What is the initial treatment for a myocardial infarction (MI)?

Initial Treatment for Myocardial Infarction

For patients presenting with ST-segment elevation myocardial infarction (STEMI), immediate reperfusion therapy—either primary percutaneous coronary intervention (PCI) within 90 minutes of first medical contact or fibrinolytic therapy within 30 minutes if PCI is not available within 120 minutes—combined with aspirin, oxygen (if hypoxemic), pain relief with opioids, and continuous ECG monitoring represents the cornerstone of initial management to reduce mortality. 1

Immediate Actions Upon First Medical Contact

Diagnosis and Risk Stratification

• Obtain a 12-lead ECG within 10 minutes of first medical contact to identify ST-segment elevation or new left bundle branch block 1
• Begin continuous ECG monitoring immediately for arrhythmia detection, as sudden ventricular fibrillation is the major preventable cause of early death 1
• Place patient on bed rest with supplemental oxygen if arterial oxygen saturation falls below 90% or if respiratory distress is present 1

Pain Management

• Administer opioids (morphine or meperidine) for chest pain relief, as pain control is a primary immediate concern 1, 2
• Give sublingual or intravenous nitroglycerin for ongoing chest pain to reduce myocardial oxygen demand 1, 3

Antiplatelet Therapy

• Administer aspirin 75-150 mg immediately (non-enteric coated for faster buccal absorption) 1, 3
• This should be given as soon as MI is suspected, even before laboratory confirmation 2

Reperfusion Strategy Selection

For STEMI Patients (within 12 hours of symptom onset)

Primary PCI pathway (preferred if available):

• Transfer directly to catheterization laboratory if PCI can be performed within 90 minutes of first medical contact (60 minutes for early presenters) 1
• Implement "fast-track" systems bypassing emergency departments when diagnosis is confirmed pre-hospital 1
• Door-to-balloon time should not exceed 90 minutes 1

Fibrinolytic therapy pathway (if PCI unavailable):

• Administer fibrinolytic drugs within 30 minutes of hospital arrival if PCI cannot be achieved within 120 minutes of first medical contact 1
• Pre-hospital fibrinolytic administration by trained paramedics is the most effective way to shorten delay times 1
• Treatment within the first hour saves 65 lives per 1000 patients, compared to 25 lives per 1000 when given 4-6 hours after symptom onset 1

For Non-ST Elevation MI (NSTEMI)

• Initiate aspirin, clopidogrel (once registered), low-molecular-weight heparin or unfractionated heparin, beta-blocker, and nitrates for persistent pain 1
• High-risk patients (recurrent ischemia, elevated troponins, hemodynamic instability, major arrhythmias, diabetes) should proceed to coronary angiography as soon as possible 1

Adjunctive Pharmacological Therapy

Beta-Blockers

• Initiate early intravenous beta-blocker therapy (metoprolol 5 mg IV every 2 minutes for three doses) in hemodynamically stable patients during the acute phase 4
• Follow with oral metoprolol 50 mg every 6 hours for 48 hours, then 100 mg twice daily 4
• Contraindicated in patients with severe heart failure, shock, or bradycardia 1

ACE Inhibitors

• Begin within 24 hours of symptom onset in hemodynamically stable patients (systolic BP >100 mmHg) 5
• Start with lisinopril 5 mg orally, followed by 5 mg after 24 hours, 10 mg after 48 hours, then 10 mg daily for at least 6 weeks 5
• Reduce initial dose to 2.5 mg if systolic blood pressure is 100-120 mmHg 5

Anticoagulation

• Administer unfractionated heparin or low-molecular-weight heparin as adjunct to reperfusion therapy 1
• Continue for duration of hospitalization in high-risk patients 1

Critical Monitoring and Support

Hemodynamic Monitoring

• Arterial pressure monitoring is indicated for patients in cardiogenic shock 1
• Balloon flotation catheters should be used for assessment of low cardiac output, suspected ventricular septal defect, or papillary muscle dysfunction 1

Arrhythmia Surveillance

• Continue ECG monitoring for at least 24 hours or until alternative diagnosis is made 1
• Prolonged monitoring is appropriate for patients with heart failure, shock, or serious arrhythmias 1

Common Pitfalls to Avoid

• Do not wait for cardiac biomarker results before initiating reperfusion therapy in patients with ST-elevation or new LBBB 1
• Avoid nonsteroidal anti-inflammatory drugs (except aspirin) as they increase risks of mortality, reinfarction, and myocardial rupture 1
• Do not delay treatment for patients presenting 12-24 hours after symptom onset if evidence of ongoing ischemia exists 1
• Recognize that elderly patients may present atypically with fatigue, dyspnea, or syncope rather than chest pain 1
• General practitioner delays can be substantial (median 82 minutes for decision-making); immediate ambulance activation is critical 6

Time-Critical Benchmarks

• First medical contact to ECG: ≤10 minutes 1
• Door-to-needle (fibrinolysis): ≤30 minutes 1
• Door-to-balloon (primary PCI): ≤90 minutes 1
• First medical contact to device: ≤120 minutes 1