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No Evidence Blood Clot Filters Help

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The Journal of the American Medical Association pointed out in March 2013 that IVC blood clot filters are widely used despite a dearth of efficacy evidence. Some 250,000 Americans get a Bard IVC filter or some other blood clot filter implanted in their chests each year, despite the fact that such implantations have shown evidence of harm without evidence of benefit.

JAMA asks, “How could a medical device be so well accepted without any evidence of efficacy?” Answers to that question show the deplorable state of medical device safety testing and monitoring in the U.S.

Checkered History of IVC Blood Clot Filters

The first blood clot filter device, introduced in the late 1960s, was plagued by high rates of inferior vena cava occlusion in more than half the patients, pulmonary embolism (PE), and migration. The stainless steel Kimray-Greenfield filter was the next filter to hit the market, in 1973. It was reportedly tested first on 156 patients who most commonly had VTE and were contraindicated for anticoagulation. By 1988 the company had tested the filter on 469 patients, getting long-term follow up for just 146 people, while 190 patients were lost to the study, and 133 (28%) died. Greenfield noted 17 deaths from PE and nine (9) cases of nonfatal PE. Almost half (44%) of patients were left with chronic venous stasis.

JAMA analysis of the study was that the results were “nearly uninterpretable because of the lack of a control group and the loss of nearly half of study participants.”  Nonetheless, the study’s results serve as the evidence base for all IVC blood clot filters.

No Evidence Blood Clot Filters Help

Virtually all medical experts agree that an IVC blood clot filter should be used only in patients with VTE and a contraindication to anticoagulation. Nevertheless, the only randomized controlled trial (RCT) – the gold standard for safety and efficacy testing – which was ever done failed to include one single person who met this criteria.

The PRECIP (Prevention du Risque d’Embolie Pulmonaire par Interruption Cave) study was published in 1998, with an 8-year followup reported in 2005. PRECIP enrolled 400 adults with acute proximal DVT who were considered high risk for PE. At two (2) years, PRECIP found no difference in mortality between two different groups (1 of 2 types of anticoagulation therapy), but a 10% higher rate of DVT among those who received the filter. JAMA reported, “Most importantly, mortality was indistinguishable between the groups.”

510(k) Approval bi-passes real testing

So how did IVC blood clot filters garner FDA approval with such poor evidence of safety or efficacy? They were all approved on 510(k), an approval mechanism that JAMA reports the Institute of Medicine recommends be discontinued. The 510(k) process bi-passes thorough testing. Meanwhile, the benefits of the IVC filter remain difficult to assess, while the complications are becoming legion. JAMA called for proper RCTs to assess what, if any, are the merits of IVC blood clot filter devices.



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