ST elevation myocardial infarction classification

Associate Editors-In-Chief:

Classification
Acute myocardial infarction is a type of acute coronary syndrome, which is most frequently (but not always) a manifestation of coronary artery disease. The acute coronary syndromes include ST segment elevation myocardial infarction (STEMI), non-ST segment elevation myocardial infarction (NSTEMI), and unstable angina (UA).

Depending on the location of the obstruction in the coronary circulation, different zones of the heart can become injured. Using the anatomical terms of location, one can describe anterior, inferior, lateral, apical and septal infarctions (and combinations, such as anteroinferior, anterolateral, and so on). For example, an occlusion of the left anterior descending coronary artery will result in an anterior wall myocardial infarct.

Another distinction is whether a MI is subendocardial, affecting only the inner third to one half of the heart muscle, or transmural, damaging (almost) the entire wall of the heart. The inner part of the heart muscle is more vulnerable to oxygen shortage, because the coronary arteries run inward from the epicardium to the endocardium, and because the blood flow through the heart muscle is hindered by the heart contraction.

The phrases transmural and subendocardial infarction used to be considered synonymous with Q-wave and non-Q-wave myocardial infarction respectively, based on the presence or absence of Q waves on the ECG. It has since been shown that there is no clear correlation between the presence of Q waves with a transmural infarction and the absence of Q waves with a subendocardial infarction, but Q waves are associated with larger infarctions, while the lack of Q waves is associated with smaller infarctions. The presence or absence of Q-waves also has clinical importance, with improved outcomes associated with a lack of Q waves.

The phrase "massive heart attack" is not a recognized medical term.