Fig. 46.1
Diagrammatic representation of normal circulation (right panel) and truncus arteriosus (left panel). Note that in truncus arteriosus, there is only one semilunar valve and this is referred to as the “truncal valve.” It can be tricuspid or quadricuspid (as is shown in the diagram). Abbreviations: RA right atria, LA left atria, RV right ventricle, LV left atrium (Reproduced or adapted from Driscoll D (2006) Fundamentals of pediatric cardiology. Lippincott Williams & Wilkins, with permission of the author and publisher)
46.2 Pathologic Physiology
Cyanosis occurs because of a right-to-left shunt at the level of the ventricular septal defect and is dependent upon the volume of pulmonary blood flow. The relative volume of pulmonary and systemic blood flow depends on the relative resistance to flow into the pulmonary vascular bed and into the systemic vascular bed. The resistance to flow into the pulmonary vascular bed also will be effected by the presence, absence, and severity of pulmonary arterial stenosis.
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