Last updated: 11/24/2009

Blood clots can form in any vein within the body. Deep vein thrombosis (DVT) can be quite serious. DVT occurs when a blood clot forms in the legs or pelvis. If it is large enough, it can block the blood flow within the vein, cutting off oxygen to the...

tissues. An embolus or a clot that breaks away from the wall of the blood vessel can travel into the lung, the heart, or the brain where it can disrupt the normal functioning of these organs and become life-threatening. Some blood clots distend the walls of the blood vessel, creating a sac called an aneurysm. Sometimes the aneurysm bursts, causing blood to leak out. If this occurs within the brain, the heart, or the lungs, it can be fatal.

Venous thrombosis can occur for several reasons. The patient may have disease within the blood vessels such as an inflammation of the walls of the vein (phlebitis) or hereditary blood clotting disorders. The patient may also develop blood clots because of other medical conditions such as heart disease, heart failure, stroke, or cancer. They can also occur after surgery or prolonged bed rest or inactivity. People who smoke and take oral contraceptives may be more susceptible to blood clots.

Pulmonary embolism is one of the most common, but highly fatal, blood clots that patients experience. The American Heart Association estimates 600,000 people in the United States develop pulmonary embolisms each year, with 10% of those ending in death. Sometimes there is little or no warning, causing sudden death. About 90% of these embolisms are the result of DVT that forms in the legs or the pelvis and moves into the lung and blocks the pulmonary artery. Most often the DVT occurs in the recovery period after surgery, though there is an alarming trend of DVT events that are the result of airline travel. In 1999, nearly 2,000 Americans, many of them young and fit, died from travel-related DVT strokes. In 2003, NBC reporter David Bloom, who was embedded with the United States Army as he covered the war in Iraq, died of a pulmonary embolism due to his riding in a cramped position for long hours over several days.