Heparin Infusion Protocol for Acute Coronary Syndrome
For patients with Acute Coronary Syndrome (ACS), the recommended unfractionated heparin (UFH) protocol is an initial loading dose of 60 IU/kg (maximum 4000 IU), followed by an initial infusion of 12 IU/kg per hour (maximum 1000 IU/h) adjusted to maintain an activated partial thromboplastin time (aPTT) of 60-80 seconds. 1
Initial Dosing Based on ACS Type
For Medical Management (Non-PCI Approach):
- Initial bolus: 60 IU/kg (maximum 4000 IU)
- Initial infusion: 12 IU/kg/hour (maximum 1000 IU/hour)
- Target aPTT: 60-80 seconds
- Monitoring: Check aPTT at baseline, 6 hours after initiation, and then every 6 hours until stable
For PCI Support:
- If patient received prior anticoagulant therapy: Additional UFH as needed to achieve an activated clotting time (ACT) of 250-300 seconds
- If no prior anticoagulant therapy: 70-100 U/kg initial bolus to achieve target ACT of 250-300 seconds 1
For Fibrinolytic Therapy:
- Initial bolus: 60 IU/kg (maximum 4000 IU)
- Initial infusion: 12 IU/kg/hour (maximum 1000 IU/hour)
- Target aPTT: 60-80 seconds 1
Monitoring and Dose Adjustment
The heparin dose should be adjusted according to aPTT results using a standardized protocol:
| aPTT (seconds) | Bolus | Hold Infusion | Rate Change | Repeat aPTT |
|---|---|---|---|---|
| <50 | 40 IU/kg | No | Increase by 2 IU/kg/h | 6 hours |
| 50-59 | No | No | Increase by 1 IU/kg/h | 6 hours |
| 60-80 | No | No | No change | Next day |
| 81-100 | No | No | Decrease by 1 IU/kg/h | 6 hours |
| >100 | No | 1 hour | Decrease by 2 IU/kg/h | 6 hours |
Duration of Therapy
- Continue heparin until revascularization (CABG or PCI) is performed 1
- Premature discontinuation of anticoagulation is associated with a transient rebound increase in thrombin activity and activated protein C, with the greatest risk for reinfarction occurring in the first 4-8 hours after discontinuation 1
- If no revascularization is planned, continue for 48 hours or until clinically stable 1
Alternative Anticoagulants for ACS
While UFH remains a standard option, other anticoagulants may be considered:
- Enoxaparin: 1 mg/kg subcutaneous every 12 hours (reduce to 1 mg/kg daily if CrCl <30 mL/min)
- Bivalirudin: 0.75 mg/kg bolus, followed by 1.75 mg/kg/h infusion during PCI
- Fondaparinux: 2.5 mg subcutaneous daily (contraindicated if CrCl <30 mL/min and should not be used to support PCI due to risk of catheter thrombosis) 1
Important Considerations and Pitfalls
- Weight-based dosing is critical: Fixed, non-weight-adjusted dosing leads to overanticoagulation, particularly in patients with lower body weight, elderly patients, and women 2, 3
- Bleeding risk: Excess heparin dosing (>70 U/kg bolus or >15 U/kg/h infusion) is associated with increased bleeding risk 3
- Early therapeutic levels: The lower-dose weight-adjusted regimen (60 U/kg bolus, 12 U/kg/h infusion) achieves target aPTT more consistently and requires fewer dose adjustments than higher-dose regimens 2
- Monitor for thrombocytopenia: Daily platelet counts should be performed to monitor for heparin-induced thrombocytopenia 1
- Avoid crossover: Switching between UFH and LMWH is not recommended 1
The weight-adjusted heparin protocol has been shown to be superior to fixed dosing in achieving therapeutic anticoagulation more rapidly and consistently, which is critical for reducing recurrent ischemic events in ACS patients 4, 2.