Fifth Universal Definition of Myocardial Infarction (MI) published: What it says for your CDI, coding, and clinical teams

The Fifth Universal Definition of Myocardial Infarction (MI) has been published in the Journal of the American College of Cardiology.

What is the new definition?

The fifth definition removes the fourth definition’s numerical classification (i.e., MI types 1, 2, 3, 4a, 4b, 4c, 5) and replaces them with three categories: Primary MI, Secondary MI, and Procedure-Related MI.

These are defined as follows.

1. Primary MI: Occurs spontaneously due to atherothrombosis or an alternative acute coronary pathology. The diagnosis is confirmed and etiology defined if atherothrombosis or an alternative acute coronary pathology is identified.
2. Secondary MI: Occurs secondary to another acute condition where supply-demand imbalance unmasks obstructive coronary artery disease or results in a new ventricular impairment
3. Procedure-Related MI: Occurs as a complication of percutaneous or surgical cardiac procedures within 30 days of the procedure, causing immediate coronary or graft occlusion.

The .pdf published in JACC adds considerable detail to each of these, including rationale for change. We recommend reading it (see link below).

In addition, the new definition:

• Refines criteria for acute and chronic myocardial injury and discusses the underlying mechanisms
• Discusses the diagnosis of MI following sudden death, and provides new, objective criteria for silent or unrecognized MI
• Updates the definition of MINOCA (MI with Non-Obstructive Coronary Arteries, a heart attack that happens even though the main heart arteries do not have major blockages) to ‘myocardial injury with non-obstructive coronary arteries’ in recognition that this is a working rather than final diagnosis.

Why does this matter?

This document represents the views of an authoritative international body that includes the ESC, ACC, AHA, and WHF, and was produced after careful consideration of the scientific and medical knowledge and the available evidence at the time of its development.

In short, it will be adopted both clinically and by payers, if not immediately than in time.

MIs have significant quality and severity weight. Accurate capture in documentation and coded data is a must.

What are the problems?

Clinical adoption lag. New definitions take time to permeate clinical practice.

Coding misalignment. The new definition is aligned with ICD-11, which has not been adopted in the U.S. and likely won’t for some time (60 countries are on I-11). No new guidance is offered for ICD-10, which imperfectly captures the 4^th universal definition. Type 1 uses I21.0–I21.4, Type 2 uses I21.A1, and Types 3, 4a, 4b, 4c and 5 all collapse into I21.A9.

The document proposes new ICD-11 codes that align with the new definition, as follows:

• Distinct ICD-11 codes for primary, secondary, and procedure-related MI.
• For the first time, an ICD-11 code for acute MI differentiating STEMI (BA41.0) from NSTEMI (BA41.1)
• Additional sixth digit stem codes to identify the underlying acute coronary pathology in primary MI and differentiate primary from secondary and procedure-related MI.

Reference

Fifth Universal Definition of MI, JACC: https://www.jacc.org/doi/epdf/10.1016/j.jacc.2026.07.025