there are some conditions where you want to avoid sauna, but i think a lot of people with af would do well do try it.
if you do it gradually and make sure you are hydrated, there isn't much risk. also, though you do of course lose electrolytes (along with toxins), you can always drink during and after a sauna. this is not a permanent loss!!!
furthermore the FIR (Far-Infrared-Sauna) saunas do exactly what they are advertised to do. in other words the ambient temperature in the box is not very high, but you will wind up sweating 2-3x more than a conventional sauna. these add another degree of safety to the equation. there is no rule that you have to spend 2 hours in the box your first go round. you can literally try 5 minutes and just heat up your body a bit and not sweat if you are that gun shy.
the potential benefits completely outweigh the risks because of the upside in detoxing heavy metals and chemicals without burdening your kidneys or liver.
gradually bringing up your body temp through sauna will also begin to retrain your thyroid.
using the skin for detoxification is like getting a free get out of jail pass if your kidneys and liver are not up to snuff, and given time and patience you can move mountains one shovelful at a time.