Low carbohydrate and high fat (or Paleo) diets for ENDURANCE are not just VIABLE, but possibly can lower chronic inflammation, especially during long periods of training. This could be more important in the long-term because you can avoid getting sick, over any potential performance related effects.
AMPK, one of the molecules at the center of ENDURANCE adaptation also can regulate, or at least signal, to your brain and the rest of your body what fuel to utilize when.
When you are consuming LOTS OF GLUCOSE in one form or another, you are likely to decrease AMPK – bad for adaptations, and it seems, also bad for symptoms of atrial fibrillation. Once more: try to be FLEXIBLE in your FOOD strategies :).