What is the recommended heparin regimen after Tenecteplase (TNK) for ST-Elevation Myocardial Infarction (STEMI)?

Heparin Regimen After TNK for STEMI

Unfractionated heparin (UFH) should be administered as a 60 U/kg IV bolus (maximum 4,000 U) followed by 12 U/kg/hour infusion (maximum 1,000 U/hour), adjusted to maintain aPTT at 1.5-2.0 times control (50-70 seconds), and continued for at least 48 hours up to 8 days or until revascularization. 1, 2, 3

Standard UFH Dosing Protocol

For patients receiving TNK (tenecteplase), the ACC/AHA guidelines establish UFH as the Class I recommendation with the following weight-based regimen: 1

• Initial bolus: 60 U/kg IV (maximum 4,000 U) 1, 2
• Maintenance infusion: 12 U/kg/hour (maximum 1,000 U/hour for patients >70 kg) 1, 2
• Target aPTT: 1.5-2.0 times control (approximately 50-70 seconds) 1, 3

Monitoring Requirements

aPTT monitoring is essential and should be performed at specific intervals: 2, 3

• Check aPTT at 3,6,12, and 24 hours after initiation 2
• Recheck 4-6 hours after any dose adjustment 3
• Daily platelet count monitoring to detect heparin-induced thrombocytopenia 1, 2

More frequent aPTT monitoring and full weight adjustment may decrease non-cerebral bleeding complications. 2

Duration of Therapy

Anticoagulation duration depends on the clinical pathway: 2, 3

• Minimum duration: 48 hours 2
• Preferred duration: Throughout index hospitalization, up to 8 days 2, 3
• If revascularization performed: Continue until procedure 2, 3

Enoxaparin as Alternative

Enoxaparin may be considered as an acceptable alternative to UFH in select patients, but with important restrictions: 1

Appropriate Candidates for Enoxaparin:

• Age <75 years 1
• Normal renal function (serum creatinine ≤2.5 mg/dL in men or ≤2.0 mg/dL in women) 1
• Dosing: 30 mg IV bolus followed by 1.0 mg/kg subcutaneous every 12 hours 1

Contraindications for Enoxaparin (Class III):

• Age ≥75 years 1, 3
• Significant renal dysfunction 1

Research evidence from ENTIRE-TIMI 23 demonstrated that enoxaparin with full-dose TNK achieved similar TIMI 3 flow rates as UFH (51% vs 50%) but significantly reduced death/recurrent MI at 30 days (4.4% vs 15.9%, P=0.005) with comparable major hemorrhage rates. 4 The ExTRACT-TIMI 25 trial further confirmed enoxaparin superiority over UFH in fibrin-specific lytic-treated STEMI patients, reducing death or nonfatal MI from 12.0% to 9.8% (P<0.001). 5

Dose Modifications with GP IIb/IIIa Inhibitors

If glycoprotein IIb/IIIa inhibitors are planned, reduce the UFH bolus: 1

• Bolus: 50-70 U/kg (instead of 60 U/kg) 1
• Target ACT during PCI: 200-250 seconds (vs 250-300 seconds without GP IIb/IIIa) 1, 2

Common Pitfalls to Avoid

Critical errors that compromise outcomes: 2

1. Failing to use weight-based dosing - The predominant variable mediating heparin effect is patient weight 1, 3
2. Inadequate aPTT monitoring - Subtherapeutic anticoagulation increases reocclusion risk 2, 3
3. Premature discontinuation - Stopping heparin before 48 hours or before revascularization increases ischemic events 2
4. Not adjusting dose with GP IIb/IIIa inhibitors - Full-dose UFH with these agents increases bleeding 2
5. Using enoxaparin in elderly (≥75 years) - This is a Class III (Harm) recommendation 1, 3

Special Populations

For patients with heparin-induced thrombocytopenia, bivalirudin represents an alternative: 1, 3

• Dosing: 0.25 mg/kg bolus followed by 0.5 mg/kg/hour for 12 hours, then 0.25 mg/kg/hour for 36 hours 1
• Reduce infusion if PTT >75 seconds within first 12 hours 1

The European Society of Cardiology guidelines emphasize that UFH remains the standard therapy for STEMI patients undergoing primary PCI, and switching between UFH and LMWH should be avoided. 1