Guide — Cardiac
STEMI vs NSTEMI for Nurses
STEMI and NSTEMI are both myocardial infarctions, but differ critically in ECG findings, coronary occlusion type, reperfusion urgency, and treatment approach. Understanding these differences is essential for triage, ACLS, and NCLEX success.
10 min read · Cardiac
Educational use only. STEMI and NSTEMI require immediate provider involvement and institutional protocols. This guide supports learning and NCLEX preparation. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
Definitions
Complete occlusion of a coronary artery causing transmural (full-thickness) myocardial ischemia and necrosis. Identified by ST elevation in ≥2 contiguous ECG leads. A cardiovascular emergency requiring immediate reperfusion.
Partial or near-complete coronary occlusion causing subendocardial (partial thickness) ischemia with myocardial necrosis. Troponin rises, but no ST elevation on ECG. Urgency determined by risk score and hemodynamic stability.
ECG Differences
| ECG Finding | STEMI | NSTEMI |
|---|---|---|
| ST segment | Elevation in ≥2 contiguous leads | Depression or no change; ST elevation absent |
| T-wave changes | Peaked early; later inversion | T-wave flattening or inversion common |
| Q waves | Develop hours–days after occlusion | Usually absent; may develop if large NSTEMI |
| Reciprocal changes | Present — ST depression in opposite leads | May be absent or minimal |
| New LBBB | Treated as STEMI equivalent if new onset | Does not apply (LBBB = STEMI equivalent if new) |
| ECG lead pattern | Identifies affected territory (inferior: II, III, aVF; anterior: V1–V4; lateral: I, aVL, V5–V6) | May be diffuse or non-localizing |
Coronary Occlusion Differences
| Feature | STEMI | NSTEMI |
|---|---|---|
| Occlusion degree | Complete (100%) | Partial to near-complete (≥70–99%) |
| Thrombus type | Occlusive, platelet-rich thrombus — no residual flow | Non-occlusive thrombus — some residual flow preserved |
| Depth of ischemia | Transmural — full thickness of myocardium at risk | Subendocardial — inner layers most vulnerable |
| Collateral circulation | Absent or insufficient to prevent ischemia | May partially protect territory |
| Infarct size risk | Large — entire territory of occluded vessel | Smaller — partial territory or subendocardium |
Troponin Findings
- ›Rises within 2–4 hours of symptom onset
- ›Peaks at 12–24 hours
- ›Remains elevated 7–14 days (can track infarct size)
- ›Initial troponin may be normal — do not wait for result to activate STEMI protocol
- ›Serial troponins still drawn to confirm diagnosis and track
- ›Rises within 2–4 hours of symptom onset
- ›Must be elevated to diagnose NSTEMI (differentiates from unstable angina)
- ›Serial troponins required — draw at presentation, 3 hours, 6 hours
- ›Rising or falling trend confirms ischemic cause
- ›Magnitude of rise correlates with infarct size and prognosis
Treatment Priorities
| Intervention | STEMI | NSTEMI |
|---|---|---|
| Reperfusion strategy | Immediate PCI (preferred) — goal ≤90 min; or thrombolytics ≤30 min if no PCI available | Early invasive strategy (cath within 24–72 hrs for high-risk; conservative approach for low-risk) |
| Aspirin | 325 mg non-enteric chewed immediately | 325 mg non-enteric chewed immediately |
| P2Y12 inhibitor | Loading dose immediately (ticagrelor or clopidogrel) | Loading dose — timing based on risk and planned procedure |
| Anticoagulation | Heparin or bivalirudin per PCI protocol | LMWH (enoxaparin) or unfractionated heparin |
| Beta-blocker | Oral within 24 hours if hemodynamically stable; avoid in cardiogenic shock | Oral within 24 hours if hemodynamically stable |
| Statin | High-intensity statin (atorvastatin 80 mg) | High-intensity statin initiated |
| Nitroglycerin | Use with caution; avoid in inferior MI with RV involvement (can cause severe hypotension) | SL NTG for ongoing pain; IV NTG for refractory pain or HTN |
Nursing Implications
NCLEX Pearls
- ›STEMI = ST elevation on ECG + complete coronary occlusion = immediate reperfusion needed.
- ›NSTEMI = troponin elevation + NO ST elevation = partial occlusion, subendocardial injury.
- ›Unstable angina = chest pain at rest + NO troponin elevation + NO ST elevation.
- ›Do not wait for troponin results to activate STEMI protocol — decision is made on ECG.
- ›Inferior STEMI (II, III, aVF) = RCA involvement → RV infarct possible → avoid NTG.
- ›New LBBB in the context of ACS symptoms is treated as a STEMI equivalent.
- ›Door-to-balloon time ≤90 minutes for STEMI PCI; ≤30 minutes for thrombolytics.
Related Resources
Standards & sources
Fact-checked Jun 20, 2026This page is written to align with American Heart Association (AHA) · American College of Cardiology (ACC) · AHA ACLS Guidelines. It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →