Tetralogy of Fallot (TOF or"Tet) Low oxygen levels in the blood cause the lips,fingers,and toes to look blue(cyanotic) Pumorary Vahes 20 15 盖” 10 0 199619971998199920002001200220032004200520060 5 10 15 20 25 30 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 发 生 率 城镇 乡 村全 国