WHAT IS A DVT?
DVT is the initialism for a Deep Vein Thrombosis. A DVT is a blood clot in a deep vein most commonly in the leg.
WHY IS A DVT IMPORTANT?
The deep veins are the main drainage veins for blood to travel back to the heart. Blockage of these veins can cause local problems where the blockage occurs such as pain and swelling in the short term and skin damage and even leg ulcers in the long term. The blood clot can also break away and then travel through the blood stream to damage vital organs such as to the lungs, where it can cause a Pulmonary Embolus, which can be life threatening by blocking the oxygen supply to the body.
Having had a DVT greatly increases the chances of a further DVT in the future. Also a history of having had a DVT can impact on future life insurance, surgery, pregnancies, medication use such as oestrogen and long haul travel.
IS A DVT COMMON?
The annual incidence is about 1 per 1,000 in the general population, which is about 20,000 Australians each year. Globally it is estimated that 10 million people have a DVT each year.
WHO GETS A DVT?
Anyone can potentially develop a DVT. There are many recognised risk factors that increase the risk of developing a DVT and studies have shown that the risk of DVT increases in proportion to the number of predisposing factors. It is important to realise that the predictive value of these risk factors is not equal.
The strongest risk factors are
- Fractures of the hip or leg
- Hip or knee replacement (with estimates of 10% incidence of DVT after hip replacement and 25% after knee replacement)
- Major general surgery (anaesthetic more than 30 minutes)
- Major trauma
- Spinal cord injury
Moderate risk factors are
- Knee arthroscopy
- Heart or respiratory failure
- Oestrogen medication (Oral Contraceptive or Hormone Replacement Therapy)
- Thrombophilia (Inherited tendency to clot more easily)
- Stroke causing paralysis.
Weak risk factors are
- Bed rest (over 3 days)
- Increasing age (over 40 risk significantly increases then risk doubles again with each subsequent decade)
- Immobility with long haul travel (risk doubles with flights over 4 hours and 5% of patients admitted to hospital with a DVT appear travel related)
- Varicose Veins
Multiple risk factors can coexist in the one individual and when a DVT occurs and significant risk factors are able to be identified then this is called a Provoked DVT.
It is important to realise that the period of increased risk for DVT can extend for some time after a particular event. For example after major joint surgery or cancer surgery the period of increased risk of DVT is thought to extend out to 4 weeks after surgery and after a long haul plane flight the risk is said to remain high for a week after landing.
Certain chronic medical conditions such as active cancer, inflammatory bowel disease and Antiphospholipid syndrome increase both the risk of a DVT in the first place and then of recurrent DVT’s in the future.
Sometimes there is no known reason why a DVT occurs (called Unprovoked DVT) and the distinction between a DVT that is provoked or not provoked is important as it influences the risk of further DVT’s in the future (Recurrent DVT) and how long treatment of a DVT with anticoagulant medication is needed.
Where there is no obvious reason for a DVT it is important to consider the possibility of an undiagnosed cancer as around 10% of patients with an unprovoked DVT are diagnosed with a cancer in the year after the DVT.
HOW DO YOU KNOW IF YOU HAVE A DVT?
Symptoms of a DVT typically include pain and swelling in one leg. Signs include swelling in one leg that can dent with finger pressure (called pitting oedema), localised tenderness along distribution of the deep venous system and pain on flexing the ankle (called Homans sign).
If there is a suspicion of a DVT then doctors often use a clinical algorithm called the Wells score to determine the probability that there is a DVT.
The appropriate investigation to diagnose if there is a DVT is an Ultrasound scan which is non-invasive and painless.
It is important to understand that there may be no symptoms with a DVT, especially in the calf, and that the first presentation in some patients is when a clot has already gone to the lungs and caused a pulmonary embolism. This underlies the importance of strategies to prevent a DVT before it occurs.