Flecainide is pretty good at preventing flutter but won't usually stop it, as you said. If I were you I would start taking the flecainide daily as prescribed along with either the metoprolol or diltiazem, whichever was most recently prescribed. That way when you do come out of it you'll already have flecainide on-board to prevent a relapse. I spent several years dealing with flutter and I never found any prescription drug that could be used as a PIP against it. The trouble with flutter is that, unlike afib, it's a stable rhythm. So once it gets started, electricity is often the only thing that will stop it.