Dr. David Rosenthal Speaks with VDM at the VEITH Symposium About Bioconvertible IVC Filters for the Prevention of Pulmonary Embolism

Why did you first think that a permanent bioconvertible IVC filter was the answer for patients with pulmonary embolism?

Vena caval filters came about in the early 1970s to prevent pulmonary embolisms. In the 1990s, they developed retrievable filters, but this involved its own risks and costs so we thought that a bioconvertible filter was best for protection during the high-risk period against pulmonary embolism.

The FDA stepped in in August 2010 because only 25-30% of all retrievable filters are ever actually taken out.

Why is it that they weren’t taking these filters out?

Sometimes trauma patients never came back for follow-up. Others had 5 or 6 operations and told the doctor they just don’t want another surgery to have it removed. Patient compliance is often an issue and some of the filters were embedded into the scar tissue and couldn’t be removed.

What patient benefits occur as a result of a permanent device rather than one that must be removed?

The only real benefit of a permanent filter is that it protects the patient from PE indefinitely. However, there are long-term risks of permanent filters, which include filter fracture, erosion, migration, and an increased risk of DVT.   

Are there any complications with bioconvertible filters that are currently not an issue with removable filters?

Not that we know of. The only thing we don’t know is  the mechanism of how the filter of the device converts from a filter to stent-like configuration. The trial will soon start to show how well the filter functions. The study will evaluate accuracy of device placement, device transition from its filter to stent-like function, filter complications, and PE.

How long does it take from the time of implantation for the filter to change? Does this depend upon the patient? What factors influence this process?

The diameter of the filament generally determines when it opens but we try to keep the filter in position for a minimum of 60 days.

Are you finding any complications that must be corrected in the animal testing prior to human trials?

The animal trials were in sheep and we had no filter related complications. At necropsy, there were no PE to the lungs and all filters converted as planned.   

What makes bioconvertible IVC filters the best prevention for patients with pulmonary embolism?

I think we have 2 unique benefits. Number 1 is that this device offers protection from pulmonary embolism during the patient’s high-risk period, but avoids the necessity to retrieve the vena caval filter, which is an invasive procedure that has its own inherent risks and costs. There’s evidence that leaving a filter in the vena cava over the long-term increases the incidence of deep vein thrombosis. This is also avoided as the device converts from a filter to a stent and the vena cava remains widely patent as the device is endothelialized.

Is there anything that we haven’t discussed that you would like to share regarding this treatment?

There’s one thing we found that was very interesting and this was a study by PhD researcher at the University of Virginia, George Stookenborg. We looked at to the 2004/2005 Healthcare Utilization Project: National In-Patient Sample and we identified 24,000 patients with a diagnosis of pulmonary embolism. What was fascinating was that within 14 days of hospitalization, over 90% of the pulmonary emboli occurred and by 60 days, the time when the device converts from its filter to stent-like configuration, the chance of having a PE were vanishingly small. Remember that by 60 days after implantation­, the patients are usually ambulatory, can tolerate anticoagulents, and the chances of PE are minimal.

Dr. David Rosenthal is the Chief of Vascular Surgery at the Atlanta Medical Center in Atlanta, Georgia. He is also the Program Director for Vascular Surgery and Clinical Professor of Surgery at the Medical College of Georgia. Dr. Rosenthal received his medical degree from the State University of New York, Downstate Medical Center in Brooklyn, New York, and trained in peripheral vascular surgery at Tufts New England Medical Center in Boston, Massachusetts.