From the Guidelines
Myocardial infarction (MI) is a condition where the blood flow to the heart is blocked, causing damage to the heart muscle.
Definition of Myocardial Infarction
The definition of MI is based on the detection of a rise and/or fall of cardiac biomarkers, such as cardiac troponin levels, with at least one value above the 99th percentile upper reference limit, and with at least one of the following: symptoms of ischemia, new or presumed new significant ST-segment–T wave changes or new left bundle branch block, development of pathological Q waves in the electrocardiogram (ECG), imaging evidence of new loss of viable myocardium or new regional wall motion abnormality, or identification of an intracoronary thrombus by angiography or autopsy 1.
Classification of Myocardial Infarction
MI can be classified into five types, based on pathological, clinical, and prognostic differences, along with different treatment strategies:
- Type 1: Spontaneous myocardial infarction related to atherosclerotic plaque disruption with superimposed thrombus formation in a coronary artery.
- Type 2: Myocardial infarction secondary to an ischemic imbalance, where a condition other than coronary artery disease contributes to an imbalance between myocardial oxygen supply and/or demand.
- Type 3: Myocardial infarction resulting in death when biomarker values are unavailable.
- Type 4: Myocardial infarction related to percutaneous coronary intervention (PCI) or stent thrombosis.
- Type 5: Myocardial infarction related to coronary artery bypass grafting (CABG) 1.
Key Points
- MI is a major cause of death and disability worldwide.
- The incidence of MI can be used as a proxy for the prevalence of coronary artery disease (CAD) in a population.
- The management of patients with MI has significantly improved, resulting in less myocardial injury and necrosis, despite a similar clinical presentation.
- The Third Universal Definition of Myocardial Infarction consensus document provides a precise and consistent definition of MI, which is essential for clinical trials, observational studies, and quality assurance programs 1.
From the Research
Definition of Myocardial Infarct
- Myocardial infarction (MI) is defined as sudden ischemic death of myocardial tissue 2
- It is a term used for an event of heart attack which is due to formation of plaques in the interior walls of the arteries resulting in reduced blood flow to the heart and injuring heart muscles because of lack of oxygen supply 3
Causes of Myocardial Infarct
- Myocardial infarction is usually due to thrombotic occlusion of a coronary vessel caused by rupture of a vulnerable plaque 2
- It can also be caused by atrial ischemia, which results in greater atrial electrophysiological changes and propensity for atrial fibrillation 4
Types of Myocardial Infarct
- Incomplete myocardial infarction (MI) is characterized by a small infarct size and a large mass of viable but jeopardized myocardium within the perfusion zone of the infarct-related vessel 5
- Complete MI is characterized by a larger infarct size and more extensive damage to the myocardium 5
Pathophysiology of Myocardial Infarct
- Ischemia induces profound metabolic and ionic perturbations in the affected myocardium and causes rapid depression of systolic function 2
- Prolonged myocardial ischemia activates a "wavefront" of cardiomyocyte death that extends from the subendocardium to the subepicardium 2
- Infarct healing is dependent on an inflammatory cascade, triggered by alarmins released by dying cells, and is characterized by the formation of a scar 2