IVC Filter as a Treatment for Pulmonary Embolism
Deep vein thrombosis and pulmonary embolisms are together known as venous thromboembolism (VTE). VTE is generally treated with blood thinners like Heparin or other anticoagulants, like Coumadin. For patients who have a high risk of developing pulmonary embolism (PE) and in cases where blood thinners either cannot be used or have not proven successful in preventing VTE, other medical procedures may be necessary.
Implanting the IVC Filter
To place the IVC filter, doctors insert a catheter—a thin tube—into a large vein in the neck or groin. The catheter is advanced through the vein to the inferior vena cava. The filter is then fed through the catheter to the IVC and released. The legs or struts of the device then expand and attach to the walls of the vein.
Types of IVC Filters
There are two main types of IVC filters—permanent and retrievable.
Permanent IVC Filter
The first IVC filters were permanent by design. They were built surgically by stitching a grid-like filter across the inferior vena cava, using strands made of dacron, a synthetic polyester fiber, soaked in Teflon. This procedure was first tried in 1957 by Marion S. DeWeese and D.C. Hunter Jr., and was performed on 112 patients between 1957 and 1972. In a 1973 article summarizing his 15-year experience with this type of surgery, Dr. Weese remarked, “There are no hazards of migration, [or] late perforation of the wall of the vena cava…” Migration and perforation are two principal complications of today’s IVC filters. It is interesting to see that doctors were aware of these dangers over 40 years ago.
The DeWeese filter required major surgery and general anesthesia (patient is completely unconscious). But in the late 1960s, an umbrella-shaped filter similar to modern devices was developed by Kazi Mobin-Uddin. Like the modern filter, it was implanted under local anesthesia with a catheter. The filter was released for general use in 1970, but it had high rates of filter blockage, pulmonary embolism and migration. The Kim-Ray Greenfield filter began to be used in 1972, and by 1990 over 120,000 had been implanted in the U.S.
In the early 1990s, 400 patients were recruited for a study of permanent filters known as the PREPIC (Prevention du Risque d’Embolie Pulmonaire par Interruption Cave) study. Four different permanent filters were used in the study. All the patients had anticoagulation therapy, but only half were treated with an IVC filter. The study results were not encouraging. As reported in a 2013 editorial in JAMA Internal Medicine (a journal of the American Medical Association), at two years there was no difference in mortality between the two groups, but the patients who receive a filter had a higher rate of deep vein thrombosis (DVT). There was a slight reduction in PE in the filter-treated patients, but it was not statistically significant. At eight years, the death rate in the two groups was nearly identical and the rate of DVT remained significantly higher in the patients who had received a filter. The overall rate of venous thromboembolism (DVT + PE) was comparable between the two groups.