What is the recommended heparin (anticoagulant) bolus and infusion rate for patients with ST-Elevation Myocardial Infarction (STEMI)?

Heparin Dosing for STEMI

For patients with ST-Elevation Myocardial Infarction (STEMI), unfractionated heparin should be administered as a weight-based bolus of 60 U/kg (maximum 4000 U) followed by an initial infusion of 12 U/kg per hour (maximum 1000 U/hour), with dose adjustments to maintain activated partial thromboplastin time (aPTT) at 1.5 to 2.0 times control (approximately 50-70 seconds). 1, 2

Dosing Based on Treatment Strategy

Primary PCI

• Bolus dose: 100 U/kg if no GPIIb/IIIa inhibitors are used; 60 U/kg if GPIIb/IIIa inhibitors are used 1
• Target ACT: 250-350 seconds (200-250 seconds if GPIIb/IIIa antagonists are used) 1
• Monitoring: Procedure performed under activated clotting time (ACT) guidance 1

With Fibrinolytic Therapy

• Fibrin-specific agents (alteplase, reteplase, tenecteplase):

  • Bolus: 60 U/kg IV (maximum 4000 U)
  • Infusion: 12 U/kg/hour (maximum 1000 U/hour)
  • Target aPTT: 1.5-2.0 times control (50-70 seconds) 1, 2

• Non-selective fibrinolytic agents (streptokinase, anistreplase, urokinase):

  • Indicated for patients at high risk for systemic emboli (large or anterior MI, atrial fibrillation, previous embolus, or known LV thrombus) 1
  • May be reasonable for all patients receiving streptokinase (Class IIb recommendation) 1

Without Reperfusion Therapy

• Bolus: 60 U/kg IV (maximum 4000 U)
• Infusion: 12 U/kg/hour (maximum 1000 U/hour) 1
• Target aPTT: 50-70 seconds 1

Monitoring and Dose Adjustments

• First aPTT check: 4-6 hours after starting infusion 2
• Subsequent monitoring: Every 6 hours until therapeutic, then daily 2
• Platelet counts should be monitored daily to detect heparin-induced thrombocytopenia 1, 2

aPTT-Based Dose Adjustments

aPTT (seconds)	Action
<35 (<1.2× control)	Bolus 80 U/kg; increase infusion by 4 U/kg/h
35-45 (1.2-1.5× control)	Bolus 40 U/kg; increase infusion by 2 U/kg/h
46-70 (1.5-2.3× control)	No change (therapeutic range)
71-90 (2.3-3.0× control)	Decrease infusion by 2 U/kg/h
>90 (>3.0× control)	Stop infusion for 1 hour, then decrease by 3 U/kg/h

Special Considerations

High Bleeding Risk Patients

• Elderly patients (>75 years): Consider lower doses and careful monitoring 2
• Patients with renal failure: Unfractionated heparin is preferred over LMWH 2

Alternative Anticoagulants

• Bivalirudin: Consider in patients with heparin-induced thrombocytopenia

  • Dosing: 0.75 mg/kg IV bolus followed by infusion of 1.75 mg/kg/h during PCI 1, 2

• Low Molecular Weight Heparin (LMWH):

  • May be considered for patients <75 years without significant renal dysfunction receiving fibrinolytic therapy 1
  • Not recommended for patients >75 years receiving fibrinolytic therapy 1
  • Not recommended for patients with significant renal dysfunction (serum creatinine >2.5 mg/dL in men or >2.0 mg/dL in women) 1

Common Pitfalls to Avoid

1. Excess dosing: Nearly half of fibrinolytic-treated STEMI patients receive excess heparin doses, which increases bleeding risk 3

   • Particularly common in patients with low body weight and women

2. Failure to use weight-based dosing: Can lead to under or overdosing 2

3. Not adjusting for maximum dose limits: Exceeding 4000 U bolus or 1000 U/hour infusion can lead to adverse outcomes 2

4. Inadequate monitoring: Failure to check aPTT or platelet counts can lead to subtherapeutic or supratherapeutic anticoagulation 2

5. Using LMWH inappropriately: Avoid in elderly patients (>75 years) or those with significant renal dysfunction who are receiving fibrinolytic therapy 1, 2

The weight-adjusted heparin dosing regimen has been shown to be superior in achieving early aPTTs within the target range and reducing the need for infusion changes 4, which is critical for reducing bleeding complications while maintaining efficacy in preventing thrombotic events.