Myocardial infarction (MI) occurs when prolonged ischemia causes irreversible myocardial cell death, almost always from rupture of an atherosclerotic coronary plaque followed by thrombus formation. MI is part of the broader spectrum of acute coronary syndrome (ACS) and is classified by ECG pattern and biomarker elevation: - STEMI (ST-elevation MI): complete occlusion of a coronary artery, with ST elevation in two or more contiguous leads. Requires emergent reperfusion — primary percutaneous coronary intervention (PCI) within a door-to-balloon time of 90 minutes or less, or fibrinolytics within 30 minutes if PCI is unavailable. - NSTEMI (non-ST-elevation MI): partial or temporary occlusion with elevated troponin but no ST elevation; managed with anticoagulation and early catheterization, typically within 24 to 72 hours. - Unstable angina: ischemic chest pain without troponin elevation — no necrosis yet, but high risk of progression to infarction. MI remains a leading cause of death in US adults, and modifiable risk factors (smoking, hypertension, dyslipidemia, diabetes, obesity) drive most cases. For the NCLEX-RN, recognize the classic and atypical presentations (women, older adults, and people with diabetes often present atypically...