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/
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.
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.