Myocardial Infarction: A New Universal Definition

Why this matters in primary care

MI remains one of the most common cardiovascular conditions GPs will encounter, affecting an estimated 3.8% of people under 60 and 9.5% of those over 60. It continues to be a leading cause of death worldwide, so clear, consistent classification isn't just an academic exercise — it directly shapes how patients are diagnosed, referred, and treated.

The previous system relied on a numerical typing scheme (Type 1, Type 2, Type 4c, and so on). While useful for specialists, it was often difficult to apply consistently in day-to-day clinical practice and rarely translated into language that made sense to patients. The four societies have now replaced this with a simplified, cause-based framework designed to be more intuitive for clinicians and more meaningful for the people sitting across the desk from you.

The three new categories

Rather than numerical subtypes, every MI now falls into one of three clinical settings:

• Primary MI — arises spontaneously from an acute problem in a coronary artery. Most often this is due to rupture of an atherosclerotic plaque, but it can also result from a tear in the coronary wall (spontaneous coronary artery dissection, or SCAD), coronary spasm, or a clot.
• Secondary MI — results from a mismatch between oxygen supply and demand in the heart, triggered by another underlying condition such as severe hypertension, hypotension, or a very fast heart rate.
• Procedure-related MI — occurs within 30 days of a cardiac procedure (e.g. coronary stenting) or cardiac surgery (e.g. coronary artery bypass grafting).

The updated document also specifies the diagnostic tests and investigations required to confirm each category, giving clearer guidance on the work-up needed at every stage.

Better conversations with patients

One of the more practical benefits for frontline clinicians is communication. As ACC/AHA Task Force Chair Professor Kristin Newby (Duke University Medical Center) noted, clinicians rarely used the old numerical terminology directly with patients because it was too technical. The new cause-based labels make it far easier to explain why a patient had their MI — and why particular follow-up tests or treatments are being recommended.

Aligned with ICD-11 coding

For the first time, the universal MI definition has also been aligned with International Classification of Disease (ICD) coding. Developed in collaboration with the WHO, the new ICD-11 codes are intended to standardise how MI data is captured across health systems. According to WHF Chair Associate Professor Sarah Zaman (University of Sydney), this alignment should eventually improve public health monitoring and health system planning, while also enabling better-powered research into under-recognised causes of MI.

One area likely to benefit is spontaneous coronary artery dissection (SCAD) — a cause of primary MI that predominantly affects women and is currently under-diagnosed. Standardised coding could support much-needed large-scale research into this condition.

The takeaway for GPs

• Expect to see cause-based terminology (primary, secondary, procedure-related) replacing numerical MI types in discharge summaries and specialist correspondence.
• The new framework should make it easier to explain a patient's diagnosis in plain language during follow-up consultations.
• Keep SCAD on your radar, particularly in younger female patients presenting with MI symptoms and few traditional risk factors — it may be more common than current coding suggests.
• ICD-11 alignment is a long-term shift; full implementation will take time, but it lays the groundwork for better data and future research.