STEMI Heparin Protocol
For STEMI patients, unfractionated heparin (UFH) dosing depends on the reperfusion strategy: with fibrinolytic therapy, give 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); for primary PCI, give 70-100 U/kg IV bolus (maximum 5,000 U) when used alone, or 60 U/kg (maximum 4,000 U) with glycoprotein IIb/IIIa inhibitors. 1, 2
Fibrinolytic Therapy Strategy
Initial Dosing
- Administer 60 U/kg IV bolus (maximum 4,000 U) followed immediately by 12 U/kg/hour continuous infusion (maximum 1,000 U/hour for patients >70 kg). 1, 2, 3
- This weight-adjusted approach is critical because body weight is the predominant variable affecting heparin response. 1
Target and Monitoring
- Maintain aPTT at 1.5-2.0 times control (approximately 50-70 seconds). 1, 2, 3
- Check aPTT at 3,6,12, and 24 hours after initiation, then recheck 4-6 hours after any dose adjustment. 2, 3
- Monitor platelet counts daily to detect heparin-induced thrombocytopenia. 1, 2, 3
Duration
- Continue anticoagulation for a minimum of 48 hours, preferably for the duration of hospitalization up to 8 days, or until revascularization if performed. 2, 3
Common Pitfall
Approximately 49% of fibrinolytic-treated STEMI patients receive excess heparin dosing in clinical practice, particularly low-weight patients and women, leading to increased bleeding risk. 4 Strict adherence to weight-based dosing caps is essential.
Primary PCI Strategy
Initial Dosing
- Give 70-100 U/kg IV bolus (maximum 5,000 U) when UFH is used alone. 2
- Reduce to 60 U/kg IV bolus (maximum 4,000 U) when administered with glycoprotein IIb/IIIa inhibitors. 2
Target and Monitoring
- Target activated clotting time (ACT) of 250-350 seconds when UFH is used alone. 2
- Target ACT of 200-250 seconds when used with GP IIb/IIIa inhibitors. 2, 3
Duration
- Heparin infusion is typically discontinued at the end of the primary PCI procedure. 2
No Reperfusion Therapy
Dosing
- Administer 60-70 U/kg IV bolus followed by 12-15 U/kg/hour infusion as soon as possible. 1, 2
- This higher dosing range (compared to fibrinolytic therapy) reflects the absence of concurrent thrombolytic agents. 1
Management
- Consider angiography before hospital discharge, similar to patients after successful fibrinolysis. 2
Alternative: Low-Molecular-Weight Heparin (LMWH)
Enoxaparin for Fibrinolytic Therapy
- For patients <75 years old without significant renal dysfunction (creatinine >2.5 mg/dL in men or >2.0 mg/dL in women), enoxaparin is an acceptable alternative: 30 mg IV bolus followed by 1.0 mg/kg subcutaneous every 12 hours. 1, 2, 3
- For patients ≥75 years old, omit the IV bolus and give 0.75 mg/kg subcutaneous every 12 hours. 2, 5
- Enoxaparin reduces reinfarction rates (3.2% vs 4.8% with UFH) but increases major bleeding (2.4% vs 1.8%). 6 The net clinical benefit favors enoxaparin in appropriate patients. 5
Contraindications
- Do NOT use LMWH in patients ≥75 years receiving fibrinolytic therapy (Class III recommendation). 1
- Do NOT use LMWH in patients with significant renal dysfunction (Class III recommendation). 1
Special Populations
Heparin-Induced Thrombocytopenia
- Use bivalirudin as an alternative: 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, 3
- Reduce infusion rate if PTT exceeds 75 seconds within the first 12 hours. 1
Critical Pitfalls to Avoid
- Failing to cap the bolus dose at 4,000 U (fibrinolytic) or 5,000 U (PCI) leads to excess bleeding, especially in low-weight patients. 4
- Inadequate aPTT monitoring increases both thrombotic and bleeding complications. 2
- Switching between UFH and LMWH should be avoided. 3
- Discontinuing heparin prematurely in high-risk patients (large anterior MI, atrial fibrillation, known LV thrombus) increases embolic risk. 1