Fifth Universal Definition of Myocardial Infarction (2026): A Comprehensive Clinical Guide

​Fifth Universal Definition of Myocardial Infarction (2026): 

A Comprehensive Clinical Guide

1. What Is New in the 5th UDMI 2026 Definition?

• Retirement of Numerical Subtypes: The traditional numerical classification (Types 1, 2, 3, 4a–c, and 5) has been retired. Myocardial infarction is now classified into three pathophysiological clinical entities: Primary MI, Secondary MI, and Procedure-Related MI.
  
  
• Elimination of "Type 3 MI": Sudden cardiac death before biomarkers can be drawn is no longer termed Type 3 MI. These cases are now classified under Primary, Secondary, or Procedure-related MI based on clinical circumstances or post-mortem findings, with an ICD-11 code for "Unspecified MI" (BA41.Z) when unevaluated.
  
  
• Objective Diagnostic Criteria for Secondary MI: Secondary MI now requires objective confirmation of underlying obstructive coronary artery disease (CAD) or new regional wall motion abnormalities (RWMA) / loss of myocardial viability to prevent overdiagnosis in non-cardiac acute illness.
  
  
• Harmonized Procedure-Related MI Definition: The arbitrary biomarker cutoffs (e.g., >5x URL for PCI, >10x URL for CABG) have been replaced with a unified framework requiring documented procedural complications and/or imaging evidence of new myocardial damage within 30 days.
  
  
• MINOCA Redefined: The acronym MINOCA is now officially defined as "Myocardial Injury with Non-Obstructive Coronary Arteries", emphasizing that it is a working diagnosis rather than a final entity.
  
  
• Sex-Specific Troponin Cutoffs: Strict adherence to sex-specific 99th percentile Upper Reference Limits (URLs) is mandated to prevent the under-diagnosis of myocardial infarction in females.
  
  
• Alignment with ICD-11: Dedicated codes distinguish STEMI (BA41.0) and NSTEMI (BA41.1), with 6th-digit stem codes covering specific acute coronary pathologies.
  
  

2. Acute vs. Chronic Myocardial Injury

Myocardial injury remains defined by an elevated cardiac troponin (cTn I or T) above the sex-specific 99th percentile URL.

• Acute Myocardial Injury: Defined as a dynamic rise and/or fall of cardiac troponin with at least one value above the sex-specific 99th percentile URL. It can be ischemic (MI) or non-ischemic (e.g., myocarditis, sepsis, Takotsubo, cardiotoxic drugs, pulmonary embolism).
  
  
• Chronic Myocardial Injury: Defined as persistently elevated troponin with < 20% variation on serial measurements in a stable clinical setting, associated with structural cardiac conditions (e.g., ischemic or non-ischemic cardiomyopathy, hypertensive heart disease, heart failure) or reduced renal clearance in chronic kidney disease.
  
  

3. The 3 New Clinical Classifications of Myocardial Infarction

A. Primary Myocardial Infarction (Spontaneous Presentation)

Occurs spontaneously due to a primary acute coronary pathology without an external acute supply-demand trigger or recent cardiac procedure.

• Clinical Suspicion (Likely Diagnosis): Acute myocardial injury (rise/fall of cTn above sex-specific 99th percentile URL), AND at least one ischemic feature: ischemic symptoms, new ischemic ECG changes (ST-elevation, ST-depression, T-wave inversion), or new pathological Q waves.
  
  
• Definitive Confirmation: Identification of an acute coronary pathology on invasive coronary angiography or intravascular imaging (IVUS/OCT): Atherothrombosis (plaque rupture/erosion), Spontaneous Coronary Artery Dissection (SCAD), coronary embolism, coronary vasospasm, or late stent/graft failure (> 30 days post-procedure), OR cardiac imaging demonstrating a new or presumed new RWMA or loss of viable myocardium in a matching coronary distribution.
  
  

B. Secondary Myocardial Infarction (Supply-Demand Imbalance)

Occurs secondary to another acute clinical condition that creates a mismatch between myocardial oxygen supply and demand (e.g., tachyarrhythmia, severe hypotension, hypoxia, severe anemia, malignant hypertension).

• Diagnostic Criteria (Prioritizing Specificity): Acute myocardial injury (dynamic troponin rise/fall), AND clinical or ECG evidence of myocardial ischemia in the setting of an acute secondary condition, AND objective confirmation via imaging.
  
  
• Objective Confirmation via Imaging: Obstructive CAD on angiography/CCTA (>= 70% epicardial stenosis, or > 50% with functional significance by FFR/iFR/RFR) without an acute plaque event, AND/OR new or presumed new RWMA or loss of viable myocardium on echocardiography or CMR.
  
  
• Clinical Caveat: If imaging reveals normal/non-obstructive coronary vessels without new wall motion abnormalities, the patient is classified as having acute non-ischemic myocardial injury, not secondary MI.
  
  

C. Procedure-Related Myocardial Infarction (<= 30 Days)

Occurs as a complication of any percutaneous cardiac intervention (PCI, structural valve interventions, ablation) or open cardiac surgery (CABG, valve replacement) within 30 days.

• Universal Diagnostic Criteria: Suspected or evident coronary complication with acute myocardial injury (troponin elevation significantly higher than expected baseline post-procedure), AND angiographic evidence: acute side-branch occlusion, stent thrombosis, iatrogenic dissection, slow-flow/no-reflow, bypass graft occlusion, coronary impingement/embolism, OR imaging evidence: new or presumed new RWMA or loss of viable myocardium in the territory of the treated vessel.
  
  
• Special Rule for Intraprocedural / Acute MI Settings: If the complication occurs during the index procedure or during an intervention for acute MI, both angiographic confirmation of a complication AND imaging confirmation of new myocardial damage/RWMA are strictly required.
  
  

4. Comparison: 4th UDMI (2018) vs. 5th UDMI (2026)

Parameter	4th Universal Definition (2018)	5th Universal Definition (2026)
Classification System	Numerical subtypes: Types 1, 2, 3, 4a, 4b, 4c, and 5	Clinical entities: Primary MI, Secondary MI, and Procedure-Related MI
Plaque Rupture vs. SCAD/Spasm	Atherothrombosis = Type 1; SCAD/Spasm = Type 2	All acute coronary mechanisms are grouped under Primary MI
Secondary MI Diagnostic Rule	Clinical suspicion of supply-demand mismatch + troponin rise	Requires objective demonstration of obstructive CAD (>= 70%) or new RWMA
Stent / Graft Failure Timing	Type 4b/4c or Type 5 at any point post-procedure	<= 30 days = Procedure-Related MI; > 30 days = Primary MI (de novo pathology)
Surgical MI (CABG) Threshold	Isolated troponin cutoff > 10x URL within 48 hours	Removed arbitrary cutoffs; requires angiographic complication and/or new RWMA on imaging
MINOCA Terminology	Myocardial Infarction with Non-Obstructive Coronaries	Myocardial Injury with Non-Obstructive Coronary Arteries (working diagnosis)
Sudden Death Category	Type 3 MI	Term retired; classified by clinical context or coded as Unspecified MI (BA41.Z)

5. Electrocardiographic Criteria for Acute Coronary Occlusion

A standard 12-lead ECG remains essential for rapid triage. The 2026 consensus emphasizes STEMI equivalents and patterns of acute coronary occlusion:

• ST-Elevation Criteria (at the J-point in >= 2 contiguous leads):

                    Leads V2–V3: >= 2.5 mm in men < 40 years;  >= 2.0 mm in men >= 40 years; >= 1.5 mm in women of any age.
                     All other leads: >= 1.0 mm in men and women.

• Posterior MI: ST-segment depression >= 1.0 mm in leads V1–V3 with dominant R waves, confirmed by ST-elevation >= 0.5 mm in posterior leads V7–V9.
  
  
• Right Ventricular MI: ST-elevation in right precordial leads (V3R–V6R), often accompanied by ST-elevation in lead aVR.
  
  
• Occlusion Patterns & STEMI Equivalents:
  
  
  • Modified Sgarbossa Criteria (for LBBB or Ventricular Pacing): Concordant STE >= 1 mm, concordant STD >= 1 mm in V1–V3, or excessively discordant STE with an ST/S ratio <= -0.25.
  • de Winter Pattern: Upsloping ST-segment depression in precordial leads with tall, symmetric, hyperacute T waves (indicates acute proximal LAD occlusion).
    
    
  • Wellens Pattern: Deeply inverted or biphasic T waves in V2–V3 during pain-free intervals (critical proximal LAD stenosis).
    
    
  • Aslanger Pattern: ST-elevation isolated to lead III with concomitant ST-depression in leads V4–V6 and a positive T wave in lead III (indicates acute inferior occlusion in multivessel disease).
    
    
  • South African Flag Sign: ST-elevation in leads I, aVL, and V2 with reciprocal ST-depression in lead III (high lateral / diagonal branch occlusion).
    
    

6. Biomarker Best Practices: High-Sensitivity Cardiac Troponin (hs-cTn)

• Sex-Specific Cutoffs: Healthy females have significantly lower 99th percentile reference levels than males. Using uniform cutoffs leads to underdiagnosis of female infarction.
  
  
• Accelerated Pathways (0/1h and 0/2h): Validated rapid rule-out and rule-in algorithms use optimized decision cutoffs for emergency disposition. Rule-out thresholds operate well below the 99th percentile URL to guarantee high negative predictive value.
  
  
• Analytical Interference: Discrepant or fluctuating troponin values without clinical correlation should prompt investigation for macrotroponin complexes, heterophile antibodies, or hemolysis.
  
  

7. Multimodality Imaging in MI Confirmation

• Invasive Angiography & Intravascular Imaging (IVUS/OCT): Essential for identifying non-atherosclerotic acute mechanisms (SCAD, thrombosis, spasm) and resolving angiographically ambiguous culprit lesions.
  
  
• Cardiac Magnetic Resonance (CMR): The gold standard for non-invasive confirmation. It discriminates ischemic myocardial infarction (subendocardial/transmural late gadolinium enhancement [LGE]) from non-ischemic injury such as acute myocarditis (subepicardial/mid-wall LGE) and Takotsubo cardiomyopathy (transmural edema without LGE).
  
  
• Echocardiography: Bedside modality of choice to establish baseline regional wall motion abnormalities, quantify left ventricular ejection fraction, and rule out acute mechanical complications (e.g., acute mitral regurgitation, ventricular septal defect, free wall rupture).
  
  

8. Summary for Clinical Practice

• Classify by Mechanism: Identify whether the event is Primary (spontaneous coronary pathology), Secondary (supply-demand mismatch), or Procedure-Related (<= 30 days post-intervention).
  
  
• Apply Objective Imaging: For suspected Secondary MI, do not rely on troponin elevation alone; obtain anatomical or functional imaging to verify underlying obstructive CAD or new RWMA.
  
  
• Use Sex-Specific hs-cTn URLs: Prevent systematic under-recognition of acute myocardial injury in female patients.
  
  

Reference

• Mills NL, Newby LK, Zaman S, et al. Fifth Universal Definition of Myocardial Infarction (2026). Joint ESC/ACC/AHA/WHF Task Force. European Heart Journal, doi:10.1093/eurheartj/ehag101.
  
  
• Disclaimer: This summary is intended solely for educational, academic, and examination preparation purposes and does not constitute formal clinical management guidance.