I'm 64, and have been experiencing paroxsysmal atrial tachacardia since I was 16-- it's a part of my life that I've gotten accustomed to dealing with. By the time ablations were developed as an alternative to medication, I had been on a steady dose of beta blockers for many, many years. I never had a problem with them becoming a "poison" to my system, but every decade or so (!) the dose I'm on becomes less effective, and my current "cocktail" is altered a bit.) I'm currently on a combination of atenolol and digoxin. I've been told that I am not a candidate for ablation at this point, partly because I've been on meds so long. My only regret is the inability to have a glass of wine (alcohol of any kind is one of my triggers, but an episode can begin at the drop of a hat with no obvious trigger.) BUT with the right meds, my episodes are very few and far between now.
My point is-- any type of procedure has some risks, and if meds do the trick, it's not a terrible way to have to deal with it.
I think it more likely that one's body becomes unresponsive to a medication when it is taken long term.. not much change of it poison... more likely that one would develop troubling symptoms.. maybe that's a form of poison, not deadly but no pleasant either.
It may be possible to get the "numbers" on an ablation specialist before committing. You want someone who does a lot of them, if not every day then at least a few a week with hundreds or more in total to date. Then get the success rate, and the problem rate if possible - I went through this process when I decided on a heart surgeon to perform open heart surgery and valve repair on me. He did heart surgery several times a week sometimes several in a day. The day I went in I think I ended up being second or third. I was scheduled earlier, but I was not an emergency case and one showed up at the "door" and was put in line before me. Open heart surgery is more "serious" or risky than Ablation, I bring it up only as an example of doing what I recommend.
I have had 2 ablations, one in 2005 and one last May. I got so tired of being on the meds I just decided to have the ablation. at that point, I felt that even if I woke up with a pacemaker, it would be better than going to the hospital and getting converted all the time. I am not sure about the meds acting as poison to your system after a time, but I know with me the meds didn't work afterwhile. I had a wonderful doctor and felt very confident in his skill. Maybe do some research to find doctors that specializes in ablations in your area and interview them until you find one that you feel confident and comfortable with? It is really scary and I know how you feel, but I am very glad I went ahead with it. Blessings on your journey!!