Why is heparin given to a patient with a pulmonary embolism?

Heparin in Pulmonary Embolism Treatment

Heparin is the mainstay of treatment for pulmonary embolism because it has been proven to reduce the incidence of fatal recurrent embolism by providing immediate anticoagulation to prevent clot propagation and allow for natural thrombolytic processes to dissolve existing clots. 1

Mechanism and Efficacy

• Heparin provides immediate anticoagulation that prevents further clot formation and extension of existing thrombi, allowing the body's natural fibrinolytic system to gradually dissolve the pulmonary emboli 1
• Anticoagulation with heparin has been shown to significantly reduce mortality and morbidity in patients with pulmonary embolism 2
• Heparin should be started immediately when there is high or intermediate clinical suspicion of pulmonary embolism, even before diagnostic confirmation, unless contraindicated 1

Administration Protocol

• Initial treatment typically involves a loading dose of 5,000-10,000 units followed by 400-600 units/kg daily as a continuous infusion 1, 2
• Dosing should be titrated to maintain activated partial thromboplastin time (APTT) at 1.5-2.5 times control values 1, 3
• APTT should be measured 4-6 hours after starting treatment, repeated 6-10 hours after every dose change, and then at least daily 1, 2
• Weight-based dosing causes fewer APTT fluctuations and achieves therapeutic levels more quickly 1

Treatment Duration and Transition

• Heparin should be continued until adequate maintenance anticoagulation with warfarin is achieved 1
• A five-day course appears to be as effective as a 7-10 day course 1, 3
• If continued beyond five days, platelet count must be monitored due to the risk of heparin-induced thrombocytopenia with thrombosis 1
• Warfarin may be started as soon as the diagnosis is confirmed 1

Low-Molecular-Weight Heparin (LMWH) vs. Unfractionated Heparin

• LMWH is at least as effective as unfractionated heparin for treating pulmonary embolism 1
• LMWH offers more predictable pharmacokinetics and anticoagulant effects 4, 5
• For deep vein thrombosis, LMWH has been shown to be superior to unfractionated heparin, particularly for reducing mortality and major bleeding risk 1
• Current guidelines from the American College of Physicians/American Academy of Family Physicians recommend LMWH over unfractionated heparin for initial inpatient treatment of DVT, while either is appropriate for pulmonary embolism 1

Special Considerations

• In massive pulmonary embolism with hemodynamic instability, thrombolytic therapy may be considered over heparin alone, particularly in the presence of hypotension 1
• Thrombolysis results in more rapid resolution of pulmonary emboli than heparin alone but carries a higher risk of bleeding complications 6, 1
• Major bleeding is the primary complication of anticoagulation, occurring in approximately 1% of low-risk patients and up to 10% in high-risk patients 1
• Absolute contraindications to heparin include recent hemorrhage, stroke, and current gastrointestinal bleeding 1

Monitoring and Complications

• Regular monitoring of APTT, platelet count, hematocrit, and occult blood in stool is essential during heparin therapy 2
• An unexpectedly poor response to heparin may suggest pre-existing thrombophilia 1
• High-risk patients for bleeding complications include those who have undergone recent surgery, obstetric delivery, or have a history of peptic ulcer disease or bleeding disorders 1

Heparin remains a cornerstone in pulmonary embolism treatment due to its proven efficacy in preventing recurrent thromboembolism and reducing mortality, despite newer anticoagulant options becoming available 7, 4.