A Preliminary Analysis of Inferior Vena Cava Filters with and without Anticoagulation vs Anticoagulation Only: Readmission and Mortality Rates.

Inferior vena cava (IVC) filters are an increasingly popular option for patients with thrombosis and the advent of temporary filters may make this procedure an even more desirable alternative. We decided to evaluate how patients with inferior vena cava filters fared when compared to patients without such filters. A new software program, Clinical Looking Glass, replicates hospital records for statistical access with or without identifiers as defined by IRB-approved protocols. A cohort of patients who had a discharge diagnosis of deep venous thrombosis (DVT) and who had had an IVC filter insertion from 10/1/97 until 5/19/04 was defined. Within this group, a subgroup who had a filter and who had anticoagulation (AC) with an INR between 1.5 and 10 within 3650 days after filter were defined (F-AC) and within this group, a further subgroup whose INR values were between 1.5 and 10 within one year of filter insertion were defined. (F-AC 1YR). Those patients with filters but without any elevations in their INR were classified as ‘Filter - No AC’. The comparison groups were patients without filters who were discharged with a diagnosis of DVT and whose INR values were between 1.5 and 10 within the first year (DVT-AC 1YR). All patients were analyzed for their readmission rates for any diagnosis, for readmission for DVT, and for mortality. 749 patients were classified as DVT- AC 1YR, 533 patients as Filter - No AC, 103 patients as F-AC, and 63 patients as F-AC 1YR. Patients with inferior vena cava filters and anticoagulation were readmitted with the diagnosis of DVT significantly more often than patients without inferior vena cava filters (p<0.0003, RR 1.75 (95%CI 1.51, 2.03), and the mortality tended to be higher at 1 yr (p=.051). In comparison, the group with filter and no anticoagulation had a lower rate of readmission (23.3%, p vs. filter AC p<1x10⁻⁸, p vs. DVT AC 1 Yr <0.0003).

When 5-year mortality was analyzed for those patients with an IVC filter who were not anticoagulated (Filter -No AC) vs. those who were (F-AC 1YR), there was a very significant difference in favor of anticoagulation but when these were age adjusted (initial median age difference 75yr vs. 66 yrs respectively), no differences were noted. There was no significant gender difference in readmissions for filter patients with or without anticoagulation. For patients with anticoagulation only, a mild gender difference in readmission rate was demonstrated (female: male 41%: 32%, n=785, p<0.04). Although this study suggests that filters with AC do not give added benefit over simple AC to patients, these preliminary analyses have not been performed incorporating severity of illness, indication for filter placement, comorbidities, time in therapeutic AC range or duration of anticoagulation. These retrospective analyses are forthcoming but these preliminary data suggest that a controlled prospective study which examines the efficacy of inferior vena cava filters with and without anticoagulation is necessary to determine its role in antithrombotic therapy.