History of Previous Pulmonary Embolism and Treatment Classification
A history of previous pulmonary embolism does NOT automatically classify a patient as needing "secondary prevention" treatment—the terminology depends on the treatment phase and clinical context. The American Society of Hematology (ASH) 2020 guidelines clearly distinguish between "primary treatment" (the initial 3-6 months after any VTE event) and "secondary prevention" (indefinite anticoagulation after completing primary treatment) 1.
Understanding the Treatment Phases
Primary treatment refers to the initial 3-6 months of anticoagulation for ANY venous thromboembolism event, whether it's the patient's first PE or a recurrent event 1. This phase treats the acute thromboembolic event itself. The duration remains 3-6 months regardless of whether this is the patient's first or subsequent PE 1.
Secondary prevention refers to indefinite anticoagulation continued AFTER completing the primary treatment phase, with the specific goal of preventing future recurrent events 1. This decision is made after the initial 3-6 month treatment period is complete 1.
Clinical Decision Algorithm for Patients with Prior PE History
If the patient presents with a NEW/RECURRENT PE event:
- Start primary treatment for 3-6 months 1
- Use therapeutic-dose anticoagulation (rivaroxaban 15 mg twice daily for 21 days, then 20 mg once daily; or apixaban 10 mg twice daily for 7 days, then 5 mg twice daily) 2
- The fact that they had a previous PE does not change this initial treatment phase 1
After completing 3-6 months of primary treatment:
For patients with unprovoked PE who have a history of a PREVIOUS unprovoked VTE, the ASH guideline panel provides a STRONG recommendation for indefinite anticoagulation therapy 1. This represents the highest-risk population, with recurrence rates as high as 10% by 1 year and 30% by 5-10 years if anticoagulation is discontinued 1.
For patients whose current PE was provoked by a transient risk factor BUT who have a history of previous unprovoked VTE, indefinite anticoagulation should be strongly considered 1. These patients require the same decision-making process as for their initial unprovoked event 1.
Key Terminology Pitfall
The confusion arises because older terminology used "long-term" and "extended" inconsistently across guidelines 1. The ASH 2020 guidelines deliberately chose "primary treatment" and "secondary prevention" to reflect the distinct clinical intentions rather than duration 1.
Anticoagulation Options for Secondary Prevention
If continuing anticoagulation for secondary prevention after completing primary treatment:
Anticoagulation is preferred over aspirin (conditional recommendation) 1. Aspirin increases recurrent PE risk 3-fold (RR 3.10) and DVT risk 3-fold (RR 3.15) compared to continued anticoagulation 3.
For DOACs, either standard-dose OR reduced-dose regimens are acceptable (conditional recommendation) 1. Reduced-dose options include rivaroxaban 10 mg daily or apixaban 2.5 mg twice daily 1, 2.
For warfarin, maintain INR 2.0-3.0 (strong recommendation) 1.
Annual Reassessment Requirement
All patients on indefinite anticoagulation for secondary prevention must be reevaluated at least annually 1. This reassessment should review:
- The clinical indication for continuing indefinite therapy 1
- Any bleeding complications sustained 1
- New bleeding risk factors acquired 1
- Risk factors for bleeding include older age, history of prior bleeding, cancer, hepatic/renal insufficiency, hypertension, thrombocytopenia, prior stroke, need for antiplatelet therapy, anemia, alcohol abuse, and frequent falls 1
Common Clinical Pitfall
Do not confuse "having a history of PE" with automatically being on "secondary prevention." If the patient completed treatment for their previous PE and stopped anticoagulation, then presents with a new PE, they restart PRIMARY treatment for 3-6 months 1. Only after completing THIS course of primary treatment does the decision about secondary prevention arise 1.