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Lesson

STEMI Mimics in the Field

12 min Cardiac & ECG Skip to quiz

Objective: Use simple field checks to separate a STEMI (ST-elevation myocardial infarction) from common look-alikes. If you are unsure, transmit the tracing. Do not tell the hospital the tracing is nothing.

Why this matters

Get the 12-lead, then decide whether to transmit it. Crews both over-call and under-call STEMIs. False cath-lab activations happen. So do closed arteries that wait in the hallway because someone called them early repolarization. Common look-alikes are benign early repolarization (BER), left-ventricular hypertrophy (LVH) with strain, pericarditis or myopericarditis, left bundle-branch block (LBBB), and a paced rhythm.

Use a few field checks instead of a memorized score. Reciprocal ST depression, except in aVR or V1, is not BER and it is not ordinary pericarditis. BER is usually a younger patient with a fish-hook J point and no change during your call. Symptoms plus new ST elevation in one region are ACS (acute coronary syndrome, a heart-attack workup) until the receiving physician says otherwise. If you are unsure, transmit the tracing. Do not cancel the catheterization laboratory from the ambulance.

Key points
  • One 12-lead is a snapshot. Repeat it if symptoms continue. See the serial 12-lead lesson.
  • Look for reciprocal depression in the opposite wall. That finding supports “this is likely an occlusion.”
  • Age and the story matter. A fish-hook J point in a 22-year-old with sharp pain that changes with position is not the same as a 64-year-old who is sweating.
  • 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 or paced, and I am still concerned.”

Clinical sequence

  1. Protect the airway, breathing, and circulation. Get a 12-lead when ACS is possible, including symptoms that stand in for chest pain.
  2. Map the ST elevation. Is it one region, or is it everywhere? Is there reciprocal depression, a hyperacute T wave, or a new Q wave?
  3. If it looks like BER or pericarditis, still ask whether it could be an occlusion. When you are unsure, transmit it and let the receiving team decide.
  4. Do not talk a concerning tracing down because the computer said “nonspecific” or because the patient is young.

Teaching points

  • BER: often a younger patient, concave ST elevation in V2–V5, a notched or slurred J point (a “fish hook”), a prominent T wave, no reciprocal depression, and no change during your call.
  • Pericarditis or myopericarditis: more widespread ST elevation, PR depression, and pain that is often positional or pleuritic. Reciprocal depression beyond aVR and V1 argues against simple pericarditis. Treat that finding as a possible closed artery.
  • LVH strain: tall voltage, and the ST segment and T wave point opposite the QRS. ST elevation in V1–V3 can look alarming. It is often the mirror of lateral strain. Still transmit if the story is ACS.
  • LBBB and paced rhythms: some ST elevation in the opposite direction from the QRS is expected. ST elevation in the same direction as the QRS, or too much of the opposite change, is the concerning pattern (Sgarbossa or Smith-style rules). You do not need the score memorized. Say the left bundle-branch block looks worse than this patient’s usual tracing, and transmit.
  • A look-alike may explain some ST elevation. It does not let you skip the aspirin or the destination your protocol already requires. Do not keep the tracing to yourself.
Verbalize
  • Is the ST elevation in one region, or is it widespread?
  • If there is reciprocal depression, it is not BER.
  • A young patient with a fish-hook J point is not a 60-year-old with ACS.
  • If I am unsure, I transmit.

Common errors

  • Calling anterior ST elevation “early repolarization” in a middle-aged patient who is sweating.
  • Calling it pericarditis only because the ST segment is concave. A concave or scooped ST segment does not rule out a closed artery. Do not quote a percentage as a field rule. Reciprocal change and the story decide whether you transmit.
  • Ignoring reciprocal depression.
  • Not transmitting because you are afraid of a false activation.

Practice

One-minute check

Partner: a 24-year-old with sharp pain, a fish-hook J point in V4, no reciprocal change, and looks well. Then a 58-year-old with similar concave ST elevation in V2–V4 plus depression in III. What changes?

Related: STEMI on the 12-Lead, STEMI Equivalents, 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

Questions drawn only from this lesson. 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 field action is:
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