What are the recommendations for heparin (unfractionated heparin) drip in patients with myocardial infarction (MI)?

Recommendations for Heparin Drip in Myocardial Infarction

For patients with ST-elevation myocardial infarction (STEMI), unfractionated heparin (UFH) should be administered as a weight-adjusted IV bolus of 60 U/kg (maximum 4000 U) followed by an initial infusion of 12 U/kg/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 to 70 seconds). 1, 2

Dosing Recommendations by Treatment Strategy

For Patients Receiving Fibrin-Specific Thrombolytics (alteplase, reteplase, tenecteplase)

• Initial bolus: 60 U/kg (maximum 4000 U) 1
• Initial infusion: 12 U/kg/hour (maximum 1000 U/hour) 1
• Target aPTT: 1.5-2.0 times control (approximately 50-70 seconds) 1, 2
• Duration: Continue anticoagulation until revascularization (if performed) or for the duration of hospital stay up to 8 days 1

For Patients Undergoing Primary PCI

• Initial bolus: 60-70 U/kg IV 1
• Initial infusion: 12-15 U/kg/hour 1
• Additional boluses may be needed during PCI to maintain therapeutic anticoagulation 1
• Monitor ACT during procedure (target 250-300 seconds with HemoTec device or 300-350 seconds with Hemochron device if no GP IIb/IIIa inhibitors are used) 1

For Patients Not Receiving Reperfusion Therapy

• Weight-adjusted dosing as above: 60-70 U/kg IV bolus followed by 12-15 U/kg/hour infusion 1
• Consider subcutaneous heparin (7500 U twice daily) for patients not at high risk for systemic embolism 1

Monitoring and Adjustment

• Check aPTT 4-6 hours after initiation of therapy and after any dose change 1, 2
• Monitor platelet counts daily in patients receiving UFH 1, 3
• Monitor for signs of bleeding and hematoma formation 2
• Adjust dosing based on aPTT results to maintain therapeutic range (50-70 seconds) 1, 2

Alternative Anticoagulants

• Enoxaparin is superior to UFH for patients receiving fibrinolytic therapy (30 mg IV bolus followed by 1 mg/kg SC every 12 hours) 4
• For patients ≥75 years old receiving enoxaparin: omit initial bolus and start with 0.75 mg/kg SC every 12 hours 1
• For patients with renal dysfunction (CrCl <30 mL/min): reduce enoxaparin to 1 mg/kg once daily 1
• Fondaparinux (2.5 mg IV followed by 2.5 mg SC daily) may be considered for patients with serum creatinine <3.0 mg/dL 1
• Bivalirudin may be considered for patients with heparin-induced thrombocytopenia 1

Important Considerations and Caveats

• UFH has a short half-life (approximately 1.5 hours) and immediate anticoagulant effect when given intravenously 3
• Weight-based dosing is critical as the effect of a given dose of heparin is primarily mediated by patient weight 1
• Risk of heparin-induced thrombocytopenia increases with duration of therapy; monitor platelet counts regularly 3
• When transitioning from heparin to warfarin, continue full heparin therapy until INR reaches therapeutic range 2
• For patients undergoing CABG, heparin should not be discontinued prior to surgery 1
• Avoid intramuscular injections during heparin therapy to prevent hematoma formation 2

Special Populations

Pediatric Patients

• Initial dose: 75-100 U/kg IV bolus over 10 minutes 2
• Maintenance:
  • Infants: 25-30 U/kg/hour (infants <2 months have highest requirements) 2
  • Children >1 year: 18-20 U/kg/hour 2
• Target aPTT: 60-85 seconds 2

Elderly Patients

• Consider lower initial doses and more frequent monitoring due to increased bleeding risk 1
• LMWHs should not be used as an alternative to UFH in patients over 75 years receiving fibrinolytic therapy 1

The evidence strongly supports the use of anticoagulation with heparin in patients with STEMI, with dosing regimens tailored to the reperfusion strategy. The most recent guidelines emphasize weight-adjusted dosing to achieve optimal anticoagulation while minimizing bleeding complications.