I am also so sorry to read that this is going on w. you. I was one of the lucky ones and they got all of my SVT the first round altho i have had a couple of scary incidences over the past four years. I know that my heart doc had to put me on a low dose beta blocker antenolol after my procedure to keep the rest of it at bay and it worked for me and to this day i still take 25 mg. as a safety net and that has seemed to work for me. I don't know you may just have an irritable heart as my surgeon says and are still experiencing these random episodes which are not unheard of believe me. You may not know for sure that the second ablation didn't work since you are just six months out....did your doc put you on a low dose beta blocker to take the edge off of the episodes...for alot of us on this site it really does seem to help...i too know about those long episodes as Ireneo does...mine would go a couple of hours and my pulse rate would soar into the lower 300's until i had the ablation done and i have had i think maybe three tough incidents since then that two of the times i had to be cardioconverted but the beta blockers did wonders for me...i would talk to the doc and see if you are possibly a candidate to try a low dose...it certainly isn't going to hurt....good luck to you and thats where my money is on this one...................remember it may not be a fail because its pretty commen to have random erratic runs.....don't give up yet!!!!
I'm sorry the tachy has come back. Sometimes the ablation just damages the trouble spot a bit but it heals over and comes back. Sometimes they get one spot killed off just for another one to slip out of hiding and cause problems. If it's any consolation, I've had 3 ablations: first time they thought they got it under control but it came back; second time they knew it was still acting up but they stopped after 7 hours; third time they got it pretty well under control but like you, I just have short bursts of tachy now and then. That's where I'm at now and it's been 5 years since my 3rd ablation. This is tolerable and I think I'm about as fixed as I can get.
Some of us just have very messy hearts and they're hard to clean up. You may have to go in another time but I hope they can really zap it under control. Those 45 minute episodes are too hard to live with.
Be sure to call your EP cardio and let him/her know.