What is the treatment for myocardial infarction (MI)?

Treatment of Myocardial Infarction

For patients with ST-segment elevation myocardial infarction (STEMI), immediate reperfusion therapy via primary PCI (if achievable within 90-120 minutes) or fibrinolysis (if PCI cannot be performed within this timeframe) is the cornerstone of treatment that reduces mortality by 21% when initiated early. 1

Immediate Emergency Department Management (First 10-20 Minutes)

Upon arrival, the following must be administered immediately while obtaining a 12-lead ECG within 10 minutes: 1

• Oxygen via nasal prongs (though routine oxygen is not recommended if SaO2 ≥90%) 1
• Aspirin 160-325 mg orally (chewed immediately) 1
• Sublingual nitroglycerin unless systolic BP <90 mmHg or heart rate <50 or >100 bpm 1
• Morphine sulfate for adequate analgesia 1
• Continuous cardiac monitoring with defibrillator capacity 1

The 12-lead ECG determines the reperfusion strategy: ST-segment elevation ≥1 mV in contiguous leads or new left bundle branch block indicates need for immediate reperfusion therapy. 1

Reperfusion Strategy Selection (Time Zero = STEMI Diagnosis)

Primary PCI is preferred if it can be performed within 90 minutes of first medical contact (or 120 minutes from STEMI diagnosis). 1 If this timeframe cannot be met, initiate fibrinolysis within 10 minutes of STEMI diagnosis. 1

Primary PCI Approach:

• Radial access and drug-eluting stent implantation are standard of care 1
• Routine thrombus aspiration or deferred stenting are contraindicated 1
• Treatment of non-infarct-related artery severe stenosis should be considered before hospital discharge 1
• In cardiogenic shock, non-infarct-related artery PCI should be considered during index procedure 1

Fibrinolysis Approach:

The mortality benefit is time-dependent: 1

• Within first hour: 35 lives saved per 1,000 patients treated
• 7-12 hours after onset: 16 lives saved per 1,000 patients treated
• Definite benefit exists up to 12 hours from symptom onset 1

Important caveat: The previously proposed "facilitated PCI" strategy (full-dose fibrinolysis followed by immediate PCI) is harmful and no longer recommended. 1 However, a pharmacoinvasive strategy with immediate transfer to PCI facility after fibrinolysis is beneficial for high-risk patients. 2

Antithrombotic Therapy

For Primary PCI: 1

• Unfractionated heparin (enoxaparin or bivalirudin as alternatives)
• Loading dose of aspirin plus prasugrel or ticagrelor (not clopidogrel)
• Maintenance DAPT: aspirin plus prasugrel/ticagrelor for one year

For Fibrinolysis: 1

• Enoxaparin (unfractionated heparin as alternative)
• Loading dose of aspirin plus clopidogrel 75 mg daily 1
• Continue heparin for 48 hours if alteplase (tPA) was used 3

Critical point: Oral clopidogrel should be added to aspirin in all STEMI patients regardless of reperfusion strategy, with duration varying by stent type (no stent: 14 days; bare-metal stent: minimum 1 month, ideally 1 year; drug-eluting stent: 1 year). 1

First 24 Hours Management

Beta-Blocker Therapy:

• Oral beta-blockers should be initiated within 24 hours in patients without contraindications (heart failure, hypotension, bradycardia, heart block) 1
• Intravenous beta-blockers should NOT be given routinely in STEMI 1
• Continue for at least 6 weeks, though longer duration is beneficial 3

Nitroglycerin:

• Intravenous nitroglycerin for 24-48 hours if no hypotension, bradycardia, or excessive tachycardia 3
• This allows proper dose titration compared to oral nitrates 3

Additional Therapies:

• ACE inhibitors should be started, particularly for anterior MI or left ventricular dysfunction 3, 2
• Prophylactic antiarrhythmic agents are contraindicated 3
• Continuous cardiac monitoring for at least 24 hours 1

Special Considerations for High-Risk Subsets

Anterior MI:

Anterior myocardial infarctions carry higher risk and require specific attention: 3, 2

• Higher risk for left ventricular dysfunction and heart failure 3
• Higher risk for LV mural thrombus formation and embolic stroke 3
• Anticoagulation with intravenous heparin should be strongly considered 3
• Echocardiography to evaluate LV function and detect mural thrombus 3
• If mobile or protuberant thrombi detected, treat with IV heparin followed by oral anticoagulation for 3-6 months 1

Cardiogenic Shock:

• Immediate transfer to facility capable of cardiac catheterization and revascularization (PCI and CABG) 1
• Consider PCI of non-infarct-related arteries during index procedure 1

Diabetes:

• Strict glycemic control with insulin-glucose infusion followed by multiple-dose insulin reduces long-term mortality 1
• Diabetes is NOT a contraindication to fibrinolysis, even with retinopathy 1
• Beta-blockers and ACE inhibitors appear even more effective than in non-diabetics 1

Contraindications to Fibrinolysis:

• Immediate transfer to PCI-capable facility within 30 minutes 1
• Age >65 years, body weight <70 kg, and hypertension increase intracranial hemorrhage risk with tPA 1

Post-Reperfusion Management

Ambulation and Discharge:

• Bed rest for first 12-24 hours for patients with significant LV damage 1
• Uncomplicated patients can sit out of bed late on first day, use commode, and undertake self-care 1
• Ambulation starts day 2, progressing to 200m walking and stairs within days 1
• Early discharge is optimal for uncomplicated patients 1

Long-term Medications:

• Aspirin 160-325 mg daily indefinitely 3
• DAPT for one year (aspirin plus prasugrel/ticagrelor) 1
• Beta-blockers for minimum 6 weeks 3
• ACE inhibitors, especially for anterior MI or LV dysfunction 3

Medications to AVOID:

• NSAIDs (except aspirin) must be discontinued due to increased risks of mortality, reinfarction, hypertension, heart failure, and myocardial rupture 1
• Calcium channel blockers have not shown mortality benefit and may be harmful 3

Critical Pitfalls to Avoid

• Delaying reperfusion beyond 90-120 minutes when PCI is available significantly reduces effectiveness 1, 3
• Using facilitated PCI strategy (full-dose fibrinolysis before immediate PCI) is harmful 1
• Administering IV beta-blockers routinely in acute STEMI increases harm 1
• Failing to have emergency equipment immediately available (atropine, lidocaine, pacing, defibrillator, epinephrine) 3
• Not performing echocardiography in anterior MI to detect LV thrombus 3
• Continuing NSAIDs in patients who routinely took them before MI 1