His decision was not based entirely on the 12 lead, but he seemed to weight it very strongly. I kept the information vague because I was looking for more general answers, rather than a critique of this specific call since I wasn't there and don't have all the info. Apparently, the patient had had at least one MI with the new heart, and this is what if felt like. In this specific case, the pain did also change to some degree after their arrival and may have began to feel more like indigestion to the patient (I only spoke a bit about this call with my friend so I do not have all the information.)
Thanks to everyone for the input!