Note: Descriptions are shown in the official language in which they were submitted.
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FILTER CATHETER
The present invention relates to a filter for medical
use, adapted to stop the blood clots circulating in a vein,
and to the catheter for introducing it into the vein. More
especially, it relates to a filter whose use is temporary,
i.e. which may be withdrawn from the vein when the
treatment administered to the patient is judged
satisfactory and the presence of the filter is no longer
justified.
Such temporary filters are known, particularly by
Patent FR-A-2 580 504. They are fixed to the distal end of
a catheter for introduction and their structure is such
that, during introduction into the vein, the elements
ensuring filtration are folded into a sheath extending the
catheter, and, when the filter has been placed in the vein,
said filtering elements open out thanks to remotely
controlled means. In the filter of FR-A-2 580 504, the
filtering means are legs which extend, at rest,
approximately parallel to one another along the generatrix
of a cylinder and the means for opening them out are
reversible expansion means located inside the cylinder
defined by the filtering legs; by deformation, the
expansion means exert on the legs a thrust from the inside
so as to open them out in the manner of the spokes of an
umbrella, by a sufficient amplitude for each leg to be
applied at least in its distal zone against the wall of the
vein.
These known filters present two drawbacks: On the one
hand, they necessitate a complementary sheath for
protecting the filtering legs, arranged at the distal end
of the catheter, and adapted to be withdrawn when the
filter is opened out in the vein. On the other hand, they
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require complementary, complex expansion means for opening
out the filtering elements, remotely controllable in
reversible manner, for example an inflatable balloon with a
conduit supplying the corresponding fluid. This renders the
structure of the filter and catheter assembly complex and
delicate.
In order to overcome the drawbacks set forth
hereinabove, document FR-A-2 606 642 proposes a filtering
element which is borne at the distal end of the catheter
and which comprises a plurality of flexible legs; the
opposite ends of these flexible legs are interposed between
two members joined together by a means for modifying the
relative positions thereof, with the result that approach
of the two members along the longitudinal axis provokes the
transverse expansion of the flexible legs.
One embodiment cited in document FR-A-2 606 642
provides that the flexible legs result from the cut-out of
the tube constituting the distal part of the catheter, said
distal part being fast with an inner conduit which may
slide longitudinally inside the tube.
This embodiment is particularly simple.
However, Applicant has observed that the presence of
such a filter-catheter in a vein might cause blood clots to
appear, localized in the immediate proximity of said
filter.
The present invention is directed towards
a filter-catheter of the type mentioned above, which
overcomes the drawback observed.
In accordance with one aspect of the present
invention, there is provided a filter for partial and at
least temporary interruption of a vein which includes a
tube having towards its distal end longitudinal notches
distributed symmetrically around its periphery and defining
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flexible bands, and a conduit within the tube, the tube and
the conduit being firmly attached by their distal ends, the
distal end of the filter being provided with a radio-opaque
organ; the tube and the internal conduit being made of
polytetrafluoroethylene, the distal ends of the tube and
the conduit being thermowelded, the radio-opaque material
which is contained between the distal ends of the tube and
the conduit and attached to these during the thermowelding.
It is known that polytetrafluoroethylene is a material
which is only very slightly thrombogen. However, the
invention's merit lies in the fact that this material has
been chosen as presenting a proven sufficient flexibility
to effect transverse expansion of the flexible bands pre-
cut-out on its periphery.
The filter-catheter according to the invention
preferably comprises towards its distal end no other
material than the polytetrafluoroethylene in contact with
the blood flow. In that case, the tube and the inner
conduit are joined by thermo-welding.
However, it is desirable to be able to follow the
penetration and placing of the catheter inside the vein.
To that end, it is known to employ a radio-opaque element
near the filtering element. In the present case, the
filter-catheter comprises a ring made of a radio-opaque
material, for example gold, which is included between the
tube and the inner conduit and fixed thereto during thermo-
welding.
In this way, this radio-opaque element is not visible
and cannot be a source either of catching on the wall of
the vein nor of possible formation of blood clots.
It has been observed that, after a prolonged dwell
time in the vein, the flexible polytetrafluoroethylene
bands, opened out transversely, underwent a deformation
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bands, opened out transversely, underwent a deformation
under the effect of the inherent weight of the filtering
assembly. Such deformation is manifested in the form of a
greater spacing apart of the lowermost bands and therefore
a collapse of the filter, which causes a non-homogeneous
distribution of the bands in the transverse section of the
vein and in particular which brings about phenomena of
turbulence of the blood flow around certain bands, fit for
the appearance of blood clots.
In order to overcome this drawback, at least the
distal part of the filter-catheter according to the
invention is subjected to a prior thermo-setting, the
purpose of which is to increase the mechanical resistance
to deformation of the flexible bands of
polytetrafluoroethylene. This thermo-setting treatment may
consist for example of baking in a micro-wave oven for 4 to
5 minutes.
During this thermo-setting, the flexible bands are
preferably positioned in their opened out state. In this
way, the polytetrafluoroethylene undergoes a sort of
tempering which memorizes this opened out state in the
polymeric structure of the material.
According to another version, the tube is held
upstream of the notches and the tube downstream of the
notches is subjected to a rotation on itself so as to give
the flexible bands a twisted form, then a heat treatment is
applied on the distal part of the filter-catheter in this
configuration, the flexible bands being either at rest or
in the opened out state. In this case, during use of the
filter-catheter, the flexible bands naturally resume the
helical form.
The invention will be more readily understood on
reading the following description with reference to the
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accompanying drawings, in which:
Figure 1 is a schematic view, in section, of the
filter at rest.
Figure 2 is a schematic view, in section, of the
5 filter opened out.
Figure 3 is a view in transverse cross section of the
filter along axis D of Figure 2.
Figure 4 is a schematic view, in section, of the
distal end of a filter.
Figure 5 is a schematic side view of the device for
holding the filter-catheter during the thermosetting
treatment.
Referring now to the drawings, the filter-catheter 1
of the invention is essentially composed of a hollow tube 2
and of a hollow conduit 3 which is placed coaxially inside
tube 2. These two elements, tube 2 and conduit 3, are made
of polytetrafluoro-ethylene.
In the present specification, the terms "proximal" and
"distal" are employed, taking as reference the part of the
patient's body through which the filter is introduced. The
distal end of the filter, shown to the right in Figures 1
and 2, is thus the end most remote from that part of the
body, and the proximal end is the closer one.
The distal ends, 2a of tube 2 and 3a of conduit
3, respectively, are thermo-welded together and around
a metal ring 4, made of stainless steel, platinum
or gold. This ring 4 is made of a radio-opaque material,
detectable during positioning of the filter.
As is clearly shown in Figures 1 and 2, the
ring 4 is placed between tube 2 and the distal end
3a of conduit 3, the distal end 2a of the tube being
bent inside conduit 3 and covering the distal end
3a of said conduit. These elements are thermo-welded
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5A
together to form the end 15 of the filter-catheter.
According to another embodiment illustrated in Figure 4,
thermo-welding occurs whilst the distal end 3a of the inner
conduit 3 projects beyond the metal ring 4 and flares
outwardly, coming into contact with the distal end 2a of
tube 2.
2~~~~~~3~
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Upstream of its distal end 2a, tube 2 comprises
six notches 5, made in the longitudinal direction
over a length d of 30 mm; they are regularly distribu-
ted over the periphery of the tube. These notches
5 define six identical bands 6, each occupying an
angular space of 60° of the tube 2. For a tube 2
with a diameter of 3 mm, each band 6 has a width
of about 1.5 mm.
The conduit 3 is hollow and comprises a central
channel 7, in which a metal rod 8 serving as guide
rod during introduction of the filter-catheter, may
freely slide.
Towards the proximal end, but outside the pa-
tient's body, the tube 2 is fixed to a device 9 for
maintaining and for supply. This device 9 comprises
a cylindrical tube 10 and end rings 11 and 12. The
first annular ring 11 joins the proximal end 2b of
tube 2 to the front part of tube 10. The second ring
12 surrounds conduit 3 and closes the rear part of
the tube 10. An elbow 13 opens out obliquely in the
body of the tube 10.
The proximal end 3b of conduit 3 extends beyond
tube 10. Ring 12 hermetically surrounds this distal
end 3b; however, conduit 3 may~slide longitudinally
in ring 12 with respect to tube 10_and therefore
to tube 2.
A blocking ring 14 blocks Conduit 3 against
ring 12.
Tube 10 is fixed in known manner near the patient
on a frame supporting two systems for supply of pro-
ducts to be injected, opening out, for the first,
in the proximal end 3b of the conduit and, for the
second, in the elbow 13 of tube 10.
The filter-catheter functions under the following
conditions:
In a first phase, the guide rod 8 is introduced
by the percutaneous route into the appropriate vein,
until its distal end 8a is in position in the patient's
inferior vena cava.
In a second phase, the filter-catheter 1 is
slid from outside the patient's body along the guide
rod 8 until the ring 4 is in position in the vena
cava, where the filter is to be implanted.
Whilst 'this second phase is being carried out,
the bands 6 are at rest, i.e. 'they are in line with
the tube 2.
In a third phase illustrated in Figure 2 and
corresponding to the opening out of the filter, the
blocking ring 14 is loosened so as to allow conduit
3 to slide in ring 12. The proximal end 3b of conduit
3 is then displaced with precaution rearwardly in
the direction of arrow F. In this phase, the whole
of conduit 3 moves as well as ring 4, fast with the
distal end 3a of the conduit. Being given that tube
10 and therefore tube 2 are maintained in position,
the ring 4 can move back in the direction of arrow
F only thanks to the presence of the flexible bands
6. Each band 6 folds individually, consequently crea-
ting a homogeneous transverse deformation of the
tube in the zone of notches 5. The displacement and
length of the bands 6 are chosen so~that, in opened
out position, the median parts 15 of the bands 6,
corresponding to plan D of curvature, abut on the
inner wall 16 of the vein. Once the filter is correctly
opened out, the blocking ring 14 is tightened so
as to prevent any displacement of conduit 3 with
respect to tube 2 and therefore to maintain the band
6 in their state of transverse deformation.
As is clearly apparent in Figure 3, which is
a section along plane D, the six bands 6 are opened
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out transversely with respect to tube 2 and partially
obturate the interior 17 of the vein 18. In this
way, the blood clots moving inside (17) the vein
18 are stopped by the bands 6 whilst the blood can
circulate freely.
Prior to the use of the filter-catheter, th.e.
~.atter was subjected to a heat treatment of thermo-
setting. This treatment consisted in giving a thermal
shock to the distal part of the filter, whilst the
flexible bands 6 are in their opened out state, as
illustrated in Figure 2. The duration of this treatment
and the temperature are determined so that the shape
taken by the bands is to some extent memorized in
the polymeric structure of the polytetrafluoroe~thylerie.
This treatment increases the resistance of the bands
6 to deformation and avoids collapse of the filter
inside the vein 18 and the risk of thrombogenesis
due to the turbulences created in the blood flow
by the heterogeneous arrangement of 'the bands 6 in
the vein.
According to another embodiment of the therm~o-
setting treatment illus~rated in Figure 5, the heat
treatment is applied on the distal part of the filter-
catheter whilst the flexible bands 6 have a twisted
form. To that end, a mandrel 19 is fitted in the
inner conduit 3 so as to rigidify the distal part
of the filter-catheter; the distal end 2a of tube
2 is blocked in position in the front leg 20 of a
holding support 21; 'tube 2 is subjected to a rotation
on itself, which gives the flexible bands 6 the twisted
shape illustrated in Figure 5; then tube 2 is blocked
in position upstream of said flexible bands 6 in
the rear leg 22 of the support 21. The support 21
and the distal part of the filter-catheter are placed
in a baking oven, for example a micro-wave oven,
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in order to undergo the thermal treatment for 4 to
minutes. It will be noted that, during use of the
filter, the flexible bands 6 tend to taye the helical
form given during the thermal treatmen t. On support
5 21, the bands 6 may of course be in the rest position
as shown in Figure 5 or in the opened out state.
A product for therapeutic treatment may be injec-
ted upstream of the filter through conduit 3, from
the proximal end 3b thereof. This is an anti-coagulant
of the heparin type or a fibrinolytic. The conduit
3 may comprise orifices, for example disposed spirally,
in the zone opposite bands 6. In this way, the product
for therapeutic treatment introduced into conduit
3 may be distributed both upstream and at the level
of the filter itself.
The same product, or possibly another product
for therapeutic treatment, may be injected into the
zone immediately downstream of the filter through
tube 2, from the elbow 13 of tube 10.
Once the treatment is judged satisfactory, the
filter is withdrawn in the following manner: the
blocking ring 14 is loosened and the proximal end
3b of conduit 3 is pushed in the direction opposite
arrow F until the bands 6 resume their position of
rest, rectilinear and parallel to one another. The
ring 14 is then tightened again, and the conduit
3/tube 2 assembly is withdrawn from the vein..
Tests run with the filter-catheter according
to the invention have made it possible to observe
the absence of any formation of blood clots due to
the presence of the filter in the vein.
The present invention is nat limited to the
embodiment which has been described by way of no.n-
limiting example, but covers all the variants thereof.
In particular, the guide rod 8 may be hollow and
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allow the injection of product for treatment downstream
of the filter and even well beyond the distal end
of the filter-catheter 1.
