Early data from a multicentre, single-arm study that set out to evaluate the safety and effectiveness of a novel approach to inferior vena cava filtration using the VenaTech convertible filter (B Braun Interventional Systems) suggest that the use of this device yields favourable results.
Eric J Hohenwalter, Department of Radiology, Medical College of Wisconsin, USA, presented the research at the Society of Interventional Radiology’s (SIR’s) Annual Scientific Meeting (28 February–5 March, Atlanta, USA). This paper was one of two classified as “abstracts of the year” at the conference.
The VenaTech convertible filter can be converted into a stent configuration (to be left in the inferior vena cava) after the temporary need for a filter to prevent pulmonary embolism has passed. It has a hook and locking mechanism at the filter head and anchoring hooks for filter attachment to the vena cava wall. These encourage endothelialisation of the legs into the vessel wall. It also has self-centring stabilising legs. Its design is based on permanent filters, which may translate to fewer long-term filter complications compared to long-term use of retrievable filters, said Hohenwalter.
“The inferior vena cava is a thin-walled dynamic structure. All current retrievable filter designs have minimal contact points with the caval wall which could be stress points. The benefit of a filter is greatest during the acute period of venous thromboembolism risk and diminishes over time in most patients. Most retrievable filters remain in place after the period of risk has passed,” explained Hohenwalter.
The primary objective of the study was to determine whether the rate of successful filter conversion was no lower than reported retrieval success rate. The secondary objectives were to estimate the six-month major device-related adverse event rate in patients with a converted filter and to determine the device deployment success rate. The results were evaluated by an independent core lab.
“This study showed that the conversion rates are favourable compared to published retrieval rates. The early results show no inferior vena cava perforation vs. current retrievable filter designs,” Hohenwalter reported.
Patients were included if they had a time-limited risk of pulmonary embolism. They had to have a filter indicated because anticoagulants were contraindicated, or if they had experienced failure of anticoagulation. Patients could also be included if they needed emergency treatment following massive pulmonary embolism. Their inferior vena cava diameter needed to have been less than or equal to 28mm as evaluated by contrast venography and corrected for magnification.
“Nearly 150 patients have been enrolled at 11 sites. Eighty filters have been converted, of which just over 60 have been followed for a minimum of six months post-conversion. There have been 25 “permanent” filters followed for a minimum of six months,” he noted.
Hohenwalter told delegates: “All the filters were deployed successfully with a median time of 12.5 minutes, and there were no complications. There were 83 filter conversion attempts and 80 conversions to date. There were 77 “successful” conversions based on the protocol definition. There was a 93% technical success rate. There were six technical complications associated with the conversion procedures; three instances of being unable to snare the filter hook and three instances of incomplete opening of filter legs, following conversion. The median number of days to filter conversion was 122 (range 15–231).”
With regard to reported technical complications, there were 13 in total including one early filter migration. There were no reports of filters being deployed in unintended positions, extravascular perforation of the inferior vena cava, filter fracture, inadequate distribution or incomplete opening of the filter legs, or spontaneous conversion.
There were nine device-related serious adverse events in 2% of the study participants (3/148). These included caval thrombosis/occlusion, compromise of cardiac valve function due to filter embolization and deep vein thrombosis. There were no instances of perforation of the inferior vena cava and/or adjacent organs or vertebral bodies.
Hohenwalter noted that with the convertible filters, the conversion itself was largely classified as easy by physicians performing the procedure. Most procedures used accessory devices and the procedure was still seen as straightforward with no complications.
“With convertible filters, what is left behind is an inferior vena cava stent, and there is no inferior vena caval perforation seen in this study due to the stent. In the case of retrievable filters, the filter is designed to be removed. However, many are left behind and can result in inferior vena cava perforation and adjacent organ damage,” said Hohenwalter.
