Had stess test 6 months ago and passed. Had testing EKG today and dr found scarring. Why would scarring not show up on stress test by did on ekg?

Compare ECG. You should ask your doctor if the ECG has changed since last time. If there is change in the ekg you may need further cardiac testing.
Experts differ. Stress ECG is used to look for "induced ischemia" of reduced blood flow to your heart. Resting ekg is different, various experts trained by different schools will read ekg differently. I don't really understand what "scarring" mean. It could mean that you have old sings of heart attack. The bottom line, ekg may not be enough to be specific to detect your potential scars of the heart. ...