I have right and left heart failure, and always a ECG shows a problem. I'm not a doctor or health professional, but do know that the stress test will be much more specific. Keep in mind, the ECG tracks the heart for only eight seconds. Certainly a ST depression always gets the attention of doctors, in my experience.
I'm sure you are already concerned, but it will be good to get more information from a much better test. I hope you keep us informed.