New MI definition replaces numbered subtypes with three clinical categories

Clinical takeaway: Clinicians should transition from the familiar type 1-5 MI framework to a new three-part classification: primary MI, secondary MI, and procedure-related MI. The update also places greater emphasis on confirming diagnoses with coronary and cardiac imaging and using sex-specific cardiac troponin thresholds.

A major international task force has released the Fifth Universal Definition of Myocardial Infarction (MI), the first update since 2018 and the first jointly aligned with ICD-11 coding. Published in Circulation on August 27, 2026, and presented at ESC Congress 2026 in Munich, the document aims to make MI classification more clinically intuitive while improving consistency in diagnosis, treatment, research, and public health reporting.

The headline change is the retirement of the long-standing numerical classification system (types 1, 2, 3, 4a-c, and 5). In its place, MIs are now categorized into three clinically meaningful groups based on the setting in which they occur.

Primary MI refers to a spontaneous event caused by an acute coronary pathology. While atherothrombotic plaque rupture remains the most common mechanism, the definition now explicitly includes other causes such as spontaneous coronary artery dissection (SCAD), coronary embolism, vasospasm, and late stent or graft failure.

Secondary MI describes myocardial ischemia caused by an oxygen supply-demand imbalance resulting from another acute illness or condition, such as tachyarrhythmia, severe hypertension, hypotension, hypoxia, or anemia. The new definition introduces more objective criteria and recommends coronary and cardiac imaging when feasible to distinguish true secondary MI from myocardial injury.

Procedure-related MI encompasses infarctions occurring as complications of percutaneous or surgical cardiac procedures within 30 days. Notably, the new framework moves away from reliance on arbitrary troponin thresholds alone and instead emphasizes imaging evidence of ischemic myocardial damage and procedural complications.

The document also refines the distinction between myocardial infarction and myocardial injury, an area that has become increasingly important with widespread use of high-sensitivity troponin testing. Acute myocardial injury remains defined by a rise and/or fall in troponin with at least one value above the sex-specific 99th percentile upper reference limit, but the authors stress that myocardial injury should not automatically be equated with MI.

Several other updates reflect advances in imaging and diagnostics. The authors formally recommend sex-specific troponin thresholds to reduce under-recognition of myocardial injury and MI in women. They also update the term MINOCA to mean “myocardial injury with non-obstructive coronary arteries,” emphasizing that it is a working diagnosis requiring further investigation rather than a final diagnosis.

Importantly, the revised framework may create new opportunities to study under-recognized causes of MI. The authors highlight SCAD, which disproportionately affects women and is often underdiagnosed, as one area where the new classification and ICD coding structure may facilitate future research.

As the task force concluded: “By simplifying classification, we hope to make a diagnosis of MI more meaningful and consistent to better inform treatment, enhance patient understanding and improve opportunities for monitoring and research.”

What's changed

• Replaces numbered MI subtypes (types 1, 2, 3, 4a-c, and 5) with three categories: primary, secondary, and procedure-related MI.
• Expands primary MI to include all acute coronary pathologies, including SCAD, coronary embolism, vasospasm, and late stent or graft failure.
• Introduces more objective diagnostic criteria for secondary MI, with greater reliance on coronary and cardiac imaging.
• Revises procedure-related MI definitions and reduces dependence on arbitrary biomarker thresholds alone.
• Reinforces use of sex-specific 99th percentile troponin thresholds to avoid underdiagnosis in women.
• Updates MINOCA to mean “myocardial injury with non-obstructive coronary arteries,” recognizing it as a working diagnosis.
• Aligns MI classifications with new ICD-11 codes to improve disease surveillance, coding consistency, and research.
• Adds guidance for diagnosing MI in low-resource settings.
• Provides updated recommendations on high-sensitivity troponin testing, accelerated diagnostic pathways, and imaging-based confirmation of MI.

Source: Mills NL, et al. (2026 Aug 27) Circulation. 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