Experimental comparison of percutaneous vena caval devices: titanium Greenfield filter versus bird's nest filter

Detection of iatrogenic cardiac tamponade by transesophageal echocardiography during vena cava filter procedure

PURPOSE

To present a patient who developed cardiac tamponade during insertion of an inferior vena cava (IVC) filter. Intraoperative transesophageal echocardiography (TEE) was used as a means to diagnose the cardiac tamponade and to facilitate guiding of pericardiocentesis.

CLINICAL FEATURES

A 45-yr-old man with protein S deficiency complicated by repeated attacks of deep vein thrombosis and pulmonary thromboembolism was scheduled for insertion of an IVC filter. He had history of chronic renal insufficiency, heart failure, and cerebral infarction with mild left hemiparesis. Current medication included diltiazem (30 mg, I tab tid ), prednisolone (5 mg, 2 tabs qd ), and warfarin (2.5 mg daily). Preoperative transthoracic echocardiography demonstrated bilateral pleural effusions, moderate mitral regurgitation and tricuspid regurgitation, left atrial appendage thrombus and severe generalized hypokinesia of left ventricle. Nuclear medicine examination by (99)Tc showed ejection fractions of left ventricle and right ventricle as 20% and 22%, respectively. Under the impression of protein S deficiency with multiple attacks of thromboembolism and failure of anticoagulant therapy, he was arranged for the procedure of vena caval filter insertion. Unfortunately, iatrogenic cardiac tamponade occurred during the course of the procedure with rapid hemodynamic deterioration. Because of the expedient of routine monitoring of cardiac condition with TEE, a prompt diagnosis was made. We successfully improved the patient's hemodynamic status after transthoracic echo-guided pericardiocentesis.

CONCLUSION

Intraoperative TEE is recommended to be used routinely in patients undergoing vena cava filter procedures. The availability of echocardiographic monitoring in the operation room allows the confirmation of the diagnosis and facilitation pericardiocentesis.

In vitro model for the evaluation of inferior vena cava filters: effect of experimental parameters on thrombus-capturing efficacy of the Vena Tech-LGM filter

PURPOSE

To determine the experimental parameters in an in vitro model that influence the thrombus-capturing efficacy of the Vena Tech-LGM filter.

MATERIALS AND METHODS

The Vena Tech-LGM filter was evaluated in an in vitro model of the vena cava with a computer-controlled flow system with a total of 5,200 thrombi. The influences of the following experimental parameters on the capture rate were analyzed with a multiple logistic regression model: type of testing (single, double, and multiple shot testing), thrombus diameter and length, IVC diameter and orientation, flow quality and quantity, flow velocity, and the length of the prepositioned thrombus.

RESULTS

A significant influence on the capture rate could be demonstrated for the type of testing, the thrombus diameter and length, the IVC diameter, and with double shot testing for the length of the prepositioned thrombus and the IVC orientation. The flow quality and the peak velocity were not significant. Based on these results, a protocol for in vitro testing of IVC filters was designed.

CONCLUSIONS

Experimental parameters influence the thrombus-capturing efficacy of the Vena Tech-LGM filter and should be taken into account when in vitro testing is performed.

A physiologic in vitro model of the inferior vena cava with a computer-controlled flow system for testing of inferior vena cava filters

RATIONALE AND OBJECTIVES

The authors develop a physiologic in vitro model of the inferior vena cava (IVC) for testing of filters.

METHODS

The model is driven by a centrifugal pump. A computer-controlled electromagnetic valve is used for generation of different flow patterns. Limitation of the pressure increase in case of IVC occlusion is achieved by a bypass circuit. A glycerin solution is used for perfusion. Artificial clots are made from polyacrylamide gel. Data acquisition includes continuous monitoring of flow and difference pressure over the filter and video recording of the testing events.

RESULTS

The model can generate constant and pulsatile flows. The pressure increase can be limited to 70 mm Hg in case of occlusion. Calculation of the flow velocities in the IVC is possible. A classification of thrombus capturing is presented. The testing of most of the results are reproducible.

CONCLUSIONS

The in vitro model simulates the physiologic conditions in the IVC. It can be used for comparative testing of different filters and the evaluation of new filter designs.

In vitro assessment of the hemodynamic effects of a partial occlusion in a vena cava filter

PURPOSE

Flow fields surrounding a vena cava filter were studied with a noninvasive method of flow visualization to examine the underlying hemodynamic factors that contribute to its function and patency.

METHODS

The photochromic technique was used to measure axial velocity profiles and wall shear stress distributions in a 12F titanium Greenfield filter partially occluded with a simulated volume of entrapped thrombi. These results were compared with similar measurements obtained for an unoccluded filter and with a theoretic prediction of the velocity profile and wall shear stress without a vena cava filter. Shear stress distributions were obtained along the vessel wall and for the partially occluded filter along the surface of the simulated clot.

RESULTS

The unoccluded filter was observed to have little effect on the flow field. In the case of the partially occluded filter, the results of these measurements show that caval blood flow is preserved by the creation of an annular region of increased flow around the periphery of the clot. Within this region high shear stresses that develop as a result of the increased flow are observed along the vessel wall and along the surface of the simulated clot. No vortices or turbulence were observed with either the unoccluded or the partially occluded filter.

CONCLUSIONS

The elevated levels of shear stress may be a factor in the lysis of trapped clots observed in vivo. Although increased shear stress is reported to cause thrombogenesis in an in vivo study in canines, particularly under turbulent flow conditions, the levels of shear measured in this study around the simulated clot were well below such values.

Clinical follow-up of patients with percutaneously inserted inferior vena caval filters

This is a retrospective clinical follow-up study of 45 consecutive patients who had percutaneous placement of inferior venal caval (IVC) filters in the period 1987 to 1993 to prevent mortality, or severe morbidity, from pulmonary embolism (PE). Ten patients had Gunther filters (GF) and 35 had bird's nest filters (BNF) from 1989. Clinical indications for filter placement were: 23 patients with anticoagulation contraindications, six with anticoagulation failure and recurrent PE, 10 with anticoagulation complications, two with critical PE and four with leg thrombi and PE. Two patients died from recurrent PE after filter placement, one with a GF migrating after replacement, and one with a BNF. Two patients died from severe PE, occurring prior to filter placement. Fifteen patients died in the study period, none due to recurrent PE. Twenty-five patients remain alive, with a mean follow-up period of 21 months, with none having recurring PE. One patient was lost to clinical follow-up. One patient suffered technical difficulty in BNF placement, and underwent surgical removal of a hook penetrating an iliac vein wall. Inferior vena cava filters are efficacious in preventing potentially fatal pulmonary embolism, in both the acute period and the medium term. There are low rates of morbidity associated with their use.

Comparative efficacy and complications of vena caval filters

PURPOSE

A variety of vena caval filters (VCFs) are available for usage. The choice of filter type depends on physician preference and certain patient variables. An evaluation of the different VCFs used in our institution was done to compare their efficacy and complication rates.

METHODS

The medical records of all patients who underwent insertion of a VCF from January 1987 to June 1993 at the University of Iowa Hospitals & Clinics and the affiliated Veterans Administration Medical Center were reviewed. One hundred ninety-nine VCFs were placed in 196 patients (123 males, 73 females), with a mean age of 61 years (range 13 to 87 years). Thirty-five (18%) VCFs (30 stainless steel Greenfield filters [SGFs] and five titanium Greenfield filters with modified hook [TGF-MHs]) were inserted in the operating room via an open technique. The remaining 164 VCFs (82%) were inserted in the radiology suite by a percutaneous technique (38 SGF, 23 TGF-MH, 51 Vena Tech filters [VTFs], 48 Bird's nest filters [BNFs] and 4 Simon Nitinol filters). Thromboembolic risk factors in these 196 patients included malignancy (99), trauma (21), recent surgery (27), cerebrovascular accident with paralysis (6), and miscellaneous conditions (43). Indications for VCF placement included a contraindication to anticoagulation (92), complication of anticoagulation (44), failure of anticoagulation (26), prophylaxis (31), adjunct to pulmonary embolectomy (1), noncompliance (1), hemodynamically unstable patient (1), and prior VCF complication (3). Mean follow-up of the patients was 12 months (range 0 to 87 months). Because there were only four Simon Nitinol filters inserted during the study period, they were excluded from further analysis.

RESULTS

A comparative analysis revealed that there was a significantly higher incidence of symptomatic IVC thrombosis with the use of the BNF (n = 7) (14.6%) versus the SGF (n = 0) (0%), TGF-MH (n = 1) (3.6%), or VTF (n = 2) (4%) (p < 0.05 by chi-squared testing). The VCF-related mortality rate was also higher with the BNF (n = 5) (10.9%) versus the SGF (n = 1) (1.5%), TGF-MH (n = 1) (3.6%), or VTF (n = 0) (0%) (p < 0.05 by chi-squared testing). However there was no significant difference in the occurrence of clinically apparent recurrent pulmonary embolism during follow-up between the four different filter types (2 [4.2%] BNF, 3 [4.4%] SGF, 1 [3.6%] TGF-MH, and 1 [2%] VTF).

CONCLUSION

These data indicate that the use of the BNF was associated with increased morbidity and mortality rates compared with the use of the SGF, TGF-MH, and VTF filters.

Early and late results after Bird's Nest filter placement in the inferior vena cava: clinical and duplex ultrasound follow up

From February 1989 to November 1992, 61 Bird's Nest filters were placed in the infrarenal vena cava in 61 patients (36 men and 25 women; mean age +/- s.d., 63 +/- 15, range (16-83). In 27 (44.3%), the filter was inserted because of contraindication to anticoagulation, in 19 (31.1%) for anticoagulation failure and in 15 (24.6%) as prophylaxis against pulmonary embolism in high risk patients. All the filters were introduced by percutaneous puncture of the femoral vein after preliminary screening venography demonstrated that the iliac vein was free of thrombus. Two deaths occurred within 24 h of filter placement (periprocedure mortality 3.3%) while five other patients died within 1 month (30 day cumulative mortality 11.5%). At follow-up, 2-40 months later (mean +/- s.d., 17 +/- 9), a further 13 patients had died (cumulative mortality 32.8%). At 36 months, the probability of survival, calculated by the Kaplan-Meier Product Limit Method, was 55% (95% confidence intervals 37-74%). Apart from the two patients dying within 24 h, none of the early or late deaths were attributable to the procedure and there were no recurrent pulmonary emboli. Thirty-seven of the surviving 41 patients were recalled for clinical examination and Duplex ultrasound interrogation of the vena cava and the lower limb veins. No new venous thromboses in the legs were observed and no increase or onset of leg swelling was reported. The vena cava patency was 100% in these 37 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Deployment problems with the titanium Greenfield filter

PURPOSE

The authors retrospectively reviewed their initial experience with deployment of the modified hook titanium Greenfield filter.

PATIENTS AND METHODS

Twenty-three patients underwent filter placements over a 1-year period. Radiographs were obtained immediately after placement to confirm filter position in all cases. Follow-up images were available in 15 patients (65%).

RESULTS

Twenty-four filters were placed in 23 patients. Tilting of the filter (> 15 degrees) was evaluated in 22 placements without complications and was present in five (23%). In 17 of 24 placements (71%), distribution of filter legs was poor, with wide gaps between clustered legs. Manipulation of the filter legs with an angiographic catheter resulted in improved distribution in three of six attempts but also resulted in a caudal displacement, which necessitated placement of a second filter. At follow-up (range, 4-16 months; mean, 9 months), three cases of asymptomatic inferior vena caval thrombosis and one recurrent pulmonary embolism were discovered.

CONCLUSION

No untoward event resulting from filter placement was demonstrated. Further study and review of the deployment mechanism may be necessary.

Acute clot-trapping efficiency in dogs with compacted versus elongated wires in bird's nest filters

PURPOSE

The clot-trapping efficiency of the Bird's Nest filter was studied in dogs with the stainless steel wires in a compacted versus fully elongated configuration.

MATERIALS AND METHODS

Bird's Nest filters were placed infrarenally with the wires compacted in 10 dogs and with the wires elongated in an additional 10 dogs. The dogs were separated into two groups, five dogs with each wire configuration in each group. In group 1, 10 unlabeled 6 x 30-mm blood clots were injected into the inferior vena cava. In group 2, six 6 x 10-mm, four 6 x 15-mm, and four 6 x 30-mm labeled clots were introduced.

RESULTS

In group 1, clot-trapping efficiencies were 82% for the compacted versus 86% for the elongated configuration, as seen on serial cavograms and pulmonary angiograms. In group 2, clot-trapping efficiencies were 90% for the compacted versus 97% for the elongated configuration, as seen at fluoroscopy. Clot size did not affect trapping efficiency.

CONCLUSION

Acute clot-trapping efficiency of Bird's Nest filters did not differ when the wires were in a compacted versus elongated configuration. This study suggests that placement of a Bird's Nest filter in the elongated configuration may be satisfactory and may not indicate placement of a second filter.

Effectiveness of a prolapsed bird's nest filter

PURPOSE

The authors evaluated the variable deployment of the Bird's Nest filter, including frequency and extent of prolapse in clinical use, and analyzed the effects of this variability on clot-trapping efficiency with an in vitro model.

MATERIALS AND METHODS

In the clinical placement of 20 filters, the average length of cephalic filter wires from the center of the filter was measured from radiographs obtained immediately after placement. To analyze the effects of prolapse, a variable-rate pump was used to mimic the effects of respiration on IVC flow. Four clot sizes (5 x 20, 5 x 40, 10 x 20, and 10 x 40 mm) were evaluated with four filter configurations with wires stretched to different lengths in a cephalic direction from the center of the filter: 2 cm (normal-tight), 5 cm (normal-loose), 8 cm (moderate prolapse), and to a maximum of 12 cm (maximum prolapse). Ten passes for each clot size were performed with each filter configuration in both the horizontal and vertical positions. The smallest clots were also tested with a slower constant-rate pump.

RESULTS

In clinical use, the average length of the filter wire was 5.4 cm (range, 1.2-9.0 cm). With the variable flow pump, the in vitro degree of prolapse did not significantly decrease the trapping efficiency for any but the smallest (5 x 20-mm) clots, for the maximum prolapse configuration in the horizontal position (P = .01). In addition, for these clot sizes, the filter was more efficient with the slower constant rate compared with the faster variable rate; this difference was only statistically significant in the horizontal position for the maximum prolapse configuration (P = .007).

CONCLUSION

The results suggest that in clinical practice, a prolapsed Bird's Nest Filter remains effective for all but small clots.

Use of the Greenfield filter in adolescents for deep vein thrombosis and pulmonary embolism

Serious venous thromboembolic disease is now recognized more frequently in the pediatric age group. Caval interruption is indicated most commonly for prophylaxis against life-threatening or recurrent pulmonary embolism (PE) when anticoagulation is ineffective or contraindicated. Greenfield vena caval filters have been utilized locally in 415 adult patients with 97% long-term patency and 5% recurrent embolization. Its application in adolescents is reported herein. Standard adult (30-mm) vena caval filters were placed in ten patients, ages 13 to 18. Four filters were required following PE, six were used for deep venous thrombosis (DVT) when anticoagulation was contraindicated, and one was inserted prophylactically. In eight patients, filter insertion was accomplished with local anesthesia, while two underwent filter placement under general anesthesia administered for other procedures. One filter was misplaced into the right renal vein, requiring a second filter insertion. All patients have been followed from 1 to 11 years with yearly vascular duplex imaging and radionuclide venograms documenting caval patency without clinical embolic sequelae. This duplicates the adult experience in safety and efficacy. As recognition of venous thromboembolism becomes more frequent in the pediatric age group, safe caval interruption may be necessary for those excluded from or not responsive to anticoagulation. This technique may be extended to smaller patients with miniaturization of both filter and carrier.