This happens a lot (expecting moms with tachyrhythmias). It more common than you think but you never hear of it hurting Mom or baby. I've been on this board since 2009, I monitor it 95% of the time and have never come across anyone getting hurt by it.
Talk with your OB/GYN to get some reassurance and plan it out how to address during delivery. Talking about it and taking proactive action will help reduce your anxiety levels.
I had bad arrhythmia issues back in 2009. I had to have a surgery in 2013 that was complex, I was scared to death. I didn't have any problems.