What is deep vein thrombosis?

Deep Vein Thrombosis (DVT) is a thrombus that forms in one of the deep veins of the body, usually the legs. Thromboses of the deep veins in the upper limbs and unusual sites such as mesenteric veins constitute less than 10 per cent of DVT cases. DVT in the legs can be divided into three main types based on their location.

• Iliofemoral DVT: affects the major vein in the pelvis (iliac vein) and may also involve the femoral vein in the thigh.
• Femoral-popliteal DVT: predominantly affects the femoral vein in the thigh and the popliteal vein behind the knee.
• Calf vein DVT: predominantly affects the smaller deep veins in the lower leg. Calf vein DVTs have the lowest risk of complications.

If a leg DVT is not treated there is a risk of pulmonary embolism (PE). PE (symptomatic or asymptomatic) occurs in about 50 per cent of patients with proximal (popliteal and above) DVT and in about 5 per cent of those with distal DVT.
 

What are the warning signs/symptoms of DVT?

• Swelling, tenderness and warmth in the affected limb, especially in the calf.
• Up to 50 per cent show no signs.
• Symptoms are not specific and can vary widely in their presentation and severity.

Other conditions present with similar symptoms to DVTs including muscle strain, phlebitis, cellulitis, dermatitis or ruptured Bakers cyst.

 

What are the causes of DVT?

In 25 per cent of cases, no clinical cause can be ascertained.

Risk factors

• The single most powerful risk factor is a prior history of DVT, seen in 25 per cent of patients.
• Venous disorders such as varicose veins.
• Immobility, examples include long haul flights or car journeys (>8 hours), travel or work in seats with small, cramped leg space, prolonged hospitalisation (>3 days), major surgery in previous 4 weeks, hip or knee replacement surgery, fractures of the hip or lower limb, major trauma, spinal cord injury, obesity and advancing age.

Predispositions

• Pregnancy: post-partum.
• Cancer and other medical conditions: e.g. Sepsis, Rheumatoid arthritis, Lupus, Crohn's.
• Inherited or acquired blood clotting disorders: Factor V Leiden, Prothrombin gene mutations, Protein C, S or Antithrombin III deficiency, Antiphospholipid antibodies.

Medications that predispose to thrombosis include:

• Hormone therapy (Oral Contraceptive Pill /Hormone Replacement Therapy).
   

Assessment and diagnosis

• Clinical diagnosis is not reliable. Among adults in primary care settings who have signs and/or symptoms of DVT, only 29 per cent had ultrasound scans proven DVT.
• Duplex Ultrasonography is the diagnostic imaging of choice to evaluate lower and upper limbs for DVT because it is non-invasive and safe. Other methods include Venography, CT and MRI especially for DVT in the abdomen and pelvis.
• CT/MRI or venography may be indicated in patients with unexplained swelling of the entire leg and a negative scan, the possibility of pelvic vein thrombosis should be considered
• Blood tests for a hypercoagulable state are required if there is no obvious cause - FBC, Activated protein C resistance, Antithrombin III levels, Antiphospholipid antibodies, Lupus anticoagulant, Protein C and Protein S.

 

What are the treatment options for DVT?

Anticoagulation

In recent years, clinical practice has shifted to favour using Novel Oral Anticoagulant (NOAC) over low molecular weight heparin for treatment of DVT. Although there has been some debate over the value of treating isolated distal deep vein thrombosis, as opposed to serial imaging in two weeks, the most recent advice is to commence anticoagulation. A patient with the first episode of a proximal vein thrombosis should receive anticoagulants for six months if there are no contraindications.

Surgery

• IVC Filter: This is reserved for those who have contraindications to anticoagulation. IVC filter is designed to prevent pulmonary embolism.
• Thrombolysis: This is reserved for iliofemoral DVTs, to dissolve the clot to reduce post-thrombotic syndrome. The process has been improved with the introduction of mechanical thrombectomy catheters which also does thrombolysis concurrently.

Compression Stockings

Knee-high graded compression stockings are strongly recommended to prevent post-thrombotic syndrome (PTS), which occurs in 60 per cent of patients following DVT. It is characterised by pain, swelling and the possible development of pathological changes of venous hypertension, including leg ulceration.

Graduated compression stockings reduce the incident and severity of the post-thrombotic syndrome, and are indicated in most cases of DVT. Studies show a number needed to treat (NNT) of 4.3 to prevent 1 PTS. They should be worn for up to 18 months and patients should be encouraged to mobilise early as this results in decreased pain and swelling and does not increase the risk of PE.

If you develop chest pain, haemoptysis, SOB or syncope, call 000 or attend your nearest Emergency Department.

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