What are the AHA (American Heart Association) guidelines for thrombolysis in acute myocardial infarction (MI)?

AHA Guidelines for Thrombolysis in Acute Myocardial Infarction

Thrombolytic therapy is recommended for patients with ST-segment elevation myocardial infarction (STEMI) or new left bundle branch block (LBBB) who present within 12 hours of symptom onset and do not have contraindications, especially when primary percutaneous coronary intervention (PCI) cannot be performed within 120 minutes of first medical contact. 1, 2

Patient Selection for Thrombolytic Therapy

Indications

• ST-segment elevation ≥1 mm in contiguous leads on ECG
• New or presumably new LBBB
• Presentation within 12 hours of symptom onset
• Absence of contraindications

Contraindications

Absolute contraindications include:

• Previous hemorrhagic stroke at any time
• Other strokes or cerebrovascular events within 1 year
• Known intracranial neoplasm
• Active internal bleeding
• Suspected aortic dissection 3

Relative contraindications include:

• Severe uncontrolled hypertension (BP >180/110 mmHg)
• History of prior cerebrovascular accident
• Current use of anticoagulants in therapeutic doses (INR >2-3)
• Recent trauma or major surgery (within 2-4 weeks)
• Noncompressible vascular punctures
• Recent internal bleeding (within 2-4 weeks)
• Pregnancy
• Active peptic ulcer 1

Time-Dependent Benefits

The benefit of thrombolytic therapy is highly time-dependent:

• Greatest benefit when administered within 1 hour of symptom onset (35 lives saved per 1000 patients treated)
• Significant benefit when given within 6 hours (21% reduction in 35-day mortality)
• Definite but reduced benefit when given between 7-12 hours (16 lives saved per 1000 patients treated) 1

Initial Management Protocol

1. Immediate assessment (within 10 minutes of arrival)

   • 12-lead ECG
   • Vital signs
   • Brief targeted history for indications/contraindications

2. Initial interventions

   • Oxygen by nasal prongs
   • Sublingual nitroglycerin (unless SBP <90 mmHg or HR <50 or >100 bpm)
   • Adequate analgesia (morphine sulfate or meperidine)
   • Aspirin 160-325 mg orally (chew and swallow) 1, 2

3. Door-to-needle time goal: <30 minutes 1

Thrombolytic Regimens

Accelerated Alteplase (tPA) Regimen

For patients >67 kg:

• 15 mg IV bolus
• 50 mg over first 30 minutes
• 35 mg over next 60 minutes

For patients ≤67 kg:

• 15 mg IV bolus
• 0.75 mg/kg over first 30 minutes
• 0.50 mg/kg over next 60 minutes 3

Streptokinase Regimen

• 1.5 million units IV over 60 minutes 1

Adjunctive Therapies

• Aspirin: 160-325 mg initially, then 75-100 mg daily indefinitely 2
• Anticoagulation: Heparin is recommended with fibrin-specific agents (alteplase)
• P2Y12 inhibitors: Ticagrelor or prasugrel preferred over clopidogrel 2
• Beta-blockers: Indicated for patients with heart failure and/or LVEF <40% 2
• ACE inhibitors: Start within 24 hours for patients with heart failure, LV dysfunction, diabetes, or anterior infarct 2
• Statins: High-intensity statin therapy started as early as possible 2

Primary PCI vs. Thrombolysis

Primary PCI is preferred over thrombolysis when:

• It can be performed in a timely fashion (within 120 minutes of first medical contact)
• Performed by skilled operators in high-volume centers
• Supported by experienced personnel with access to emergency CABG 1, 2

Special Considerations

Elderly Patients

• Patients >75 years have increased risk of intracranial hemorrhage with thrombolytic therapy
• However, elderly patients still derive mortality benefit and should not be excluded based on age alone 3

Risk Factors for Intracranial Hemorrhage

• Age >65 years
• Body weight <70 kg
• Hypertension on admission
• Use of tissue plasminogen activator 1

Post-Thrombolysis Management

• Continuous ECG monitoring
• Serial cardiac biomarkers
• Echocardiography during hospital stay to assess ventricular function
• Transfer to a PCI-capable center for angiography within 2-24 hours after successful fibrinolysis 2

Common Pitfalls to Avoid

1. Delayed administration - Every 30-minute delay reduces the benefit of thrombolytic therapy
2. Inappropriate contraindication assessment - Overly cautious interpretation of relative contraindications can deny potentially life-saving therapy
3. Failure to recognize reperfusion failure - Requires rescue PCI
4. Inadequate adjunctive therapy - Aspirin and anticoagulation are essential components
5. Missing high-risk patients - Elderly and those with anterior MI derive substantial benefit despite higher bleeding risk

Thrombolytic therapy remains a critical reperfusion strategy for STEMI patients, particularly when timely access to primary PCI is not available, with significant reductions in mortality when administered promptly after symptom onset.