Deep Vein Thrombosis (DVT)

Veins may be damaged during surgery or during an injury to an arm or leg, by the injection of irritating substances, by inflammation, or by certain disorders, such as thromboangiitis obliterans. They may also be injured by a clot, making formation of a second clot more likely.

Some diseases, such as cancer and inherited disorders of blood clotting, cause blood to clot when it should not. Some medications, including oral contraceptives, estrogen therapy, or medications that act like estrogen (such as tamoxifen and raloxifene), can cause blood to clot more readily. Smoking also increases the tendency of blood to clot. Sometimes blood clots more readily after childbirth or surgery. Among older adults, dehydration commonly causes the blood to clot more readily and can therefore contribute to deep vein thrombosis.(such as tamoxifen and raloxifene), can cause blood to clot more readily. Smoking also increases the tendency of blood to clot. Sometimes blood clots more readily after childbirth or surgery. Among older adults, dehydration commonly causes the blood to clot more readily and can therefore contribute to deep vein thrombosis.

During prolonged bed rest and other occasions when the legs are not moving normally, blood flow slows because the person is lying down and the calf muscles are not contracting and squeezing the blood toward the heart. For example, deep vein thrombosis may develop in people who have had a heart attack or other serious disorder (such as heart failure, chronic obstructive pulmonary disease [COPD], or a stroke) and lie in a hospital bed for several days without sufficiently moving their legs or in people whose legs and lower body are paralyzed (paraplegia). Deep vein thrombosis can develop after major surgery, particularly pelvic, hip, or knee surgery. Thrombosis can even occur in healthy people who sit for long periods, for example, during long drives or airplane flights, but thrombosis is uncommon in this circumstance and usually occurs in people with other risk factors.

In people who have deep vein thrombosis, a blood clot may break loose from an affected vein in the leg. A clot that breaks loose is called an embolus. The embolus can travel through the bloodstream, through the heart, and into the lungs, where it lodges in a blood vessel, blocking blood flow to a portion of the lung. This blockage is called pulmonary embolism and can be fatal, depending on how large the embolus is and the size of the blocked lung artery. Generally, only thrombi in the deep veins are potentially dangerous if they break off and travel to the lungs; the small blood clots that occur in superficial venous thrombosis usually do not become emboli.

Blood clots in the legs or pelvis are more likely to become emboli than blood clots in the arms, perhaps because the squeezing action of the calf and leg muscles can dislodge them.

The consequences of pulmonary embolism depend on the size and number of emboli:

• A small embolus may block a small artery in the lungs, causing the death of a small piece of lung tissue (called pulmonary infarction).

• A large pulmonary embolus can block all or nearly all of the blood traveling from the right side of the heart to the lungs, leading to low blood pressure and low oxygen levels and quickly causing death.

Large emboli are not common, but no one can predict which case of deep vein thrombosis, if untreated, will lead to a large embolus.

Multiple emboli may occur. Multiple emboli typically go to different parts of the lungs.

Sometimes, people have an abnormal opening between the right and left upper chambers of the heart (the atria), called a patent foramen ovale . If this opening is present, an embolus can pass into the arterial circulation and block an artery in another part of the body, such as the brain where it will cause a stroke.

Some blood clots heal by being converted to scar tissue, which may damage the valves in the veins. The damaged valves prevent the veins from functioning normally, a disorder called chronic venous insufficiency. In this disorder, fluid accumulates (a condition called edema) and the ankle and sometimes lower leg swells. The skin can become scaly, itchy, and reddish brown on light skin or purple and/or brown on dark skin. Sometimes open sores (ulcers) can develop in the leg, ankle, or foot.

Rarely, a very large blood clot in a leg causes so much swelling that it blocks the blood flow through the leg. The leg becomes pale or blue and extremely painful. Gangrene (dead tissue) can develop if the blood flow is not restored.

Infection can develop in venous clots, although it is rare. A bacterial infection of the internal jugular vein and surrounding tissues in the neck, called jugular vein suppurative thrombophlebitis or Lemierre syndrome, may follow an infection of the tonsils. Blood clots may develop in the pelvis after childbirth and become infected, causing fever. Infection and clotting of a superficial vein, called suppurative or septic thrombophlebitis, is usually caused by placement of an IV.

Anticoagulants are sometimes called blood thinners. They decrease the blood’s ability to clot, so they can prevent new clots from forming and can stop existing clots from getting bigger. They do not break up or dissolve clots that have already formed. Almost all people with deep venous thrombosis are given anticoagulants. However, use of anticoagulants increases the risk of bleeding, both internally and externally, so doctors take the individual person's risk of bleeding into account when recommending specific anticoagulant medications for blood clots.

Doctors usually use an injectable heparin (either a low molecular weight Doctors usually use an injectable heparin (either a low molecular weightheparin such as enoxaparin, or regular "unfractionated" such as enoxaparin, or regular "unfractionated"heparin) or fondaparinux, also given by injection under the skin (subcutaneously), followed by longer term treatment with an anticoagulant medication that can be taken by mouth. The injectable medications work immediately. In some cases, people continue taking the injectable medication and do not start an oral medication at all. ) or fondaparinux, also given by injection under the skin (subcutaneously), followed by longer term treatment with an anticoagulant medication that can be taken by mouth. The injectable medications work immediately. In some cases, people continue taking the injectable medication and do not start an oral medication at all.

When an oral medicine is used, it may be a direct oral anticoagulant (DOAC), which include rivaroxaban, apixaban, edoxaban, and dabigatran; or warfarin. DOACs and When an oral medicine is used, it may be a direct oral anticoagulant (DOAC), which include rivaroxaban, apixaban, edoxaban, and dabigatran; or warfarin. DOACs andwarfarin work equally well, but warfarin requires periodic blood tests to monitor its effectiveness and often takes longer to become effective. DOACs, on the other hand, are generally more expensive. For people whose clots are thought to be related to cancer, many doctors prefer to use the injectable medications or a DOAC rather than warfarin. Several days of treatment with the injectables are needed before starting some of the DOACs.

The effect of DOACs on people's blood is more predictable than the effect of warfarin. Therefore, people taking DOACs do not need to have frequent blood tests to adjust the dose. Also, DOACs tend to cause fewer episodes of serious bleeding than warfarin. However, bleeding caused by DOACs can be harder to stop because antidotes for these medications are not as widely available as antidotes for warfarin.

If people are going to use warfarin, it takes several days to be fully effective, and the person must start taking it while still receiving the injectable anticoagulant. Once the warfarin has taken effect, people stop taking the injectable medication.

People taking warfarin must have periodic blood tests to see how much their blood is anticoagulated. Doctors then use the blood test result to adjust the dose of warfarin. The blood tests are usually done once or twice a week for 1 or 2 months, and then every 4 to 6 weeks thereafter.

Many different medications and foods change how the body breaks down warfarin (see also Drug Interactions). Some medications and foods increase its breakdown, making a warfarin dose less effective and increasing the risk of another blood clot. Other medications and foods slow warfarin's breakdown, making a dose more effective but also more likely to cause bleeding. Some people are also more sensitive to warfarin and may need warfarin-sensitivity testing to help doctors adjust their levels.

How long people continue anticoagulants (with DOACs, warfarin, or an injectable medication) varies according to the degree of risk. People whose deep vein thrombosis resulted from a specific, temporary cause (such as surgery or a medication they have stopped taking) usually continue anticoagulants for 3 to 6 months. When a specific cause is not found, the cause is not temporary (for example, a blood clotting disorder), or people have had 2 or more episodes of deep vein thrombosis, people are usually on anticoagulants for a longer period of time (sometimes for the rest of their life).

Excessive bleeding, which may be life-threatening, is the most common complication of anticoagulants. Risk factors for excessive bleeding include being age 65 years or older or having:

• A recent heart attack, stroke, or bleeding in the digestive tract

• Diabetes

• Kidney failure

• A low platelet count (because platelets help blood clot)

• Cancer

For people who are taking warfarin, doctors can give vitamin K, transfusions of plasma (which contains clotting factors), or prothrombin complex concentrate to reverse the effects of the For people who are taking warfarin, doctors can give vitamin K, transfusions of plasma (which contains clotting factors), or prothrombin complex concentrate to reverse the effects of thewarfarin and stop the bleeding. For people who are taking heparin, doctors can give protamine to partially reverse the effects.and stop the bleeding. For people who are taking heparin, doctors can give protamine to partially reverse the effects.

For people taking some of the DOACs, doctors can give andexanet alfa or prothrombin complex concentrate to reverse the effects of the DOACs and stop the bleeding.

Very rarely, as an alternative to anticoagulants, doctors place a filter (formerly called an umbrella) inside a large vein between the heart and the area affected by deep vein thrombosis, usually the inferior vena cava. The inferior vena cava is a large vein that returns blood to the heart from the lower part of the body. The filter can trap emboli, preventing them from reaching the lungs.

However, unlike anticoagulants, filters do not prevent new clots from forming. Filters are usually reserved for people in whom anticoagulant therapy is not possible.

Inferior Vena Cava Filters: One Way to Prevent Pulmonary Embolism in People who Cannot Take Anticoagulants

In people who have deep vein thrombosis, a blood clot may break loose from an affected vein in the leg and travel through the bloodstream. A clot that breaks loose is called an embolus. The embolus travels toward the heart and passes through the right atrium and ventricle and into one of the pulmonary arteries, which carry blood to the lungs. The clot may lodge in an artery in a lung and block blood flow, resulting in pulmonary embolism. Pulmonary embolism may be life threatening, depending on how large the embolus is and the size of the blocked artery. To prevent pulmonary embolism, doctors usually use medications that limit blood clotting (anticoagulants, or blood thinners). However, for some people, doctors may recommend that a filter be temporarily or permanently placed in the inferior vena cava. The inferior vena cava is a large vein that returns blood to the heart from the lower part of the body. The filter typically is recommended when anticoagulants cannot be used, for example, when a person is also having bleeding. The filter can trap emboli before they reach the heart but allow blood to flow through freely. Emboli that are trapped sometimes dissolve on their own. However, filters do not completely eliminate the risk of emboli. Sometimes other veins from the legs enlarge, allowing blood and emboli to bypass the filter. Also, filters can break loose or become blocked by a clot. Filters are much less effective at preventing pulmonary embolism than treatment with anticoagulants.

Doctors only occasionally use intravenous medications, such as alteplase, to dissolve venous blood clots. These medications (also called thrombolytic, fibrinolytic, or clot-busting drugs) may be given to a person with extensive blood clots. When they are used, usually a catheter is placed into the vein so the medicine can be directed into the clot. Clot-dissolving medications have a higher risk of bleeding complications.Doctors only occasionally use intravenous medications, such as alteplase, to dissolve venous blood clots. These medications (also called thrombolytic, fibrinolytic, or clot-busting drugs) may be given to a person with extensive blood clots. When they are used, usually a catheter is placed into the vein so the medicine can be directed into the clot. Clot-dissolving medications have a higher risk of bleeding complications.

Doctors sometimes use clot-dissolving medications in combination with mechanical removal methods in people who have large clots in their upper leg. In such cases, doctors may put a small, flexible tube (catheter) into the blocked vein, remove as much clot as possible with an instrument, and then administer the clot-dissolving medication through the catheter.

If pulmonary embolism occurs, treatment usually includes oxygen (usually given by a face mask or nasal prongs), analgesics to relieve pain, and anticoagulants. If pulmonary embolism is life threatening, clot-dissolving medications are given or surgery is done to remove the embolus.

In many cases, the veins never completely recover after deep vein thrombosis develops. Elastic compression stockings worn below the knee may be helpful if chronic venous insufficiency develops. Treatment of this condition, and the painful skin ulcers (venous stasis ulcers) that can develop with it, are discussed in Post-Thrombotic Syndrome.