What anticoagulation regimen is recommended for a patient presenting with ST-Elevation Myocardial Infarction (STEMI), considering factors such as renal function and bleeding risk?

Anticoagulation for STEMI

All STEMI patients require anticoagulation therapy as adjunctive treatment to reperfusion, with the specific regimen determined by whether the patient receives primary PCI or fibrinolytic therapy, their age, and renal function. 1

Primary PCI Strategy

For patients undergoing primary PCI, unfractionated heparin (UFH) remains the standard anticoagulant with weight-based dosing critical for optimal outcomes. 1

UFH Dosing for Primary PCI

• Administer 60-70 U/kg IV bolus followed by 12-15 U/kg/hour infusion when UFH is used without fibrinolytics 1
• Target aPTT of 1.5-2.0 times control (approximately 50-70 seconds) 1
• Monitor platelet counts daily to detect heparin-induced thrombocytopenia 1

Alternative: Bivalirudin

• Consider bivalirudin for patients with high bleeding risk or known heparin-induced thrombocytopenia 1
• Dosing: 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
• Reduce infusion rate if PTT exceeds 75 seconds within first 12 hours 1

Critical Pitfall: Weight-Based Dosing

Fixed-dose heparin results in subtherapeutic anticoagulation in 82% of patients, particularly those with higher body weight. 2 A prospective study of 1,533 STEMI patients receiving fixed 5,000 IU boluses found only 14% achieved therapeutic ACT levels, with increased weight being the only independent predictor of inadequate anticoagulation 2. This underscores the absolute necessity of weight-adjusted dosing.

Fibrinolytic Therapy Strategy

Patients receiving fibrinolytic therapy require anticoagulation for minimum 48 hours and preferably for the duration of hospitalization, up to 8 days or until revascularization. 1

First-Line: Enoxaparin (Preferred over UFH)

Enoxaparin is superior to UFH when used with fibrinolytic therapy, showing lower rates of death/recurrent MI (4.4% vs 15.9%, p=0.005) with similar bleeding risk. 3

Age-Based Dosing for Enoxaparin:

• Age <75 years: 30 mg IV bolus, followed 15 minutes later by 1 mg/kg subcutaneously every 12 hours (maximum 100 mg for first 2 doses) 1
• Age ≥75 years: NO bolus, 0.75 mg/kg subcutaneously every 12 hours (maximum 75 mg for first 2 doses) 1
• Duration: Until hospital discharge, up to 8 days or until revascularization 1

Renal Adjustment for Enoxaparin:

If creatinine clearance <30 mL/min: 1 mg/kg subcutaneously every 24 hours regardless of age 1

Alternative: UFH with Fibrin-Specific Agents

For patients receiving alteplase, reteplase, or tenecteplase:

• 60 U/kg bolus (maximum 4,000 U) followed by 12 U/kg/hour infusion (maximum 1,000 U/hour initially) 1
• Adjust to maintain aPTT 1.5-2.0 times control 1

Critical Contraindications for LMWH:

LMWH should NOT be used in the following situations: 1

• Age >75 years receiving fibrinolytic therapy (Class III recommendation) 1
• Significant renal dysfunction (serum creatinine >2.5 mg/dL in men or >2.0 mg/dL in women) 1

The 2004 ACC/AHA guidelines explicitly state these as Class III (harmful) recommendations, meaning LMWH should be avoided in these populations when used with fibrinolytics 1. However, the 2013 guidelines provide renal dosing adjustments for enoxaparin, suggesting it can be used cautiously with appropriate dose reduction 1.

For Non-Selective Fibrinolytics (Streptokinase)

UFH is indicated only for high-risk patients: those with large or anterior MI, atrial fibrillation, previous embolus, or known LV thrombus 1

Fondaparinux Option

Fondaparinux 2.5 mg IV initial dose, then 2.5 mg subcutaneously daily is an alternative for fibrinolytic therapy but is NOT recommended for primary PCI 1

Common Dosing Errors to Avoid

Excess heparin dosing occurs in approximately 49% of fibrinolytic-treated patients, with 18% receiving major excess dosing. 4 This is associated with significantly higher major bleeding (19.2% vs 12.4%, p=0.004) and transfusion rates (13.5% vs 4.7%, p=0.0002) 4. Factors associated with excess dosing include low body weight and female sex, requiring particular attention in these populations. 4

Duration of Anticoagulation

Continue anticoagulation for minimum 48 hours, preferably for duration of hospitalization up to 8 days, or until revascularization is performed. 1