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Deep Vein Thrombosis

Deep vein thrombosis (DVT) affects 1 in every 1,000 people. It may occur without warning and without any previous history of medical problems. This article aims to explain what DVT is, its risk factors, prevention, diagnosis and treatment.

What is a DVT?

DVT is a clot that forms in the deep veins of the legs, but it may potentially occur in any deep vein. In addition, clots can also form in more superficial veins. This is referred to as superficial thrombophlebitis. Except for some soreness, this condition is usually harmless.

In an instance of DVT, a clot results in the blockage of a deep vein. Pressure then builds up behind the clot, and the vein walls start to leak. This results in the following symptoms:

Swelling
Redness and a sensation of heat
Pain in the affected limb (usually below the knee, in the calf area)

The most serious consequence, of DVT is a ruptured blood clot. A clot fragment, known as an embolism, may travel upwards and become lodged in the vessels of the lung. This would create a pulmonary embolism, which is potentially fatal. Another serious, but rare complication, can result in severely reduced blood flow to the affected limb. This can happen if the pressure behind the clot is so high that it prevents blood flowing from arteries in the limb.

Am I at risk of DVT?

DVT is more likely to occur in veins that have damaged walls, stagnant blood flow and/or thick viscous blood. Each of the factors listed below will increase your risk of suffering from DVT. The risk increases down the list:

Obesity
Use of the combined oral contraceptive
Patients suffering with any form of cancer
Some cancer treatments, e.g. Tamoxifen
Immobility, especially associated with illness
Long distance travel, seated for greater than 4-6 hours
Pregnancy
Disorders that make the blood more likely to clot
Previous DVT
Major surgery or trauma involving the pelvis or legs*

*The risk does depend on the type of surgery and can be greatly mitigated if appropriate preventative measure are taken by the surgical team.

DVT prevention in hospital

When admitted into a hospital, if the patient is not mobile, or is returning from surgery, their doctor will commence them on daily low molecular weight heparin injections. Heparin is a blood thinning agent which helps to reduce the risk of clot formation. The patient will be advised to wear compression stockings in order to aid blood flow back from the veins in the legs to the heart.

In addition to heparin, NICE has approved new drugs such as dabigatran and rivaroxaban, which can be used in the prevention of DVT. Currently rivaroxaban is being trialled in some UK hospitals. Rivaroxaban prevents the need of daily heparin injections and instead is taken orally, once a day and does not require regular blood tests like warfarin. The use of this drug is mainly being trialled in orthopaedic leg surgery, where the risks of DVT are higher. The drug is started after surgery and continued for a few weeks.

Travelling and DVT prevention

The principle of prevention can also be applied to long distance travel (greater than 4 hours), such as flying and long coach trips. Travellers should be advised to try and get up and walk around every two hours, though this may not always be possible. The act of walking and using the muscles in the legs helps to squeeze blood back to the heart, avoiding sluggish blood flow. While sitting down, exercise both feet by bending the feet up and down frequently. It is also important to stay well hydrated, as dehydration is thought to be a contributing factor for DVT. Wearing graduated compression flight stocking (class 2) are a good idea, as they prevent blood pooling in the legs.

With regards to taking aspirin, there is not enough evidence regarding its use in the prevention of DVT for long haul travel.

How is it diagnosed?

Doctors will usually suspect DVT when a patient presents with pain in the calf region and physical signs of swelling, tenderness, redness and associated risk factors.

In cases where there is diagnostic uncertainty, the doctor may first proceed with a blood test called a D-dimer. A negative D-dimer result makes DVT very unlikely. A positive result however, is usually less helpful and normally requires further investigation.

In cases where the D-dimer is positive, or where there is a high degree of suspicion of DVT, the first line test is usually an ultrasound doppler. In rare cases, an ultrasound doppler may be inconclusive, and doctors will then proceed to use contrast venography. This is a test which involves injecting dye into the vein, making the veins visible on x-ray. This test will detect any obstructions to blood flow in the veins caused by DVTs.

Treatment

The mainstay of DVT management involves the following treatments:

Low molecular weight heparin (LMWH)
Warfarin
Compression stockings
Surgery

Patients strongly suspected of having a DVT are normally started on daily LMWH injections until the diagnosis can be confirmed with an ultrasound doppler. If DVT is excluded, then the LMWH injections are stopped and an alternative diagnosis is sought.

In confirmed cases of DVT, LMWH is continued until the patient can be stabilised on warfarin. Duration of warfarin therapy in patients with a first time DVT of unknown cause, is usually only for three months. Treatment may continue for six months if the patient has a persistent risk factor. In patients with previous DVT, cancer or a high risk blood clotting disorder, treatment is usually indefinite.

Warfarin requires taking daily tablets and frequent blood tests to monitor the degree of blood thinning. The blood test is called an INR and tells doctors how “thin” the patients blood is. A normal INR is 1.0. In DVT therapy the aim is usually to achieve an INR of between 2.0 to 3.0. Initially monitoring is required weekly, but as the INR stabilises, blood tests can be taken less frequently.

Compression stocking are used to reduce pain and swelling by aiding blood flow back to the heart. Some patients with DVT, they may develop chronic swelling and pain. For them, compression stockings can be particularly helpful.

Surgery for DVT is exceptionally rare. It is usually a last resort used for patients who are unable to take anticoagulants as well as for those with recurrent clots while on anticoagulants. In the latter group, surgeons will also insert a filter into the inferior vena cava (large vein carrying blood from the lower part of the body back to the heart) to prevent potential future embolisms travelling to the lungs.

Author: Dr Shazan Chughtai, MB BS

Editor: Dr Ahmed Farooq, BMedSci, BDS,MJDF (RCS Eng)

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