By Brian G DeRubertis
Surgical caval interruption for prevention of fatal pulmonary embolisation had been performed since the 1950s, though the modern era of pulmonary embolism prevention began with the introduction of the implantable inferior vena cava filters. Initial experience with percutaneously inserted permanent inferior vena cava filters for patients with known venous thromboembolism demonstrated reduction in pulmonary embolism and long-term caval patency rates as high as 98% in some series.
Although multiple studies have demonstrated reduction in pulmonary embolism rates in patients with indwelling inferior vena cava filters, evidence from the randomised controlled PREPIC trial and other studies have suggested that inferior vena cava filters are associated with increased rates of recurrent deep venous thrombosis (35.7% vs. 27.5% , p=0.042) without an overall survival benefit. Additionally, multiple recent case reports and small case series have demonstrated a number of other serious complications related to inferior vena cava filters, including caval perforation, intestinal erosions, filter strut factures, filter or filter component migration, and chronic filter-associated pain. Furthermore, these complications have been more commonly reported with contemporary retrievable filters.
With the advent of these retrievable filters, not only have filter-associated complications seemed to increase in frequency, but the incidence of inferior vena cava filter usage in the USA has increased dramatically. In the USA alone, there has been a roughly five-fold increase in annual inferior vena cava filter implantation since 1999, presumably due to the assumption that these are low-risk devices that are removed following cessation of the need for caval interruption. Unfortunately, contemporary data have shown that removal rates of retrievable filters are dismally low. In a 2007 study published in the Journal of Trauma, almost 80% of the 449 retrievable filters were placed for prophylactic reasons in patients without known venous thromboembolism, yet the retrieval rate was only 22%. Similarly, in a 2009 report of 72 patients undergoing filter placement in a US military population, 32% were placed for prophylactic indications and the retrieval rate was only 18%. This low retrieval rate, the rapidly increasing rate of filter utilisation, and the growing number of reports detailing the hazards of some of these retrievable filters should be cause for concern.
There are multiple potential reasons for failure to retrieve an inferior vena cava filter, including continued need for caval interruption (though contraindications to anticoagulation are generally short-lived), technical factors pertaining to the retrieval attempt itself and lack of appropriate patient follow-up.
Technical factors leading to difficulty with filter removal can present at the time of removal attempts. The cause of the majority of these retrieval failures includes filter tilt, leading to inability to snare or grasp the retrieval hook, or densely adherent filters that resist the normal force required for filter removal. Several recent publications have detailed manoeuvres designed to assist in the retrieval of tilted or heavily embedded filters, including centring techniques and the “loop over guidewire” technique. These techniques can be performed through coaxial sheaths used for dissection of tissue from the struts of the filter in those that are heavily embedded in the caval wall due to long dwell times or prior caval or peri-filter thrombosis. Though most of these obstacles to retrieval can be overcome with these manoeuvres, there is little doubt that they lead to increased procedural risk that may ultimately outweigh the benefits of retrieval. Patients should be appropriately counselled regarding these risks before aggressive attempts at retrieval of tilted or heavily embedded filters, and intervention in these patients may be most justified in those who are symptomatic or who are at particularly high risk of recurrent iliocaval thrombosis.
As more of these high-risk retrievals are being performed, interventionalists should remember that the most common cause of retained filters is related to lack of follow-up and failure to appropriately schedule patients for filter retrieval within instructions for use-designated windows. Perhaps the most effective strategy to increase retrieval rate may be the establishment of prospective filter registries that target patients with filters for directed follow-up and organised plans for retrieval within a defined period. Data on these approaches appear to support the efforts involved in starting such registries, and common sense would suggest that interventionalists should improve efforts at increasing filter retrieval rates overall before beginning programmes directed at these high-risk retrieval procedures.
Brian G DeRubertis is associate professor of Surgery, Division of Vascular Surgery, University of California, Los Angeles, USA