STEMI Criteria: ST Elevation Thresholds on the 12-Lead
The ST elevation thresholds from the Fourth Universal Definition of Myocardial Infarction, contiguous leads and reciprocal changes, the patterns that matter without meeting the numbers, and the common mimics.
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STEMI stands for ST-elevation myocardial infarction: a heart attack in which a coronary artery is usually completely blocked, and the 12-lead ECG shows ST segments lifted above the baseline over the injured part of the heart. Recognizing it in the field matters because the treatment, opening the artery, is time-critical, and an early ECG transmitted or reported ahead lets the receiving facility be ready.
If you are still learning to place the electrodes or read the basic 12-lead, start with the 12-lead placement guide and the 12-lead interpretation basics guide in this library. Lead placement errors can produce a false STEMI.
The criteria
The thresholds below are from the Fourth Universal Definition of Myocardial Infarction (2018), written by a joint task force of the European and American cardiology societies and the World Heart Federation. ST elevation is measured at the J point, where the QRS ends and the ST segment begins, and it must appear in at least two contiguous leads, in the absence of left ventricular hypertrophy or left bundle branch block (the mimics below explain why).
| Leads | Who | New ST elevation at the J point |
|---|---|---|
| All leads other than V2 and V3 | Everyone | 1 mm or more |
| V2 and V3 | Men 40 and older | 2 mm or more |
| V2 and V3 | Men under 40 | 2.5 mm or more |
| V2 and V3 | Women of any age | 1.5 mm or more |
| V7 to V9 (posterior) | Everyone except men under 40 | 0.5 mm or more |
| V7 to V9 (posterior) | Men under 40 | 1 mm or more |
| V3R and V4R (right-sided) | Everyone except men under 30 | 0.5 mm or more |
| V3R and V4R (right-sided) | Men under 30 | 1 mm or more |
On standard paper at standard calibration, 1 mm is one small box. The V2 and V3 thresholds are higher because those leads normally show some ST elevation, especially in young men.
Contiguous leads
Contiguous leads are anatomic neighbors. In the chest leads, any two adjacent leads, V1 to V6 in order, are contiguous, including across the regions below. In the limb leads the neighbors are II, III and aVF inferiorly, and I and aVL laterally. The regions below are a guide to territory, not a rule for which pairs count.
| Region | Leads | Usual artery |
|---|---|---|
| Inferior | II, III, aVF | Right coronary artery, sometimes the circumflex |
| Septal | V1, V2 | Left anterior descending |
| Anterior | V3, V4 | Left anterior descending |
| High lateral | I, aVL | Circumflex or diagonal branches |
| Low lateral | V5, V6 | Circumflex or diagonal branches |
| Posterior | V7, V8, V9 (ST depression in V1 to V3 on the standard 12-lead) | Circumflex or right coronary artery |
| Right ventricle | V3R, V4R | Right coronary artery |
Reciprocal changes
ST depression in leads facing the opposite wall supports a true STEMI. An inferior STEMI commonly shows reciprocal depression in aVL and I; an anterior one can show depression in the inferior leads. Reciprocal change makes a mimic less likely, but its absence does not rule out a STEMI.
Patterns that do not meet the numbers but matter
Some patterns signal a blocked or nearly blocked artery without classic ST elevation. They are named here so you recognize them and report them; your protocol decides what each one triggers.
- Posterior MI: ST depression with upright T waves in V1 to V3. Posterior leads V7 to V9 show the elevation directly.
- De Winter T waves: upsloping ST depression with tall, symmetric T waves in the precordial leads.
- Wellens pattern: deep inverted or biphasic T waves in V2 and V3, often in a patient whose pain has eased. It is a high-risk sign of a critical narrowing of the left anterior descending artery that can occlude.
- Widespread ST depression with ST elevation in aVR, which can mean disease of the left main artery or several vessels.
Mimics
Several conditions raise the ST segment without a blocked artery. They are the common reasons a field STEMI call turns out not to be one.
| Mimic | What tends to give it away |
|---|---|
| Left bundle branch block | Wide QRS with ST changes that point opposite the QRS. Criteria named after Sgarbossa help identify an infarct inside an LBBB, and are beyond this guide |
| Paced rhythm | Pacer spikes before wide QRS complexes |
| Left ventricular hypertrophy | Very tall QRS voltages with ST changes that follow them |
| Pericarditis | Widespread ST elevation in many leads without reciprocal change, PR depression, and pain that changes with position or breathing |
| Early repolarization | Usually a young patient, a notched J point and concave ST elevation, unchanged on repeat ECGs |
| Brugada pattern | Coved ST elevation in V1 and V2 with a right bundle branch pattern |
| Hyperkalemia | Tall peaked T waves, widening QRS, and a kidney or dialysis history |
A normal ECG is not a normal heart
A first 12-lead can be normal in a patient having a heart attack, and the changes can appear minutes later. Repeat the 12-lead when symptoms change and at the intervals your protocol sets, and compare it with the first. Report the patient's symptoms and the ECG together; neither alone tells the whole story.
Practice naming rhythms on a lead II strip
The short version
- STEMI means new ST elevation at the J point in two contiguous leads, absent LVH or LBBB.
- 1 mm in most leads; in V2 and V3, 2 mm for men 40 and older, 2.5 mm for men under 40, 1.5 mm for women.
- Look for reciprocal depression, and for the patterns that matter without meeting the numbers: posterior MI, de Winter, Wellens, aVR elevation.
- Know the mimics: LBBB, paced rhythm, LVH, pericarditis, early repolarization, Brugada, hyperkalemia.
- Repeat the ECG. Who activates the cath lab and where the patient goes are your protocol's decisions.