Deep Vein Thrombosis
Deep vein thrombosis (DVT) is the development of a blood clot (thrombus) in the deep veins of the legs, pelvis, or arms. Clots can form in superficial veins (called superficial thrombophlebitis or simply "phlebitis") and in deep veins. While blood clots in superficial veins rarely cause serious problems, clots in deep veins require immediate medical evaluation.
Deep veins that lie near the center of the leg are surrounded by powerful muscles that contract and force deoxygenated blood back to the lungs and heart. One-way valves prevent the backflow of blood between the contractions. (Blood is squeezed up the leg against gravity and the valves prevent it from flowing back to our feet.)
When the circulation of the blood slows down due to illness, injury, or inactivity, blood can accumulate or "pool," which provides an ideal setting for clot formation. Blood clots in deep veins can grow in size, break loose, and then travel through the bloodstream to the lungs, resulting in a life-threatening pulmonary embolism.
Deep vein thrombosis can cause other long-term complications. In about 25% of cases, deep vein thrombosis damages the affected vein and leads to long-lasting post-thrombotic syndrome. This condition can cause pain, swelling, discoloration, and leg sores.
Blood clots can form in veins when you are inactive; for example, if you are paralyzed or bedridden or must sit while on a long flight or car trip. DVT has also been referred to as "Economy Class Syndrome" due to the occurrence after sitting on long flights.