I Walk 2 Miles At A Brisk Pace And Ride

I walk 2 miles at a brisk pace and ride bike 5 miles every day. I am in afib continuously and my cardiologist told me I can have sudden cardiac arrest at anytime due to having an ef of 25%. He wants to give me a cardiac defibrillator right away. Seems like I need a second opinion. Please help. Thanks Bud