An elevated level of troponin in the blood, in itself, is not a conclusive diagnosis of heart attack, and may indicate several other cardiac or non-cardiac conditions. Recognizing this complexity, the main cardiology entities around the world have revised the criteria for defining and classifying myocardial infarction.
This update appears in the 5th Universal Definition of Myocardial Infarction, published in the European Heart Journal. The new document replaces the previous division of five types (1, 2, 3, 4 and 5), adopting a grouping that considers the specific mechanism that caused the cardiac injury.
The development of the consensus involved the collaboration of the European Society of Cardiology (ESC), American College of Cardiology (ACC), American Heart Association (AHA) and World Heart Federation (WHF), bringing together experts from twelve nations and five continents.
The new division of heart attacks: from five to three categories
From now on, cases will be organized into three main groups, based on the cause of the problem. Primary infarction is the result of an acute change directly in the coronary artery. Secondary heart attack occurs when a different medical condition creates an imbalance in the demand and supply of oxygen to the heart muscle. Finally, procedure-related heart attack is a complication of surgical interventions on the heart.
Previously, the classification numbered heart attacks according to the mechanism and scenario of the event. However, this structure grouped very different situations, such as the old type 2, which included both acute coronary problems such as dissection, embolism or vasospasm, as well as conditions in which other pathologies caused a lack of oxygen in the heart.
The experts involved in the review considered that the old structure was complex to apply universally and did not always clearly identify the cause of the event. According to Ricardo Kazunori, cardiovascular surgeon at BP – A Beneficência Portuguesa in São Paulo, the main progress of the review is to link the classification to the exact origin of the infarction.
Understand the primary infarction, which originates in the artery itself
Primary infarction occurs due to a sudden change in the coronary circulation, the arterial system responsible for irrigating the heart muscle. The most common cause is still atherothrombosis, where an atherosclerosis plaque in the vessel wall ruptures or wears away, promoting the formation of a clot that reduces or blocks blood flow.
This category now also encompasses other acute coronary mechanisms, such as spontaneous artery dissection, embolism, vasospasm, restenosis or stent thrombosis in specific scenarios, and graft failure that occurs thirty days after revascularization.
Ricardo Kazunori clarifies that the common factor in all these cases is the origin: an acute change in the coronary artery itself. Identification of the exact mechanism remains crucial, as different causes require different investigative and therapeutic approaches. Therefore, the new definition emphasizes the importance of coronary angiography and other tests to visualize what is happening inside the vessels.
How other health conditions can lead to secondary heart attack
Unlike primary, secondary infarction does not require sudden arterial obstruction by a clot. It results from an imbalance: another clinical condition causes the oxygen supply to the heart to be insufficient to meet the organ’s needs at that moment.
The reduction in oxygen supply can occur due to severe anemia, low blood oxygenation or very low blood pressure. On the other hand, oxygen demand can increase drastically in cases of certain tachycardias and severe hypertension. Ricardo Kazunori exemplifies the lack of oxygen to the heart muscle with very low levels of hemoglobin in severe anemia, or hypoxemia.
Elzo Mattar, director of the Arterial Hypertension Department of the Brazilian Society of Cardiology (SBC) and professor at the State Faculty of Medicine of São José do Rio Preto (Famerp), mentions more critical situations, such as septic shock, where the heart attack can be a consequence of another serious illness.
For this category, the new definition establishes more rigorous criteria. It is not enough to just have a disease that causes the imbalance and have elevated troponin. It is essential to collect evidence of ischemia and cardiac muscle injury that is consistent with a heart attack, helping to distinguish between a true ischemic event and cardiac injury from another cause.
Catheter and heart surgery complications are now a single group
The third grouping covers heart attacks resulting from cardiac procedures, including catheter interventions and surgeries, when the event results from a complication that affects the heart’s circulation. Previously, percutaneous procedures and revascularization surgery were classified into separate categories, with troponin requirements five or ten times above the reference limit.
The update aims to standardize these diagnoses, no longer using multiples of the troponin marker as the main criterion. Now, it considers complications from the procedure within a period of up to thirty days, based on objective imaging criteria and assessment of muscle damage.
Ricardo Kazunori exemplifies situations such as a patient who, when implanting a stent, develops a complication that occludes an artery, or someone who undergoes revascularization surgery and has a problem with the anastomosis that results in a heart attack. The objective is to differentiate the fluctuations in markers, expected after any intervention, from a heart attack actually caused by a significant complication.
The elimination of type 3 in the classification of infarction
The review not only rearranges the groups, but also deletes a category. Type 3 heart attack was attributed to cardiac deaths where the heart attack was the probable cause, but the patient died before confirmatory tests were carried out.
These cases are now classified as primary, secondary, or procedure-related infarcts depending on the clinical context or autopsy results, if available.
Why high troponin alone does not mean a heart attack
Troponin is central to this investigation as it is a marker of heart cell damage, a protein released into the bloodstream when there is heart muscle damage. The new definition considers acute myocardial injury when troponin levels increase or decrease in sequential measurements, and at least one result exceeds the 99th percentile established as a reference limit.
However, the isolated presence of high troponin does not mean a heart attack. Its levels can also rise in several other conditions, such as myocarditis, sepsis, acute heart failure, pulmonary embolism, severe hypertension, Takotsubo syndrome, stroke, epileptic seizures, intense physical activity and certain oncological treatments.
Ricardo Kazunori explains that the crucial distinction lies in ischemia: if the marker increases and there are indicators of ischemia, the diagnosis of infarction is appropriate; otherwise, other causes must be investigated. To confirm the diagnosis, the doctor analyzes the complete clinical scenario, considering, in addition to troponin, characteristic symptoms, new changes in the electrocardiogram and imaging tests. The consensus itself admits that no single criteria is sufficient for all diagnoses.
There is also the situation of chronic myocardial injury, where troponin remains elevated without evidence of new injury. This occurs in stable patients with chronic heart disease or other structural changes in the heart.
Kidney function also influences this reading, as a reduced ability to eliminate troponin from the bloodstream can keep its levels elevated. Therefore, what is important is not just the punctual value of the exam, but how it evolves over time and correlates with other clinical findings.
Specific troponin criteria for women seek accurate diagnosis
The update emphasizes the adoption of separate troponin reference values for each sex. The 99th percentile, used as a cutoff, is generally lower in women. Using a single cutoff point for both sexes could lead to underidentification of cardiac injuries, including heart attacks, in female patients.
According to the consensus, the adoption of sex-specific values minimizes this bias and the risk of inaccurate diagnoses in women. Ricardo Kazunori highlights that the importance is not restricted to the laboratory aspect, as the cutoff point determines which patients will require additional investigation and which can be discharged.
MINOCA: a new look at diagnosis without coronary obstruction
Another revised concept is MINOCA, an acronym that refers to patients with heart damage and coronary arteries that do not present significant obstruction.
The 5th definition now addresses MINOCA as “myocardial injury with non-obstructive coronary arteries,” and positions it as a working diagnosis—an initial stage of the investigation, not the conclusion. Detection of elevated troponin without significant obstruction does not end the search for the cause; In the words of Ricardo Kazunori, this situation pushes the investigation to a deeper level.
Exams such as cardiac magnetic resonance imaging and more detailed techniques for evaluating the coronary arteries are useful tools for differentiating coronary problems from other illnesses that can affect the heart muscle.
The crucial role of imaging tests in the diagnosis of heart attack
Imaging methods gain greater relevance both in confirming the infarction and in identifying its mechanism. Invasive coronary angiography remains the standard for evaluating coronary arteries in selected patients, capable of identifying not only the obstruction, but also the underlying acute change. Depending on the situation, echocardiography, coronary tomography and cardiac magnetic resonance are also used.
Ricardo Kazunori states that the integration of all this information, and not just the troponin analysis, is essential to complete the diagnosis. This is particularly important in atypical cases, where symptoms and the electrocardiogram do not provide conclusive answers.
Diagnosis of heart attack in resource-limited settings
The document devotes considerable attention to health services that do not have access to laboratory tests and advanced imaging techniques, an aspect that Elzo Mattar is keen to emphasize.
This point is crucial due to a global contrast: in 2021, 31.9 million new cases of ischemic heart disease were recorded worldwide, representing an increase of 31.8% since 2010. However, access to resources to diagnose a heart attack remains unequal. A study referenced in the consensus revealed that in Uganda, only 43% of the health services evaluated carried out troponin measurement and 55% had an electrocardiogram.
For these regions, the guideline establishes specific criteria: the diagnosis can be considered probable when the patient presents symptoms of ischemia in conjunction with typical changes on the electrocardiogram, such as new ischemic changes or the appearance of pathological Q waves.
Elzo Mattar explains that, in the absence of troponin and advanced imaging tests, the doctor relies on clinical assessment, the type of pain reported and the electrocardiogram. Authorization for this presumed diagnosis allows professionals in low-resource areas to act quickly, preventing patients with acute heart attacks from being discharged without adequate treatment.
The consensus also mentions telemedicine for the interpretation of electrocardiograms and the expansion of troponin tests carried out at the point of care.
Impact of the new classification on health statistics
The classification of a heart attack has implications that go beyond the patient’s medical record. This categorization determines how cases are recorded on hospitalization and mortality bases, how participants are selected for clinical studies, and how results are compared between different countries.
However, the accuracy of the statistics faced difficulties. The expansion of high-sensitivity troponin testing and predefinition resulted in an 11% increase in former type 1 diagnoses and a 22% increase in type 2 diagnoses. However, in two European countries, less than 20% of patients who met the previous criteria for type 2 received an ICD-10 infarction code.
With the aim of reducing this gap, the new classification was developed in partnership with the World Health Organization. It suggests ICD-11 codes that allow the differentiation of primary, secondary and procedure-related infarctions, in addition to distinguishing events with and without ST segment elevation on the electrocardiogram.
The consensus authors hope that by simplifying the categories and linking them directly to the mechanism of injury, there will be greater convergence between clinical diagnoses made and data recorded in statistics and research studies.
