What is the management approach for chest pain due to myocardial infarction (MI)?

Management of Chest Pain in Myocardial Infarction

Immediate aspirin administration (162-325 mg chewed, non-enteric coated) combined with rapid reperfusion therapy—primary PCI within 120 minutes or fibrinolytic therapy if PCI is delayed—forms the cornerstone of MI management and directly reduces mortality. 1, 2

Immediate Pre-Hospital Actions

Patient Self-Administration:

• Chew non-enteric coated aspirin 162-325 mg immediately at symptom onset while awaiting EMS 1
• Take one nitroglycerin dose sublingually; if symptoms persist or worsen after 5 minutes, call 9-1-1 immediately (do not wait for three doses) 1
• Transport by EMS/ambulance rather than private vehicle—this is associated with shorter reperfusion times and lower mortality 1

Critical Pitfall: Approximately one-third of MI patients present without chest pain, particularly elderly women who may have only fatigue, dyspnea, faintness, or syncope 1, 2. Patient delays average 1.5-2 hours because symptoms don't match expectations of "crushing chest pain" 1.

Emergency Department/Hospital Initial Management

Immediate Diagnostic Steps:

• Obtain 12-lead ECG within 10 minutes of arrival 1
• For suspected posterior MI, immediately obtain leads V7-V9 looking for ST elevation ≥0.05 mV 2
• ST elevation ≥1 mm in two contiguous leads or new left bundle branch block mandates immediate reperfusion therapy 1
• Do NOT wait for cardiac biomarkers (CK-MB, troponins) to initiate reperfusion treatment 1

Pain Management (Paramount Importance):

• Morphine 4-8 mg IV initially, then 2 mg every 5 minutes until pain relieved 1, 2
• Administer antiemetic (metoclopramide 5-10 mg IV) concurrently with morphine 2
• Avoid intramuscular injections 1
• Pain relief is critical because pain-associated sympathetic activation causes vasoconstriction and increases cardiac workload 1

Immediate Pharmacotherapy:

• Aspirin 160-325 mg orally (if not already given pre-hospital) 2, 3
• Sublingual nitroglycerin for ongoing chest pain 2
• Oxygen 2-4 L/min by mask or nasal prongs, especially if breathless, heart failure, or shock 1

Critical Pitfall for RV Infarction: If inferior MI with suspected RV involvement (hypotension, clear lungs, elevated JVP, ST elevation in V4R), avoid nitrates and diuretics—these reduce preload and can cause profound hypotension 4. Instead, give IV normal saline volume loading 4.

Reperfusion Strategy (Time-Critical)

Primary PCI (Preferred):

• Target door-to-balloon time ≤120 minutes from first medical contact 1, 2, 3
• Primary PCI reduces mortality from 9% to 7% compared to no reperfusion 2
• Administer high-dose IV heparin during procedure 2

Fibrinolytic Therapy (If PCI Delayed >120 Minutes):

• Administer within 30 minutes of hospital arrival if PCI cannot be achieved within 120 minutes 1, 2, 3
• Use fibrin-specific agents: tenecteplase, alteplase, or reteplase 3
• Greatest benefit occurs within first 6 hours of symptom onset; minimal benefit after 12 hours 1, 2, 3

Beta-Blocker Administration

Immediate IV Beta-Blocker (If No Contraindications):

• Metoprolol 5 mg IV every 2 minutes for 3 doses, monitoring BP and HR closely 2, 5
• Begin 15 minutes after last IV dose: metoprolol 50 mg PO every 6 hours for 48 hours in patients tolerating full IV dose 5
• For patients with intolerance, start 25-50 mg PO every 6 hours depending on degree of intolerance 5

Contraindications to monitor: Heart rate <60 bpm, systolic BP <100 mmHg, moderate-severe heart failure, signs of peripheral hypoperfusion, PR interval >0.24 seconds, second or third-degree heart block 5

Long-term: Continue oral beta-blocker for at least 6 weeks, ideally indefinitely 2, 3

Dual Antiplatelet Therapy

P2Y12 Inhibitor Addition:

• Loading dose: Clopidogrel 300 mg PO for patients needing antiplatelet effect within hours 6
• Maintenance: Clopidogrel 75 mg daily 6
• Continue dual antiplatelet therapy (aspirin + P2Y12 inhibitor) for 12 months after PCI 3

Critical Pitfall: Avoid concomitant omeprazole or esomeprazole with clopidogrel—these significantly reduce antiplatelet activity 6. Consider alternative PPI or use ticagrelor/prasugrel instead 7.

Additional Pharmacotherapy

ACE Inhibitors:

• Start within first 24 hours if evidence of heart failure, LV systolic dysfunction, diabetes, or anterior infarction 3
• Example: Lisinopril 5 mg initially, titrate to 10 mg daily if hemodynamically stable 2

Statins:

• High-intensity statin therapy started as early as possible and maintained long-term 3
• Target LDL <100 mg/dL 2

Anticoagulation:

• Unfractionated heparin, low-molecular-weight heparin, bivalirudin, or fondaparinux 7

Management of Specific Complications

Right Ventricular Infarction (Occurs in 50% of Inferior MIs):

• Maintain RV preload: IV normal saline for hypotension 4
• Maintain AV synchrony: AV sequential pacing for symptomatic high-degree heart block unresponsive to atropine 4
• Inotropic support: Dobutamine if cardiac output fails to increase after volume loading 4
• Consider intra-aortic balloon pump for persistent shock 4

Bradycardia/Conduction Disturbances:

• Atropine 0.3-0.5 mg IV, repeat up to 1.5-2.0 mg total for symptomatic bradycardia with hypotension 4
• Temporary pacing for symptomatic high-degree AV block unresponsive to atropine 4

Cardiogenic Shock:

• Hemodynamic support devices, emergency coronary angiography followed by PCI or CABG 4, 3
• Volume expansion with normal saline for RV shock 4
• Inotropic agents if hypotension persists 4

Long-Term Management

Indefinite Medical Therapy:

• Aspirin 75-100 mg daily 3
• Beta-blocker 2, 3
• ACE inhibitor 2, 3
• High-intensity statin 3

Lifestyle Modifications:

• Smoking cessation with support, nicotine replacement, varenicline, or bupropion 3
• Exercise: minimum 20 minutes brisk walking at least 3 times weekly 2, 3
• Diet low in saturated fat and cholesterol 2, 3
• Cardiac rehabilitation program participation 3

Pre-Discharge Evaluation:

• Echocardiography to assess LV/RV function, detect mechanical complications, exclude LV thrombus 3
• Exercise testing: submaximal at 4-7 days or symptom-limited at 10-14 days 3

Evidence Quality Note

The 2013 ACC/AHA STEMI guidelines 1 provide the primary framework, with the European Society of Cardiology guidelines 1 offering concordant recommendations. The most recent high-quality evidence from 2024 8 demonstrates that early aspirin administration (within 4 hours) delays 13,016 deaths annually in the US, with benefits outweighing bleeding risks 10-fold, at a cost-effectiveness ratio of $3.70 per year of life saved.