Heparin Therapy for Pulmonary Embolism

Initial Treatment and Monitoring

The European Society of Cardiology recommends unfractionated heparin should be continued for a minimum of 5 days and discontinued only after warfarin achieves a therapeutic INR of 2.0-3.0 for at least 2 consecutive days 1, 2
Initial heparin dosing should start with a bolus of 5,000-10,000 IU (or 80 IU/kg weight-adjusted) followed by continuous infusion of 1,300 IU/hour (or 18 IU/kg/hour weight-adjusted) to achieve rapid therapeutic anticoagulation 3, 4
The infusion rate should be adjusted to maintain aPTT at 1.5-2.5 times control (45-75 seconds) 3, 4, 2
aPTT should be checked 4-6 hours after the initial bolus, then 6-10 hours after any dose adjustment, and daily once therapeutic 3, 4

The critical principle is that heparin must continue for at least 5 days regardless of how quickly the INR becomes therapeutic, based on evidence showing that shorter durations result in increased recurrence rates 1, 2, 5
The European Heart Society recommends that heparin should not be discontinued before day 5, even if INR is therapeutic, as this is associated with increased recurrence risk 1, 2, 5

In patients with high-risk PE (hemodynamic instability), unfractionated heparin rather than LMWH should be used, and continued until hemodynamic stability is achieved before transitioning to oral anticoagulation 1, 2, 5
In patients with severe renal dysfunction (creatinine clearance <30 mL/min), UFH with aPTT monitoring rather than LMWH should be used due to accumulation risk 5
After thrombolytic therapy, heparin should be resumed at maintenance dose (without bolus) once aPTT falls below 2 times the upper limit of normal 3, 6

For most non-high-risk PE patients, LMWH (enoxaparin 1 mg/kg SC every 12 hours or 1.5 mg/kg once daily) is preferred over UFH due to equal efficacy, improved safety profile, and ease of use 1, 2, 7, 5
The same 5-day minimum duration and INR overlap requirements apply to LMWH 1, 2, 5