Ask Dr. Stephan Moll

These questions have been submitted by folks on the mailing list and answered by Dr. Moll, Director of the Thrombophilia Program at the Carolina Cardiovascular Biology Center, Department of Medicine, Division of Hematology-Oncology, UNC Chapel Hill (North Carolina, USA). Why am I doing this?

4. Greenfield filter

Q: I have a Greenfield filter. Is it important to stay on a blood thinner to make sure the filter or the blood does not form clots and clog the filter?

A: It is not known whether everybody who has a Greenfield filter should stay forever on blood thinner, because no clinical studies have been done to find out. Such studies are badly needed. I recommend to most patients with a Greenfield filter to stay on long-term coumadin® (= warfarin), if the bleeding risk is not too high. However, as always, an individual decision needs to be made.

Filters are sometimes placed into the big vein in the abdomen, the inferior vena cava (= IVC), so that blood clots that break loose from a DVT (= deep vein thrombosis) in the leg get caught in the filter and can not travel to the lung. The most devastating complication of DVT, a pulmonary embolism (= PE), can thus be prevented. Unfortunately, the filters that used to be placed until about a year ago, could not be removed and had to sty in lifelong. In that situation I mostly recommended lifelong warfarin (coumadin).

Within the last year temporary (transient) IVC filters have become available which can be placed at times when a patient is at high risk for DVT and PE. Some of these filters can stay in for 2 weeks and can then be removed. A recently FDA approved transient filter, the Venatech® filter, can still be removed after several months. Transient filters avoid the need to have a patient on lifelong warfarin.

References

1. Information on IVC filters, including pictures: http://www.greenfieldfilter.com
2. An excellent medical review article on vena cava filters: Blood 2000; volume 95:3669-3677.
3. The most important clinical study on vena cava filters: New England Journal of Medicine 1999; volume 338;409-415.

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