Dear Ben,
There's not really a 'limit' on the number of ablations an individual can have. It's true that the
radiationCystitis - noninfectious
Radiation therapy exposure is a limiting factor but for an average individual multiple ablation procedures would not add up to enough to be harmful. Remember that the doctors who do the procedure are doing this every day, day in and day out. (Of course they use lead shielding and monitor their radiation exposure very closely but it still adds up to more than you will ever receive).
The AV node can be ablated and the ventricle paced with a pacemaker but this would be a last resort only.
My doctor has done many VT ablations. He claims that the chance of success is about 85%.
af