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 90-120 minutes or fibrinolytic therapy within 30 minutes of first medical contact—combined with aspirin, oxygen (if hypoxemic), pain relief with opioids, and continuous ECG monitoring represents the cornerstone of initial management to reduce mortality and limit infarct size. 1

Immediate Emergency Care (First Minutes)

Diagnosis and Monitoring

• Obtain a 12-lead ECG within 10 minutes of first medical contact to identify ST-segment elevation or new left bundle branch block 1
• Start 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 emergency resuscitation equipment and defibrillator immediately available 1

Initial Pharmacological Therapy

• Aspirin 75-325 mg should be administered immediately (non-enteric coated for faster buccal absorption) 1, 2, 3, 4
• Opioids (morphine) for pain relief if chest pain persists despite nitrates 1, 3
• Oxygen should be given if arterial oxygen saturation is <90% or if respiratory distress is present 1
• Nitroglycerin (sublingual or intravenous) for ongoing chest pain to reduce myocardial oxygen demand 1, 3, 4

Reperfusion Strategy (Within First Hours)

For STEMI Patients (ST-elevation or new LBBB)

The choice between primary PCI and fibrinolytic therapy depends on time from symptom onset and availability:

Primary PCI (Preferred if Available)

• Primary PCI is the preferred reperfusion strategy if it can be performed within 120 minutes of first medical contact (or within 90 minutes if presenting early) 1
• Door-to-balloon time should be ≤90 minutes (≤60 minutes in early presenters) 1
• Patients should be transferred directly to the catheterization laboratory, bypassing the emergency department when possible 1

Fibrinolytic Therapy

• Administer fibrinolytic therapy within 30 minutes ("door-to-needle time") if primary PCI cannot be achieved within the recommended timeframe 1
• Greatest benefit occurs when given within the first hour of symptom onset (65 lives saved per 1000 patients), with decreasing benefit over time (25 lives saved per 1000 if given at 4-6 hours) 1
• Tissue plasminogen activator (alteplase), streptokinase, or urokinase should be administered within 3 hours of symptom onset 5, 3
• Pre-hospital administration by trained paramedics is the most effective way to shorten delay times 1

For Non-ST-Elevation ACS (NSTEMI/Unstable Angina)

Initial medical management without immediate reperfusion, followed by risk stratification:

• Aspirin 75-150 mg daily 1
• Clopidogrel 300 mg loading dose, then 75 mg daily (in addition to aspirin) reduces cardiovascular death, MI, and stroke by 20% 2
• Low-molecular-weight heparin or unfractionated heparin 1
• Beta-blockers unless contraindicated 1, 4
• Nitroglycerin (oral or intravenous) for persistent or recurrent chest pain 1

Risk Stratification and Timing of Intervention

High-Risk Features Requiring Urgent Angiography

Patients with the following should proceed to coronary angiography as soon as possible 1:

• Recurrent ischemia (chest pain or dynamic ST-segment changes)
• Elevated troponin levels
• Hemodynamic instability
• Major arrhythmias (ventricular tachycardia, ventricular fibrillation)
• Early post-infarction unstable angina
• Diabetes mellitus

Timing Considerations

• For STEMI: Reperfusion therapy is indicated within 12 hours of symptom onset with persistent ST-elevation 1
• Between 12-24 hours: Primary PCI may be considered if evidence of ongoing ischemia exists 1
• Beyond 24 hours: Routine PCI of a totally occluded artery in stable patients without signs of ischemia is not recommended 1
• For NSTEMI: Immediate intervention (within 70 minutes) versus delayed intervention (next working day) showed no difference in outcomes, suggesting that urgent but not emergent intervention is appropriate for stable patients 6

Critical Time Targets

The European Society of Cardiology and American Heart Association emphasize these time-dependent goals:

• First medical contact to ECG: ≤10 minutes 1
• Door-to-needle (fibrinolysis): ≤30 minutes 1
• Door-to-balloon (primary PCI): ≤90 minutes (≤60 minutes in early presenters) 1

Common Pitfalls to Avoid

• Do not wait for cardiac biomarker results before initiating reperfusion therapy in STEMI patients 1
• Do not administer NSAIDs (except aspirin), as they increase mortality, reinfarction, hypertension, heart failure, and myocardial rupture risk 1
• Recognize atypical presentations in elderly patients (fatigue, dyspnea, syncope rather than chest pain) to avoid diagnostic delays 1, 7
• Women ≥65 years have significantly longer delay times (median 266 minutes vs 148 minutes in younger women) and less frequently present with chest pain (81% vs 95%), requiring heightened clinical suspicion 7
• Patient delay remains the longest component of pre-hospital time, with 51% of patients calling for help within 30 minutes but general practitioner decision-making adding a median of 82 minutes 8

Adjunctive Therapies After Initial Stabilization

Once reperfusion is initiated and the patient is stabilized 1, 4:

• ACE inhibitors (particularly if anterior MI, heart failure, or left ventricular dysfunction)
• Beta-blockers (unless contraindicated by bradycardia, hypotension, or heart failure)
• Anticoagulation therapy as indicated
• Statin therapy for lipid management