Updated October 2026 — based on the 2023 ESC Acute Coronary Syndromes Guidelines.
NSTE-ACS: NSTEMI versus unstable angina
Acute coronary syndrome without persistent ST-segment elevation (NSTE-ACS) is a working diagnosis based on symptoms, ECG and clinical assessment. It includes non-ST-elevation myocardial infarction (NSTEMI) and unstable angina. A normal or non-diagnostic initial ECG does not exclude acute coronary occlusion.
- NSTEMI: an acute rise and/or fall in cardiac troponin with at least one result above the assay-specific 99th percentile and clinical evidence of myocardial ischaemia, without persistent conventional STEMI criteria. Elevated troponin alone does not establish a type 1 MI.
- Unstable angina: acute myocardial ischaemia without evidence of acute cardiomyocyte necrosis on serial high-sensitivity troponin measurements; with modern assays it is less commonly diagnosed.
ECG clues
Look for new or dynamic horizontal/downsloping ST depression, new or dynamic T-wave inversion and transient ST elevation. Record serial ECGs when symptoms persist or recur; consider posterior leads V7–V9 and right-sided leads when clinically indicated. ST depression in V1–V3 with positive terminal T waves may indicate posterior occlusion and require an immediate reperfusion pathway rather than routine NSTE-ACS triage.
High-sensitivity troponin
Use a validated assay-specific ESC 0 h/1 h or 0 h/2 h algorithm, interpreting absolute concentrations and serial changes together with time from symptom onset and the clinical context. If results are inconclusive, repeat testing and reassessment are required. A single negative early troponin is not sufficient to rule out ACS.
Risk-based invasive strategy
- Immediate angiography: haemodynamic instability or cardiogenic shock, refractory/recurrent ongoing ischaemic pain, acute heart failure attributed to ongoing ischaemia, life-threatening arrhythmia or cardiac arrest after presentation, mechanical complication, or recurrent dynamic ischaemic ECG changes (particularly intermittent ST elevation).
- Inpatient angiography, considering an early strategy (<24 h): confirmed NSTEMI, dynamic ST/T-wave changes, transient ST elevation, or GRACE score >140.
- Other patients: individualise risk assessment, observation and testing; strong suspicion of unstable angina also warrants an inpatient invasive approach.
Clinical safety: Do not await troponin results when the clinical picture/ECG suggests ongoing coronary occlusion or very-high-risk ACS. Activate local emergency pathways.
Source: 2023 ESC Guidelines for the management of acute coronary syndromes.
