Efficacy and safety of a novel vena cava filter on pulmonary embolism prophylaxis: a prospective, multicenter, randomized, parallel, positive-controlled, noninferiority clinical trial

Introduction

Pulmonary embolism (PE), with a mortality rate of up to 9.4%, is a common and preventable condition resulting from lower extremity deep vein thrombosis (LEDVT) (1,2). Besides the pharmacologic strategy of anticoagulants, which are the mainstay management for DVT, the inferior vena cava filter (VCF) is a mechanical strategy devised to prevent PE by trapping thrombi within metal struts in high-risk patients who have absolute contraindication or for whom anticoagulation has been ineffective (3,4). Over the past few decades, various types of VCFs have emerged, including permanent and retrieval filters (4). Permanent VCFs have been shown to reduce the initial risk of PE and provide long-term, sometimes lifelong protection. However, they have inherent risks, such as recurrent LEDVT and complications related to indwelling devices, including inferior vena cava (IVC) stenosis/occlusion, strut perforations, or filter fracture (1,5,6).

Concerns regarding the scenario described above have driven the development of various types of retrievable VCFs, particularly for patients who only temporarily require a filter, as it can be removed when clinically feasible, potentially eliminating the long-term risks of permanent filters. Currently, there are different types of VCF available in clinical practice (3). However, limited data exist to determine whether one type is superior to another, and no single VCF is universally recommended in clinical guidelines (3). The choice of filter is largely influenced by operator preference, economic considerations, and device availability at different institutions. Each VCF features a unique design aimed at maximizing retrievability and minimizing complications associated with long-term indwelling (6). The development of new VCFs continues to expand the range of available options, although this area remains underexplored.

This paper reports the results of a multicenter, randomized, parallel positive-controlled, noninferiority trial conducted in 10 hospitals across 6 provinces in China between October 2017 and March 2019. The trial was designed to evaluate the placement and retrieval of a new VCF, Octoparms, in patients with identified LEDVT, PE, or a temporarily increased risk of PE requiring filter placement. The Octoparms VCF was compared with the Celect filter (7) in terms of filter placement, retrieval, and indwelling complications. We present this article in accordance with the CONSORT (for noninferiority or equivalence randomized trial) reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-24-879/rc).

Methods

Trial design and oversight

This was a multicenter, randomized, parallel, positive-controlled, noninferiority trial conducted in 10 hospitals across 6 provinces in China, but it was not registered on any registration platform. This study was performed in accordance with Declaration of Helsinki (as revised in 2013) and was reviewed and approved by the institutional review board of Nanjing First Hospital (No. QX20170714-02). All participating hospitals were informed and agreed with the study. Written informed consent was obtained from every patient or their legal surrogates. An independent data and safety monitoring committee provided oversight throughout the study. The Center for Statistics in Medicine at Nanjing First Hospital maintained the web-response randomization portal, updated the clinical database, and conducted all analyses independently from the investigators. The authors vouch for the completeness and accuracy of the data and ensure the adherence of the trial to the project. The Octoparms filter received regulatory approval from the National Meidical Products Administration in 2021.

Trial sample size, population, and randomization

Based on previous clinical research results of venous filters, the primary effective indicator, clinical success rate, was determined to be 95% when compared to the control product. A noninferiority margin of 10% was established through collaboratively between statistical and clinical experts. This margin was used to define the sample size and to evaluate the noninferiority of the Octoparms filter compared to the Celect filter in this study.

The sample size for this trial was based on the assumption that the clinical success rate would be 95% and the noninferiority margin would be 10% for both filters. Using PASS statistical software (NCSS, Kaysville, UT, USA), it was calculated that 94 participants per group, accounting for a 20% dropout rate, would be required to achieve a power of 0.80 and a significance level of 0.05 to detect differences between the two groups. The inclusion and exclusion criteria are listed in Table S1, and the study flowchart is shown in Figure 1. Between October 2017 and March 2019, 188 patients who had confirmed LEDVT or PE or who were at risk of PE with a clinical indication for VCF placement due to contraindication to or failure of anticoagulant therapy were included in the trial. Before enrollment, each patient underwent baseline testing, including routine hematological tests, electrocardiography, Doppler and compression ultrasonography of the legs, and computed tomography pulmonary artery (CTPA). Non-menopausal women additionally underwent a negative pregnancy test. For patients without contraindication, anticoagulant treatment was initiated immediately when thrombosis was identified. Eligible patients were randomly assigned to receive either a new VCF [Octoparms, Kosell MedTech (Suzhou) Co., Ltd., Suzhou, China] or an existing VCF (Celect, Cook Medical Inc., Bloomington, IN, USA) at a 1:1 ratio using a web-based central system. Ultimately, 94 patients were assigned to the Octoparms group and 94 to the Celect group.

Figure 1 The study flowchart of the inclusion and exclusion of patients with LEDVT who received VCFs. LEDVT, lower extremity deep vein thrombosis; VCF, vena cava filter.

The new VCF device and procedures

The novel VCF, Octoparms, is depicted in Figure 2. Constructed from a nickel-titanium alloy, it features a conical-shaped mesh structure with four pairs (eight) curved balancing arms and four support rods. The torsion-type fixed rivet at the end of each support rod attaches the filter to the IVC wall after placement. The retrieval hook is designed with a 360° configuration, allowing it to pass through a 0.035-inch guidewire.

Figure 2 A schematic representation of the Octoparms filter and the procedure of its placement and retrieval. (A) Schematic of the design and structure of the Octoparms filter, showcasing its key features and components. (B) The filter is placed into the designated location. (C) Venography following the filter placement showing a well-performed placement and an unobstructed blood flow. (D) Retrieval procedure.

Octoparms filters are available in two diameter options, 34 and 40 mm, suitable for IVCs with diameters of 12–20 and 15–30 mm, respectively. The training and standardization procedures for clinicians performing the VCF placement and retrieval were performed to ensure consistency across sites. Following IVC venography, the filter introducer sheath was percutaneously inserted via either the femoral vein or the internal jugular vein approach. Using a pusher, the filter was advanced through the sheath, positioned within the IVC by unsheathing and deploying it. The procedure is illustrated in Figure 2. Once the placement was completed, anterior-posterior and lateral venography of the IVC was performed to confirm the proper positioning of the filter. The decision and timing for filter removal were individualized by the referring interventional radiologist based on the patient’s condition, with factors such as the resolution of PE risk or the patient’s ability to tolerate anticoagulation being considered. Before filter retrieval, additional anterior-posterior and lateral venography of the IVC was obtained. The VCF was then retrieved using a 10- to 12-Fr filter retrieval sheath.

Endpoints and safety

The primary endpoint of the study was the clinical success rate as a composite endpoint, including both technical and clinical success of filter placement and retrieval. Technical success of filter placement or retrieval was defined as the filter being placed or retrieved completely intact without any immediate complications. Clinical success of filter placement was determined by evaluating whether the filter was appropriately positioned in the IVC to provide sufficient mechanical interruption to prevent incident symptomatic PE and by the absence of adverse events related to filter placement. These adverse events included filter migration, fracture, titling, IVC occlusion, filter- or procedure-related death, or failure of filter placement. Clinical success of filter retrieval was achieved when the filter was successfully and completely removed without requiring complex techniques or the encountering of complications that necessitated further intervention (8).

The definitions for incident PE, filter migration, fracture, penetration, and tilt were in accordance with the Society of Interventional Radiology guidelines (8). Incident PE was defined as the occurrence of PE after filter placement as confirmed by CTPA or an altered ventilation/perfusion lung scan. Filter migration was defined as a significant change in the filter position of more than 20 mm (cranial or caudal direction) compared with the baseline deployed position as assessed by radiography, computed tomography, or venography. Filter fracture was defined as a loss of structural integrity of the filter (i.e., breakage or separation of filter components) as detected through imaging or autopsy. Filter penetration was defined as penetration of a filter leg or arm more than 3 mm outside the IVC wall as measured by computed tomography, ultrasound, or venography, or identified during autopsy. Filter tilt was categorized as greater than 15° based on the angle between the longitudinal axis of the target vein and the filter. Presence of filter thrombosis, indicated by a filling defect within the filter on venography, was recorded but not considered a clinical failure.

Adverse events, defined as untoward medical occurrences to the procedure or device, were recorded by the study investigators. The secondary endpoint of the study was the safety of filter placement and retrieval, with a focus on both procedure-related and filter-related complications; the former was associated with the procedure process, including bleeding at the access site or inflammation, while the latter was related to filter migration, deformation, vessel wall penetration, bleeding, peripheral organ damage, and IVC stenosis/occlusion. New or worsening LEDVT or IVC thrombosis was defined as the extension of LEDVT to a new venous segment in patients with documented evidence of thrombosis at baseline.

Statistical analysis

Statistical analyses were performed using SPSS 23 (IBM Corp., Armonk, NY, USA) and R statistical language software version 4.2.1 (The R Foundation for Statistical Computing, Vienna, Austria). Normality and homogeneity of variances were determined using the Shapiro-Wilk test and the Levene test. Continuous data are presented as the mean ± standard deviation (SD) and as the median and 25^th and 75^th percentiles, while categorical data are expressed as counts and percentages. To assess correlations between two groups and compare continuous data (e.g., age, circumference, IVC diameter, tilt angle, and time to filter retrieval), a t-test or Wilcoxon rank-sum test was used. Significance of categorical data was evaluated using the chi-square test or the Fisher exact test. Ranked data were assessed with the Wilcoxon rank-sum test or the Cochran-Mantel-Haenszel (CMH) test. The relationship between filter tilt during placement and retrieval was evaluated with a pairing graph using R software. Findings with P<0.05 (two-tailed) were deemed statistically significant.

Results

Patients and baseline characteristics

Between October 2017 and March 2019, a total of 188 eligible patients were enrolled and randomized into two groups based on the filter types: the Octoparms group (n=94) and the Celect group (n=94). The mean age of the patients was 58.4 years, and 52.1% (98/188) were male. The majority of patients were of Han ethnicity (96.8%). A body mass index (BMI) ≥28 kg/m² was observed in 17.0% (32/188) of patients. Regarding symptoms and signs of LEDVT, 64.9% (122/188) reported limb pain and 90.4% (170/188) reported limb swelling, with the mean circumference of the involved limb being 46.9 cm. Approximately 20.7% (39/188) had a D-dimer value ≥10 µg/mL (reference value <0.5 µg/mL). Concerning the thrombus distribution, a majority of the included patients experienced proximal LEDVT (85.1%) and involvement of the left limb (64.4%). Concurrent PE identified by CTPA was present in 49.5% (93/188) of patients. The most prevalent comorbidities and risk factors among patients with LEDVT were hypertension (30.3%) and trauma (29.8%). Baseline characteristics were comparable between the two groups (P>0.05). The demographics, LEDVT presentation, laboratory examinations, thrombus characteristics, concurrent PE, comorbidities, and risk factors for LEDVT in patients who received VCFs are summarized in Table 1.

Procedure and primary endpoints

Technical success of filter placement was achieved in 100% (188/188) of the patients enrolled in the study. VCFs were placed in the infrarenal vein (97.9%) and suprarenal vein (2.1%) via the access site of internal jugular vein (22.9%) or femoral vein (77.1%). There were no statistically significant differences observed in filter locations or access sites (P>0.05). The mean IVC diameter at the site of filter placement was 20.3±3.3 mm. Thus, the 40-mm Octoparms and the 65-mm Celect filter types were selected. Clinical success of VCF placement was achieved in 100% (94/94) of patients in both the Octoparms group (94/94) and the Celect group (94/94).

There was a median dwelling time of 11.0 days (range, 4–190 days) in the Octoparms filter group and of 12.0 days (range, 4–113 days) in the Celect filter group (P>0.05) as shown in Figure 3. Ten VCFs were left in situ as permanent devices due to patient refusal (n=4), physician’s decision due to severe illness (n=4), or non-filter-related death (n=2). The access site of filter retrieval for the remaining 178 patients was primarily via the right internal jugular vein (97.8%). Retrieval attempts were successfully completed in all cases, representing a 100% (178/178) technical success rate of filter retrieval. Clinical success rates of filter retrieval were also 100% in both groups (P>0.05). Filters were removed intact in all successful retrieval cases. Prior to filter retrieval, one patient (1/82, 1.22%) in the Octoparms group and two (2/82, 2.44%) in the Celect group were identified as incident PEs by CTPA, and all patients were asymptomatic. No new LEDVT or IVC thrombus were noted following venography at retrieval. No death was noted. Clinical successes of the two groups were 92.6% (87/94) for the Octoparms group and 96.8% (91/94) for the Celect group, with a difference of −4.2% [hazard ratio (HR) 2.441, 95% confidence interval (CI): 0.612–9.741; P=0.206]. The lower limit was lower than the noninferiority margin of −10%, indicating that the clinical success rate of the Octoparms group was noninferior to that of the Celect group.

Figure 3 Dwelling time before VCF retrieval. VCF, vena cava filter.

Secondary endpoints

Eight patients experienced a total of eight procedure-related complications, including infection, sepsis, hypersensitivity reactions, fever, constipation, nausea, and lower abdominal pain, which are detailed in Table 2. The differences between the two groups were not statistically significant (P>0.05). During follow-up, two out-of-hospital deaths occurred in the Octoparms group due to an unknown cause (3 weeks after placement) and esophageal cancer (7 months after placement). With respect to VCF-related complications, no instances of filter migration, deformation, IVC penetration, peripheral organ damage, or IVC stenosis/occlusion were observed. Moreover, 24 patients (27.6%) in the Octoparms group and 34 in the Celect (37.4%) group experience VCF thrombosis during IVC venography prior to retrieval (P>0.05). Two patients in the Celect group had massive clots necessitating the relinquishing of the VCFs as permanent devices under physician’s decision. Clots in Octoparms were small and nonfloating, exerting minimal impact on the IVC hemodynamics and not impeding filter retrieval. The distributions of filter tilt angle at placement and retrieval are shown in Figure 4. Two cases in the Octoparms group and one in the Celect group lacked tilt data at retrieval; however, the difference in filter tilt between the groups was not significant (P>0.05). During placement, one patient (1/94, 1.06%) in each group exhibited a tilt >15°. Tilt angle in the Octoparms group decreased from 19.2° to 1.9°, and thus there were no cases of tilt >15° in the Octoparms group. In the Celect group, one case showed an increase to 17.5°, and another case exhibited an increase to 19.8°, resulting in a total of two cases (2/90, 2.22%) with a tilt >15°.

Figure 4 The distributions of filter tilt angle at the time of placement and retrieval for both groups. (A) In the Octoparms group, there was no statistically significant difference between filter tilt angles at the time of placement and the time of retrieval (P=0.61). (B) In the Celect group, there was statistically significant difference between filter tilt angles at the time of placement and the time of retrieval (P<0.05).

Discussion

Over the past half a century, VCF research and development has progressed and has been investigated in a number of prospective studies and applied in a variety of clinical practices (5-7,9-13). Conical VCFs, in various forms, have advanced significantly from the introduction of the Greenfield filter in 1973 to the more recent Denali filter in 2014. These innovations have catalyzed substantial improvements in various aspects of filter technology. However, each filter has distinct advantages and disadvantages, and prospective comparative studies on different types of filters remain limited (1,3,6). Data on the retrieval characteristics of different filter types will be instrumental in guiding VCF selection in clinical practice (6). In our study, we compared the Octoparms filter with the Celect filter based on two primary factors. First, the Octoparms filter shares several characteristics with the Celect filter, including a similar morphological structure, characterized by a conical shape with four support struts and a four-paired inverted Y-shape balance arms; for another, the Celect filter is widely available in China and has been extensively used among the conical VCFs, with reports indicating its efficacy and safety.

In our study, among the 188 patients who received VCFs, the clinical success rate was 92.6% for those who received the Octoparms filter, compared to 96.8% for those who received the Celect filter. This slightly lower rate for the Octoparms filter may be attributable to a conservative definition of clinical success, which comprehensively evaluated both technical and clinical success from placement to retrieval. However, the success rate of the Octoparms filter was noninferior (within the established threshold value of −10%) to that of the Celect filter. Among the 10 patients classified as clinical failures, the filters were left in situ as permanent devices, resulting in a failure to meet the primary endpoint. Apart from these 10 cases, the remaining 178 patients who underwent intended filter retrieval experienced complete clinical success.

In this study, preoperative compressive ultrasonography confirmed the presence of LEDVT in all 188 patients. Among these patients, 49.5% were found to have PE according to CTPA, which is consistent with the 58.9% incidence rate reported in a previous study (14). The higher morbidity rates of PE observed in our study and that of Jin et al. (14) likely stemmed from the increased use of CTPA for detection. However, in most clinical cases, CTPA is typically performed only patients with LEDVT and symptomatic PE, potentially leading to an underestimation of PE and missed diagnoses in asymptomatic patients with LEDVT. These findings suggest that patients with LEDVT may have a higher propensity for silent PEs during the disease course, highlighting the clinical implications of CTPA in these patients. The potential risk of incident PE arises from clots escaping even after filter placement (6). The incident PE rate reported in previous filter trials ranges from 1% to 6% (6,9-13), which is in line with the results of our study. The rates were comparable between the two filter types (1.22% vs. 2.44%; P>0.05). Fortunately, all three cases with incident PEs were asymptomatic, likely due to the small volume of clots captured by the filter and distal branch embolism of the pulmonary artery. Additionally, these patients had good cardiopulmonary fitness, reducing the risk of symptomatic PE.

The overall retrieval rate of retrievable filters is reported to be 20–50%, primarily due to concerns over the risks associated with permanent placement and the lack of a planned follow-up for patients (6). In our study, 94.7% of participants returned to the outpatient clinic and underwent clinical and imaging assessments for filter retrieval, in accordance with the study procedure. This indicated the paramount effectiveness of a dedicated VCF program and a patient planned follow-up by implanting physicians or clinicians in improving overall filter retrieval rates. Of the 178 patients who underwent filter retrieval attempts, all had their filters successfully retrieved without the need for any complex technique or experiencing complications requiring intervention. No instances of filter migration, deformation, IVC penetration, bleeding, peripheral organ damage, or IVC stenosis/occlusion were observed between the time of filter placement and retrieval, supporting the safety of the Octoparms filter.

As previously reported, the incidence of IVC thrombosis is 4–15%. However, the incidence of IVCF thrombosis is more variable, ranging from 1.6% to 33% across different studies (15). In our present study, the overall incidence of IVCF thrombosis with conical VCFs was 32.6%, which is lower than that reported previously (15). This may be partly attributable to the improved design of the VCFs and the lower inherent thrombogenicity, as demonstrated in other study (16). The incidence of VCF thrombosis was 27.6% for the Octoparms filter and 37.4% for the Celect filter. It is possible that the thrombi detected were either formed at the insertion site or were intercepted from LEDVT migration by the filter, but these possibilities were not adequately explored. Notably, the definition of VCF thrombosis in this study was conservative, as patients with filling defects in the filter on venography were considered to have thrombosis. This may have led to an overestimation of the incidence. A more accurate CT-based diagnosis for filter thrombosis was not used in our study.

It is worth noting that a filter tilt >15° is considered to be risk factor for increased filter hook embedment and the need for complex filter retrieval techniques (17). In the study by Bos et al. (12), the complex retrieval rate was 18.9% in the Celect group. Although two patients in our study exhibited anterior-posterior angulation >15° in preretrieval according venography imaging, nonstandard filter retrieval techniques such as forceps retrieval or the loop-snare technique were not required. It is well-established that prolonged indwell time, along with filter tilt, is a recognized risk factor for complex retrieval, leading to higher rates of penetration, tilt, and filter tip embedment. The discrepancy between our findings and those of Bos et al. (12) may be explained by the prolonged indwelling time of 128.2 days in their study compared to the shorter indwelling time (12 and 105 days) in our study. This highlights the importance of retrieving the filter as early and as decisively as possible when clinically appropriate.

Although the relationship between vascular access and filter tilt has been previously documented (18,19), the impact of vascular access on VCF placement remains controversial. In a retrospective cohort study of 78 patients, Choi et al. (18) reported no significant difference in filter tilt between the vascular access of internal jugular veins and femoral veins. In a larger study that involved 13,003 patients in which the association between internal jugular vein and femoral vein access was evaluated, Grullon et al. (19) found that the internal jugular vein approach might allow for more precise placement and less tilt. In our study, the selection of vascular sites was comparable between the two groups. The incidence of filter tilt angle >15° at the time of placement was 1.1% for the Octoparms filter and 1.1% for the Celect filter. Prior to filter retrieval, no tilt angle >15° was observed in the Octoparms group, and the reduction in angulation from prefilter retrieval to postplacement seemed be for pronounced in the Octoparms group than in the Celect group. A potentially clinically relevant finding of this trial was a slightly higher self-adjustment and self-centering capacity of the Octoparms filter.

This involved several limitations that merit discussion. First, as a manufacturer-sponsored device trial, inherent bias might have affected the interpretation of results and should be considered. Second, although this trial was prospective in nature, its design including a comparison with the Celect filter rather than with other types of VCFs may introduce certain limitations. Third, the use of CTPA imaging both pre-VCF placement and pre- or post-VCF retrieval might have resulted in an increased radiation dose compared with other IVC filter trials. In addition, the high incidence of filter thrombosis observed in this study needs further explanation (20). It is possible that the detected thrombi were either formed at the insertion site or intercepted from LEDVT migration by the filter, but these possibilities were not thoroughly explored. Furthermore, the sample size in this study was relatively small for comprehensive assessment. The short duration of filters being left in situ could have reduced the statistical power to demonstrate any potential differences in complications between the two types of filters. In addition, the costs of the filters and the radiological procedural time were not reported. Future studies with larger sample sizes are necessary to address these limitations and provide a more robust understanding of this new filter.

Conclusions

The Octoparms filter exhibited a high rate of clinical success with a low rate of complications during placement and retrieval, demonstrating noninferiority to the Celect filter. The Octoparms filter may provide an option for VCFs in patients requiring PE prophylaxis due to LEDVT.

Acknowledgments

We would like to thank all the investigators from 10 centers who prepared and executed the trial (https://cdn.amegroups.cn/static/public/qims-24-879-1.docx).

Funding: This work was supported by the Jiangsu Medical Association Special Fund Project (No. SYH-3201140-0088[2023035]), the Nanjing Medical Science and Technology Development Project (No. YKK23116), and the Nanjing Medical University Science and Technology Development Fund Project (No. NMUB20230163).

Footnote

Reporting Checklist: The authors have completed the CONSORT (for noninferiority or equivalence randomized trial) reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-24-879/rc

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-24-879/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was performed in accordance with Declaration of Helsinki (as revised in 2013) and was reviewed and approved by the institutional review board of Nanjing First Hospital (No. QX20170714-02). All participating hospitals were informed and agreed with the study. Written informed consent was obtained from every patient or their legal surrogates.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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