Heparin Dosing for NSTEMI
For patients with NSTEMI, administer unfractionated heparin (UFH) as an initial IV bolus of 60 U/kg (maximum 4,000 U) followed by an infusion of 12 U/kg/hour (maximum 1,000 U/hour), adjusted to maintain aPTT at 1.5-2.0 times control (approximately 50-70 seconds), and continue for 48 hours or until PCI is performed. 1, 2
Initial Dosing Algorithm
Weight-based dosing is mandatory to avoid the excessive bleeding seen with fixed-dose regimens, particularly in elderly patients and women who tend to receive relative overdoses with standard 5,000 U boluses. 3
- Bolus dose: 60 U/kg IV (maximum 4,000 U) 1, 2
- Infusion rate: 12 U/kg/hour IV (maximum 1,000 U/hour) 1, 2
- Target aPTT: 1.5-2.0 times control (approximately 50-70 seconds) 1, 2
- Duration: Continue for 48 hours or until PCI is performed 1, 2
The maximum caps (4,000 U bolus and 1,000 U/hour infusion) apply to patients weighing >70 kg to prevent excessive anticoagulation. 1, 4
Monitoring and Dose Adjustment
- Check aPTT 6 hours after initiating therapy and 6 hours after any dose adjustment 2
- Adjust infusion rate based on aPTT results to maintain therapeutic range 1, 2
- Monitor platelet counts daily to detect heparin-induced thrombocytopenia 1
- Critical pitfall: Excess dosing (>70 U/kg bolus or >15 U/kg/hour infusion) significantly increases major bleeding risk, with a dose-dependent relationship above these thresholds 3
Dosing During PCI
The target activated clotting time (ACT) depends on whether GP IIb/IIIa inhibitors are used:
- With GP IIb/IIIa inhibitors: Target ACT of 200-250 seconds with 50 U/kg UFH bolus 1, 2
- Without GP IIb/IIIa inhibitors: Target ACT of 250-300 seconds (HemoTec device) or 300-350 seconds (Hemochron device) with 60 U/kg UFH bolus 1, 2
Alternative Anticoagulation Options
While UFH is a Class I recommendation, alternative agents may be preferred in specific circumstances:
Enoxaparin (Preferred Alternative)
- Dosing: 1 mg/kg subcutaneously every 12 hours 1, 2
- Renal adjustment: Reduce to 1 mg/kg once daily if CrCl <30 mL/min 1, 5
- Advantages: No aPTT monitoring required, more predictable anticoagulation, may reduce reinfarction rates 6, 7
- PCI timing: If PCI occurs within 8 hours of last subcutaneous dose, no additional anticoagulation needed; if 8-12 hours, give 0.3 mg/kg IV bolus 1
Bivalirudin
- Dosing: 0.1 mg/kg IV bolus followed by 0.25 mg/kg/hour infusion 1, 2
- Use: Only for patients managed with early invasive strategy 1
- Advantage: Lower bleeding risk when used with provisional (not routine) GP IIb/IIIa inhibitors 1
Fondaparinux
- Dosing: 2.5 mg subcutaneously once daily 1, 2
- Critical requirement: Must add UFH or bivalirudin during PCI due to catheter thrombosis risk 1, 2
Critical Pitfalls to Avoid
Never switch between anticoagulants during the same admission - this dramatically increases bleeding risk without improving outcomes. 1, 2, 5, 8 If a patient arrives on enoxaparin, continue enoxaparin; do not add UFH to "bridge" to PCI.
Do not use fixed doses - the most common error is administering standard 5,000 U boluses and 1,000 U/hour infusions regardless of weight, which causes excess dosing in 35% of patients, particularly elderly women. 3
Do not continue UFH beyond 48 hours unless there are ongoing indications for anticoagulation (such as large LV thrombus, atrial fibrillation, or extensive residual dissection after PCI). 2
Avoid post-procedural heparin infusions when GP IIb/IIIa inhibitors are used, as this increases bleeding without benefit. 1
Special Populations
Renal Insufficiency
UFH is preferred over enoxaparin in severe renal impairment (CrCl <30 mL/min) because it does not require dose adjustment and allows better control through aPTT monitoring. 2, 5 If enoxaparin is used, reduce to once-daily dosing. 1, 5
Elderly Patients (≥75 years)
Use strict weight-based dosing as elderly patients are at highest risk for excess dosing and bleeding complications. 3 Consider enoxaparin as an alternative, but omit the 30 mg IV bolus used in younger patients. 5, 8