Metoprolol is a fairly low key beta blocker too. Chances are, your body will make adjustments for the pressure lowering effects. I always had low pressure and when I was on a bit of meds for the rhythms, my heart just somehow adjusted. However, now that I am on a bucket of meds... I really struggle with the bp. The metoprolol just might help with the skipping and fluttering. It's nice when something actually helps. Hope you are feeling much better soon.
Some PVCs are benign, your doctor should have a view.
If you also have a high heart rate, then the Metoprolol may help, it will also lower you blood pressure whether you need it or not.
On the other hand 25 mg is a low dose and if it helps I wouldn't worry about being on it. It may be the most widely used heart medication there is, so there it has been extensively tested, by real patients, me included.
Have you tried posting on one of the congenital heart website forums where there are a lot of people with tetrology of the fallot and may have had the same experience.
There is teh uk organisation - www.guch.org.uk
and the american one ACHA - http://www.achaheart.org/