Heart attacks get renamed: types 1 to 5 become primary, secondary and procedure-related

For eighteen years, clinicians have classified heart attacks by number. Type 1 was the classic one, a clot on a ruptured plaque. Type 2 was a supply-and-demand mismatch caused by something else going wrong in the body. Types 4a, 4b, 4c and 5 covered infarctions after stents and bypass surgery.

The Fifth Universal Definition of Myocardial Infarction, released on 28 August at ESC Congress 2026 and published simultaneously in Global Heart and the European Heart Journal, retires that numbering [s1] [s2]. Myocardial infarction is now classified into one of three clinical types: primary, secondary, or procedure-related [s1] [s3].

Who wrote it and why it matters

The Fifth UDMI is a joint statement from the European Society of Cardiology, the American College of Cardiology, the American Heart Association and the World Heart Federation, written by a global task force with representation from 12 countries across five continents [s1] [s3]. It is endorsed by the European Association for Cardio-Thoracic Surgery and the Society of Thoracic Surgeons, with affirmation of value by the Society for Cardiovascular Angiography and Interventions [s1].

Definitions like this are not academic housekeeping. What counts as a myocardial infarction determines who gets treated as one, what a hospital reports, what a trial measures, and what national statistics record. The lineage runs back to a World Health Organization task force in 1979, when the diagnosis rested on symptoms, electrocardiographic criteria and cardiac enzymes and excluded coronary angiography [s1].

What changed

The task force's stated reason for replacing the numerical classification is that the old categories were difficult to apply consistently — particularly when infarction followed another acute illness, or followed a coronary intervention or cardiac surgery [s1].

Primary myocardial infarction now covers all acute coronary pathologies, not only atherothrombosis: spontaneous coronary artery dissection, coronary embolism, vasospasm, and restenosis, stent thrombosis or graft failure more than 30 days after a procedure [s1]. The last of those is a genuine reclassification — late stent or graft failure is now treated as new disease rather than as a complication of the original procedure [s1]. The task force describes the change as prioritising sensitivity, so that no primary acute coronary pathology is missed [s1].

Secondary myocardial infarction is narrowed rather than widened. Under the Fourth UDMI, type 2 covered oxygen supply-demand imbalance from either a non-atherothrombotic coronary pathology or an alternative acute condition [s1]. Under the Fifth, secondary infarction requires an alternative acute condition and either obstructive coronary artery disease without acute coronary pathology, or a new or presumed new regional wall motion abnormality or absence of viable myocardium [s1]. The stated rationale is specificity: to separate myocardial infarction from acute myocardial injury in conditions that raise troponin without infarcting muscle [s1].

Procedure-related myocardial infarction now applies to any cardiac procedure, percutaneous or surgical, and no longer relies on biomarker multiples [s1]. The Fourth UDMI required troponin greater than five times the 99th percentile for type 4a and greater than ten times for type 5 [s1]; the task force describes those thresholds as arbitrary [s1]. The new definition requires a coronary complication within 30 days resulting in acute myocardial injury, with one or more supporting features — and both features when the complication arises during the procedure itself or in the setting of an acute myocardial infarction [s1].

Type 3 is gone. Where infarction is the likely cause of death, the clinical classification is applied based on setting or post-mortem findings [s1].

The parts that are not new but are reinforced

Sex-specific 99th percentile upper reference limits for cardiac troponin remain the basis for defining myocardial injury [s1] [s3]. The reasoning is explicit and worth restating: for high-sensitivity troponin I and T assays, the 99th percentile in females is lower than a uniform reference limit while the 99th percentile in males is above it, so a single threshold systematically under-recognises myocardial injury — and therefore myocardial infarction — in women [s1].

Acute myocardial injury is defined as a rise and/or fall in cardiac troponin I or T with at least one value above the sex-specific 99th percentile [s1]. Chronic myocardial injury is identified when two or more values are above that limit in a stable clinical setting [s1].

Unstable angina survives. The document notes that the diagnosis has become progressively less common as high-sensitivity assays reclassified many such patients as having infarction, but that it has not disappeared from practice and remains part of the acute coronary syndrome spectrum [s1].

MINOCA is redefined as "myocardial injury with non-obstructive coronary arteries" — a change of one word from infarction to injury, made in recognition that it is a working rather than a final diagnosis [s1].

Codes, and counting

The classification is paired with proposed ICD-11 codes so the categories can be recorded in hospital episode statistics and public health monitoring [s1] [s3]. ICD-11 already carries distinct codes for STEMI (BA41.0) and NSTEMI (BA41.1) [s1]; the task force proposes sixth-digit extensions distinguishing atherothrombosis, dissection, embolism, vasospasm and late stent or graft failure within primary infarction, and separate codes for secondary and procedure-related infarction [s1].

The task force worked with the WHO on the taxonomy, and states that the proposed codes were under review by the WHO Family of International Classifications' Classification and Statistics Advisory Committee at the time of publication [s1]. So the codes are proposed, not adopted.

The low-resource problem is addressed directly

New guidance is provided for diagnosing myocardial infarction where high-sensitivity troponin testing is not available [s1]. The document cites the scale of the problem: 31.9 million new cases of ischaemic heart disease globally in 2021, 31.8% more than in 2010 [s1], against access figures including a study from Uganda reporting that only 43% of healthcare facilities had troponin testing and 55% had electrocardiography [s1].

A definition that cannot be applied where most of the disease is occurring is a definition with a distribution problem, and this is the first UDMI to give the point its own section.

What to watch

Whether the ICD-11 extension codes are adopted by the WHO committee reviewing them [s1]. Without the codes, the new categories exist in journals but not in the datasets that describe national cardiovascular burden — and the task force's own stated aim is that adoption in practice and research makes the diagnosis meaningful across healthcare settings [s1].

The second thing to watch is comparability. Trials, registries and quality measures built on types 1 to 5 do not map cleanly onto primary, secondary and procedure-related, particularly where late stent failure has moved category. Anyone comparing infarction rates across the transition will need to know which definition produced them.

This article describes a consensus classification document. It is not medical advice.

Sources

• Fifth Universal Definition of Myocardial Infarction (2026), Global Heart, 28 August 2026
• Fifth Universal Definition of Myocardial Infarction (2026), European Heart Journal, 28 August 2026
• 2026 Fifth Universal Definition of Myocardial Infarction, European Society of Cardiology, 28 August 2026