CA2119814C

CA2119814C - Recoverable thrombosis filter

Info

Publication number: CA2119814C
Application number: CA002119814A
Authority: CA
Inventors: Toshiyuki Irie
Original assignee: Scimed Life Systems Inc
Current assignee: Boston Scientific Scimed Inc
Priority date: 1993-03-26
Filing date: 1994-03-24
Publication date: 1999-02-09
Anticipated expiration: 2014-03-24
Also published as: CA2119814A1; US5370657A; GB9404772D0; FR2702953A1; US5626605A; GB2276325A; GB2276325B; FR2702953B1; DE4410256A1

Abstract

A thrombosis filter that has an improved filtering function and can be securely anchored at a desired location and be removed through an endovenous route even after the growth of neointima. The thrombosis filter of this invention includes a first and a second filtering and holding unit, each unit including a coupling mechanism at its outer extremity in the form of a hook, and a plurality of resilient struts which include vein wall junction portions that lie parallel to the vein wall and are biased into contact therewith. The preferred embodiment includes picks that impale the vein wall to a limited depth.
The units are interconnected by a core shaft which consists of a compression member and a pair of core wires.

Description

2119~1~

R~ u~ RT-lZ THRO~BOSI8 FILTER
~ACK~ROmiD OF THE INV~TION

The present invention relates to thrombosis filters for trapping blood clots. To be more specific, it relates to thrombosis filters which can be securely fixed at a selected location in the vascular system, and removed when it is no longer required.
In recent years, p~ n~ry embolism has heS - an incre~i ngly C ~ -n medical emergency.
PUl ~ry embolisms may be caused by venous thrombosis that in turn may be c~-~ee~ by blood flow retention, venous intima ~ -, or coagulation abnormalities.
EmergeJ~y or prophylactic treatments for these conditions include anticoagulant therapy, thrombolytic therapy, thrombectomy and inferior vena cava blocking ~LOC~ es.
Among these therapeutic options, when an inferior vena cava bloc~ing procedure is selected, one - --option i8 to perform a laparotomy under ~ene~al anesthesia during which the inferior vena cava is ligated, ~uLu~ed and shortened, or clipped. A
laparotomy however, requires a general anesthetic and is ~lqceptible to thrombosis formation due to the Al~continuation of anticoagulant therapy prior to surgery. Another option is to intrav~nou~ly insert a ., .'~; ~.. ' ,, .' ..~., ', "

:' . . , :

21 ~ 981~ -thrombosis filter into the inferior vena cava which requires a local anesthetic. Percutaneous filter -insertion is now more widely employed since it requires ;
only a local anesthetic. However, such filters become fixed in the inferior vena cava wall by neointimal hyperplasia within two or three weeks after being implanted after which they cannot be removed percutaneously.
Blood is ~e~rlled to the heart from the lower part of the human body through the inferior vena cava and from the upper part of the body through the . . .
superior vena cava. The neck vein, known as the ~-jugular vein, leads to the superior vena cava which is a vein that enters the upper part of the heart. A -~
percutaneously inserted catheter that extends through the jugular vein, the superior vena cava and then into -the heart can be manipulated to exit the heart through ~
the mouth of the inferior vena cava that opens into the ~ ~ -heart. The inferior vena cava, a vein that enters the -lower part of the heart, can be acc~cseA through the patients femoral vein. Thus, the inferior vena cava can be reached through two endovenous routes, both of which are available percutaneously.
A prior Thrombosis Filter is shown in Figure 1. A filter of the tvpe shown in Figure 1, is the sub~ect of PCT application No. PCT/US92/11311. The Thrombosis Filter disclosed in that PCT application can be inserted in the patient and be r~ _ ~ed when no 211981~

longer required requiring only a local anesthetic. The structure of the filter illustrated in Figure l is such that the ends of the struts contact the vein wall at an acute angle and could under some conditions penetrate the wall of the vein in which it has been inserted. If a penetration of this type does occur, in addition to the trauma of a punctured blood vessel, the position of the filter within the blood vessel shifts to a less than optimum position, the likelihood of additional penetrations by other struts increases and removal of the filter he~ -5 more difficult.

8UMMARY OF TH~ INVENTION
The subject invention fulfills the need of a medical filter which can be positively located and retained at a selected area of a vein with i n i damage to the vein wall and non-surgically removed even after neointima has developed.
The filter includes a first and a second unit, each unit including a plurality of outwardly radiating struts. The units are connected together and extend along a longitud2na1 axis. The struts of one unit, the heart side unit, form a filtering basket that is blood permeable. The convex side of the filtering basket faces the heart and the concave side opens away from the heart such that blood flowing through the vena cava inferior flows into the concave side of the filtering basket. The basket sh~red portion of the ~- :
'~' ' ' .

CA 02119814 1998-0~-29 other unit, the anchoring unit, opens toward the heart and the blood flow is toward its convex side. Each unit includes a coupling mechanism in the form of a hook which is used in the removal procedure. Each strut includes an initial portion that extends at an acute angle to the longitudinal axis of the filter and a vein wall junction portion that is biased into contact with the vein wall and functions to anchor the filter in place within the vein. The units are interconnected by a core shaft which includes a compression member and a pair of core wires. The compression member can be fractured in response to a tension force of a predetermined quality to divide the filter into separate units that are removed independently.
In one aspect the invention provides an improved thrombosis filter to be placed in the blood vessel of a patient for trapping clots, of the type that is formed along a longitudinal axis and includes first and second units that are spaced from each other along the filterls longitudinal axis.
Each of the units includes a central hub to which a plurality of struts are anchored and from which the struts radiate outwardly at an acute angle to the longitudinal axis in the direction toward the other of the units. The first and second units are interconnected by a compression member that extends along the longitudinal axis. The struts of the first unit include initial portions that form a concave filter basket that functions to capture clots that are flowing through the blood vessel toward the concave side of the filter basket. The free ends of the struts of the first unit are bent toward the longitudinal axis at the ends of their initial portion to form vein wall junction portions that extend parallel to the vein wall and are biased into engagement therewith such that the vein wall junction portions function to anchor the filter at a desired position within the blood vessel. The struts of the second unit include initial portions that form a cone, the free ends of the struts of the second unit being bent toward the CA 02119814 1998-0~-29 - 4a -longitudinal axis at the ends of their initial portion to form vein wall junction portions that extend parallel to the vein wall.
In the preferred embodiment, each strut has a free end portion that extend back toward the longitudinal axis of the filer to avoid penetration of the vessel wall by the free ends of the vein wall junction portions. Also, picks are provided that extend from the hub in the same direction as the initial portion of the struts and continue a short distance past the intersection between the initial and the vein wall junction portions of the strut.
In another aspect the invention provides a method of constructing the above described filter.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of a prior art thrombosis ~/////////

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Figure 2 is a perspective view of the preferred ~ ho~i ~nt of the thrombosis filter of this invention.
Figure 3 is an enlarged view of a portion of the an anchoring unit of Figure 2 that is impinged in the wall of a blood vessel.
Figure 4 is a perspective view of another embodiment of the thrombosis filter of this invention.
Figure 5 is a cross-sectional view illustrating a step in the method for removing the thrombosis filter of this invention from a patient.
Figure 6 is a cross-sectional view -illustrating a step in the method for removing the thrombosis filter of this invention from a patient. -Figure 7 is a cross-sectional view ~-illustrating a step in the method for removing the thrombosis filter of this invention from a patient. -Figure 8 os a cross-sectional view, similar -to Figure 5 but illustrating another .~ '-'i -~t of tools to be used in the ~ l ~Loced~Le.

D~TAIBED DF8CRIPTION OF TBE ~nRED E~BODI~ENT
Figure 1 is a pe~ye~ive view, of the filtering and holding device that is the subject matter of the above identified PCT Application No.
PCT/US92/11311. The invention disclosed in this application is based upon and is an improvement upon 211981~

the filtering and holding device disclosed in PCT/US92/11311.
The filter device shown in Figure 1 includes -~
two units I and II that are connected by a compression member in the form of a coil spring 18. As for the structure of the filter units facing each other, this arrany~ -~t serves to stabilize and anchor the filter inside the blood vessel and to permit indPpPndent movement of one unit relative to the other which benefits the ~ l plocedure. This filter device is unique in that it can be removed through an endovenous route that is available percutaneously, and requiring only a local anesthetic. The struts 12 and 13 that radiate from the central hubs 10 and 11 respectively, -of the filter shown in Figure 1, are straight and their free ends engage the inner surface of the patients vein. Although the struts 12 and 13 engage the vein -wall at a shallow angle, under some conditions one or more struts could penetrate the patients vein wall.
This filter is fabricated mainly from stainless steel wires. The wire is 0.05 to 0.50 millimeters in ;
diameter. The struts 12 and 13 of the units I and II
radiate from the central hubs 10 and 11 respectively in conical configurations and are arranged such that their concave sides face each other. The anchor ends of core wires 14 and 15 are c~ e.;~ed to the central hub or fixation parts 10 and 11 along with the straight ends of hooks 16 and 17. The core wires 14 and 15 extend 211~

through the lumen formed by coil spring 18 and function as a part of the core shaft to reinforce the coil spring 18 in h~n~ i ng. The core wires 14 and 15 are firmly anchored in the central hubs 24 and 25. When the coil spring is initially bent, the core wires 14 and 15 have no effect on bPnAing~ only the resistance to bending of the coil spring must be overcome. When the bending angle is such that the core wires 14 and 15 engage the inner surface of the coil spring, then further ~n~ing must also overcome the bending resistance of the core wires. The unanchored ends of core wires 14 and 15 are free. The core wires within the c _ession h~r function to improve the bending quality of the core shaft as well as to achieve a desired flexibility for the compression h~r.
The coupling -ch~n;~ , in the form of a hook element provided at the head of each filter unit, functions to connPct the unit to --h~ni that can be manipulated through an endovenous route at the time of '~
removal. Hooks 16 and 17 are used in the removal p~ocedu~e and are cons~.~cted of tungsten or stainless steel wires that have been bent into the shape shown in Figure 1.
It should be noted that each of the units illustrated in Figure 1 have six (6) struts, and all 9iX of the struts from Unit II are shown in the illustration. Since the six struts are equally spaced ~ -. . . ' ' , . ' .

, .

2~ l 98~

around the unit, in Unit I some of the six struts are hidden b~hin~ fore~l~und struts.
Referring now to Figure 2 the preferred embodiment of the invention will be described. The filter of this invention includes a filter basket that is permeable to the blood flow but which will catch emboli and thrombus that are being carried in the blood stream and also hold the filter firmly in a selected location and permit ~ ~al through an endovenous route. The filtering and holding device of this medical filter includes two units that face each other and are biased toward each other. The units are formed of resilient struts that have initial and vein wall junction portions.
Although the present thrombosis filters can be made from a number of materials the material must be a flexible and must reLu~.. to its original shape after -being deformed such as identity elastic alloy wire, ~ ;~
high elastic alloy wire such as stainless steel, Lu.. ~sLen, platinum, piano wire, shape memory alloy wire, super elastic metal wire and chromium alloy. It i8 important that the coupling -chAni! - be cons~ructed of or include material such a tungsten, platinum or gold that can be seen on a fluoroscope, to aid in the p~ocess of attaching the coupling mechanisms.
Each unit of the filter includes multiple struts that are anchored in the corresponding central .~'' ; :~'' ,,,': '',, ' ' . '' , ' ' ' 2ll98l 4 g hub and extend therefrom at regular spaced intervals.
The initial portions of the struts of each unit lie on the surface of a cone or basket with an anchoring portion of the struts at the apex of the cone. The anchoring portions of the struts are connected to and are a part of the central hub. The thi~kn~ss of the wire from which the struts are formed is preferably 0.05 to 0.50 millimeters in diameter.
The two units are connected by a core shaft that is flexible, ~p~n~hle and facilitates maneuvering the filter units into the recovery sheath or sheathes for 1~ v~l. The core shaft includes a compression member that allows relative movement of the units along the filter's longitu~in~l axis. The ~5 c ession member can be designed to fracture when ~YpQse~ to a predetermined tension force, can be provided with a weakened area that will fracture in --r~sponce to a tension force of a predeteL ;n~ amount or can be anchored to the unit hub such that it will be uprooted in response to a tension force of a predetermined L. The ideal outside diameter of the compression ~-r is in the range of 0.5 to 2 millimeters. Inside the compression - her a core wires extends from each of the filter units and function to reinforce the compression h~r in b9nd~ ng.
The overall size of the thrombosis filters, will be dete~ ~ned by the site of its application and -the size of the particular vein into which it will be implanted. -In this : ~o~i ?nt the free end sections are contoured to avoid penetration of the vessel wall and picks are provided that are implanted into the surface of the vessel wall to thereby positively anchor the .
filter in a desired location. The depth to which the picks can be implanted is limited and thus the trauma and disadvantages associated with uncontrolled penetration of the vessel wall has been eliminated.
The picks enter the vein wall at an angle to the filter's longitn~in~l axis and in the direction such that the fluid flow exerts a constant pressure to force ~-the picks deeper into the vein wall. Thus blood flow through the vein exerts a force on tha filter mainta;ninq the limited penetration of the picks in the vein wall.
In the preferred : ~';ment there are fewer - -struts in the anchoring unit than in the heart side unit and there are fewer picks in the anchoring unit than struts. In the specific : ~odi -nt disclosed herein the heart side unit has six struts and the anchoring unit has four struts and two picks. The length of the pick~ available for implanting into the vein wall is relatively short, being about equal to the thi~n~s of the vein wall. Since the picks are inserted into the vein wall at an angle, provided their length is equal to the thi~kn~cs of the vein wall, they 211981~

will not extend completely through the vein wall.
However, the picks effectively serve their purpose of providing the filter with means for positively securing the filter in a preferred location. They serve this purpose while doing mini damage to the vein wall.
When the filter is removed the unit carrying the picks is pulled upstream of the blood flow. Thus, withdrawal of the picks from the vein wall is non-damaging to the vein wall. ~-~
The filter device of this : ~o~i -nt consists of units I and II, that are spaced from each other F
along the filter's longitu~;nAl axis and which face each other and are connected by a c~ _ession member such as a coil spring 48. The term compression '-r means a member that will draw the filtering and holding units toward each other to thereby ini i ze the overall longit~i n~ 1 length of the filter. The compression ~- -member could be formed from a flexible, elastic material that has a smooth outer surface. Each unit ~' has a central hub 44, 45 from which a plurality of struts 40, 41 radiate. The struts 40, 41 include initial portions 42 that are anchored in the central hubs 44 and 45 and radiate therefrom at equal angles to the filters longitudin~l axis. The struts 40 and 41 also include vein wall junction portions 43 that are bent down toward the filter's longitudinal axis.
It should be understood that some of the struts 40 and 41 could be straight as in the Figure 1 , 2~l98l~ ~
~ - ~

filter with the result that the straight struts would exert a greater anchoring force and the struts with the -~
vein wall junction portions would stabilize the filter and prevent the straight struts from penetrating the vein wall.
The angles at which the initial portions 42 extend to the longitudinal axis and the downward angle of the vein wall ~unction portion are dependent upon a number of factors such as the size of the vein in which it will be implanted, the material from which the struts are con~.ucted and the diameter of the strut wire. The unstressed diameter of the filter must be greater than the inside diameter of the vein in which it will be implanted. A filter having an unstressed ; -diameter that is equal to 1.3 times the diameter of the vein into which it is to be implanted has been found to be optimum. When the filter has been implanted in a vein the vein wall junction portions of the strut is parallel to the inner surface of the vein wall and can be hia~ed against it.
In this emhodi -~t, a short sections 53 of the Qnds of the vein wall junction portions 43 are bent inwardly to thus provide assurance that the free ends of the struts 40 and 41 will not pierce the vein wall.
Unit I of the preferred embodiment, illustrated in Figure 2, has four struts 40 as compared to the six struts 41 in Unit II. The six struts 41 of Unit II form a filter basket to catch blood clots.

, 2ll~8l~

Units I and II are connected together by a compression --hDr 48 and there are core wires 52, 49 anchored in the central hubs 44, 45. This e ho~i -nt also includes hooks 46, 47 that are used in the ~t v~l procedu~e.
Struts 40 are anchored in central hub 44, are equally --~
spaced around hub 44 and radiate therefrom at equal angles.
Unit I of the preferred : ho~i -nt, includes a plurality of anchor legs 54 that are securely anchored in central hub 44 and radiate therefrom at the same angle as struts 40. The anchor legs 54 are straight and terminate in pick portions 55. The anchor legs 54 are located such that they are adjacent to ~ :co~s~on~;ng struts 40 and could be secured thereto by welding or ~h~eive. In the preferred embodiment illustrated in Figure 2, Unit I has four struts 40 and two anchor legs 54. In this arrangement the anchor legs 54 would be located such that they are ~ L~ically opposite each other. The pick portions 55 of anchor legs 54 extend beyond the intersection of the initial portion 44 and vein wall junction portion 43 of the struts 40. The ends of the pick portions 55 ~: :
can be sharpened to a point. The length of the pick portion i8 in the range of 0.50 to 1.00 millimeters, which does not ~Ycee~ the usual thicknPse of the vein wall. Since the picks extend into the vein wall at an angle, picks having a length equal to or less than the usual vein wall will not extend through the vein wall.

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In Figure 3 the vein wall is identified as 60. When the filter of the preferred embodiment is being inserted in a vein, and Unit I tends to moves to the left as seen in Figures 2 and 3, causing picks 55 to pierce the vein wall at an angle. The vein wall junction portion 43 of strut 40 will however limit the penetration of pick 55. Thus the cooperation between the vein wall junction portions 43 and the picks 55 will positively anchor the filter at the selected location in the vein wall as well as limit the penetration depth of the picks 55. During the removal procedure Unit I will be pulled to the right, as seen in Figure 3, and the pick 55 will smoothly slide out of the hole that it has made in the vein wall 60 without causing damage to the vein wall.
In Figure 4 another : ~o~i -nt of this invention is illustrated that consists of units I and II, that are spaced from each other along the filter's longitudinAl axis and which face each other and are co~ c~ed by a compression - ~r such as a coil spring 28. Each unit has a central hub 24, 25 from which a plurality of struts 20, 21 radiate. The struts 20, 21 include initial portions 22 that are anchored in the central hubs 24 and 25 and radiate therefrom at equal angles to the filters longitudinal axis. The struts 20 and 21 also include vein wall junction portions 23 that are bent down toward the filter's longituAinal axis.
The angles at which the initial portions 22 extend to ~ .:: ~ -~
.... ~.. : ~.. .. .

;; ~ ~~ ~
.. ;. ~ .. . . . - .
. .... .. . l ..

211~81~

the longit~l~; nal axis and the downward angle of the ~-~
vein wall junction portion are dependent upon a number of factors such as the size of the vein in which it will be implanted, the material from which the struts are constructed and the diameter of the strut wire.
When the filter has been implanted in a vein, the vein wall junction portions of the strut are parallel to the inner surface of the vein wall and are be biased against it.
The filter, illustrated in Figure 4, is implanted in the vein such that blood flows into the ' concave sh~r~ basket formed by the struts 21 of Unit 1. The ~u~s 21 form a filter basket that is pervious to the flow of blood but will catch and contain blood clots. The initial portions 22 of struts 20 cross the initial portions 22 of struts 21 and thus a portion of struts 20 are within the filtering basket formed by struts 21. The struts are formed from thin resilient -wire, for example stainless steel wire, and the angles of the initial portion to the longitu~inal axis of the filter and the angle between the initial portion and the vein wall junction portion vary ~ep~n~ing upon whether the filter is unconfined, compressed for in~ertion and removal or in place within a blood vessel.
The struts are resilient and their vein wall ~unction portions are parallel to and can bear aga~nst the inner wall of the vein, when implanted -.. .

.

211981~

therein. The anchoring of an embodiment of this - ;
filter, is accompli~h~ by orientating the two units such that their concave side opens in opposite directions and the entire length of the vein wall junction portion of the struts, of both units, are biased into engagement with the inner wall of the blood vessel. As a result, there is a relatively large friction surface in engagement with the vessel wall that functions to anchor the filter in place. The length of the vein wall junction portions is about 5 millimeters. The pressure exerted by the vein wall junction portions of the struts against the vessel wall is of course determined by the material of the strut, its diameter and the un~Lessed angles that are built into the filter.
The filter units I and II, of Figure 4, also include core wires 32, 29, a compression h~r 28 and ~-hooks 26, 27. The anchor ends of struts 20, 21 are securely anchored in the central hubs 24, 25 such that they radiate at an angle to the filter~s longitl-~inal axis. Core wires 32, 29 are anchored in the units and have free ends that extend from their anchored ends, through compression member 28, toward the other unit.
The struts 20, 21 are formed from spring type material and thus can be biased inwardly to decrease the una~ essed diameter of the filtering and holding device when it is located in the vein as well as in the insertion and removal tubes. This embodiment relies ' ' '~ :,~ .;'; ' '' " ' ' ' ' .. ... . ....

2ll~8l~

upon the spring pressure causing the vein wall junction portions to bear against the inner surface of the vein wall to anchor the filter in place. A force must be applied to the filter, sufficient to overcome the friction forces between the twelve vein wall junction -portions and the inner surface of the vein wall, in order to move the filter from the location where it was originally implanted.
A welding or binder material is used for brazing the ends of the hooks 26, 27, core wires 32, 29, the struts 20, 21 and the ends of compression hqr 28 to the central hub or fixation parts 24 and 25. It should be noted that the compression member 28, hooks 26, 27 core wires 32, 29 and the struts 20, 21 --can all be fabricated from the same material or each of these parts could be fabricated from different material that will provide the desired characteristics for the particular part. -It is important to --~ure the inside - -diameter of the patients inferior vena cava so that the filter that is implanted has an appropriate diameter.
If the filter is undersized there is a danger that it could migrate and if it is oversized it is more likely to penetrate the vein wall. A filter having an uns~essed diameter equal to 1.3 times the diameter of the vein into which it will be implanted has been found to be optimum. A device has been developed for measuring the inside diameter of the patients inferior . .. . .................. . . .

. . . ~, . . ~ , .

2~19gl4 vena cava. The device resembles one of the Units of the filter illustrated in Figure 4 except nine rather ~- -than six splaying legs are anchored in the hub. The hub has a longitu~i n~ 1 length of 1 centimeter. The device is inserted into the patients inferior vena cava at the location where the filter will be implanted and a contrast medium is injected. The device is viewed on a scope and the diameter of the inferior vena cava and the length of the hub are measured. Since the scope magnifies, the exact diameter of the inferior vena cava, in centimeters, can be obtained by dividing the measured diameter of the inferior vena cava by the measured diameter of the hub.
Referring now to Figures 5-7 the method of implanting and removing the thLI hQSiS filter will be ~iecl~esed and explained. This discussion will be referenced to the preferred ; '~ t illustrated in ~ - ~
Figure 2 but is should be understood that the ~-~iecl~RRion applies equally to the : ho~i -nt --illustrated in Figure 4. The two units are biased together by a ~ , ession member which elongates during the L~ -v~l procedure until it reaches a point where it fractures thus separating Units I and II of the filter 80 that the two units can be r~ ved individually~
The thrombosis filter is dimensioned such that it can be stored in the distal end of a thin tube ~2 to 3 millimeters inside diameter). This insertion tube is percu~aneo~ely inserted into the patient and ~: .. : . - .. ,, .:

2~1~81~

follows an endovenous route into the patient's inferior ;
vena cava. This procedure is performed under local anesthetic. When the distal end of this tube reaches -the target site, the filtering and holding device stored inside the tube is caused to exit the distal end of the tube where it bec~ ? implanted in the patient's lnferior vena cava. A pusher rod is extended through the insertion tube and is maneuverable from the proximate end of the insertion tube for forcing the filtering and holding device out the distal end of the -insertion tube. It should be noted that insertion of the filter is monitored on a fluoroscope.
The filtering and holding device after being released from the tube into the patient's inferior vena cava, through the above described procedura, is in the :::
form as shown in Figure 2. Within several weeks after the filtering and holding device has been implanted in the inferior vena cava, the struts 40 and 41 he-~ ?
COV~I ed by neointima.
When it heS - r nec~cs~ry or desirable to remove the filtering and holding device, the following -~LGCedU~a iS followed. A recovery device is provided that can be inserted percutaneously and threaded through the en~o~ei~o~s route to the filtering and holding device. The ~ec~ve~ device includes a first tube 64, a second tube or sheath 61, a third tube 63 and a fourth tube or sheath 62.

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Referring to Figure 5, a doubled over cord 71 '-is inserted through the proximal end of the first tube 64 such that the cord emerges, in the form of a loop, at the distal end of the tube 64 where it functions as a coupling -chAni! . The tube 64 is then passed through the second tube or sheath 61 which has been percutAneou~ly inserted into the patient via the right internal ~ugular vein, through the superior vena cava and into the inferior vena cava, such that its distal end i8 adjacent the filtering and holding device. The ' tube 64 is advanced, through tube or sheath 61, to the filtering and holding device where it is manipulated ; -such that its coupling -ch~ni ! iS grasped by the complementary hook coupling --~ni! 47 In the same ~nn~r, a doubled over cord 72 is ~-pAcsed through third tube 63 such that a loop that functions as a coupling ?ch~ni emerges from the ~ -distal end of the tube. Third tube 63 is threaded ~ -through a fourth tube or sheath 62 which was percutAn~o~ly inserted into the patient via the femoral vein such that its distal end is in the patient's inferior vena cava The third tube 63 is manipulated such that its coupling mechanism is grasped by the complementary hook coupling mechanism 46~ Cords 71 and 72 are made of or include radiopaque material such as stainless steel so that the coupling of the loops with hooks 46 and 47 can be monitored on a scope.
Referring now to Figure 6, after cord 71 is ~ . . .

2~1981~ ~

connected to hook 47 and cord 72 is connected to hook 46 the cords 71 and 72 are simultaneously plllled in opposite directions, causing units I and II to move away from each other. The compression h~r 48 initially ~Yp~n~.c to permit this relative movement of units I and II. The relative movement of units I and II has resulted in a corresponding ~ nt of the struts 40 and 41 relative to the vessel wall and the filter have been freed from the neointima. This ~ nt has also pulled the picks 55 from their nest in the vessel wall 60.
The next step in the removal procedure of the filtering and holding device is illustrated in Figure -7. Tension on cords 71 and 72 have been increased to the point where ~ __ession - h~r 48 has fractured and -Units I and II have separated from each other.
Compression member-48 is made from material that can be --~
: - ., .
fractured by manually applying tension in opposite --directions to cords 71 and 72. After compression ~-member 48 has fra~Lu~ed the cords 71 and 72 would be pulled sufficiently to insure that the loose ends of compression member 48 are completely confined within sheathes 61 and 62 and then sheaths 61 and 62 are withdrawn from the patient. Sheath 61 is thus removed from the patient along with Unit I and sheath 62 is removed from the patient along with Unit II.
Referring now to Figure 8, which is a view similar to Figure 5, showing the first step in the ..

.. . . .. ..... . . ..... . .. . . .............. . . . . ..

: ~ . : ~ . . . ~ , , ~' 211~814 removal procedure using different removal tools. In Figure 8, a wire 91 having a loop 95 formed in its distal end is used instead of the cord 71 and first -tube 64 that were used in the removal procedure illustrated in Figures 5-7. The wire 91 has sufficient stiffness that it can be guided and manipulated from its proximal end to couple loop 95 with hook 47 and also possess the nec~ssAry flexibility that it can follow the turns and curves of sheath 61. Wire 91 can be made of wire of the type used in the construction of angioplasty guide wires. In this removal procedure the sheath 61 is percutaneously inserted into the patient via the right internal jugular vein, through the superior vena cava and into the inferior vena cava, - .
such that its distal end is adjacent the filtering and - ;
holding device. The wire 91 is threaded, loop 93 first, through sheath 61 from its pr~Y; -l end. While being viewed on a scope the loop 95 is coupled with the hook 47. In the Figure 8 removal proceduLe : ~o~i -nt, a cecond wire 93 having a loop 97 formed at its distal end is used instead of the cord 72 and third tube 63 that were used in the ~. -v~l procedure shown in Figures 5-7. Although closed loops 9 and 97 have been disclosed, hook ~hApe~ couplers could also be used.
Wires 91 and 93 are made of the same material and function in the same way to couple to both ends of the filter's hooks 47 and 46. After the coupling has been made between wires 91 and 93 with hooks 47 and 46 ~ . ; . . ~ . -~! ',.~...' ,,.

2~1~83~

respectively, the same procedure is followed as describes above with reference to Figures 6 and 7 for separating Unit I and Unit II. The force on wires 91 and 93 in opposite directions is then increased until the compression - h~r 48 is fractured. Compression member 48 is designed to fracture at a predete~ ined tension force. At this point of the removal procedure Units I and II are indep~nd~ntly stored in sheaths 61 and 62, which can be removed from the patient.
When the filters used for the present invention are employed in blood vessels, in order to prevent the adhesion of th~l ~osis it is preferable to ~-coat the filters with an antithrombotic agent (such as ' heparin, urokinAce and antithrombotic material including hydloxy methacrylate-styrene copolymer).
During the implanting process an insertion ~ -tube, containing the filter, is percut~n~oll~ly inserted ~---into the patient's inferior vena cava through the femoral vein. The filtering and holding device is ~
~Ypelled from the distal end of the insertion tube, by ~ -a pusher rod and is implanted at a selected location in the inferior vena cava. When the filter is expelled from the insertion tube it is propelled, by blood flow, in the direction that will cause the picks S5 to impale the wall of the vein and thus insure that the filter will remain at the selected location.
It is intended that the accompanying Drawings and foregoing detailed description is to be considered : .

- - ~-.

211981~

in all respects as illustrative and not restrictive, the scope of the invention is intended to embrace any equivalents, alternatives, and /or modifications of elements that fall within the spirit and scope of the invention, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

1. An improved thrombosis filter to be placed in the blood vessel of a patient for trapping clots, of the type that is formed along a longitudinal axis and includes first and second units that are spaced from each other along the filter's longitudinal axis and wherein the improvement comprises:
each of said units including a central hub to which a plurality of struts are anchored and from which said struts radiate outwardly at an acute angle to said longitudinal axis in the direction toward the other of said units, said first and second units being interconnected by a compression member that extends along said longitudinal axis, the struts of the first unit including initial portions that form a concave filter basket that functions to capture clots that are flowing through the blood vessel toward the concave side of the filter basket, the free ends of the struts of the first unit being bent toward the longitudinal axis at the ends of their initial portion to form vein wall junction portions that extend parallel to the vein wall and are biased into engagement therewith such that the vein wall junction portions function to anchor the filter at a desired position within the blood vessel, the struts of the second unit including initial portions that form a cone, the free ends of the struts of the second unit being bent toward the longitudinally axis at the ends of their initial portion to form vein wall junction portions that extend parallel to the vein wall.

2. The invention as set forth in claims 1 in which said second unit further including anchor legs that are anchored in said central hub and radiate outwardly therefrom at an acute angle to said longitudinal axis, the free ends of said anchor legs extend past the intersection of the initial and vein wall junction portions of the second unit struts and terminate in picks that can pierce the vein wall surface at an acute angle thereto.

3. The invention as set forth in claims 1 or 2, wherein said compression member is connected to the central hubs of said units.

4. The invention as set forth in claims 1 or 2, wherein each unit of said filter includes a core wire, one end of each core wire being anchored in the unit's central hub and extends from its anchor toward the other unit, said core wires terminating in free ends short of said other unit.

5. The invention as set forth in claims 1 or 2 wherein said filter includes a coupling mechanism at each of its ends, each of said coupling mechanisms being accessible percutaneously through the blood vessel in which the filter is implanted.

6. The invention as set forth in claims 1 or 2 wherein the struts of said first and second units are made of spring material and include anchoring portions that are rigidly anchored in said central hubs, said struts being equally spaced from adjacent struts such that engagement by the vein wall junction portions of the struts causes the corresponding central hub to be located along said longitudinal axis.

7. The invention as set forth in claim 1 or 2 wherein the struts of the first unit are bent toward the longitudinally axis at the ends of their vein wall junction portion to form inwardly directed end portions that will avoid piercing the vein wall.

8. The invention as set forth in claims 1 or 2 wherein the struts of the second unit are bent toward the longitudinally axis at the ends of their vein wall junction portion to form inwardly directed end portions that will avoid piercing the vein wall.

9. The invention as set forth in claims 1 or 2 wherein said first unit has at least six struts and the second unit has at least four struts.

10. A method of constructing a filter to be placed in the blood vessel of a patient for trapping clots, said filter being of the type that is formed along a longitudinal axis and includes first and second units that are spaced from each other along the filter's longitudinal axis and wherein the improvement comprises the steps of:
(a) providing a first central hub;
(b) anchoring a plurality of outwardly diverging struts in first central hub such that they radiate outwardly from said first central hub to form a concave filter basket;
(c) providing a second central hub;
(d) anchoring a plurality of outwardly diverging struts in said second central hub, such that they radiate outwardly from said second central hub, (e) connecting said first central hub to said second central hub by a compression member such that the outwardly diverging struts of said first central hub extend toward said second central hub and said outwardly diverging struts of said second central hub extend toward said first central hub; and (f) providing said second central hub with picks that will pierce the surface of the vein wall such that said second central hub function to anchor the filter in place within the blood vessel.