is caused by occlusion of the left anterior descending coronary artery
. It is on the outside of the heart and has nothing to do with the valves.
OK, you can rest easy. Malpractice insurance is very costly and nobody would let you knowingly get up and walk away IF you were having a heart attack; not even if you seemed to have just had one.
What concerns me is that somebody would say "oh, probably the leads weren't on right" and not correct the problem and redo the test.
Tell your doctor you were not happy with that lab and don't want to be sent there again; call the manager of the lab, tell them what happened and ask for an explanation - if they do not offer to redo the test without charge, tell them you will not pay for a sloppy test.