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The 6-F Nitinol TrapEase Inferior Vena Cava Filter: Results of a Prospective Multicenter Trial
Clinical Studies
The 6-F Nitinol TrapEase Inferior Vena Cava Filter: Results of a Prospective Multicenter Trial Hervé Rousseau, MD, Pierre Perreault, MD, Phillippe Otal, MD, Luc Stockx, MD, Jafar Golzarian, MD, Vincent Oliva, MD, Phillippe Reynaud, MD, Frank Raat, MD, Ferenc Szatmari, MD, Gennaro Santoro, MD, G. Emanuelli, MD, Michel Nonent, MD, and Yvonne Hoogeveen, PhD1
PURPOSE: The authors report the first results of a new 6-F symmetrically designed permanent nitinol inferior vena cava (IVC) filter, the Cordis TrapEase, evaluated in a multicenter prospective study with 6-months of follow-up. MATERIALS AND METHODS: A total of 65 patients (29 men, 36 women) who ranged in age from 37 to 96 years (mean age, 68 years) and who were at high risk of pulmonary embolism (PE) were enrolled in 12 centers in Europe and Canada. The study was approved by the institutional review boards at all centers. Study objectives were to evaluate filter effectiveness, filter stability, and caval occlusion. Indications for filter placement were deep vein thrombosis with recurrent thromboembolism and/or free-floating thrombus with contraindication to anticoagulation in 37 patients, and complications in achieving adequate anticoagulation in 28 patients. Follow-up included clinical examination, plain film, Doppler ultrasound, CT scan, and nuclear medicine. RESULTS: The analysis of the data revealed a technical success of 95.4% (three filter-system related implantations not at the intended site, no events of filter tilting) and a clinical success of 100% at 6 months (no cases of symptomatic PE), the study primary endpoint. There were no cases (0%) of filter migration, insertion site thrombosis, filter fracture, or vessel wall perforation. During the study period, there were two cases of filter thrombosis: one case of early symptomatic thrombosis that was successfully treated in the hospital, and one case of nonsymptomatic filter thrombosis detected at 1-month follow-up, with spontaneous recanalization at 3 months. In the latter patient, some residual thrombus was still detected at 6 months. Of the study population of 65 patients, there were 23 deaths. These deaths were not related to the device or the implantation procedure but to the underlying disease process. CONCLUSION: This study demonstrates the new nitinol permanent IVC filter to be a safe and an effective device, with a low overall complication rate, for use in patients with thromboembolic disease at high risk of PE. Index terms:
Embolism, pulmonary
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J Vasc Interv Radiol 2001; 12:299 –304 Abbreviations: IVC ⫽ inferior vena cava, PE ⫽ pulmonary embolism
THE implantation in the inferior vena cava (IVC) of a permanent vena cava filter can be regarded as a therapy modality for the prevention of pulmonary
embolism (PE) in the management of venous thromboembolic disease. Since the inception, in 1967, of the first IVC filter (1), a wide range of filters with
From the Radiology Department (H.R., P.O.), CHU Rangueil, Toulouse, Hoˆpital De La Cavale Blanche (M.N.), CHU Brest, Pneumonologue Agre´e´ (P.R.), Hoˆpital Laennec, Paris, France; CHUM Hospital Group (P.P.), St. Luc Campus, Hospital Notre Dame (V.O.), Montreal, Quebec, Canada; Department of Radiology (L.S.), University Hospital Leuven, Hopital Erasme KLB de Bruxelles (J.G.), Brussels, Department of Radiology (F.R.), A.Z. St. Lucas, Gent, Cordis Europa (Y.H.), Roden, The Netherlands; Department of Radiology (F.S.), Petz Aladar County Hospital, Gye´r, Hungary; Department of Cardiology
(G.S.), Clinica S. Luca, Firenze, and 2nd Department of Vascular Surgery (G.E.), Ospedale San Gerardo di Monza, Monza, Italy. Received June 1, 2000; revision requested July 18; final revision received and accepted November 20. Address correspondence to H.R., Service de Radiologie, CHU Rangueil, 01 Av J Poulhes, F-31054 Toulouse Cedex, France; E-mail: [email protected] 1 This author has disclosed the existence of a potential conflict of interest. © SCVIR, 2001
varying configurations have been developed, approved, and subsequently improved in line with increased clinical application and attained knowledge. In the published literature, the major drawbacks of currently available filters are reported to include (i) recurrent symptomatic PE, (ii) caval obstruction, (iii) filter migration, and (iv) local insertion site complications (1,2). A new nitinol permanent IVC filter (TrapEase; Cordis Europa, Roden, The Netherlands) was designed with a low profile (6-F) and characteristics intended to ensure protection of PE, with a theoretically low risk of filterassociated complications. We report
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Table 1 Baseline Patient Demographics and Clinical Characteristics Patient Characteristics
No.
Age (y) Mean ⫾ SD Range (min, max) Sex (M/F) History CAD CVD Risk factors Protein C Protein S Cancer Resistance to protein C activation Location of DVT Lower legs IVC/iliac and lower legs Free-floating thrombus with DVT IVC/iliac Lower legs Associated treatment before filter placement Anticoagulation Initial course of heparin followed by oral anticoagulants Antiaggregates Antimitotics NSAID Antibiotics
67.8 ⫾ 12.5 37–96 29/36 18.7% (12/64) 14.1% (9/64) 1.6% (1/63) 1.6% (1/63) 39.7% (25/63) 1.6% (1/63) 90.3% (56/62) 9.7% (6/62) 33.8% (21/62) 9.5% (2/21) 90.5% (19/21) 52.0% (33/64) 10.9% (7/64) 1.6% (1/64) 1.6% (1/64) 10.9% (7/64)
Note.—CAD ⫽ coronary artery disease; CVD ⫽ cerebral vascular disease; DVT ⫽ deep venous thrombosis; IVC ⫽ inferior vena cava; NSAID ⫽ nonsteriodal antiinflammatory drug.
the results of a prospective multicenter study with this device.
MATERIALS AND METHODS Study Endpoints The primary study objective was to evaluate the effectiveness of the filter in preventing major embolic complications in patients who have venous thromboembolic disease clinically judged to be at high risk of pulmonary embolism. The secondary objectives were to assess (i) the stability of the filter in the IVC (ie, incidence of migration ⬎2 cm) during the 6-month follow-up period; and (ii) the rate of caval (and/or filter) occlusion. Study Population Twelve centers in Europe and Canada enrolled a total of 65 patients who had venous thromboembolic disease, with a high risk of pulmonary embolism, into the study in a 12-month period from May 1998 to May 1999. Study approval was obtained by the local in-
stitutional review board of each participating center. All patients were required to give informed consent. The patient group (N ⫽ 65) consisted of 29 men and 36 women, with a mean age of 67.8 ⫾ 12.5 years (range, 37–96 years). Baseline demographics and clinical characteristics are listed in Table 1. Inclusion/Exclusion Criteria The study included patients with confirmed thromboembolic disease at high risk of PE and with had an absolute contraindication for anticoagulation, patients with recurrent thromboembolism despite adequate anticoagulation, and patients with proximal free-floating thrombus. Patients were also required to have a vena cava diameter of 18–30 mm, inclusive, and be 18 years of age or older. Indications for filter placement were DVT with recurrent thromboembolism and/or free-floating thrombus with contraindication to anticoagulation in 37 patients and complications in achieving adequate anticoagulation in 28.
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Exclusion criteria were pregnancy, lack of cooperation, uncontrolled infectious disease, life expectancy of less than 3 months, and current enrollment in another medical investigation. Adverse Events A major adverse event was defined as any adverse event occurring during treatment with use of the device, or within 14 days after cessation of study device treatment, that is life-threatening or results in death, permanent or substantial disability, or hospitalization or prolongation of hospitalization. This category includes death, myocardial infarction, need for revascularization, major bleeding, any severe or unexpected malfunction of the device, or any other event that the investigator or monitor judges to be severe or that would suggest a significant hazard, contraindication, side effect, or precaution. An adverse event that does not fall into the major adverse event category (as defined previously) was classified as a minor adverse event. Filter Design and Deployment The filter used was a double-basket, symmetric nitinol vena cava filter (TrapEase) made from a single nitinol tube. The filter has a nonexpanded maximum length of 65 mm and a length of 50 mm when expanded to its maximum diameter of 35 mm in vitro. The proximal and distal baskets, each composed of six petal-shaped openings, are connected by six straight struts (Fig. 1). A proximal and distal hook is located on each connecting strut for fixation of the filter to the vena cava wall. The filter is available in one size only for IVC diameters of 18 –30 mm. The filter is implanted through a 6-F, 55-cm-long straight introducer sheath with a radiopaque marker at the distal tip. A pusher serves to advance the filter through the sheath to the implantation site. Before implantation, the diameter of the IVC was assessed by cavography with quantitative measurement by means of contour marking of the angiographic catheter, to determine study inclusion eligibility (18 –30 mm). By means of a standard percutaneous procedure, the long 6-F (filter delivery) sheath was introduced under fluoroscopy via either the femoral or jug-
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Figure 1. Schematic top and side views of the Cordis percutaneous vena cava filter. The proximal and distal baskets, each composed of six petal-shaped openings, are connected by six straight struts. A proximal and distal hook is located on each connecting strut for fixation of the filter to the vena cava wall.
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cardiac anomalies; failing consciousness, or lack of consciousness). The follow-up examinations before hospital discharge or during the first 12 days of hospitalization included clinical and duplex US examination of the insertion site and duplex US of the IVC and lower legs. Follow-up at 1, 3, and 6 months included duplex US of the lower limbs and the IVC and abdominal radiography. Computed tomography (CT) of the filter was performed at 6 months only. Filter migration either caudal or cranial of more than one vertebra, as seen at abdominal radiography, or filter tilt of more than 15° from the axis of the IVC, was considered positive. The data were documented in a case report form, which was subsequently forwarded to a trial coordination center. All severe adverse events were assessed by an independent Clinical Events Committee composed of three physicians. Statistical Analysis Statistical analysis is descriptive only.
RESULTS Filter Implantation Procedure
Figure 2. Contrast vena cavogram and abdominal plain film. Via a percutaneous femoral approach, a long 6-F sheath was introduced under fluoroscopy over a 0.035-inch guide wire in the IVC. After controlling that the filter was in the correct position in the IVC, the sheath was retracted and the filter deployed just below the renal veins.
ular vein over a standard 0.035-inch guide wire to the intended implantation site in the IVC. After removing the guide wire, the filter was introduced into the sheath and advanced to the tip of the sheath by means of the pusher. After controlling that the filter was in the correct position in the IVC, the sheath was retracted and, in this way, the filter was deployed just below the renal veins. Control cavography was then performed to determine the final position of the filter in the IVC (Fig. 2).
Follow-up Before inclusion into the study, patients underwent duplex Doppler US of the lower limbs and IVC to determine the underlying disease state. Baseline ventilation-perfusion scanning and chest radiography were performed before or immediately after filter implantation. Subsequent lung scintigraphy and chest radiography were indicated only in the event of signs suggesting clinically symptomatic PE (dyspnea, with thoracic pain and positive blood gas measurements; hypotension;
Before commencing filter implantation, the mean diameter of the IVC was assessed to be 20.8 mm ⫾ 2.9 (range, 18 –30 mm). In four patients, thrombus was detected in the IVC. The puncture site for filter implantation was the right femoral vein in 42 patients, the left femoral vein in 13 patients, and the right jugular vein in nine patients (one not specified). No filters were introduced through the left jugular vein. The level of implantation in the IVC, using the lumbar vertebrae as reference, was L1–2 in four patients, L2–3 in 35 patients, L3– 4 in 22 patients, and L4 –5 in one patient (three not specified). In 60 of the 65 patients, the final filter position was at the intended, or preferred, site just below the renal veins. In three of the five patients, the filter was positioned either too caudal (15 mm) (n ⫽ 1) or too cephalic (10 mm) (n ⫽ 2) than intended and was reported to be due to the mechanism of release (specifically, filter shortening). These were there-
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Table 2 Clinical Postprocedural Outcomes (N ⴝ 65) Time Period* Measure
In-hospital†
30 Days
90 Days
6 Months
Clinical success 100% (64/64) 100% (51/51) 100% (46/46) 100% (39/39) (no acute symptoms of PE) Acute symptoms of PE 1.5% (1/64) 0% (0/51) 0% (0/46) 0% (0/39) with unchanged VQ scan Filter migration (⬎2 cm) 0% (0/60) 0% (0/40) 0% (0/39) 0% (0/37) Filter fracture 0% (0/60) 0% (0/40) 0% (0/38) 0% (0/37) Vessel wall perforation 0% (0/60) 0% (0/40) 0% (0/39) 0% (0/37) Filter thrombosis 1.8% (1/57) 5.1% (2/39) 0% (0/37) 2.9% (1/35) (by duplex US) Lower limb DVT 77.2% (44/57) 64.1% (25/39) 48.6% (18/37) 45.7% (16/35) (by duplex US) IVC thrombosis above filter 1.9% (1/53) 8.3% (3/36) 0% (0/37) 2.8% (1/35) IVC thrombosis below filter 5.3% (4/57) 7.7% (3/39) 0% (0/37) 0% (0/35) (by duplex US) Vessel wall perforation by NA NA NA 0% (0/33) CT scan at 6 months * Denominators for each measure reflect the number of patients who had data for that measure at each of the time points. † Includes from 24 hours follow-up to discharge or 10 days in-hospital stay.
fore regarded as technical failures. In the remaining two patients, the preferred site could not be realized due to the presence of thrombus. In one of the latter patients, the distal end of the filter was intentionally placed partially within the thrombus present in the IVC extending to just below the renal veins. There were no clinical sequelae associated with the filter implantation reported during the follow-up survival period of this patient. In the second patient, uneventful filter placement was above the thrombus. None of the latter five filter positions were regarded as compromising the patient or the procedure. Predischarge or In-Hospital Follow-up At 24-hour follow-up, there were no reports of filter-related symptomatic PE (0%) (Table 2). One patient was reported to have symptoms of PE, however, these were a continuation of the symptoms already present prior to filter placement. Control of the insertion site by means of duplex and clinical examination gave no reports of complications at the insertion site (no hematoma; no insertion site thrombosis). Duplex US scanning (performed on 57 patients) and/or clinical examination of the lower limbs revealed one case of thrombo-
phlebitis of the common and superficial femoral veins on the side of filter implantation. The relation of this event to the device was reported as “highly probable.” No action was taken. The event was without clinical sequelae and extended hospitalization was not required; the patient experienced a full recovery and no residual effects. No other complications pertaining to the filter procedure were reported. Of these 65 patients, 60 were examined, one was not seen because of death unrelated to the device, and four were not seen because of hospital logistics and treatment for the underlying disease. Three of the latter patients were examined at 30-day follow-up. One patient could not be examined because of complications related to the underlying disease (the patient subsequently died on day 17) and the fifth patient was undergoing treatment for breast cancer. There were no cases reported of filter-related symptomatic PE (0%). Abdominal radiography was performed during this period to primarily ascertain filter stability (migration) in the vena cava and, additionally, to detect any other filter anomalies, such as filter fracture and vessel wall perforation. There were no reported cases of filter migration or other filter-related complications. There was one case of symptomatic filter thrombosis during hospitalization,
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which was successfully treated with urokinase and heparin. Some thrombus was still detected at 1-month follow-up. In four nonsymptomatic patients, thrombus was detected below the filter, one of which extended to the iliac veins. The latter patient underwent anticoagulation therapy during the entire follow-up period. The thrombus was found to be completely resolved at 3-month follow-up (1-month follow-up examination was not performed because of the logistics of the prolonged hospitalization). These thromboses were not regarded as filter-related and were not reported as such. Three deaths occurred within a 10day period after placement of the filter (day 7, day 10, and day 10, respectively). The patients who died on day 10 had undergone the designated follow-up examinations. The deaths were not related to the device but were caused by complications related to their underlying disorders (small lung carcinoma, uterine cancer, and pneumonia superimposed on PE sustained before filter implantation, respectively). Six-Month Follow-up Data The clinical outcomes of the 1-, 3-, and 6-month follow-up are detailed in Table 2. During the follow-up period to 6 months, no cases (0%) of symptomatic PE, filter migration, or vessel wall perforation were reported. There were two cases of filter thrombosis detected by duplex US scan at 1 month. One of these patients (described previously) had a symptomatic thrombosis during the initial hospitalization. Duplex US examination at 1 month follow-up in the second patient, who had an extended hospitalization of several weeks after implantation, revealed an asymptomatic filter thrombosis. The patient was contraindicated for thrombolysis. At 3-month follow-up, the patient was undergoing anticoagulation therapy, and duplex US revealed an apparently spontaneous recanalization with some thrombus remaining; this thrombus was also detected at 6-month follow-up. There were no clinical sequelae and the patient remains asymptomatic. Thrombosis judged by the treating physician as non-device—related was detected by duplex US in the vena cava above the filter (but not in or below the filter) in three cases. None of the patients were symptomatic. Two of the patients were treated with anti-
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coagulants and, at 3-month follow-up, the thrombus was shown to have resolved. In the third patient, the thrombus persisted at 6-month follow-up but remained nonsymptomatic and no treatment was given. Premature Withdrawals One patient was prematurely withdrawn from the study at 1-month follow-up and regarded as lost to follow-up. Major Adverse Events Twenty-seven major adverse events were reported during the study period, of which 23 were deaths, one was a stroke, one was rehospitalization caused by the presence of a fistula between the bowel and bladder, and one was filter thrombosis that was judged to be major. All deaths were judged by the Clinical Events Committee not to be device-related but caused by the underlying disease process. The cases of stroke and rehospitalization (one case each) were also not device-related. Of the two filter thromboses previously described, only one case was judged to be device-related. The thrombosis was not treated and there were no clinical sequelae.
DISCUSSION Percutaneous filter placement to achieve partial mechanical interruption of the IVC is well established as a method of preventing life-threatening PE caused by lower extremity DVT (3). Filter implantation is most commonly performed in patients in whom anticoagulation is either contraindicated or ineffective (4). Conditions in which filter placement is generally regarded as effective include cancer, trauma, orthopedic surgery, neurosurgery, and DVT during pregnancy. Specifically, in patients with cancer, the incidence of PE varies from 6% to 35%, depending on the type of tumor (5). Anticoagulation therapy is associated with a high complication rate of recurrent PE and major bleeding; 8%–19% and 25–32%, respectively, (6,7). Patients undergoing orthopedic hip surgery have a reported risk for PE as high as 20% (8), and a fatal PE rate of 1%–3% (8 –10).
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The frequency of recurrent, symptomatic PE in patients with an IVC filter is reported to be between 2%– 6% (1), with fatal PE occurring in 0.8 –3.7% of cases (11,12). These data indicate the effectiveness of the filter in saving the patient from potentially life-threatening PE. In the current study, the incidence of recurrent, symptomatic PE was 0%. Symptoms of PE at early follow-up (⬍10 days) were reported to be related to the preimplantation status of the patient and did not signify a worsening of the pulmonary status because of possible recurrent PE. Follow-up to 6 months was intended for the entire cohort; however, in our study population of 65 patients, there were 23 deaths that were not related to the device or the implantation procedure but were related to the underlying disease process. These deaths could be explained by our inclusion criteria and, in general, because patients for whom permanent filter implantation is considered are often in poor health and have progressive life-threatening disease. Filter migration is a complication of concern because of the potentially fatal consequences. The risks include migration to a location or position where the device no longer protects against PE, or embolization of the filter into the heart or pulmonary artery. Filter migration occurs most often distally (ie, in the opposite direction of blood flow), with rates reported to be between 0 – 48.8% in the currently most frequently deployed filters (13). To detect distal or proximal filter migration, abdominal radiography must be performed. In this study, control abdominal radiography was performed at day 10 or earlier, and at 1, 3, and 6 months after implantation. There were no cases of migration (0%). Caval obstruction and/or filter thrombosis has been reported to occur with the currently most frequently deployed filters at rates of 3.5%–17.5% (13). Filter occlusion may result from successful clot trapping. An initial partial occlusion may develop into a total occlusion. Or, occlusion may be due to the presence of the device in the vena cava. In filter thrombosis, it is difficult to determine which of the latter two possibilities could have been responsible for the event. Although thrombosis due to successful clot trapping by the filter is an undesired event, it represents a
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trade-off situation between possible thrombosis and potentially fatal PE due to inadequate clot trapping. Two cases of filter thrombosis were reported in the current filter study, one of which was judged to be related to the filter. Caval or filter thrombosis is not always clinically manifested, as was the case with this latter patient. The presence of thrombus in the filter was only detected upon duplex US of the filter at 1-month follow-up. The patient was not symptomatic and no further treatment was undertaken; there were no clinical sequelae. At 90-day follow-up, the thrombus was found to have partly resolved, spontaneously, and flow was detected through the filter; the IVC was patent below and above the filter and the patient remained asymptomatic. Upon filter implantation, it is possible to malposition a filter. Malpositioning can include tilting of the filter, asymmetry or entwining of struts of the device, and improper anatomic placement. There are numerous publications on all these aspects. Tilting and the asymmetric positioning of the device can lead to decreased filter filtration or effectiveness because of the larger-than-intended spaces between the filter struts. This can increase the risk for larger-than-intended-size thrombi to pass through the filter and, inadvertently, into the lungs. Tilting has been observed in the Venatech filter (Braun Veratech, Evanston, IL) in as many as 16% of placements (14), while asymmetry or entwining of struts has been reported with the titanium Greenfield filter at an incidence of up to 71% (15). In this study, there were no reported cases (0%) of tilting or asymmetry. The design of the Cordis TrapEase filter would appear to be such that the chance of tilting and asymmetric placement are minimized because of the long side struts being directly connected to the proximal and distal baskets. This may reduce the possibility of individual side struts attaching to the vessel wall asymmetrically at filter release during placement. Improper placement of the filter has been reported to occur in the heart (16), renal vein (17,18), spermatic vein (18), iliac vein (19), lumbar vein (20), and suprarenal caval vein (20,21). In this study, all filters were implanted in the IVC. Of these, the final position of three TrapEase filters in the IVC was not at the intended site (just below the
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renal veins) due to the mechanism of filter release, but 15 mm caudally in one case and 10 mm cephalad in the other two cases. The filter locations of these three cases were judged to not compromise the patient or filter functioning, and to be clinically acceptable. The latter three implantations were performed at the beginning of the study and could be attributed to the early inexperience with use of the filter. The data on the exact amount of filter shortening during deployment related to the diameter of the vena cava were generated based on feedback of the first implantation events. Insertion site thrombosis is an important complication because it poses an additional risk for PE. When introduction is via the femoral route, the filter device protects against PE from insertion site thrombosis, whereas this protection is absent when the jugular route is chosen. The size of the introducer system is important in minimizing the risk for incidence of insertion site thrombosis. In the days after filter implantation, femoral insertion of the titanium Greenfield filter (14-F outer diameter introducer system) has been reported to give a high incidence of insertion site thrombosis, ranging between 19 – 41% (22,23); 28% for the Simon nitinol filter with a smaller introducer sheath (7-F) (24). The introducer sheath for the TrapEase permanent IVC filter is only 6 F, which is the smallest system of all vena cava filters currently available. Duplex US of the insertion site in this study revealed there to be no cases (0%) of insertion site hematoma. There was one case of thrombophlebitis reported at the site of implantation in the period between 24 hours and discharge. This event did not extend hospitalization and was without clinical sequelae. In addition, there were no other complications that are known to be associated with filter insertion and which could have occurred, such as air embolism, PE due to freed or dislodged thrombus as a result of catheter manipulation, and wound infection. Another advantage of the small size of the sheath is the possibility to introduce the filter by a brachial approach. Overall, the new TrapEase filter would appear to have several advantages over currently available filters. First, the TrapEase has the smallest introduction system of all permanent IVC
filters (6 F), thereby reducing the risk of insertion site complications. Its doublebasket, symmetric design, with long connecting side struts, appears to make for a low risk of tilting, a phenomenon often observed with umbrella filters, thereby reducing the risk of compromised clot trapping. In addition, the symmetry of the filter not only allows for introduction through both jugular and femoral routes with a single kit but also removes the risk of a filter being implanted incorrectly orientated, as could occur with asymmetric devices. In conclusion, based on the clinical experience described in this report, the new 6-F TrapEase filter appears to be a safe and effective device for use in the prevention of PE in patients who are at high risk of PE and who require partial caval interruption. References 1. Ferris EJ, McCowan TC, et al. Percutaneous inferior vena cava filters: follow-up of seven designs in 320 patients. Radiology 1993; 188:851– 865. 2. Neuerburg J, Günther RW. Developments in inferior vena cava filters: a European viewpoint. Semin Intervent Radiol 1994; 11:349 –357. 3. Goldfaber SZ, Grassi CJ. Management of pulmonary embolism. In: Sabeston DC, ed. Textbook of surgery, 8th ed. Philadelphia: WB Saunders, 1990; 115–127. 4. Decousus H, Leizorovicz A, Parent F, et al. A clinical trial of vena cava filters in the prevention of pulmonary embolism in patients with proven proximal deep vein thrombosis. N Engl J Med 1998; 338:409 – 415. 5. Van Beek EJR, Buller HR, ten Cate JW. Epidemiology of venous thromboembolism. In: The epidemiology and diagnosis of pulmonary embolism. 1994; 15–50. 6. Whitney BA, Kerstein MD. Thrombocytopenia and cancer: use of the KimrayGreenfield filter to prevent thromboembolism. South Med J 1987; 80:1246 –1248. 7. Cohen JR, Grella L, Citron M. Greenfield filter instead of heparin as primary treatment for deep venous thrombosis in patients with cancer. Cancer 1992; 70:1993–1996. 8. Consensus Conference. Prevention of venous thrombosis and pulmonary embolism. JAMA 1986; 256:744 –749. 9. Nicolaides AN, Arcelus J, Belcaro G, et al. Prevention of venous thromboembolism. European Consensus Statement, 1–5 November 1991, developed at Oakley Court Hotel, UK (editorial) (review). Int Angiol 1992; 11:151–159. 10. Paiement GD, Desautels C. Deep vein thrombosis: prophylaxis, diagno-
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sis, and treatment–lessons from orthopedic studies (review). Clin Cardiol 1990; 13:V119 –V122. Ballew KA, Philbrick JT, Becker DM. Vena cava filter devices. Clin Chest Med 1995; 16:295–305. Athanasoulis CA, Kaufman JA, Halpern EF, Waltman AC, Geller SC, Fan CM. Inferior vena caval filters: review of a 26-year single-center clinical experience. Radiology 2000; 216:54 – 66. Reekers JA, Harmsen H, Hoogeveen YL, Günther RW. Vena cava filter devices. In: Oudkerk M, Van Beek EJR, Ten Cate JW, eds. Diagnosis and treatment of pulmonary embolism. Malden, MA: Blackwell Science, 1999:330 –349. Ricco JB, Crochet DP, Sebilotte P, et al. Percutaneous transvenous caval interruption with the “LGM” filter: early results of a mutlicentre trial. Ann Vasc Surg 1988; 2:242–247. Sweeny TJ, Van Aman ME. Deployment problems with the titanium Greenfield filter (see comments). JVIR 1993; 4:691– 694. Roehm JOF, Johnsrude IS, Barth MH, Gianturco C. The Bird’s Nest inferior vena caval filter: progress report. Radiology 1988; 168:745–749. Grassi CJ. Inferior vena caval filters: analysis of five currently available devices (review). AJR Am J Roentgenol 1991; 156:813– 821. Jaeger HR, Jackson JE, Allison DJ. Delayed pulmonary embolism after therapeutic vascular embolization of an arteriovenous malformation: treatment with a venous filter. J Intervent Radiol 1993; 7:153–156. Cimochowski GE, Evans RH, Zarins CK, et al. Greenfield filter versus Mobin-Ubbin umbrella: the continuing quest for the ideal method of vena caval interruption. J Thorac Cardiovasc Surg 1980; 79:358 –365. Greenfield LJ, Cho K, Proctor M, et al. Results of a muticentre study of the modified hook-titanium Greenfield filter. J Vasc Surg 1991; 14:253–257. Brenner DW, Brenner CJ, Scott J, et al. Suprarenal Greenfield filter placement to prevent pulmonary embolus in patients with vena caval thrombi. J Urol 1992; 147:19 –23. Mewissen MW, Erickson SJ, Foley WD, et al. Thrombosis at venous insertion sites after inferior vena caval filter placement. Radiology 173:155–157. Kantor A, Glanz S, Gordon DH, Sclafani SJ. Percutaneous insertion of the Kimray-Greenfield filter: incidence of femoral vein thrombosis. AJR Am J Roentgenol 1987; 149:1065–1066. Simon M, Athanasoulis CA, Kim D, et al. Simon nitinol inferior vena cava filter: initial clinical experience–work in progress. Radiology 1989; 172:99 –103.
The 6-F Nitinol TrapEase Inferior Vena Cava Filter: Results of a Prospective Multicenter Trial Hervé Rousseau, MD, Pierre Perreault, MD, Phillippe Otal, MD, Luc Stockx, MD, Jafar Golzarian, MD, Vincent Oliva, MD, Phillippe Reynaud, MD, Frank Raat, MD, Ferenc Szatmari, MD, Gennaro Santoro, MD, G. Emanuelli, MD, Michel Nonent, MD, and Yvonne Hoogeveen, PhD1
PURPOSE: The authors report the first results of a new 6-F symmetrically designed permanent nitinol inferior vena cava (IVC) filter, the Cordis TrapEase, evaluated in a multicenter prospective study with 6-months of follow-up. MATERIALS AND METHODS: A total of 65 patients (29 men, 36 women) who ranged in age from 37 to 96 years (mean age, 68 years) and who were at high risk of pulmonary embolism (PE) were enrolled in 12 centers in Europe and Canada. The study was approved by the institutional review boards at all centers. Study objectives were to evaluate filter effectiveness, filter stability, and caval occlusion. Indications for filter placement were deep vein thrombosis with recurrent thromboembolism and/or free-floating thrombus with contraindication to anticoagulation in 37 patients, and complications in achieving adequate anticoagulation in 28 patients. Follow-up included clinical examination, plain film, Doppler ultrasound, CT scan, and nuclear medicine. RESULTS: The analysis of the data revealed a technical success of 95.4% (three filter-system related implantations not at the intended site, no events of filter tilting) and a clinical success of 100% at 6 months (no cases of symptomatic PE), the study primary endpoint. There were no cases (0%) of filter migration, insertion site thrombosis, filter fracture, or vessel wall perforation. During the study period, there were two cases of filter thrombosis: one case of early symptomatic thrombosis that was successfully treated in the hospital, and one case of nonsymptomatic filter thrombosis detected at 1-month follow-up, with spontaneous recanalization at 3 months. In the latter patient, some residual thrombus was still detected at 6 months. Of the study population of 65 patients, there were 23 deaths. These deaths were not related to the device or the implantation procedure but to the underlying disease process. CONCLUSION: This study demonstrates the new nitinol permanent IVC filter to be a safe and an effective device, with a low overall complication rate, for use in patients with thromboembolic disease at high risk of PE. Index terms:
Embolism, pulmonary
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J Vasc Interv Radiol 2001; 12:299 –304 Abbreviations: IVC ⫽ inferior vena cava, PE ⫽ pulmonary embolism
THE implantation in the inferior vena cava (IVC) of a permanent vena cava filter can be regarded as a therapy modality for the prevention of pulmonary
embolism (PE) in the management of venous thromboembolic disease. Since the inception, in 1967, of the first IVC filter (1), a wide range of filters with
From the Radiology Department (H.R., P.O.), CHU Rangueil, Toulouse, Hoˆpital De La Cavale Blanche (M.N.), CHU Brest, Pneumonologue Agre´e´ (P.R.), Hoˆpital Laennec, Paris, France; CHUM Hospital Group (P.P.), St. Luc Campus, Hospital Notre Dame (V.O.), Montreal, Quebec, Canada; Department of Radiology (L.S.), University Hospital Leuven, Hopital Erasme KLB de Bruxelles (J.G.), Brussels, Department of Radiology (F.R.), A.Z. St. Lucas, Gent, Cordis Europa (Y.H.), Roden, The Netherlands; Department of Radiology (F.S.), Petz Aladar County Hospital, Gye´r, Hungary; Department of Cardiology
(G.S.), Clinica S. Luca, Firenze, and 2nd Department of Vascular Surgery (G.E.), Ospedale San Gerardo di Monza, Monza, Italy. Received June 1, 2000; revision requested July 18; final revision received and accepted November 20. Address correspondence to H.R., Service de Radiologie, CHU Rangueil, 01 Av J Poulhes, F-31054 Toulouse Cedex, France; E-mail: [email protected] 1 This author has disclosed the existence of a potential conflict of interest. © SCVIR, 2001
varying configurations have been developed, approved, and subsequently improved in line with increased clinical application and attained knowledge. In the published literature, the major drawbacks of currently available filters are reported to include (i) recurrent symptomatic PE, (ii) caval obstruction, (iii) filter migration, and (iv) local insertion site complications (1,2). A new nitinol permanent IVC filter (TrapEase; Cordis Europa, Roden, The Netherlands) was designed with a low profile (6-F) and characteristics intended to ensure protection of PE, with a theoretically low risk of filterassociated complications. We report
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Table 1 Baseline Patient Demographics and Clinical Characteristics Patient Characteristics
No.
Age (y) Mean ⫾ SD Range (min, max) Sex (M/F) History CAD CVD Risk factors Protein C Protein S Cancer Resistance to protein C activation Location of DVT Lower legs IVC/iliac and lower legs Free-floating thrombus with DVT IVC/iliac Lower legs Associated treatment before filter placement Anticoagulation Initial course of heparin followed by oral anticoagulants Antiaggregates Antimitotics NSAID Antibiotics
67.8 ⫾ 12.5 37–96 29/36 18.7% (12/64) 14.1% (9/64) 1.6% (1/63) 1.6% (1/63) 39.7% (25/63) 1.6% (1/63) 90.3% (56/62) 9.7% (6/62) 33.8% (21/62) 9.5% (2/21) 90.5% (19/21) 52.0% (33/64) 10.9% (7/64) 1.6% (1/64) 1.6% (1/64) 10.9% (7/64)
Note.—CAD ⫽ coronary artery disease; CVD ⫽ cerebral vascular disease; DVT ⫽ deep venous thrombosis; IVC ⫽ inferior vena cava; NSAID ⫽ nonsteriodal antiinflammatory drug.
the results of a prospective multicenter study with this device.
MATERIALS AND METHODS Study Endpoints The primary study objective was to evaluate the effectiveness of the filter in preventing major embolic complications in patients who have venous thromboembolic disease clinically judged to be at high risk of pulmonary embolism. The secondary objectives were to assess (i) the stability of the filter in the IVC (ie, incidence of migration ⬎2 cm) during the 6-month follow-up period; and (ii) the rate of caval (and/or filter) occlusion. Study Population Twelve centers in Europe and Canada enrolled a total of 65 patients who had venous thromboembolic disease, with a high risk of pulmonary embolism, into the study in a 12-month period from May 1998 to May 1999. Study approval was obtained by the local in-
stitutional review board of each participating center. All patients were required to give informed consent. The patient group (N ⫽ 65) consisted of 29 men and 36 women, with a mean age of 67.8 ⫾ 12.5 years (range, 37–96 years). Baseline demographics and clinical characteristics are listed in Table 1. Inclusion/Exclusion Criteria The study included patients with confirmed thromboembolic disease at high risk of PE and with had an absolute contraindication for anticoagulation, patients with recurrent thromboembolism despite adequate anticoagulation, and patients with proximal free-floating thrombus. Patients were also required to have a vena cava diameter of 18–30 mm, inclusive, and be 18 years of age or older. Indications for filter placement were DVT with recurrent thromboembolism and/or free-floating thrombus with contraindication to anticoagulation in 37 patients and complications in achieving adequate anticoagulation in 28.
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Exclusion criteria were pregnancy, lack of cooperation, uncontrolled infectious disease, life expectancy of less than 3 months, and current enrollment in another medical investigation. Adverse Events A major adverse event was defined as any adverse event occurring during treatment with use of the device, or within 14 days after cessation of study device treatment, that is life-threatening or results in death, permanent or substantial disability, or hospitalization or prolongation of hospitalization. This category includes death, myocardial infarction, need for revascularization, major bleeding, any severe or unexpected malfunction of the device, or any other event that the investigator or monitor judges to be severe or that would suggest a significant hazard, contraindication, side effect, or precaution. An adverse event that does not fall into the major adverse event category (as defined previously) was classified as a minor adverse event. Filter Design and Deployment The filter used was a double-basket, symmetric nitinol vena cava filter (TrapEase) made from a single nitinol tube. The filter has a nonexpanded maximum length of 65 mm and a length of 50 mm when expanded to its maximum diameter of 35 mm in vitro. The proximal and distal baskets, each composed of six petal-shaped openings, are connected by six straight struts (Fig. 1). A proximal and distal hook is located on each connecting strut for fixation of the filter to the vena cava wall. The filter is available in one size only for IVC diameters of 18 –30 mm. The filter is implanted through a 6-F, 55-cm-long straight introducer sheath with a radiopaque marker at the distal tip. A pusher serves to advance the filter through the sheath to the implantation site. Before implantation, the diameter of the IVC was assessed by cavography with quantitative measurement by means of contour marking of the angiographic catheter, to determine study inclusion eligibility (18 –30 mm). By means of a standard percutaneous procedure, the long 6-F (filter delivery) sheath was introduced under fluoroscopy via either the femoral or jug-
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Figure 1. Schematic top and side views of the Cordis percutaneous vena cava filter. The proximal and distal baskets, each composed of six petal-shaped openings, are connected by six straight struts. A proximal and distal hook is located on each connecting strut for fixation of the filter to the vena cava wall.
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cardiac anomalies; failing consciousness, or lack of consciousness). The follow-up examinations before hospital discharge or during the first 12 days of hospitalization included clinical and duplex US examination of the insertion site and duplex US of the IVC and lower legs. Follow-up at 1, 3, and 6 months included duplex US of the lower limbs and the IVC and abdominal radiography. Computed tomography (CT) of the filter was performed at 6 months only. Filter migration either caudal or cranial of more than one vertebra, as seen at abdominal radiography, or filter tilt of more than 15° from the axis of the IVC, was considered positive. The data were documented in a case report form, which was subsequently forwarded to a trial coordination center. All severe adverse events were assessed by an independent Clinical Events Committee composed of three physicians. Statistical Analysis Statistical analysis is descriptive only.
RESULTS Filter Implantation Procedure
Figure 2. Contrast vena cavogram and abdominal plain film. Via a percutaneous femoral approach, a long 6-F sheath was introduced under fluoroscopy over a 0.035-inch guide wire in the IVC. After controlling that the filter was in the correct position in the IVC, the sheath was retracted and the filter deployed just below the renal veins.
ular vein over a standard 0.035-inch guide wire to the intended implantation site in the IVC. After removing the guide wire, the filter was introduced into the sheath and advanced to the tip of the sheath by means of the pusher. After controlling that the filter was in the correct position in the IVC, the sheath was retracted and, in this way, the filter was deployed just below the renal veins. Control cavography was then performed to determine the final position of the filter in the IVC (Fig. 2).
Follow-up Before inclusion into the study, patients underwent duplex Doppler US of the lower limbs and IVC to determine the underlying disease state. Baseline ventilation-perfusion scanning and chest radiography were performed before or immediately after filter implantation. Subsequent lung scintigraphy and chest radiography were indicated only in the event of signs suggesting clinically symptomatic PE (dyspnea, with thoracic pain and positive blood gas measurements; hypotension;
Before commencing filter implantation, the mean diameter of the IVC was assessed to be 20.8 mm ⫾ 2.9 (range, 18 –30 mm). In four patients, thrombus was detected in the IVC. The puncture site for filter implantation was the right femoral vein in 42 patients, the left femoral vein in 13 patients, and the right jugular vein in nine patients (one not specified). No filters were introduced through the left jugular vein. The level of implantation in the IVC, using the lumbar vertebrae as reference, was L1–2 in four patients, L2–3 in 35 patients, L3– 4 in 22 patients, and L4 –5 in one patient (three not specified). In 60 of the 65 patients, the final filter position was at the intended, or preferred, site just below the renal veins. In three of the five patients, the filter was positioned either too caudal (15 mm) (n ⫽ 1) or too cephalic (10 mm) (n ⫽ 2) than intended and was reported to be due to the mechanism of release (specifically, filter shortening). These were there-
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Table 2 Clinical Postprocedural Outcomes (N ⴝ 65) Time Period* Measure
In-hospital†
30 Days
90 Days
6 Months
Clinical success 100% (64/64) 100% (51/51) 100% (46/46) 100% (39/39) (no acute symptoms of PE) Acute symptoms of PE 1.5% (1/64) 0% (0/51) 0% (0/46) 0% (0/39) with unchanged VQ scan Filter migration (⬎2 cm) 0% (0/60) 0% (0/40) 0% (0/39) 0% (0/37) Filter fracture 0% (0/60) 0% (0/40) 0% (0/38) 0% (0/37) Vessel wall perforation 0% (0/60) 0% (0/40) 0% (0/39) 0% (0/37) Filter thrombosis 1.8% (1/57) 5.1% (2/39) 0% (0/37) 2.9% (1/35) (by duplex US) Lower limb DVT 77.2% (44/57) 64.1% (25/39) 48.6% (18/37) 45.7% (16/35) (by duplex US) IVC thrombosis above filter 1.9% (1/53) 8.3% (3/36) 0% (0/37) 2.8% (1/35) IVC thrombosis below filter 5.3% (4/57) 7.7% (3/39) 0% (0/37) 0% (0/35) (by duplex US) Vessel wall perforation by NA NA NA 0% (0/33) CT scan at 6 months * Denominators for each measure reflect the number of patients who had data for that measure at each of the time points. † Includes from 24 hours follow-up to discharge or 10 days in-hospital stay.
fore regarded as technical failures. In the remaining two patients, the preferred site could not be realized due to the presence of thrombus. In one of the latter patients, the distal end of the filter was intentionally placed partially within the thrombus present in the IVC extending to just below the renal veins. There were no clinical sequelae associated with the filter implantation reported during the follow-up survival period of this patient. In the second patient, uneventful filter placement was above the thrombus. None of the latter five filter positions were regarded as compromising the patient or the procedure. Predischarge or In-Hospital Follow-up At 24-hour follow-up, there were no reports of filter-related symptomatic PE (0%) (Table 2). One patient was reported to have symptoms of PE, however, these were a continuation of the symptoms already present prior to filter placement. Control of the insertion site by means of duplex and clinical examination gave no reports of complications at the insertion site (no hematoma; no insertion site thrombosis). Duplex US scanning (performed on 57 patients) and/or clinical examination of the lower limbs revealed one case of thrombo-
phlebitis of the common and superficial femoral veins on the side of filter implantation. The relation of this event to the device was reported as “highly probable.” No action was taken. The event was without clinical sequelae and extended hospitalization was not required; the patient experienced a full recovery and no residual effects. No other complications pertaining to the filter procedure were reported. Of these 65 patients, 60 were examined, one was not seen because of death unrelated to the device, and four were not seen because of hospital logistics and treatment for the underlying disease. Three of the latter patients were examined at 30-day follow-up. One patient could not be examined because of complications related to the underlying disease (the patient subsequently died on day 17) and the fifth patient was undergoing treatment for breast cancer. There were no cases reported of filter-related symptomatic PE (0%). Abdominal radiography was performed during this period to primarily ascertain filter stability (migration) in the vena cava and, additionally, to detect any other filter anomalies, such as filter fracture and vessel wall perforation. There were no reported cases of filter migration or other filter-related complications. There was one case of symptomatic filter thrombosis during hospitalization,
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which was successfully treated with urokinase and heparin. Some thrombus was still detected at 1-month follow-up. In four nonsymptomatic patients, thrombus was detected below the filter, one of which extended to the iliac veins. The latter patient underwent anticoagulation therapy during the entire follow-up period. The thrombus was found to be completely resolved at 3-month follow-up (1-month follow-up examination was not performed because of the logistics of the prolonged hospitalization). These thromboses were not regarded as filter-related and were not reported as such. Three deaths occurred within a 10day period after placement of the filter (day 7, day 10, and day 10, respectively). The patients who died on day 10 had undergone the designated follow-up examinations. The deaths were not related to the device but were caused by complications related to their underlying disorders (small lung carcinoma, uterine cancer, and pneumonia superimposed on PE sustained before filter implantation, respectively). Six-Month Follow-up Data The clinical outcomes of the 1-, 3-, and 6-month follow-up are detailed in Table 2. During the follow-up period to 6 months, no cases (0%) of symptomatic PE, filter migration, or vessel wall perforation were reported. There were two cases of filter thrombosis detected by duplex US scan at 1 month. One of these patients (described previously) had a symptomatic thrombosis during the initial hospitalization. Duplex US examination at 1 month follow-up in the second patient, who had an extended hospitalization of several weeks after implantation, revealed an asymptomatic filter thrombosis. The patient was contraindicated for thrombolysis. At 3-month follow-up, the patient was undergoing anticoagulation therapy, and duplex US revealed an apparently spontaneous recanalization with some thrombus remaining; this thrombus was also detected at 6-month follow-up. There were no clinical sequelae and the patient remains asymptomatic. Thrombosis judged by the treating physician as non-device—related was detected by duplex US in the vena cava above the filter (but not in or below the filter) in three cases. None of the patients were symptomatic. Two of the patients were treated with anti-
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coagulants and, at 3-month follow-up, the thrombus was shown to have resolved. In the third patient, the thrombus persisted at 6-month follow-up but remained nonsymptomatic and no treatment was given. Premature Withdrawals One patient was prematurely withdrawn from the study at 1-month follow-up and regarded as lost to follow-up. Major Adverse Events Twenty-seven major adverse events were reported during the study period, of which 23 were deaths, one was a stroke, one was rehospitalization caused by the presence of a fistula between the bowel and bladder, and one was filter thrombosis that was judged to be major. All deaths were judged by the Clinical Events Committee not to be device-related but caused by the underlying disease process. The cases of stroke and rehospitalization (one case each) were also not device-related. Of the two filter thromboses previously described, only one case was judged to be device-related. The thrombosis was not treated and there were no clinical sequelae.
DISCUSSION Percutaneous filter placement to achieve partial mechanical interruption of the IVC is well established as a method of preventing life-threatening PE caused by lower extremity DVT (3). Filter implantation is most commonly performed in patients in whom anticoagulation is either contraindicated or ineffective (4). Conditions in which filter placement is generally regarded as effective include cancer, trauma, orthopedic surgery, neurosurgery, and DVT during pregnancy. Specifically, in patients with cancer, the incidence of PE varies from 6% to 35%, depending on the type of tumor (5). Anticoagulation therapy is associated with a high complication rate of recurrent PE and major bleeding; 8%–19% and 25–32%, respectively, (6,7). Patients undergoing orthopedic hip surgery have a reported risk for PE as high as 20% (8), and a fatal PE rate of 1%–3% (8 –10).
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The frequency of recurrent, symptomatic PE in patients with an IVC filter is reported to be between 2%– 6% (1), with fatal PE occurring in 0.8 –3.7% of cases (11,12). These data indicate the effectiveness of the filter in saving the patient from potentially life-threatening PE. In the current study, the incidence of recurrent, symptomatic PE was 0%. Symptoms of PE at early follow-up (⬍10 days) were reported to be related to the preimplantation status of the patient and did not signify a worsening of the pulmonary status because of possible recurrent PE. Follow-up to 6 months was intended for the entire cohort; however, in our study population of 65 patients, there were 23 deaths that were not related to the device or the implantation procedure but were related to the underlying disease process. These deaths could be explained by our inclusion criteria and, in general, because patients for whom permanent filter implantation is considered are often in poor health and have progressive life-threatening disease. Filter migration is a complication of concern because of the potentially fatal consequences. The risks include migration to a location or position where the device no longer protects against PE, or embolization of the filter into the heart or pulmonary artery. Filter migration occurs most often distally (ie, in the opposite direction of blood flow), with rates reported to be between 0 – 48.8% in the currently most frequently deployed filters (13). To detect distal or proximal filter migration, abdominal radiography must be performed. In this study, control abdominal radiography was performed at day 10 or earlier, and at 1, 3, and 6 months after implantation. There were no cases of migration (0%). Caval obstruction and/or filter thrombosis has been reported to occur with the currently most frequently deployed filters at rates of 3.5%–17.5% (13). Filter occlusion may result from successful clot trapping. An initial partial occlusion may develop into a total occlusion. Or, occlusion may be due to the presence of the device in the vena cava. In filter thrombosis, it is difficult to determine which of the latter two possibilities could have been responsible for the event. Although thrombosis due to successful clot trapping by the filter is an undesired event, it represents a
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trade-off situation between possible thrombosis and potentially fatal PE due to inadequate clot trapping. Two cases of filter thrombosis were reported in the current filter study, one of which was judged to be related to the filter. Caval or filter thrombosis is not always clinically manifested, as was the case with this latter patient. The presence of thrombus in the filter was only detected upon duplex US of the filter at 1-month follow-up. The patient was not symptomatic and no further treatment was undertaken; there were no clinical sequelae. At 90-day follow-up, the thrombus was found to have partly resolved, spontaneously, and flow was detected through the filter; the IVC was patent below and above the filter and the patient remained asymptomatic. Upon filter implantation, it is possible to malposition a filter. Malpositioning can include tilting of the filter, asymmetry or entwining of struts of the device, and improper anatomic placement. There are numerous publications on all these aspects. Tilting and the asymmetric positioning of the device can lead to decreased filter filtration or effectiveness because of the larger-than-intended spaces between the filter struts. This can increase the risk for larger-than-intended-size thrombi to pass through the filter and, inadvertently, into the lungs. Tilting has been observed in the Venatech filter (Braun Veratech, Evanston, IL) in as many as 16% of placements (14), while asymmetry or entwining of struts has been reported with the titanium Greenfield filter at an incidence of up to 71% (15). In this study, there were no reported cases (0%) of tilting or asymmetry. The design of the Cordis TrapEase filter would appear to be such that the chance of tilting and asymmetric placement are minimized because of the long side struts being directly connected to the proximal and distal baskets. This may reduce the possibility of individual side struts attaching to the vessel wall asymmetrically at filter release during placement. Improper placement of the filter has been reported to occur in the heart (16), renal vein (17,18), spermatic vein (18), iliac vein (19), lumbar vein (20), and suprarenal caval vein (20,21). In this study, all filters were implanted in the IVC. Of these, the final position of three TrapEase filters in the IVC was not at the intended site (just below the
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renal veins) due to the mechanism of filter release, but 15 mm caudally in one case and 10 mm cephalad in the other two cases. The filter locations of these three cases were judged to not compromise the patient or filter functioning, and to be clinically acceptable. The latter three implantations were performed at the beginning of the study and could be attributed to the early inexperience with use of the filter. The data on the exact amount of filter shortening during deployment related to the diameter of the vena cava were generated based on feedback of the first implantation events. Insertion site thrombosis is an important complication because it poses an additional risk for PE. When introduction is via the femoral route, the filter device protects against PE from insertion site thrombosis, whereas this protection is absent when the jugular route is chosen. The size of the introducer system is important in minimizing the risk for incidence of insertion site thrombosis. In the days after filter implantation, femoral insertion of the titanium Greenfield filter (14-F outer diameter introducer system) has been reported to give a high incidence of insertion site thrombosis, ranging between 19 – 41% (22,23); 28% for the Simon nitinol filter with a smaller introducer sheath (7-F) (24). The introducer sheath for the TrapEase permanent IVC filter is only 6 F, which is the smallest system of all vena cava filters currently available. Duplex US of the insertion site in this study revealed there to be no cases (0%) of insertion site hematoma. There was one case of thrombophlebitis reported at the site of implantation in the period between 24 hours and discharge. This event did not extend hospitalization and was without clinical sequelae. In addition, there were no other complications that are known to be associated with filter insertion and which could have occurred, such as air embolism, PE due to freed or dislodged thrombus as a result of catheter manipulation, and wound infection. Another advantage of the small size of the sheath is the possibility to introduce the filter by a brachial approach. Overall, the new TrapEase filter would appear to have several advantages over currently available filters. First, the TrapEase has the smallest introduction system of all permanent IVC
filters (6 F), thereby reducing the risk of insertion site complications. Its doublebasket, symmetric design, with long connecting side struts, appears to make for a low risk of tilting, a phenomenon often observed with umbrella filters, thereby reducing the risk of compromised clot trapping. In addition, the symmetry of the filter not only allows for introduction through both jugular and femoral routes with a single kit but also removes the risk of a filter being implanted incorrectly orientated, as could occur with asymmetric devices. In conclusion, based on the clinical experience described in this report, the new 6-F TrapEase filter appears to be a safe and effective device for use in the prevention of PE in patients who are at high risk of PE and who require partial caval interruption. References 1. Ferris EJ, McCowan TC, et al. Percutaneous inferior vena cava filters: follow-up of seven designs in 320 patients. Radiology 1993; 188:851– 865. 2. Neuerburg J, Günther RW. Developments in inferior vena cava filters: a European viewpoint. Semin Intervent Radiol 1994; 11:349 –357. 3. Goldfaber SZ, Grassi CJ. Management of pulmonary embolism. In: Sabeston DC, ed. Textbook of surgery, 8th ed. Philadelphia: WB Saunders, 1990; 115–127. 4. Decousus H, Leizorovicz A, Parent F, et al. A clinical trial of vena cava filters in the prevention of pulmonary embolism in patients with proven proximal deep vein thrombosis. N Engl J Med 1998; 338:409 – 415. 5. Van Beek EJR, Buller HR, ten Cate JW. Epidemiology of venous thromboembolism. In: The epidemiology and diagnosis of pulmonary embolism. 1994; 15–50. 6. Whitney BA, Kerstein MD. Thrombocytopenia and cancer: use of the KimrayGreenfield filter to prevent thromboembolism. South Med J 1987; 80:1246 –1248. 7. Cohen JR, Grella L, Citron M. Greenfield filter instead of heparin as primary treatment for deep venous thrombosis in patients with cancer. Cancer 1992; 70:1993–1996. 8. Consensus Conference. Prevention of venous thrombosis and pulmonary embolism. JAMA 1986; 256:744 –749. 9. Nicolaides AN, Arcelus J, Belcaro G, et al. Prevention of venous thromboembolism. European Consensus Statement, 1–5 November 1991, developed at Oakley Court Hotel, UK (editorial) (review). Int Angiol 1992; 11:151–159. 10. Paiement GD, Desautels C. Deep vein thrombosis: prophylaxis, diagno-
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