btbw,
Thats quite an array of testing. To answer your question shortly, it probably doesn't mean much, although I would have to see the ecgs to give you a formal interpretation. Specifically the nonspecific ST changes refer to a segemnt of the ECG that represents the electrical activity of the heart. In the right setting changes in this area of the ecg can reveal clues about abnormalities of the heart itself.
Given your normal echocariogram they probably do not mean much. You can show your doc the tracings and ask him/her about the specific areas in question.