LMWH Before Angioplasty in MI Patients
Direct Recommendation
For MI patients undergoing primary PCI (angioplasty), unfractionated heparin (UFH) is preferred over LMWH, with a bolus dose of 70-100 U/kg IV (or 60 U/kg if using GP IIb/IIIa inhibitors), targeting an ACT of 250-350 seconds. 1 LMWH should generally be avoided in the primary PCI setting due to lack of robust supporting evidence and increased bleeding risk when switching between anticoagulants. 2
Context-Specific Guidance
For STEMI Patients Undergoing Primary PCI
UFH is the standard anticoagulant for STEMI patients proceeding directly to primary PCI, administered as 70-100 U/kg IV bolus when used alone, or 60 U/kg IV bolus (maximum 4,000 U) when combined with GP IIb/IIIa inhibitors. 1
Target ACT should be 250-350 seconds with UFH alone, or 200-250 seconds when combined with GP IIb/IIIa inhibitors. 1
Enoxaparin may be considered as an alternative only in patients <75 years without significant renal dysfunction, using 30 mg IV bolus followed by 1.0 mg/kg subcutaneous every 12 hours. 1, 3 However, this is less preferred than UFH for primary PCI. 2
For NSTE-ACS Patients with Planned Early Invasive Strategy
UFH is preferred in high-risk NSTE-ACS patients with a planned invasive strategy. 2
The SYNERGY trial demonstrated that enoxaparin showed similar efficacy to UFH in NSTE-ACS patients undergoing early revascularization, but excess bleeding occurred when patients were switched between anticoagulants. 2
If enoxaparin was started before arrival, timing of the last dose determines additional anticoagulation needs: no additional dose if PCI occurs within 8 hours of last subcutaneous dose; give 0.3 mg/kg IV if PCI occurs 8-12 hours after last dose. 3
For MI Patients Receiving Fibrinolytic Therapy Before PCI
Enoxaparin is reasonable as an alternative to UFH in STEMI patients <75 years receiving fibrinolytic therapy, using 30 mg IV bolus followed by 1.0 mg/kg subcutaneous every 12 hours. 1, 3
For patients ≥75 years receiving fibrinolysis, omit the IV bolus and use 0.75 mg/kg subcutaneous every 12 hours. 3
Continue anticoagulation for minimum 48 hours, preferably for duration of hospitalization up to 8 days, or until revascularization. 1
Critical Evidence Considerations
The evidence shows divergent outcomes based on clinical context:
ESSENCE and TIMI 11B trials demonstrated enoxaparin superiority over UFH in medically managed NSTE-ACS patients, with reduced death/MI rates. 2
SYNERGY trial showed no efficacy advantage of enoxaparin over UFH in patients undergoing early invasive strategy, with increased bleeding when switching between anticoagulants occurred. 2
ASSENT Plus study in STEMI patients receiving alteplase showed dalteparin reduced early coronary occlusion and reinfarction compared to UFH, but events increased after cessation of LMWH, eliminating long-term benefit. 4
European guidelines state that data on LMWHs as sole anticoagulant during PCI in stable CAD patients is limited, and UFH should be added if patients arrive on LMWH pre-treatment. 2
Critical Pitfalls to Avoid
Never switch between UFH and LMWH during the same hospitalization, as this significantly increases major bleeding risk. 2, 1, 5
Do not use LMWH in patients ≥75 years receiving fibrinolytic therapy without appropriate dose adjustment (omit IV bolus, reduce to 0.75 mg/kg). 1, 3
Avoid LMWH in significant renal dysfunction (CrCl <30 mL/min) without dose reduction to once-daily dosing. 1, 5
Do not discontinue anticoagulation prematurely in high-risk patients, as rebound thrombotic events can occur. 1
The FRAMI study showed that high-dose dalteparin (150 U/kg twice daily) with thrombolytics caused significantly increased major hemorrhage including fatal cerebral hemorrhages. 2
Renal Dysfunction Adjustments
For creatinine clearance <30 mL/min, reduce enoxaparin to 1 mg/kg subcutaneous once daily rather than twice-daily dosing. 5
Consider UFH over LMWH in dialysis patients or severe renal impairment, as UFH does not require renal clearance. 3, 5