Does it affect the arm with any type of movement?
ANy nausea? or shortness of breath?
Have you taken your pulse or blood pressure today?
Your blood pressure seems good, heart rate a little low but if you are on a beta blocker that is normal for it to be low, however, if you are experiencing dizziness or weakness then your low heart rate could be a factor. I don't think that is connected to the fluttering feeling though.
It is quite possible that you do have an irritated nerve ending and it will make your muscle feel like it is twitching. If you had a muscle strain or inflammation it would cause some type of pain and that is not what you are describing. Therefore, it is most likely due to a nerve.
You could try anti-inflammatory meds like ibuprofen or advil to see if that helps. But if it does not go away and you get pain started then you will need to be examined.
How long can I expect this sort of thing to continue if it is due to a nerve? I'll certainly schedule an exam if it doesn't stop.