- A task force of four major cardiac societies has introduced a new international heart attack definition, replacing the previous five-number classification system with three broader categories.
- The new system focuses more on the underlying cause of a heart attack.
- Doctors are also encouraged to distinguish damage to heart muscle from a heart attack, which occurs directly due to a lack of blood flow and oxygen.
- The updated definition could improve care and research by making diagnoses easier to communicate, supporting more consistent classification, and improving understanding of less common causes of heart attack.
Myocardial infarctions, or heart attacks, typically occur when a blockage or other complication causes reduced blood flow to part of the heart muscle.
In the United States, someone has a heart attack
The Universal Definition of Myocardial Infarction exists to give healthcare professionals a standard, agreed way of diagnosing and classifying heart attacks.
Previously, in the
Now, a new international definition could make it easier for doctors to identify why a heart attack has occurred, replacing the previous numerical system used to classify different types of myocardial infarction with three broader clinical categories.
The Fifth Universal Definition of Myocardial Infarction was developed by the European Society of Cardiology (ESC), American College of Cardiology (ACC), American Heart Association (AHA), and World Heart Federation (WHF). It was presented at ESC Congress 2026 in Munich, Germany.
3 categories replace previous numerical system
Under the previous system, heart attacks were divided into numerical categories. Although this system helped standardize medical terminology, some of its categories could be difficult to apply consistently in everyday clinical practice.
The new definition instead focuses on the clinical setting and underlying mechanism of the heart attack.
“The definition is simplified,” ACC/AHA Chair, Kristin Newby, MD, from Duke University Medical Center, Durham, explained to Medical News Today.
“(Heart attack) is now defined as one of three classifications — primary, secondary, procedure-related — that reflect the underlying pathology and align with clinical care, making it easier to apply in practice and allowing more precise treatment based on the underlying cause,” Newby told us.
How are heart attacks classified now?
Under the new definition, heart attacks classified into 3 clinical settings:
Primary myocardial infarction
Primary myocardial infarction occurs spontaneously because of a problem involving a coronary artery, which is the artery that supplies blood to the heart.
Typically, this can occur due to a blood clot, but other causes may include:
- spontaneous coronary artery dissection, or SCAD
- coronary artery spasm
- coronary embolism
- certain problems involving previously placed stents or bypass grafts.
This broader definition aims to reduce the risk of overlooking less common causes of myocardial infarction, such as SCAD, which predominantly affects females and can be underdiagnosed.
Secondary myocardial infarction
Secondary myocardial infarction occurs when another medical problem causes an imbalance between the heart’s oxygen demand and the oxygen supply.
For example, a very rapid heartbeat or extremely high or low blood pressure can place the heart under considerable stress and contribute to myocardial ischemia.
The important distinction is that the infarction is triggered by another condition rather than by a primary coronary artery problem.
Procedure-related myocardial infarction
The third category covers heart attacks occurring as a complication of a cardiac procedure.
This includes infarctions occurring after procedures such as coronary stenting or heart surgery, with the new definition specifically addressing events occurring within 30 days of a cardiac procedure.
Change could make conversations with patients easier
Experts suggest that the new terminology may make heart attack diagnoses easier to explain. Instead of telling a patient that they have had a particular numerical “type” of heart attack, clinicians can describe the underlying reason it happened.
The new approach allows clinicians to discuss the cause of the heart attack and why particular tests or treatments may be necessary.
“(B)ecause the new classification considers both the context in which the myocardial infarction occurred and the underlying pathology that caused it, it should be easier for doctors to explain the diagnosis and for patients and their families and other non-experts to understand,” Newby added.
For the individual, this distinction could be particularly meaningful.
A heart attack caused by a coronary blockage may require a different evaluation and treatment strategy from one caused by severe stress, for example.
Understanding the cause can therefore help explain why doctors may recommend particular investigations, medications, procedures, or follow-up care.
A heart attack is not diagnosed using a single test
Additionally, the new definition also emphasizes that heart attacks are a clinical diagnosis rather than something that can be established from one measurement alone. Assessment for a heart attack can involve:
- symptoms and clinical findings
- cardiac troponin blood tests
- electrocardiography (ECG)
- coronary imaging
- cardiac imaging.
The document notes that no single criterion is sufficient to confirm a heart attack. For example, cardiac troponin is a protein released into the bloodstream when heart muscle cells are damaged.
A higher troponin level can indicate myocardial injury, but this is not automatically the same thing as a heart attack. Other conditions can also cause heart muscle injury and elevated troponin levels.
Therefore, the new definition emphasizes determining whether the injury is caused by a lack of adequate blood flow and oxygen to the heart muscle.
“Many things can cause myocardial injury (eg trauma, toxins, infections, etc); myocardial infarction is a special case of myocardial injury that is caused by ischemia (a state of lessened oxygen delivery to the myocardium (heart muscle)),” Newby told MNT.
“It is critical to make this distinction to allow appropriate and precise treatment that is tailored to the underlying cause,” she stressed.
“An emphasis on imaging is used to both confirm the diagnosis and determine the underlying etiology of the MI, again fostering more precise care,” Newby added.
The updated document also includes sex-specific reference limits for cardiac troponin, an approach intended to reduce potential under-recognition of myocardial injury and heart attack in females.
“The requirement for use of sex-specific troponin thresholds is important because throughout the lifespan women have lower normal levels of troponin in their blood than men,” Newby highlighted.
“Using sex-specific upper limits of normal will prevent systematic bias in assessing myocardial injury and under-diagnosis of myocardial infarction in women,” she told us.
The new system could improve research, too
The change is not only about terminology. The organizations behind the definition have also worked with the World Health Organization (WHO) to propose ICD-11 codes that correspond with the new myocardial infarction categories.
ICD codes are used internationally to classify diseases and health conditions. Aligning the classification of heart attacks with these codes could eventually make it easier for health systems to collect and compare information about different causes of heart attacks.
Researchers could also benefit from more consistent data. For example, better identification of SCAD could help researchers study a condition that can be difficult to recognize and that predominantly affects females.
“When adopted worldwide, these codes will allow more precise collection of epidemiological data systematically,” Newby explained to MNT.
“For the first time we will be able to determine how frequently myocardial infarction occurs in the setting of another acute medical illness (secondary (heart attack)) or a cardiac procedure (procedure-related (heart attack)),” she continued.
“In addition, because the codes will add detail to primary (heart attack), it will allow researchers to more easily identify and understand the incidence of the less common acute coronary causes of primary (heart attack) — eg, spontaneous coronary artery dissection or embolism — study them and potentially develop new treatments,” Newby concluded.
