The Fifth Universal Definition of Myocardial Infarction (2026) introduces an important shift in how myocardial infarction is diagnosed and classified. The emphasis moves away from numerical MI types toward a mechanism-based approach that asks two fundamental questions: Is this truly myocardial infarction, and what caused it?
The numerical MI classification has been replaced
The previous Type 1–5 framework has been replaced by three clinically meaningful categories. The goal is to classify MI according to its underlying mechanism and clinical setting, rather than relying primarily on numerical labels.
| Clinical category | Definition |
|---|---|
| Primary MI | Spontaneous MI caused by a primary acute coronary pathology |
| Secondary MI | MI caused by myocardial oxygen supply–demand imbalance from another acute condition |
| Procedure-related MI | MI caused by a complication of a percutaneous or surgical cardiac procedure within 30 days |
Primary MI is broader than the previous Type 1 MI
Primary MI includes spontaneous infarction caused by an acute coronary process. The diagnosis requires acute myocardial injury plus evidence of myocardial ischaemia, with the coronary pathology or ischaemic myocardial damage established when possible.
- Atherothrombosis
- Spontaneous coronary artery dissection (SCAD)
- Coronary embolism
- Coronary vasospasm
- Restenosis occurring more than 30 days after intervention
- Stent thrombosis occurring more than 30 days after intervention
- Bypass graft failure occurring more than 30 days after revascularisation
Secondary MI requires more than acute illness plus elevated troponin
Secondary MI occurs when another acute condition creates a significant imbalance between myocardial oxygen supply and demand. Typical triggers include tachycardia, severe hypertension, hypotension, hypoxia and anaemia.
| Obstructive CAD criterion | Threshold |
|---|---|
| Epicardial coronary stenosis | ≥70% by angiography |
| Physiologically flow-limiting stenosis | ≥50% |
Troponin elevation in a sick patient should not automatically be labelled secondary MI. The definition emphasizes objective evidence supporting ischaemia, such as obstructive coronary artery disease without acute coronary pathology or a new or presumed new ischaemic wall-motion abnormality or loss of viable myocardium.
If ischaemia cannot be established, the more appropriate diagnosis may be acute myocardial injury rather than MI.
Procedure-related MI has been substantially redefined
Procedure-related MI refers to infarction caused by a complication of a percutaneous or surgical cardiac procedure occurring within 30 days.
The diagnosis no longer relies on cardiac biomarker thresholds alone. Greater emphasis is placed on demonstrating a relevant coronary procedural complication and/or new ischaemic myocardial damage on imaging, depending on the procedural setting and timing.
This is particularly important after cardiac surgery, where substantial troponin elevations are common without true infarction. Stent thrombosis, restenosis or graft failure occurring more than 30 days after revascularisation is classified as primary MI rather than procedure-related MI.
Troponin elevation does not automatically mean MI
Acute myocardial injury is identified by a rise and/or fall in cardiac troponin, with at least one value above the sex-specific 99th-percentile upper reference limit.
Acute myocardial injury is not equivalent to myocardial infarction. For MI to be diagnosed, clinicians must also establish that myocardial ischaemia caused the injury.
Troponin results should therefore be interpreted alongside the clinical presentation, ECG findings and, when required, coronary or cardiac imaging.
Use sex-specific troponin thresholds
The Fifth Universal Definition emphasizes sex-specific 99th-percentile upper reference limits for defining myocardial injury.
Normal high-sensitivity cardiac troponin concentrations differ between females and males. Using a single threshold can contribute to under-recognition of myocardial injury and infarction in women. Clinicians should use the sex-specific upper reference limit validated for the particular assay being used.
Imaging has a greater role in defining the mechanism
The new framework places considerable importance on establishing why myocardial injury occurred. Imaging is especially valuable when the diagnosis is uncertain, when differentiating secondary MI from non-ischaemic myocardial injury, and when angiography does not reveal an obvious culprit lesion.
- Coronary angiography
- Echocardiography
- Cardiac magnetic resonance (CMR)
- Coronary CT angiography (CCTA)
- Intracoronary imaging with OCT or IVUS
MINOCA has been redefined
MINOCA now refers to myocardial injury with non-obstructive coronary arteries.
It should be considered a working diagnosis—not the final aetiological diagnosis. Further investigation should determine the underlying cause, which may be an ischaemic mechanism or an alternative diagnosis such as myocarditis, Takotsubo syndrome or another cardiac or non-cardiac condition.
Practical take-home points
The Fifth Universal Definition asks clinicians to confirm injury, establish ischaemia and then identify the underlying mechanism.
- Classify MI as primary, secondary or procedure-related.
- Troponin elevation alone does not diagnose MI.
- First establish acute myocardial injury, then determine whether ischaemia caused it.
- Use sex-specific 99th-percentile troponin upper reference limits.
- Do not automatically diagnose secondary MI in every acutely ill patient with elevated troponin.
- Procedure-related MI is not defined by arbitrary troponin multiples alone.
- Remember the 30-day window for procedure-related MI.
- Use coronary and cardiac imaging to establish the mechanism when needed.
- MINOCA is a working diagnosis requiring further investigation.
Full reference
Fifth Universal Definition of Myocardial Infarction (2026): On behalf of the Joint European Society of Cardiology (ESC)/American College of Cardiology (ACC)/American Heart Association (AHA)/World Heart Federation (WHF) Task Force for the Universal Definition of Myocardial Infarction. European Heart Journal. Published 28 August 2026. doi:10.1093/eurheartj/ehag101.