A thrombus (clot) formed in deep venous circulation
Aetiology
Thrombosis is considered to arise from the interplay between the three factors that make up Virchow’s triad:
Pathophysiology
- DVTs form predominantly in the venous valve pockets and other sites of assumed stasis
- Distal vein thrombosis: refers to DVT of the calves
- Proximal vein thrombosis: DVT of the popliteal or femoral vein, more likely to embolise
Clinical presentation
Clinical features of DVT arise from:
- Venous obstruction → ↑ venous pressure
- Inflammation of the vein wall
→ Leads to localized edema, pain, and inflammatory signs
Asymptomatic DVT
- Up to 50% of cases
- Detected incidentally or after complication (e.g., Pulmonary Embolism)
Symptomatic DVT (Typical Presentation)
✅ Classic Triad
- Swelling
- Pain
- Erythema
Unilateral Leg Swelling (Most Common)
- Sudden onset
- Affected limb larger than the other
- Pitting edema present
Tenderness
- Along the course of the vein
- Especially calf or femoral region
Warmth & Erythema
- Local inflammation
- Skin appears:
- Red
- Warm
Pain
- Dull, aching, or cramping
- Usually in:
- Calf (most common)
- Thigh (proximal DVT)
Dilated Superficial Veins
- Due to venous obstruction
- Collateral circulation becomes visible
Location-Based Manifestations
Distal (Calf) DVT
- Mild symptoms
- Often limited swelling
- Lower risk of embolism
Proximal DVT (Femoral/Iliac)
- More severe symptoms:
- Marked swelling
- Severe pain
- Higher risk of:
- Pulmonary Embolism
Iliofemoral DVT
- Massive swelling
- Cyanosis
- Limb heaviness
⚠️ Severe Variant: Phlegmasia
1. Phlegmasia Alba Dolens
- Pale, swollen limb
- Severe pain
2. Phlegmasia Cerulea Dolens
- Cyanotic limb
- Severe venous congestion
- Risk of:
- Venous gangrene
Physical Examination Findings
Inspection
- Unilateral edema
- Increased calf circumference (>3 cm difference)
- Skin tightness
Special Tests
Homan’s Sign
- Pain on dorsiflexion of foot
⚠️ Low sensitivity and specificity → not reliable clinically
Palpation
- Tenderness along deep veins
- Increased temperature
Investigations
Clinical Probability Assessment
Wells Score for DVT
Criteria and Scoring
Clinical Feature | Points |
Active cancer (treatment ongoing/recent/palliative) | +1 |
Paralysis, paresis, or recent immobilization of lower limb | +1 |
Bedridden >3 days OR major surgery within 12 weeks | +1 |
Localized tenderness along deep venous system | +1 |
Entire leg swollen | +1 |
Calf swelling ≥3 cm vs asymptomatic leg | +1 |
Pitting edema (confined to symptomatic leg) | +1 |
Collateral superficial veins (non-varicose) | +1 |
Previous DVT | +1 |
Alternative diagnosis as likely as DVT | −2 |
Interpretation
Score | Probability |
≤0 | Low |
1–2 | Moderate |
≥3 | High |
Clinical Importance
- Guides further testing:
- Low probability → D-dimer first
- Moderate/high → imaging directly
Laboratory Testing
D-Dimer
Principle
- Measures fibrin degradation products
Interpretation
- Negative D-dimer → rules out DVT (in low-risk patients)
- Positive → non-specific
Causes of False Positives
- Infection
- Surgery
- Pregnancy
- Malignancy
Imaging
Compression Ultrasonography
Principle
- Normal vein = compressible
- DVT = non-compressible vein
Findings
- Loss of compressibility
- Visible thrombus
- Absence of flow
Doppler Ultrasound
Principle
- Evaluates blood flow
Findings
- Reduced or absent venous flow
- Abnormal flow patterns
Management
Core Principle
- Prevent thrombus extension
- Prevent embolization → Pulmonary Embolism
- Reduce recurrence
- Prevent post-thrombotic syndrome
Initial Management
Anticoagulation (Mainstay — Start Immediately)
Options
- DOACs (preferred):
- Rivaroxaban
- Apixaban
- Parenteral anticoagulation:
- LMWH
- UFH (if unstable, renal failure)
Duration
Scenario | Duration |
Provoked DVT (surgery, trauma) | 3 months |
Unprovoked DVT | ≥3–6 months (consider extended) |
Recurrent DVT / cancer | Long-term or indefinite |
Special Situations
Cancer-Associated DVT
- LMWH or DOAC preferred
- Extended duration
Pregnancy
- LMWH (safe)
- Avoid warfarin & DOACs
Thrombolytic Therapy
Indications
- Massive proximal DVT
- Limb-threatening ischemia
- Phlegmasia cerulea dolens
Agents
- Alteplase (tPA)
💊 Pharmacology
Drug Class | Examples | Mechanism | Route | Typical Dose (DVT Treatment) | Key Notes |
Unfractionated Heparin (UFH) | Heparin | ↑ Antithrombin → inhibits IIa & Xa | IV / SC | IV bolus 80 units/kg, then 18 units/kg/hr infusion (titrate to aPTT) | Preferred in renal failure, short half-life, reversible (protamine) |
Low Molecular Weight Heparin (LMWH) | Enoxaparin | Inhibits Xa > IIa | SC | 1 mg/kg SC every 12 hr OR 1.5 mg/kg once daily | Avoid in severe renal impairment, outpatient use |
ㅤ | Dalteparin | Same | SC | 200 IU/kg once daily or 100 IU/kg every 12 hr | Preferred in cancer |
Fondaparinux | Fondaparinux | Indirect Xa inhibitor | SC | Weight-based: <50 kg → 5 mg daily; 50–100 kg → 7.5 mg daily; >100 kg → 10 mg daily | Contraindicated if CrCl <30 mL/min |
Vitamin K Antagonist (VKA) | Warfarin | ↓ Factors II, VII, IX, X | Oral | Start 5 mg daily (adjust to INR 2–3) | Requires heparin bridging ≥5 days |
DOAC – Factor Xa inhibitors | Rivaroxaban | Direct Xa inhibitor | Oral | 15 mg twice daily × 21 days, then 20 mg once daily | No heparin bridging needed |
ㅤ | Apixaban | Same | Oral | 10 mg twice daily × 7 days, then 5 mg twice daily | Lower bleeding risk vs rivaroxaban |
ㅤ | Edoxaban | Same | Oral | 60 mg once daily (after 5–10 days parenteral anticoagulation) | Reduce to 30 mg if renal impairment/low weight |
DOAC – Direct Thrombin Inhibitor | Dabigatran | Direct thrombin (IIa) inhibitor | Oral | 150 mg twice daily (after 5–10 days parenteral anticoagulation) | Renal clearance important |
Parenteral Direct Thrombin Inhibitors | Argatroban | Direct thrombin inhibitor | IV | Start 2 mcg/kg/min, titrate to aPTT | Used in HIT |
ㅤ | Bivalirudin | Same | IV | 0.15–0.2 mg/kg/hr infusion | Alternative in HIT |
Thrombolytics | Alteplase (tPA) | Converts plasminogen → plasmin | IV | 100 mg over 2 hr (massive DVT/PE) | High bleeding risk, reserved cases |
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