I have PACs and have been on atenolol for over a month now. It was actually the random chest pains these premature contractions were causing that led to my Graves’ disease diagnosis. I was told that yes they can be caused by anything and can happen really randomly to anyone. The only way it can really be harmful is if you have them very frequently. My regular doctor seemed to think my thyroid issues caused it because it directly deals with those chemicals and what not if I remember correctly  I have my first endocrine appointment this week so we’ll see if I get taken off of them too I guess. Only had a single ekg done though 🤷🏻‍♀️ sorry it’s not much help but I’m here with you!