Which electrocardiographic finding is typical of NSTEMI as opposed to STEMI?

• A. ST Elevation
• B. ST Depression
• C. T Wave Inversion Only
• D. Q Waves

Answer: (B)

ST segment depression reflects subendocardial ischemia from partial coronary occlusion, which is characteristic of NSTEMI. In NSTEMI, the injury is not full-thickness, so you don’t see the classic ST-segment elevation that indicates transmural injury. Instead, the ECG often shows ST depression (and may have T-wave inversions) in the leads corresponding to the affected territory. ST elevation would point toward STEMI, where a complete wall infarction produces current of injury that elevates the ST segment. Q waves can develop later in infarction but are not the acute hallmark of NSTEMI. So, ST depression is the finding that best differentiates NSTEMI from STEMI.