Non-ST-Elevation Myocardial Infarction (NSTEMI)
Plaque rupture or erosion infarcts myocardium without producing persistent ST elevation, so the ECG cannot time treatment and a mortality risk score does it instead.
Definition
NSTEMI is myocardial infarction without persistent ST-segment elevation. It requires a rise and/or fall in cardiac troponin with at least one value above the assay-specific 99th-percentile upper reference limit. It also requires evidence of acute myocardial ischaemia. That means ischaemic symptoms, new ST-T change or new left bundle branch block, pathological Q waves, imaging evidence of new loss of viable myocardium, or intracoronary thrombus at angiography. Transient ST elevation is compatible with the diagnosis, and the label says nothing about how occluded the culprit artery is.
First principles
The ECG has already told you everything it can
In ST-elevation myocardial infarction (STEMI) the ECG decides both the treatment and the clock. In NSTEMI it does not. The culprit artery may be occluded, partly occluded, collateralised or already reperfused, and the tracing cannot tell you which. So the decision changes from whether to reperfuse immediately to how soon this person needs the catheter laboratory. A validated risk score plus the bedside picture answers that question, not the ST segments.
This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.