Potentially this disease is correctable by surgery. Because of the complicated anatomy this lesion is treated slightly later than the usual TOF. Our policy is to wait till 2 to 2.5 years. In the meantime regular follow up with saturations every three months is mandatory and if it drops below 65-70% then an interim surgery in the form of BT shunt will need to be done. Also if the baby has spells (severe cyanosis with loss of consciousness) anytime, then immediate treatment (BT shunt) is warranted.
Remember that each institution has its own policy. I am basing my opinion after discussion with my surgeon. Some institutions may want to do a complete correction early. Also please understand surgery for the heart does not in any way affect the natural history of the Downs Syndrome. Proper counselling from a Geneticist is mandatory.