CA2484752C - Mechanism for the deployment of endovascular implants - Google Patents

Abstract

A mechanism for the deployment of a filamentous endovascular implant (20) includes a flexible deployment tube (10) having an internal lumen extending between open proximal and distal ends (11, 13), and a coupling element (14) attached to the proximal end of the implant. The tube has a retention sleeve (12) that extends distally past the distal end of the tube. The coupling element is releasably held within the sleeve. The deployment tube and the attached implant attached are passed intravascularly by a microcatheter unti l the implant is located within a target vascular site. To detach the implant from the tube, a liquid is injected through the lumen so as to apply pressur e to the coupling element, which is thus pushed out of the retention sleeve by fluid pressure. The coupling element may include a purge passage for purging air from the microcatheter prior to the intravascular passage of the implant .

Description

MECHANISM FOR THE DEPLO'Y1vtENT
OF END OVA.S CTJLAR IMPL,ANTS
BACKGROUND OF THE INVEN'I'ION
This invention relates to ifie field of inethods and devices for the embolization of vascular axa.eueysms and similar vascular abnornl~ities.
More specifically, the present invention relates to a mecbanism for deploying an endovastalar implant, such as a microcoil, into a targeted vascular site, and releasing or detaching the implant in the site.
The embol)zation of blood vessels is desired in a number of clinical situa.tions. For ctample, vascular embolization has been used to control vascular bleeding, to occlude the blood supply to tumors, and to occlude vascular aneurysms, particuiarly infracranial aneurysms. In tecent years, vascular embolization for the treaizuent of aneurysms has received much attention. Several different treatment modalities have been employed in the prior art. U.S. Patent No. 4,819,637 - Dormandy, Jr. et al,, for example, describes a vascular emboiization system that employs a detachable balloon delivered to the aneurysm site by an intravascular catheter. The balloon is carried into the aneurysm at the tip of the catheter, and it is inflated inside the aneurysm with a solidifyin,g luxd (typicaUy a poly.m.erizable resin or gel) to occlude the aneurysm. The balioon is then detaota,ed from the catheter by gentle traction on the catheter. While the balloon type embolization device can provide an SUBSTITUTE SHEET (RULE 26) effective occlusion of many types of aneurysms, it is difficult to retrieve or move after the solidifying fluid sets, and it is difficult to visua]i.ze unless it is filled with a contrast rri.aterial. Furfh.ermore, there are risks of balloon rupture during inflation and of premature detachment of the balloon fiom the catheter.
Another approach is the direct injection of a liquid polynn.er embolic agent into the vascular site to be occluded. One type of liquid polymer used in the direct injection technique is a rapidly polymerizing liquid, such as a cyanoacrylate resin, particularly isobutyl cyanoacrylate, that is delivered to the target site as a liquid, au.d then is polymerized in situ.
,Alternatively, a liquid polymer that is precipitated at the target site from a carrier solution has been used. An example of this type of embolic agent is a cellulose acetate polymer miked with bismuth trioxide and dissolved in dimethyl sul#'oxide (DMSO). Another type is ethylene vinyl alcohol dissolved in DMSO. On contact with blood, the DMSO diffuses out, and the polymer precipitates out and rapidly hardens into an embolic mass that conforms to the shape of the aneurysm. Other examples of materials used in this "direct injection" method are disclosed in the following U.S.
Patents: 4,55I,132 - Pdsztor et al.; 4,795,741 - Leshchiner et al.; 5,525,334 - Ito et al.; and 5,580,568 - C'xreff et aJ..
The direct injection of liquid polymer embolic agents has proven difficult in practice. For example, migration of the polymeric material from the aneurysm and into the adjacent blood vessel has presented a pz'oblem. In addition, visualization of the embolization material requires that a contrasting agent be zxlixed with it, and selecting em.bolization matezial8 and contrasting agents that are mutually compatible may result in performance compromises that are less than optimal. Furthermore, piecise control of the deployment of the polymeric embolization material is difficult, leading to the risk of improper placement and/or premature , solidification of the material. Moreover, once the em.bolization material is SUBSTITUTE SHEET (RULE 26) deployed and solidified, it is difh.cuit to move or retrieve.
Another approach that has shown promise is the use of thxombogenic filaments, or filamentous embolic implants. One type of filamentous iin.plant is the so-called "micxocoiX". Microcoils may be made of a biocompatible metal alloy (typically platinum and tungsten) or a suitable polymer. If made of metal, the coil may be provided with Dacron fibers to increase throixtbogenicity. The coil is deployed thr'ough a microcatheter to the vascular site. Examples of microcoils are disclosed izl the following U.S. patents: 4,994,069 - Ritchart et al.; 5,133,731- Butler et a1.; 5,226,911 - Chee et aX.; 5,312,415 - Palermo; 5,382,259 -1'helps et a1.;
5,382,260 - Dormandy, Jr. et a1.; 5,476,472 - Dorrxiandy, Jr. et al.;
5,578,074 - Mirigian; 5,582,619 - Ken; 5,624,461 - Ivlariant; 5,645,558 -Horton; 5,658,308 - Snyder; and 5,718,711 - Berenptein et aI.
The microcoil appxoach has met with some success in treating small aneurysms with narrow necks, but the coil must be tightly packed into the aneurysm to avoid shifting that can lead to recanalization. Microcoils have been less successful in the treatment of larger aneurysms, especially those with relatively wide necks. A disadvantage of microcoils is that they are not easily retrievable; if a coil migrates out of the aneurysm, a second procedure to retrieve it and move it back into place is necessaryy.
Furthenn.ore, complete packing of an an.eurysm using microcoils can be dffficulto to achieve in practice. , A specific type of micarocoil that has achieved a measure of success is the Guglielmi Detachable Coil ("GDC"). The GDC employs a platinum wire coil fixed to a stainl.ess steel guidewire by a welded connection. After the coil is placed inside an aneurysm, an electrical current is applied to the guidewire, which oxidizes the weld connecti.on, thereby detaching the coil from the guidewire. The application of the current also creates a positive electrieal charge on the coil, which attracts negatively-charged blood ce11s, platelets, and fibrinogen, thereby increasing SUBSTITUTE SHEET (RULE 26) the thrombogenicity of the coil. Several coils of different diameters and lcngths can be packed into an aneurysm until the aneurysm is completely filled. The coils thus create and hold a thxombus within the aneurysm, inYubiting its displacement and its fragmentation.
The advantages of the GDC proceduxe are the ability to withdraw and relocate the coil if i.t, migrates from its desired location, and the enhanced ability to promote the formation of a stable thrombus within the aneurysm. Nevertheless, as in conventional microcoil techniques, the successful use of the GDC procedure has been substantially limited to small aneurysms with narrow necks.
A more recently developed type of filamentous embolic implan.t is disclosed in U.S. Patent No, 6,015,424 - Rosenblu.th et al., assxgned to the assignee of the present invention. This type of filamentous embolic implant is controllably transformable from a soft, compliant state to a rigid or semi-rigid state. Specifically, the transformable filax,nentous implant may include a polymer that is transformable by contact with vascular blood or with injected saline solution, or it may include a metal that is transformable by electrolytic corrosion. One end of the implant is releasably attached to the distal end of an elongate, hollow deployment wire that is insertable through a microcatheter to the target vascular site.
The implant and the deployment wire are passed thxou,gh the microcatheter until the distal end of the deployment wire is located within or adjacent to the target vascular site. At this poilit, the filamentous implant is detached from the wire. In this device, the distal end of the deployment wire terminates in a cup-like holder that frictionally engages the proximal end of the fiilamentous implant. To detach the filamentous implant, a fluid (e.g,, saline solution) is flowed through the deployment wire and enters the cup-like holder through an opening, thereby pushing the filamentous implant out of the holder by fluid pressure.
While filamentous embolic implants have shown great promise, SUBSTITUTE SHEET (RULE 26) improvement has been sought in the mechanisms for deploying these devices. In particular, improvements have been sought in the coupling m.echanisms by which the em.bolic implant is detachably attached to a deploymerXt instrument for installation iu a target vascular site. Examples of recent developments in this area are described in the following patent publications: U,S, 5,814,062 - Sepetka et a1.; U.S. 5,$91,130 - Palermo et a1.; U.S- 6,063,100 - Diaz et al.; U.S. 6,068,644 - Lulu et al.; and EP 0 941 703 Al - Cordis Corporation. +
There is still a need for fu.tt'.her improvements in field of coupling mechanisms for detachably attachirsg an embolic implant to a deployment instrument, Specjfically, there is still a need for a coupling mechanism that provides for a secure attachment of the embolic implant to a deployment instrument during the deployxn.ent process, while also all.owing for the easy and reliable detachment of the embolic implant once it is properly situated w;ith respect to the target site. It would also be advantageous for such a mechanism to allow improved control of the implant during deployment, and specifieally to allow the implant to be easily repositioned before detachment. Furtherm,ore, the coupling mechanism should be adaptable for use with a wide variety of endovascular implants, and it should not add appreciably to their costs.

SITMMA.RY OF THE INVENTION
Broadly, the present invention is a mechanism for the deployment of a filamentous eadovascular device, such as an embolic iunplan.t, comprising an elongate, flexible, hollow deployment tube having an open proximal end, and a coupling element attached to the proximal end of the endovasculaa' device. The deployment tube includes a distal section tenmxn.ating in an opexi distal end, with a].umen defined between the proximal and distal ends. A retention sleeve is fixed around the distal section and includes a distal eXtension extending a short distance past the SUBSTITUTE SHEET (RULE 26) distal end of the deployment tube. The endovascular device is attached to the distal end of the depXoyment tube during the manufacturi-ag process by fixing the retention sleeve around the coupling element, so that the coupling element is releasably held within the distal extension proximate the distal end of the deployment tube. In use, the deployment tube, with the implant attached to its distal end, is passed intravascul,arly thxough a microcath.eter to a target vascular site until the endovascular device is fully deployed tvx.thin the site. To detach the endovascular device from the deployment tube, a biocompatible liquid (such as saline solution) is i.n.jected tb.rough the lumen of the deployment tube so as to apply pressure to the upstreana (interior) side of the coupling element. The coupling element is thus pushed out of the retention sleeve by the fluid pressure of the liquid, thereby detaching the endovascular device from the deployment tube.
The coupling element may be a solid "plug" of polymeric material or metal, or it may be formed of a hydrophilic polymer that softens and becoznes somewhat lubricious when contacted by the injected liquid.
With the latter type of material, the hydration of the hydrophilic material results in physical changes that reduce the adhesion between the coupling element and the sleeve, thereby facilitating the removal of the couplixig element i'xom the sleeve upon the application of liquid pressure, .Al,ternatively, the coupling element can be made principally of a non hydrophilic material (polymer or metal), coated with a hydrophilic coating.
In a specific preferred embodiment, the retention si,eeve is made of polyethylene terephthala.te (PET), and the coupling element is made of a hydrogel, such as a polyacrylami.de/acrylic acid .m.ixwre. In another preferred embodiment, both the retention sleeve and the coupling element are made of a polyoiefin. In still another preferxed embodiment, the retention sleeve is formed of a #luoropolymer, and the coupling element is SUBSTITUTE SHEET (RULE 26) formed of a rxletal.. Hydrophili.c coatings, such as those disclosed iu. U.S.
Patents Nos. 5,001,009 and 5,331,027, may be applied to any of the non-hydrophilxc coupling elements, In an alternative embodiment, the retention sleeve is made of a shape memory metal, such as the nickel-titanium alloy Ianown as nitinol.
In this altem.ative embodiment, the coupling element would be made of one of the hydrophilic materials men,tioned above, or it may be made of a non-hyd.rophil.ic material with a hydrophilic coating.
The deployment tube, in the preferred embodiment, comprises a main section having an open proximal end, a distal section terminating in an open distal end, and a trarksition section connected betvveen the main and distal sections. A continuous tuid passage lumen is defined between the proximal and distal ends. The distal section is shorter and more flexible than the transition section, and the transition section is shorter and more flexible than the main section. Thi's varying flexibility is achieved by making the main section as a continuous length of flexible, hollow tube, the transition section as a length of hollow, flexl'ble laser-cut ribbon coil, and the distal section as a length of flexible, hollow, helical coil. The secci.ons may be joined together by any suitable means, such as soldering.
Preferably, an air purge passage is provided either through or around the coupling element. The purge passage is dimensioned so that a low viscosity fluid, such as saline solution, is allowed to pass freely through it, but a xelatively high viscosity fluid, such as a contrast agent, can pass through it only slowly. Before the deployment tube and the attached implant are imoduced intravascularly to the target site, a saline solution is injected under low pressure tbrough the lumen of the deployment tube to displace air from the XuXxa,en out through the purge passage. After the iunplant is located within the target site, a high viscosity contrast agent is injected. into the ddeployment tube lumen to purge the remaining saline solution tbrough the purge passage, but, because the SUBSTITUTE SHEET (RULE 26) contrast agent cannot pass quickly and freely ftough the purge passage, it builds up pressure on the proximal suYace of the coupling element until the pressure is sufficient to push the couplix'ig element out of the retention sleeve.
Any of the embodiments may employ an anti-airflow mechanism for preventing the inadvex-fient i.ntroduct'ion of air into the vasculature during deployment of the implant. One such mechanism comprises an airtight, compliant membranesealintgly disposed over the distal end of the deployzuent tube. The sra.embrane is expanded or distended distally in response to the injection of the liquid, thereby forcing the implant out of the retention sleeve.
Another such anti-airflow mechanism comprises an intern.al stylet disposed axially through the deployment tube. The stylet has a distal outlet opening adjacent the distal end of the deployment tube, and a proximal inlet opening in a fitting attached to the proximal end of the deployment tube. The fitting includes a gasf ai.r venting port in fluid communicafiion, with the proximal end of the deployment tube. The gas venting port, in turn, includes a stop-cock valve. rn use, the liquid is injected through the stylet with the stop-cock valve open. The injected liquid flows out of the stylet outlet opening and into the deployment tube, hydraulically pushing any entrapped air out of the venting port. When liquid begins flowing out of the venting port, indicaxyng that any entrapped air has been full.y purged from the deployment tube, the stop-cock is closed, allowing the continued flow of the liquid to push the implant out of the retention sleeve, as described above.
As wi1]. be appreciated more fully from the detailed description below, the present invention provides a secure attachment of the embolic implant to a deployment instrument durizag the deployment process, while also allowing for the easy and reliable detachment of the enlbolic implant once it is properly situated with respect to the target site. The present SUBSTITUTE SHEET (RULE 26) invention also provides improved control of the implant during deployment, and specifically it allows the implant to be easily repositioned before detachment. F'urthermore, the present invention is readily adaptable for use with a wide variety of endovascular implants, without adding appreciably to their costs.

BRIEF DFSCItIPTION OF THE DRAWINGS
Figure 1 is an elevational view of an endovascular device deployment mechanism in accordance with a prefexred embodiment of the present invention, showing the mechanism with an endovascular itnplant device attached to it;
Figure 2 is a longitudinal cross-sectional view of the deployment mechanism and the endovascular implant of Figure 1, taken along line 2-2 of Figure 1;
Figure 3 is a cross-sectional vievtr, similar to that of Figure 2, showing the first step in sepaxating the implant from the deployment tube of the deployment mecharlism;
Figure 4 is a cross-sectional view, similar to that of Figure 3, showing the deployment mechanism and the implant after the act of separation;
Figure 5 is a cross-sectional view of the endovascular implant deployment mechanism incorporating a first type of anti-airflow n7leChaniS]m;
Figure 6 is a cross sectional view of the depl.oyment mechanism of Figure 5, showing the mechanism with an endovasculaT implant device attached to it;
Figure 7 is a cross-sectional view, similar to that of Figure 6, showing the irnplant in the process of deployment;
Figure 8 is a cross-sectional view, similar to that of Figu~re 7, showing deployment device after the implant lZas been deployed;
SUBSTITUTE SHEET (RULE 26) Figure 9 is an elevational view of the endovascular implant deployment device incorporating a second type of anti-airflow mechanism, showing the device wi.th an implant attached to it;
Figure 10 is a cross-sectional view of the distal portion of the deployment device of Figure 9 and the proximal portion of the implant, taken alon.g line 10 -10 of Figure 9;
Figure 1 I is a cross-sectional view of the deployment device and the attached implant;
Figure 12 is a cross-sectional view, similar to that of Figure 11, showing the implant in the process of deployment;
Figure 13 is an elevationat view of an endovascular implant deployment device in accordance with a modified form of the preferred embodiment of the invention, showing the devi,ce with an implant attached to it;
Fi,guire 14 is a cross-sectional view taken along line 14 - 14 of Figure 13;
Figures 15-17 are cross-sectional views, similar to that of Figure 14, showing the process of deploying the itn.plant;
Figure 1 S is a cross-sectional view of the endovascular implant deployment device incorporating a modified form of the first type of anti-airflow mechanism, showing the device with an implant attached to it;
Figure 19 is a cross-sectional view, similar to that of p`igure 18, showing the irapl.ant in the process of deplo}ment;
Figure 20 is an axial cross-sectional view of the distal end of a deployment device and the proximal end of an implant in accordance with the present invention, showulg, a modified form of the coupling element with a peripheral air purge passage;
Figure 21 is a cross-sectional view taken along line 21- 21 ofFigure 20; aad Figure 22 is an elevational view, partially in axial cross-section, of SUBSTITUTE SHEET (RULE 26) the distal end of a deployment device and the proximal end of an implant in accordance with the present invention, showing another modified form of a coupling element with a peripheral air purge passage.

DETAILED DESCRIPTIOIq OF THE I;N'VENTION
Referring first to Figure 1, a deployment mechanism for an endovascular device, in accordance with the present invention, comprises an elongate, flexible, hollow deployment ttYbe 10 ha-vin.g an open proximal end 11 (see Figure 11) and a distal section terminating in an open distal end 13, with a continuous fluid passage lumen 15 defined between the proximal and distal ends. A retention sleeve 12 is fixed around the distal section of the deployment tube 10, and it includes a distal extension.17 extending a short distance past the distal end 13 of the deployment tube.
The depXoyment mecbanism fu.rther comprises a coupling element 14 fixed to the proximal end of a filamentous eadovascular device 16 (only the proximal porti.on of which is shown), which may, for example, be an embolic implant.
The deployment tube 10 is made of stainless steel, and it is preferabXy formed in three sections, each of which is dimensioned to pass through a typical zniarocatheter. A proximal or main sectiou. 10a is the longest section, about 1.3 to 1.5 meters in length. The main section l0a is formed as a continuous length of flexible, hollow tubing having a solid wall. of unifox,n inside and outside di.am.eters, In a specific preferred embodiment, the inside diameter is about 0.179 mm, and the outside diameter is about 0.333 mm. An intermediate or transition section 10b is soldered to the distal end of the main section IOa, and is formed as a length of hollow, flexible laser-cut ribbon coil, In a specific preferred embodiment, the transition section l0b has a length of about 300 mm, an inside diameter of about 0.179 mm, and an outside diameter of about 0.279 mm. A. distal section lOc is soldered to the distal end of the SUBSTITUTE SHEET (RULE 26) transirion section Xob, and is formed as a leAgrh of Sexible, holloW helical coil. In a specific preferred embodiment, the distal section 10c has a length of about 30 mm, an inside diameteer of about 0.179 msn, and an outside diameter of about 0.253 mm, A. xadiopaque m.arker (not shown) may optionally be placed about 30 mxn pwidmaY from the distal end of the distal section 10c. It wBI be appreciated that the transition section 10b wM
be more Sex%le than the main section.l0a, and that the distat sect3,om 10c will be more flexible than the transition secdon 10b.
The coupling elcment 14 is astened to the lxroxmW end of the endovascuiar device 16. The endovasculat device 16 is advantageou.sly of the type disclosed aud clairned in co-pending applioation Setial N'o.
09/410,970, assign,ed to the assignee of the present invention, although the inventron can read3ly be adapted to other types of endovascular devices.
Specifically, the endovascular device 16 is an embolization devige that com,prises a pluxalfty ofbiocompatUle, bift-expansible, hydrophgic embolizing elements 20 (only one of which is showrt iu the dt'a.wlrtg,s), disposed at spaced intervals along a f lamentous =Aer 22 in the foxm of a suitable iength of a very thin, hi" flexifiIe f lanaent of nickex/titanium alloy. The embolizing elements 20 are separated from each other on the carrier by radiopaque spacers in the form of higYily flexible microcops 24 (only one of wbich is shown in the drawings) made of platinum or platinum/tungsten alloy, as in the tbxom.bogeni,c microco1-Is of the prior art, as despaibed above. In a preferred embodiment, the embolizing elements 20 are made of a h,ydrophic, macroporous, polymeric, hydrogel foam ma.telFax, in pa,rticular a vvater..swellable foam ma.trix forrned as a m.acroporous solid comprising a foam stabi]iziug agmt ap,d, a polymer or copolyMer of a free radical, polymerizable b.ydxophjc o1efn monomer ecoss-linked witla, up to about .10a/o by wei,ght of a muitiole=-fanQional a' ss'!*ing ageIIt, Such a material is desca'bed in, U.S. Patent No.

5,750,585 - Park et al.

SUBSTITUTE SHEET (RULE 26) WO 03/094751 PCTlUS03/14580 The rnaterial may be modified, ar provided with additives, to make the implant visible by conveniion.al ima.giUg tecbhni,ques.
The endovascular device 16 i.s modified by extending the filamentous carrier 22 proximaJly so that it provides an attachment site for the coupling element 14 at the proximal end of the carrier 22. A sealing retainer 26 terminates the proximal end of the caixier 22, providing a sealing engagement against the dsstal end of the coupling eleznent 14.
The coupling element 14 is removably atiached to the distal end of the deployment tabe by the retention steeve 12, wbich is secured to the deployment tube 10 by a su.itable adhesive or by solder (preferably gold-tin solder). The retention sleeve 12 advantageousfy covers the transitim section:l0b aud the distal seedon,l0c of the deployment tube, and its proximW end is atached to the dlsW end of the main secEion 10a of the deploym,eat tube 10, The xetent3on sleeve 12 has a distal poartion that extends dntally past the distal end of the deployment tube 10 and surroun.ds and encloses the coupling element 14. The coupling element 14 has an outside diameter that is greater than the normal or relaxed inside diameter of the retention sleeve 12, so that the coupling element 14 is retained witl)an the retention. sleeve 12 by fiicti.on and/or the rad.ial,l,y Inwardly-ditected polymeric forces applied by the retention sleeve 12.
The r:oupling element 14 may be a solid "plug" of polymeric material. or m.etnl., or it may be formed of a hydrophilic polymer that softens and becomes somewhat lubricious when contacted by a hydrating liquid, as drscvssed below. With the 1aite.r type of materi.al, the hydration of the hydrophilic material results in physica.l, changes that reduce the frictYOnal adh,esion, between the coupling eleme,o,t 14 and the sleeve 12, thereby facHitating the removal Of the coupling elem.ent 14 from the sleeve 12 upon the application of liquid pressure to the upstream (pro=mal) side of the coupling elernent 14, as will be descxi-bed below. Alternafively, the coupling element 14 can be made princ.ipally of a non-hydrophilic material SUBSTITUTE SHEET (RULE 26) (polymer or meta2), and coated with a hydro '' coatiug.
In a first pxeferred em.bodhaerlit, the rctenfiion sleeve 12 is made of polyethylene tetephthalate (kE'T) or polYim,ide, and the coupling element 14 is made either of aimetal(preferably p]a'Iinum) or of abydrogel., such as a polyacrylamide/acrylic acid mixture. In another preferred embodiment, both the retendon sJ,eeve 12 and the coupling element 14 are made of a polyolef n.. In sffl anoth= prefexred embodiment, the retention sleeve 12 is formed of a fluoropolymer, and the coupling element 14 is formed of a metal. Hydrophilic coatings, such as those disclosed in U.S. Patents Nos.
5,001,009 and 5,331,027 may be applied to any of the non-h,ydrophMc coupfing elements 14. In these embodiumts, the retention sl+aewe 12 may be formed as a"sbrink tube" that is $tted over the coupling element 14 and then shrunk in place by the application of heat to secure the coupliaag element in pla.ce. The heat sh=SW pxocess senoi.-crystallizes the polymeri.c chayns so that sleeve is som.ewhat stiffened and made resistant to radi.at expansion (although stiU expu>5ible axialiy). Aftexnatively, the xeteciti.on sleeve 12 may bermade of an elastic pollrnler that is stretched to receive the coupling ekment 14, and then retains the coupling element 14 by the resulting eLastoraeric forces tllat are directed Yadxally invc-ardly, ln an albernative embodiment, the rc:Yention sleeve 12 is made of a shape nzemory metal, such as the nickel4itadum alloy known as nidno2.
In tbis alternati.~ue embodiment, the coupling elenien.t 14 would be Ma.de of one of the hydrophfiic nlaterials mentioned above, or it may be w.de of a non hydrophilic materjg with a hydroPhilic coating. I
xa this embodiment, the rebeniion sleeve 12 is ra.dially stretched to receive the coupling e.lemen.t 14, and it retains the couplin.g element.Z4 by the forces resuWng from the tendency of the shape memory metal to return to its original conf guraiion.
Use of the deployment mechanisr:a of the present inventlon is ~Ilus~rated in Figrues 3 and 4. The endovascular device 16 and the SUBSTITUTE SHEET (RULE 26) deployrrient tube 10 are passed intravascularly through the lumen of a miacocatheter (not shown) until the endovascular device 16 is situated in a targeted vascular site, such as an aneurysm. A suitable liquid 30, such as saline solution, is then injected into the interior of the deployment tube, under pressure, as show in Figure 3. The pressure of the liquid against the upstream side of the coupling element pushes the coupling element 14 out of the retention sleeve 12 to separate the endovascular device 16 from the deployment tube, as shown in Figure 4. While a polymer retention sleeve may deform in the axial directi.on during the separation process, it does not substantially expand in the radial d.irection. (For a metal retention sleeve, there would be no significant deformation.) If the coupling element 14 is made of a hydrophilic material, or if it has a hydrophilic coating, the physical changes in the coupling element 14 due to the hydrophilic properties of the coupling element 14 or its coating, as described above, will facilitate the separatxon process. The deployment tube 10 and the microcatheter are then withdrawn.
It will be appreciated that, until the liquid 30 is injected, the deployment tube 10 can be .m.azxi.pulated to shift the position of the endovascular device 16, which will stay attached to the deployment tube 10 during the manipulation. Thus, repositioning of the endovascular device 16 is facilitated, thereby providing better placement of the device 16 within the targeted site.
= In many instances, it wi11 be desired to take special,precauti-ons against the introduction of air into the vasculature. Accordingly, the present invention may be adapted to incorporate an anti-airflow mecb.anism-. A fixst type of anti-auflow mechanism, iJJ.ustrated in Figures S- 8, comprises a flexible, expansible, compliant membrane 40, preferably of silicone rubber, seali.ngly disposed over the distal end of the deployment tube 10. The distal end of the deployment tube 10 is covered by a thin, flexible, polymeric sheath 42, and the membrane 40 is attached to the SUBSTITUTE SHEET (RULE 26) sheath 42 by a suitable biocompatible adhesive, such as cyanoacrylate. As shown in Figure 6, the endov'ascular device 16 is attached to the deployment tube 10 by means of the retention sleeve 12 and the coupling element 14, as described above, with the membrane 40 disposed between the distal end of the deployment tube 10 and the proximal end of the coupling element 14.
In use, as shown in Figures 7 and 8, the liquid 30 is iujected into the deployment tube, as descn`bed above. Instead of directly impacking the coupling element 14, however, it expands the membrane 40 distally from the distal end of the deployment tube 10 (Fig. 7), thereby pushing the coupling element 14 out of the retention sleeve to deploy the endovasGuXax device 16. After the deployment, the membrane resiliently returns to its original position (Fig. 8). Thus, the injected liquid 30 is completely contained in a closed system, and any air that may be entrapped in the deployment tube 10 is prevented from entering the vasculature by the aistight barrier present by the membrane 40.
FXgu.res 9- 12 illustrate a second type of anti-aiiflow mecharaism that may be used with the present invention. This second type of anti-airflow mechanism comprises an internal stylet 50 disposed axially through the deployment tube 10. The stylet 50 has a flexible distal portion 52 term.iuiating in an outlet opening 54 adjacent the distal end of the deployment tube 10, and a proximal inlet opening 56 that communicates with an inlet port 58 in a fittiug 60 attached to the proximal end of the deployment tube. The fitting 60 includes a gas venting port 62 in fluid comxnunication with the proxunal end of the deployment tube. The gas venting port 62, in tum, includes a stop-cock, valve 64.
The operation of the second type of anti-airflow mechanism during deployment of the endovascular device 16 is shown in Figures 11 and 12.
As shown in Figure 11, with the stop-cock valve 64 open, the liquid 30 is injected into the stylet 50 through the inlet port 58 by means suchas a SUBSTITUTE SHEET (RULE 26) syiin.ge 66. The injected liquid, 30 flows through the stylet 50 and out of the stylet outlet opening 54 and into the deployment tube 10, hydxaulically pushing any entrapped air (indicated by arrows 68 in Figure 11) out of the venting port 62. When the liquid 30 beg'uYs flovving out of the venting port 62, indicating that any entrapped air has been fiilly purged from the deployment tube 10, the stop-cock valve 64 is closed (as shown in p'igure 12), allowing the continued flow of the liquid 30 to push the en.dovascular device 16 out of the retention sleeve 12, as described above.
Figures 13-17 illustrate a modification of the prefexred embodiment of th-c invention that facilitates the performance of an air purging step before the deployment tube and the endovascular device are intravascularly passed to the target site. This modification includes a modified coupling element 14' havara.g an axial air purge passage 72 through its interior. The purge passage 72 is provided through a central coupling element portion 74 contained v,+ithi.n an inner xnicrocoil segment 76 located coaxiafl.y within the coupling element 14'. The diameter of the purge passage 72 is preferably between about 0.010 mm and about 0,025 mm, for the purpose to be described below.
A deta.chm.ent zone indicator sleeve 70, attached to the distal extension.17 of the retention sleeve 12 by a bond joint 7 1, is disposed coaxially axound a pacox2naa] porta,on (approximately one-half) of the distal extension 17 of the retention sleeve 12, leaving approximately the distal half of the distal extension 17 exposed. The detachment zone indicator , sleeve 70 thus overlaps the juncture between the coupling element 14' and the distal end of the deployment tube 10, and reinforces the retention sleeve 12 at this juncture against the stresses resulting from the bending of the assembly as it is passed intravascularly to the target vascul.ar site.
Fwrrhermore, the detachment zone indicator sleeve 70 restrains the retention sleeve 70 from radial expansion. The detachment zone indicator sleeve 70 m-ay be made of polyimide or platinum. If made of polyimide, SUBSTITUTE SHEET (RULE 26) its color is advantageously one that contrasts with the color of the retention sleeve 12, so that the detachmen.t zone (i.e., the juncture between the coupling element 14' and the deployment tube 10) can be easily visualized before the intravascular deploym.ent. Xf made of platinum, the detachment zone can be visualized tivi.thin the body by X-ray or other conventional visua.lization methods. I
As shown in Figure 15, before the deployment tube 10 and the endovascular device are introduced intravascularly, as desciibed above, saline solution 30 is injected into the lumen 15 to purge air from the mechanism. The purged air exits through the purge passage, as indicated by the arrows 78 in Figure 15, and out the distal end (not shown) of the endovascular device. It may be advantageous to place the distal end of the endovascular device in a receptacle of sterile saline solution, so that the cessation of air bubbles may be noted, indicating a complete purging of air. The saline is injected at a sufficiently low pressure (such as by use of a 3 cc syringe), that the coupling element 14' is not pusbed out of the retention sleeve 12. Some of the saline solution 30 also is purged through the purge passage 72, the diameter of which is sufficiently large to allow the relatively free flow of the saline solution 30 through it.
After the endovascular device has been located in the target vascular site, as described above, a contrast agent 73 is injected into the lumen 15, as shown in Figure 16. The contrast agent 73 has a much higher viscosity than the saline solution 30 (2-10 cP vs. approximately I cP'). Therefore, the contrast agent 73 pushes the remaining saline solution 30 out through the purge passage 72. Because of the relatively high viscosity of the contrast agent 73 and the relatively small diameter of the purge passage 72, the purge passage 72 restricts (but does not completely block) the flow of the contrast agent 73 thxough it; thus, the contrast agent 73 does not pass quickly or easily through the purge passage 72. As the contrast agent 73 continues to flow into the lumen 15, pressure builds up on the proximate SUBSTITUTE SHEET (RULE 26) side of the coupling element 14', untiX it is pushed out of the retention sleeve 12, as shown in Figure 17.
Alternatively, detachment of the endovascular device can be aclii.eved by injecting saline solution at a high enough pressure or flow rate to push the coupling element 14' of the retention sleeve 12, notwithstanding the flow of the saline solution through the purge passage 72.
A modified form of the first type of anti-airflow mechanism is shown'in Figures 1S an.d.19. This modificati.on comprises a flexible, but non-compliant barrier ita, the form of a non-compliant membrane 40', preferably of PET, sealingly disposed over the distal end of the deployment tube 10. The distal end of the deployment tube 10 is covered by a thin, flexible, polymeric sheath 42', and the membrane 40' is attached to the sheath 42' by a suitable biocompatible adhesive, such as cyanoacrylate. As shown in Figure 18, the x.aembrane 40' is shaped so that it normally assumes a.first or relax.ed position, in which its central portioa extends proximally into the Iumen 15 of the deployment tube 10. The endovascular device 16 is attached to the deployment tube 10 by means of a frictional fit between the membrane 40' and the coupling element 14, the former forming a tight-fitting receptacle for the latter. The retention may be enhanced by a suitable adhesive (e.g., cyanoacryiate), T}ie coupling eiemeat 14 is thus contained within lumen 15 near the distal end of the deployment tube 10.
Figtire 19 shows the use of the modified form of the first type of anti.-airfl.ow device in the deployment of the endovascular device 16. As described above, the liquid 30 is injected into the deployment tube 10, pushing the membrane 40' distally fromi, the distal end toward a second or extended position, in which projects distally from the distal end of the deployment tube 10. As the membrane 40' is pushed toward its extended position, it pushes the coupling element 14 out of the distal end of the SUBSTITUTE SHEET (RULE 26) deployment tube 10 to deploy the endovascular device 16. Thus, the ,i,n.jected liquid 30 is coinpletely contained in a closed system, and any air that may be entrapped in the deployment tube 10 is prevented from entering the vasculature by the aixtight barrier present by the membrane 40.
Figures 20 and 21 show a modified coupling element 80 attached to the proxuri.al end of an endovascular implant 82, similar to any of the previously described implants. The coupling element 80 is preferably form.ed of one of the metals described above (preferably platinum), ox it may be made of a suitable polymer (as desczibed above). It is confi,gured as a substantiaRy cylindrical member having at least one, and preferably several, longitudinal flutes or grooves 84 extending along its exterior periphery for most of its length. Although four such grooves or flutes 84 are shown, as few as one such groove or flute may be employed, or as many as six or more. Each of the gtooves or flutes 84 forms a peripheral air purge passage aJ.oiag the exterior surface of the coupling element 80;
that is, between the exterior surface of the coupling element 80 and the retention sleeve (described above but not show;n, in these hgures).
The couplin~ element 80 terminates in an integral, substantially cylindrxcal distal extension or plug 86 of reduced diameter. The distal plug 86 is inserted into the proxiunal end of the implant 82 and attached to it by a suitable biocompatible bonding agent or adhesive 88, Alternatively, if the coupling element 80 is made of metal, the attachmen.t may be by soldering or welding.
Figure 22 iliuslxates a device having another modi.fied coupiiug element 90 attached to the proximal end of an implant 92. This coupling el.ement 90 may also, be made of one of the above-described metals (preferably platinum), or one of the above-described polymers. It is con,figuTed as a substantially cylin.drical member having a helical groove or flute 94 fozined in its exterior surface. The flute or groove 94 forms a SUBSTITUTE SHEET (RULE 26) peripheral aix purge passage along the exte.rio.r surface of the coupling element 90, as do the longitudinal flutes or grooves of the embodiment of Figures 20 and 21. The coupling element 90 includes an integral distal extension or plug 96, of reduced diameter, that is inserted into the proximal end of the implant 92 and attached to it by means of a suitable biocompatible bonding agent 98 (e.g., solder or adhesive) or by welding, depending on the material of which the coupling element 90 is made.
The longitudinal flutes or grooves 84 (in the coupling element 80) and helical flute or groove 94 (in the coupling element 90) provide fluid passages for purging air and saline solution, as does the internal axial passage 72 in the embod.iment descr~,`bed above and shown in Figures 13-17, Accordingly, for this purpose, the flutes or grooves 84, 94 are dimensioned to allow the free passage of a low viscosity fluid (such as saliu.e solution), while allowing only a relatively slow passage of a relatively high viscosity fluid (such as a typical contrast agent). Thus, as described above, the pressure on the upstream side of the coupling element is allowed to build up when the contrast agent is injected until the coupling element is d3slodged from the retention sleeve. Alternatively, a low viscosity fluid, such as saline solution, may be injected at a sufficiently high flow rate or pressure to push the coupling element out of the retention sleeve, notwithstanding the flow of the saline solution through the purge passage.
' Furthermore, the fluted oz' grooved surface of the coupling elements 80, 90 enhances the frictional engagement between the coupling element and the retention sleeve. To provide even 1'urther enhancement of this frictional engagement, the surface of the coupling element and/or the interior surface of the retention sleeve may be treated with a stiitable biocompatible coating or surface treatment (as wilt be known to those skilled in the pertinent arts), or the coupling element may be forrned with a micro-textured surface, in accordance with known techniques.

SUBSTITUTE SHEET (RULE 26) It will thus be appreciated that the present invention provides a coupling mechanism that yields a secure attachment of the endovascular device to a deployment instrumen.t d.urin.g the deployment process, whi.le also allowing for the easy and reliable detachment of the endovascular device once it is properly situated with respect to the target site. The couplita.g mechanism of the present invention also provides urYproved control of the endovascui.ar device during deployment, and specificall.y it allows the endovascular device to be easily repositioned before detachment. In addition, the coupling mechanism of the present invention advantageously includes an effective mechanism for pxecluding airflow into the vasculature during the deployment process. Furthermore, the couplin.g mechanism of the present invention is readily adaptable for use with a wide variety of endovascular devices, without adding appreciab.iy to their costs.
Although a number of specific embodiments are descri.~6ed above, it should be appreciated that these eznbodiments are exemplary only, "
particularly in ternis of materials and dimensions. For example, many suitable matezla.l.s for both the coupling element 14 and the retention sleeve 12 may be found that will yield satisfactory performance in pard.cLlar applications. Also, the exemplary dimensions given above maybe changed to suit different specific cli.nical needs. These modifications and others that may suggest themsel.ves to those skilled in the perCment arts are deemed to be within the spirit and scope of the present invention, as defined in the claims that follow.

SUBSTITUTE SHEET (RULE 26)

Claims (7)

Claims

1. A deployment mechanism for deploying a filamentous endovascular device having a proximal end, comprising:

an elongate, flexible, hollow deployment tube having an open proximal end, a distal section terminating in an open distal end, and a lumen defined between the proximal and distal ends;
a retention sleeve fixed around the distal section of the deployment tube and having a distal extension extending a short distance past the distal end of the deployment tube; and a coupling element attached to the proximal end of the endovascular device and releasably held within the distal extension of the retention sleeve proximate the distal end of the deployment tube so as to be displaceable from the retention sleeve in response to fluid pressure applied to the coupling element through the lumen and the distal end of the deployment tube;
wherein the coupling element has an exterior periphery and a purge passage that is formed on the exterior periphery and that is dimensioned so as to provide a substantial restriction to the flow therethrough of a fluid having a viscosity that is substantially greater than that of saline solution.

2. The deployment mechanism of Claim 1, wherein the coupling element is formed from a non-hydrophilic material.

3. The deployment mechanism of Claim 2, wherein the retention sleeve is made of a fluorocarbon and the coupling element is made of metal.

4. The deployment mechanism of Claim 1, wherein the purge passage extends longitudinally along the exterior periphery of the coupling element.

5. The deployment mechanism of Claim 1, wherein the purge passage is a first purge passage, and wherein the coupling element is formed with at least a second purge passage extending longitudinally along the exterior periphery of the coupling element.

6. The deployment mechanism of Claim 1, wherein the purge passage is helical.

7. The deployment mechanism of Claim 1, wherein the purge passage is dimensioned to provide a substantial restriction to the flow therethrough of a fluid having a viscosity greater than or approximately equal to 2 cP.