Can a car accident cause atrial fibrillation in your heart?

Atrial fib: Yes but usually not persistent atrial fib unless you have that tendency anyway.

No: Our best understandings of afib require that the heart muscle have undergone changes over a prolonged period of time to enable afib. While it's possible the stress of an accident could have "set off" an afib attack, if it sticks around, you were likely at risk in the first place. A truly severe wreck can bruise the heart, but the fib would pass as the bruise heals.