Anticoagulation does Not Prevent Venous Thromboembolism Following IVC Filter Placement: A Retrospective Study of 702 Patients.

Inferior vena cava filters (IVCF) are extensively used in the United States to treat venous thromboembolism (VTE). Although IVCF prevent pulmonary embolism (PE), IVCF are associated with an increased incidence of deep vein thrombosis (DVT) and IVC thrombosis (IVCT). It remains unclear whether anticoagulation (AC) could reduce thrombotic events post-filter placement. The purpose of this study was to examine the impact of AC on clinical outcomes post-IVCF placement

After institutional review board approval was obtained, consecutive patients who received an IVCF at the Johns Hopkins Hospital were identified using Current Procedural Terminology (CPT) codes. Demographic and clinical data were retrieved from the institutional electronic medical record (EMR). Clinical events including objectively-documented VTE were confirmed by an independent EPR review by two investigators. Clinical outcomes with and without AC were compared using non-parametric and parametric statistics. Marginal structural models were used to model the impact of anticoagulation on VTE

Between January 1, 2002 and December 31, 2006, 702 patients had an IVCF placed at the Johns Hopkins Hospital. AC was used in 276 patients(39.4%) post-filter placement. 46.8% of patients were female and 60.1% were white and these parameters did not differ based upon AC status (p > 0.45). Patients on AC were younger than patients not on AC (54.9 years versus 59.0 years, p = 0.0025). The most common reason for IVCF placement in both groups was a contraindication to AC. Patients subsequently treated with AC were equally likely to present with DVT (p = 0.852) but were more likely to present with PE (p < 0.001) and IVC thrombus (p = 0.043). Retrievable filter use was more common in patients who were treated with AC. (p = 0.002). The mean duration of follow up was 434 days (range 1 - 2638 days). Follow up was longer for patients on AC than patients not on AC (576 versus 341 days, p < 0.001). All-cause mortality was lower for patients treated with AC (37.7% versus 56.0%, p <0.001). Post-filter placement, VTE occurred in more patients on AC than off AC (63/235, 26.8% versus 54/378, 14.1%, p<0.001). DVT (20.3% versus 11.1%, p = 0.001), PE (7.3% versus 3.5%, p=0.027) and IVCT (6.9% versus 2.1%, p=0.002) were more common in patients who were treated with AC.

In a large retrospective single center cohort study, AC use was associated with a reduced all cause mortality but an increased frequency of VTE in patients after IVCF placement. These data suggest AC may not protect patients from thrombotic complications associated with IVCF placement and warrant prospective confirmation. IVCF should be reserved for patients who have acute VTE and a contraindication to anticoagulation.

No relevant conflicts of interest to declare.