Immediate Management of Suspected Myocardial Infarction in a Patient Already on Aspirin
If the patient is already taking aspirin, continue it and do not administer an additional loading dose—instead, immediately add a second antiplatelet agent (dual antiplatelet therapy) along with other acute MI interventions. 1
Aspirin Management
- Continue the current aspirin regimen without administering an additional loading dose if the patient has already taken aspirin 1
- The maintenance dose should be 75-162 mg daily (not higher doses like 325 mg), as lower doses provide equivalent efficacy with significantly reduced bleeding risk—major bleeding occurs in 2.0% with <100 mg versus 4.0% with >200 mg daily 1, 2
- Non-enteric-coated formulations provide more rapid buccal absorption, but if the patient is already on enteric-coated aspirin, continue it rather than switching formulations during the acute event 1
Immediate Dual Antiplatelet Therapy
- Add a P2Y12 inhibitor immediately to the existing aspirin therapy—this is the critical intervention that must not be missed 3, 4
- Ticagrelor 90 mg twice daily is preferred over clopidogrel based on mortality benefit in contemporary guidelines 3
- If ticagrelor is contraindicated or not tolerated, use clopidogrel 75 mg daily as an acceptable alternative 3, 5
- Continue dual antiplatelet therapy for up to 12 months in all patients with ACS without contraindications 3
Additional Immediate Interventions
- Call 9-1-1 immediately and transport by ambulance (not by friends or relatives) 1
- Administer oxygen by nasal prongs 1
- Give sublingual nitroglycerin (unless systolic BP <90 mmHg or heart rate <50 or >100 bpm)—if pain is unimproved or worsening after 5 minutes and one NTG dose, call 9-1-1 before taking additional NTG 1
- Provide adequate analgesia with morphine sulfate (usually up to 10 mg IV) or diamorphine (up to 5 mg IV), titrated against residual pain with an antiemetic like metoclopramide 10 mg IV 1
- Obtain a 12-lead ECG within 10 minutes of arrival—ideally performed in the field by EMS providers 1
Risk Stratification Based on ECG
- ST-segment elevation ≥1 mV in contiguous leads or new LBBB: Immediate reperfusion therapy (primary PCI preferred, or fibrinolysis if PCI will be delayed >120 minutes) 1, 4
- No ST-segment elevation: Do NOT give thrombolytic therapy; proceed with risk stratification and consider early invasive strategy with PCI 1, 4
Parenteral Anticoagulation
- Initiate parenteral anticoagulation with unfractionated heparin, low-molecular-weight heparin, bivalirudin, or fondaparinux 4
- If primary PCI is performed, use high-dose intravenous heparin 1
Additional Medical Therapies
- High-intensity statin therapy (e.g., rosuvastatin 20 mg daily or atorvastatin 80 mg daily) should be initiated immediately 3
- Beta-blocker therapy: Administer early intravenous beta-blocker followed by oral therapy if no contraindications (hypotension, bradycardia, heart failure signs) 1
- ACE inhibitor: Consider if LVEF ≤40%, heart failure, hypertension, or diabetes present 3
- Proton pump inhibitor: Add if patient is at high risk for gastrointestinal bleeding given dual antiplatelet therapy 3, 4
Critical Pitfall to Avoid
The most critical error is discharging or managing an ACS patient on aspirin monotherapy—dual antiplatelet therapy is mandatory and must be initiated immediately in the acute setting 3. The patient being "already on aspirin" does not eliminate the need for adding a second antiplatelet agent.