have close but separate origins from the truncal root's posterior aspect

3. Type III: Right and left branch pulmonary arteries have separate origins, also from the truncal root

4. Type IV: Right and left branch pulmonary arteries originate from the descending aorta

Collett and Edwards Type IV truncus arteriosus is currently considered a form of pulmonary atresia. This differentiation emphasizes the specific developmental irregularities in each condition, distinguishing between truncus arteriosus' characteristic septation abnormalities and pulmonary atresia's subpulmonary myocardial developmental anomalies.

Meanwhile, the Van Praagh classification includes the following truncus arteriosus subtypes:

1. Type A1: A main pulmonary trunk arises from the truncal root, as in Collett and Edwards Type I. This type has a partially formed aorticopulmonary septum and is the most common (50%).

2. Type A2: The right and left branch pulmonary arteries have separate origins, like Collett and Edwards Types II and III. The aorticopulmonary septum is absent. This type is the second most common form of truncus arteriosus (21%).

3. Type A3: This category has unilateral pulmonary branch atresia. Blood flow to the affected lung tissue is facilitated through collateral vessels originating from the aortic arch or other collateral arteries.

4. Type A4: This type has an aortic arch interruption, most commonly between the left common carotid and subclavian arteries.

The Society of Thoracic Surgeons classifies truncus arteriosus into 3 categories by modifying the Van Praagh classification as follows:

1. Truncus arteriosus with confluent or near confluent branch pulmonary arteries (includes Van Praagh types A1 and A2)

2. Truncus arteriosus with the absence of one branch pulmonary artery (same as Van Praagh type A3)

3. Truncus arteriosus with interrupted aortic arch or coarctation (same as Van Praagh type A4)