Diltiazem
"I've been taking 180mg timed-release dilt capsules for two years after my 95%-effective catheter ablation for atrial flutter.  I still get mild and transient afibs most mornings at 5 a.m. or so.  They stop after ten minutes or when i sit up or get up to use the restroom.  I think the vagus nerve responds to bladder pressure and sends a wrong signal to the heart to act up.

   I'm on low dosage by prefernce. Perhaps I'll ask for higher dosage if the transient episodes start to last longer or feel more severe. I can barely feel the "quivering' sensation that afib causes in my chest so I am happy for now."