Dad has pacemaker and defib and was told he is on 100% afib what does that mean for him?

Name misleading: Device's name refers to ventricular, not atrial fibrilation. He probably underwent an electrophysiological study and they determined he also has a tendency to ventricular fibrilation.

Atrial fintillation: The most important thing for your dad is to be on a blood thinner like Coumadin (warfarin) or Pradaxa to decrease the risk is stroke the defibrillator is protecting him from arrhythmia.