Plenty of us have or have had sustained SVT at rates of 220 to 260. As a 6 year old child, I had a rate of 312 bpm that was measured in a hospital. Mine would run on for hours...8f I allowed it to. Sometimes, it can be difficult to determine VT vs. SVT with an aberrancy. Note, "With an aberrancy". Do you have classic SVT, or are there some things in the waveform that could raise a question? There a number of "algorithms" that can be used to determine the difference.
Look...I'm can only give you my feeling on this. My feeling is that you're pushed along into this. There is typically a "path" patients take that eventually may lead them into the electrophysiology lab. You are NOT on this path.
Based on what you've said here, I'd have absolutely no confidence in the entire cardiology practice who have been seeing you!
After a lifetime, 54 years of SVT, I decided it was time to do something about it. My cardiologist put me on a 30 day monitor which caught a couple of my 3 to 5 times a month events. I was then put in contact with several electrophysiologists. I wasn't assigned one, I CHOSE the electrophysiologist that felt I had confidence in, and one who made me feel.... right. If it were me, I'd pull back a little bit, and rethink this. For me, this is all going way to fast. Cardiac ablation freed me from a lifetime of SVT. I heartily recommend it. But I would research and investigate further into what you experiencin before heading into the lab. Just my opinion...