Below is an instruction from Human. Write a response.
    ### Instruction:
    What is the outlook for Atrial Fibrillation and Stroke ?
    ### Response:
    AF, which affects as many as 2.2 million Americans, increases an individuals risk of stroke by 4 to 6 times on average. The risk increases with age. In people over 80 years old, AF is the direct cause of 1 in 4 strokes. Treating individuals with warfarin or new blood thinners reduces the rate of stroke for those who have AF by approximately one-half to two- thirds.
    