Several professional societies recommend using an inferior vena cava (IVC) filter for patients with venous thromboembolic (VTE) disease and a contraindication to anticoagulation. The filters are placed inside the vein and designed to trap large clots before they can travel to the heart or lungs.
While this seems useful in theory, a retrospective study published July 13 in JAMA Network Open suggests the treatment is associated with an increased risk of 30-day mortality for these patients.
The authors believe their findings differ from previous observational studies because they adjusted for immortal time bias, unlike the prior reports.
“Immortal time bias … is the interval between hospital admission and IVC filter placement, during which time death cannot occur in the intervention group but can occur in the control group,” wrote Tyson E. Turner, MD, MPH, and coauthors—all from Washington University School of Medicine in St. Louis. “Failing to account for this potential source of bias can erroneously skew the results in favor of the intervention by falsely conferring a survival advantage to the treated group.”
Turner et al. studied outcomes of 126,030 patients hospitalized with VTE—deep vein thrombosis, pulmonary embolism or both—who had contraindications for anticoagulants. The average age of the cohort was 66.9 years and 36.3 percent were treated with an IVC filter.
After multivariable adjustment—including a time-dependent variable for IVC filter placement to account for immortal time bias—device implantation was associated with an 18 percent increased risk of 30-day mortality. The mortality risk associated with the filter remained unchanged when propensity matching was added.
“Retrospective observational studies may be subject to various types of bias that persist despite various techniques to adjust for differences in baseline characteristics,” the authors noted. “Therefore, these results should be considered hypothesis generating only.”
Turner et al. believe additional randomized trials are warranted to determine the efficacy of this relatively widespread therapy. IVC filters have been available since the 1960s and are implanted in about 100,000 U.S. patients each year, they said, despite the absence of quality data supporting their use.
“Turner and colleagues should be commended for their attempt to add to the current dearth of data for IVC filter use,” wrote corresponding author Robert W. Yeh, MD, MSc, and colleagues in an accompanying editorial. “We believe the greatest value of the study is to call out how limited our current evidence base is to support such a commonly used device, and to challenge the clinical and research communities to demand higher-quality studies before practices become ingrained.”
Even so, the editorialists said the research community would have to decide whether a randomized trial is ethical or fair to ask of clinicians when there are “strong clinical beliefs about the effectiveness of an intervention.”
They pointed out there is no causal explanation for the mortality increase associated with the IVC filters and said data were limited in exploring the timing and severity of VTE, as well as the overall condition and frailty of the patients. Selection bias may have skewed the mortality results in either direction, they said.
“It is possible that those with a more severe VTE presentation had an IVC filter placed, as placement of an IVC filter in those with limited cardiopulmonary reserve, regardless of candidacy for anticoagulation, is also guideline indicated,” Yeh et al. wrote. “Turner and colleagues argue that sicker patients may be less likely to undergo a procedure; however, given the ease at which IVC filters can be placed, including at the bedside, this may not be the case.”