‘Bioconvertible’ IVC Filter Does Its Job Then Moves On: SENTRY Trial

HOLLYWOOD, FL—For patients at risk of pulmonary embolism (PE), a new type of inferior vena cava (IVC) filter may resolve issues inherent to earlier models by neither remaining in place nor needing to be retrieved.

The device “represents an important paradigm shift in the prevention of PE,” said investigator Michael Dake, MD (Stanford University, CA), presenting 1-year findings from the SENTRY study at the recent International Symposium on Endovascular Therapy 2018.

“I think it’s fair to characterize the field of IVC filters over the last decade as rife with controversy,” Dake commented. With the advent of retrievable filters, use rose between 2005 and 2010. But use then fell following the 2010 US Food and Drug Administration’s alert over complications associated with the devices.

“What’s not controversial is pulmonary embolism,” he stressed, noting that one in 10 hospital deaths are PE-related. “Used correctly, IVC filters save lives and reduce injury and costs related to PE.” However, existing technologies are not meeting the needs of patients or clinicians, Dake said.

Made of a stable frame plus filter arms held together by a bioabsorbable filament, Sentry (Novate Medical) is meant to provide patients with protection against PE during transient periods of high risk. After about 60 days, hydrolysis of the filament enables the arms to retract against the IVC, with the “bioconvertible” device leaving behind a patent lumen.

This not only reduces the risk of IVC occlusion and other complications, Dake stressed, but also removes the need for retrieval and its associated risk and cost.

SENTRY IVC Filter Trial

For the SENTRY IVC Filter Trial, Dake and colleagues implanted the Sentry filter in 129 subjects at 23 sites; all had either documented deep vein thrombosis or PE or were at temporary risk of developing either condition but were unable to use anticoagulation. Ultrasound and CT venography were performed at the time of the index procedure, with additional imaging conducted over the course of follow-up.

Freedom from symptomatic PE during the 60-day protection period was 100%. There were two cases of symptomatic caval thrombosis (on days 8 and 31) that did not recur after treatment. No instances of tilting, migration, embolization, fracture, or perforation were observed.

By 12 months, none of the patients had developed symptomatic PE and no complications were detected on imaging. The bioconversion rate of 96% “compares favorably to retrieval rates,” which are estimated to be at less than 50%, said Dake.

You’re still leaving behind a permanent implant in the IVC. People think that that’s not a big deal, and it may very well not be, but we just don’t know. Kush R. Desai

Kush R. Desai, MD (Northwestern University, Chicago, IL), who was not involved in SENTRY, told TCTMD “it’s an interesting concept [that] combats the historic low retrieval rates of retrievable IVC filters.” Because the device “autoconverts itself,” he said, “it does a good job of addressing that question.”

Yet the device doesn’t disappear entirely, Desai pointed out. Though its arms retract, the filter remains in the body.

“You’re still leaving behind a permanent implant in the IVC,” he observed. “People think that that’s not a big deal, and it may very well not be, but we just don’t know. Certainly, I think a lot of people originally thought that it wasn’t a big deal to leave a retrievable filter in place forever and we now know that’s not the case.”

Desai noted another caveat: “Today’s patients are complex and frequently don’t fit in the box of 60 days.” For example, a trauma patient often doesn’t need protection against PE beyond 2 weeks and, if young, could be unnecessarily left with an implant that remains in place indefinitely, he said. A patient with cancer, on the other hand, may be at risk for an extended period of time beyond 60 days.

Sentry also is not the only convertible device. Another model, VenaTech (B. Braun), doesn’t shift to an open configuration on its own but rather requires interventionists to “go in and remove the hook percutaneously through an endovascular procedure,” Desai explained.

Two-year follow-up of the SENTRY IVC Filter Trial is now in progress.