Deep Vein Thrombosis (DVT)
Deep Vein Thrombosis is a common disorder relating to the formation of blood clots in major veins. It can affect people of any age but the risk of developing a DVT increases after the age of 40 years. DVT has been linked in recent years with long distance air travel.
Life-threatening complications can arise from DVT when blood clots dislodge, travelling through the body and lodging in other veins or arteries, forming an embolism. This can be life threatening, especially when the embolism occurs in the lungs, heart or brain. Pulmonary embolism (a blood clot in the lung) is the most common of these serious DVT complications.
Veins are blood vessels that carry blood from the tissues of the body back to the heart. Veins that lie just beneath the skin surface are referred to as “superficial veins” while veins found deep inside the muscles are referred to as “deep veins”. Other veins connect the superficial and deep veins, allowing blood to flow between them.
When a blood clot occurs in a vein it is referred to as a venous thrombosis. A deep vein thrombosis (DVT) is a blood clot that occurs in the deep veins. DVTs can occur in any of the deep veins but most commonly occur in the leg and pelvic veins. The clot will either partially or completely block the flow of blood through the affected vein. When the blood clot is associated with inflammation of the vein it is referred to as thrombophlebitis.
A DVT is usually more serious than a blood clot in one of the superficial veins, as there is a much greater risk that part of the clot may dislodge and circulate through the body.
A DVT is more likely to occur when the blood flow through the deep veins is slowed or where there is some factor that makes the blood more likely to clot.
General factors that increase the risk of developing a DVT include:
- Obesity
- Smoking
- Having previously had a DVT
- Having a family member who has had a DVT.
Factors that can slow the blood flow include:
- Immobility - blood flow is slowed when a person remains immobile for long periods of time. Situations where this can occur include:
o Paralysis eg: following a stroke or injury
o Being bedridden eg: following surgery or due to illness
o Having a leg in a plaster cast or splint
o Sitting for long periods of time while travelling eg: in a bus, plane or car. "Economy class syndrome" is a term that has been used to describe a reported increased incidence of DVTs after long distance plane flights. The level of this increased risk continues to be debated.
- Injury to a vein eg: as a result of a broken bone or severe muscle injury.
- Surgery - particularly orthopaedic and cancer surgery
- Heart disease - particularly heart failure
- Varicose veins
- Phlebitis (inflammation of the walls of the vein)
Factors that can make the blood more likely to clot:
- Hormone medications - some research studies have indicated that there may be an increased risk of DVT associated with some types of oestrogen-containing oral contraceptive pills, as well as some hormone replacement therapies (HRT).
- Inherited disorders - such as the deficiency of some blood clotting factors eg: protein C; or defective blood clotting factors eg: Factor V Leiden
- Inflammatory bowel diseases eg: Crohn's disease
- Certain cancers
- Pregnancy.
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A DVT does not always cause symptoms. If symptoms do occur the first symptom is usually a cramp-like aching pain - often in the calf muscles. This pain might worsen when walking but does not subside with rest. Other symptoms of a DVT may include:
- Swelling
- Tenderness
- Localised redness and warmth
- A mild fever.
If a pulmonary embolism occurs it can produce very mild, barely noticeable symptoms such as mild chest discomfort and mild breathlessness. However it can also produce more noticeable symptoms such as sharp chest pain, a rapid heart rate, breathlessness and coughing up blood. As a pulmonary embolism is a serious situation that requires prompt medical treatment, it is important to seek urgent medical attention even if only mild symptoms are experienced.
If a DVT is suspected, it is important to seek medical attention promptly. Accurate diagnosis and appropriate treatment are required to reduce the risk of complications such as pulmonary embolism.
Because a DVT can occur without any obvious symptoms, diagnosis can sometimes be difficult. Initially the doctor will examine the affected area, take a full medical history and may recommend a blood test called a D-Dimer. This test measures a breakdown substance of fibrinogen (a protein essential for blood clotting). If the D-Dimer test is negative, the patient is unlikely to have a DVT. If the test is positive, further tests to confirm the diagnosis are likely to be ordered.
One of the most common diagnostic tests for DVT is an ultrasound scan. The type of scan used is called a Doppler ultrasound. The scan is painless and is able to detect up to 95% of DVTs.
If there is doubt about the diagnosis, venography may be recommended. This diagnostic test involves injecting a specialised dye into the veins. This dye can be seen by x-ray as it flows through the veins, allowing them to be easily visualised.
Other tests that may be used to assist with diagnosis include:
- Blood tests to check for irregularities in the blood clotting system or for inherited disorders.
- Impedance plethysmography (IPG): This test measures the blood pressure at various places in the leg in order to identify the location of the blood clot.
- Iodine 125 fibrinogen scan: This involves injecting into the veins a radioactive substance which adheres to the clot. A specialised camera is used to visualise this substance, thereby demonstrating the location of the clot.
If a pulmonary embolism is suspected, a VQ scan may be recommended. During this scan the patient inhales a special aerosol and a special dye is injected into a vein (intravenously). The aerosol and dye can be seen on x-ray as they move through the lungs. A series of x-rays are then taken which assess the flow of blood and air through the lungs. Abnormalities may suggest a pulmonary embolism.
Specialised CT scans or pulmonary angiography (where dye is injected into the arteries of the lungs through a long catheter threaded up to the heart via a vein in the groin) may also be used to diagnose a pulmonary embolism.
The immediate goal of treatment is to prevent complications and to limit the size of the clot and its movement. Treatment will depend on the location and severity of the clot. Some small clots may resolve spontaneously without treatment, however a DVT is generally treated intensively. Usually the person is admitted to hospital for treatment and observation for signs of complications. Treatment may include:
Medications
Anticoagulants:
These medications "thin" the blood, reducing its ability to clot. Anticoagulant medications can be administered as a continuous infusion into a vein (intravenously), as an injection under the skin (subcutaneously), or in tablet form. Blood tests to monitor their effectiveness are required regularly and dosage changes may be required.
On admission to hospital it has been common to be give an intravenous anticoagulant called heparin, which acts quickly to thin the blood. At the same time an anticoagulant tablet called warfarin is also given. The warfarin is slow acting and can take several days to become effective. Once the warfarin tablets becomes effective, the intravenous heparin is stopped.
Anticoagulant treatment, in the form of tablets or heparin injections, needs to be maintained for at least three months to be fully effective in treating a DVT. In some cases it may be required on a long-term basis.
Thrombolytic agents:
In some cases these medications are given to help dissolve the clot. They are given intravenously, however they can cause side effects such as severe bleeding. Because of this, they are usually only used in life-threatening situations, such as the presence of a large pulmonary embolus.
Compression stockings:
These graded, elasticised compression stockings give support to the lower legs. This encourages the return of blood to the heart and helps to reduce swelling. It is generally recommended that compression stockings are worn in situations where immobility is likely.
Surgery:
In high-risk cases, where there have been recurrent or severe DVTs, surgery to insert a small filter into the main vein leading to the heart (the vena cava) may be recommended. This traps any blood clots travelling through the blood stream thus preventing the clot travelling to the heart and lungs.
General measures to help lower the risk of developing a DVT include not smoking, maintaining a healthy body weight and undertaking regular exercise.
When certain medical conditions or inherited disorders are present, long-term anticoagulant treatment to minimise the risk of DVT may be recommended.
The risk of complications can be minimised by seeking prompt medical attention if a DVT is suspected.
Other factors that can reduce the risk of DVT include:
- For long distance travel:
- Compression stockings
- Drink plenty of non-alcoholic fluids
- Leg and ankle exercises to encourage blood flow in the legs.
- People at high risk of DVT may be prescribed anticoagulant tablets or injections whilst travelling. Anyone at risk of DVT is advised to see their doctor prior to travelling to discuss preventative measures.
When bedridden after surgery or due to illness:
- Compression stockings
- Anticoagulant medications such as heparin
- Specific leg and breathing exercises to promote blood flow.
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After a DVT some people may develop a chronic (long-term) condition called "post-phlebotic syndrome". This is due to damage and scarring to the veins and is characterised by swelling, discomfort and skin pigmentation in the affected area. It can increase the likelihood of subsequent DVTs.
Recurrent pulmonary emboli can lead to a condition called pulmonary hypertension - where the blood pressure within the lungs is increased. This can cause serious problems with the functioning of the heart.
Certain medications, compression stockings and in rare cases, surgery, may be recommended to help treat these long-term complications.
Charlesworth, P. and Shaw, M. (2001). Airline travel and blood clots. New Ethicals Journal, March, p33
De Milto, L. (2006). Deep vein thrombosis. The Gale Encyclopedia of Medicine. Third Edition. Jacqueline L. Longe, Editor. 5 vols. Farmington Hills, MI: Thomson Gale.
Hoby, K. (2001) Clotting a risk for all travellers Auckland: New Zealand Herald, 13/08/01 (page unknown)
New Zealand Medicines and Medical Devices Safety Authority (Medsafe) (2002) Oral contraceptives and blood clots. Wellington: Ministry of Health -
http://www.medsafe.govt.nz/Consumers/leaflets/
oralcontraceptives.asp
Reuters (2002) Scans will spot deadly blood clots much faster Auckland: New Zealand Herald, 21/01/02 p. A8
Last Reviewed - 12/06/07
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