Is it acceptable to not treat asymptomatic patients with subsegmental pulmonary embolism (PE) who do not have evidence of deep vein thrombosis (DVT)?

Management of Isolated Subsegmental Pulmonary Embolism

In patients with isolated subsegmental PE who are at low risk for recurrent VTE and have no proximal DVT, clinical surveillance without anticoagulation is an acceptable management strategy. 1

Risk Stratification Framework

The decision to withhold anticoagulation hinges on two critical assessments that must be performed systematically:

1. Exclude Proximal DVT (Mandatory First Step)

• Bilateral lower extremity ultrasound must be performed before considering withholding anticoagulation 1
• If clinically suspected elsewhere (e.g., upper extremity symptoms), ultrasound that location as well 1
• The presence of proximal DVT mandates anticoagulation regardless of PE size 1

2. Assess VTE Recurrence Risk

Low-risk patients (favor clinical surveillance): 1

• Ambulatory outpatients with good mobility
• No active cancer (especially not metastatic or receiving chemotherapy)
• Presence of reversible risk factors (recent surgery, trauma)
• Good cardiopulmonary reserve
• Minimal or no symptoms attributable to PE
• Not pregnant

High-risk patients (favor anticoagulation): 1

• Hospitalized or reduced mobility
• Active cancer, particularly metastatic or on chemotherapy
• No identifiable reversible risk factor (unprovoked)
• Pregnancy
• Poor cardiopulmonary reserve
• Marked symptoms that cannot be attributed to another condition

Confirming True-Positive SSPE

Before withholding anticoagulation, consider whether the imaging finding represents a true PE versus artifact: 1

Features suggesting true PE:

• Defects seen on multiple consecutive images
• Defects surrounded by contrast (not adherent to vessel walls)
• Visible on multiple projections
• Patient is symptomatic
• High clinical pretest probability
• Elevated D-dimer (particularly if markedly elevated and unexplained)

The 2019 European Society of Cardiology suggests confirmatory imaging when isolated subsegmental defects are seen on CT pulmonary angiography 1

Clinical Surveillance Protocol

If anticoagulation is withheld, structured surveillance is mandatory: 1

• Patient education on warning signs: worsening dyspnea, chest pain, leg swelling, or other symptoms suggesting progressive thrombosis
• Clear instructions to return immediately if symptoms develop or worsen
• Consider serial ultrasound imaging (though recent data questions its utility) 2
• Document the decision-making process and risk assessment thoroughly

Important Caveats and Pitfalls

The Evidence Is Evolving

• A recent large prospective study (2024) of low-risk SSPE patients managed without anticoagulation showed higher-than-expected VTE recurrence rates and was prematurely terminated 3
• This suggests the risk-benefit calculation may favor anticoagulation more than previously thought 3
• No randomized controlled trials exist to definitively guide management 4

Asymptomatic/Incidental PE Is Different

• If SSPE is discovered incidentally (asymptomatic), the same anticoagulation as symptomatic PE should be given 1
• This recommendation carries moderate-certainty evidence and applies particularly to cancer patients 1
• Asymptomatic PE carries similar prognosis to symptomatic PE based on observational data 1

Bleeding Risk Considerations

When bleeding risk is high, this favors withholding anticoagulation even in borderline cases 1

Practical Algorithm

1. Confirm SSPE diagnosis → Review imaging quality and features suggesting true PE 1
2. Perform bilateral leg ultrasound → If proximal DVT present → Anticoagulate 1
3. If no proximal DVT → Assess VTE recurrence risk factors 1
4. Low risk + good cardiopulmonary reserve + symptomatic presentation → Clinical surveillance acceptable 1
5. High risk OR poor cardiopulmonary reserve OR incidental finding → Anticoagulate 1
6. If surveillance chosen → Educate patient, document rationale, ensure follow-up 1

The strength of recommendation for withholding anticoagulation in low-risk patients is weak with low-certainty evidence, reflecting genuine clinical equipoise 1. Given recent data suggesting higher recurrence rates than expected 3, when in doubt, anticoagulation is the safer choice to prioritize mortality and morbidity outcomes.