Is this ventricular tachycardia or supraventricular tachycardia? They're quite different. With VT, you could be at risk for some problems. With SVT, it's not uncommon and it isn't typically dangerous.
ARVD is often genetic, from my understanding. Do you have a family history of heart problems?
If they have mentioned ARVD, then you probably do have ventricular tachycardia (VT). The puzzle comes in when determining whether you have VT caused by ARVD or not.
Vagal maneuvers may not help if it's ARVD, but beta blockers are a course of treatment either way and you're on the Metoprolol, which is good. I would want to be working closely with a cardiologist if I were you.
Best wishes, congrats on your pregnancy, and I hope all goes perfectly.