Stopping Clots from Traveling

Deep vein thrombosis (DVT) occurs when a blood clot, or thrombus, develops in the large veins of the legs, arms, or pelvic area. There are numerous settings which increase the risk for clots: trauma, cancer, hospitalization or prolonged bed rest, recent pregnancy, use of birth control pills, or history of a previous DVT. With prompt diagnosis and treatment, the majority of DVTs are not life-threatening. However, a blood clot that forms in the invisible "deep veins" can be an immediate threat to one's life, as compared to a more innocuous clot that forms in the visible "superficial" veins, the ones beneath the skin. A clot that forms in the large, deep veins is more likely to break free and travel through the vein; it is then called an embolus. When an embolus travels from the legs or pelvic area and lodges in the lungs, it causes a condition known as a "pulmonary embolism" (PE), a potentially fatal condition if not immediately diagnosed and treated. Research shows that a PE originates in the deep veins of the leg or pelvis at least 90 percent of the time. In order to reduce this risk, most patients with DVT are placed on an anticoagulant (blood-thinning) medication.

This treatment does not work for all people or in all situations. Some people cannot use blood-thinning medications because of bleeding or a history of developing complications from blood thinners. Other patients may be at a very high risk of developing DVT (but do not actually have a clot), such as certain trauma victims and obese patients. For these patients, a filter may be placed within the inferior vena cava (IVC), which is the main vein in the abdomen. Blood from the legs passes through the IVC to return to the heart and lungs. An IVC filter traps clots that move up the vein before they can reach the lungs and cause a PE.

Typically, IVC filters are left in place permanently. Recently, however, removable IVC filters have been developed. There are certain situations where a removable filter may be more desirable than a permanent one. Some people develop complications when the filter is left in place for a long time. Complications include clotting of the leg veins, an IVC fracture (or breaking off) of a piece of the filter, movement of the filter, and thrombosis of the filter. Some people need protection from a PE for only a short, well-defined time period. For example, some patients may regain their mobility and no longer be at high risk for DVT or no longer have a need for blood thinners.

An IVC filter is inserted through a vein in the neck (jugular vein) or groin (femoral vein). The procedures for placing both permanent and removable filters are similar. The medical team will clean the insertion area and numb it with local anesthetic. A patient might also receive intravenous (IV) sedation. A guide wire is advanced into the vein under x-ray guidance through a small nick in the skin. A sheath (a long, skinny, hollow tube), is positioned in the area where the physician will place the filter. A venacavagram might also be performed by injecting x-ray dye through the sheath or another catheter. This will help the doctor determine the size of the IVC and whether or not it is clotted. It can also help to determine the location of other veins such as the renal (kidney) veins. Once this is done, the IVC filter is placed through the sheath into the correct position in the IVC. The physician might do another venacavagram to confirm the position of the filter. The sheath is then removed and pressure is applied to the insertion site to stop bleeding. The entire procedure usually takes less than an hour.

Removing a filter is similar to inserting a filter. Again, access into a vein is obtained, often through a jugular vein. A sheath is again placed into the vein under x-ray guidance. A snare or a special device to grab the filter is used to pull the filter into the sheath. A venacavagram may be done to confirm that the IVC is not damaged. The sheath is removed and pressure is applied to the site to stop bleeding.

Removable filters must be removed within a certain time frame. Depending on the type of filter, the time frame may be from several weeks to several months after the filter is placed. If the filter is not removed within the specified time frame, it will be left in place permanently. There are certain reasons why a filter cannot be taken out within the time frame. These reasons include patients with continuing contraindications to blood thinners, patients who are still at high risk for developing DVT or PE and cannot have blood thinners, and/or patients who have significant amounts of blood clot trapped within their removable filter.

These filters are used to save lives. Only a doctor can decide if a patient needs a filter and whether he or she needs a removable filter or a permanent filter.

About the Author: Meghal Antani, MD is an interventional radiologist in the Washington DC area.