Single institution prospective evaluation of the over-the-wire Greenfield vena caval filter

Vena Caval Filters: A Review for Intensive Care Specialists

Venous thromboembolism (VTE) is a common complication among patients in the intensive care unit. While anticoagulation remains standard therapy, vena caval filters are an important alternative when anticoagulation is contraindicated. To determine the safety and efficacy of vena caval filters in the treatment of VTE, a comprehensive review of the English-language medical literature was performed. Except for one randomized controlled trial, the literature supporting the use of vena caval filters consists almost exclusively of case series, which in many instances are limited by incomplete and short follow-up. While case series suggest that filters function effectively in the prevention of pulmonary embolism (2%-4% symptomatic pulmonary embolism [PE], fatal PE < 2%), recent higher quality studies indicate that filters may not provide significant additional protection to that provided by anticoagulation alone. Furthermore, filters are associated with a 2- fold increase in the incidence of recurrent DVT. Until randomized comparative studies are available, the safety and efficacy of all the available devices should be considered to be roughly equivalent. Since filters do not inhibit continued clot formation, all filter patients should receive anticoagulation for durations appropriate for their thrombotic disorder. Although extended anticoagulation may prevent thrombotic complications associated with filter placement, this strategy has yet to be experimentally tested. While many additional indications for vena caval filter use have been proposed (VTE in cancer patients, PE prophylaxis in trauma patients, etc), well-designed clinical trials demonstrating their efficacy in these situations are lacking. Further development of temporary/retrievable filters, which offer the potential to avoid the long-term complications of permanent filters, should be a research priority. Until additional data are available, vena caval filters should generally be restricted to patients with VTE who cannot receive anticoagulation.

Evidence-Based Evaluation of Inferior Vena Cava Filter Complications Based on Filter Type

Many inferior vena cava (IVC) filter types, along with their specific risks and complications, are not recognized. The purpose of this study was to evaluate the various FDA-approved IVC filter types to determine device-specific risks, as a way to help identify patients who may benefit from ongoing follow-up versus prompt filter retrieval. An evidence-based electronic search (FDA Premarket Notification, MEDLINE, FDA MAUDE) was performed to identify all IVC filter types and device-specific complications from 1980 to 2014. Twenty-three IVC filter types (14 retrievable, 9 permanent) were identified. The devices were categorized as follows: conical (n = 14), conical with umbrella (n = 1), conical with cylindrical element (n = 2), biconical with cylindrical element (n = 2), helical (n = 1), spiral (n = 1), and complex (n = 1). Purely conical filters were associated with the highest reported risks of penetration (90-100%). Filters with cylindrical or umbrella elements were associated with the highest reported risk of IVC thrombosis (30-50%). Conical Bard filters were associated with the highest reported risks of fracture (40%). The various FDA-approved IVC filter types were evaluated for device-specific complications based on best current evidence. This information can be used to guide and optimize clinical management in patients with indwelling IVC filters.

Braile vena cava filter and greenfield filter in terms of centralization

The aim of this study was to evaluate complications experienced during implantation of the Braile Vena Cava filter (VCF) and the efficacy of the centralization mechanism of the filter. This retrospective cohort study evaluated all Braile Biomédica VCFs implanted from 2004 to 2009 in Hospital de Base Medicine School in São José do Rio Preto, Brazil. Of particular concern was the filter's symmetry during implantation and complications experienced during the procedure. All the angiographic examinations performed during the implantation of the filters were analyzed in respect to the following parameters: migration of the filter, non-opening or difficulties in the implantation and centralization of the filter. A total of 112 Braile CVFs were implanted and there were no reports of filter opening difficulties or in respect to migration. Asymmetry was observed in 1/112 (0.9%) cases. A statistically significant difference was seen on comparing historical data on decentralization of the Greenfield filter with the data of this study. The Braile Biomédico filter is an evolution of the Greenfield filter providing improved embolus capture and better implantation symmetry.

The Transition to IVUS-Guided IVC Filter Deployment in the Nontrauma Patient

While prior reports have demonstrated intravascular ultrasound (IVUS)-guided inferior vena cava filter (IVCF) deployment to be feasible, larger reviews using the latest generation of filters in the nontrauma setting are absent. We review our experience with the deployment of 104 IVCFs using IVUS, whereby we transition from a combined use of IVUS with traditional road mapping techniques (venography and/or renal vein cannulation) to the sole use of the IVUS as the road mapping tool for IVCF insertion. The use of IVUS for IVCF deployment minimizes radiation exposure to patients and staff, minimizes patient contrast exposure, and minimizes dependency on auxiliary staff for fluoroscopy. Intravascular ultrasound IVCF deployments can be performed without increasing morbidity and mortality, case duration, or overall costs when compared to standard deployments. The learning curve for transitioning into the use of the IVUS as the primary road mapping tool for IVCF deployments is approximately 20 cases.

Evaluation of an active vena cava filter for MR imaging in a swine model

PURPOSE

To evaluate the feasibility of magnetic resonance (MR) imaging-guided placement of an active vena cava filter (AVCF) in a swine model, the effectiveness of the system in filtering thrombi, and the detection of thrombi with MR imaging.

MATERIALS AND METHODS

This study was approved by the government committee on animal investigations. An AVCF tuned to the Larmor frequency of a 1.5-T MR unit was placed in the inferior vena cava (IVC) of seven pigs under real-time MR imaging guidance. Steady-state free precession sequences with four different flip angles (90°, 40°, 25°, and 15°), T1-weighted turbo spin-echo sequences with two flip angles (90° and 15°), and black-blood proton-density-weighted sequences with a flip angle of 90° were performed before and after filter placement. In six cases, extracorporeally produced thrombi were injected through the femoral access to test filter function. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were assessed before and after filter deployment and compared by using the signed-rank test.

RESULTS

All AVCFs were successfully deployed. Significant differences (P < .05) in the SNR and CNR of the IVC were found before and after AVCF placement and between sequences with different flip angles. Intravenous thrombi were caught in all cases and clearly depicted with MR imaging. On black-blood proton-density-weighted images, high-signal-intensity thrombi inside the filter were clearly detectable without any overlaying artifacts.

CONCLUSION

MR imaging-guided deployment and monitoring of an AVCF is feasible. The AVCF enhances the SNR and CNR, resulting in clear depiction of thrombi inside the filter without the need for contrast material. Design modifications for improved intracaval fixation and retrieval of the prototype AVCF will be required.

Vena Cava Filter Performance Based on Hemodynamics and Reported Thrombosis and Pulmonary Embolism Patterns

PURPOSE

Three inferior vena cava (IVC) filters of different designs were studied to identify the potential links between published clinical results for thrombosis and recurrent pulmonary embolism (PE) rates and in vitro hemodynamics patterns in the region of the filters.

MATERIALS AND METHODS

The filters studied were the Greenfield over-the-wire filter (Medi-tech/Boston Scientific, Watertown, Mass), TrapEase filter (Cordis Europa, Roden, the Netherlands), and Mobin-Uddin umbrella filter (Edwards Laboratories, Santa Ana, Calif). To assess hemodynamics, velocity contour maps were generated for each filter by using the in vitro photochromic flow visualization technique. Results were obtained for both the unoccluded and partially occluded states. Steady flow (R(e) = 600) was used to model physiologic conditions. To estimate the rates of IVC occlusion and recurrent PE, the authors analyzed published clinical studies spanning more than 30 years and a U.S. Food and Drug Administration database.

RESULTS

For both the unoccluded and partially occluded Mobin-Uddin and TrapEase filters, regions of flow stagnation and/or recirculation and turbulence developed downstream of the filter. The Greenfield filter did not produce any prothrombotic flow patterns for either the unoccluded or partially occluded states. Results of published clinical studies supported the hemodynamic findings, with the TrapEase and Mobin-Uddin filters having high rates of IVC occlusion and recurrent PE compared with those of the Greenfield filter.

CONCLUSIONS

Flow stagnation or recirculation and turbulence have been linked to thrombosis and thrombus and/or PE formation. Thus, the hemodynamic results from this study may help explain the relatively higher rates of filter thrombosis and PE for the Mobin-Uddin and TrapEase filters versus the Greenfield filter.

Complications of Inferior Vena Cava Filters

Inferior vena cava (IVC) filters offer a safe and effective means of preventing pulmonary embolus and have reduced complications when compared to earlier techniques of caval interruption. However, despite continued improvement in filters and insertion methods, complications still occur. Pneumothorax, hemorrhage, and vessel injury may result while obtaining vascular access. Filter misplacement, excessive tilt, and vascular injury have been reported with insertion, but preinsertion cavography is helpful in preventing these insertion-related complications. Attention to detail, proper use of guidewires, and preinsertion imaging are vital in preventing insertion-related complications as well. Long-term complications occur in a minority of patients and include recurrent pulmonary embolus, caval occlusion, and filter migration. Overall, the benefits of preventing pulmonary embolism far exceed the risks related to filter placement in properly selected patients.

Artifacts of vena cava filters ex vivo on MR angiography

We evaluated magnetic susceptibility artifacts of nine types of vena cava filters in MR angiography (MRA) at 1.0T ex vivo in order to assess the filters' compatibility with MRA. Each filter (tulip filter, tulip MReye filter, stainless Greenfield filter, titanium Greenfield filter, TrapEase filter, Simon filter, LGM Vena-Tech filter, Antheor temporary filter, and Bird's nest filter) was inserted into an acrylic tube (20 or 25 mm in diameter, 15 or 30 cm in length). Gd-DTPA was poured into each tube at a concentration of 1/500 and each was placed in a water-filled container for imaging. We evaluated artifacts of the filters according to the following criteria: signal void beyond the tube, 3+; signal void within the tube but at more than one-half the diameter of the tube, 2+; and signal void within the tube but at less than one-half the diameter of the tube, 1+. We evaluated artifacts originating at the tip, intermediate portion, and distal end of the filters. We judged the artifacts as follows: tulip (3+, 3+, 3+); tulip MReye (2+, 1+, 1+); stainless Greenfield (2+, 1+, 2+); titanium Greenfield (1+, 1+, 1+); TrapEase (1+, 2+, 1+); Simon (2+, 2+, 1+); LGM (2+, 2+, 1+); Antheor (2+, 2+, 2+); and Bird's nest (3+, 3+, 3+). The numbers in parentheses refer to the degree of signal void at the tip, intermediate portion, and distal end of the filter, respectively. The tulip filter and Bird's nest filter made of 304 stainless steel caused extensive signal voids beyond the areas defined by the filters. The signal voids in the remaining seven filters were limited to within the tube. We concluded that seven of the nine filters were compatible with MRA ex vivo.

In vitro hemodynamic evaluation of a Simon nitinol vena cava filter: possible explanation of IVC occlusion

PURPOSE

To evaluate the local hemodynamics in the region of the Simon nitinol filter (SNF), used to prevent pulmonary emboli by capturing clot and promoting lysis.

MATERIALS AND METHODS

The hemodynamics of the Simon nitinol inferior vena cava (IVC) filter were evaluated under steady flow (Re = 600) in a 20-mm-diameter IVC model. The photochromic dye tracer technique was used to estimate the velocity and wall shear stress. These flow features were determined for the unoccluded and partially occluded (clot volume = 1,500 mm(3)) states of the SNF along its center plane.

RESULTS

A region of low velocities developed around the central axis of the filter extending from the leading edge of the central strut to the filter tip. This phenomenon was created by the strong redirection of flow toward the periphery of the filter. With the presence of the clot, these effects were enhanced, causing flow separation and recirculation. In addition, the shear stress on the hip of the clot was about 30 times that of the upstream value, and turbulence developed in the near-downstream region.

CONCLUSIONS

The extended region of almost-stagnant flow near the midsection of the umbrella region could lead to organization of thrombus and fibrin mesh network development. The presence of a simulated clot led to a significant increase in the size of the stagnant, thrombus-prone region as well as turbulence, which, overall, may contribute to caval occlusion.

The percutaneous greenfield filter: outcomes and practice patterns

OBJECTIVE

The percutaneous steel Greenfield filter (PSGF) is similar in appearance to the titanium Greenfield filter (TGF) but differs in the length and orientation of the attachment hooks and in the over-the-wire delivery system. Because these differences improve ease of insertion and attachment, they may affect patient outcomes and physician practices. The purpose of this study was to evaluate the performance of the PSGF relative to the TGF and to determine whether there had been a change in physician practices.

METHODS

The Michigan Filter Registry contains data for a prospective cohort of 2188 patients with Greenfield filters. Procedural and long-term outcomes for patients with a PSGF were abstracted. These events were compared with rates for Registry patients who had a TGF. Trends for indication for placement, delivery route, and filter location were also compared with published series.

RESULTS

Since 1995, 600 PSGFs have been placed in 599 patients. A 1-year mortality rate of 42% left 349 patients available for annual follow-up, and studies were completed for 231 (66%). Periprocedural events occurred in 2.5% of cases with associated morbidity in 1.5%. The rate of new pulmonary embolism was 2.6%, and vena caval patency was 98.3%. The combined rate of new venous thromboembolic events was 12.5%. Left-sided femoral vein placements increased to 20%, and the major indication for filter placement has become prophylaxis (46%).

CONCLUSIONS

The PSGF is similar to the TGF with respect to patient outcomes, and it provides decreased rates of asymmetry along with excellent fixation. The flexible carrier system has allowed more frequent access through the left femoral vein. The ease of use and favorable patient outcomes have resulted in more frequent placement for prophylactic indications.

Bedside diagnostic ultrasound and therapeutic ultrasound-guided procedures in the intensive care setting

The availability, portability, safety, and other features of ultrasound have ushered this relatively new imaging modality into the everyday clinical practice of multiple disciplines. Features unique to ultrasound lend this imaging modality the opportunity for extensive use in the ICU. A review of its uses in this capacity includes bedside diagnosis of common disorders seen in the ICU setting, such as DVT, cholecystitis, and abscess. Bedside sonography also can aid in the treatment of such disorders, including DGC of pseudoaneurysms, fluid aspirations, and abscess drainages. This article is a review and could not possibly cover all bedside uses of ultrasound or provide in-depth information of specific uses described in this article. Hopefully, this article will spark an interest and prove as a starting point on a rewarding learning adventure.