WO2002066109A1

WO2002066109A1 - Blood clot filtering system

Info

Publication number: WO2002066109A1
Application number: PCT/US2002/005770
Authority: WO
Inventors: Mark Goldberg; Ron Mallick; Lev Melinyshyn
Original assignee: Mark Goldberg
Priority date: 2001-02-20
Filing date: 2002-02-20
Publication date: 2002-08-29
Also published as: US20020116024A1; US20030097145A1; US6506205B2

Abstract

A blood clot filtering system including an anchor (100) which is permanently affixed in a blood vessel (200), and a filter (10) which is removably attached to the anchor (100).

Description

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when it is necessary or desirable to remove the filter, it may readily be separated from the anchor and withdrawn, leaving a permanently attached anchor that does not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.

Claims

What we claim is:

1. A blood clot filtering system comprising: an anchor including means for permanently emplacing the anchor in a blood

vessel; and a blood clot filter removably attached to the anchor.

2. The blood clot filtering system of claim 1 in which the anchor is radially self-

expanding.

3. The blood clot filtering system of claim 2 in which the anchor is 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.

4. The blood clot filtering system of claim 3 in which there are 6-18 zig and zag legs.

5. The blood clot filtering system of claim 3 in which the anchor is made of a

series of separate wire segments.

6. The blood clot filtering system of claim 3 in which the wire spring material is

chosen from the group consisting of stainless steel and nitiniol.

7. The blood clot filtering system of claim 3 in which spring hinges are formed at

each of the vertices.

8. The blood clot filtering system of claim 7 in which the spring hinges are offset

from each other.

9. The blood clot filtering system of claim 3 in which at least two hooks are

provided respectively at at least two distal vertices space equidistantly on a circle

defined by the distal vertices.

10. The blood clot filtering system of claim 5 in which hooks are provided at at

least two distal vertices and the hooks are formed from protruding end portions of the separate wire segments.

11. The blood clot filtering system of claim 1 in which the blood clot filter

includes two stages which cooperate to provide enhanced clot catching.

12. The blood clot filtering system of claim 11 in which the first stage comprises a series of distally projecting legs evenly spaced about the longitudinal axis of the system.

13. The blood clot filtering system of claim 12 in which three or more evenly

spaced distally projecting legs are provided.

14. The blood clot filtering system of claim 12 in which the distally projecting legs

are made of a spring-like material that gives each leg rigidity along its longitudinal axis while permitting each leg to flex laterally.

15. The blood clot filtering system of claim 14 in which the distally projecting

legs, in their fully open, non-in vivo position, are at an angle ranging from about 2° to about 22° to the longitudinal axis of the system.

16. The blood clot filtering system of claim 14 in which the distally projecting legs, in their fully open, non-in vivo position, are at an angle of about 12° to the

longitudinal axis of the system.

17. The blood clot filtering system of claim 14 in which the distally projecting legs

are made from stainless steel wire having a diameter of about 0.008 inch to 0.012 inch.

18. The blood clot filtering system of claim 12 in which the first stage is also provided with a series of flexible filamentous tethers.

19. The blood clot filtering system of claim 18 in which the flexible filamentous

tethers cooperate with the distally projecting legs to aid in catching clots.

20. The blood clot filtering system of claim 18 in which the tethers are located

between adjacent pairs of distally extending legs.

21. The blood clot filtering system of claim 18 in which the tethers are made of a

material chosen from the group consisting of nitinol, stainless steel, and synthetic

filamentous materials.

22. The blood clot filtering system of claim 18 in which the tethers are flat are

made from nitinol, and have a width of about 0.005 inch.

23. The blood clot filtering system of claim 18 in which the tethers extend

between the filter and the anchor to removably attach the filter to the anchor.

24. The blood clot filtering system of claim 11 in which the second stage

comprises a series of generally radially projecting legs generally evenly spaced about

the longitudinal axis of the system.

25. The blood clot filtering system of claim 24 in which each of the second stage

legs is positioned so that, in the deployed filter, it will generally bisect the space

between each of the distally projecting legs and its adjacent tether.

26. The blood clot filtering system of claim 24 in which about 6 to 12 radially

projecting second stage legs are provided.

27. The blood clot filtering system of claim 24 in which the radially projecting legs

are made of a spring-like material that gives each leg rigidity along its longitudinal

axis while permitting each leg to flex laterally.

28. The blood clot filtering system of claim 24 in which the radially projecting

legs, in their fully open, non-in vivo position, are at an angle ranging from about 50° to about 90° to the longitudinal axis of the filter.

29. The blood clot filtering system of claim 24 in which the radially projecting

legs, in their fully open, non-in vivo position, are at an angle of about 70° to the

longitudinal axis of the filter.

30. The blood clot filtering system of claim 24 in which the radially projecting legs

31. The blood clot filtering system of claim 24 in which the radially projecting legs

are made from round wire.

32. The blood clot filtering system of claim 1 in which the surfaces of the anchor are coated with a surface modifier for reducing or preventing endothelializtion.

33. The blood clot filtering system of claim 32 in which the surface modifier is

chosen from the group consisting of rapamycin and paclitaxil.

34. The blood clot filtering system of claim 18 in which the filter includes means

for removably retaining at least one end of each of the flexible filamentous tethers.

35. The blood clot filtering system of claim 34 in which the retaining means

comprises a spring-loaded jaw.

36. The blood clot filtering system of claim 35 in which one end of each tether is

fixed to the jaw, and the opposite end passes through a proximal vertex of the

anchor and back to the jaw where it is removably held so that, when the tether end

is released from the jaw, the filter may be detached from the anchor.

37. The blood clot filtering system of claim 35 in which the spring-loaded jaw

includes a conical cavity and a conical member shaped and sized to seat displaceably

therein under a spring force provided by the jaw, with at least a portion of the

outer surface of the conical member abutting at least a portion of the inner surface

of the conical cavity, whereby at least one end of each of the flexible filamentous

tethers is removably retained between the abutting surfaces of the conical cavity

and the conical member.

38. The blood clot filtering system of claim 37 in which one end of each of the

flexible filamentous tethers is removably retained between the abutting surfaces of the conical cavity and the conical member and the other end of each of the flexible

filamentous tethers is fixed to the jaw.

39. The blood clot filtering system of claim 36 in which the anchor is 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 and the

tethers pass through selected ones of the proximal vertices.

40. The blood clot filtering system of claim 39 in which spring hinges are formed

at the vertices and the tethers pass through the spring hinges at the proximal

vertices.

41. The blood clot filtering system of claim 35 in which movable abutting surfaces of the jaw are coated with a material which minimizes sticking.

42. The blood clot filtering system of claim 40 in which the tethers each pass

through more than one of the spring hinges.

43. The blood clot filtering system of claim 41 in which the coating is chosen from

the group consisting of silicone grease and polytetrafluoroethylene.

44. A blood clot filter emplacement system comprising a blood clot filter system

having an anchor with means for permanently emplacing the anchor in a blood

vessel and a blood clot filter removably attached to the anchor, and means for emplacing the system in a blood vessel.

45. The blood clot emplacement system of claim 44 in which the emplacing

means includes a flexible receiving catheter for retaining the filtering system in a

radially collapsed pre-loaded configuration prior to emplacement and for positioning the catheter in the desired location in a blood vessel, and means for deploying the

filter system from the catheter into the blood vessel.

46. A blood clot filter removal system for use with a blood clot filtering system, as in claim 36, which has previously been emplaced in a blood vessel, comprising

means for first unseating the conical member from the conical cavity of the jaw,

thereby permitting at least one end of each of the tethers to be released from the

jaw, and then withdrawing the filter from the vessel.

47. The blood clot filtering system of claim 46 in which the means for unseating

comprises a hook associated with the conical member of the jaw, means for snaring

the hook and means for restraining the jaw while the hook is pulled upwardly to

unseat the conical member.

48. The blood clot filter removal system of claim 46 including umbrella means for deploying during removal of the filter to capture any clots that are freed during the

removal process.

49. A method for emplacing a radially compressible blood clot filter in a blood

vessel to provide either permanent or temporary protection from emboli comprising:

providing a blood clot filtering system including an anchor with means for

permanently emplacing the anchor in the blood vessel and a blood clot filter

removably attached to the anchor by flexible tethers; radially collapsing the blood clot filtering system, deploying the system in the

vessel at the desire location with the anchor permanently emplaced, and permitting

the system to expand radially in the vessel; and

if and when it is desired to remove the filter, detaching the filter from the anchor and removing the filter from the anchor by passing it up through the blood vessel and out of the body.