What are the current guidelines for managing out-of-hospital thrombosis in myocardial infarction (MI)?

Out-of-Hospital Antithrombotic Management for STEMI

For patients with suspected STEMI in the out-of-hospital setting, immediate aspirin administration (150-325 mg chewed) is mandatory, and pre-hospital fibrinolysis should be initiated when primary PCI cannot be performed within 120 minutes of diagnosis. 1, 2

Immediate Pre-Hospital Antiplatelet Therapy

Aspirin Administration

• Aspirin 150-325 mg (oral, chewed) or 250-500 mg IV if unable to swallow must be given as soon as STEMI is recognized, unless absolute contraindication exists 1, 2
• The European Society of Cardiology recommends 162-325 mg loading dose specifically 1
• Lower doses (162 mg) appear equally effective with potentially less bleeding risk compared to 325 mg 3
• This should occur at first medical contact, not delayed until hospital arrival 1, 2

P2Y12 Inhibitor Considerations

• Clopidogrel can be administered pre-hospital in conjunction with fibrinolytic therapy 1, 4
• For patients proceeding to primary PCI, potent P2Y12 inhibitors (prasugrel or ticagrelor) should be given before or at the time of PCI 1, 2
• Critical timing restriction: Prasugrel must not be given sooner than 24 hours after fibrin-specific thrombolytic administration 1, 5

Pre-Hospital Fibrinolysis Protocol

Indications for Pre-Hospital Fibrinolysis

Pre-hospital fibrinolysis is recommended when:

• Symptoms present ≤12 hours from onset 1, 4
• ST-segment elevation or new left bundle branch block confirmed on 12-lead ECG 1, 2, 4
• Primary PCI cannot be performed within 120 minutes of STEMI diagnosis 1, 2, 4
• No contraindications present 1, 4

Fibrinolytic Agent Selection

• Fibrin-specific agents are mandatory: tenecteplase, alteplase, or reteplase 1, 4
• Tenecteplase is preferred for pre-hospital use due to single-bolus administration 2, 4
• For patients ≥75 years: reduce tenecteplase dose by 50% to minimize stroke risk 2, 4

Mandatory Adjunctive Anticoagulation with Fibrinolysis

Anticoagulation must be initiated with fibrinolytic therapy:

• Enoxaparin IV bolus followed by subcutaneous dosing (preferred over UFH) 1, 4
• Alternative: UFH as weight-adjusted IV bolus followed by infusion 1, 4
• Continue until revascularization or for duration of hospital stay up to 8 days 1, 4

Post-Fibrinolysis Out-of-Hospital Management

Immediate Transfer Protocol

• All patients receiving pre-hospital fibrinolysis must be transferred immediately to a PCI-capable center 1, 4
• Transfer should occur directly to the catheterization laboratory, bypassing emergency department 1, 2
• This applies even if fibrinolysis appears successful 1, 4

Assessment for Rescue PCI

• At 60-90 minutes post-fibrinolysis, assess ST-segment resolution in the lead with greatest initial elevation 1, 4
• <50% ST-segment resolution indicates failed fibrinolysis requiring immediate rescue PCI 1, 4
• Emergency PCI also indicated for hemodynamic instability, electrical instability, worsening ischemia, or cardiogenic shock regardless of ST-segment changes 1, 4

Critical Contraindications and Safety Considerations

Absolute Contraindications to Fibrinolysis

• Prior intracranial hemorrhage 1
• Structural cerebral vascular lesion or malignant intracranial neoplasm 1
• Ischemic stroke within past 3 months (except acute ischemic stroke within past 3 hours) 1
• Suspected aortic dissection 1
• Active bleeding (except menses) or bleeding diathesis 1
• Significant closed head or facial trauma within past 3 months 1

Relative Contraindications Requiring Careful Assessment

• Chronic, severe, poorly controlled hypertension or BP >180/110 mmHg on presentation 1
• Ischemic stroke 3+ months ago, dementia, or known intracranial pathology 1
• Traumatic or prolonged CPR (>10 minutes) 1
• Major surgery within past 3 weeks 1
• Internal bleeding within past 2-4 weeks 1
• Pregnancy, active peptic ulcer, or current anticoagulant use with elevated INR 1

Common Pitfalls to Avoid

Do not delay aspirin administration for any reason - it should be given at symptom recognition, not after ECG confirmation or hospital arrival 1, 2

Do not combine full-dose fibrinolysis with planned immediate PCI (facilitated PCI) - this strategy increases mortality and is no longer recommended 1, 4

Do not administer prasugrel within 24 hours of fibrin-specific thrombolytics (48 hours for streptokinase) - this significantly increases bleeding risk 1, 5

Do not use fondaparinux as sole anticoagulant if PCI is planned - it requires additional anti-IIa agent due to catheter thrombosis risk 1

Do not withhold fibrinolysis in eligible patients when PCI delays exceed 120 minutes - mortality benefit of timely reperfusion outweighs theoretical advantages of PCI 1, 2, 4