These webpages from the American Heart Association give pretty good details about both Evan's heart defect as well as his chromosomal abromality:
Tetralogy of Fallot
What is DiGeorge syndrome?
DiGeorge syndrome (Also known as Shprintzen, velo-cardio-facial, and 22q11.2 deletion syndrome.) - A genetic disease caused by a missing piece of chromosome material on chromosome #22 that results in many different health problems, and affects the normal fetal development of the heart, thymus, and parathyroid glands
- Description taken from the Children's Hospital Website.