Myocardial Infarction
Cardiology
Illness script · Cardiology
Myocardial Infarction
Irreversible myocardial ischemia causing cardiomyocyte necrosis, most often from acute coronary artery occlusion by thrombus on ruptured atherosclerotic plaque.
This illness script for Myocardial Infarction covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.
01
Predisposing factors
- CAD risk factors: HTN, DM, hyperlipidemia, smoking, obesity, family hx
- Men >45 yo, postmenopausal women (estrogen loss removes protection)
- Cocaine use → vasospasm + thrombosis even in young patients
- Prior MI, peripheral artery disease, or stroke (shared atherosclerotic burden)
- Hypercoagulable states and chronic kidney disease increase risk
02
Presentation
- Crushing/pressure substernal chest pain radiating to jaw or left arm, >20 min
- Diaphoresis, nausea/vomiting, dyspnea are classic associated symptoms
- Diabetics/elderly/women: atypical — fatigue, dyspnea, epigastric pain (silent MI)
- Exam: S4 gallop, new mitral regurgitation murmur (papillary muscle dysfunction)
- Inferior MI (RCA): hypotension + bradycardia; Right-sided leads needed
- Anterior MI (LAD): highest risk of LV dysfunction and cardiogenic shock
03
Pathophysiology
- Atherosclerotic plaque rupture → platelet aggregation → thrombus → vessel occlusion
- Prolonged ischemia (>20 min) → irreversible cell death via ATP depletion and Ca²⁺ overload
- STEMI = complete occlusion (transmural); NSTEMI = partial occlusion (subendocardial)
- Necrosis triggers inflammatory cascade → troponin release into bloodstream
04
Diagnostics
- 12-lead ECG first — ST elevation (STEMI) or depression/TWI (NSTEMI/UA)
- Serial troponin I/T (high-sensitivity): rises 1–3 h, peaks 12–24 h, gold standard for necrosis
- New LBBB on ECG treated as STEMI equivalent
- Echocardiogram: regional wall motion abnormalities confirm ischemic territory
- Coronary angiography: gold standard for defining anatomy and directing revascularization
05
Management
- STEMI: activate cath lab immediately — goal door-to-balloon ≤90 min (PCI)
- If PCI unavailable within 120 min: fibrinolysis (tPA/tenecteplase) within 12 h of symptom onset
- NSTEMI: anticoagulation (heparin) + dual antiplatelet (aspirin + P2Y12 inhibitor); urgent angiography
- All ACS: aspirin 325 mg chewed immediately + supplemental O₂ only if SpO₂ <90%
- Post-MI: beta-blocker, ACE inhibitor, high-intensity statin, continued DAPT ×12 months
06
Clinical pivots
How to separate this script from the look-alikes that show up on exams and on the wards.
Unstable Angina
UA has no troponin elevation — identical presentation but zero myocardial necrosis
Aortic Dissection
Dissection pain is maximal at onset, tearing/ripping, radiates to back — thrombolytics are lethal
Pulmonary Embolism
PE shows right heart strain on ECG (S1Q3T3), hypoxia, pleuritic pain, not ST changes
Pericarditis
Pericarditis has diffuse saddle-shaped ST elevation + PR depression, positional/pleuritic pain, friction rub
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Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.