Figure 1: (A) Commonest form of PDA as an isolated lesion (Krichenko Type A) seen on the lateral projection. Cone-shaped ductus with wide ampulla and constriction at the pulmonary end arising from the proximal part of the descending aorta. (B-G) Variation of ductal morphology in duct-dependant cyanotic CHD. (B) Ductus in a neonate with tricuspid atresia resembling Krichenko type A PDA. (C and D) Ductuses in cyanotic CHD tend to arise more proximally, have a more elongated and tubular shape one or more curves. (E and F) Very proximal origin of ductuses, arising from the underside of the aortic arch are seen more commonly in TOF-PA. (G) A long tubular ductus arising from the subclavian/innominate artery in a patient with TOF-PA and right aortic arch.