MAPCAs(Major Aortopulmonary Collateral Arteries) and PDA in case of Pulmonary atresia with VSD
The presence of PA as a component of tetralogy of Fallot is designated as an extreme form. In such patients, the
lungs are supplied by extracardiac sources such as patent ductus arteriosus, previous systemic-pulmonary shunts,
and, most commonly, MAPCAs. These discrete arteries arise commonly from the descending thoracic aorta, but
they may arise from the aortic arch branches and, rarely, from the abdominal aorta MAPCAs transmit blood
to the pulmonary arterial circulation at variable pressures.