When is heparin indicated?

Indications for Heparin Therapy

Heparin is indicated for the treatment of deep vein thrombosis (DVT), pulmonary embolism (PE), unstable angina, non-ST elevation myocardial infarction (NSTEMI), ST-elevation myocardial infarction (STEMI) with thrombolytic therapy, and in patients with mechanical heart valves requiring temporary anticoagulation. 1, 2

Specific Clinical Indications

Venous Thromboembolism (VTE)

• Deep Vein Thrombosis (DVT): Treatment requires initial bolus of 5000 U IV followed by 32,000 U per 24 hours by IV infusion or 35,000-40,000 U per 24 hours subcutaneously 1
• Pulmonary Embolism (PE): Same dosing as for DVT
• Duration: At least 5 days of therapy is as effective as 10 days when transitioning to oral anticoagulants 1

Acute Coronary Syndromes

• Unstable Angina/NSTEMI:

  • Initial bolus of 60-70 U/kg (maximum 5,000 U) followed by 12-15 U/kg/hour infusion (maximum 1,000 U/hour) 2, 3
  • Reduces risk of MI and recurrent angina 1
  • When combined with aspirin, reduces short-term rates of cardiovascular death and MI by approximately 30% compared to aspirin alone 1

• STEMI with Thrombolytic Therapy:

  • Initial bolus of 60 U/kg (maximum 4,000 U) followed by 12 U/kg/hour infusion (maximum 1,000 U/hour) 1, 2, 3
  • Improves coronary patency following tissue plasminogen activator therapy 1
  • Duration: 24-48 hours post-thrombolysis 1

Other Cardiac Indications

• Mechanical Heart Valves: When temporary IV anticoagulation is needed (e.g., during perioperative period)

  • 5,000 U IV bolus followed by 32,000 U per 24 hours by IV infusion 2
  • More aggressive anticoagulation for mechanical mitral valves compared to aortic valves 2

• Post-Infarction Unstable Angina: Continuation of heparin (particularly LMWH) may be beneficial in patients at high risk for progression to MI in whom revascularization is not possible 1

Dosing and Monitoring

Weight-Based Dosing Protocol

• Weight-based dosing achieves therapeutic anticoagulation more rapidly and reduces recurrent thromboembolism compared to fixed-dose regimens 2, 4
• Initial IV bolus: 80 U/kg (with appropriate maximums per indication)
• Continuous infusion: 18 U/kg/hour, adjusted based on aPTT 2

Monitoring Parameters

• Target aPTT: 1.5-2.5 times control value (approximately 50-70 seconds) 2, 3
• Check aPTT 6 hours after starting therapy or after any dose change 2
• Once stable, check aPTT daily 2

Important Considerations

Bleeding Risk

• Major bleeding occurs in approximately 1.9% of patients on therapeutic heparin 1
• Risk factors: high heparin dose, concomitant use of fibrinolytic agents or antiplatelet drugs, recent surgery/trauma, renal insufficiency, age >60 years 2
• More frequent aPTT monitoring and careful dose adjustment can decrease bleeding complications 1

Special Populations

• Obese patients: Use actual body weight for initial dosing without arbitrary dose capping 2
• Renal impairment: Unfractionated heparin is preferred over LMWH in severe renal impairment 2

Potential Complications

• Heparin-induced thrombocytopenia (HIT): Monitor platelet count regularly and discontinue heparin immediately if HIT is suspected 2

Practical Algorithm for Heparin Use

1. Identify indication (VTE, ACS, mechanical valve)
2. Select appropriate weight-based dosing regimen based on indication
3. Administer initial bolus followed by continuous infusion
4. Monitor aPTT at 6 hours and adjust dose according to results
5. Continue monitoring daily once therapeutic range achieved
6. Transition to oral anticoagulation when appropriate (for VTE, continue heparin until INR is therapeutic for at least 24 hours)

The lower dose weight-adjusted heparin regimen (60 U/kg bolus, 12 U/kg/hour infusion) is superior in achieving early therapeutic aPTTs and reducing the need for infusion adjustments 4, making it the preferred approach for most indications.