What is the recommended treatment for a patient diagnosed with subsegmental pulmonary embolism (PE)?

Management of Subsegmental Pulmonary Embolism

For patients with isolated subsegmental PE and low risk for recurrent VTE, clinical surveillance without anticoagulation is preferred over anticoagulation, but only after excluding proximal DVT with bilateral leg ultrasound. 1

Critical First Step: Exclude Proximal DVT

• Perform bilateral lower extremity compression ultrasound before deciding to withhold anticoagulation to exclude proximal deep vein thrombosis, as isolated subsegmental PE (ISSPE) is frequently associated with DVT 1
• If proximal DVT is found, treat as standard PE with full anticoagulation 1
• Consider ultrasound of other locations (e.g., upper extremity) if clinically suspected 1

Risk Stratification for Treatment Decision

The 2021 CHEST guidelines provide a risk-based approach for ISSPE management:

Low Risk for Recurrent VTE

• Clinical surveillance is suggested over anticoagulation (weak recommendation, low-certainty evidence) 1
• Low risk characteristics include: absence of active cancer, no prior VTE, provoked PE with resolved risk factor, good cardiopulmonary reserve 1

High Risk for Recurrent VTE

• Anticoagulation is suggested over clinical surveillance (weak recommendation, low-certainty evidence) 1
• High risk characteristics include: active cancer, prior unprovoked VTE, persistent risk factors, limited cardiopulmonary reserve 1

Important Nuance: Recent Evidence Shows Higher Than Expected Recurrence

A large prospective study was prematurely terminated because untreated low-risk SSPE patients had higher VTE recurrence rates than initially deemed acceptable 2. In another cohort study, the overall recurrence rate was 5% (95% CI 2.4-10.7%), with half occurring in cancer patients 3. This suggests the risk-benefit calculation may favor anticoagulation more often than previously thought.

Confirming the Diagnosis

• The 2019 European Society of Cardiology guidelines suggest further imaging to confirm PE when isolated subsegmental filling defects are seen on CT pulmonary angiography, as some may represent false-positive findings 1
• Consider whether ISSPE represents a true positive finding versus imaging artifact before making treatment decisions 1

If Anticoagulation is Chosen

When anticoagulation is initiated for SSPE, use the same regimen as for proximal PE:

• Prefer direct oral anticoagulants (DOACs) over vitamin K antagonists - specifically apixaban, rivaroxaban, dabigatran, or edoxaban 1, 4, 5, 6
• Apixaban: 10 mg twice daily for 7 days, then 5 mg twice daily 5
• Rivaroxaban: 15 mg twice daily for 21 days, then 20 mg once daily 6
• Treat for at least 3 months minimum 1, 4
• For provoked SSPE with resolved risk factor, discontinue after 3 months 1, 4
• For unprovoked SSPE or persistent risk factors, consider extended anticoagulation beyond 3 months 1, 4

If Clinical Surveillance is Chosen

• Provide thorough patient education about signs and symptoms of progressive thrombosis (leg swelling, chest pain, shortness of breath) that require immediate return for reassessment 1
• Close monitoring is essential, though specific surveillance imaging intervals are not well-defined for SSPE (unlike the weekly ultrasound protocol for isolated distal DVT) 1

Special Populations

Incidentally Discovered Asymptomatic SSPE

• Treat the same as symptomatic PE with standard anticoagulation regimens (weak recommendation, moderate-certainty evidence) 1

Active Cancer Patients

• Anticoagulation is strongly recommended as cancer patients have approximately 20% recurrence rate in the first 12 months 1
• Half of recurrent VTE events in SSPE cohorts occurred in cancer patients 3
• Prefer LMWH for the first 6 months, or consider edoxaban or rivaroxaban as alternatives in non-gastrointestinal cancers 1
• Continue indefinitely or until cancer is cured 1

Common Pitfalls to Avoid

• Do not withhold anticoagulation without first excluding proximal DVT - this is the most critical error, as concurrent DVT mandates treatment 1
• Do not assume all subsegmental filling defects are true PE - consider confirmatory imaging, especially if clinical probability is low 1
• Do not use DOACs in severe renal impairment (CrCl <30 mL/min for rivaroxaban, dabigatran, edoxaban; <25 mL/min for apixaban) 1, 4, 6
• Do not use DOACs in antiphospholipid syndrome - use vitamin K antagonists instead 1, 4
• Do not underestimate risk in cancer patients - they require anticoagulation regardless of subsegmental location 1, 3

The Reality of Clinical Practice

While guidelines suggest surveillance may be appropriate for low-risk ISSPE, the weak strength of recommendations and recent evidence showing higher-than-expected recurrence rates (4-5%) mean that anticoagulation remains a reasonable default approach 1, 3, 2. The decision ultimately depends on bleeding risk, patient preference regarding treatment burden versus VTE risk, and confidence in the diagnosis. When in doubt, err on the side of anticoagulation for at least 3 months, as the mortality and morbidity from recurrent VTE outweigh the inconvenience and modest bleeding risk of short-term anticoagulation in most patients.