Myocardial infarction definition
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Understanding Myocardial Infarction: Definition and Key Criteria
Definition of Myocardial Infarction
Myocardial infarction (MI), commonly known as a heart attack, is defined as the death of myocardial tissue due to prolonged ischemia. This condition is typically caused by the thrombotic occlusion of a coronary vessel following the rupture of a vulnerable plaque . The universal definition of MI emphasizes the detection of myocardial injury through abnormal cardiac biomarkers, particularly cardiac troponins, in the context of acute clinical myocardial ischemia .
Key Diagnostic Criteria
Cardiac Biomarkers
The primary feature of the universal definition of MI is the recognition of a rise and/or fall in cardiac biomarker values, with at least one value being elevated above the 99th percentile of the upper reference limit. Cardiac troponins (cTn) are the preferred biomarkers due to their high sensitivity and specificity for myocardial injury 16.
Clinical and Electrocardiographic Evidence
In addition to elevated cardiac biomarkers, at least one of the following criteria must be met to diagnose MI:
- Symptoms of ischemia, such as chest pain or discomfort 16.
- New significant ST/T wave changes or new left bundle-branch block on an electrocardiogram (ECG) 16.
- Development of pathological Q waves on an ECG 16.
- Imaging evidence of new loss of viable myocardium or new regional wall motion abnormality 16.
- Identification of an intracoronary thrombus by angiography or autopsy .
Pathophysiology of Myocardial Infarction
MI occurs due to the sudden ischemic death of myocardial tissue, often resulting from the thrombotic occlusion of a coronary artery. This ischemia leads to significant metabolic and ionic disturbances in the affected myocardium, causing rapid depression of systolic function. Prolonged ischemia triggers a wavefront of cardiomyocyte death, extending from the subendocardium to the subepicardium . The heart's limited regenerative capacity means that the infarcted myocardium heals through scar formation, involving an inflammatory cascade and subsequent tissue remodeling .
Epidemiological and Clinical Implications
From an epidemiological perspective, the incidence of MI in a population can serve as a proxy for the prevalence of coronary artery disease. MI is a major cause of death and disability worldwide and can be a minor or catastrophic event, potentially leading to sudden death or severe hemodynamic deterioration . The term MI carries significant psychological, social, and legal implications and is a critical outcome measure in clinical trials and observational studies 27.
Conclusion
Myocardial infarction is a critical medical condition defined by the death of myocardial tissue due to ischemia, primarily diagnosed through elevated cardiac biomarkers and clinical evidence of ischemia. Understanding the pathophysiology, diagnostic criteria, and broader implications of MI is essential for effective management and treatment of this life-threatening condition.
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