What are the differences in presentation, diagnosis, and treatment between STEMI (ST-Elevation Myocardial Infarction) and NSTEMI (Non-ST-Elevation Myocardial Infarction)?

STEMI vs NSTEMI: Presentation, Diagnosis, and Management

The fundamental difference between STEMI and NSTEMI is the presence of complete coronary occlusion in STEMI versus partial occlusion in NSTEMI, which manifests as ST-segment elevation on ECG in STEMI versus ST-depression, T-wave inversion, or normal ECG in NSTEMI. 1, 2

Clinical Presentation

Symptoms

• Both STEMI and NSTEMI typically present with:

  • Deep, poorly localized chest or arm discomfort
  • Pressure, heaviness, tightness, aching, fullness, or squeezing sensation
  • Radiation to left arm, neck, or jaw
  • Episodes lasting >20 minutes
  • May be accompanied by dyspnea, nausea, vomiting, diaphoresis 2

• Atypical presentations more common in:

  • Older adults (≥75 years)
  • Women
  • Patients with diabetes
  • Chronic renal failure
  • Dementia 2, 1

Key Differences in Presentation

• STEMI:

  • More likely to have sudden, severe onset
  • Persistent symptoms with minimal/no relief without intervention
  • Higher likelihood of cardiogenic shock at presentation 2

• NSTEMI:

  • May have more gradual onset
  • Symptoms may partially respond to nitroglycerin/rest
  • More variable presentation 2, 1

Diagnostic Approach

Initial Evaluation

1. 12-lead ECG within 10 minutes of first medical contact 1
2. Cardiac biomarkers (preferably high-sensitivity troponin)
3. Risk stratification using validated tools (TIMI, GRACE scores)

ECG Findings

• STEMI:

  • ST-segment elevation in ≥2 contiguous leads
  • New or presumed new LBBB (with caution - not all LBBB indicates STEMI)
  • Posterior MI: ST depression in V1-V3 with tall R waves 1

• NSTEMI/UA:

  • ST-segment depression
  • T-wave inversion
  • Non-specific changes or normal ECG 1, 2

Cardiac Biomarkers

• STEMI: Elevated troponin (may be normal very early)
• NSTEMI: Elevated troponin
• Unstable Angina: Normal troponin 2

Pathophysiology

• STEMI: Complete/occlusive thrombus formation
• NSTEMI: Partial/non-occlusive thrombus formation 1, 2

Diagnostic Challenges

1. Silent and Unrecognized Events:

   • Up to half of all MIs may be clinically silent
   • One-third of patients present without chest discomfort
   • Higher mortality in patients without chest pain (23.3% vs 9.3%) 1

2. ECG Interpretation:

   • 40% of patients with acute coronary occlusion do not present with STEMI criteria 3
   • LBBB can mask or mimic STEMI 1

3. Early Biomarker Negativity:

   • Initial troponin may be negative in early presentation
   • Serial measurements often necessary 1

Management Differences

STEMI Management

• Immediate reperfusion therapy is critical:
  • Primary PCI within 90-120 minutes of first medical contact (preferred)
  • Fibrinolytic therapy if PCI not available within timeframe 2, 4
  • Door-to-balloon time target: <90 minutes 1

NSTEMI Management

• Risk-stratified approach:
  • Very high-risk features: Immediate invasive strategy (<2 hours)
  • High-risk features: Early invasive strategy (<24 hours)
  • Intermediate-risk: Invasive strategy within 72 hours
  • Low-risk: Non-invasive testing first 1

Pharmacotherapy for Both

• Antiplatelet therapy:
  • Aspirin (162-325 mg loading, then 81 mg daily)
  • P2Y12 inhibitor (clopidogrel, ticagrelor, or prasugrel) 5
• Anticoagulation:
  • Unfractionated heparin, enoxaparin, or bivalirudin
• Anti-ischemic therapy:
  • Beta-blockers
  • Nitrates
  • Statins 2

Outcomes and Prognosis

• Short-term mortality:

  • Higher in-hospital mortality for STEMI if untreated
  • Higher mortality in NSTEMI patients without chest pain 1

• Long-term outcomes:

  • NSTEMI has worse long-term prognosis than STEMI due to:
    • Higher burden of comorbidities
    • Older age
    • More extensive CAD
    • Less complete revascularization 6

• Complications:

  • STEMI: Higher risk of mechanical complications (ventricular rupture, papillary muscle rupture)
  • NSTEMI: Higher risk of recurrent ischemia 2

Common Pitfalls to Avoid

1. Delayed diagnosis of NSTEMI:

   • Patients without chest pain often receive less aggressive treatment
   • Women and elderly more likely to have atypical presentations 1

2. Overlooking STEMI equivalents:

   • Posterior MI
   • Right ventricular MI
   • New LBBB in appropriate clinical context 1

3. Focusing solely on ECG for triage:

   • 40% of patients with acute coronary occlusion do not meet STEMI criteria 3
   • Clinical assessment and risk stratification are essential

4. Delayed reperfusion in high-risk NSTEMI:

   • NSTEMI with ongoing symptoms, hemodynamic instability, or electrical instability should receive urgent angiography 1

5. Underestimating Type 2 NSTEMI:

   • Focus on treating underlying cause (hypoxemia, anemia, hypertension) 2
   • Higher mortality, often from non-cardiac causes