Unstable angina (UA), NSTEMI, and STEMI are all part of Acute Coronary Syndromes (ACS) — a spectrum of conditions caused by sudden reduction of blood flow to the myocardium due to plaque rupture and thrombosis.
Let’s go step-by-step:
⚙️ 1. Underlying Mechanism (shared)
All three result from rupture or erosion of an atherosclerotic plaque → platelet aggregation and thrombus formation → ↓ coronary blood flow.
What differs is the degree and duration of ischemia and whether there’s myocardial necrosis.
🩸 2. Pathophysiologic Differences
| Feature | Unstable Angina (UA) | NSTEMI | STEMI |
|---|---|---|---|
| Coronary occlusion | Partial or transient | Partial or prolonged | Complete and sustained |
| Myocardial necrosis | ❌ None | ✅ Present (subendocardial) | ✅ Present (transmural) |
| Troponin | Normal | Elevated | Elevated (higher rise) |
| ST segment | Normal or ↓ (depression) | ST depression or T wave inversion | ST elevation (≥1 mm in ≥2 contiguous leads) |
| Q waves | Absent | Usually absent | Often develop later |
3. Clinical Presentation
All three cause chest pain:
- Typical angina pain: heavy, squeezing, retrosternal, may radiate to arm, neck, jaw.
- Unstable angina: occurs at rest, more severe or frequent than stable angina.
- NSTEMI/STEMI: more intense, lasts >20 minutes, may be associated with diaphoresis, nausea, or dyspnea.
🔬 4. Diagnostic Criteria
| Test | UA | NSTEMI | STEMI |
|---|---|---|---|
| ECG | ST depression / T inversion / normal | ST depression / T inversion | ST elevation / new LBBB |
| Cardiac enzymes (Troponin, CK-MB) | Normal | Elevated | Elevated |
| Imaging (Echo) | May show ischemia, no necrosis | Wall motion abnormalities | Wall motion abnormalities |
💊 5. Management Summary
| Step | UA & NSTEMI | STEMI |
|---|---|---|
| Initial | MONA: Morphine, O₂ (if SpO₂ <90%), Nitrates, Aspirin | Same |
| Antithrombotic | Dual antiplatelet (Aspirin + P2Y12 inhibitor) + Anticoagulant (Heparin/Enoxaparin) | Same |
| Reperfusion | Early invasive strategy (angiography + PCI within 24–72 hrs) | Immediate reperfusion: PCI (preferred) or fibrinolysis if PCI unavailable |
| Beta-blocker, ACEI, statin | Long-term therapy | Long-term therapy |
6. Quick Mnemonic
UA = Pain, no damage
NSTEMI = Pain + subendocardial damage
STEMI = Pain + full-thickness damage
🧠 Summary Table
| Feature | UA | NSTEMI | STEMI |
|---|---|---|---|
| Troponin | Normal | ↑ | ↑↑ |
| ST changes | Depression/T inversion | Depression/T inversion | Elevation |
| Coronary blockage | Partial | Partial | Complete |
| Myocardial necrosis | ❌ | ✅ (partial) | ✅✅ (transmural) |
| Urgency | Urgent (PCI <24h) | Urgent (PCI <24h) | Emergent (PCI <90 min or thrombolysis <12h) |
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