In a patient with confirmed ST‑segment elevation myocardial infarction (STEMI) presenting within 12 hours and unable to undergo primary percutaneous coronary intervention (PCI) within the recommended time window, what is the recommended thrombolytic therapy, including drug selection, dosing, contraindications, and adjunctive antiplatelet and anticoagulant management?

Thrombolysis for STEMI

When primary PCI cannot be performed within 120 minutes of first medical contact in a STEMI patient presenting within 12 hours of symptom onset, administer fibrinolytic therapy immediately—preferably tenecteplase as a single weight-based IV bolus—along with aspirin, clopidogrel, and enoxaparin, then transfer the patient to a PCI-capable center for angiography within 2-24 hours. 1

When to Choose Fibrinolysis Over Primary PCI

The critical decision point is 120 minutes from first medical contact to device activation 1. If you cannot achieve primary PCI within this window:

• Administer fibrinolytics immediately (Class I, Level A recommendation) 1, 2
• This time window shortens to 90 minutes for patients <75 years with large anterior infarctions presenting within 2 hours of symptom onset 1
• The benefit is time-dependent and greatest when administered early, especially within the first 3 hours 3

Critical caveat: Even "successful" fibrinolysis is not definitive therapy—every patient requires subsequent transfer to a PCI-capable center 2, 4.

Drug Selection and Dosing

Preferred Fibrinolytic Agent: Tenecteplase (TNK-tPA)

Tenecteplase is superior to other agents due to single-bolus administration, equivalent 30-day mortality to alteplase, and reduced non-cerebral bleeding 1.

Weight-based dosing 1:

• <60 kg: 30 mg
• 60-69 kg: 35 mg
• 70-79 kg: 40 mg
• 80-89 kg: 45 mg
• ≥90 kg: 50 mg

Alternative Agents (if tenecteplase unavailable) 1:

Reteplase: Two 10-unit IV boluses, 30 minutes apart

Alteplase:

• ≥67 kg: 15 mg bolus, then 50 mg over 30 min, then 35 mg over 60 min
• <67 kg: 15 mg bolus, then 0.75 mg/kg over 30 min (max 50 mg), then 0.5 mg/kg over 60 min (max 35 mg)

All fibrin-specific agents are strongly preferred over non-fibrin-specific agents (Class I, Level B) 2.

Absolute Contraindications

The 2025 ACC/AHA guidelines list these absolute contraindications 1:

• Any prior intracranial hemorrhage
• Known structural cerebrovascular lesion (e.g., arteriovenous malformation)
• Known malignant intracranial neoplasm (primary or metastatic)

Important: Fibrinolysis is contraindicated (Class III: Harm) in patients with isolated ST-segment depression (unless true posterior STEMI suspected) due to increased risk of hemorrhagic stroke and major bleeding 1.

Adjunctive Antiplatelet Therapy

Aspirin (Class I, Level B) 2:

• Oral or IV (if unable to swallow)
• Administer as soon as possible

Clopidogrel (Class I, Level A) 2:

• Loading dose: 300 mg (implied from guidelines, though 600 mg used in some protocols)
• Continue 75 mg daily
• Not prasugrel or ticagrelor—these potent P2Y12 inhibitors are reserved for PCI, not fibrinolysis

Adjunctive Anticoagulation

Enoxaparin is preferred over unfractionated heparin (Class I, Level A) 2:

• Initial IV bolus followed by subcutaneous dosing
• Continue until revascularization or up to 8 days of hospitalization

Unfractionated heparin (Class I, Level B) 2:

• Weight-adjusted IV bolus followed by infusion
• Use if enoxaparin unavailable or contraindicated

Post-Fibrinolysis Management Algorithm

Immediate Transfer (Class I, Level A) 2:

All patients require transfer to a PCI-capable center immediately after fibrinolysis—this is non-negotiable.

Timing of Angiography Depends on Clinical Response:

1. Emergency angiography (immediately) 2:

• Heart failure or cardiogenic shock
• Hemodynamic instability
• Electrical instability (arrhythmias)

2. Rescue PCI (immediately) 2:

• Failed fibrinolysis: <50% ST-segment resolution at 60-90 minutes
• Worsening ischemia at any time
• Recurrent chest pain

3. Routine angiography (2-24 hours after successful fibrinolysis) 2, 4:

• This is the standard approach for successful fibrinolysis
• The TRANSFER-AMI trial demonstrated that routine early PCI (median 2.8 hours) reduced ischemic complications compared to delayed angiography (median 32.5 hours) 4
• Do not perform angiography before 2 hours unless emergency indications present

Special Populations and Situations

Late Presenters (12-24 hours) 1:

• Fibrinolysis benefit not established beyond 12 hours
• Exception: Consider fibrinolysis if large area of myocardium at risk or hemodynamic instability when PCI unavailable
• Otherwise, transfer for primary PCI is reasonable (Class IIa)

Elderly Patients (≥75 years):

• Use same tenecteplase dosing as younger patients
• Higher bleeding risk but mortality benefit may still outweigh risks in appropriate candidates

Common Pitfalls to Avoid

1. Delaying fibrinolysis while arranging transfer: If PCI cannot be achieved within 120 minutes, give the lytic immediately—every 30-minute delay increases mortality

2. Treating isolated ST-depression: This causes harm through increased bleeding without benefit 1

3. Using prasugrel or ticagrelor with fibrinolysis: These are for PCI patients only; use clopidogrel with lytics

4. Skipping post-lysis angiography: Even "successful" fibrinolysis requires angiography within 2-24 hours 2, 4

5. Performing immediate angiography after successful lysis: Wait 2-24 hours unless rescue PCI indicated—the STREAM trial showed prehospital fibrinolysis with timely angiography was effective 3

Monitoring for Success or Failure

Assess ST-segment resolution at 60-90 minutes post-fibrinolysis 2:

• <50% resolution = failed fibrinolysis → immediate rescue PCI
• ≥50% resolution = successful → routine angiography in 2-24 hours