What are the indications for thrombolysis in acute ischemic stroke, ST‑segment elevation myocardial infarction, and massive or submassive pulmonary embolism?

Thrombolysis Indications

Thrombolysis is indicated for acute ischemic stroke within 4.5 hours of symptom onset, ST-elevation myocardial infarction within 12 hours of symptom onset, and hemodynamically unstable (massive) pulmonary embolism, with each condition having specific time windows and clinical criteria that directly impact mortality and functional outcomes.

Acute Ischemic Stroke

Time-Based Treatment Windows

For acute ischemic stroke, IV alteplase (0.9 mg/kg, maximum 90 mg over 60 minutes with 10% as initial bolus) should be administered as soon as possible within 4.5 hours of symptom onset 1. The evidence strongly supports different recommendation strengths based on timing:

• Within 3 hours: Strong recommendation (Grade 1A) with substantial mortality and disability reduction 2
• 3 to 4.5 hours: Weaker recommendation (Grade 2C) with diminishing but present benefit 2
• Beyond 4.5 hours: Contraindicated unless specific imaging criteria are met (Grade 1B against routine use) 2

Extended Window Criteria

For patients presenting 4.5-9 hours from symptom onset or with wake-up stroke, thrombolysis can be considered if advanced imaging demonstrates salvageable tissue 1:

• DWI-FLAIR mismatch on MRI for wake-up strokes or unclear onset time
• CT or MRI perfusion mismatch showing core/perfusion mismatch when mechanical thrombectomy is not planned

Critical Pre-Treatment Requirements

Only blood glucose assessment must precede alteplase administration 1. Hypoglycemia (glucose <60 mg/dL or 3.3 mmol/L) must be corrected immediately. Other blood tests (CBC, electrolytes, creatinine, INR, PTT, troponin) should be obtained but must not delay treatment 1.

Blood pressure must be lowered below 185/110 mmHg before initiating thrombolysis 1. This is an absolute requirement for treatment eligibility.

Important Clinical Considerations

• Age is not a contraindication: Patients over 80 years benefit equally to younger patients, particularly when treated within 3 hours 3
• Give thrombolysis even if mechanical thrombectomy is planned - do not wait to assess response before proceeding to thrombectomy 1
• Brain imaging (CT or MRI) is mandatory before any stroke treatment 1

ST-Elevation Myocardial Infarction (STEMI)

Thrombolytic therapy for STEMI is indicated when treatment can be initiated within 12 hours of symptom onset, with maximum benefit achieved within the first hour (50% mortality reduction) 4, 5. The benefit decreases progressively with time, but treatment within 6 hours still provides substantial mortality reduction 4.

Agent Selection

Available thrombolytics include streptokinase, alteplase, reteplase, and anistreplase 4, 5. While efficacy is similar among agents, streptokinase is 10 times less expensive and causes fewer intracranial hemorrhages compared to alteplase 4. Anistreplase offers the advantage of 5-minute bolus administration versus 1-hour infusion for streptokinase or 3-hour infusion for alteplase 4.

Adjunctive Therapy

Heparin must be administered with both alteplase and streptokinase 4. Aspirin, beta-blockers, nitrates, and lidocaine are useful adjunctive therapies 4.

Pulmonary Embolism

Massive PE (Hemodynamically Unstable)

Thrombolytic therapy is strongly indicated for hemodynamically unstable PE - defined as persistent hypotension (systolic BP <90 mmHg for >15 minutes), obstructive shock, or need for cardiopulmonary resuscitation 6, 7, 8. This represents a Level B recommendation where benefits clearly outweigh bleeding risks 6.

Available FDA-approved agents include:

• Streptokinase: 250,000-unit bolus followed by 100,000 units/hour for 24 hours
• Alteplase (rt-PA): 100 mg infused over 2 hours 6

Submassive PE (Hemodynamically Stable with RV Dysfunction)

For submassive PE, evidence is insufficient to make routine recommendations for thrombolysis 6. However, the 2026 AHA/ACC guideline 8 provides updated severity classification that may guide decision-making. Consider thrombolysis in carefully selected patients with:

• Echocardiographic evidence of right ventricular dysfunction
• Elevated cardiac biomarkers (troponins, pro-BNP)
• Clinical deterioration despite anticoagulation

The Management Strategies and Prognosis of Pulmonary Embolism-3 trial demonstrated that alteplase (100 mg over 2 hours) reduced need for emergency escalation of treatment in submassive PE without fatal or cerebral bleeding 9.

Special Consideration: Patent Foramen Ovale

Screen for PFO with agitated saline bubble study in massive or submassive PE for risk stratification (Class IIb) 7. If impending paradoxical embolism is identified (thrombus trapped in PFO), surgical embolectomy may be considered over thrombolysis 7.

Absolute Contraindications to Thrombolysis (All Conditions)

• Active internal bleeding
• Known pregnancy
• Uncontrolled hypertension (>185/110 mmHg for stroke; specific thresholds vary for MI/PE)
• Aortic dissection
• Intracranial neoplasm
• History of hemorrhagic stroke 4

Critical Pitfalls to Avoid

1. Do not delay stroke thrombolysis for complete laboratory results - only glucose is mandatory 1
2. Do not withhold thrombolysis in stroke patients over 80 years - they benefit equally 3
3. Do not wait to assess thrombolysis response before mechanical thrombectomy in stroke 1
4. Do not use thrombolysis for hemodynamically stable PE without RV dysfunction - bleeding risks outweigh benefits 6, 9
5. Do not rely on negative D-dimer in high-risk PE patients - it can be falsely negative in central PE 10