In patients with a TAC only one vessel originates from the heart chambers. Generally the common vessel (truncus) overrides a ventricular septal defect. Depending on the origin of the pulmonary artery, different types are distinguished in the Van Praagh classification (A1-A4; B, without VSD, is rare):
- type A1-2 (most common types): the pulmonary artery stem arises as a singular vessel (type 1) or as separate pulmonary arteries (type 2, LPA,RPA) from the ascending aorta
- type A3: only one pulmonary artery arises from the ascending aorta, the others from the aortic arch, descending aorta or right ventricle (previously known as hemitruncus)
- type A4: truncus with aortic isthmus stenosis or interrupted aortic arch.