Problems With Current Retrievable Vena Cava Filters

In spite of the impressive technological advances associated with the development of RVCFs, there are still a number of limiting factors that deserve to be pointed out. Removal of many if not most of the current temporary filters becomes increasingly difficult with passage of time because of thrombus in the filter and/or adherence at points of endothelial contact. As a result many have simply been left in. Throm bus in a filter can be interpreted as good (a potential PE has been trapped) or bad (device thrombogenicity). This problem in retrieving temporary filters may have resulted in renaming them optional filters, meaning that they can be used as either temporary/retrievable filters or left in as permanent filters. This implies that it is quite permissible (i.e., no significant penalty) to leave them in. This name change may be a marketing ploy because, as of this writing, no good long-term outcome data on these new optional filters has been published to justify leaving them indefinitely (e.g., low rates of recurrent PE, filter migration, filter or caval thrombosis, distal DVT, etc.). The design goal of a filter that optionally can be used either as a temporary filter (i.e., left in longer, as long as the temporary need for protection persists, then safely retrieved) or as a permanent filter (that can be safely left in indefinitely), is a worthy one, but reported experiences suggest that most of the current temporary filters can be left in only a few weeks or months before encountering increasing problems with either contained thrombus or contact point endothelialization, either of which can compromise retrievability. Instructions with some retrievable devices advise removal in 14 or 21 days; others give less specific advice, but two have suggested permissible indwelling times of up to three months. The evidence on this aspect deserves further consideration.

The reported experience with the greatest claim regarding the safe duration before retrieving a temporary VCF has been with the Recovery (Bard) device,4 which concluded that it "demonstrates the feasibility and safety of retrieval up to 134 days after implantation." In 24 of 32 patients (75%), the filters were retrieved between five and 134 days (mean 53 days!). Clot was present in seven (22%), in two large enough to be presumed to be trapped emboli, and presented difficulties with removal. Four patients were alive with their filters still in; three died with filters in place, and in one the filter was removed surgically.

The Tempofilter II (B. Braun) has a similar suggested safe removal time as the Bard Recovery device (i.e., up to three months). Data from a multicenter French study that support this claim has been submitted for publication. This device differs from the others in that introduction and withdrawal is through a tethered catheter with a subcutaneous anchoring device. Thus, leaving it in is not an option but its overall design facilitates the retrieval process.

In a recent report of this approach in multiple trauma victims, by Rosenthal et al.,5 using the Optease retrievable filter (Cordis Endovascular) and ICU bedside insertion under ultrasound guidance, the filters were successfully placed in 91 of 94 patients, but successfully retrieved in only 31 of 91 (34%) between five to 25 days (mean 19 days). Removal caused a 0.5 cm defect in the caval wall of one patient but without contrast extravasation. Of the 44 filters left in, 41 were not removed "because of the severity of the injury prevented—initiation of—anticoagulation prophylaxis," but three were left in because of trapped thrombi. One patient had a PE after filter removal.

One makeshift solution to this problem has been to reposition the filter every 12 to 14 days. Offner et al.6 reported repositioning the filter every 12 days if it was not ready to be retrieved. But this was done in less than one-quarter (9/44) of patients, and in three patients the filter could not be removed because of either trapped clot (n = 2) or angula-tion (one case).

A Spanish experience with the Gunther Tulip7 also reported repositioning as a way of achieving a longer indwelling time than the recommended 14 days. They used this strategy in 26% of 87 patients. Seventy of 88 filters (almost 80%) eventually had their filters removed. The mean indwelling time was 34.8 days; the average number of repositionings was 1.5, and the mean repositioning interval 13.8 days. Eighteen patients had their VCFs left in permanently: in one, fixation in the IVC prevented removal at 16 days; two were left in because of large entrapped thrombus; and all had "varying amounts of fibrous and fibrotic material adhering to the filter struts." Focal tears, associated with intramural hematomas as large as 10 mm in diameter, were visualized angiographically after filter removal, but there were no transmural lacerations or contrast extravasations.

Finally, it should be pointed out that each intervention to change filter position or retrieve the VCF is, to a degree, invasive and presents some risk of patient harm. These retrieval procedures represent an additional cost ($3000-$5000), which is not currently reimbursed in the United States.8 This begs the issue: if there is a permanent filter that can be left in for long periods of time without significant penalty, why not use it rather than a retrievable VCF? The results of the PREPIC trial were not stratified for the different permanent filters used (some of which may have been described in the previous two chapters). Nevertheless, one of the de-vices used, the Titanium Greenfield filter, was a low-profile version of the original stainless steel Greenfield filter, which has reported excellent 12- and 20-year results in terms of recurrent PE, caval patency, and DVT,9,10 and which has since been supplemented by an over-the-wire stainless steel Greenfield. Both of these low-profile, permanent filters appear to mimic the performance of their prede-cessor.11,12 Pending the correction of existing problems with current RVCFs, an alternative strategy then is to use permanent filters even for prophylactic reasons, which is currently the majority practice. The duration of safe indwelling time was recognized as a significant limitation of temporary filters in a survey of North American and European practices conducted by B. Braun, being identified as a major issue by 40% of those using RVCFs, and the majority of those continuing to use only permanent filters gave this as a major reason (B. Braun, personal communication). A minor objection to persisting with this approach is that there is a small but definite need, even in the best permanent filter, for repositioning or retrieval on occasion.

So, in summary, many if not most of the current temporary filters develop progressive problems with entrapped thrombus and endothelial incorporation with time, sufficient to compromising their retrievability. The safe removal time recommended by the manufacturer for different devices varies from three weeks to three months but is not well documented by reported data. Early removal of the device because of these limitations has resulted in PEs occurring after removal. Repositioning, to extend the safe indwelling time, has met with only limited success. Further design modifications may well be needed to extend the reliable time for completely safe removal. If this were extended to somewhere between six weeks and three months it would greatly widen RVCF application. As matters stand, retrievable RVCFs have not replaced permanent VCFs, even for prophylactic indications.

PROPHYLACTIC INDICATIONS: CRITICAL APPRAISAL

The major and steady increases in the use of prophylactic indications over the last three or four decades, to the point where it clearly dominates over therapeutic indications, have a number of likely reasons, but because all the conditions for which VCFs are being applied were all present by the time effective permanent VCFs were available, in the late 1960s, it seems appropriate to question the justification for such a large increase, particularly since there does not appear to be good data-based evidence for most prophylactic indications. Some general statements can be made about prophylactic indications in some respects but in other respects, it is necessary to focus on individual categorical prophylactic indications to pinpoint key issues.

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