A blow to the chest can indeed cause an rythym problem. It generates a minute bit of electrical charge to the heart. I'm a paramedic and we sometimes used to use a "precordial thump" to start a heart in arrest. RARE BUT POSSIBLE.
Your question is too broad for most of us, suppose that's why no other replies yet.
Atrial Fibrillation and Flutter are electrical signal problems, not sure how that relates to the vagus nerve, but I doubt that an accident (a blunt blow or something like that I assume) would cause either condition.