Deep vein thrombosis (DVT) and Pulmonary Embolism (PE ) Revision Notes
DVT is a clot in the veins. They can occur in any vein, although they are much more likely in the veins of the pelvis and legs. On their own, they are not particularly significant, however, they are dangerous because they can embolise, and cause a pulmonary embolism – these can be fatal.
Aetiology
- Stasis/immobility – e.g. hospital bed, long flight
- Dehydration
- Oestrogen (pregnancy, and to a lesser extent, the COC pill)
- Genetic clotting defect (e.g. lack of protein C)
- Obesity (atherosclerosis)
- Age (old)
- Varicose veins
- Surgery
- Previous DVT/embolism
- Trauma
- Infection
- Malignancy
Virchow’s triad of risk factors:
- Stasis
- Hypercoagulability
- Vessel wall injury
Signs / symptoms
- Red, swollen leg (particularly calf)
- Tenderness
- Pitting oedema
- Fever
Diagnosis
This is often made clinically, using the Well’s score. this is a list of risk factors, worth 1 point each. (see page tow for furthur details)
- Score >3 – Treat as DVT – and also perform a compression USS to confirm
- Score 1-2 – Treat as DVT – and perform compression USS to confirm
- Score 0 – do a D-dimer test. If negative, then unlikely to be DVT. If positive, Treat as DVT, and perform compression USS.
Differentials
- Ruptured Baker’s cyst
- Cellulitis
- Lymphadenopathy
A clot develops at a sight of damage to a vessel wall (e.g. an atherosclerotic plaque, or perhaps a site of trauma). This can impair venous drainage of the leg. Clots below the knee will rarely embolise, but above the knee, they are far more dangerous. They will often spontaneously resolve over time, however, they are usually treated to reduce the risk of embolism.
- If they appear in a superficial vein, then they do not embolise, and can be left to resolve, you just have to raise the leg.
Investigations
- Venography – this is the gold standard test. A radio-opaque dye is injected into the foot, and then you can see if it is blocked off as it travels up the leg
- D-dimer – a negative test rules out DVT, but a positive test does not diagnose DVT. D-dimer is a breakdown product of fibrin, and can be released by many things, including MI, malignancy, pregnancy, inflammation, stroke, infract, trauma, and is often raised post-operatively.
- Leg measurement – you should measure the diameter of the calf at the same point on each leg, usually 10cm below the tibial tuberosity. If the difference between legs is >3cm this is significant for DVT.
- USS – has about 90% sensitivity above the knee, but only 50% sensitivity for DVT below the knee. This is the test most often performed as it is cheap and reasonably reliable; and along with clinical factors, is all that is needed for diagnosis.
Treatment
The aim is to prevent embolism
- LMWH – this is usually started as soon as the diagnosis is made, and is normally continued for a minimum of 5 days. It is usually stopped when the INR is in the target range (2-3)
- Warfarin – also started at the same time as heparin, but warfarin actually increases coagulability in the first few days of use; hence the use of heparin initially. Warfarin is continued for:
o 6 months if it is the first DVT
o 3 months if it is the first DVT and occurred post operatively
o Indefinately if it is a recurrent DVT or if there is a genetic clotting disorder, or if there are other large risk factors.
Thrombolysis may be used if the PE is termed 'massive'
Paradoxical Embolism
This is basically an embolism that goes through a defect in the heart, and goes on to cause a stroke. The clot passes from a vain to an artery, through some sort of ‘fistula’ – usually a cardiac defect
For example, a DVT could embolise, and travel to the heart. This might in a normal individual, cause a PE. But in the case of a paradoxical embolism it will travel through a defect in the heart from the right side to the left side, and thus miss out the pulmonary circulation. It is then free to travel through the arterial circulation, until it reaches an artery that is so small it cannot travel down it, and thus causes an ischaemic blockage.
- They will often travel to the brain, and cause a stroke.
These account for about 2% of arterial emboli.
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