Heart attacks are life-threatening — and nurses are often the first to spot the signs. Knowing how to read an EKG for STEMI and NSTEMI helps you catch problems early and get your patient lifesaving treatment fast.
This guide breaks down what these heart attacks look like, how to tell them apart, and what to do next.
🫀 What’s a STEMI and What’s an NSTEMI?
Both STEMI and NSTEMI mean the heart muscle is not getting enough oxygen because of a blocked artery. But they look different on an EKG and need slightly different actions.
STEMI means:
✅ ST-Segment Elevation Myocardial Infarction
✅ Full blockage of a coronary artery
✅ Heart muscle is dying quickly
✅ Needs urgent treatment to open the artery — usually a cath lab within minutes
NSTEMI means:
✅ Non-ST-Segment Elevation Myocardial Infarction
✅ Partial blockage of a coronary artery
✅ Some damage to the heart muscle
✅ No ST elevation on EKG — but other signs show ischemia
✅ Needs treatment fast — but less immediate than STEMI
Both are dangerous — but STEMI is more urgent.
🩺 How a Heart Attack Happens
- Plaque rupture: A cholesterol plaque in a coronary artery tears open.
- Clot forms: A blood clot forms at the tear site.
- Blood flow stops or slows: If fully blocked → STEMI; if partially blocked → NSTEMI.
- Heart muscle starves: No oxygen = muscle starts to die.
- EKG changes: Electrical signals change because of damaged cells.
📊 Key EKG Changes in STEMI
A classic STEMI has clear EKG signs:
✅ 1. ST-Segment Elevation
This is the biggest red flag.
- What to look for:
- ST elevation in two or more contiguous leads (leads that look at the same part of the heart)
- Elevation must be >1 mm in limb leads or >2 mm in precordial leads
Example:
- V1–V4: Anterior STEMI
- II, III, aVF: Inferior STEMI
- I, aVL, V5–V6: Lateral STEMI
✅ 2. Reciprocal Changes
- ST depression in opposite leads.
- Example: Inferior STEMI → depression in I and aVL.
✅ 3. Possible Pathological Q Waves
- Deep Q waves may appear later — sign of muscle death.
⚠️ Red Flag Signs for STEMI
- New ST elevation in a pattern matching chest pain.
- Patient says: “Feels like an elephant on my chest,” pain in arm or jaw.
- Pale, sweaty, anxious.
- Hypotension or shock signs.
👉 ACT FAST: Call the rapid response team, get cardiology, prepare for cath lab!
📊 Key EKG Changes in NSTEMI
NSTEMI doesn’t show the big ST elevation — but there are other hints:
✅ 1. ST-Segment Depression
- Horizontal or downsloping ST depression in two or more leads.
- Sign of ischemia — the heart muscle is starving but not fully dead yet.
✅ 2. T-Wave Inversions
- Deep inverted T waves, especially in V2–V6.
- Shows that parts of the heart muscle are not getting enough oxygen.
✅ 3. No Q Waves (Usually)
- Because there’s no full-thickness damage like STEMI.
⚡ STEMI vs. NSTEMI Cheat Sheet
| Feature | STEMI | NSTEMI |
|---|---|---|
| ST Elevation | Yes, in contiguous leads | No |
| ST Depression | Reciprocal changes only | Yes, common |
| T-Wave Inversion | Possible | Common |
| Q Waves | Possible | Rare |
| Blockage | Complete | Partial |
| Damage | Full thickness | Partial thickness |
| Treatment | Immediate reperfusion (PCI or fibrinolytics) | PCI, but less urgent |
🏥 Nursing Actions for Suspected Heart Attack
When you see possible STEMI or NSTEMI signs, do this immediately:
✅ 1. Stay with the patient.
Don’t leave them alone.
✅ 2. Call for help.
Activate your rapid response or chest pain protocol.
✅ 3. Get a 12-lead EKG.
Repeat if needed — EKG can change quickly.
✅ 4. Put patient on oxygen if needed.
Only if O2 sat < 90%.
✅ 5. Get vital signs.
Watch for hypotension, arrhythmias.
✅ 6. Start IV access.
Two large-bore IVs if possible.
✅ 7. Prepare meds:
- Aspirin (chewable)
- Nitroglycerin (unless hypotensive)
- Morphine (if pain not relieved)
✅ 8. Notify cardiology.
Prepare patient for cath lab if STEMI.
📌 What NOT to Miss
🚫 Don’t ignore vague signs:
Older adults, women, and diabetics may have mild chest pain or just shortness of breath.
🚫 Don’t delay EKG:
First EKG should be done within 10 minutes of chest pain.
🚫 Don’t give nitro if hypotensive or suspect RV infarct (ST elevation in V4R).
🗂️ Extra: STEMI Mimics
Some conditions can look like a STEMI — nurses should know these:
- Pericarditis: Diffuse ST elevation, no reciprocal depression.
- Early repolarization: Young healthy patients.
- Left Bundle Branch Block (LBBB): Wide QRS, ST changes.
- Ventricular aneurysm: Old MI scar.
If unsure, get help from a cardiologist ASAP!