When to Start Heparin Drip After TNK
Start unfractionated heparin (UFH) infusion immediately after completing the TNK bolus, with a 60 U/kg IV bolus (maximum 4000 U) followed by 12 U/kg/h infusion (maximum 1000 U/h), targeting an aPTT of 50-70 seconds or 1.5-2.0 times control. 1, 2, 3
Dosing Algorithm
The standard approach for heparin after fibrinolytic therapy follows this sequence:
- Initial bolus: 60 U/kg IV (maximum 4000 U)
- Continuous infusion: 12 U/kg/h (maximum 1000 U/h)
- Target aPTT: 50-70 seconds (1.5-2.0 times control)
- Duration: 24-48 hours or until revascularization 1, 2, 3
Monitor aPTT at 3,6,12, and 24 hours after starting treatment to ensure therapeutic anticoagulation 1, 3.
Timing Considerations
The heparin infusion should begin immediately following TNK administration—there is no waiting period. 1, 2 The 2013 ACC/AHA STEMI guidelines explicitly state that UFH should be started as adjunctive therapy to support fibrinolytic reperfusion, with the bolus and infusion initiated right after the thrombolytic 2.
Alternative Anticoagulant Options
If UFH is not suitable, consider these alternatives with fibrinolytic therapy:
Enoxaparin (preferred over UFH in some guidelines):
- Age <75 years: 30 mg IV bolus, then 15 minutes later start 1 mg/kg SC every 12 hours (maximum 100 mg for first two doses)
- Age ≥75 years: No IV bolus; start with 0.75 mg/kg SC every 12 hours (maximum 75 mg for first two doses)
- Creatinine clearance <30 mL/min: 1 mg/kg SC every 24 hours
- Duration: Up to 8 days or until revascularization 1, 2
Fondaparinux:
- 2.5 mg IV bolus followed by 2.5 mg SC once daily
- Duration: Up to 8 days or hospital discharge
- Contraindicated if creatinine clearance <30 mL/min 1, 2
Critical Caveats
Do not delay heparin for 24 hours after TNK—this is a common misconception. The 24-hour restriction applies to antiplatelet agents other than aspirin (like clopidogrel loading doses >300 mg in elderly patients), not to heparin 1, 2. Heparin is essential for maintaining vessel patency after thrombolysis and preventing reocclusion 3.
If the patient proceeds to PCI after fibrinolysis: Adjust heparin dosing based on timing of last dose and whether GP IIb/IIIa inhibitors are used. For patients already on UFH, give additional boluses as needed during PCI (50-60 U/kg if using GP IIb/IIIa inhibitors; 70-100 U/kg without) 1, 2.
Monitor for heparin-induced thrombocytopenia (HIT): If heparin continues beyond 5 days, platelet counts must be monitored due to HIT risk 4.
The evidence strongly supports immediate anticoagulation with heparin following fibrinolytic therapy to prevent reocclusion and improve outcomes in STEMI patients 1, 2, 3.