Indications
IVC filters are small devices made of wires that are placed directly into the Inferior Vena Cava in order to prevent clot in the legs (DVT) from reaching the blood vessels. They are usually offered to patients who cannot be treated with blood thinners (due to an increased risk of bleeding) or with catheter-directed thrombolysis. Filters can also be placed in patients who are felt to be at significantly increased risk for DVT formation who would be unable to tolerate a pulmonary embolism. The filter stays within this vein and traps clot that travels from the legs before it is able to reach the lungs. Filters can be a permanent device, but often they are removed when they are no longer needed. This procedure is performed at one of our local hospitals.
Procedural Details
The IVC filter placement procedure first involves placing a small catheter tube into a patient's vein. We most commonly access the right or left common femoral vein in the groin or the right internal jugular vein in the neck to place a filter. However, other veins such as a small vein of the arm or the popliteal vein behind the knee can be used for filter placement as well. Once a small catheter is placed into the vein, it is directed into the Inferior Vena Cava (IVC). Contrast, or x-ray dye, is injected into this catheter, and images of the Inferior Vena Cava are obtained. These images allow us to determine the size of the IVC, whether clot is present within the IVC, whether the IVC is normal in appearance or if there is a congenital variation present which may impact filter placement, and where the renal veins enter the IVC (since that determines where the filter is placed within the IVC). Once all of this information has been obtained, we proceed to filter placement. This simply involves placing the filter, which is attached to a wire, into the catheter and positioning it appropriately within the IVC. Once the filter is where it needs to be, it is released from the wire and deployed in the vein.
Today, all of the filters placed are retrievable, which means that we have the potential to remove the filter at some point in the future. Once a patient is no longer considered to be at risk for DVT and PE, we can perform a retrieval procedure. This procedure involves gaining access into the right internal jugular vein with a catheter. This catheter is moved into the IVC and positioned above the filter. Retrievable filters have hooks at the apex of the filter. This hook can be grabbed with a device known as a snare (which can be thought of as a lasso). The snare is positioned over the hook of the filter and tightened. This allows us to move the catheter over the filter so that the filter is captured within the catheter. At that point, the catheter and filter are removed from the body. In some cases, extensive maneuvers are required to angle the filter in such a way to allow it be captured by the snare. In other cases, it is simply not possible to remove the filter. In those cases, the filters are left in place to provide life-long protection for the patient from DVT and PE. All of the filters used today can be considered appropriate for permanent placement.
Results
The reason for placing a filter in the IVC is to prevent clot from traveling from the veins of the leg into the arteries of the lungs. In other words, we want to prevent a DVT from becoming a PE. Filters are very effective at accomplishing this goal. With only rare exceptions, clinically significant PEs do not happen in patients with IVC filters. Therefore, it is our desire to leave an IVC filter in place for as long as the patient is considered to be at risk for DVT and PE.
Over time, we have come to appreciate that there are potential risks to leaving an IVC filter in place for an indefinite amount of time. In recent years, the long-term risks of filters have been publicized, raising public awareness of these potential complications. The presence of a filter can lead to clot formation within the IVC. While the filter prevents this clot from traveling to the lungs, the clot can lead to leg swelling and other symptoms of chronic venous disease. Even if this does occur, it is rare for this to become clinically significant for most patients. In addition, filters can fracture and potentially migrate from the IVC into the heart, which can lead to internal damage to the heart. If that occurs, a significant procedure would be required to remove the filter. Fortunately, this is quite rare. Finally, the wire legs of the filter have been shown to actually enter and potentially pass through the wall of the IVC in time. While this is not felt to be dangerous to most patients, it can rarely lead to pain or damage to nearby organs such as the intestines. These are the reasons why we now assess all patients for filter retrieval. It is our preference to remove a filter as soon as the patient can be treated with anticoagulation or is no longer considered to be at risk for DVT and PE.