What are the diagnostic criteria and treatment options for a patient presenting with symptoms suggestive of ST-Elevation Myocardial Infarction (STEMI)?

STEMI Diagnostic Criteria and Treatment

ST-Elevation Myocardial Infarction (STEMI) is diagnosed by the presence of ST-segment elevation on ECG in at least two contiguous leads, with elevation ≥2.5 mm in men <40 years, ≥2 mm in men ≥40 years, or ≥1.5 mm in women in leads V2-V3, and/or ≥1 mm in other leads, in the appropriate clinical context of acute chest pain or equivalent symptoms. 1

Diagnostic Criteria

ECG Criteria

• Timing: 12-lead ECG recording and interpretation should be obtained within 10 minutes of first medical contact 1
• ST-segment elevation thresholds:
  • ≥2.5 mm in men <40 years in leads V2-V3
  • ≥2 mm in men ≥40 years in leads V2-V3
  • ≥1.5 mm in women in leads V2-V3
  • ≥1 mm in all other leads
• Other ECG findings:
  • New or presumably new left bundle branch block (LBBB)
  • ST-segment depression in leads V1-V3 with positive T-wave (posterior MI)
  • ST-segment elevation ≥0.5 mm in posterior leads V7-V9 (posterior MI)
  • ST-segment elevation in right-sided leads V3R and V4R (right ventricular infarction)

Clinical Presentation

• Classic symptoms: Chest discomfort/pain lasting >15-20 minutes 1
• Associated symptoms: Shortness of breath, diaphoresis (sweating), nausea, vomiting, dizziness
• Atypical presentations more common in:
  • Older patients
  • Black patients
  • Women (who may present with fatigue, dyspnea, or other non-specific symptoms) 2

Initial Management Algorithm

Immediate Actions (First 10 minutes)

1. Obtain 12-lead ECG within 10 minutes of first medical contact 1
2. Establish ECG monitoring with defibrillator capacity 1
3. Establish IV access
4. Administer aspirin 160-325 mg (chewable/soluble) 1
5. Assess oxygen saturation - administer oxygen only if SaO2 <90% 1

Early Management (10-30 minutes)

1. Determine reperfusion strategy based on:

   • Time from symptom onset
   • Anticipated time to PCI
   • Contraindications to fibrinolysis

2. For Primary PCI strategy:

   • Administer P2Y12 inhibitor:
     • Prasugrel 60 mg loading dose (preferred if no contraindications) 1, 3
     • Ticagrelor as alternative
     • Clopidogrel 600 mg if others contraindicated
   • Anticoagulation with unfractionated heparin or bivalirudin
   • Transport directly to catheterization laboratory, bypassing ED 1

3. For Fibrinolytic strategy (if PCI cannot be performed within 120 minutes of first medical contact):

   • Administer within 30 minutes of first medical contact 1
   • Use fibrin-specific agent (tenecteplase, alteplase, or reteplase) 1
   • Add clopidogrel 300 mg (75 mg if >75 years old) 1
   • Anticoagulation with enoxaparin (preferred) or unfractionated heparin 1
   • Transfer to PCI-capable center immediately after fibrinolysis 1

Reperfusion Decision-Making

Primary PCI

• Preferred when:
  • Can be performed within 120 minutes of first medical contact 1
  • For high-risk patients (cardiogenic shock, Killip class III or greater)
  • Contraindications to fibrinolysis exist
  • Late presentation (>3 hours from symptom onset) 1

Fibrinolysis

• Preferred when:
  • Primary PCI cannot be performed within 120 minutes of first medical contact
  • Early presentation (<3 hours from symptom onset) and PCI not readily available 1
  • No contraindications to fibrinolysis
  • Should be followed by transfer to PCI center for angiography within 2-24 hours 1

Post-Reperfusion Care

• Continue dual antiplatelet therapy (DAPT):
  • Aspirin 75-100 mg daily
  • P2Y12 inhibitor for 12 months (prasugrel 10 mg daily, ticagrelor 90 mg twice daily, or clopidogrel 75 mg daily) 1, 3
• Echocardiography to assess ventricular function and detect complications 1
• Secondary prevention measures (statins, beta-blockers, ACE inhibitors as appropriate)

Common Pitfalls to Avoid

1. Delayed ECG acquisition - must be obtained within 10 minutes of first medical contact
2. Misdiagnosis in atypical presentations - one in five STEMI patients present atypically, particularly older patients and Black patients 2
3. Overlooking STEMI mimics - conditions like aortic dissection can present with STEMI-like ECG changes 4
4. Delayed reperfusion - "time is muscle" - every minute counts in reducing mortality
5. Inappropriate fibrinolysis when contraindicated - increases bleeding risk without benefit
6. Missing right ventricular or posterior infarctions - requires specific lead placement (V3R-V4R or V7-V9)

The most recent guidelines emphasize rapid diagnosis, immediate decision-making regarding reperfusion strategy, and timely implementation of the chosen strategy to minimize myocardial damage and improve survival outcomes in STEMI patients.