Boy, you really have to walk a tightrope! If the medical community knew anything about
atrial fib, it might make figuring out what to do a bit easier. Between bleeding and flaring, balancing your body chemistry is going to be tricky. Are they sure that the atrial fib was not the result of electrolyte imbalance caused by diarrhea? It would be a lot easier to control your electrolytes (and stop the coumadin) than to avoid flares.
Anyway, suggestions... The medical route for flares is prednisone which you are already getting. They may be holding back a bit on the pred because it alters your electrolytes somewhat. You might do better with endocort which acts more locally on your GI tract.
You could try going on the SCD plan (see: http://www.scdiet.org/
) which might be able to get you out of the flare. If you want to go the medical route, their version of this solution is the enteral diet or the elemental diet. This approach has been shown to be as effective as prednisone in controlling flares. It is not a gourmet treat, but you would be on it for a few weeks for it to kick in.
Do you use probiotics? The right ones have been shown to help control inflammation. Good ones include Culturelle, Align and VSL#3.
Finally, if you are taking iron supplements, do not use ferrous sulphate or any ferrous salts. They do more harm than good. The only real solution is heme iron. There is a supplement called Proferrin that is more effective than ferrous salts.