Is the heparin (unfractionated heparin) dose for a patient with atrial thrombus the same as for venous thromboembolism (VTE)?

Heparin Dosing for Atrial Thrombus vs VTE

Yes, the unfractionated heparin dose for atrial thrombus should be the same as for VTE treatment, using weight-based dosing with an 80 units/kg IV bolus followed by 18 units/kg/hour continuous infusion, adjusted to maintain aPTT at 1.5-2.5 times control. 1

Standard UFH Dosing Regimen

The established therapeutic anticoagulation protocol applies to both conditions:

• Initial bolus: 80 units/kg IV 1
• Maintenance infusion: 18 units/kg/hour 1
• Target aPTT: 1.5-2.5 times control (typically 46-70 seconds), corresponding to anti-Xa levels of 0.3-0.7 units/mL 1

This weight-based nomogram has been validated in randomized trials and significantly reduces recurrent thromboembolism compared to fixed-dose regimens. 1

Alternative Dosing Approach

If weight-based dosing is not used, the acceptable alternative is:

• Initial bolus: 5,000 units IV 1
• Maintenance infusion: At least 32,000 units per 24 hours (approximately 1,333 units/hour) 1

However, the weight-based approach is strongly preferred as it achieves therapeutic anticoagulation more rapidly. 1

Monitoring and Dose Adjustment

Critical timing: Achieving therapeutic aPTT within 24 hours is essential, as delays are associated with higher recurrence rates and increased mortality. 1

Use a standardized dose-adjustment nomogram based on aPTT results: 1

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

Important Distinctions from Other Indications

Do not confuse with acute coronary syndrome dosing, which uses significantly lower heparin doses (60-70 units/kg bolus, maximum 5,000 units; 12-15 units/kg/hour infusion, maximum 1,000 units/hour). 1 These lower doses are inadequate for treating established thrombus in either atrial or venous locations.

Common Pitfalls to Avoid

• Underdosing in the first 24 hours: This is associated with a 25% risk of recurrent thromboembolism compared to 2% with adequate dosing. 1
• Using ACS protocols: The lower doses recommended for unstable angina are insufficient for thrombus treatment. 1
• Inadequate monitoring: aPTT should be checked 6 hours after initiation and 6 hours after each dose adjustment until stable in therapeutic range. 1
• Institutional aPTT variability: The therapeutic aPTT range must be calibrated to your institution's specific reagent and coagulometer, as different systems show wide variation in responsiveness to heparin. 1

Duration of Therapy

Heparin should be continued for a minimum of 5 days with overlap of oral anticoagulation (warfarin or DOAC) until INR is ≥2.0 for at least 24 hours (if using warfarin). 1 Evidence supports that 5-day courses are as effective as 10-day courses for VTE treatment. 1

Alternative Anticoagulants

While the question specifically asks about UFH, low-molecular-weight heparins (enoxaparin 1 mg/kg subcutaneously every 12 hours or 1.5 mg/kg once daily) are equally effective alternatives for both VTE and can be considered for atrial thrombus, though less extensively studied in the latter indication. 1, 2 DOACs at VTE treatment doses (not stroke prevention doses) are also appropriate once acute management is complete. 1