Code 3 Workshop

Paramedic Education
Home/All lessons/Cardiac & ECG/STEMI Mimics in the Field
Lesson

STEMI Mimics in the Field

12 min Cardiac & ECG Skip to quiz

Objective: Use simple field rules to tell STEMI from common mimics, and transmit when you are unsure instead of talking a tracing down.

Why This Is Hard

Paramedics over-call and under-call. False cath-lab activations are real — and so are occlusions labeled “early repol” that wait in the hallway. Common mimics: benign early repolarization (BER), LVH (left-ventricular hypertrophy) with strain, pericarditis/myopericarditis, LBBB (left bundle-branch block), and a paced rhythm.

Simple field rules beat memorizing formulas. Reciprocal ST depression (except aVR/V1) is not BER or garden-variety pericarditis. BER is usually a younger patient with a fish-hook J and no evolution. Symptoms plus a new regional convex ST elevation is ACS (a heart-attack workup) until the receiving physician says otherwise. Your job is acquire, think, transmit — not to be the cath-lab canceller.

On this truck
  • One 12-lead is a snapshot. Serial tracings if symptoms persist (see the serial 12-lead lesson).
  • Look for reciprocal depression in the opposite wall. That is your friend for “this is likely occlusion.”
  • Age and story matter. Fish-hook J-point in a 22-year-old with sharp, positional pain is not the same as a 64-year-old with diaphoresis.
  • LBBB and paced rhythms are hard. If your protocol has Sgarbossa-style language (concordant ST elevation rules), use it. If not, transmit and say “LBBB / paced, still concerned.”

Street Sequence

  1. Protect ABCs. Get a 12-lead when ACS is on the table — including anginal equivalents.
  2. Map the ST elevation: one region versus everywhere. Reciprocal depression? Hyperacute T? New Q?
  3. If it looks like BER or pericarditis, still ask: could this still be an occlusion? When unsure, transmit and let the receiving team argue.
  4. Do not talk a concerning tracing down because the computer said “nonspecific” or because they are young.

Field Rules

  • BER: often younger, concave ST elevation in V2–V5, notched/slurred J (“fish hook”), prominent T, no reciprocal depression, does not evolve over your call.
  • Pericarditis / myopericarditis: more widespread ST elevation, PR depression, pain often positional/pleuritic. Reciprocal depression (beyond aVR/V1) argues against simple pericarditis — think occlusion.
  • LVH strain: tall voltage, ST/T opposite the QRS (discordant). ST elevation in V1–V3 can look scary. It is often the mirror of lateral strain. Still transmit if the story is ACS.
  • LBBB and paced: expected discordant ST elevation. Concordant ST elevation or excessive discordance is the concerning pattern (Sgarbossa / Smith-style rules). You do not need the score memorized to say “this LBBB looks worse than usual” and transmit.
  • Field rule: mimics explain some ST elevation. They do not give you permission to skip aspirin/destination conversations your protocol already owns, or to sit on a tracing.
Say out loud
  • Regional vs widespread ST elevation
  • Reciprocal? Then it is not BER
  • Young + fish-hook ≠ 60-year-old ACS
  • Unsure — transmit

Field Pitfalls

  • Calling anterior STE “early repol” in a middle-aged diaphoretic patient.
  • Diagnosing pericarditis because the ST is concave — about a third of anterior occlusions start concave.
  • Ignoring reciprocal depression.
  • Not transmitting because you are afraid of a false activation.

Practice

60-second drill

Partner: 24-year-old, sharp pain, fish-hook J in V4, no reciprocal change, looks well. Then: 58-year-old, same-looking concave STE in V2–V4 plus depression in III. What changes?

Related: STEMI on the 12-Lead, STEMI Equivalents: Transmit Anyway, Serial 12-Leads in ACS.

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. Reciprocal ST depression in an opposite wall most often means:
2. A fish-hook J-point and concave ST elevation in a well-appearing young adult is most consistent with:
3. Concave ST elevation:
4. If the tracing is LBBB or paced and you are worried, the street move is:
← Serial 12-Leads in ACS Pediatric SVT vs Sinus Tachycardia →