Venous Thromboembolism

Overview – Venous Thromboembolism

Venous thromboembolism encompasses Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE). It arises from thrombus formation in the deep veins, usually of the lower limbs, which can dislodge and embolise to the pulmonary arteries. Early diagnosis and management are essential to prevent life-threatening complications.

Definition

VTE = DVT (clot in deep venous system) ± PE (embolus travels to lungs).
It represents a spectrum of the same disease process driven by Virchow’s Triad:
1. Vessel wall injury
2. Venous stasis
3. Hypercoagulability

Virchow’s Triad

1. Endothelial/Vessel Wall Injury
   • Surgery
   • Hypertension
   • Smoking
2. Stasis
   • Prolonged immobility (e.g. long-haul flights, bed rest, post-operative)
   • Congestive heart failure
   • Obesity
   • Pregnancy
3. Hypercoagulability
   • Malignancy (e.g. adenocarcinoma)
   • Congenital disorders (e.g. antithrombin III deficiency, Factor V Leiden)
   • Oestrogen therapies (e.g. oral contraceptive pill, hormone replacement therapy)
   • Polycythaemia

Deep Vein Thrombosis (DVT)

Synonyms: Phlebothrombosis, Thrombophlebitis

Aetiology

• Venous valve incompetence
• Prolonged immobilisation (e.g. surgery, long-haul travel, bedrest)
• Risk factors = Virchow’s Triad:
  • Vessel wall damage: surgery, smoking, hypertension
  • Stasis: travel, obesity, pregnancy, CCF, post-operative states
  • Hypercoagulability:
    • Cancer (esp. adenocarcinoma)
    • Congenital: Antithrombin III deficiency, Factor V Leiden
    • Drugs: OCP, HRT
    • Others: pregnancy, polycythaemia

Pathogenesis

Incompetent venous valves or immobility → ↓muscle pump → venous pooling → clot formation in deep leg veins (esp. calf)

Clinical Features

• Local symptoms (calf):
  • Tenderness on palpation or passive dorsiflexion
  • Redness, warmth, swelling
  • Superficial venous dilation
  • Distal oedema and cyanosis
• Complication:
  • Pulmonary Embolism may be the first sign → sudden dyspnoea, chest pain, collapse

Investigations

• Duplex Doppler Ultrasound: 93% sensitivity, 98% specificity

Management

• Anticoagulation (oral DOAC or LMWH if contraindicated)
• +/- Thrombectomy
• +/- IVC filter if high PE risk or anticoagulation contraindicated

Pulmonary Embolism (PE)

Aetiology

• 95% originate from DVT (usually of lower limbs)

Pathogenesis

• DVT → thrombus embolises to pulmonary arteries →
  • Ventilation-perfusion (V/Q) mismatch → respiratory failure
  • Increased pulmonary vascular resistance → right heart strain → heart failure

Clinical Features

• Symptoms:
  • Pleuritic chest pain ± pleural rub
  • Dyspnoea, tachypnoea
  • Cough ± haemoptysis
  • +/- leg symptoms of DVT
• Signs:
  • Right heart failure: raised JVP, tricuspid regurgitation
  • Syncope, shock
  • Fever

Investigations

• CT Pulmonary Angiogram (CTPA): gold standard – shows emboli in pulmonary arteries
• ECG: S1Q3T3 pattern
• V/Q scan: useful if CTPA contraindicated (e.g. renal impairment)
• CXR: later may show wedge-shaped infarct

Treatment

• Oxygen
• Anticoagulation (oral or heparin)
• Thrombolysis (TPA) if haemodynamic compromise
• +/- Surgical thrombectomy or IVC filter

Prevention

• Compression stockings
• Prophylactic anticoagulation
• IVC filter in severe risk or contraindication to anticoagulants

Summary – Venous Thromboembolism

Venous thromboembolism includes both deep vein thrombosis and pulmonary embolism, commonly resulting from stasis, hypercoagulability, and endothelial injury. Clinical presentation may be subtle or catastrophic, requiring a high index of suspicion. Prompt diagnosis via Doppler ultrasound or CT pulmonary angiography is essential, followed by appropriate anticoagulation and, where necessary, thrombolysis or thrombectomy. For a broader context, see our Cardiovascular Overview page.