STEMI: new ST elevation in two or more contiguous leads, ideally with reciprocal ST depression.
Before you read
Test yourself first: 5 questions
Question 1 of 5
A STEMI pattern on a 12-lead is defined by ST elevation:
Answer: A. Two contiguous leads view the same wall from neighboring angles, so agreement between them is what separates a regional injury pattern from a single-lead artifact or normal variant. Elevation in one isolated lead is far more likely to be positional or a baseline problem, which is why it does not meet the definition.
Question 2 of 5
Lead I shows a negative P wave and a negative QRS while the chest leads look entirely normal. The most likely explanation is:
Answer: A. Reversing the arm electrodes flips the axis of lead I, so P wave and QRS both point downward while the precordial leads, which use different electrodes, stay normal — that combination is the signature of the error. A true lateral infarction changes ST segments rather than inverting the P wave, and it would show in the neighboring chest leads as well.
Question 3 of 5
A 12-lead ECG shows ST elevation in leads II, III and aVF. This suggests an infarction of the:
Answer: A. Leads II, III and aVF look at the inferior surface of the heart. Inferior infarctions often involve the right ventricle, which makes the patient sensitive to drugs that reduce preload, so right-sided leads are checked before giving nitrates.
Question 4 of 5
A patient with chest pain has horizontal ST depression in V1 through V3 with tall R waves in V2. What is the most appropriate next step?
Answer: A. Anterior ST depression with tall R waves can be the mirror image of a posterior STEMI, which the standard leads do not face directly. Posterior leads showing elevation confirm an occlusion needing reperfusion. Labeling it ischemia alone misses a STEMI-equivalent, right-sided leads assess the right ventricle, and waiting delays reperfusion.
Question 5 of 5
ST elevation in lead V4R in a patient with an inferior STEMI indicates involvement of which region?
Answer: A. V4R is placed in the right fifth intercostal space, midclavicular line, and ST elevation there indicates right ventricular infarction, usually from a proximal right coronary occlusion. This matters because RV involvement makes the patient preload dependent. The septum and high lateral wall are viewed by left-sided leads.
Keep the streak going with more questions like these, each with a full rationale.
What is 12-lead & stemi mimics?
Candidates must localize a STEMI by contiguous leads, look for reciprocal change, and recognize the patterns that imitate it.
Key points to remember
- STEMI: new ST elevation in two or more contiguous leads, ideally with reciprocal ST depression.
- Inferior II, III, aVF · septal V1–V2 · anterior V3–V4 · lateral I, aVL, V5–V6.
- ST depression in V1–V3 may be a posterior MI — obtain posterior leads V7–V9.
- Inferior MI: obtain right-sided V4R; right ventricular involvement is preload-dependent.
- Mimics: bundle branch block, paced rhythm, LV hypertrophy, early repolarization, pericarditis, hyperkalemia.
Field priorities
- Acquire a 12-lead within 10 minutes of contact for suspected ACS.
- Transmit or activate early — the goal is to shorten time to reperfusion.
- Repeat the 12-lead: a normal first tracing does not rule out ACS.
Coaching the patient
- Pericarditis: diffuse ST elevation, PR depression, pain better leaning forward.
- Avoid nitrates when right ventricular infarction or hypotension is present.
Red flags: act now
- Inferior STEMI with hypotension (right ventricle)
- Diffuse ST elevation read as STEMI
- Peaked T waves with a wide QRS
12-Lead & STEMI Mimics: FAQs
What are the priority actions for 12-Lead & STEMI Mimics in the field?
Acquire a 12-lead within 10 minutes of contact for suspected ACS. Transmit or activate early — the goal is to shorten time to reperfusion. Repeat the 12-lead: a normal first tracing does not rule out ACS.
What findings in 12-Lead & STEMI Mimics change your plan or your transport decision?
Inferior STEMI with hypotension (right ventricle). Diffuse ST elevation read as STEMI. Peaked T waves with a wide QRS.
What do I need to know about 12-Lead & STEMI Mimics for the NREMT?
STEMI: new ST elevation in two or more contiguous leads, ideally with reciprocal ST depression. Inferior II, III, aVF · septal V1–V2 · anterior V3–V4 · lateral I, aVL, V5–V6. ST depression in V1–V3 may be a posterior MI — obtain posterior leads V7–V9. Inferior MI: obtain right-sided V4R; right ventricular involvement is preload-dependent.
What should the crew communicate or document for 12-Lead & STEMI Mimics?
Pericarditis: diffuse ST elevation, PR depression, pain better leaning forward. Avoid nitrates when right ventricular infarction or hypotension is present.
