Anxiety and worry, any emotional strain can cause heart symptoms. From what you say, and given your heart medical test results, I'd say that looks like your problem, not a heart problem. If my saying this helps you on that point it should give you something to build on.
I have no experience with panic attacks, but I do understand they can be completely debilitating, really very awful, so have a lot of good reasons to put in the effort to put your mind on the track that you do not have a heart problem.
Have your discussed your symptoms on a forum/community discussing anxiety and panic? Take a look at:
http://www.medhelp.org/forums/show/71