Harvard Heart Letter

Vena cava filters: Tiny cages that trap blood clots

These special filters protect against pulmonary embolism but also carry risks.

A common complication after surgery, trauma, or a prolonged period of bed rest is the formation of a blood clot in a vein deep inside the legs. Doctors call this a deep vein thrombosis, or DVT. If the clot breaks free of the vessel wall, it can travel through the bloodstream and lodge in a lung artery, causing a catastrophic stoppage of blood flow. This consequence, known as a pulmonary embolism, can be deadly.

An alternative to anti-clotting drugs

Blood thinners such as warfarin are widely used as a hedge against clot formation. However, some people can't take these drugs because they could worsen conditions such as a hemorrhagic (bleeding) stroke or bleeding in the gastrointestinal tract, says Dr. Piotr Sobieszczyk, an interventional cardiologist at Harvard-affiliated Brigham and Women's Hospital. "In the old days, one of the treatments for these people would be to clamp or staple the inferior vena cava, the main vein running through the abdomen that carries blood from the lower body back to the heart. If large clots from the legs did break up, they wouldn't be able get past that point and reach the lungs. Clearly, it was not a great idea, but that's what they had available," explains Dr. Sobieszczyk.

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