ST segment depression is a downward displacement of the ST segment on ECG below the isoelectric baseline (typically >0.5-1 mm). It indicates myocardial ischemia, subendocardial injury, or other non-ischemic causes. Let me pull comprehensive textbook content on this.

Good results. Now let me pull the detailed textbook content from the most relevant sources.

Good content from Pfenninger and Miller's Anesthesia. Let me now pull from Tintinalli's, Braunwald's, and Harrison's for the ECG criteria and clinical context.

Excellent. Now let me get the Frameworks for Internal Medicine section on UA/NSTEMI and the Miller's ECG criteria section for more detail.

I have rich content. Let me now fetch the ECG images to include in the response.