Should I start intravenous (IV) heparin for a patient admitted with unstable angina?

IV Heparin for Unstable Angina

Yes, you should start IV heparin for a patient admitted with unstable angina as it is considered a fundamental Class IA therapy when given in conjunction with antiplatelet agents. 1

Rationale for IV Heparin in Unstable Angina

Heparin plays a critical role in the management of unstable angina by:

• Preventing acute myocardial infarction and recurrent angina 1
• Reducing the incidence of refractory angina (from 22.9% to 8.5%) 1
• Decreasing fatal and non-fatal MI when used in combination with aspirin by approximately 30% 1

Studies have demonstrated that heparin is highly effective in preventing acute MI, with one study showing reduction in MI incidence from 11.9% in placebo to just 0.8% in the heparin group 1.

Dosing Recommendations

For unstable angina, follow this dosing protocol:

1. Initial bolus: 60-70 U/kg (maximum 5000 U) IV 1
2. Maintenance infusion: 12-15 U/kg/hour 1
3. Target aPTT: 50-70 seconds (approximately 1.5-2.0 times control value) 1, 2

Monitor aPTT at 6 hours after initiation and adjust according to results. Studies show that with standard regimens, 25% of patients may be subtherapeutic at 6 hours 3.

Duration of Therapy

Continue IV heparin for at least 48 hours after admission. Evidence suggests that:

• Optimal duration is up to 48 hours 4
• Longer therapy (>48 hours) has been associated with increased adverse consequences 4
• Continue for the duration of hospitalization, up to 8 days, if medical therapy is selected as post-angiography management 1

Combination with Other Therapies

Always use heparin in combination with:

• Aspirin (162-325 mg) 1
• Consider adding clopidogrel with a loading dose of 300-600 mg 1

Monitoring and Adjustments

1. Check aPTT at 6 hours and 12 hours after initiation 3

2. Adjust dose according to aPTT results:

   • If aPTT <35 seconds: Give 80 units/kg bolus and increase infusion by 4 units/kg/hour 5
   • If aPTT 35-45 seconds: Give 40 units/kg bolus and increase by 2 units/kg/hour 5
   • If aPTT 46-70 seconds: No change (therapeutic range) 5
   • If aPTT 71-90 seconds: Reduce infusion by 2 units/kg/hour 5
   • If aPTT >90 seconds: Stop infusion for 1 hour, then reduce by 3 units/kg/hour 5

3. Monitor platelet counts regularly between days 4-14 to detect heparin-induced thrombocytopenia 5

Potential Complications and Precautions

• Bleeding risk: Major bleeding occurs in approximately 1.9% of patients 1
• Heparin-induced thrombocytopenia: Risk is higher with unfractionated heparin (up to 5%) compared to LMWH 5
• Contraindications: Active major bleeding, severe thrombocytopenia, known hypersensitivity to heparin 2

Alternative Options

If heparin is contraindicated or if you prefer an alternative:

• Low molecular weight heparin (enoxaparin): May be preferable to unfractionated heparin unless CABG is planned within 24 hours 1
• Fondaparinux: Consider if no PCI is planned within 24 hours 1
• Bivalirudin: Consider especially if PCI is planned 1

Transitioning from Heparin

When transitioning from heparin to oral anticoagulants:

• For warfarin: Continue full heparin therapy until INR reaches stable therapeutic range 2
• For other oral anticoagulants: Stop IV heparin immediately after administering first dose 2

Remember that the combination of aspirin and heparin has shown superior outcomes compared to either agent alone in unstable angina patients, making IV heparin an essential component of treatment.