Acute Myocardial Infarction (AMI)

Definition & Classification

The pathophysiology is dynamic — patients can rapidly progress from UA → NSTEMI → STEMI during initial evaluation and treatment.

Clinical Presentation

• Chest pain/pressure — classic, often radiating to left arm, jaw, or back
• Diaphoresis, nausea, vomiting
• Dyspnea, especially with reduced LV function
• Silent MI — particularly in diabetics and elderly (no chest pain)
• Killip classification guides severity assessment (I–IV)

Diagnosis

1. ECG

• New ST elevation ≥1 mm in ≥2 contiguous limb leads
• ST elevation ≥2 mm in ≥2 contiguous precordial leads (≥2.5 mm in men <40 y)
• New LBBB (treat as STEMI equivalent)

• ST depression, T-wave inversions, or non-specific changes
• Normal ECG does not exclude MI

Anterolateral STEMI: ST elevation V1–V6, leads I and aVL; reciprocal depression in II, III, aVF; consistent with proximal LAD occlusion.

2. Cardiac Biomarkers

• High-sensitivity troponin (hs-cTn) — gold standard; rises within 1–3 hrs, peaks at 12–24 hrs
• 0h/1h or 0h/2h rapid rule-out/rule-in protocols (ESC recommended)
• CK-MB useful for re-infarction detection (shorter half-life)

3. Imaging

• Echo — regional wall motion abnormalities, EF, mechanical complications
• Coronary angiography — definitive; performed at PCI

Management

STEMI — Time-Critical Reperfusion

• Target: door-to-balloon ≤90 min (≤120 min if transfer required)
• If PPCI unavailable within 120 min: fibrinolysis within 10 min of diagnosis
• Post-fibrinolysis: transfer for angiography within 3–24 hrs ("pharmaco-invasive")

NSTEMI — Risk-Stratified Invasive Strategy

• Very high risk (refractory ischemia, hemodynamic instability, VT/VF): immediate angiography (<2 hrs)
• High risk (elevated troponin, dynamic ECG changes, GRACE score >140): early invasive (<24 hrs)
• Low-to-intermediate risk: selective invasive strategy

Antithrombotic Therapy (Management of Acute Coronary Syndromes, p. 36)

Antiplatelet

• Aspirin 150–300 mg loading dose → 75–100 mg/day indefinitely
• P2Y12 inhibitor (DAPT for 12 months):
  • Ticagrelor 180 mg → 90 mg BID (preferred in NSTEMI/STEMI)
  • Prasugrel 60 mg → 10 mg/day (STEMI undergoing PCI; avoid if prior stroke/TIA, age >75, weight <60 kg)
  • Clopidogrel 300–600 mg → 75 mg/day (if above unavailable/contraindicated; preferred in elderly >70–80 yrs)

Routine pre-treatment with a P2Y12 inhibitor in NSTE-ACS patients planned for early invasive strategy (<24 h) when coronary anatomy is unknown is not recommended.

Anticoagulation

Other Acute Medications

• Beta-blockers — start within 24 hrs if no contraindications (HF, cardiogenic shock, bradycardia)
• High-intensity statin — atorvastatin 40–80 mg immediately
• ACE inhibitor/ARB — start within 24 hrs, especially if EF <40%, anterior MI, or diabetes
• Nitrates — symptom relief; avoid if RV infarct or hypotension
• Morphine — use cautiously (may delay antiplatelet absorption)

Complications

Risk Stratification & Secondary Prevention

• GRACE score (in-hospital and 6-month mortality) — guides invasive timing in NSTEMI
• TIMI score — widely used bedside risk tool
• Echo pre-discharge — EF guides need for ICD (EF <35% after ≥40 days post-MI)
• Cardiac rehab — reduces mortality and rehospitalization
• Long-term DAPT duration individualized by bleeding vs. ischemic risk (HBR patients may shorten to 3–6 months; high ischemic risk may extend beyond 12 months)

Special Populations