5th Universal Definition of Myocardial Infarction (2026)
The Major Changes You Need to Know
The Fifth Universal Definition of Myocardial Infarction (5th UDMI), published in 2026, represents a major evolution in how myocardial infarction (MI) is defined and classified.
For the first time, the document has been developed jointly by the European Society of Cardiology (ESC), American College of Cardiology (ACC), American Heart Association (AHA), and World Heart Federation (WHF).
The major conceptual change is simple:
Instead of asking, “Is this Type 1, 2, 3, 4 or 5 MI?”
the clinician should now ask:
Is this a primary MI, secondary MI, or procedure-related MI?
The new classification is designed to better reflect pathophysiology and clinical decision-making.
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1. What is Myocardial Infarction?
Myocardial infarction is myocardial cell death caused by prolonged myocardial ischaemia.
Importantly, an elevated troponin level alone does NOT diagnose MI.
The clinical diagnosis requires:
Acute myocardial injury
PLUS
Evidence of acute myocardial ischaemia.
Evidence of ischaemia may include:
- Symptoms or other clinical evidence of acute myocardial ischaemia
- New ischaemic ECG changes
- Development of pathological Q waves
- Imaging evidence of a new loss of viable myocardium
- New regional wall-motion abnormality consistent with an ischaemic aetiology
- Evidence of an acute coronary pathology on coronary imaging
Therefore:
Troponin elevation ≠ MI
Troponin indicates myocardial injury; the diagnosis of MI requires evidence that the injury is caused by myocardial ischaemia.
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2. Myocardial Injury vs Myocardial Infarction
This distinction remains fundamental.
Acute myocardial injury
Acute myocardial injury is present when cardiac troponin is:
>99th percentile upper reference limit
with a rise and/or fall pattern.
The 5th UDMI emphasizes the use of sex-specific 99th percentile thresholds where appropriate.
Chronic myocardial injury
Persistently elevated troponin without a significant dynamic change is generally considered chronic myocardial injury.
Examples include:
- Chronic kidney disease
- Chronic heart failure
- Structural heart disease
- Cardiomyopathies
- Some infiltrative diseases
Key concept
Myocardial injury is a biomarker diagnosis.
MI is a clinical diagnosis requiring evidence of myocardial ischaemia.
This distinction prevents overdiagnosis of MI in patients with elevated troponin from non-ischaemic causes.
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3. The Biggest Change: Goodbye Type 1–5
The previous classification:
- Type 1 MI
- Type 2 MI
- Type 3 MI
- Type 4a MI
- Type 4b MI
- Type 4c MI
- Type 5 MI
has been replaced by three clinically meaningful categories:
1. Primary MI
2. Secondary MI
3. Procedure-related MI
This change is intended to make the classification easier to apply in clinical practice while better reflecting the underlying pathophysiology.
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4. Primary Myocardial Infarction
Primary MI occurs spontaneously because of an acute coronary pathology.
The most familiar mechanism is acute coronary atherothrombosis.
However, the new definition deliberately goes beyond plaque rupture and thrombosis.
Possible causes include:
- Plaque rupture
- Plaque erosion
- Coronary thrombosis
- Spontaneous coronary artery dissection (SCAD)
- Coronary vasospasm
- Coronary embolism
- Other acute coronary pathologies
This is an important conceptual change.
Previously, Type 1 MI was strongly associated with acute atherothrombosis.
The new primary MI category recognizes that spontaneous MI can occur through several different coronary mechanisms.
Practical implication
If a patient presents with acute myocardial ischaemia and imaging demonstrates SCAD, coronary spasm or embolism, the event can be classified as primary MI even without conventional plaque rupture and thrombosis.
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5. Secondary Myocardial Infarction
Secondary MI occurs when myocardial ischaemia results from an acute oxygen supply–demand imbalance caused by another acute condition.
Examples may include:
- Severe tachyarrhythmia
- Severe bradyarrhythmia
- Severe hypertension
- Severe hypotension
- Severe anaemia
- Hypoxaemia
- Respiratory failure
- Shock
- Other acute systemic conditions
The important concept is that the acute condition is responsible for the myocardial oxygen imbalance rather than an acute primary coronary pathology.
However, the new definition provides more objective criteria to distinguish secondary MI from isolated myocardial injury.
In particular, the presence of obstructive CAD alone does not automatically make an event primary MI. The clinical context and evidence for acute coronary pathology must be considered.
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6. Procedure-Related MI
The third category encompasses MI occurring as a complication of cardiac procedures.
This replaces the previous:
- Type 4a
- Type 4b
- Type 4c
- Type 5
classification.
It includes myocardial infarction associated with:
- Percutaneous coronary intervention
- Coronary stent-related complications
- Cardiac surgery/CABG
- Other relevant cardiac procedures
The new framework is designed to align the diagnosis with the timing, mechanism and clinical context of the procedure.
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7. What Happened to Type 4b and 4c MI?
This is an important exam and clinical point.
Previously:
Type 4b
= stent/scaffold thrombosis
Type 4c
= restenosis
The 5th UDMI moves away from treating these as separate numerical MI categories.
Interestingly, stent thrombosis, restenosis and graft failure occurring >30 days after a procedure are now considered within the primary MI framework when they represent an acute coronary pathology.
This reflects an important pathophysiological principle:
The mechanism matters more than the historical numerical label.
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8. MINOCA – An Important Terminology Change
Another major change concerns MINOCA.
The 5th UDMI emphasizes that MINOCA should be regarded as a working diagnosis rather than a final aetiological diagnosis.
The terminology is updated toward:
Myocardial injury with non-obstructive coronary arteries
rather than assuming that all such patients have a single disease entity.
The underlying cause should be investigated.
Potential mechanisms include:
- Plaque disruption
- SCAD
- Coronary spasm
- Coronary embolism
- Microvascular dysfunction
- Myocarditis
- Takotsubo syndrome
- Other causes of myocardial injury
Thus:
Non-obstructive coronaries do not mean “nothing is wrong.”
Further coronary and cardiac imaging may be essential to determine the actual diagnosis.
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9. Cardiac Troponin: Still Central
High-sensitivity cardiac troponin remains the cornerstone biomarker for detecting myocardial injury.
The 5th UDMI reinforces:
99th percentile upper reference limit = threshold for myocardial injury
and emphasizes sex-specific thresholds where validated.
This is particularly relevant because using a single threshold for both sexes may reduce diagnostic sensitivity in women.
However, the clinician must interpret troponin in the clinical context.
A very high troponin does not automatically mean Type 1/primary MI.
For example:
Sepsis + elevated troponin
does not automatically equal MI.
Similarly:
Tachycardia + elevated troponin
does not automatically equal MI.
The diagnosis depends on whether there is evidence of myocardial ischaemia and whether the underlying mechanism fits primary, secondary or procedure-related MI.
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10. ECG Remains Fundamental
The ECG remains one of the most important tools for identifying acute myocardial ischaemia.
Relevant findings include:
- New ST-segment elevation
- New ST-segment depression
- Dynamic T-wave changes
- New pathological Q waves
- Other new ischaemic ECG abnormalities
However, ECG findings must be interpreted together with symptoms, biomarkers and imaging.
A normal ECG does not exclude MI.
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11. Greater Emphasis on Imaging
The 5th UDMI places greater emphasis on imaging to determine the underlying cause of myocardial injury and infarction.
Useful modalities include:
Echocardiography
Useful for detecting:
- New regional wall-motion abnormalities
- LV dysfunction
- Mechanical complications
Coronary angiography
Useful for identifying:
- Atherothrombosis
- Coronary occlusion
- SCAD
- Embolism
- Other coronary pathology
Cardiac CT
Can contribute to anatomical assessment in selected patients.
Cardiac MRI
CMR is particularly valuable when the diagnosis is uncertain.
It can help distinguish:
- MI
- Myocarditis
- Takotsubo syndrome
- Other cardiomyopathies
The new definition encourages objective investigation of the underlying mechanism rather than stopping at the finding of an elevated troponin.
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12. Silent and Unrecognized MI
The 5th UDMI introduces new objective criteria for silent or unrecognized myocardial infarction.
This is particularly important because some myocardial infarctions occur without classical symptoms.
Evidence from:
- ECG
- Imaging
- Biomarkers
- Clinical history
may help establish an unrecognized infarction.
This provides a more objective framework than relying solely on retrospective symptom history.
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13. Sudden Cardiac Death
The new definition also provides guidance regarding MI in patients presenting with sudden cardiac death.
The challenge is obvious:
The patient may die before cardiac biomarkers can be obtained or before a complete diagnostic evaluation is possible.
Therefore, ECG findings, clinical circumstances, coronary findings and, where applicable, pathological examination become important in establishing the diagnosis.
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14. A Practical Approach to an Elevated Troponin
When faced with a patient with elevated hs-cTn, think systematically:
Step 1
Is troponin above the 99th percentile?
If no → myocardial injury not established.
If yes → myocardial injury is present.
Step 2
Is there a rise/fall pattern?
If yes → acute myocardial injury is likely.
If persistently elevated → consider chronic myocardial injury.
Step 3
Is there evidence of acute myocardial ischaemia?
Look for:
- Ischaemic symptoms
- Ischaemic ECG changes
- New regional wall-motion abnormality
- New loss of viable myocardium
- Acute coronary pathology
Step 4
If MI is present, determine the setting:
Primary MI?
Secondary MI?
Procedure-related MI?
Step 5
Identify the underlying mechanism.
This is where coronary imaging, echocardiography and CMR may become critical.
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15. The New Classification at a Glance
5th UDMI| Main mechanism| Examples
Primary MI| Acute primary coronary pathology| Atherothrombosis, SCAD, spasm, embolism
Secondary MI| Acute oxygen supply–demand imbalance from another condition| Severe anaemia, tachyarrhythmia, hypotension, hypoxaemia
Procedure-related MI| Complication of cardiac intervention/surgery| PCI-related MI, CABG-related MI
This replaces the previous numerical Type 1–5 system.
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16. Fourth vs Fifth UDMI — High-Yield Comparison
Feature| 4th UDMI| 5th UDMI
MI classification| Type 1–5| Primary, secondary, procedure-related
Type 1 MI| Yes| Replaced by primary MI
Type 2 MI| Yes| Replaced by secondary MI
Type 3 MI| Yes| Incorporated into updated framework
Type 4a–c| Yes| Procedure-related framework
Type 5| Yes| Procedure-related framework
Troponin| Central| Central + greater emphasis on sex-specific thresholds
MINOCA| Clinical diagnosis| Emphasized as a working diagnosis requiring further evaluation
Imaging| Important| Greater emphasis on defining aetiology
Silent MI| Recognized| New objective criteria
Low-resource settings| Limited guidance| Specific guidance added
ICD classification| Previous system| Proposed ICD-11 alignment
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17. Why Does This Matter Clinically?
The most important message of the 5th UDMI is:
Do not diagnose MI from troponin alone.
Instead:
Troponin → identify myocardial injury
↓
Clinical/ECG/imaging evidence → establish myocardial ischaemia
↓
MI diagnosis
↓
Determine mechanism
↓
Primary vs secondary vs procedure-related
This approach should reduce inappropriate labelling of patients with non-ischaemic myocardial injury as having MI.
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18. Key Take-Home Messages
1.
The 5th Universal Definition of MI was published in 2026 by ESC/ACC/AHA/WHF.
2.
The traditional Type 1–5 classification has been replaced.
3.
There are now three major categories:
Primary MI
Secondary MI
Procedure-related MI
4.
Troponin elevation alone does not diagnose MI.
5.
MI requires acute myocardial injury + evidence of myocardial ischaemia.
6.
Sex-specific 99th percentile troponin thresholds are emphasized.
7.
SCAD, coronary spasm and coronary embolism can fall under primary MI.
8.
Secondary MI results from an acute condition causing myocardial oxygen supply–demand imbalance.
9.
MINOCA should be regarded as a working diagnosis requiring identification of the underlying cause.
10.
Imaging—particularly coronary imaging, echocardiography and CMR—has an increasingly important role in determining the mechanism of myocardial injury and MI.
11.
The new framework is designed to make MI classification more clinically meaningful and more closely aligned with pathophysiology.
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Bottom Line
The 5th Universal Definition represents a shift from numerical classification to mechanism-based classification.
Instead of simply labelling an event as Type 1 or Type 2 MI, clinicians are encouraged to answer three questions:
1. Is there acute myocardial injury?
2. Is there evidence of myocardial ischaemia?
3. What is the underlying mechanism — primary, secondary or procedure-related?
That shift—from “what type number is this?” to “what caused the myocardial infarction?”—is the central message of the 2026 Fifth Universal Definition.
Reference: Mills NL, Newby LK, Zaman S, et al. Fifth Universal Definition of Myocardial Infarction (2026). European Heart Journal/JACC. Joint ESC/ACC/AHA/WHF Task Force.
For the official guideline, see "ESC — Fifth Universal Definition of Myocardial Infarction"
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