What Causes Recurring PVCs While Stopping Flecanide?

i am having pvcs and have done since last year, echo is fine and have been taking flecanide which does stop them. If i tail the flecanide off the pvcs come back worse then ever - as many as every third beat. Can you please give some idea of what may have triggered them, the physiological explanation for them and any ideas about coping I am 51 and in good health, no regular meds until now and fit