“Is more research needed in the world of filters? Yes, but is more research needed to determine whether the class itself is safe? No.” Charting the recent history of inferior vena cava (IVC) filters through the PRESERVE trial (Predicting the safety and effectiveness of inferior vena cava filters), principal investigator Matthew Johnson (Indiana University, Indianapolis, USA) speaks to Interventional News on the ins and outs of filter removal.
“Hundreds of thousands of patients with venous thromboembolism [VTE] had filters placed, yet clearly there was an incidence of filter-related complications, such as breaks or perforations.” Johnson began by discussing the rationale behind PRESERVE, recounting the “maelstrom of concern” that was raised in 2010 following the US Food and Drug Administration (FDA) warning letter. The letter stated that all “implanting physicians and clinicians responsible for the ongoing care of patients with retrievable IVC filters should consider removing the filters as soon as protection from pulmonary embolism [PE] is no longer needed”.
Sparking “multidistrict litigation” against filter manufacturers in the USA, Johnson stated that there was a “huge lack of understanding” over the role of IVC filters as they relate to VTE. This, in part, may have been due to opaque definitions of VTE which, “for example, could be a sub-centimetre gastrocnemius clot below the knee or the entire vena cava could be occluded causing massive symptoms”, he explained. “Our definitions made it difficult for us to evaluate things, because we weren’t exactly sure what the extent of disease was and how filters should be used in these populations.”
Primarily used to prevent deep vein blood clots from developing into PE, the patient population privy to this procedure is “incredibly variable” in Johnson’s experience. IVC filters are often placed in patients “immediately following trauma, as a preoperative measure in cancer patients, or for prophylaxis—which is another entirely complicated thing, placing a filter in a patient without VTE”.
In clinical practice, filters are most commonly placed in people who cannot be anticoagulated; randomised trials have sought to evaluate filter efficacy in patients who have received concomitant anticoagulation, because randomising patients who can be anticoagulated to a filter or no treatment is unethical, Jonson explained. PRESERVE—a large multicentre prospective trial without a control group but with predetermined imaging and clinical outcome evaluations—was performed to obtain the best ethical data.
Originally PRESERVE had been incited by a US FDA warning letter—“which scared people”, Johnson recalled—and which brought the Society of Interventional Radiology (SIR) and Society for Vascular Surgery (SVS) together, putting themselves forward to evaluate the safety and efficacy of IVC filters from the seven manufacturers who marketed filters in the USA.
Conducted at 54 sites in the USA between 10 October, 2015 and 31 March, 2019, Johnson et al identified 1,421 patients who had a filter implanted—1,019 of patients had existing deep vein thrombosis (DVT) or PE. Their results met primary safety and effectiveness endpoints, with investigators reporting that procedural adverse events were “uncommon” and there was a “low incidence” of clinically-significant PEs.
The investigators note that a “high rate” (44.5%) of filters were removed in this cohort and the reported low rate of adverse events was perhaps due to the “mandates for noting a plan for [IVC filter] removal at the time of placement”, accompanied by frequent follow-up. Supplying a conclusory suggestion, Johnson et al believe that, when planning IVC filter placement, physicians should consider when the device should be removed, and patients should be followed closely in the interim.
“We should—all of us who place filters—view planning a patient’s treatment pathway as a central tenet of providing comprehensive, filter-inclusive care. In today’s world you cannot place a filter and just leave it. That’s not good medicine,” Johnson said. Having demonstrated the correlation between retrieval planning and survival rate through PRESERVE, Johnson’s central takeaway is: “at the time of placement, have a plan for removal”, although he understands that that is “much easier said than done—people’s states change all the time, operation dates change, contraindications change”.
“We’re not going to do better than PRESERVE,” Johnson said, but more is yet to be done to “optimise patient care” in this population. “Newer devices are being developed, however more research is needed to evaluate a device that may be less likely to poke out of the vena cava, or is easier to remove, or may even dissolve,” said Johnson, who maintained that innovation for better outcomes in these patients will prevail through future research efforts.
