You are on the lowest dose of metoprolol like I am. Just ask your doc to bump you up a little. That should do the trick. I find mine seems less effective certain times of the month during hormonal fluctuations, or after too little sleep or other such triggers, but once I'm back on track so is the metoprolol.
Oh, also I'm on the tartrate 2x a day. Are you on time release or tartrate? And how many per day?
When I went in to see my cardiologist about my SVT he recommended an ablation over meds. He basically said I would be stuck on the medication the rest of my life and it is possible to build a tolerance to it and up it if my blood pressure could handle it. And that it wouldn't get rid of the SVT just mask it somewhat. I had my ablation in October and I've been SVT free since, if you can get it done I woud say get rid of it permanently!
At this stage, I would not opt for surgery. Try a bit higher dose or other beta blocker (there are many alternatives) and see what the effects and possible side effects are.
As others have mentioned, you are on a very low dose. It's not uncommon to take 100mg and more per day especially to control SVT. I was on 100mg for my near lifelong SVT. I experimented with all kids of dosages starting at 50mg per day, and working all the way up to 200mg. per day which left me in a zombie state until backing off to 100mg. None of these dosages prevented episodes SVT which I was getting 3 to 5 times per month. I tried Sotalol, but that med scared the heck out of me, so I went back on Metoprolol. My cardiologist convince me that the best way to deal with my SVT was the ablation procedure. It was the best decision I could have made. Free of SVT after 54 years. I've been SVT free now for over 4 years. Remember that it's not actually an "operation". There is no cutting or "opening" involved. Access to the heart is made by puncturing the area where you leg joins your torso and inserting catheters. Within 3 days, the two puncture marks were nearly gone.
The electrophysiology procedure with ablation carries no more risk that experimenting with drug therapy, and the results are usually more positive.