Deep vein thrombosis, commonly referred to as "DVT", occurs when a blood clot, or thrombus, develops in the large veins of the legs or pelvic area. Some DVT's may cause no pain, whereas others can be quite painful. With prompt diagnosis and treatment, the majority of DVT's are not life threatening. However, a blood clot that forms in the invisible "deep veins" can be an immediate threat to your life, as compared to a clot that forms in the visible "superficial" veins, the ones beneath your skin. A clot that forms in the large, deep veins is more likely to break free and travel through the vein. It is then called an embolus. When an embolus travels from the legs or pelvic areas and lodges in a lung artery, the condition is known as a "pulmonary embolism," or PE, a potentially fatal condition if not immediately diagnosed and treated.
What are the causes of DVT?
Generally, a DVT is caused by a combination of two or three underlying conditions:
- slow or sluggish blood flow through a deep vein
- a tendency for a person's blood to clot quickly
- irritation or inflammation of the inner lining of the vein.
There are a variety of settings in which this clotting process can occur. First, individuals on bed rest (such as during or after a surgical procedure or medical illness, such as heart attack or stroke), or confined and unable to walk (such as during prolonged air or car travel) are common settings. It can occur in certain families in whom there is a history of parents or siblings who have suffered from prior blood clots. It can also occur in individuals whom active cancer or its treatment may predispose the blood to clotting.
Having a recent major surgical procedure, especially a hip and knee orthopedic surgeries or those requiring prolonged bed rest, predispose the blood to clotting. Irritation or inflammation occurs when a leg vein is injured by a major accident or medical procedure.
Also, there are specific medical conditions that may increase your risk of developing a DVT via these three mechanisms, such as congestive heart failure, severe obesity, chronic respiratory failure, a history of smoking, varicose veins, pregnancy and estrogen treatment. If you are concerned that you may be at risk due to any of these conditions, please consult with your physician.
Approximately one-half of those with a DVT never have recognized symptoms.
When symptoms are present, the most common is leg pain and tenderness in the calf muscles, or one may observe swelling or a change in color of one leg to purple or blue. These signs and symptoms may appear suddenly or may steadily develop over a short time. If you observe these signs or symptoms, you should contact your doctor immediately.
Symptoms are quite different if the clot breaks loose and travels to the lungs, causing a pulmonary embolism (PE). The symptoms of PE include chest pain, shortness of breath, rapid pulse, or a cough. There may also be a feeling of apprehension, sweating, or fainting. Such symptoms are not specific to a PE, and can occur with pneumonia, heart attack, and other medical conditions.
These are always critical symptoms that demand immediate medical attention.
DVT occurs in about 2 million Americans each year and affects both men and women, all ethnic groups, and all social levels. It is seen most often in adults over the age of 40, and more frequently in elderly patients, but can occur at any age. Women in the later stages of pregnancy or around the time of delivery are at increased risk. As noted previously, other conditions may increase one's risk, and individuals who smoke and who do not exercise are at increased risk.
A suspicion of DVT is raised after a clinical exam and by identifying the associated risk factors, but a definite diagnosis of DVT (enough to guide treatment) cannot be accurately made without additional testing.
An ultrasound scan of the legs is usually ordered, because it is highly accurate, non-invasive, and relatively painless. During the ultrasound scan, any blood clots in the vein are displayed on a monitor. A specific blood test may be performed to measure "D-dimer" as a sign of recent clotting. When this test is negative, it is very unlikely that you may have suffered a DVT.
However, even with these excellent tests, there are occasions requiring more accurate information for a diagnosis. A venogram or phlebogram, a test in which dye is injected into a vein in the foot and an x-ray is taken, might be performed to more clearly view the blood flow within the leg veins. Phlebograms are rarely ordered today, but are helpful when DVT is severe and clot dissolving therapies or surgical therapies may need to be considered.
For most DVTs, physicians recommend wearing graduated compression stockings, elevating the leg, and taking anticoagulant medications to prevent blood clotting. Anticoagulant medications prevents further clots from forming and diminishes the risk of a PE . It consists of heparin, which may be given intravenously or, more frequently, by subcutaneous injection, followed by warfarin (Coumadin), which can be given orally and continued usually for several months.
In severe cases, the physician may recommend thrombolysis, which is the use of an intravenous medication that dissolves clots. With this procedure, a catheter is threaded through the vein to the clot, and then a clot-dissolving drug is injected to dissolve it. The clot-dissolving drug is injected slowly through the catheter's many tiny holes into the area of the DVT, much like a soaker hose. Sometimes a tiny device that works like a vacuum cleaner is used to remove or suck the softened clot out. Once the clot is gone, a balloon angioplasty or stenting may be necessary to keep open the narrowed vein, but this is common only in the iliac veins, located in the pelvic area. With this approach, the patient will also need anticoagulant medication (heparin and warfarin) to prevent new blood clot formation. Some patients cannot have clot-dissolving drugs. In these instances, a thrombectomy in which the clot extracted through a small incision at the groin may be recommended. Both approaches are designed to remove the clot and restore blood flow through the veins. These involve additional risk and expense and therefore are applied selectively by the appropriate vascular specialist. Clot removal, by either technique, is usually only recommended for major clots higher up in the leg, and particularly in active, healthy patients without any serious associated diseases. It can significantly reduce the serious consequences of DVT, such as chronic leg swelling, discoloration and, ultimately, ankle ulcers.
What are the late effects of DVT?
Small blood clots in the leg veins may dissolve without serious later consequences. However, larger blood clots, especially those located in the upper thigh and pelvic areas, are more likely to contribute to significant, long-term leg symptoms. The long-term consequences of a DVT can persist even when the use of medications has, in the short term, been "successful". For example, the leg veins can remain obstructed by remaining clot or scar tissue, or the valves in the vein may be damaged and not function properly. This may result in chronic swelling, skin discoloration, and ultimately, the development of chronic skin ulcers near the ankle. These problems can be diminished, if the individual who suffered a DVT will faithfully wear graduated compression stockings and elevate the legs periodically during the day.
Anticoagulant medications will reduce the risk of future DVT and PE's; these medications cannot prevent the long-term tendency for leg swelling, discomfort, and skin changes, commonly called the "post-thrombotic syndrome" (PTS). These post-thrombotic symptoms are best treated by lifelong use of compression stockings. Unfortunately, it is not often appreciated that in some individuals, persistent leg swelling or discomfort may contribute to a real decrease in quality of life, body image, and even disability in some individuals.
Can DVTs be prevented?
Regular exercise will decrease the risk of DVT. Persons who undergo major surgery are at risk to develop DVT, therefore calf and leg exercises before surgery along with promptly resuming physical activity as soon as possible after the surgery will decrease the risk for DVT. Preventing a DVT is the major reason why hospitalized patients are encouraged to be up and walking as soon as possible after surgery. Regular stretching and leg movement are important for individuals who sit at a desk all day or are traveling on long trips, particularly air travel. As always, it is important to stop smoking, as smoking increases the tendency of the blood to clot. Avoid wearing tight garments that produce constrictions below the waist.