What is Deep Vein Thrombosis?

‘Thrombosis’, or blood clotting, is a natural protective mechanism that prevents excessive bleeding when the body is injured. However, clotting becomes a problem when it obstructs blood flow. Clotting can occur in deep and superficial veins. Deep veins lie within muscles or body cavities, whereas superficial veins lie beneath the skin in the fat layer. Deep Vein Thrombosis (DVT) is the development of a blood clot in a deep vein.

Although the deep veins of the legs are most commonly affected, a DVT can also affect the deep veins of the arms, pelvis or abdomen. DVT can damage the affected deep vein, leading to chronic pain, swelling and skin changes of the affected limb. This is called post-thrombotic syndrome. DVT can also interfere with the return of blood to the heart, and result in swelling, pain and inflammation of the affected limb. If part of the blood clot breaks off and travels to the lungs, it creates a condition called Pulmonary Embolism (PE), which may be life threatening. Signs of PE can include chest pain, palpitations, shortness of breath, coughing (with or without blood) and even sudden death. DVT requires immediate medical evaluation. Prompt treatment of DVT is vital to minimise immediate or long-term complications.

When clots form in superficial veins, this is called Superficial Venous Thrombosis (SVT). If SVT leads to inflammation of the adjacent skin and fat, red tender lumps develop. This is called superficial thrombophlebitis (STP), or simply ‘phlebitis’.
While blood clots in superficial veins rarely cause serious problems.

Symptoms

Symptoms of DVT can include swelling, tenderness and warmth of the affected limb. However, up to 50 per cent of patients with a DVT show no symptoms. These are called ‘silent’ or ‘asymptomatic’ DVTs. Silent DVTs may resolve by themselves or can lead to complications such as pulmonary embolism.
Other conditions may present with similar symptoms to a DVT. These include soft tissue injury (muscle strain), inflammation of superficial veins (phlebitis), infection (cellulitis), skin inflammation (dermatitis) or a ruptured cyst behind the knee (ruptured Baker’s cyst).

What causes DVT?

Many external factors contribute to the formation of a DVT. One of the most common risk factors is immobility caused by long distance travel or hospitalisation. Some people are naturally predisposed to DVT because of an inherited tendency to clotting.
Several risk factors need to be present for a DVT to develop.

DVT Risk Factors

Reduced mobility

Contraction of the calf muscles during walking results in blood flow in the veins towards the heart. With immobility, blood flow becomes sluggish and the blood is more likely to clot. This leads to an increased risk of DVT. Patients over 60 are generally at greater risk, although patients of any age with reduced mobility (such as during long distance travel, or through illness or hospitalisation) can be affected. Long distance travel would be a trip of more than five hours, with prolonged sitting in a car, bus, train, plane or any other vehicle. In addition, the lower oxygen levels and humidity in a plane cabin may further increase the risk of developing DVT.

Injuries

Blood vessels may be damaged through trauma to the leg. Examples of such injuries include physical trauma, surgery or radiation therapy for cancer. Traumatic injuries damage the inner lining of veins, which can then trigger clot formation.

Obesity

Obesity is a known risk factor for cardiovascular diseases and is usually associated with reduced mobility, which adds to the DVT risk.

Pregnancy

Pregnancy increases the risk of DVT by several-fold. Most cases occur in the third trimester and immediately following delivery.

Oral contraceptives and hormone replacement therapy (HRT)

Hormonal medications such as oral contraceptive pills or HRT increase the risk of clotting, particularly when combined with other risk factors. Patients with a history of DVT should consult their doctor before commencing any hormonal medications or treatments.

Cancer and other illnesses

Cancers may increase the blood’s tendency to clot. Cancers of the ovaries, pancreas, lymphatic system, liver, stomach, and colon are particularly likely to provoke DVT. Infections and medical conditions such as systemic lupus erythematosus (SLE), Crohn’s disease, rheumatoid arthritis, and glomerulonephritis may also stimulate the blood clotting process and promote DVT.

Inherited clotting disorders (Thrombophilia)

If blood clots occur in more than one person in a family, there may be an inherited clotting disorder which is caused by mutations in your genes. Genetic mutations can cause defective blood clotting factors. Individuals who inherit one of these mutations from either parent may experience recurrent episodes of DVT, but the risk is highest if both parents were affected. Other inherited causes include deficiencies of certain blood components that ordinarily help dissolve blood clots, or cause increased homocysteine, a compound that increases the tendency for the blood to clot, as well increasing the risk of stroke and heart attack.

Smoking

The role of smoking in the development of DVT’s is controversial. In principle, smoking reduces the amount of oxygen in the blood stream and may damage vessel walls, potentially leading to clot formation.

How to reduce the risk of DVT

There are things we can do to mitigate the risk of developing DVT:

  • If you are scheduled for surgery or other procedures, make your GP aware if you have had a blood clot in the past.
  • When driving long distances, break up the trip with frequent rest stops at least every two hours to walk around.
  • If you are on a plane, perform heel/toe lifts frequently at regular intervals and walk around when you can.
  • Avoid sitting still for long periods. When watching TV or reading, get up and move around once an hour.
  • When sitting, perform heel/toe lifts. These exercises increase blood flow in your legs, reducing the likelihood of a clot.
  • Drink plenty of fluids, but avoid alcohol, coffee or tea. They will dehydrate you and increase the risk of clotting.
  • If you have a family history of blood clots, discuss with your GP getting a blood test to determine if it is genetic.
  • If you have had a DVT, are pregnant, or have varicose veins, discuss trying compression stockings with your GP.
  • Do not smoke.

Diagnosing DVT

If DVT is suspected, the following tests may be useful to confirm the diagnosis.

Duplex Ultrasound

This is a combination of ultrasound and Doppler (hence ‘duplex’) technology to assess the blood flow. The ultrasound waves travel through the tissue and back, enabling a computer to transform them into a moving image. Duplex ultrasound is the most popular method for diagnosing DVT; it is painless, non-invasive and relatively easy to perform.

Magnetic Resonance Imaging (MRI)

MRI uses a strong magnet to create a clear, high-quality image of the body’s internal structures. It can be very effective in diagnosing DVT, especially in the thigh and pelvic areas. However, it is an expensive procedure and is only used in special circumstances.

Diagnosing Pulmonary Embolism

The symptoms of pulmonary embolism (PE) are not very specific and can be present with many other conditions. Up to 75 per cent of patients suspected of having PE do not actually have this condition. Special diagnostic tests, therefore, need to be performed. The three tests currently used to diagnose PE are pulmonary angiography, nuclear medicine lung scans and spiral CT scans.

Treating DVT

If you are diagnosed with a DVT, treatment will begin immediately to reduce the risk of the clot extending further or breaking off.
The type of treatment depends on the location of the clot and the likelihood of further complications. Patients who receive early treatment will significantly reduce their chances of developing a Pulmonary Embolism. . the clot stabilises and attaches firmly to the wall of the vein. The risk of the clot breaking off and travelling to the lungs, therefore, decreases over time.

There are a few methods for treating blood clots, the most common being anticoagulant medications, or blood thinners. These medications make it so your blood does not clot as easily. The clot will then stabilise and attach itself firmly to the wall of the vein, where it can be absorbed back into the body. Standard anticoagulant medications include heparin and warfarin. Regular blood tests may be required to monitor the effectiveness of these medications, and it is important to take these medications exactly as prescribed. You may be asked to keep a record of your dosages.

In rare cases, clot dissolving (thrombolytic) agents are administered. For patients who are unable to tolerate medications, surgical removal of the clot (thrombectomy) or a filter may be inserted into a major vein.

How long do patients need to be treated for DVT?

Depending on the underlying condition that caused the DVT, treatment may be needed for as little as four weeks, or for the rest of the patient’s life. In patients with an obviously reversible cause of a DVT (for example, trauma, after orthopaedic surgery or prolonged bed rest), four to six weeks of therapy are usually adequate. The risk of a recurrent DVT in these patients is very low.

In patients with an identified cause of DVT that cannot be reversed (for example, cancer, inflammatory bowel disease or inherited conditions), therapy should continue for at least six to 12 months and may need to be continued indefinitely.

Patients with no identifiable cause of their DVT have been shown to experience a high incidence of recurrent blood clots if they are treated for three months or less. Most physicians, therefore, recommend at least six months of anticoagulant therapy for these patients.

Long-term consequences of DVT

Very early in the development of a DVT, the body actually produces blood factors that help dissolve the clot. If the clot is in a superficial vein of the leg, or even in a calf vein, the clot frequently will dissolve totally. However, almost 90 per cent of patients with a large DVT in the thigh or groin will be left with some abnormality in the deep veins, even after adequate treatment.

In about 25 per cent of cases, DVT damages the affected vein and leads to long-lasting post-thrombotic syndrome (PTS). This presents as brownish discoloration of the skin, itching, swelling, slow-healing sores and pain. The affected skin becomes scarred and fragile and can easily break down into an ulcer. It can also increase the risk of additional blood clots.

PTS almost always occurs within two years of the initial diagnosis of DVT. The damage may be partially prevented, however, if the patient wears graduated compression stockings as part of their long-term care for DVT.

A small number of patients suffer from recurrent pulmonary emboli, which can lead to high blood pressure in the lungs. This condition, in turn, can cause problems with the functioning of the heart and may require further medical or surgical treatment

Frequently Asked Questions

Can DVT affect young and healthy people?

DVT mainly affects the older age group. However, individuals carrying the abnormal clotting genes may suffer multiple blood clots at a young age.

Is the oral contraceptive pill a risk factor for DVT?

Yes. However, the vast majority of women on the pill do not suffer from blood clots. Other risk factors, such as prolonged immobility, should be avoided when taking the contraceptive pill.

Does being overweight increase the risk of DVT?

Obesity is a known risk factor for cardiovascular diseases, including the development of DVT. Obesity is usually associated with reduced mobility, which compounds the DVT risk.

If I develop DVT, do I have to be on treatment forever?

No, not usually. In patients with a clear DVT trigger that is reversible, treatment usually takes six to 12 weeks. For cases in which the risk of developing new thromboses remains high (such as in patients with certain cancers or genetic abnormalities), therapy may need to be continued for months to years. Some patients remain on oral medication for life.

What can I do to help prevent DVT on a long flight?

Wear comfortable, loose-fitting clothes for travel. Drink plenty of water or juice but avoid drinking alcohol. When seated, shift the position of your body periodically. You can also do simple exercises or walk around the plane when safely permitted. Wear compression stockings and avoid sleeping tablets.

Can sclerotherapy treatment on leg veins cause DVT?

The DVT risk associated with sclerotherapy is exceptionally low, making it one of the safest procedures for vein treatment. Post-treatment compression and walking are important factors that help prevent DVT.

Does taking aspirin prevent DVT?

Although commonly taken and prescribed, there is no evidence that aspirin reduces the likelihood of DVT.

Can surgery on leg veins cause DVT?

The DVT risk associated with surgery can be quite significant. Reports of five per cent DVT after varicose vein operation on one leg, and 15 per cent after varicose vein operation on both legs, have appeared in scientific literature. The risk varies depending on patient factors such as age, weight, gender and degree of mobility after surgery. Most patients are discharged on the same day and are mobile fairly quickly, which is important in prevention of DVT.