Venous Thromboembolism

Background

Venous thromboembolism (12VTE), comprising deep vein thrombosis (12VTE) and pulmonary embolism (12VTE), is a common and potentially fatal cardiovascular condition requiring structured diagnostic pathways, early risk stratification, and prompt anticoagulation for most patients. [@heit2015_corrected] ^{[1] [2]}

VTE outcomes depend on:

• Accurate pretest probability assessment with selective use of D-dimer and imaging to avoid missed PE while limiting unnecessary CTPA. ^{[3] [4]}
• Appropriate anticoagulant selection (DOACs for most; warfarin for high-risk antiphospholipid syndrome; LMWH often preferred in pregnancy). ^{[1] [2]}
• Timely reperfusion for high-risk PE and selected severe DVT (e.g., threatened limb, phlegmasia). ^{[3] [5]}

Long-term sequelae include post-thrombotic syndrome (13post-thrombotic syndrome) after DVT and chronic thromboembolic pulmonary hypertension (CTEPH) after PE; persistent symptoms warrant structured follow-up and referral. ^{[6] [7]}

See also 13CVI for chronic venous obstruction/reflux care and 3Chapter 3 for imaging principles.

Virchow's Triad

Virchow's triad

1. Venous stasis (immobility, hospitalization, surgery, trauma, paralysis, long-distance travel, heart failure).
2. Endothelial injury (trauma, surgery, central venous catheters, prior thrombosis).
3. Hypercoagulability

• Inherited: factor V Leiden, prothrombin G20210A, antithrombin deficiency, protein C/S deficiency.
• Acquired: malignancy, pregnancy/postpartum, estrogen therapy, antiphospholipid syndrome (APS), inflammatory states. [@heit2015_corrected] ^[5]

Surgical VTE risk assessment

Validated risk assessment models (e.g., Caprini) help stratify perioperative VTE risk and guide prophylaxis intensity and duration in surgical patients.

Pathophysiology

• Thrombosis occurs when the balance between coagulation and fibrinolysis shifts toward clot formation.
• Most lower limb DVTs begin in calf veins, propagating proximally.
• PE occurs when thrombus embolizes to pulmonary arteries → increased pulmonary vascular resistance, RV strain, hypoxemia.
• Long-term sequelae: venous valve destruction → reflux → venous hypertension → PTS.

^{[8] [6]}

DVT

• Unilateral swelling, pain, erythema, warmth.
• Homan's sign (calf pain on dorsiflexion) – non-specific.
• Proximal 12VTE (iliofemoral) → higher 12VTE risk.
• Long-term sequelae include post-thrombotic syndrome (13PTS).

^{[9] [6]}

PE

• Dyspnea, pleuritic chest pain, hemoptysis.
• Tachypnea, tachycardia, hypoxemia.
• Massive 12VTE → hypotension, shock, syncope, sudden death.

^[3]

Clinical prediction

Why clinical prediction matters

Clinical prediction rules help determine when D-dimer can safely exclude VTE and when definitive imaging is required (particularly for high pretest probability). ^{[10] [11]}

Suspected DVT

• Use a validated score (e.g., Wells DVT) to classify pretest probability.
• Low pretest probability:

• Obtain D-dimer; if negative, DVT is excluded without imaging. ^[10]
• If D-dimer is positive, perform compression ultrasound (CUS). ^[10]

• Intermediate/high pretest probability:

• Proceed directly to CUS; do not “rule out” with D-dimer alone. ^{[10] [5]}

Suspected PE

• Use Wells PE or Geneva (or an ED protocol), then apply D-dimer/imaging accordingly. ^{[11] [3]}
• The YEARS strategy can reduce CTPA utilization while maintaining safety when applied to appropriate populations. ^[4]

Pregnancy

A pregnancy-adapted YEARS strategy can safely reduce imaging in pregnant patients with suspected PE when combined with D-dimer thresholds and structured assessment. ^[12]

Laboratory

D-dimer (rule-out testing)

D-dimer is most useful in patients with low or intermediate pretest probability; a negative result can safely exclude DVT/PE without imaging in properly selected patients. ^{[10] [11]}

Age-adjusted threshold

For outpatients ≥50 years, age-adjusted D-dimer (age × 10 μg/L FEU) increases specificity and reduces unnecessary imaging while maintaining safety. ^[13]

Algorithm-specific thresholds

Some diagnostic strategies (e.g., YEARS and pregnancy-adapted YEARS) incorporate variable D-dimer thresholds based on specific clinical items, further reducing imaging in selected populations. ^{[4] [12]}

Practical notes

• Confirm whether your lab reports FEU vs DDU; thresholds differ by assay.
• A positive D-dimer is not diagnostic and should trigger imaging based on probability category. ^[11]

Imaging

DVT imaging

Compression ultrasound (CUS) is the first-line imaging test for suspected lower-extremity DVT. ^{[10] [5]}

• Proximal CUS (common femoral through popliteal) is widely used.
• If initial proximal CUS is negative but suspicion persists, repeat CUS (serial ultrasound) is an accepted strategy, particularly when anticoagulation is being withheld. ^{[10] [9]}

For suspected iliofemoral DVT with nondiagnostic CUS (e.g., obesity, high inguinal disease), consider CT or MR venography or focused iliac duplex in experienced labs. ^[5]

PE imaging

Computed tomography pulmonary angiography (CTPA) is the most common confirmatory test for PE; PIOPED II demonstrated high diagnostic performance in appropriate clinical contexts. ^{[14] [3]}

V/Q scanning and pregnancy

When contrast is contraindicated or in pregnancy, V/Q scanning is often preferred when the chest radiograph is normal; structured algorithms (including pregnancy-adapted YEARS) can reduce imaging while maintaining safety. ^{[3] [12]}

Echocardiography

Bedside echocardiography is not a rule-out test for PE, but is valuable in suspected high-risk PE to assess right ventricular dysfunction and guide urgent reperfusion decisions. ^[3]

Risk stratification in PE

Wells Score for PE can be used to determine pretest probability before imaging:

After clinical probability assessment:

• High-risk PE: shock or persistent hypotension.
• Intermediate-risk PE: normotensive with RV dysfunction and/or positive cardiac biomarkers (intermediate-high if both present; intermediate-low if one present).
• Low-risk PE: normal hemodynamics, normal RV, negative biomarkers; consider outpatient care in patients with low PESI/sPESI scores ^{[3] [15] [16]}.

Anticoagulation (cornerstone therapy)

Treatment phases

Anticoagulation for acute DVT/PE is typically organized into:

• Initial phase (first days): prevent early extension/embolization.
• Primary treatment (first 3 months): treat the index event.
• Extended phase (beyond 3 months): prevent recurrence in selected patients. ^{[2] [1]}

First-line agents (most patients)

• DOACs (apixaban, rivaroxaban, dabigatran, edoxaban) are first-line for most hemodynamically stable DVT/PE patients without contraindications. ^{[1] [2]}

Cancer-associated VTE

• DOACs are effective alternatives to LMWH (edoxaban; apixaban), but consider bleeding risk (especially GI/GU mucosal tumors) and drug–drug interactions. ^{[17] [18] [1]}

When warfarin (VKA) is preferred

• High-risk APS (especially triple-positive): warfarin is preferred due to increased thrombotic events seen with rivaroxaban in this population. ^{[19] [1]}
• Severe renal impairment: UFH with transition to warfarin is often used; DOAC use may be limited by labeling and evidence constraints. ^{[1] [2]}

Pregnancy

• Use LMWH during pregnancy and postpartum; avoid DOACs and warfarin in pregnancy. ^{[1] [3]}

Duration of Anticoagulation Therapy

Core duration principles

• Provoked VTE (major transient risk factor such as surgery/major trauma): 3 months is generally sufficient. ^{[2] [1]}
• Unprovoked VTE: treat for at least 3 months, then reassess recurrence vs bleeding risk; many patients benefit from extended therapy if bleeding risk is not high. ^{[2] [1]}
• Cancer-associated VTE: anticoagulate for a minimum of 6 months, and continue while cancer is active or treatment ongoing. ^[1]

Extended-phase options

Reduced-dose DOAC strategies are effective for extended secondary prevention (e.g., rivaroxaban 10 mg daily after initial treatment in appropriate patients). ^{[20] [2]}

Identifying low-risk patients after unprovoked VTE

In selected patients (notably some women) with unprovoked VTE, validated rules such as HERDOO2 can identify a subgroup with sufficiently low recurrence risk to consider stopping anticoagulation after completing primary treatment. ^[21]

Table 11.3. Duration of Anticoagulation by Clinical Scenario

Advanced and Endovascular Therapies

General principle

Most DVT/PE patients are treated with anticoagulation alone; advanced therapies are reserved for limb-threatening DVT or hemodynamically significant PE, or carefully selected intermediate-risk scenarios. ^{[3] [5] [1]}

Acute DVT thrombus removal (selected patients)

• Indications (typical)

• Acute iliofemoral DVT with severe symptoms, low bleeding risk, good functional status, and anticipated meaningful benefit (symptom relief and/or PTS reduction).
• Phlegmasia or threatened limb (urgent). ^[5]

• Catheter-directed thrombolysis (CDT) / pharmacomechanical CDT

• CAVENT suggested reduced PTS in iliofemoral DVT with CDT vs anticoagulation alone. ^[22]
• ATTRACT showed no overall reduction in PTS with pharmacomechanical CDT, but may improve early symptom burden in selected iliofemoral subgroups; bleeding risk must be considered. ^[23]

• Mechanical thrombectomy without lytic

May be considered when thrombolysis is contraindicated, recognizing that high-quality comparative data remain limited; patient selection and institutional expertise are critical. ^[5]

Acute PE reperfusion therapies

• Systemic thrombolysis

Recommended for high-risk (massive) PE with shock or persistent hypotension unless contraindicated. ^[3]

• Catheter-directed thrombolysis (PE)

Lower-dose thrombolysis strategies (including ultrasound-assisted systems) can improve RV parameters with potentially reduced bleeding compared with systemic dosing in selected patients. ^{[24] [25] [26]}

• Catheter-directed mechanical thrombectomy (PE)

Prospective device studies in intermediate-risk PE demonstrate improvements in RV/LV ratio and clinical parameters without thrombolytic use in many patients.

• FlowTriever (FLARE). ^[27]
• Indigo aspiration (EXTRACT-PE). ^[28]

• Surgical embolectomy / ECMO

Consider for high-risk PE when thrombolysis is contraindicated or unsuccessful, ideally via a multidisciplinary PE response pathway. ^[3]

Inferior vena cava (IVC) filters

• Primary indication

Acute proximal DVT and/or PE with an absolute contraindication to anticoagulation, or major bleeding requiring interruption when thrombotic risk is high. ^{[2] [9]}

• Evidence and harms

Permanent filters reduced PE but increased DVT in PREPIC long-term follow-up. ^[29] In patients who can receive anticoagulation, adding a retrievable filter did not reduce recurrent PE in PREPIC2. ^[30]

• Retrieval

When a filter is placed, plan retrieval as soon as the contraindication resolves and anticoagulation can be resumed; structured follow-up systems improve retrieval rates and reduce long-term complications. ^[31]

Follow-up and Long-Term Management

Compression and early recovery after DVT

Routine elastic compression stockings are not recommended solely to prevent PTS after proximal DVT, based on randomized trial evidence; however, compression may be used for symptomatic edema/pain with individualized fitting and reassessment. ^{[32] [1]}

Encourage early ambulation once anticoagulated and clinically stable.

Post-thrombotic syndrome (PTS)

PTS is a common sequela after proximal DVT and should be assessed in symptomatic patients (typically starting 3–6 months after the index event) using validated clinical scales (e.g., Villalta). ^{[6] [5]}

Management options (stepwise):

• Optimize anticoagulation adherence and address persistent provoking factors.
• Compression therapy for symptoms (edema, heaviness) and supervised exercise/rehabilitation.
• Evaluate for chronic venous obstruction (e.g., iliofemoral outflow obstruction) in refractory, lifestyle-limiting symptoms; selected patients may benefit from endovascular venous reconstruction (e.g., iliac venous stenting) in experienced centers. ^[33]

See 13CVI for chronic venous obstruction/reflux strategies.

PE follow-up and CTEPH

Patients with persistent dyspnea, exercise intolerance, or right heart strain after acute PE should be evaluated for chronic thromboembolic disease/CTEPH (e.g., echocardiography, referral pathways). ^{[3] [7]}

Imaging surveillance

Routine surveillance duplex ultrasound after treated DVT is not recommended in asymptomatic patients; repeat imaging is generally reserved for recurrent symptoms, anticoagulation decisions, or suspected extension/recurrence. ^{[1] [5]}

Guidelines

Major contemporary guidance (selected)

• ESC 2019 Acute PE guideline

• PE risk stratification (high-, intermediate-, low-risk), PESI/sPESI, outpatient management for selected low-risk patients, and reperfusion recommendations. ^[3]

• ESVS 2021 Venous thrombosis guideline

• Diagnostic pathways for DVT, selection for early thrombus removal in iliofemoral DVT, and long-term sequelae considerations. ^[5]

• CHEST 2021 VTE antithrombotic guideline update

• Anticoagulant selection and duration (initial/primary/extended phase) with emphasis on DOACs for most patients. ^[2]

• ASH 2018 VTE diagnosis guidelines

• Evidence-based DVT and PE diagnostic algorithms (clinical probability, D-dimer strategies, and imaging). ^{[10] [11]}

• SIR 2020 IVC filter guideline

• Indications, complications, and retrieval/follow-up systems. ^[31]

Tables

Table 11.1. Practical diagnostic pathways for suspected DVT and PE (simplified)

^{[10] [11] [13] [4]}

Table 11.2. When to consider advanced therapies or IVC filters (high-yield indications)

^{[3] [24] [26] [23] [30] [31]}

Management of isolated distal (calf) DVT and role of serial ultrasound

Isolated distal (calf) DVT requires individualized management. Anticoagulation is indicated for patients with severe symptoms, high risk of thrombus extension, or significant prothrombotic risk factors. For low-risk patients without these features, serial duplex ultrasound surveillance at 1 week and 2 weeks is an acceptable alternative to immediate anticoagulation. Management decisions should incorporate patient-centered bleeding risk assessment and shared decision-making ^[9].

Outpatient management of low-risk PE (PESI/sPESI, Hestia)

Selected patients with low-risk pulmonary embolism may be safely managed in the outpatient setting using validated risk stratification tools. The Pulmonary Embolism Severity Index (PESI) and simplified PESI (sPESI) identify candidates for outpatient therapy, with a score of 0 on sPESI indicating very low 30-day mortality risk. Exclusion criteria for outpatient management include hemodynamic instability, hypoxemia requiring supplemental oxygen, major comorbidities precluding safe home care, and social factors limiting adherence or follow-up. Patients selected for outpatient therapy require close follow-up within 24-72 hours and clear return precautions. The Hestia criteria provide an alternative validated approach to patient selection. Current ESC guidelines support outpatient management in appropriately selected low-risk patients ^{[3] [16]}.

Cancer-associated thrombosis: DOACs vs LMWH and GI/GU bleeding risk

Cancer-associated thrombosis presents unique management challenges. Key randomized controlled trials have demonstrated that direct oral anticoagulants (DOACs) are noninferior to low-molecular-weight heparin (LMWH) for cancer-associated VTE. The HOKUSAI-VTE Cancer trial showed edoxaban to be noninferior to dalteparin but with increased gastrointestinal bleeding in patients with gastrointestinal malignancies. The CARAVAGGIO trial found apixaban noninferior to dalteparin with similar bleeding rates, including in gastrointestinal and genitourinary cancers. Selection between DOAC and LMWH therapy should consider: tumor type and location (particularly gastrointestinal and genitourinary cancers with mucosal involvement), baseline thrombocytopenia or bleeding risk, significant drug-drug interactions with chemotherapy, patient preference, and cost. For patients with gastrointestinal or genitourinary cancers at high risk for mucosal bleeding, LMWH may be preferred, though apixaban appears to have a favorable safety profile ^{[17] [18]}.

Anticoagulation in special populations (pregnancy, severe renal impairment, antiphospholipid syndrome)

Anticoagulation in special populations requires tailored approaches. Pregnancy: LMWH is the preferred anticoagulant throughout pregnancy and the postpartum period, as DOACs and warfarin are contraindicated due to teratogenicity. Compression ultrasonography is the first-line imaging modality for suspected DVT. For suspected PE, ventilation-perfusion scanning is preferred when chest radiograph is normal; CTPA may be used when V/Q is unavailable or nondiagnostic, with consideration of fetal and maternal radiation exposure. Severe renal impairment: In patients with creatinine clearance <30 mL/min, DOACs are generally contraindicated or require substantial dose reduction with uncertain efficacy. Unfractionated heparin with transition to warfarin is the preferred approach, though LMWH with anti-Xa monitoring may be considered with caution. Antiphospholipid syndrome (APS): Vitamin K antagonists (warfarin) remain the preferred anticoagulant for high-risk APS, particularly in patients with triple-positive antibody status (lupus anticoagulant, anti-cardiolipin, and anti-β2 glycoprotein I antibodies), as DOACs have shown increased thrombotic events in this population ^{[1] [3] [14]}.

Evaluation after unprovoked VTE (occult cancer screening)

The optimal approach to cancer screening after unprovoked VTE remains an area of clinical uncertainty. Current evidence supports limited age-appropriate cancer screening rather than routine extensive imaging. The SOME (Screening for Occult Malignancy in patients with idiopathic venous thromboembolism) trial demonstrated that routine CT imaging of the abdomen and pelvis does not improve cancer detection rates or patient outcomes compared to standard age-appropriate screening in patients with unprovoked VTE. Therefore, the recommended approach consists of: comprehensive history and physical examination, basic laboratory tests (complete blood count, chemistry), and age-appropriate cancer screening (colonoscopy, mammography, Pap smear, prostate-specific antigen) as per standard guidelines. Extensive imaging or invasive testing should be reserved for patients with abnormal findings on initial evaluation or specific clinical suspicion ^[34].