Clot Trapping

Deep vein thrombosis (DVT) occurs when a blood clot, or thrombus, develops in the deep veins of the legs or pelvic area or, on rare occasion, in the arms. DVT involves the veins deep beneath the surface of the skin, rather than the subsurface veins that are often visible. The deep veins do much of the work of sending blood back to the heart from the limbs. Situations such as trauma, cancer, hospitalization or prolonged bed rest, recent pregnancy, use of birth control pills, or a family or personal history of a previous DVT are risk factors for DVT. With prompt diagnosis and treatment, the majority of DVTs are not life-threatening. Most DVTs form in the leg veins and may cause symptoms such as pain, aching, swelling, or warmth of the affected leg. If you experience these symptoms, consult a health professional immediately. DVTs are typically diagnosed by a test called a duplex ultrasound, a quick and painless test that uses ultrasound to look for clots in the veins. Most blood clots can be easily treated by anticoagulant medications. However, if a blood clot enlarges and breaks free, it may travel to the heart and to the blood vessels of the lungs, a condition called a pulmonary embolus (PE). PE occurs in about 500,000 Americans each year and is potentially fatal. In order to reduce the risk of PE, most patients with DVT are placed on an anticoagulant medication.

Anticoagulants, or blood thinners such as Coumadin®, heparin, or newer heparin derivatives, are effective at helping the body clear the DVT and prevent a PE. They are typically given for several months or even years after a DVT, depending on the patient's risk factors. However, blood thinners are not for everyone. Some people may experience bleeding on these medications or they cannot take blood thinners because of other injuries or medical conditions. Or patients may be facing a surgical procedure during which they cannot be on blood thinners. 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. IVC filters are small wire baskets that trap clots that move up the vein before they can reach the lungs and cause a PE. The filters are very effective at trapping and holding the clots in the IVC until the patient's body can break down the clot.

Filters have been in use for many years and are very effective in patients who cannot receive blood thinners. They typically are placed through a tiny tube or catheter that is inserted into the femoral vein in the groin (upper thigh over the hip bone) or in the jugular vein at the base of the neck. The catheter is inserted through a tiny nick in the skin while the patient is under local anesthetic or intravenous sedation. The catheter is then guided by an x-ray TV camera to the IVC. Images of the IVC are then taken while a medication called contrast material is injected through the catheter to make a detailed map of the IVC. The patient would typically have a short feeling of warmth during the injection. The filter is then collapsed into the tiny catheter and delivered into the vein, where it opens up and attaches to the wall of the IVC. The catheter is then removed and light pressure and a band-aid are applied to the skin site. The whole procedure takes about 30 minutes.

Typically, IVC filters are left in place permanently. Many patients need the ongoing protection of the filters. However, there is a small risk over time for the filter to either malfunction or become clogged with clots. Also, some patients may benefit from having the filter removed if there is minimal risk of developing another DVT or PE. There are several filters available today that are "removable." These can be left in place permanently or removed within a few weeks of placement if no longer needed. For example, a filter may be removed from someone who regains his or her mobility and no longer is at high risk for DVT, or after surgery when the patient has recovered and no longer needs blood thinners. There are certain reasons why a filter cannot be taken out within the time frame of removal. These reasons include patients who cannot take blood thinners, patients who are still at a high risk for developing DVT or PE and cannot have blood thinners, and patients who have significant amounts of blood clots trapped within their removable filter.

Removing a filter is similar to inserting a filter. Again, access into a vein in the neck or groin is obtained. A catheter is again moved into the vein under x-ray guidance. A special device attaches to the filter and is used to collapse it back into the catheter and remove it from the vein. A band-aid is applied to the nick in the skin, typically with some light pressure. Again, this is usually a short procedure performed under local or intravenous sedation.

IVC filters are useful devices to protect against damage from clots or a life-threatening PE. Should you need a filter, consult your physician regarding the type of filter that may be most appropriate for you.

About the Author: Meghal R. Antani, MD, is an interventional radiologist at Washington Hospital Center. His special area of interest is in the main vein leading back to the heart. Dr. Antani also serves on the Vascular Disease Foundation's Editorial Review Board for Keeping in Circulation.