What are the diagnostic criteria and treatment for ST-Elevation Myocardial Infarction (STEMI)?

ST-Elevation Myocardial Infarction (STEMI): Diagnostic Criteria and Treatment

STEMI is defined as a clinical syndrome characterized by symptoms of myocardial ischemia with persistent ST-segment elevation on ECG and subsequent release of cardiac biomarkers, requiring immediate reperfusion therapy to reduce mortality and morbidity. 1

Diagnostic Criteria

ECG Criteria

• ST elevation at the J point in at least 2 contiguous leads of:
  • ≥2 mm (0.2 mV) in men or ≥1.5 mm (0.15 mV) in women in leads V2–V3 1
  • ≥1 mm (0.1 mV) in other contiguous chest leads or limb leads 1
• ST depression in ≥2 precordial leads (V1–V4) may indicate posterior wall infarction 1
• Multilead ST depression with ST elevation in lead aVR may indicate left main or proximal LAD occlusion 1
• Hyperacute T-wave changes may be observed in early phases of STEMI 1

Clinical Presentation

• Characteristic symptoms of myocardial ischemia (chest pain/discomfort lasting 10-20 minutes or more) 1
• Pain may radiate to neck, jaw, or left arm 1
• Atypical presentations (especially in elderly) may include fatigue, dyspnea, faintness, or syncope 1

Diagnostic Workup

• 12-lead ECG should be performed and shown to an experienced physician within 10 minutes of emergency department arrival 1
• If initial ECG is not diagnostic but clinical suspicion remains high, serial ECGs at 5-10 minute intervals or continuous 12-lead ST-segment monitoring should be performed 1
• Cardiac troponin is the preferred biomarker for diagnosis 1
• Transthoracic echocardiography may help identify wall motion abnormalities when ECG is difficult to interpret 1

Treatment Algorithm

Immediate Management (First Medical Contact)

1. Reperfusion Strategy Decision

   • Primary PCI is the preferred reperfusion strategy if it can be performed within 120 minutes of first medical contact 1, 2, 3
   • If PCI cannot be performed within 120 minutes, administer fibrinolytic therapy immediately (within 10 minutes of STEMI diagnosis) 1, 2

2. Initial Pharmacotherapy

   • Administer loading dose of aspirin (162-325 mg) 1, 2
   • Administer P2Y12 inhibitor loading dose 2, 4:
     • Prasugrel 60 mg (preferred if no history of stroke/TIA and age <75 years) 4
     • Clopidogrel 600 mg (if prasugrel contraindicated) 5
     • Ticagrelor (preferred over clopidogrel if no contraindications) 2
   • Administer anticoagulant (unfractionated heparin, enoxaparin, or bivalirudin) 2
   • For pain relief: morphine sulfate (2-4 mg IV, with 2-8 mg IV every 5-15 minutes as needed) 1
   • Sublingual nitroglycerin (0.4 mg every 5 minutes, up to three doses) if no contraindications 1

Primary PCI Approach

• Perform coronary angiography with intent to perform PCI 1
• Use radial access preferentially over femoral access to reduce bleeding complications 2
• Implant drug-eluting stents as standard of care 2
• Consider treatment of severe non-infarct-related artery stenosis before hospital discharge 2
• In cardiogenic shock, consider non-infarct-related artery PCI during the index procedure 2

Fibrinolytic Therapy Approach (if PCI not available within 120 minutes)

• Administer fibrinolytic therapy within 30 minutes of hospital arrival 1
• Consider transfer for rescue PCI if fibrinolysis fails, as evidenced by 1:
  • Cardiogenic shock
  • Severe heart failure/pulmonary edema
  • Hemodynamically compromising ventricular arrhythmias
  • Less than 50% resolution of ST-segment elevation 90 minutes after fibrinolysis

Post-Reperfusion Care

• Implement dual antiplatelet therapy (DAPT) with aspirin plus P2Y12 inhibitor, typically for one year 2
• Initiate beta-blockers within 24 hours in hemodynamically stable patients 1
• Initiate ACE inhibitors/ARBs and statins before discharge 1, 6
• Monitor for complications including arrhythmias, heart failure, and mechanical complications 2

Special Considerations and Pitfalls

Special Scenarios

• For patients presenting 12-24 hours after symptom onset, primary PCI may still be considered if evidence of ongoing ischemia exists 2
• In patients with LBBB, ST elevation analysis may be difficult and should not be considered diagnostic of acute MI in isolation 1
• Right-sided ECG leads should be obtained in patients with inferior STEMI to screen for right ventricular infarction 1

Common Pitfalls

• Delaying reperfusion therapy due to atypical presentations or ECG patterns 2
• Failing to recognize ST depression in anterior leads (V1-V3) as possible posterior myocardial infarction 2
• Waiting for cardiac biomarker results before initiating reperfusion therapy 1
• Routine use of intravenous beta-blocker therapy in the acute phase may increase risk of cardiogenic shock 1

High-Risk Features

• Killip class II-IV at admission (acute heart failure) 6
• Left ventricular ejection fraction <35% 6
• Age older than 65 years 6
• Anterior location of myocardial infarction 6

The management of STEMI requires a coordinated systems-based approach with emphasis on minimizing total ischemic time to improve survival and reduce complications. Time is muscle - every effort should be made to establish reperfusion as quickly as possible, with primary PCI being the preferred strategy when timely access is available.