BLOOD CLOT FILTERING SYSTEM
BACKGROUND OF THE INVENTION
This invention relates generally to devices and methods for trapping blood clots
and controlling embolization and some of the complications of thrombosis in blood
vessels. More particularly, this invention relates to a blood filtering system that
comprises two separable independent parts: a permanent anchor, and a filter
removably attached to the anchor. The two parts of the system are attached in such
a way that, once emplaced, the filter is continuously maintained along the central axis
of the blood vessel to ensure that the filter operates at optimal efficiency. If and
when it is necessary or desirable to remove the filter, it may readily be separated from the anchor and withdrawn, leaving a permanently attached anchor that does not
interfere with blood flow within the blood vessel.
The presence of thrombus within the body's circulatory system presents
significant health hazards, as manifested by potential acute venous thrombosis and
chronic deep vein thrombosis. Acute venous thrombosis can lead to pulmonary
emboli, a potentially lethal condition when an embolus travels into the pulmonary
arteries. Currently, the most widespread treatment is the administration of systemic
and oral anticoagulants such as heparin and coumadin, and thromboiytic agents such as
TPA, uro inase and streptokinase.
Unfortunately, conventional drug therapy is ineffective or inappropriate for
controlling emboli within the circulatory system of some patients. In particular, since
most pulmonary emboli originate in veins of the lower limbs, pelvis or inferior vena
cava, it has been recognized that life-threatening pulmonary emboli can be
prevented from reaching the lungs by mechanically interrupting the inferior vena
cava to filter out emboli.
Indications for introducing such filters in the inferior vena cava include:
a) Pulmonary embolism in patients with a high risk of internal bleeding,
including those having surgery, anticipated surgery, recent trauma,
cerebral hemorrhage or peptic ulcer disease who are not amenable to
anticoagulant or thromboiytic therapy.
b) Recurrent pulmonary emboli notwithstanding anticoagulant therapy. c) Patients showing large free-floating thrombi in the iliofemoral veins or
inferior vena cava as identified with venography.
d) As prophylaxis against pulmonary emboli in older patients with high-
risk conditions. e) Disseminated thrombosis and profound thrombo-cytopenia in patients
displaying heparin sensitivity.
f) Prevention of recurrent pulmonary emboli after pulmonary
thrombolectomy.
In 1967-68, Eichelter and Schenk described an umbrella-like device which
they introduced under local anesthesia into the femoral vein of dogs to filter emboli.
Eichelter P. Schenk, W.G., Jr.: "A New Experimental Approach to Prophylaxis of
Pulmonary Embolism", rev Surg 24:455-456 (Nov-Dec) 1967; Eichelter P. Schenk,
W.G. Jr.: "Prophylaxis of Pulmonary Embolism." Arch Surg 97: 348-356 August
1968. The Eichelter/Schenk device was constructed by making longtitudinal
incisions circumferentially around a segment of a polyethylene tube, placing a tube
of smaller diameter inside the larger tube and flaring the end protruding beyond the
linear incisions. Light traction of the inner tube while holding the outer tube stable
produced an umbrella-like structure. Unfortunately, this structure included
numerous apertures for trapping stagnant blood and thereby promoting highly
undesirable thrombosis and potential embolization.
Eichelter and Schenk made small incisions in the right femoral veins of the
groins of the dogs used in the tests with the distal portion of the catheter tied into the femoral vein and the device open at a point lying distally to the renal veins.
After a number of weeks, the device was collapsed and removed through a small
incision. The embolization of trapped or attached emboli upon removal of the Eichelter/Schenk device precluded use of this device in humans.
A permanent implantable vena cava filter was developed by Mobin-Uddin in
1969, and described in U.S. Patent No. 4,540,431. This filter was intended to be
introduced through an incision in the jugular vein. The Mobin-Uddin filter was an
umbrella-like structure having expanding ribs carrying sharpened points at their
divergent ends which impaled the wall of the blood vessel when the filter was
positioned at the desired location and permitted to expand into its operative
structure. The Mobin-Uddin filter had a high occlusion rate and therefore was not
widely used. Finally, even if initially properly implanted, these filters could come loose and migrate to either ineffective or dangerous and life-threatening locations in
the vascular system.
The present invention solves the problems inherent in the prior art devices by
providing a system establishing a quick, safe, and well-centered reliable emplacement of an effective emboli filter which is secure in the vessel until it
becomes desirable or necessary to remove the filter. The present invention is
particularly useful for placement in the inferior vena cava. The system may also be
useful in filtering clots in other areas of the vascular anatomy.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a two stage blood
clot filtering system which can be quickly and safely emplaced within a blood vessel
to efficiently trap emboli passing through the vessel.
Yet another object of the present invention is to provide an emplacable blood
clot filtering system which, while maintaining patency, can provide either permanent
or temporary protection from emboli in blood vessels.
It is yet another object of the present invention to provide a blood clot
filtering system which can be emplaced through the femoral or internal jugular vein
in a relatively simple procedure, during the course of which the system may be
readily repositioned until optimally located in the vessel, and then positively fixed in
that location for the desired, medically appropriate period.
A further object of the present invention is to provide a blood clot filtering
system which can be steered through the vena cava under appropriate imaging
techniques.
A still further object of the present invention is to provide an emboli or blood
clot filter which, once emplaced, remains suspended along the longitudinal axis of
the vessel as blood flows through the filter, minimizing endothelialization and vessel
wall contact on the removable portion.
Another object of the present invention is to provide an emboli filter for
emplacement in a blood vessel which can be permanently emplaced but which also
can be readily removed when desired.
Yet another object of the present invention is to provide a blood clot filtering
system for emplacement in blood vessels in which the patency is optimized and
release of emboli into the bloodstream upon removal of the filter from the vessel is
minimized.
Still another object of the present invention is to provide a blood clot filtering
system including an anchor that is permanently emplacable in a blood vessel, and a removable filter attached to the anchor, in which endothelialization of the filter is
minimized.
The present invention is therefore directed to a blood clot filtering system
including an anchor which is permanently emplacable in a blood vessel and a blood
clot filter removably attached to the anchor.
The anchor is radially self-expanding. It may be made of a metal spring wire
material bent into a close zig-zag formation, with alternating zig and zag legs
meeting at sharp angles at their distal and proximal vertices. At least two hooks
may be provided respectively at at least two distal vertices spaced equidistantly on a circle defined by the distal vertices.
The filter preferably includes two stages which cooperate to provide enhanced
clot catching. The first stage comprises a series of distally projecting legs evenly
spaced about the longitudinal axis of the filter, and the second stage comprises a series
of generally radially projecting legs also evenly spaced about the longitudinal axis of the
filter. The first stage may be also provided with a series of flexible filartientous
tethers. The filter is removably attached to the anchor by way of these tethers.
Finally, the filter may include a spring-loaded jaw at its proximal end. This jaw will retain both ends of each of the tethers when the tethers are attached to the anchor,
but will release one end of each of the tethers in the process of removing the filter, leaving the anchor permanently fixed in place.
DESCRIPTION OF THE DRAWINGS
The objects and advantages of the present invention will be described with
respect to the following figures in which:
Figure 1 is a perspective view of the filtering system of the present invention
in which the filter and anchor of the system are separated for illustration purposes;
Figure 2 is an enlarged cross-sectional view of the jaw at the proximal end of
the filter of Figure 1;
Figure 3 is perspective view of the anchor of the filtering system of the
present invention;
Figure 4 is an enlarged view of one of the curls at a proximal vertex of two zig¬
zag legs of the anchor showing a tether filament passing through the loop in the curl;
Figure 5 is a perspective view of the assembled filtering system of the
invention showing the filaments of the filter tethers passing through loops at
alternating proximal vertices;
Figure 6 is a perspective view of the assembled filtering system of the
invention showing the filaments of the filter tethers passing through adjacent pairs
of proximal vertices;
Figure 7 is an elevation view of a flexible introducing catheter partially cut
away to show the assembly of the filter and anchor collapsed radially and positioned
in the catheter;
Figures 8A-8G illustrate diagrammatically the steps in emplacement of the filter system of the present invention in a blood vessel;
Figure 9A and 9B illustrate a removal catheter including an umbrella which
may be retracted and deployed from the catheter;
Figure 10 is a cross-sectional view of the removal catheter of Figures 9A and
9B, including a snare handle mounted to the catheter;
Figure 11 is an enlarged cutaway partial view of the end of the snare catheter
abutting the jaw at the proximal end of the filter;
Figure 12 illustrates an alternative design of the jaw depicted in Figure 2 in
which the proximal hook is replaced by a ball;
Figures 13A and 13B illustrate the capture of a ball at the proximal end of the
jaw and the application of a distally directed force for releasing the tether filaments
and removing the filter from a blood vessel in which it was previously deployed; and
Figure 14 is a diagrammatic representation of a blood clot filter emplacement
kit containing the filtering system of the present invention.
DESCRIPTION OF THE INVENTION
Turning first to Figure 1, the blood clot filtering system 8 of the present
invention is shown. The system includes a two stage filter 10 and an anchor 100.
Two stage filter 10 comprises a series of distally projecting legs 12a-12c, evenly spaced about the central axis A of the device, constituting one portion of the first
stage of the filter. While three distally projecting legs 12a-12c are illustrated, and
constitute a preferred embodiment, four, five, six or more generally evenly spaced legs may be used. Also, the legs are shown in their fully open, non-in vivo position,
at an angle of about 12° to longitudinal axis A, which is preferred. However, distally projecting legs 12a-12c may be at any angle ranging from about 2° to about 22° to
axis A when at rest, before placement in an introducing catheter or emplacement in
a blood vessel.
Distally projecting legs 12a-12c are made of a spring-like material which gives
each leg rigidity along its longitudinal axis while permitting it to flex laterally, thereby
enabling the filter to assume a fully closed configuration (Figure 7) in which the legs
are moved radially inward until they abut or nearly abut each other adjacent axis A
of the filter. The distally projecting legs may be made from metal, for example, from
stainless steel, nitinol, or Elgiloy® alloy (available from Egiloy L.P. of Elgin, Illinois, USA). In the illustrated embodiment, the distally projecting legs are made from
stainless steel wire, and have a diameter of about 0.008 to 0.012 inch and preferably
a diameter of about 0.010 inch.
The filter is intended to be in a fully closed configuration as it is inserted into
or removed from a blood vessel, as described in more detail below. When the filter
is deployed in a blood vessel (Figure 8G), distally projecting legs 12a-12c will be
flexed inwardly to a degree intermediate between the fully open and fully closed
positions.
The first stage of the filter also includes a series of flexible filamentous tethers
14a-14c which, in the illustrated embodiment, are located between adjacent pairs of
distally extending legs 12a-12c. Tethers 14a-14c may be round or flat and are made of a flexible, elastic material such as nitinol or stainless steel, or of nylon
monofilament or other synthetic filamentous material. In the illustrated
embodiment, the tether filaments are preferably flat and made of nitinol having a
width of about 0.005 inch.
These tethers, which are attached to the filter and loop back from the anchor,
providing filament loops, serve at least three purposes. The first is the attachment of the filter to the anchor in such a fashion that the filter will be centered and
generally continuously maintained along the central longitudinal axis of a vessel in
which the blood clot filtering system is deployed, insuring that the filter operates at peak efficiency. Second, the tethers permit the filter to be separated from the
anchor when desired, so that the filter may be removed from the vessel. Finally, the filament loops of the tethers are an important feature of the first stage of the filter
cooperating with legs 12a-12c. The tethers thus aid in first stage filtering by
increasing the surface area coverage of the filter to improve the clot catching ability
of the first stage of the filter which minimizes the likelihood of pulmonary
embolization.
Filter 10 also includes a series of generally radially projecting legs 16a-16f
which comprise the second stage of the filter. These legs are spaced generally evenly
about the longitudinal or central axis A of the filter . Preferably, each of second stage
legs 16a-16f is located in a plane defined by axis A and the proximal leg which
generally bisects the interstice between each of distally projecting legs 12a-12c and its
adjacent tethers 14a, 14b, and 14c. Although six such radially projecting second stage legs are shown in the illustrated embodiment, the number of legs may range
from about 6 to 12.
In the illustrated embodiment, when the filter is in its fully open position,
second stage legs 16a-16f extend proximaily at an angle of about 70° to the central
axis A of the filter, which is preferred. However, the radially projecting second stage
legs may be at an angle from about 50° to 90° to central axis A. As in the case of
the distally projecting legs, radially projecting second stage legs 16a-16f are made of
a spring-like material which gives each leg longitudinal rigidity while permitting it to
flex laterally. This enables the filter to assume a fully closed configuration (Figure 7)
in which the legs may be moved together until they abut or nearly abut each other
adjacent axis A of the filter . As explained above, the filter is intended to be in this
closed configuration as it is inserted or removed from a blood vessel.
The radially projecting second stage legs will be flexed inwardly to a degree
intermediate between the fully open and fully closed positions when the filter is
deployed in a blood vessel (Figure 8G). The radially projecting second stage legs
may be made, for example, from stainless steel, nitinol or Elgiloy® alloy. In the
illustrated embodiment, these legs are made from round stainless steel wire having a
diameter of about 0.008 to 0.012 inch. Flat or round wire may be used, although
round wire is preferred.
The first and second stages of filter 10 cooperate to provide enhanced clot
catching. Thus, the first stage encounters and captures most clots while the second
stage traps any emboli that might slip by the first stage, preventing emboli from proceeding beyond the filter.
Filter 10 also includes a spring-loaded jaw 24 having an open hook 40 at its
proximal end. Jaw 24 is described in more detail in the discussion of Figure 2 which
follows.
Figure 2 is an enlarged cross-sectional view of jaw 24 including a jaw body 26
having a truncated conical cavity 28, a proximal end 30, a distal end 34, and a bore
32 extending from the truncated distal end of cavity 28 to the distal end 34 of the
jaw. A top truncated conical member 36 is shaped and sized to fit in conical cavity 28 with a portion 38 of the conical member protruding beyond the proximal end 30
of the body of the jaw encircled by an annular shoulder 31 at the proximal end of
the jaw body. Hook 40 is attached to the protruding portion 38 of the conical
member, centered on the longitudinal axis of the jaw.
A rod 42 is affixed to the distal end of conical member 36 and extends distally
therefrom, along the central axis of the conical member. A cap 44 is affixed to the
distal end of rod 42. Cap 44 is cylindrically shaped and sized to fit snugly but
slideably within bore 32, and has a smooth conical distal tip 46 and an annular
shoulder 48 at its proximal end. Conical cavity 28 opens at its distal end into
cylindrical bore 32. Since the truncated distal end of the conical aperture has a
diameter less than that of the cylindrical bore, an annular shoulder 49 is formed at
this intersection. Encircling rod 42 is a compression spring 50 with the proximal end 52 of the spring resting on annular shoulder 49 at the intersection of the conical
aperture and the cylindrical bore and the distal end of the spring 54 resting on
shoulder 48 of the cap. Thus, compression spring 50 is compressed and confined in
bore 32 between shoulders 48 and 49, maintaining conical member 36 in cavity 28. In a preferred embodiment, silicone grease may be placed in bore 32 to minimize sticking in the jaw over time. Alternatively, the inner surface of the bore and/or the
outer surface 56 of the cap may be coated with polytetrafluoroethylene (Teflon®) or
another low resistance or surface-modifying material which minimizes sticking.
Cylindrical cap 44 includes longitudinal bores 62 generally evenly spaced
around rod 42 that pass through the cap. The number of bores 62 correspond to the
number of tethers in the filter . Thus, although one throughbore is shown in the
cutaway representation of jaw 24 in Figure 2, in the illustrated embodiment of the
invention there are three longitudinal throughbores 62 at roughly 120° spacings about
the central axis of the cylindrical cap corresponding to tethers 14a, 14b, and 14c. Additionally, the body of the jaw includes a like number of blind longtitudinal bores 66
extending proximaily from the distal end 34 of the body member and evenly spaced
about the longitudinal axis of the jaw. (As in the case of throughbores 62, only one
blind bore is shown in the cutaway representation of jaw 24).
Figure 2 shows one of the three tethers (14c) which, for illustration purposes,
is foreshortened. One end 70 of the filament of tether 14c is fixed in bore 66 by
conventional means such as swaging or laser welding. After being passed through
the anchor, the tether filament is passed through bore 62 past the individual coils of
compression spring 50, and out along the surface of conical cavity 28 with the distal
tip 72 of the tether filament at the proximal end 30 of the body of the jaw. Conical
member 36 which is firmly resiliently seated in cavity 28 under the biasing force of spring 50 thus locks the tether filament between the abutting surfaces of cavity 28
and conical member 36. When a force is applied proximaily to hook 40 while the
jaw is restrained along shoulder 31, spring 50 is compressed, unseating conical
member 36 and causing a gap to open up between the two abutting surfaces, releasing or unlocking tether 14c. When it is released, the tether is free to pass
back out through the coils of the spring and bore 62, so that the two stage filter 10
may be detached from anchor 100 and withdrawn proximaily from the vessel in
which it was emplaced. Jaw 24 in cooperation with tethers 14a, 14b, and 14c
therefore makes it possible to simply and efficiently separate filter 10 from anchor
100, in a procedure as described below.
Anchor 100 is self-expanding and includes a series of joined wire segments
102a, 102b, and 102c (Figure 3) which are each bent into a close zig-zag formation,
with alternating zig and zag legs 104 meeting at sharp angles at their vertices. As
shown in the figures, the vertices preferably present a rounded, rather than a pointed
tip. While the number of zig and zag legs and hence vertices may vary, in a
preferred embodiment, as illustrated in Figure 1, there are twelve zig and zag legs,
resulting in six proximal vertices 106a-106f, and six distal vertices, 108a-108f. In
practice, the number of zig and zag legs and hence vertices may range from six to
eighteen. As illustrated in Figure 3, anchor 100 may be made of a series of separate
wire segments which are spot or laser welded together as indicated in dashed lines.
Of course, the anchor may be made of a single piece of wire, if desired.
The wire or wires from which filter 100 is made are a metal spring wire
material, such as stainless steel or nitinol. In the illustrated embodiment, stainless
steel wire is used which is presently preferred. The use of spring material and the
zig-zag structure permits the anchor to be squeezed radially together, so that it
takes up a minimal amount of space radially, to facilitate emplacement of the anchor, as described in more detail below.
Spring hinges or "safety pin curis" 124 are formed at each of the vertices,
106a-106f and 108a-108f. These spring hinges are preferred, but may be dispensed
with in a less preferred embodiment of the invention. The spring hinges make for
an enhanced radially outward spring force which improves retention of the anchor in
a blood vessel. Also, it is preferred that alternate vertices be offset from each other
in order to minimize interference between adjacent hinges when the anchor is in the
fully closed position. This offsetting affects the manner in which the safety pin curls
contact each other when the anchor is collapsed into the introducing catheter. If all
pairs of zig zag legs were equal in length, the curls would "stack up" and take more
radial space when collapsed. By alternating the leg lengths, and therefore the
positions of the vertices, the curis are staggered and thus require less radial space
when the anchor is in the fully closed position.
Three hooks 130a, 130b, and 130c are provided respectively at distal vertices
108a, 108c, and 108e. At least two such hooks must be present, and preferably
from two to six hooks will be used. In all cases, the hooks are preferably spaced
equidistantly along the circle defined by the distal vertices. In the illustrated embodiment, the hooks are formed from protruding end portions of the wire
segments from which the anchor is made. Each of the hooks includes a longtitudinal
portion 132 and a radial portion 134. Radial portion 134 is preferably sharpened to
a point 136 (Figure 3). Thus, when the anchor is emplaced in a blood vessel and
permitted to expand outwardly under the spring force produced at the vertices of
the zig-zag segments, the radially outward force seats and retains the anchor in
place. Additionally sharpened points 136 engage the vessel wall, further fixing the
anchor in place.
Surface modifiers for reducing or preventing endothelialization, such as
Rapamune® (rapamycin) which is available from Wyeth-Ayerst Laboratories Division
of American Home Products or Taxol® (paclitaxil) which is available from Bristol-
Myers Squibb, may be applied to every part of the filtering system except the
anchor, including the filter legs, tethers and jaw. Such surface modifiers might not be applied to the anchor because limited endothelialization on the anchor surfaces is
desirable to cover those surfaces thereby enhancing anchoring and minimizing
contact between the blood flowing past the anchor and the metal from which the
anchor is formed.
In assembling the filter to the anchor , tethers 16a-16c are passed through
the three vertices 106a, 106c, and 106e. When safety pin curls 124 are used, it is
important, as illustrated in the enlarged partial view of Figure 4, that the tethers
(e.g., tether 14a in Figure 4) pass through the loops 126 of the safety pin curis, and
not in the space 128 between the abutting coils, as shown in the broken line
representation of the tether 14a. In the latter case, the filament could be pinched
between the abutting coils, which could interfere with separation of the filter from the anchor.
In order to clarify the way in which the filter is assembled to the anchor by
way of the tethers, the assembled system is shown in Figure 5 with the anchor fully
expanded and with its three hooks 130a, 130b, and 130c resting on a horizontal
surface 132. The filter is lowered somewhat with respect to the anchor to cause the
tethers to balloon outwardly for illustration purposes. Thus, it can be seen in this
figure that the filaments of tethers 14a, 14b, and 14c extend from jaw 24
respectively through the curl loops at vertices 106a, 106c, and 106e, and back up
into the jaw to be removably held therein, in the manner described above with
respect to the structure and operation of the jaw. When the system is deployed in a
vessel, the anchor is compressed radially inward as it abuts the walls of the vessel, as are the legs of the filter. In this in vivo configuration, the filaments of the tethers
will be elongated and drawn more closely together, generally as shown in Figure 8G,
which is discussed below.
Figure 6 shows an alternative way in which the filter may be assembled to the
anchor by way of the tethers. In this figure, tether filaments 14a, 14b, and 14c pass
from the jaw through adjacent pairs of curl loops at adjacent vertices 106a and
106b, 106c and i06d, 106e and 106f, and back to the jaw.
Before deploying the filter system of the present invention, the assembly of
the filter and anchor are collapsed radially and placed in a flexible introducing
catheter 150, as illustrated in Figure 7. In the illustrated embodiment, catheter 150
is shown, cut away in order to make it possible to view the assembled filter and
anchor in the catheter. Also shown in this figure is a pusher 152, which is used to
deploy (by pushing) the attached catheter and anchor from the annular aperture 154
at distal end 156 of the catheter when the catheter is positioned at the location within the blood vessel at which it is intended to be used.
Actual emplacement of the filter system of the present invention is shown in Figures 8A-8G which illustrate an internal jugular approach. It is important to note
that this system can be adapted to a femoral approach as well. Turning first to
Figure 8A, a portion of the vena cava vessel 200 is illustrated diagramatically at the
desired implant site 202. As can be seen in this figure, a guidewire 204 has been
inserted in the vena cava so that it extends beyond the implant site. Next, as shown
in Figures 8B and 8C, a conventional dilator 206 and sheath 208 assembly is passed
over the guidewire and advanced thereaiong until the sheath and dilator reach
beyond the implant site (Figure 8C).
Next, dilator 206 and guidewire 204 are withdrawn and sheath 208 is flushed
with heparinized saline to prevent thrombus formation in the sheath. A
venacavogram is then obtained by injecting a contrast medium through the sheath
208 so that the position of the sheath can be adjusted to optimize the later
positioning of the anchor and filter. This leaves sheath 208 deployed on guidewire
204, as illustrated in Figure 8D.
Now, introducing catheter 150, with the preloaded filter/anchor assembly as
illustrated in Figure 7, is flushed with heparinized saline, and then passed through sheath 208, until the introducing catheter protrudes beyond the end of the sheath,
as illustrated in Figure 8E. Now, pusher 152 (Figure 7) is inserted until it meets the loaded filter system and held stationary in that position while the introducing
catheter is slowly withdrawn, which deploys first the anchor, as shown in Figure 8F,
and then the entire filter system 8, as illustrated in Figure 8G.
As noted above, one advantage of the present invention is that it makes it
possible to easily remove the filter, if and when desired. As will be explained in
greater detail below, removal generally entails: 1) restraining shoulder 31, 2) snaring hook 40, 3) pulling up upon the hook to open jaw 24 and release the
tethers, making it possible to separate the filter from the anchor, and 4)
withdrawing the filter from the vessel, leaving the anchor in place. When the filter is
removed, the design of the filter, particularly the longitudinally rigid, smooth
surfaced legs of the first and second stages of the filter, act as pins which minimize
contact and resistance during withdrawal. Also, while the filter is held in place by the firmly attached anchor, the filament legs have little if any contact with the wall
of the vena cava.
For example, as shown in Figures 9A and 9B, a snare or removal catheter 300 is shown having an outer sleeve 302 and an inner hollow umbrella shaft 304. An
umbrella 306 is collapsed and resting in the distal end 308 of the removal catheter.
Thus, when the sleeve 302 is retracted, umbrella 306 is deployed and opened, as in Figure 7B.
Turning now to Figure 10, further details of the snare catheter are illustrated.
As shown in this figure, the snare catheter includes a pull ring 308 at its proximal
end, mounted to a snare handle 310 which is fit onto the proximal end 312 of the
snare catheter. The pull ring has a distally directed shaft 314 with a snare wire 316 which is attached at one end to shaft 314, and passes down through catheter and out of its distal end 318, where it forms a snare loop 320 before it passes back up
through the shaft and is attached at its other end to shaft 314. Snare loop 320 may
be angled up to 90° from the longitudinal axis of the snare catheter to make it
easier to use in snaring hook 24 (as discussed below). Also, the size of the snare
loop may be made adjustable as needed.
Thus, when it is desired or necessary to remove a previously emplaced filter,
the removal catheter is passed down through the vessel in which the filter system of
the invention is emplaced until snare loop 320 latches onto hook 40, with the distal end 318 of shaft 304 abutting the annular shoulder 31 of the jaw (Figure 11).
Umbrella sleeve 302 is then retracted to deploy umbrella 306 in the vessel. Once
the snare loop, sleeve and umbrella are in this position, the user pulls distally on the
snare ring to retract snare loop 320, pulling on hook 40, and releasing the tethers so
that the snare catheter and filter may be withdrawn through the vessel leaving the
anchor in place. Umbrella 306, which is optional, will catch any clots which may be
freed during the procedure, which otherwise could cause the clinical manifestation of
a pulmonary embolus. The umbrella should be permeable to prevent obstruction of
normal blood flow. This may be achieved, for example, by providing holes 307, as
shown in the illustrated embodiment and/or the umbrella may be made of a fine mesh material (not shown).
An alternate embodiment of the invention as it applies to the removal of the
filter system is illustrated in Figures 12 and 13. Thus, a jaw 400 is illustrated in
Figure 12. As is apparent from Figure 12, this jaw corresponds to that of Figure 2,
except that hook 40 has been replaced by a ball 402 attached to the distal end of
top conical member 36 by way of a pedestal 404. A locking sleeve 406, as shown in
Figure 13A, is provided at the end of the removal catheter. Trie locking sleeve is
shown in this figure in its extended position, with a pair of clasping jaws 410 and
412 in their open position, juxtaposed just above ball 402 of the jaw. Thus, turning
to Figure 13B, locking sleeve 406 has been moved to its fully retracted position, withdrawing the clasping jaws 410 and 412 into the catheter, causing them to pivot
radially inward and to lock upon ball 402. As in the above discussion of Figures 10
and 11, the catheter is then withdrawn, causing jaw 400 to release the tethers so
that the filter may be removed from the blood vessel.
Finally, a blood clot filter emplacement system is illustrated diagrammaticaily, in kit form, in Figure 14. This figure includes a container 500, containing an
introducing catheter 150 with a preloaded filtering system , generally as illustrated in
Figure 7, in which the filter is oriented for emplacement from above through an
upper central vein which could include the internal jugular, subclavian or brachial
vein. The position of the filter in the introducing catheter could be reversed for
emplacement from below, through the femoral vein. Container 500 also includes a
sheath 208 with a dilator 206 contained therein, a coiled guidewire 204, and a
pusher 152. The blood clot filtering system of the present invention may be
conveniently provided to a user in this kit form to facilitate the emplacement procedure.
There have been described herein a blood clot filtering system and a method
for its use free from the shortcomings of the prior art. It will be apparent to those
skilled in the art that modifications may be made without departing from the spirit
and scope of the invention. Accordingly, it is not intended that the invention be
limited except as may be necessary in view of the appended claims.