A ST elevation myocardial infarction (STEMI) most commonly occurs when thrombus formation results in complete occlusion of a major epicardial coronary vessel. The most serious form of acute coronary syndromes, STEMI is a life-threatening, time-sensitive emergency that must be diagnosed and treated promptly via coronary revascularization, usually by percutaneous coronary intervention (PCI).
Unlike unstable angina and non-ST segment elevation myocardial infarction (NSTEMI), during STEMI the 12-lead ECG will show significant ST elevation as the name implies. The terms “transmural”, “non-transmural”, “Q wave MI” and “non-Q wave MI” are no longer recommended. The differences between the types of acute coronary syndromes are below:
Unstable angina pectoris: Three different presentations of unstable angina exist.
Exertional angina of new onset. Even if relieved with rest and requiring a consistent amount of exertion to procedure symptoms, when angina first occurs it is considered unstable.
Exertional angina that was previously stable and now occurs with less physical exertion.
Anginal symptoms at rest without physical exertion.
Non-ST segment elevation myocardial infarction: Anginal symptoms at rest that result in myocardial necrosis as identified by elevated cardiac biomarkers (see Cardiac Biomarkers) with no ST segment elevation on the 12-lead electrocardiogram.
ST segment elevation myocardial infarction: Anginal symptoms at rest that result in myocardial necrosis as identified by elevated cardiac biomarkers (see Cardiac Biomarkers) with ST segment elevation on the 12-lead electrocardiogram.
The Killip Classification is frequently used to predict mortality during STEMI. First published in 1967, this system focuses on physical examination and the development of heart failure to predict risk as described below:
Class I: No evidence of heart failure (mortality 6%)
Class II: Findings of mild to moderate heart failure (S3 gallop, rales < half-way up lung fields or elevated jugular venous pressure (mortality 17%)
Class III: Pulmonary edema (mortality 38%)
Class IV: Cardiogenic shock defined as systolic blood pressure < 90 mmHm and signs of hypoperfusion such as oliguria, cyanosis, and sweating. (mortality 67%)
The original data from 1967 showed the above mortality rate in each class. This was before reperfusion therapy (thrombolytics and/or PCI). With advances in therapy, the mortality rates have declined about 30-50% in each class.