What are the criteria for thrombolysis in patients with myocardial infarction (MI)?

Thrombolysis Criteria for Myocardial Infarction

Fibrinolytic therapy is indicated for STEMI patients presenting within 12 hours of symptom onset with persistent ST-segment elevation or new left bundle branch block, when primary PCI cannot be performed within 120 minutes of diagnosis and there are no contraindications. 1

Inclusion Criteria for Thrombolysis

Clinical Presentation Requirements

• Symptoms of ischemia lasting ≤12 hours from onset to treatment 1
• Persistent ST-segment elevation on ECG 1
• New or presumed new left bundle branch block 2
• Isolated ST depression in anterior leads with ST elevation in aVR (suggesting left main or multivessel disease) 2

Timing Considerations

• Primary PCI cannot be performed within 120 minutes of STEMI diagnosis 1, 2
• Initiate fibrinolysis as soon as possible, preferably in the pre-hospital setting to minimize time delays 1
• The benefit is time-dependent, with greatest mortality reduction when administered early after symptom onset 1

Absolute Contraindications to Thrombolysis

The following are absolute contraindications where thrombolysis must not be used 3:

• Active internal bleeding 3
• History of cerebrovascular accident 3
• Intracranial or intraspinal surgery or trauma within 2 months 3
• Intracranial neoplasm, arteriovenous malformation, or aneurysm 3
• Known bleeding diathesis 3
• Severe uncontrolled hypertension 3

Recommended Fibrinolytic Agents and Dosing

Agent Selection

• Use a fibrin-specific agent: tenecteplase, alteplase, or reteplase 1
• Tenecteplase is administered as a single weight-adjusted IV bolus of 30-50 mg (0.53 mg/kg bodyweight) 3
• For patients ≥75 years old, reduce tenecteplase dose by 50% to minimize stroke risk 2

Adjunctive Antithrombotic Therapy

Antiplatelet therapy (must be administered with fibrinolysis):

• Oral or IV aspirin (150-325 mg) as soon as possible 1, 3
• Clopidogrel in addition to aspirin 1

Anticoagulation (required until revascularization or up to 8 days of hospitalization) 1:

• Enoxaparin IV followed by subcutaneous (preferred over unfractionated heparin) 1
• Unfractionated heparin as weight-adjusted IV bolus followed by infusion (alternative option) 1

Post-Fibrinolysis Management Algorithm

Immediate Transfer Strategy

• Transfer all patients to a PCI-capable center immediately after fibrinolysis 1
• Patients should bypass the emergency department and go directly to the catheterization laboratory 1

Assessment of Reperfusion Success

At 60-90 minutes after fibrinolysis initiation, assess for successful reperfusion 1:

• Measure ST-segment resolution in the lead with greatest initial ST elevation 1
• <50% ST-segment resolution indicates failed fibrinolysis 1

Rescue PCI Indications

Perform rescue PCI immediately when 1:

• Failed fibrinolysis (<50% ST-segment resolution at 60-90 minutes) 1
• Hemodynamic instability at any time 1
• Electrical instability at any time 1
• Worsening ischemia at any time 1
• Cardiogenic shock (Class I for patients <75 years; Class IIa for ≥75 years) 1

Routine Angiography After Successful Fibrinolysis

• Perform angiography and PCI of the infarct-related artery between 2-24 hours after successful fibrinolysis 1
• This pharmacoinvasive approach improves outcomes compared to conservative management 4

Emergency Angiography Indications

Perform emergency angiography and PCI immediately in 1:

• Heart failure or cardiogenic shock 1
• Recurrent ischemia after initial successful fibrinolysis 1
• Evidence of reocclusion after initial successful fibrinolysis 1

Critical Pitfalls and Caveats

Bleeding Risk Management

• TNKase causes bleeding, including intracranial hemorrhage (approximately 0.9% risk) 1, 3
• Avoid intramuscular injections and nonessential patient handling for the first few hours 3
• Perform arterial and venous punctures carefully; avoid internal jugular and subclavian access 3
• If arterial puncture is necessary, use upper extremity vessels accessible to manual compression and apply pressure for ≥30 minutes 3

Thrombolysis Plus Primary PCI is Contraindicated

• Do not routinely combine fibrinolysis with planned immediate PCI as this increases mortality (6.7% vs. 4.9%), cardiogenic shock (6.3% vs. 4.8%), heart failure (12% vs. 9.2%), recurrent MI (6.1% vs. 3.7%), and repeat revascularization (6.6% vs. 3.4%) compared to PCI alone 3
• Choose either thrombolysis OR primary PCI as the primary reperfusion strategy, not both simultaneously 3

Special Populations

• Patients with mitral stenosis or atrial fibrillation have increased risk of thromboembolic events with thrombolytics 3
• Monitor for reperfusion arrhythmias (sinus bradycardia, accelerated idioventricular rhythm, ventricular tachycardia) and have anti-arrhythmic therapy available 3
• Hypersensitivity reactions (anaphylaxis, angioedema, urticaria) can occur; monitor during and for several hours after infusion 3

When Thrombolysis Should NOT Be Used

• In asymptomatic patients >48 hours after STEMI onset, routine PCI of an occluded infarct-related artery is not indicated 1
• When primary PCI can be performed within 120 minutes, it is the preferred reperfusion strategy over fibrinolysis 1, 2