What is Deep Vein Thrombosis? What Is DVT?

Deep vein thrombosis, also known asDVT refers to the formation of a thrombus in a deep vein in the leg. A thrombus is a blood clot. Deep vein thrombosis tends to occur in leg veins, such as the popliteal or femoral veins, as well as deep veins within the pelvis. In some cases, as with Paget-Schrötter disease, they may form in the veins of the arm. If the thrombus breaks off, it is known as an embolus - a piece of blood clot - and can make its way to the lung, resulting in a pulmonary embolism. In other contexts, an embolus may also refer to a piece of fat or an air bubble.

Deep vein thrombosis and pulmonary embolism are two parts of the disease known as venous thromboembolism.

Some people may develop DVT and not be aware of it; there will be no symptoms. Commonly, though, the patient will experience pain, swelling, redness, tenderness and warmth in the affected area; superficial veins may swell up too. 

DVT must be treated as a medical emergency. 3% of DVTs that develop in the leg eventually kill the patient, mainly due to a pulmonary embolism complication.

According to Medilexicon's medical dictionary:

Deep vein thrombosis is the "formation of one or more thrombi in the deep veins, usually of the lower extremity or in the pelvis. Carries a high risk of pulmonary embolism."

DVT has developed on the patient's right leg. The swelling and slight redness is noticeable

How common is deep vein thrombosis (DVT)?

According to the National Institutes of Health (NIH), USA, DVTs affect approximately 1 in every 1,000 adults in America each year. Public health authorities estimate a total incidence of between 350,000 and 600,000 cases of DVT or PE annually. About 100,000 people lose their lives each year because of a DVT/PE related condition each year.

Although DVTs may occur in children, they are extremely rare. US authorities estimate that approximately 1 in every 100,000 children (under 18 years) in the country develops DVT each year.

In rich nations, DVT is the second most common cause of maternal death, after bleeding. In the USA, Canada and Western Europe, DVT is thought to occur in 0.5 per 1,000 pregnancies.

Patients undergoing knee- and hip-surgery have a 1% risk of developing DVT, while those undergoing knee arthroplasty run a 0.5% risk, says the NIH.

What are the signs and symptoms of deep vein thrombosis (DVT)?

The difference between a sign and a symptom - the patient feels and describes a symptom, such as a pain, while signs can be detected by other people, including doctors and nurses, and may include a rash, redness or swelling.

As mentioned earlier, some people may have developed DVT and have no symptoms. If signs and symptoms do occur, they may include:

• Pain in the affected limb. In many patients, pain starts in the calf.

• Swelling in the affected limb

• The skin of the affected leg may feel warm

• The skin may go red, especially below the knee behind the leg. The skin may be discolored.

• The surface veins of the affected limb may become dilated

• Leg fatigue

In the majority of cases, only one leg is affected. However, on rare occasions both legs may have a DVT.

If the clot becomes dislodged and finds it way to the lung, the following signs and symptoms may indicate pulmonary embolism:

• Breathlessness - this may develop slowly, or come on suddenly

• Chest pain, pain is usually more severe during inhalation, eating, coughing, stooping or bending over. During exertion the pain will get worse, and will not go away when the patient rests.

• Coughing may produce bloody or bloodstained sputum

• Wheezing

• Lightheadedness, and sometimes even fainting (collapse)

• Unexplained anxiety

• Accelerated heartbeat

What are the causes of deep vein thrombosis?

Sometimes a person can develop DVT for no clear reason. However, in the majority of cases, DVT occurrence is linked to one of the circumstances or conditions listed below.

Inactivity - if the human body is inactive for some time, blood has a tendency to accumulate in the lower limbs and pelvic area. In most cases, this is not a problem, because as soon as physical activity is resumed, blood flow accelerates and blood is redistributed around the body.

If inactivity is prolonged, however, the accumulation of blood in the legs can slow down blood flow, which in turn raises the risk of clots forming.

Inactivity may be due to being hospitalized, bed-ridden at home, seated during a long journey, or disability.

Injury or surgery - injury which damages veins, or surgery can slow down the flow of blood, thus raising the chances of blood clots. General anesthetics can dilate the veins, which makes it more likely that blood pools and clots form.

Genetics - a disorder that makes it more likely that blood will clot can be inherited. In most cases the risk is only there if it is combined with at least one other risk factor.

Pregnancy - as the fetus grows inside the mother, pressure against the veins of the legs and pelvis becomes greater. A pregnant woman's higher risk of DVT continues until a few weeks after she has given birth. Females with some inherited blood disorders have a considerably higher risk of DVT when they are pregnant, compared to other women.

Cancer - some types of cancers are associated with a higher risk of DVT, as are some cancer therapies.

Ulcerative colitis - as well as some other inflammatory bowel diseases, raise the risk of developing DVT.

Heart failure - this is when the heart does not pump blood properly around the body. People with heart failure have a considerably higher risk of DVT.

HRT (hormone replacement therapy) - postmenopausal females on HRT have a higher risk of DVT.

Oral contraceptives - a higher percentage of women on oral contraceptives develop DVT compared to women of the same age and health who do not take oral contraceptives.

Previous DVT - patients who have had deep vein thrombosis before have are at risk of recurrences.

Obesity - obese people have more pressure on their veins, especially those in the pelvis and legs.

Smoking - regular smokers are more likely to develop DVTs compared to ex-smokers or lifetime non-smokers.

Height - tall men, but not tall women, have a higher risk of DVT, compared to other men of the same age and health.

Central venous catheters - which are placed into a vein to administer medication, fluids or to obtain blood tests, are associated with a higher DVT risk.

Orthopedic casts - these are made of plaster and worn around, for example, the leg when a bone is broken so that it can heal. People with an orthopedic cast on their leg have a higher risk of developing DVT.

Economy class syndrome is a myth - a recent study says that long flights in economy class are not linked to a higher DVT risk, compared to travelling on first class. (Link to article).

How is deep vein thrombosis diagnosed?

The doctor will ask patients questions about symptoms, their medical history, and carry out a physical examination. Diagnosing DVT from just signs and symptoms is usually not enough, and the doctor may recommend some tests.

D-dimer test - D-dimer is a protein fragment which is present in blood after a blood clot is degraded by firbinolysis, if more than a certain amount is found in a blood test, it is likely that the patient has a blood clot in a vein.

Ultrasound - this type of scan can detect clots in veins, and also determine bloodflow speed within a vein. If a doctor knows blood flow has slowed down, he/she may be able to locate a clot if there is one. A Doppler ultrasound (Doppler sonography) can tell how fast blood is flowing.

Venogram - this diagnostic test may be used if the ultrasound scan and D-dimer tests are inconclusive. The doctor injects a dye into a vein in the patient's foot or groin. X-ray images can see the dye as it moves and will reveal the location of a blood clot, because the dye will not be able to flow around it - it will appear as a gap in the blood vessel.

Other imaging scans - magnetic resonance imaging (MRI) or computerized tomography (CT) scans may reveal the presence of a clot. Often, such clots are revealed when these scans are ordered for other reasons.

What are the treatment options for deep vein thrombosis (DVT)?

The doctor's aim when treating somebody with DVT is to stop the thrombus (clot) from growing, preventing it from becoming dislodged and getting into the lung and causing pulmonary embolism, preventing DVT recurrence, and minimizing the risk of other complications.

Anticoagulants - these are drugs that prevent the clot from getting bigger, as well as stopping it from breaking off and causing a pulmonary embolism. There are two types of anticoagulants used in the treatment of DVT - heparin and warfarin.

Because of heparin's immediate effect, it is administered first; usually a brief course of injections lasting less than a week. A 3 to 6-month course of warfarin oral tablets is also prescribed to prevent a recurrence of DVT.

For those with recurrent DVTs, anticoagulant medication is usually taken for the rest of the patient's life.

Thrombolysis - this means the breaking down of blood clots. Drugs that break down clots are called thrombolytics or clotbusters. Patients with more serious DVT or pulmonary embolism may require such drugs. TPA (tissue plasminogen activator) is an example. Because of their risk of side effects - namely bleeding - they are only used when the patient's life it as risk.

Inferior vena cava filter - this tiny umbrella-like device is inserted into the vein to catch blood clots and stop them moving up into the lungs, while allowing blood flow to continue. It is inserted in the vena cava, a large vein.

Compression stocking - these are worn to help reduce calf pain, swelling, and to prevent ulcers from developing. Stockings can also protect the patient from post-thrombotic syndrome. Post-thrombotic syndrome is a long-term DVT complication which affects between 20% and 50% of patients with DVT - tissue in the calf becomes damaged, resulting in pain, itching, tingling, the formation of ulcers, skin discoloration and swelling.

A patient with DVT will have to wear stockings for at least 24 months. They need to be worn all the time.

What are the possible complications of deep vein thrombosis?

There are two possible complications:

• Pulmonary embolism (PE) - the most common complication, and also often a life-threatening one. A piece of the clot becomes dislodged and makes its way through the bloodstream into the lungs, where it gets stuck. The clot undermines the flow of blood in one of the blood vessels in the lung. In mild cases the patient may not even notice it. A medium-sized clot may cause breathing problems and chest pain.

  In more serious cases, the lung might collapse and there could be heart failure, and even death.

• Post-thrombotic syndrome - also known as postphlebitic syndrome, is more common among patients with recurrent DVTs. The patient may experience persistent swelling in the calf area, pain, bleeding into the skin (purpura), ulceration, itchiness, eczematoid dermatitis, and cellulitis.