What is the management of ST-Elevation Myocardial Infarction (STEMI), including diagnosis and treatment?

STEMI Management: Diagnostics and Treatment

Initial Diagnosis and Assessment

STEMI is diagnosed by >0.1 mV ST-segment elevation in two contiguous leads, new left bundle branch block, or true posterior MI on ECG. 1

Immediate Diagnostic Steps

• Obtain 12-lead ECG immediately upon first medical contact—do not delay reperfusion therapy except when alternate diagnoses like aortic dissection or pericarditis are suspected 1
• Laboratory studies include troponin I, creatine kinase, complete blood count, INR, aPTT, electrolytes, magnesium, BUN, creatinine, glucose, and lipid panel 1
• Chest radiography is recommended but must not delay reperfusion 1

Immediate Medical Management (Pre-Reperfusion)

Antiplatelet Therapy

• Aspirin 162-325 mg oral (or 250-500 mg IV if unable to swallow) should be administered immediately—patient should chew the tablet 1, 2
• P2Y12 inhibitor loading dose before or at time of PCI: ticagrelor 180 mg, prasugrel 60 mg, or clopidogrel 600 mg 2
• Prasugrel is contraindicated in patients with prior stroke or TIA 3

Symptom Management

• Morphine sulfate 2-4 mg IV, with 2-8 mg IV every 5-15 minutes as needed for pain 1
• Nitroglycerin 0.4 mg sublingual every 5 minutes (up to three doses), but avoid in hypotension, bradycardia, right-sided ischemia, or phosphodiesterase inhibitor use within 24 hours (48 hours for tadalafil) 1
• Oxygen supplementation to maintain arterial saturation >90% if pulmonary congestion present 1

Reperfusion Strategy Selection

Primary PCI is the definitive treatment when performed by an experienced team within 120 minutes of STEMI diagnosis; if this timeframe cannot be met, immediate fibrinolytic therapy should be administered. 2

Primary PCI is Preferred When:

• Skilled PCI facility accessible (operators >75 primary PCI cases/year, team >36 cases/year) within 90-120 minutes of first medical contact 1, 2
• Diagnosis of STEMI is uncertain 1
• High-risk features present: cardiogenic shock, Killip class III or greater 1
• Contraindications to fibrinolysis exist, including increased bleeding risk 1
• Late presentation (>3 hours from symptom onset) 1
• Failed fibrinolysis requiring rescue PCI 1

Fibrinolytic Therapy is Preferred When:

• Early presentation (<3 hours from symptom onset) and PCI not readily available 1
• Anticipated time to PCI exceeds 120 minutes, particularly in pre-hospital setting 2, 4
• Invasive strategy not an option (catheterization unavailable, vascular access difficulties, skilled PCI facility not accessible) 1

Primary PCI Protocol

Anticoagulation During PCI

• Unfractionated heparin (UFH) 70-100 U/kg IV bolus if no GP IIb/IIIa inhibitor planned 2
• Bivalirudin 0.75 mg/kg IV bolus and 1.75 mg/kg/h infusion as alternative to UFH 2

Stent Selection

• Drug-eluting stents (DES) or bare-metal stents (BMS) are both acceptable 2
• Use BMS in patients with high bleeding risk, inability to comply with 1 year DAPT, or anticipated surgery within 1 year 2

Fibrinolytic Therapy Protocol

Absolute Contraindications to Fibrinolysis

• Prior intracranial hemorrhage 1
• Known structural cerebral vascular lesion (arteriovenous malformation) 1
• Known malignant intracranial neoplasm 1
• Ischemic stroke within 3 months (except acute ischemic stroke within 4.5 hours) 1
• Suspected aortic dissection 1
• Active bleeding or bleeding diathesis (excluding menses) 1
• Significant closed-head or facial trauma within 3 months 1

Fibrinolytic Agent Selection and Dosing

Tenecteplase is the preferred fibrin-specific agent due to single-bolus administration. 2, 4

Weight-adjusted tenecteplase dosing: 4, 5

• 30 mg for weight <60 kg
• 35 mg for 60-69 kg
• 40 mg for 70-79 kg
• 45 mg for 80-89 kg
• 50 mg for ≥90 kg

For patients ≥75 years old, reduce dose by 50% to minimize stroke risk 4

Adjunctive Therapy with Fibrinolysis

• Aspirin 162-325 mg oral or IV immediately 1, 4
• Clopidogrel loading dose: 300 mg for age ≤75 years, 75 mg (no loading dose) for age >75 years 1
• Anticoagulation for minimum 48 hours, preferably for duration of hospitalization up to 8 days 1
  • Enoxaparin preferred: Age <75 years: 30 mg IV bolus, then 1 mg/kg subcutaneous every 12 hours (max 100 mg first 2 doses); Age ≥75 years: no bolus, 0.75 mg/kg subcutaneous every 12 hours (max 75 mg first 2 doses) 1
  • UFH alternative: 60 U/kg IV bolus (max 4000 U), then 12 U/kg/h infusion (max 1000 U), adjusted to aPTT 1.5-2.0 times control 1

Post-Fibrinolytic Management

Transfer to PCI-capable center immediately after fibrinolysis is indicated in all patients. 4

• Rescue PCI immediately when fibrinolysis has failed (<50% ST-segment resolution at 60-90 minutes) or hemodynamic/electrical instability present 1, 4
• Routine angiography and PCI of infarct-related artery between 2-24 hours after successful fibrinolysis 4

Long-Term Antiplatelet Therapy

Dual antiplatelet therapy (DAPT) duration: minimum 12 months for drug-eluting stents and 30 days for bare-metal stents. 2

• Aspirin 75-100 mg daily indefinitely after DAPT period 2
• Continue P2Y12 inhibitor (clopidogrel 75 mg, ticagrelor 90 mg twice daily, or prasugrel 10 mg daily) for specified duration 1, 2
• Consider prasugrel 5 mg daily for patients <60 kg 3

Additional In-Hospital Management

• High-intensity statin therapy initiated as early as possible 2
• Beta-blockers started orally in patients with heart failure or LVEF <40% unless contraindicated 2
• ACE inhibitors within 24 hours in patients with heart failure, LV dysfunction, diabetes, or anterior infarct 2
• Avoid beta-blockers or calcium channel blockers acutely in patients with frank cardiac failure evidenced by pulmonary congestion or low-output state 1

Special Populations and Cardiogenic Shock

Emergency revascularization with PCI or CABG is recommended in cardiogenic shock regardless of time delay. 2

• Intra-aortic balloon counterpulsation when cardiogenic shock not quickly reversed with pharmacological therapy 1
• Early revascularization within 18 hours of shock for patients <75 years who develop shock within 36 hours of MI 1
• Selected patients ≥75 years with good prior functional status may be considered for invasive strategy 1
• Immediate angiography and PCI when indicated in out-of-hospital cardiac arrest with STEMI on ECG 2

Critical Pitfalls to Avoid

• Do not start prasugrel in patients likely to undergo urgent CABG; discontinue at least 7 days prior to surgery when possible 3
• Do not delay reperfusion for laboratory studies or chest radiography unless alternate diagnosis suspected 1
• Avoid intramuscular injections and nonessential handling for first few hours following fibrinolytic therapy 5
• Do not use fibrinolysis as planned strategy before PCI in STEMI—choose either thrombolysis or PCI as primary treatment strategy 5