When is fibrinolytic therapy indicated for acute ST‑segment elevation myocardial infarction (STEMI) and not for non‑ST‑segment elevation myocardial infarction (NSTEMI)?

Fibrinolytic Therapy Indications in STEMI vs NSTEMI

Fibrinolytic therapy is indicated ONLY for STEMI (not NSTEMI) when primary PCI cannot be performed within 120 minutes of first medical contact, provided the patient presents within 12 hours of symptom onset and has no contraindications. 1

STEMI: When Fibrinolysis IS Indicated

Primary Indications (Class I Evidence)

Fibrinolytic therapy should be administered to STEMI patients when:

• **Symptom onset <12 hours** AND anticipated delay to primary PCI >120 minutes from first medical contact 1
• Patient presents to a non-PCI-capable hospital where transfer would exceed the 120-minute window 1
• Goal: Door-to-needle time ≤30 minutes when fibrinolysis is chosen 1

Extended Window Indications (Class IIa Evidence)

Fibrinolysis is reasonable in select STEMI patients presenting 12-24 hours after symptom onset when: 1, 2

• Evidence of ongoing ischemia (persistent chest pain despite medical therapy) 2
• Large area of myocardium at risk (extensive ST elevation, <50% ST-segment resolution) 2
• Hemodynamic instability present 1, 2
• Primary PCI remains unavailable 2

Special Circumstances

Fibrinolysis should be given to STEMI patients with cardiogenic shock who are unsuitable for PCI or CABG 1

NSTEMI: When Fibrinolysis is CONTRAINDICATED

Fibrinolytic therapy is explicitly contraindicated in NSTEMI and may cause harm. 3

Why NSTEMI is Different

• NSTEMI involves partial or intermittent coronary occlusion with platelet-rich thrombus that is less responsive to fibrinolytics 3
• Risk of destabilizing the plaque and causing complete occlusion or distal embolization 3
• ST depression on ECG is a Class III (Harm) indication for fibrinolysis 1, 3

Critical ECG Distinction

The only exceptions to the "no fibrinolysis with ST depression" rule are: 1, 3

• True posterior (inferobasal) MI suspected (ST depression in anterior leads with posterior ST elevation) 1, 3
• ST elevation in lead aVR with multilead ST depression (suggests left main or severe multivessel disease) 1, 3

Absolute Contraindications to Fibrinolysis (Apply to Both)

Never administer fibrinolytics if any of these are present: 2, 4

• Any prior intracranial hemorrhage (ever) 2
• Ischemic stroke within 3 months 2
• Known intracranial neoplasm, AVM, or aneurysm 2, 4
• Active internal bleeding 4
• Intracranial/intraspinal surgery or trauma within 2 months 4
• Known bleeding diathesis 2, 4
• Severe uncontrolled hypertension 2, 4

Recommended Fibrinolytic Protocol for STEMI

Agent Selection

Tenecteplase (TNK) is recommended as a single weight-adjusted IV bolus over 5 seconds 2, 4

• Alternative fibrin-specific agents: alteplase or reteplase 1
• Preferably administered in the pre-hospital setting to minimize time delay 1, 5

Adjunctive Antithrombotic Therapy

Mandatory antiplatelet therapy: 1, 2

• Aspirin 162-325 mg loading dose, then 81 mg daily indefinitely 1, 2
• Clopidogrel 300 mg loading dose (if ≤75 years) or 75 mg (if >75 years), then 75 mg daily for at least 14 days, up to 1 year 1, 2

Mandatory anticoagulation (choose one): 1, 2

• Enoxaparin IV followed by subcutaneous (preferred over UFH) 1, 2
• UFH as weight-adjusted IV bolus followed by infusion 1, 2
• Continue for minimum 48 hours, preferably duration of hospitalization up to 8 days 2

Post-Fibrinolysis Management

Immediate Transfer

All STEMI patients receiving fibrinolysis must be transferred to a PCI-capable center immediately after drug administration 1, 2, 6

Timing of Angiography

Routine coronary angiography should be performed 2-24 hours after successful fibrinolysis, but NOT within the initial 3 hours 1, 2, 6

Rescue PCI Indications

Emergency angiography with rescue PCI is indicated immediately when: 1

• <50% ST-segment resolution at 60-90 minutes (fibrinolysis failure) 1
• Hemodynamic or electrical instability at any time 1
• Worsening ischemia or evidence of reocclusion 1
• Cardiogenic shock or heart failure develops 1

Common Pitfalls to Avoid

• Do not give fibrinolytics to NSTEMI patients – this is explicitly harmful and offers no benefit 3
• Do not delay fibrinolysis if PCI is unavailable – every 30-minute delay reduces efficacy 1, 5
• Do not perform angiography within 3 hours of fibrinolytic administration unless rescue PCI is needed 2, 6
• Do not use fibrinolysis as a substitute for timely primary PCI when PCI can be achieved within guideline-recommended times (90 minutes for direct presentation, 120 minutes for transfer) 1