of the efficacy of in vitro emboli capture using Greenfield and Braile
vena cava filters *
Domingo Marcolino Braile,1 José Maria Pereira de Godoy2, Marco Centola3, José Luiz Simon Torati4, Guilherme de Campos Marino4
Physician. Professor and Head of the Graduate Course, Faculdade de
Medicina de São José do Rio Preto (FAMERP), SP, Brazil.
2. Physician. Professor, Department of Cardiology and Cardiovascular
Surgery, FAMERP, SP, Brazil.
3. Engineer, Braile Biomédica, São José
do Rio Preto, SP, Brazil.
4. Undergraduate students, FAMERP, SP, Brazil.
The study had the support of Braile Biomédica, which provided
the peristaltic pump and the Braile filter. Regarding conflict of
interest, we state that Prof. Dr. Domingo Marcolino Braile is the
President of Indústria Braile Biomédica and Dr. Marco
Centola works for this enterprise.
Maria Pereira de Godoy
Rua Floriano Peixoto, 2950
CEP 15010-020 - São José do Rio Preto, SP, Brazil
The aim of this study was to compare the efficacy of the Greenfield
and Braile vena cava filters for clot retention in an in vitro
Methods: The Greenfield and Braile filters were evaluated
in an in vitro study. We used bovine blood and 3-mm diameter silicon
tubes to create thrombi of 10, 15, 20, and 30 mm. The filters were
installed and fastened inside a 30-mm internal diameter silicon
tube, in a vertical position and connected to a pulsating flow system
(peristaltic pump - Braile Biomédica, São Paulo, Brazil).
A saline solution (0.9%) with 40% glycerin maintained at room temperature
was used as the vehicle. The flow was adjusted to 2 l/min and 50
thrombi were released isolatedly for each embolus length, with a
total of 200 events, verifying its capture in each release. Fisher's
exact test was used for statistical analysis, considering an alpha
error of 5%.
The capture efficacy using the Greenfield filter was 78.5% of events
and 92% for the Braile filter, a statistically significant difference.
We concluded that the Braile filter proved to be more efficient
for thrombi capture in an in vitro study than the Greenfield
in vitro, vena cava filters, embolus.
Vasc Br 2005;4(1):42-6
Pulmonary thromboembolism (PTE) is still one of the main causes of morbidity and mortality all over the world and it represents one of the challenges to be overcome by medicine.1 The main form of prevention after deep venous thrombosis is the anticoagulation. However, in case it fails or it is contraindicated, vena cava filters represent a new alternative. One of the advantages of anticoagulation is that it does not have the invasive character of the filters and it prevents the secondary thrombosis. Bleeding, however, is its great complication.1-3 The filters protect the lungs, but affect the vessels since they use an invasive method in its implantation and are foreign bodies in the vena cava.1 Several filters have been developed over the past years, but they have not reached the status of an ideal filter,4,6 thus justifying the development of new models that meet these requirements. Temporary vena cava filters were developed as an alternative for permanent filters,7-9 but they bring similar problems.
available vena cava filters can be differentiated by design (cone, basket,
types of net), by material and for being removable or not. New filters
should aim at reducing the complications of the existing filters and
improve their efficacy.
aim of the study was to study a new low-profile vena cava filter for
clot retention in an in vitro model, comparing it to the Greenfield
of in vitro emboli capture was assessed using two models of vena
cava filters, the Greenfield filter and the Braile filter. The Greenfield
filter is made of stainless steel, with six legs that are joined together
at the top forming a cone. It is 5-cm long, as can be seen in Figure
1 - Schematic drawing illustrating the cone-shaped Greenfield vena
cava filter with six legs joined together at the top.
vena cava filter consists of two cones opposed by the apex. The distal
cone is formed by eight stainless steel legs, shaped like a "web", 5-cm
long with the objective of clot retention. The proximal cone is formed
by four legs, 2-cm long made of the same material, playing the role
of an anchor and filter centralization, as can be seen in Figure 2.
2 - Schematic drawing illustrating the Braile vena cava filter with
two cones opposed by the apex.
bovine blood for the tests, which was injected into 3-mm diameter silicon
tubes to create thrombi of 10, 15, 20, and 30 mm. The vena cava filters
were installed and fastened inside a 30-mm internal diameter silicon
tube, in a vertical position and connected to a pulsating flow system
(peristaltic pump - Braile Biomédica, São Paulo, Brazil), as can be
seen in Figure 3. The Greenfield filter centralization was assured during
all experiment. A parallel device was interconnected to a three-stage
valve system with a syringe for clot introduction in the circuit. A
saline solution (0.9%) with 40% glycerin maintained at room temperature
was used as the vehicle. The flow was adjusted to 2 l/min for both models
and 50 thrombi were released isolatedly for each embolus length, with
a total of 200 events for each filter, verifying its capture in each
3 - Schematic drawing showing the circuit used for assessing the
in vitro efficacy of the Greenfield and Braile vena cava filters.
Fischer's exact test was used for statistical analysis, considering an alpha error of 5%.
vena cava filter captured 78.5% of the emboli, while the Braile filter
captured 92% (Table 1).
1 - Efficacy of Greenfield and Braile vena cava filters in capturing
four different lengths of emboli
filter capture (%)
filter capture (%)
vs. 10 mm
vs. 15 mm
vs. 20 mm
vs. 30 mm
exact test showed a significant difference (P < 0.0002) concerning the
efficacy of the two models of filters. In the general evaluation, the
Braile filter was more efficient in terms of emboli capture than the
Greenfield filter. The difference of sizes was nor statistically significant,
as shown in Table 1.
study showed that the Braile vena cava filter was more efficient in
terms of emboli capture in an in vitro experiment, when compared
to the Greenfield filter. However, there was no difference when the
different sizes were compared separately. This can be a consequence
of the lower number of events analyzed. Although the in vitro
test models use the same principle (fluid flow of saline, Dextran, or
glycerin solution, circulating by means of pumps in a translucent tubulation),7,10
there are no study reports in the literature using the same model of
this experiment. Nevertheless, studies show that several factors can
influence the results, such as the number of released thrombi, thrombi
size, tube diameter used for filter fixation,11-13 as well as the horizontal
or vertical placement of the test tube. As to the number of the test
sample used in the present study, it was enough for the statistical
analysis to show a significant difference. The thrombi size used for
testing is variable: 4 x 4, 2 x 4 x 3, 5 x 5, 3 x 6, until 9 x 20.7,10,11
The choice for thrombi size in the present study was a consequence of
a pilot study that showed the interference of the embolus diameter and
size. The in vitro study, in this case, made possible to identify important
data concerning the filter before moving on to the following phase.
filter, for being a pioneer and an efficient filter, with one of the
lowest frequencies of long-term vena cava occlusion, was the most used
and analyzed in the literature,2 and, therefore,
motivated its selection for evaluating a new filter. It also served
as a model for the development and improvement of the new filter. The
development of the Braile filter was based on the cuneiform structure
of the Greenfield filter, identifying its flaws and seeking solutions.
The first objective was to improve the efficacy of in vitro emboli
capture. In order to do that, the number of filter legs was increased.
This procedure improved the capture performance, but caused an increase
in the material volume: a 48-cm steel leg against 30 cm of the Greenfield
filter. The solution for this increase was to reduce the leg length
to 32 cm. The higher number of legs reduced the space among them, allowing
smaller emboli to be captured. The number of legs is one of the differentials
between the two filters concerning the mechanism of emboli capture.
Another aspect that contributed to the increase in efficacy of the Braile
filter is the centralization mechanism. This filter design, with two
cones opposed by the apex, allowed the creation of the centralization
mechanism. One of the cones captures the emboli and the other one helps
a better placement and device centralization. Thus, it accomplishes
one of the objectives of the development of new products, that is, the
improvement and better efficacy of the filters. The emboli tendency
is the centralized displacement, and thus the cone apex region allows
the smaller emboli capture. The filter decentralization widens the distance
between the legs in the vessels central region and cause more capture
failure, since the emboli tend to move to the center.
The few clinical studies assessing this aspect showed that around 5% of implanted Greenfield filters were decentralized. However, they did not report if this fact would affect its efficacy.13-15
of the filter profile was another emphasized aspect. The Braile filter
can be implanted with a 7 F introducer, which causes fewer vessel lesions
during implantation. Thus, two great advantages were identified on the
Braile filter compared to the Greenfield filter: more efficacy in emboli
capture and the reduction of the introducer. These advantages are also
present in the Simon nitinol filter and the Bird's nest filter.12 However,
the long-term behavior of this new filter in the vena cava should be
the conditions of this in vitro model, the Braile vena cava filter proved
to be more efficient in emboli capture than the Greenfield filter.
The undergraduate students received the support of the BIC Scholarship of scientific initiation at the Faculdade de Medicina de São José do Rio Preto (FAMERP) for this study.
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