You're at the same (or lower) altitude as being on a flight to Disney World and last I heard flying to Orlando doesn't cause afib.
Cabin pressure on modern aircraft is held at about 6,000 ft (1,800 m) and 8,000 ft (2,400 m) on older aircraft.
Ken has a good point about dehydration, though, and dehydration is one of the very few things I know of that is a trigger for everyone.