My daughter had VSD, which is a hole between the ventricles. It closed on it's own by the time she turned one year old. We had to go around for a day or two at a time, a few times with her chest all taped up with a halter monitor and people would stare. There was no PACs that was picked up on ultrasound with her, but then again I developed unnoticed eclampsia with her too, so I think that my OB was not very mindful...
Did they tell you what type of PACs has been detected? I believe that they can happen in isolated incidences or they can indicate a heart anomaly.
Besides for the VSD my daughter had bradycardia when she was born because of prematurity then she had tachycardia after she "caught up". ...she is 11 now and she's just being monitored for ventricular hypertrophy because she is showing symptoms of it and it is genetic (people on her dad's side have it).
I'd ask people on both sides of your family if anybody has ever had cardiac issues... I did not know that my daughter's grandfather had a battery of cardiac issues until my daughter was 4 or 5 and I was annoyed because it would have explained a lot and saved me research and worry... sorry for the unorganized and babbling answer.
Hope your baby is healthy and you get good news
Commenting to follow this chain. I was told at my anatomy scan that baby has a single umbelical artery and am scheduled for a fetal echo on Monday to check that things are in good order as this can be indicative of heart defects. Wishing you luck with yours and that it's only good news to be had!
My daughter had this with my last pregnancy. They discovered it at 36 weeks. The fetal echo is to check the frequency of the PACs and yo make sure there isn't anything wrong with the heart anatomy itself. My daughter grew out of it at 4 months old.