Diagnosis of myocardial infarction
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Universal Definition and Diagnostic Criteria for Myocardial Infarction
The diagnosis of myocardial infarction (MI) is based on the Universal Definition, which requires evidence of myocardial injury—typically a rise and/or fall in cardiac biomarkers, especially troponins, with at least one value above the 99th percentile of the upper reference limit—combined with clinical evidence of acute myocardial ischemia. This clinical evidence can include symptoms of ischemia, new changes on the electrocardiogram (ECG), imaging evidence of new loss of viable myocardium or new regional wall motion abnormalities, or the identification of an intracoronary thrombus by angiography or autopsy 15. The 4th Universal Definition further emphasizes distinguishing between acute and chronic myocardial injury, improving risk assessment and patient management .
Cardiac Biomarkers and Troponin Assays in MI Diagnosis
Cardiac troponins are the preferred biomarkers for diagnosing MI due to their high sensitivity and specificity for myocardial injury. High-sensitivity cardiac troponin assays have significantly improved the early detection of MI, especially in patients presenting soon after symptom onset. These assays outperform standard troponin tests, providing higher diagnostic accuracy and enabling earlier rule-in or rule-out of MI in emergency settings 1246. However, the diagnostic performance of troponin can be influenced by patient age, with specificity and positive predictive value decreasing in older populations. Age-adjusted thresholds can improve specificity but may reduce sensitivity, suggesting the need for individualized diagnostic approaches in elderly patients .
Role of Electrocardiogram (ECG) and Imaging in MI Diagnosis
The ECG remains a fundamental tool for MI diagnosis. ST-segment elevation is highly specific for MI but not always sensitive. New computerized ECG analysis and serial monitoring can increase sensitivity without sacrificing specificity. When ECG findings are inconclusive, imaging techniques such as echocardiography can help identify new regional wall motion abnormalities or loss of viable myocardium. Nuclear imaging and other advanced modalities can also support diagnosis, particularly in complex cases 138.
Point-of-Care and Advanced Diagnostic Technologies
Recent advances include the development of point-of-care devices and biosensors for rapid troponin detection, such as surface plasmon resonance (SPR) and plasmonic gold nano-island (pGold) chip assays. These technologies offer ultra-sensitive, quantitative detection of cardiac biomarkers, enabling faster and more accurate diagnosis at the bedside or in resource-limited settings 46.
Special Considerations: Autopsy and Forensic Diagnosis
In post-mortem settings, diagnosing MI can be challenging, especially without clear evidence of acute coronary occlusion. Accurate histopathological assessment and correlation with clinical history are essential for distinguishing MI from other forms of myocardial injury. Familiarity with the clinical classification of MI types is important for pathologists to ensure correct interpretation and reporting .
Conclusion
The diagnosis of myocardial infarction relies on a combination of clinical assessment, cardiac biomarker testing (especially high-sensitivity troponin assays), ECG changes, and imaging evidence. Advances in biomarker assays and point-of-care technologies have improved early and accurate detection. However, factors such as patient age and the clinical context must be considered to optimize diagnostic accuracy and patient outcomes.
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