When should a patient with Non-ST-Elevation Myocardial Infarction (NSTEMI) start a heparin drip?

When to Start Heparin Drip for NSTEMI

Anticoagulation with heparin (unfractionated heparin or low molecular weight heparin) should be initiated immediately upon diagnosis of NSTEMI, as soon as the patient presents and the diagnosis is confirmed, and continued until percutaneous coronary intervention (PCI) is performed or for the duration of hospitalization if managed conservatively. 1, 2

Immediate Initiation Upon Diagnosis

• Start anticoagulation as part of initial antithrombotic therapy immediately when NSTEMI is diagnosed, alongside antiplatelet agents (aspirin and clopidogrel). 1
• The rationale is to antagonize the ongoing clotting cascade in the setting of a partially or intermittently occluding thrombus that characterizes NSTEMI. 1, 2
• Do not delay anticoagulation while awaiting cardiac catheterization or risk stratification—this is a Class I recommendation. 1

Dosing Regimens

Unfractionated Heparin (UFH)

• Initial bolus: 60-70 U/kg (maximum 5000 units) 3
• Continuous infusion: 12-15 U/kg/hour 3
• Target activated partial thromboplastin time (aPTT): 50-70 seconds 3
• Check aPTT after 3 hours and adjust accordingly 1
• Recent evidence suggests higher maximum doses (up to 10,000 unit bolus and 2250 units/hour infusion) achieve therapeutic anticoagulation more rapidly without increased bleeding, particularly in obese patients 4

Low Molecular Weight Heparin (LMWH)

• Enoxaparin is preferable to UFH unless CABG is planned within 24 hours or renal failure is present (Class IIa recommendation). 1
• Dosing: 1 mg/kg subcutaneously twice daily 5
• Continue for duration of hospitalization, up to 8 days 1

Duration of Therapy

For Invasive Strategy (Early Catheterization)

• Continue anticoagulation from presentation until PCI is performed 1, 2
• If UFH is used, continue during the procedure with ACT guidance 1
• Discontinue after successful PCI unless other indications exist 2

For Conservative Strategy (Medical Management)

• Continue for at least 48 hours, up to 8 days of hospitalization 1
• If recurrent ischemia develops despite medical therapy, add GP IIb/IIIa inhibitor and proceed to angiography 1

Critical Pitfalls to Avoid

• Do not delay heparin initiation in patients on direct oral anticoagulants (DOACs): Elevated baseline heparin anti-Xa levels from DOACs should not prevent starting heparin therapy, as these normalize within 12 hours and delays may worsen outcomes. 6
• Fibrinolytic therapy is contraindicated in NSTEMI and may be harmful—never administer thrombolytics to patients without ST-segment elevation (Class III: Harm). 1
• Adjust for renal function: In renal failure, avoid enoxaparin and use UFH instead. 1
• Plan for CABG: If CABG is anticipated within 24 hours, UFH is preferred over enoxaparin for easier reversal. 1

Special Considerations

• In obese patients, standard weight-based dosing may be inadequate; consider using higher maximum doses without capping to achieve therapeutic anticoagulation more rapidly. 4
• Enoxaparin combined with reduced-dose UFH during PCI (50-70 U/kg) is safe and effective in patients undergoing drug-eluting stent placement. 5
• For patients requiring long-term anticoagulation (e.g., atrial fibrillation), transition to triple therapy (DOAC + aspirin + clopidogrel) after PCI, then dual therapy (DOAC + clopidogrel) after 1 week to 1 month. 2