From the Guidelines
The recommended loading dose of unfractionated heparin for NSTEMI is an initial loading dose of 60 IU/kg (maximum 4000 IU). This dose is administered intravenously and is followed by an initial infusion of 12 IU/kg per hour (maximum 1000 IU/h) adjusted per activated partial thromboplastin time to maintain therapeutic anticoagulation according to the specific hospital protocol, as recommended by the 2014 AHA/ACC guideline for the management of patients with non-ST-elevation acute coronary syndromes 1. The use of heparin in this context is aimed at preventing further clot formation in the coronary arteries by enhancing the ability of antithrombin III to inactivate several coagulation factors, particularly thrombin and factor Xa. Key considerations for heparin therapy include:
- Monitoring activated partial thromboplastin time (aPTT) to adjust the heparin infusion and maintain therapeutic anticoagulation
- Continuing heparin for 48 hours or until PCI is performed, as part of the management strategy for NSTEMI patients
- Being aware of the potential for bleeding complications and taking appropriate precautions to minimize this risk. The guideline recommendations are based on the best available evidence, including studies that have demonstrated the efficacy and safety of heparin in the management of NSTEMI, such as those cited in the 2014 AHA/ACC guideline 1.
From the Research
Unfractionated Heparin Dosing in NSTEMI
- The loading dose of unfractionated heparin in Non-ST-Elevation Myocardial Infarction (NSTEMI) is typically an initial bolus of 60 to 70 U/kg (maximum, 5000 U) 2.
- This is followed by a 12- to 15-U/kg/h infusion, with the goal of achieving an activated partial thromboplastin time of 50 to 70 seconds 2.
- Excess weight-adjusted dosing, defined as >70 U/kg for bolus or >15 U/kg per hour for infusion, has been associated with an increased risk of major bleeding in patients with NSTEMI 3.
- Factors such as age and female sex have been identified as being strongly associated with excess weight-adjusted dosing 3.
Specific Dosing Recommendations
- An initial heparin bolus of 60 U/kg (maximum, 4000 U) followed by a 12-U/kg/h infusion (maximum 1000 U/h) is recommended for ST-elevation myocardial infarction, but a higher bolus dose of 60 to 70 U/kg (maximum, 5000 U) may be used for NSTEMI 2.
- The use of weight-based dosing nomograms, with capped initial bolus and maintenance doses, may lead to inadequate anticoagulation in obese patients 4.
- Larger absolute doses (U/h) of unfractionated heparin, but reduced uncapped total body weight-based doses (U/kg/h), may be necessary as patient weight increases 4.