IPM Take
Heart attack diagnosis has long relied on a supposedly simple question: has cardiac troponin crossed the threshold?
The problem is that the threshold is not biologically identical in women and men.
The new Fifth Universal Definition of Myocardial Infarction makes sex-specific 99th-percentile troponin limits part of the definition of myocardial injury, explicitly warning that uniform thresholds can systematically under-recognise injury in female patients. It also reorganises myocardial infarction around underlying biology rather than a numbered taxonomy and brings coronary mechanisms such as spontaneous coronary artery dissection, or SCAD, into the primary MI category.
But there is an important reality check. Previous implementation research found that sex-specific testing identified substantially more women with myocardial injury, yet women still received fewer cardiovascular treatments and outcomes did not improve. Better definitions can reveal the gap. Health systems still have to act on what they find.
Executive Summary
Published jointly by the European Society of Cardiology, American College of Cardiology, American Heart Association and World Heart Federation, the Fifth Universal Definition of Myocardial Infarction replaces the previous numbered classification with three clinical groups: primary MI, secondary MI and procedure-related MI.
Primary MI now encompasses acute coronary pathologies beyond atherothrombosis, including SCAD, coronary embolism and vasospasm. The document specifically notes that SCAD should be considered particularly in women under 50 and during pregnancy or the postpartum period.
The definition also states that acute myocardial injury requires a rise or fall in cardiac troponin with at least one measurement above the sex-specific 99th-percentile upper reference limit. A diagnosis of MI then requires additional clinical evidence that the myocardial injury resulted from ischaemia, such as symptoms, ECG changes or imaging findings.
Why it matters
- HTA bodies: The update may influence diagnostic pathways built around high-sensitivity troponin testing. Assessment of testing strategies increasingly needs to consider not only analytical accuracy but whether different thresholds reduce clinically important diagnostic disparities.
- Payers: Laboratories and emergency pathways that still rely on uniform reference limits may face pressure to review reporting practices, assays and clinical protocols. Implementation also extends beyond the test itself to downstream investigation and treatment.
- Industry / innovation partners: Diagnostic manufacturers and clinical-decision-support developers will need to ensure that assays, reference intervals and digital pathways correctly operationalise sex-specific thresholds and the revised MI classification.
The world’s major cardiovascular societies have changed how a heart attack is defined.
The Fifth Universal Definition of Myocardial Infarction, published in August, replaces the previous numerical system with a classification designed to follow the clinical cause of the event. A myocardial infarction is now described as primary, when an acute coronary pathology is responsible; secondary, when myocardial oxygen supply and demand become imbalanced because of another acute condition; or procedure-related, when it follows a cardiac intervention.
The change may sound semantic. It is not.
Under the previous framework, type 1 MI centred on atherothrombosis, while several other acute coronary mechanisms could fall under type 2. The new primary-MI category instead includes the major acute coronary pathologies together, including plaque rupture or erosion, SCAD, coronary embolism and vasospasm.
That has particular relevance for women.
SCAD is an important cause of myocardial infarction in younger women and can occur in patients without the conventional cardiovascular-risk profile expected in atherosclerotic disease. The new document specifically highlights women younger than 50 and those who are pregnant or postpartum as populations in whom SCAD should be considered.
ABC’s coverage of the change focused on precisely this problem, using the case of a fit 47-year-old woman whose myocardial infarction resulted from SCAD rather than conventional obstructive coronary disease. Australian experts interviewed by ABC argued that the new framework could make clinicians more alert to coronary mechanisms disproportionately affecting women.
The second major change is biochemical.
Cardiac troponin concentrations differ by sex. The new definition specifies that myocardial injury should be identified using sex-specific 99th-percentile limits and says these thresholds are necessary to avoid systematic under-recognition in female patients. With contemporary high-sensitivity troponin T testing, the document notes that the female upper reference limit can be around half the male value in a representative healthy population.
Yet a positive troponin result is not synonymous with a heart attack.
The definition retains a critical distinction between myocardial injury and myocardial infarction. Troponin can rise because of inflammation, kidney disease, physiological stress and numerous other conditions. To diagnose MI, clinicians still need evidence that acute myocardial injury occurred because of myocardial ischaemia.
And changing the threshold is only part of the equity problem.
In the High-STEACS study of more than 48,000 patients with suspected acute coronary syndrome, introducing high-sensitivity troponin testing with sex-specific thresholds increased identification of myocardial injury by 42% in women compared with 6% in men. But women with myocardial injury remained substantially less likely to undergo revascularisation or receive therapies such as dual antiplatelets and statins, and the diagnostic change did not improve their one-year outcomes.
That finding puts the new definition into perspective.
A diagnostic system can stop overlooking women biologically.
It cannot, by itself, stop the healthcare system overlooking them clinically.
