Define Deep Vein Thrombosis & Venous Thromboembolism. Describe its pathophysiology, clinical features, investigations and prevention.

The Concept

Deep vein thrombosis (DVT) is the formation of a thrombus within a deep vein, usually of the leg or pelvis. Its great importance is that part of the clot can break off and travel to the lungs as a pulmonary embolism (PE) — the two together being called venous thromboembolism (VTE), a major, often preventable, cause of hospital death. So the topic is really about recognising, treating and — above all — preventing clot in the deep veins.

Pathophysiology — Virchow's Triad

Thrombosis is driven by Virchow's triad of three contributing factors: venous stasis (immobility, surgery, long-haul travel), endothelial injury (trauma, surgery), and hypercoagulability (malignancy, pregnancy, the oral contraceptive pill, inherited thrombophilia, sepsis). Any clinical situation combining these raises VTE risk.

Risk Factors

Key risk factors are recent surgery (especially orthopaedic and pelvic), immobility, malignancy, pregnancy and the combined oral contraceptive pill, previous VTE, obesity, thrombophilia, and long-haul travel.

Clinical Features

A DVT typically causes a unilateral, swollen, painful, warm, red leg with calf tenderness and dilated superficial veins — though it may be silent. A PE presents with pleuritic chest pain, breathlessness, haemoptysis and, if massive, collapse — always to be feared in a patient with a DVT.

Investigation

Assessment uses a clinical probability score (the Wells score) to guide testing. A D-dimer is sensitive but not specific — a normal D-dimer in a low-probability patient helps exclude VTE, but a raised one is non-specific. Duplex ultrasound of the leg confirms a DVT, and CT pulmonary angiography (CTPA) diagnoses PE.

Management & Prevention

• Anticoagulation is the mainstay — a direct oral anticoagulant (DOAC such as rivaroxaban or apixaban), or LMWH bridging to warfarin; the duration depends on whether the VTE was provoked or unprovoked.
• An IVC filter is used if anticoagulation is contraindicated.
• Prevention (thromboprophylaxis) is crucial in hospital patients — a combination of mechanical measures (graduated compression stockings, intermittent pneumatic compression) and pharmacological prophylaxis (LMWH), along with early mobilisation, based on individual risk assessment.

Complications of DVT are PE (life-threatening) and the post-thrombotic syndrome (chronic venous insufficiency of the leg).

Provoked VS Unprovoked Vte

The distinction between provoked and unprovoked VTE guides the duration of anticoagulation. A provoked event has a clear transient cause (recent surgery, immobility, pregnancy) and, once the provoker resolves, may need only a defined course (e.g. 3 months). An unprovoked event, with no obvious trigger, carries a higher recurrence risk and may warrant long-term anticoagulation, and prompts consideration of an occult malignancy or thrombophilia. Tailoring duration to this distinction balances recurrence risk against bleeding risk.

Massive PE — an Emergency

The feared complication, massive pulmonary embolism, is a distinct emergency: a large embolus obstructing the pulmonary circulation causes acute right heart strain, hypotension and collapse, and may be rapidly fatal. It is treated with resuscitation and, in the haemodynamically unstable patient, thrombolysis (or embolectomy), rather than anticoagulation alone. Recognising the shocked, breathless patient with a swollen leg as a possible massive PE is life-saving.

The Primacy of Prevention

The overarching message of VTE in a surgical setting is prevention, because most hospital-associated VTE is avoidable. Every admitted patient should undergo a VTE risk assessment balanced against bleeding risk, and receive appropriate prophylaxis — early mobilisation, mechanical measures (compression stockings, intermittent pneumatic compression), and pharmacological prophylaxis (LMWH) for those at risk. This systematic approach has substantially reduced deaths from hospital-acquired PE and is a routine part of surgical care.

A Note on Thrombophilia & Malignancy

Two associations deserve mention. An unprovoked or recurrent VTE, VTE at a young age, or a strong family history prompts consideration of an inherited thrombophilia (such as factor V Leiden, protein C/S or antithrombin deficiency, or the antiphospholipid syndrome). Equally, an unprovoked VTE in an older patient can be the first sign of an occult malignancy (cancer causes hypercoagulability — Trousseau's sign of migratory thrombophlebitis), so appropriate assessment for an underlying cancer is considered. These links explain why the cause of a 'spontaneous' clot is always sought.

• Virchow's triad: stasis, endothelial injury, hypercoagulability.
• Investigate: Wells score → D-dimer (rule out if low probability) → duplex ultrasound (DVT)/CTPA (PE).
• Treat with a DOAC (rivaroxaban/apixaban); prevent with LMWH + mechanical prophylaxis + early mobilisation.

Prophylaxis prevents more deaths than any treatment.

• DVT = thrombus in a deep vein (leg/pelvis); risk of PE (together = venous thromboembolism, VTE) — a preventable cause of death.
• Virchow's triad: stasis (immobility, surgery, travel), endothelial injury, hypercoagulability (malignancy, pregnancy/OCP, thrombophilia).
• Unilateral swollen, painful, warm leg; PE → pleuritic chest pain, dyspnoea, haemoptysis.
• Wells score + D-dimer (rule out if low probability) + duplex ultrasound (DVT)/CTPA (PE).
• Anticoagulate (DOAC); IVC filter if anticoagulation contraindicated; prevent with LMWH + mechanical prophylaxis + early mobilisation.