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Lesson

12-Lead STEMI Recognition

12 min Cardiac & ECG

Objective: Get a 12-lead early, recognize a STEMI-alert pattern, transmit, and choose a PCI-capable destination — without delaying a crashing patient for a perfect tracing.

Why This Is Hard

Time is muscle. The 12-lead you skip on scene is the 12-lead the ED does after registration. Mimics (early repol, pericarditis, LBBB, paced, hyperK, LVH with strain) make medics afraid to call anything. Your job is not to be an electrophysiologist. It is to acquire early, recognize a concerning pattern, transmit, and destination correctly.

Street Sequence

  1. ABCs and a pulse. Cardiac arrest is not a 12-lead problem first.
  2. If ACS is on the table (pressure, radiation, diaphoresis, unexplained SOB, syncope, ROSC), get a 12-lead as soon as it will not delay life-saving care. The 2025 ACC/AHA/ACEP/NAEMSP ACS guideline recommends acquiring and interpreting a 12-lead within 10 minutes of first medical contact.
  3. Serial 12-leads if symptoms persist or change — one normal tracing does not close the case.
  4. Transmit and use your STEMI-alert language. Tell the hospital what you see, not just “chest pain.”
  5. Aspirin and other meds only per protocol (see the aspirin lesson). Destination: PCI-capable center when criteria are met.

What “STEMI thinking” Looks Like (Education)

  • ST elevation in a territorial pattern with reciprocal change is the classic teaching picture — know your system’s mm and lead rules.
  • Inferior patterns: watch BP and consider a right-sided tracing if protocol includes it before nitro.
  • Mimics exist. When unsure, transmit and say “possible STEMI vs mimic — need cath-lab capable evaluation.”
  • LBBB, paced rhythms, and Sgarbossa (including modified Sgarbossa) rules are advanced; do not let uncertainty delay transport or a STEMI-alert conversation.
Say out loud
  • ACS on the table — 12-lead within 10 minutes of first medical contact
  • Lead II is monitoring only — not a STEMI call
  • Territorial pattern + STEMI-alert / transmit language
  • PCI-capable destination (and serial ECGs if symptoms continue)

Field Pitfalls

  • Waiting for a “better tracing” while the patient sits on the couch.
  • Calling STEMI off Lead II alone.
  • Skipping transmission because “they’ll repeat it anyway.”

Practice

60-second drill

Time a full 12-lead on a training partner (skin prep → acquire → interpret out loud → transmit/STEMI-alert sentence). Target under 5 minutes. This is a 12-lead skill — do not practice STEMI calls off a single Lead II strip.

Related: Aspirin in ACS, ROSC & Post-Arrest Care.

Sources & Further Study

Named guidelines for further study. They are not clinical orders and do not replace your protocol or medical direction.

Education only. Apply learning within your protocols and medical direction. This is not clinical care guidance.

Check Your Understanding

Street decisions from this lesson only. After you check, the key is highlighted. Education practice — not a certification exam.

1. When ACS is suspected, acquire and interpret a 12-lead:
2. Lead II on the monitor:
3. If you see a concerning territorial ST-elevation pattern you should:
4. A single normal 12-lead in ongoing symptoms means:
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