13 Truncus Arteriosus

• Characterized by a single great artery arising from the base of the heart, which gives origin to systemic, pulmonary, and coronary arteries
  
• Presence of only one arterial trunk is necessary for the diagnosis without any remnant of an atretic pulmonary artery or aorta.
  
• Almost always centered over a large ventricular septal defect
  
• Commonly used synonyms: persistent truncus arteriosus and common arterial trunk
  
• Collett and Edwards’s classification relates to the site of origin of the pulmonary arteries from the common arterial trunk (Fig. 13.1, upper panel)
  
  
  
  • • Type I: Origin of a short main pulmonary artery from the base of the truncus
    
  • • Type II: Separate posterior origins of pulmonary artery branches from the truncus
    
  • • Type III: Separate lateral origins of pulmonary artery branches from the truncus
    
  • • Type IV: Branches to the lungs originating from descending aorta; this type is regarded as a variant of tetralogy of Fallot with pulmonary atresia in which each lung is supplied by a major aortopulmonary collateral artery.
  
  
• Van Praagh and Van Praagh’s modification (Fig. 13.1, lower panel)
  
  
  
  • • Type A1: Origin of a main pulmonary artery from the base of the truncus
    
  • • Type A2: Separate origins of pulmonary artery branches from the truncus
    
  • • Type A3: Absent left, right, or both pulmonary arteries, with the absent pulmonary artery originating from a ductus arteriosus or collateral artery
    
  • • Type A4: With obstructive lesion of the aortic arch

Fig. 13.1 Collett and Edwards’s (top panel) and Van Praagh and Van Praagh’s (bottom panel) classification systems.

Pathophysiology

• Intracardiac admixture lesion at ventricular septal defect level due to similar pressures in both ventricles
  
• Extracardiac left-to-right shunt at truncal level with a significant increase in pulmonary flow when pulmonary vascular resistance decreases
  
• Occasionally the pulmonary blood flow may be restrictive when there is associated obstruction
  
  
  
  • • Ostial stenosis from an obstructive truncal leaflet
    
  • • Pulmonary artery may be underdeveloped and hypoplastic or have an intrinsic stenosis.
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