Thanks for your concerns,
I am an MD but not a cardiologist. BUT, I am a former 8 time Ironman finisher including 4 finishes in Hawaii. I have always had an interest in this topic due to my own concerns of the potential dangers of ultra endurance racing and training.
It is important to know that this has not been thoroughly studied. The studies which have been done have shown a link between certain arrythmias as well as potential cardiac damage and chronic cardiac scarring.
Getting an ablation is a BIG DEAL. IF they can fix your problem (it is not always successful and can occasionally make things worse) you should be very grateful and not tempt further problems. Just because some people have successfully finished an Ironman does not mean it is safe or that you will be so lucky. There is a lot about this phenomenon which is simply unknown. There are a lot of well known triathletes who have had significant heart issues. I personally know a few locally as well.
Finishing an Ironman is no big deal. It is kind of a huge waste of time to be honest with you. I have gotten out of the sport and don't miss it.
Having a properly functioning heart is a VERY big deal. Why would you screw around with that just to say "I am an Ironman"? Is it really that important to say you completed some arbitrarily concocted race distance?
Why do you REALLY want to do this?