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tags: #medical/cardiology, #clinical/emergency, #exam/high-yield

Acute Myocardial Infarction

Quick Reference

[!tip] Clinical Pearl Time is muscle! Door-to-balloon time <90 min for STEMI. Remember MONA-BASH (Morphine, Oxygen if <90%, Nitroglycerin, Aspirin - Beta-blocker, ACE-inhibitor, Statin, Heparin)

Overview

Definition: Acute myocardial necrosis due to prolonged ischemia from coronary artery occlusion ICD-10: I21 (Acute myocardial infarction) Prevalence: ~605,000 new attacks annually in the US

Etiology & Risk Factors

Modifiable

  • Smoking
  • Hypertension
  • Diabetes mellitus
  • Dyslipidemia
  • Obesity
  • Sedentary lifestyle

Non-modifiable

  • Age (♂ >45, ♀ >55)
  • Male sex
  • Family history of premature CAD
  • Genetic factors

Pathophysiology

graph TD
    A[Atherosclerotic Plaque Rupture] --> B[Platelet Activation]
    B --> C[Thrombus Formation]
    C --> D[Coronary Occlusion]
    D --> E[Myocardial Ischemia]
    E --> F[Cell Death if >20 min]
    F --> G[Myocardial Infarction]

Clinical Features

History

  • Classic Presentation: Severe substernal chest pain >20 min, crushing/pressure-like
  • Associated Symptoms: Dyspnea, diaphoresis, nausea, radiation to left arm/jaw
  • Atypical in: Elderly, diabetics, women (may present with fatigue, dyspnea only)

Physical Examination

  • Vital Signs: Tachycardia, hypo/hypertension, tachypnea
  • Inspection: Diaphoresis, anxiety, pallor
  • Auscultation: S3/S4 gallop, new murmur (papillary muscle dysfunction/VSD)
  • Signs of complications: Pulmonary edema, cardiogenic shock

Investigations

First-line

  1. ECG within 10 minutes
  2. STEMI: ST elevation ≥1mm in 2 contiguous leads
  3. NSTEMI: ST depression, T wave inversion, or normal
  4. Cardiac Biomarkers
  5. Troponin I/T: Most specific, rises 3-4h, peaks 24h
  6. CK-MB: Less specific, useful for reinfarction

If indicated

  • Chest X-ray (pulmonary edema, cardiomegaly)
  • Echocardiography (wall motion, complications)
  • Coronary angiography (definitive diagnosis + treatment)

Differential Diagnosis

  1. Acute Pericarditis
  2. Pulmonary Embolism
  3. Aortic Dissection
  4. Pneumothorax
  5. GERD/Esophageal Spasm

Management

Acute (STEMI)

  • Primary PCI: Goal door-to-balloon <90 min
  • Fibrinolysis: If PCI not available within 120 min
  • Contraindications: Recent stroke, bleeding, recent surgery

Medications

Drug Dose Frequency Duration Notes
Aspirin 162-325mg Once Then 81mg daily Chew for rapid absorption
Clopidogrel 300-600mg Loading Then 75mg daily Or ticagrelor/prasugrel
Heparin 60 U/kg bolus Continuous During PCI Max 4000U bolus
Metoprolol 25-50mg BID Lifelong If no contraindications
Atorvastatin 80mg Daily Lifelong High-intensity statin
Lisinopril 2.5-5mg Daily Lifelong Start within 24h

Complications

Immediate (minutes-hours)

  • Ventricular arrhythmias (VF/VT)
  • Cardiogenic shock
  • Acute heart failure

Early (days)

  • Pericarditis (2-4 days)
  • Ventricular septal rupture
  • Papillary muscle rupture → acute MR

Late (weeks-months)

  • Ventricular aneurysm
  • Dressler syndrome
  • Heart failure

Prognosis

  • 30-day mortality: STEMI ~5-6% with PCI, NSTEMI ~3-5%
  • 1-year mortality: ~10%
  • Better outcomes with early reperfusion

Key Points for Exams 🎯

  • ECG changes: STEMI vs NSTEMI criteria
  • Troponin timing: Rises 3-4h, peaks 24h, elevated 7-14 days
  • Time goals: Door-to-ECG <10 min, door-to-balloon <90 min
  • TIMI risk score components
  • Absolute contraindications to fibrinolysis

References