What is the recommended heparin (unfractionated heparin) dosing for a patient with ST-Elevation Myocardial Infarction (STEMI)?

Heparin Dosing in STEMI

Dosing Strategy Based on Reperfusion Approach

The recommended unfractionated heparin (UFH) dose for STEMI depends critically on whether the patient receives fibrinolytic therapy or primary PCI, with weight-adjusted dosing essential to minimize bleeding while maintaining therapeutic anticoagulation.

For Patients Receiving Fibrinolytic Therapy

Administer UFH as a 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 (approximately 50-70 seconds). 1, 2, 3, 4

• This dosing applies specifically to fibrin-specific agents (alteplase, reteplase, tenecteplase) 1
• The maximum caps are critical: patients >70 kg should receive no more than 4,000 U bolus and 1,000 U/hour infusion 1, 2
• Continue anticoagulation for minimum 48 hours, preferably for duration of hospitalization up to 8 days, or until revascularization 2, 3, 4

Monitoring protocol: Check aPTT at 3,6,12, and 24 hours after initiation, then recheck 4-6 hours after any dose adjustment 2, 3, 4

For Patients Undergoing Primary PCI

Administer UFH as a 70-100 U/kg IV bolus (maximum 5,000 U) when used alone, or reduce to 60 U/kg IV bolus (maximum 4,000 U) when co-administered with glycoprotein IIb/IIIa inhibitors. 2, 3

• Target ACT of 250-350 seconds when UFH used alone 2, 3
• Target ACT of 200-250 seconds when used with GP IIb/IIIa inhibitors 2, 3, 4
• Heparin infusion typically discontinued at end of PCI procedure 3

For Patients NOT Receiving Reperfusion Therapy

Administer UFH as a 60-70 U/kg IV bolus followed by 12-15 U/kg/hour infusion. 1, 3

• This higher dosing range reflects absence of concurrent fibrinolytic or antiplatelet therapy 1

Critical Safety Considerations

Weight-Adjusted Dosing is Mandatory

Failure to use weight-adjusted dosing results in marked overanticoagulation and increased bleeding risk. 5, 6

• Nearly 50% of patients in contemporary practice receive excess heparin doses when weight-adjustment is not used 5
• Excess dosing (>60 U/kg bolus or >12 U/kg/hour infusion) significantly increases major bleeding (19.2% vs 12.4%) and transfusion requirements (13.5% vs 4.7%) 5
• Low body weight and female sex are strongest predictors of excess dosing 5

Mandatory Monitoring

Daily platelet count monitoring is required to detect heparin-induced thrombocytopenia. 1, 2, 3

• More frequent aPTT monitoring and full weight adjustment decreases non-cerebral bleeding complications 3

Alternative: Enoxaparin (LMWH)

For patients <75 years without significant renal dysfunction (creatinine >2.5 mg/dL men, >2.0 mg/dL women), enoxaparin represents an acceptable alternative: 30 mg IV bolus followed by 1.0 mg/kg subcutaneous every 12 hours. 1, 2, 3, 4

• Class III contraindications (do NOT use): Patients ≥75 years receiving fibrinolytic therapy, or patients with significant renal dysfunction 1, 2, 3
• Never switch between UFH and LMWH during acute management 4

Special Population: Heparin-Induced Thrombocytopenia

For patients with known HIT, use bivalirudin: 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, 2, 4

• Reduce infusion rate if PTT exceeds 75 seconds within first 12 hours 1

Common Pitfalls to Avoid

• Failing to cap bolus doses at maximum thresholds leads to excess anticoagulation 2, 3, 5
• Not adjusting dose when adding GP IIb/IIIa inhibitors increases bleeding risk 3, 4
• Inadequate aPTT monitoring prevents timely dose adjustments 2, 3
• Premature discontinuation in high-risk patients (large anterior MI, atrial fibrillation, known LV thrombus) increases thrombotic complications 1, 2, 3
• Using LMWH in elderly (≥75 years) or renal dysfunction patients receiving fibrinolytics is contraindicated 1, 2, 3