We don't really know
Af can be due to normal wear and tear as occurs in HTN and the aging process.
Aging causes insertion of non-conducting tissue (scar) between normal heart
cells which is bad. All old people get this but not all old people get af. Why? We know that nests of cells fire crazily at times triggering af. These nests are frequently located in pulmonary veins. But why, and what triggers them?