What is a deep vein thrombosis?
Deep vein thrombosis (DVT) is a blood clot in a major vein, usually in the legs and/or pelvis. Thrombosis occurs when the blood changes from a liquid to a solid state thereby producing a clot. If the blood clot occurs within a major vein, the condition is known as deep vein thrombosis (DVT). The most common veins affected by DVT are those of the legs or within
the pelvis (lower abdomen).
Deep vein thrombosis is a common but difficult to detect illness that can be fatal if not treated effectively. According to the American Heart Association, more than two million Americans develop deep vein thrombosis annually. An estimated 600,000 of these develop pulmonary embolism, a potentially fatal complication where the blood clots break off and form pulmonary emboli, plugs that block the lung arteries. Sixty thousand people die of pulmonary embolism each year. Deep vein thrombosis is also called venous thromboembolism, thrombophlebitis or phlebothrombosis.
Thrombi can occur either in the deep leg veins, causing deep vein thrombosis, or in the superficial leg veins, causing superficial thrombophlebitis (see Venous Disorders: Superficial Thrombophlebitis). Thrombophlebitis is a disorder in which the formation of blood clots (thrombosis) and inflammation of the vein (phlebitis) occur together. Because thrombosis is almost always accompanied by phlebitis, some doctors use thrombosis and thrombophlebitis interchangeably. However, there is an important distinction between deep vein thrombosis and thrombophlebitis. Deep vein thrombosis causes only a little inflammation. The less inflammation around a thrombus, the less tightly the thrombus adheres to the vein wall and the more likely it will break loose (becoming an embolus), travel through the bloodstream, and lodge in an artery downstream, blocking blood flow. In addition, the squeezing action of the calf muscles can dislodge a thrombus in a deep vein, especially when a convalescing person becomes more active. Thus, only thrombi in the deep veins are potentially dangerous. Superficial thrombophlebitis is painful but comparatively harmless, because thrombi in small, superficial veins usually do not become emboli.
Because blood in the leg veins travels to the heart and then to the lungs, emboli originating in the leg veins usually pass through the heart and block one or more arteries in the lungs, a condition called pulmonary embolism (see Pulmonary Embolism). The seriousness of pulmonary embolism depends 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 (pulmonary infarction). However, a large pulmonary embolus can block all or nearly all of the blood traveling from the right side of the heart to the lungs, quickly causing death. Such massive emboli are not common, but no one can predict which case of deep vein thrombosis, if untreated, will lead to a massive embolus. Thus, doctors are greatly concerned about every person who has deep vein thrombosis.
Deep vein thrombosis is a major complication in patients who have had orthopedic surgery or pelvic, abdominal, or thoracic surgery. Patients with cancer and other chronic illnesses (including congestive heart failure), as well as those who have suffered a recent myocardial infarction, are also at high risk for developing DVT. Deep vein thrombosis can be chronic, with recurrent episodes.