What is the management of myocardial infarction (MI)?

Management of Myocardial Infarction

The management of acute myocardial infarction (MI) requires immediate reperfusion therapy with either primary percutaneous coronary intervention (PCI) or fibrinolysis for patients presenting within 12 hours of symptom onset, followed by comprehensive pharmacological therapy and cardiac rehabilitation. 1

Initial Assessment and Management

• Obtain a 12-lead ECG within 10 minutes of first medical contact to diagnose STEMI (ST-segment elevation or new LBBB) 2
• Immediately administer aspirin 162-325 mg (chewed or crushed) to all patients with suspected MI unless contraindicated 1, 2
• Establish continuous ECG monitoring with defibrillator capacity for all patients with suspected MI 2
• Administer supplemental oxygen only if oxygen saturation is <90% 2
• Provide pain relief with IV morphine (2-4 mg IV, with 2-8 mg IV every 5-15 minutes as needed) 1

Reperfusion Strategy

Primary PCI (Preferred Strategy)

• Primary PCI is the preferred reperfusion strategy when it can be performed within 120 minutes of STEMI diagnosis by an experienced team 1, 2
• Transfer patients directly to the catheterization laboratory, bypassing the emergency department 1, 2
• Administer a potent P2Y12 inhibitor (prasugrel or ticagrelor, or clopidogrel if these are unavailable) before or at the time of PCI 1, 2
• Use unfractionated heparin (UFH) as an IV bolus at 100 U/kg (60 U/kg if GPIIb/IIIa inhibitors are used) during PCI 2
• Fondaparinux is not recommended for primary PCI 1, 2

Fibrinolytic Therapy

• Initiate fibrinolysis as soon as possible (ideally within 30 minutes of first medical contact) if primary PCI cannot be performed within 120 minutes 1
• Use a fibrin-specific agent (tenecteplase, alteplase, or reteplase) 1, 2
• Administer clopidogrel in addition to aspirin 1, 2
• Provide anticoagulation with enoxaparin (preferred) or UFH until revascularization or for the duration of hospital stay (up to 8 days) 1, 2
• Transfer to a PCI-capable center immediately after fibrinolysis 1
• Perform rescue PCI immediately if fibrinolysis fails (<50% ST-segment resolution at 60-90 minutes) 1

Early In-Hospital Management

• Administer IV nitroglycerin for 24-48 hours in patients without hypotension, bradycardia, or excessive tachycardia 1
• Initiate beta-blocker therapy within 24 hours in hemodynamically stable patients 1, 3
  • For metoprolol: Begin with IV administration of three 5 mg boluses at 2-minute intervals, followed by oral therapy (50 mg every 6 hours) 15 minutes after the last IV dose 3
  • Do not administer IV beta-blockers to patients with hypotension, acute heart failure, AV block, or severe bradycardia 1
• Continue aspirin 75-100 mg daily indefinitely 1, 2
• Maintain dual antiplatelet therapy (DAPT) with aspirin plus a P2Y12 inhibitor for 12 months after PCI 1, 2
• Administer high-intensity statin therapy as early as possible 1, 2
• Start ACE inhibitors within 24 hours in patients with heart failure, LV systolic dysfunction, diabetes, or anterior infarct 1, 2
• Discontinue NSAIDs (except aspirin) due to increased risks of mortality, reinfarction, and heart failure 1

Management of Complications

• For heart failure: Administer IV furosemide and an afterload-reducing agent 1
• For cardiogenic shock: Consider insertion of a hemodynamic support device (intra-aortic balloon pump), emergency coronary angiography, and revascularization 1
• For right ventricular infarction: Provide vigorous intravascular volume expansion with normal saline and inotropic agents if hypotension persists 1
• For recurrent chest pain due to pericarditis: Administer high-dose aspirin (650 mg every 4-6 hours) 1
• For recurrent ischemic chest pain: Treat with IV nitroglycerin, analgesics, and antithrombotic medications (aspirin, heparin) and consider coronary angiography 1

Pre-Discharge Assessment

• Perform standard exercise testing before discharge or shortly thereafter (submaximal at 4-7 days or symptom-limited at 10-14 days) to assess functional capacity and risk stratify 1
• Conduct routine echocardiography to assess LV and RV function, detect mechanical complications, and exclude LV thrombus 1, 2

Long-Term Management

• Continue aspirin 75-100 mg daily indefinitely 1, 2
• Maintain DAPT for 12 months after PCI unless there are contraindications 1, 2
• Add a proton pump inhibitor for patients at high risk of gastrointestinal bleeding 1, 2
• Continue beta-blocker therapy in patients with heart failure and/or LVEF <40% 1, 2
  • Note: Recent evidence suggests that beta-blockers may not provide benefit in patients with preserved ejection fraction (>40%) who received modern invasive care 4
• Target LDL-C to <70 mg/dL or reduce by at least 50% if baseline is between 70-135 mg/dL 1, 2
• Provide smoking cessation counseling with pharmacological support 1, 2
• Recommend participation in a cardiac rehabilitation program 1, 2

Common Pitfalls and Caveats

• Delay in obtaining ECG and initiating reperfusion therapy significantly worsens outcomes - aim for "door-to-balloon" time <90 minutes for PCI or "door-to-needle" time <30 minutes for fibrinolysis 1, 2
• Calcium channel blockers have not been shown to reduce mortality in MI patients and may be harmful in certain patients 1
• While high-dose aspirin (325 mg) has been traditionally used, low-dose aspirin (81 mg) appears equally effective for long-term management with potentially lower bleeding risk 5, 6
• Avoid routine use of oxygen in patients with normal oxygen saturation (≥90%) 2
• Do not administer IV beta-blockers to hypotensive patients or those with signs of heart failure 1