@fuzzlepuff have you had a patch monitor for a week or a month to see what is going on? You could also get a smart watch or Kardia device (though it sounds like something continuous would be best).

A positive ANA does not always mean an autoimmune disorder, I have been told. Do you see a rheumatologist? Some autoimmune issues can involve the heart though I don't know much about it.

Sorry you are going through this and someone else will chime in!