Hi , I'll try and answer your question and so sorry I didn't notice earlier. I've had about 8 Ablations and typically the EP Cardiologist will prior to the actual ablation do what is called mapping. This typically is done first with the decision to move into an ablation during the same procedure. They will explain that and usually get your permission to do both prior to moving into the Cat Lab.
During the mapping period they with a type of xray and these patches they put on your skin both front and back will initiate an arrhythmia to watch the paths and determine how many and the location of paths causing the arrhythmia. Once they have that information will decide usually based on where they are a method to seal off the bad pathways. These pathways are kind of like electric lines that grow and connect the good pathways to the wrong parts of the heart muscle and cause incorrect beating of the heart. So depending again on the location will use either heat or freezing to basically cut off the pathways they want to eliminate. So I hope that answers your questions? Please ask any other questions you have.
I also was reading recently that Mayo clinic has been working on a third method which sounded very promising for those who have difficult locations to reach here is the link
https://newsnetwork.mayoclinic.org/discussion/first-in-human-trial-shows-promise-for-hard-to-treat-ventricular-tachycardia-heart-rhythms/

@becky1024 you might be interested in this article also with your heart issue
Blessings