by Eileen Masciale
When the American Venous Forum first conceived of the idea of the American Venous Registry, the purpose was to collect patient data expediently in order to answer research questions and improve clinical practice. This spring, the AVF released the second of five planned modules for the registry – the Inferior Vena Cava (IVC) Filter Module, and it was received the medical community with great enthusiasm.
“There is now more than ever a real need for the patient data and analysis with which the AVR promises to enhance patient care and outcomes,” said Brajesh K. Lal, MD, Chairman of the American Venous Registry (AVR), and Associate Professor and Chief of Vascular Surgery, Physiology & Bioengineering, University of Maryland, Baltimore.
The medical community and industry have embraced the AVR, which was launched in February with the release of the varicose vein module.The AVF has also broken new ground with the IVC filter module, the first and only national registry of IVC filters placed and retrieved in the United States.
The purpose of IVC filters
IVC filters are placed in patients who have a history of, or who are at risk of, developing blood clots in the legs. The purpose of the filter is to trap large clot fragments and prevent them from traveling through the vena cava vein to the lungs, where they could cause severe complications or even death.
The filter is placed in the inferior vena cava, the large vein in the abdomen that returns blood from the lower body to the heart. Until recently, IVC filters were available only as permanently implanted devices. Recently, newer filters have been developed that may be left in place permanently or have the option to be removed from the blood vessel later.
The IVC Filter Module will enable physicians to enter and track the indications for which they are placing filters,
the types of filters they are using, how frequently they are retrieving filters and any complications. They will be able to compare this information from their patients with the national aggregate.
“By tracking specific aspects of the IVC filter practice nationally, physicians will get a better idea of how IVC filters are being used, determine their complications and filter retrieval rates, and compare these aspects of their practices to the experience of other physicians,” says John Rectenwald, MD , Assistant Professor of Vascular Surgery, University of Michigan Health System, and Chair of the IVC Filter Module of the AVR .
A look at IVC filters
IVC filters have been used in the US since the late 1960s. In 2003, the first retrievable IVC filter was introduced in
the U.S., but it was taken off the market two years later due to issues with filter fracture and migration. Since then,
improvements have been made in the filter design to resolve problems of structural integrity and increase the ability to remove the filter after longer periods of time.
The primary difference between retrievable and permanent filters is that the retrievable filters have hooks or other structures that allow for recapturing the IVC filter for removal. Permanent filters do not have these. In addition, some retrievable filters are made materials, such as nitinol, which can fracture. As noted by the FDA, the fracturing of the filter can cause potential complications; thus the FDA released an alert in August 2010 advising physicians to remove retrievable filters whenever possible.
“The IVC Filter Module is launching at an extremely appropriate time as the FDA , doctors and patients are struggling with critical questions about who should get filters, how many retrievable filters are actually getting retrieved, and which filter designs are associated with complications,” said Robert McLafferty, MD, Professor, Division of Vascular Surgery, Southern Illinois University School of Medicine, and President-Elect of the American Venous Forum.
According to Joseph Raffeto, MD, VA Boston Healthcare System, and Chair of the Research Committee of the AVF, the number of retrievable filters placed since 2005 has increased sharply. Industry has responded to the demands of the medical community; the past six filters that have been developed are all retrievable filters. There have not been any new permanent filters developed since 2005.
Retrievable filters are used rather than permanent filters based on the PREPIC Study Group which conducted the PREPIC (Prevention du Risque d’Embolie Pulmonaire par Interruption Cave) Randomized Study. This research consisted of a randomized trial in patients with proximal deep-vein thrombosis. After two years, permanent vena cava filters reduced the incidence of pulmonary embolism (PE), but increased that of deep-vein thrombosis (DVT). The study also included five- and eight-year follow-up tests to assess the longer term impact of the filters and risk of DVT .
Lazar Greenfield, MD, Professor of Surgery and Chair Emeritus, University of Michigan – who developed the Greenfield filter, which has been implanted into more than 600,000 patients since it was developed in 1970 – points out that the PRECI P study resulted in different conclusions as far as filter-associated DVT is concerned, and that the results have not been replicated. Yet this study has created a certain perception among physicians. Importantly, more long-term data exists on permanent filters and, to date there is no follow-up on the long-term performance of retrievable IVC filters.
Said Dr. Rectenwald, “Permanent filters tend to be tested, tried and true.” However, he went on to explain: “My perception is that most physicians have gone to using just retrievable filters for all patients, regardless of the indication for the filter, as all retrievable filters were initially approved by the FDA for permanent placement.”
But what is the best practice vis-à-vis the retrievable vs. permanent IVC filter? Which patients have the best outcomes? What are the predictors of the optimal outcome?
Even further, what is the risk of having a filter vs. not having a filter? Dr. Rectenwald points out the logic that “you can’t have a filter complication (IVC thrombosis, filter fracture or migration, penetration/perforation of the IVC) if there is no filter in place, but you can have a recurrent pulmonary embolism.”
Thus, the need for the American Venous Registry and, specifically, the IVC Filter Module. The module, which is pre populated with patient data from Dr. Greenfield, gives physicians from throughout the US the ability to enter their patient data and then compare their results with the national aggregate. On a larger scale, once the data from all participating physicians has been compiled and analyzed, the evidence will exist to answer the pressing questions about IVC filters.
The benefit of the IVC Filter Module is that it captures data from patients that will otherwise not be captured in a randomized clinical trial with a large cohort and a very thorough follow-up to get an accurate impression of complication and retrieval rates.
About the American Venous Forum and the American Venous Registry
The American Venous Forum (AVF) is an international consortium of venous and lymphatic specialists dedicated to improving patient care. Its mission is to promote venous and lymphatic health through innovative research, education and technology. According to Dr. Lal, the AVF created the American Venous Registry to:
- Standardize the collection and analysis of clinical information on venous disease
- Identify practice patterns or venous disease diagnosis and treatment nationwide
- Answer research questions prioritized by the AVF
- Provide a real-time clinical practice tool to assist the practices of individual participating physicians
The Registry will be comprised of five modules; two have been launched and three are under development. Each module focuses on one particular aspect of venous disease and offers several clinical practice tools and the ability to run specific benchmarking queries in real time. The modules are:
- Varicose vein module, which was launched in February 2011
- IVC filter module, which was launched in June 2011
- Stent module, which is scheduled to launch in the Fall of 2011
- DVT thrombectomy/ysis module
- Upper Extremity DVT module