Patent Publication Number: US-2013253570-A1

Title: Apparatus and methods for filtering emboli during precutaneous aortic valve replacement and repair procedures with filtration system coupled to distal end of sheath

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority of U.S. Provisional Application Ser. No. 61/613,896, filed Mar. 21, 2012. 
    
    
     FIELD OF THE INVENTION 
     This application generally relates to filtering emboli during interventional procedures, particularly percutaneous aortic valve replacement and repair procedures. 
     BACKGROUND OF THE INVENTION 
     The recent development of prosthetic valves that can be placed through a catheter into the heart without thoracotomy represents a significant advance in the field of cardiovascular medicine. Early results are very promising and overall reduction in mortality has been achieved with transcatheter aortic valve implantation (TAVI) in high surgical risk patients when compared to medical therapy. One of the limitations for wide acceptance of this technology is the inherent risk of embolic complication during valve access, dilation and implantation. For example, each guidewire, introducer, balloon, cutter, or prosthetic valve that is introduced into the heart via the peripheral arteries and the ascending aorta may inadvertently dislodge one or more emboli, e.g., fragments of unstable plaque, irregular atherosclerotic calcified lesions, or mural thrombus, from the aortic arch, the area surrounding the aortic valve, or the chambers of the heart. The great vessels, which branch off the greater curve of the aortic arch, may transport such emboli to vulnerable locations like the eyes and brain causing stroke or blindness. In addition embolic material can flow past the arch and occlude vessels to the spinal cord causing paralysis, to the bowel causing life threatening mesenteric ischemia/infarction, or to the renal vessels causing kidney failure, for example. 
     Numerous filters have been developed with the purpose of preventing emboli from entering the great vessels, particularly the carotid artery. For example, U.S. Pat. No. 8,062,324 to Shimon et al. describes a filter that is supported by a skeleton having a horizontal plane, and that is pressed against the upper portion of the aortic arch by one or more bows so as to filter any blood passing into the great arteries. Shimon describes that the filter may be inserted using a catheter. However, Shimon does not disclose how to remove the filter in such a manner as to prevent filtered emboli from re-entering the blood stream, nor so as to prevent additional emboli from being dislodged by the edges of the skeleton or the bows during removal. Additionally, if additional devices are percutaneously introduced via the ascending aorta, such devices may scrape against the filter and thus potentially cause trauma to the aortic wall or dislodge emboli from the filter. In any such device designed to deflect particles by resting on the greater curve of the arch there is also the issue of device interaction and entanglement since the typical valve is a high profile stiff catheter that will have significant outward bias along the greater curve during advancement across the arch. This type of interaction could result in marriage of the devices together with catastrophic consequences as well as product incompetence if it folds up during catheter exchanges. 
     U.S. Pat. No. 8,052,713 to Khosravi et al. describes an apparatus for filtering emboli from the ascending aorta, that includes a thin, flexible, blood permeable sac having a mouth defined by a support hoop affixed to a guide wire, and a relatively short delivery sheath with a tapered proximal nose and a square distal end. Khosravi describes that the sac and support hoop may be disposed in the delivery sheath, which may be introduced to the ascending aorta via a guidewire. Khosravi describes that the sac may be deployed in the ascending aorta by retracting the support hoop proximally relative to the delivery sheath (in the direction away from the tapered nose), which draws the hoop out of the sheath and allows the sac to open across the aorta, proximal of the brachiocephalic trunk. Khosravi describes that the sac may be retrieved by advancing the support hoop back into the delivery sheath to collapse the sac, and then retracting the delivery sheath back down the ascending aorta. However, the square distal end of the delivery sheath may scrape the aortic arch as it is retrieved and thus potentially loosen additional occlusive material, such as emboli, from the aortic arch. Additionally, because the sac spans the aorta when deployed, the sac may impede the physician&#39;s ability to percutaneously introduce other devices to the aorta because such devices may become trapped in the sac, or alternatively may create a gap between the edge of the sac and the aortic wall, thus providing an avenue for emboli or other occlusive material to bypass the sac. 
     Thus, there is a need in the art for embolic filters that may be deployed in the ascending aorta, that safely sequester any filtered occlusive material, such as emboli or thrombus, are shaped to avoid dislodging additional when retrieved, provide protection during all stages of the procedure and allow percutaneous valve replacement or repair procedures to be performed via the peripheral arteries and the ascending aorta without increasing the profile of the delivery sheath, which already may be at the limits of femoral vessel tolerance. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention provide apparatus and methods for filtering occlusive material such as emboli or thrombus during percutaneous valve replacement and repair procedures. Such apparatus and methods may safely sequester any filtered emboli, are shaped to avoid dislodging additional emboli when retrieved, are fully compatible with percutaneous valve replacement or repair procedures performed via the peripheral arteries and the ascending aorta, and do not require use of a delivery sheath larger than those already adopted for such percutaneous procedures (e.g., 18 French). 
     Under one aspect of the present invention, an apparatus for filtering emboli during a percutaneous aortic valve replacement or repair procedure comprises a sheath and a filter. The sheath has proximal and distal ends and a lumen therebetween. The distal end is configured for introduction into the aortic arch via the peripheral arteries and ascending aorta, while the proximal end being configured to be disposed outside of the body. The lumen is sized to permit percutaneous aortic valve replacement or repair therethrough. The filter has a frame and an emboli-filtering mesh attached to the frame. The frame has an inlet and an outlet. The inlet is configured to substantially span the aortic arch in a region between the aortic valve and the great arteries. The outlet is coupled to the distal end of the sheath without leaving any gaps through which emboli could pass and without obstructing the lumen at the distal end of the sheath. 
     In some embodiments, a release line is coupled to the frame of the filter and passes out of the body through the lumen, and is retractable from outside of the body to detach the outlet of the filter from the distal end of the sheath. A groove may be defined in the lumen of the sheath and configured to receive the release line. A snare may be coupled to the frame of the filter and pass out of the body through the lumen, and may be retractable from outside of the body to draw the filter into the lumen. A groove may be defined in the lumen of the sheath and configured to receive the snare. 
     In an alternative embodiment, a snare may be coupled to the frame of the filter and pass out of the body through the lumen, and may be retractable from outside of the body to both detach the outlet of the filter from the distal end of the sheath and to draw the filter into the lumen. 
     In some embodiments, the frame comprises a distal, generally cylindrical ring defining the inlet and/or a proximal, generally cylindrical ring defining the outlet. The frame further may comprise a plurality of struts between the rings defining the inlet and the outlet. 
     In some embodiments, the sheath has an inner diameter of 18 French or less. The outlet of the filter may have an outer diameter that is greater than the inner diameter of the sheath. Alternatively, the outlet of the filter may have an inner diameter that is greater than an inner diameter of the sheath. 
     In some embodiments, the filter has a compressed state and a deployed state. The apparatus may further include a guidewire and an introducer for use in percutaneously introducing the filter and the distal end of the sheath into the aortic arch. The introducer may include a tapered distal nose, a proximal end, a guidewire lumen configured to receive the guidewire, and a recess between the distal nose and the proximal end. The recess may be configured to receive the filter in the compressed state. The introducer may be configured for insertion within the lumen at the distal end of the sheath when the filter is expanded and coupled distally. The filter may be crimped into the recess during the manufacturing process and retained the compressed state within the recess. The introducer, the filter, and the distal end of the sheath may be percutaneously introducible into the aortic arch by pushing the introducer and sheath in their married position (or coupled together) over the guidewire. A control wire may be coupled to the introducer, and the control wire may be configured to advance the introducer while the sheath is maintained in position, allowing for slow deliberate expansion of the filter and avoiding traumatic sudden expansion and advancement out the end of the sheath. The introducer may be retrievable through the outlet of the filter and the lumen of the sheath after the filter expands to the deployed state by retracting the control wire. A portion of the sheath may be pre-curved to conform to the aortic arch, and the introducer may straighten the pre-curved portion of the sheath when inserted therein. 
     Under another aspect of the present invention, a method of filtering emboli during a percutaneous aortic valve replacement or repair procedure may include providing a sheath having proximal and distal ends and a lumen therebetween; and providing a filter coupled to the distal end of the sheath. The filter may have a compressed state and a deployed state, a frame, and an emboli-filtering mesh attached to the frame. The frame may have an inlet and an outlet, the inlet being configured to substantially span the aortic arch in a region between the aortic valve and the great arteries in the deployed state. The outlet of the filter is coupled to the distal end of the sheath within the aortic arch without leaving any gaps through which emboli could pass and without obstructing the lumen at the distal end of the sheath. The filter may be advanced through the previously positioned sheath via an introducer with a recess that will accommodate the filter and a control wire mechanism coupled to the introducer may be used to control expansion during deployment of the filter. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  illustrates a perspective view of a catheter for use in percutaneous aortic valve replacement or repair including an embolic filter and sheath assembly in an expanded configuration, according to some embodiments of the present invention. 
         FIG. 1B  illustrates a detailed perspective view of the embolic filter and sheath assembly of  FIG. 1A . 
         FIG. 2A  illustrates a perspective view of an exemplary coupling/release mechanism that may be used with the embolic filter and sheath assembly of  FIGS. 1A-1B . 
         FIG. 2B  illustrates a perspective view of the distal end of an exemplary sheath that may be used with the embolic filter and sheath assembly of  FIGS. 1A-1B . 
         FIG. 2C  illustrates a plan view of a pre-curved sheath that optionally may be used with the embolic filter and sheath assembly of  FIGS. 1A-1B . 
         FIGS. 3A-3F  illustrate cross-sectional views of an introducer that may be used with the embolic filter and sheath assembly of  FIGS. 1A-1B . 
         FIG. 4  illustrates steps in a method of using the embolic filter and sheath assembly of  FIGS. 1A-1B  and the introducer of  FIGS. 3A-3F  in an aortic arch during a percutaneous procedure. 
         FIGS. 5A-5C  illustrate cross-sectional views of the embolic filter and sheath assembly of  FIGS. 1A-1B  and the introducer of  FIGS. 3A-3F  in an aortic arch during various steps of the method of  FIG. 4 . 
         FIGS. 6A-6C  illustrate perspective views of an exemplary release mechanism that may be used to remove the embolic filter and sheath assembly of  FIGS. 1A-1B . 
         FIGS. 7A-7I  illustrate perspective views of another exemplary release mechanism that may be used to remove the embolic filter and sheath assembly of  FIGS. 1A-1B . 
         FIGS. 8A-8C  illustrate perspective views of another exemplary release mechanism that may be used to remove the embolic filter and sheath assembly of  FIGS. 1A-1B . 
         FIGS. 9A-9D  illustrate perspective views of the operation of an exemplary release mechanism that may be used to remove the embolic filter and sheath assembly of  FIGS. 1A-1B . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the invention provide embolic filters that readily may be used during percutaneous aortic valve replacement and repair procedures and that overcome the above-noted shortcomings of previously-known systems. The inventive filters may be coupled to the distal end of a sheath suitable for percutaneous delivery into the aorta, e.g., an 18 F sheath, and then compressed and mounted on an introducer that has a tapered nose and is disposed in the distal end of the sheath. The sheath, introducer, and compressed filter then are introduced to the aortic arch via the peripheral arterial system (e.g., femoral artery) and ascending aorta. The filter then is deployed from the distal end of the sheath by advancing the introducer relative to the sheath such that the filter expands to a deployed configuration at a location upstream of the great arteries, and the introducer then removed via the lumen of the sheath. The filter is securely coupled to the distal end of the sheath in such a manner that the full lumen of the sheath may be used for additional percutaneous procedures, e.g., to percutaneously introduce a guidewire, introducer, balloon, cutter, and/or prosthetic valve to the heart via the sheath. Then, when the percutaneous procedure is complete and any other devices have been removed from the lumen of the sheath, a release line may be retracted from outside of the body to detach the filter from the end of the sheath, and a snare on the filter may be used to close the filter and retract the filter and any captured emboli into the lumen of the sheath after venting the sheath. The sheath then may be removed by refracting it from the ascending aorta and peripheral arterial system. As such, the inventive filters do not interfere with other percutaneously introduced devices, are compatible with 18 French sheaths, safely sequester filtered emboli when removed, and are shaped to avoid dislodging additional emboli when removed. 
     First, an overview of a catheter system including the inventive embolic filter and sheath assembly will be described. Then, further details will be provided on the construction of the sheath and embolic filter, respectively. Lastly, some alternative embodiments will be described. 
       FIG. 1A  illustrates percutaneous catheter  100  including sheath  110 , filter  120 , and handle  130 . Sheath  110  generally is in the form of an elongated tube having proximal end  111  and distal end  112 , with lumen  113  therebetween. Preferably, sheath  110  has a diameter suitable for percutaneous use, e.g., has an inner diameter of 18 French or smaller. In some embodiments, sheath  110  includes reinforcing rings of metal or polymer to inhibit collapse of the sheath when curved around the aortic arch. 
     Filter  120  includes a frame and an emboli-filtering mesh attached to the frame. The frame defines an inlet and an outlet of filter  120 . Preferably, the inlet has lateral dimensions approximately equal to those of the aortic arch between the aortic valve and the great arteries, where the filter will be deployed, so that the emboli-filtering mesh will filter substantially all of the blood passing through the aorta and remove emboli therefrom. The outlet of filter  120  is detachably coupled to distal end  112  of sheath  110 , preferably without any gaps therebetween that would allow emboli to pass. The outlet of filter  120  also preferably has an inner lumen with a diameter that is at least as large as the inner diameter of sheath  110 , so that filter  120  does not obstruct the lumen at the distal end of the sheath, thus allowing a physician to perform percutaneous procedures via the sheath without interference from filter  110 . 
     Handle  130  is coupled to proximal end  111  of sheath  110 , and includes release line  131  via which filter  120  may be detached from distal end  112  of sheath  110  while deployed, snare control  132  via which filter  120  may be retrieved by retracting the filter into the lumen at the distal end  112  of sheath  110 , and various additional ports and passages, generally designated  139 , via which a physician may introduce additional percutaneous devices. Handle  130  also may include a controller line (not shown) for controlling an introducer that may be used to deploy the filter, such as described below with reference to  FIGS. 3A-3C . 
     Note that as used herein with reference to elements for insertion into the body, the term “distal” refers to the end that is inserted into the body first, e.g., the leading end of sheath  110  or filter  120  during advancement into the body, whereas the term “proximal” refers to the opposite end. 
       FIG. 1B  illustrates a perspective view of an assembly including filter  120  and distal end  112  of sheath  110 . Filter  120  includes frame  121  and mesh  122  attached thereto, e.g., by sutures, adhesives, dip molding, laser bonding, sandwich layers on each side of the struts melted or glued together, heat setting or the like. In the illustrated embodiment, frame  121  includes first and second generally cylindrical rings  123 ,  124 . First ring  123  defines the inlet of filter  120 , which as noted above preferably is of similar dimension to the ascending aorta in the region where the filter is to be deployed, e.g., between the aortic valve and the great arteries, so as to securely seat against the aortic wall and prevent emboli from slipping past the filter. Second ring  124  defines the outlet of filter  120 , which is of similar dimension to distal end  112  of sheath  110 . Specifically, second ring  124  is sized such that it does not obstruct lumen  113  of sheath  110  at distal end  112 , so that the physician may conduct percutaneous procedures through lumen  113  without interference from filter  120 . For example, second ring  124  may have an inner diameter that is equal to, or larger than, the inner diameter of lumen  113 , and/or may have an outer diameter that is larger than the inner diameter of lumen  113 . 
     First and second rings  123 ,  124  preferably are formed of a shape memory material, e.g., a metallic alloy such as Nitinol, stainless steel, MP35N, elgiloy or a shape memory polymer such as polyurethane or a block copolymer thereof, polyethylene terephthalate or a block copolymer thereof, polyethylene oxide or a block copolymer thereof, and the like. First and second rings  123 ,  124  respectively include struts  125 ,  126 , which may be sinusoids, zigzags, or other suitable shape that permits rings  123 ,  124  to be radially compressed into a compressed state for delivery and to return to a deployed state when expanded in the aortic arch. Optionally, frame  121  includes struts  127  that extend between first and second rings  123 ,  124 . Struts  127  may have any suitable shape, including linear, sinusoids, or curves, and may extend within the interior surface of mesh  122  and/or may extend outside of the exterior surface of mesh  122 . In other embodiments, only mesh  122  extends between first and second rings  123 ,  124 , allowing the rings to freely move relative to one another so as to lessen the effect of blood-flow-induced torque that otherwise may cause filter  120  to tilt relative to sheath  110  and thus form a gap through which emboli may pass. 
     Mesh  122  preferably covers the entire outer surface of filter  120 , including first and second rings  123 ,  124 , such that substantially all of the blood in the aorta flows through filter  120  with no gaps. Mesh  122  has a surface area and pore size suitable to allow a sufficient volume of blood to pass therethrough to maintain the patient&#39;s blood pressure in a normal range, and also to avoid pressure buildup that otherwise may rupture mesh  122 . Mesh  122  may include any suitable material known in the art, including a fabric, polymer, or flexible metal having pores of appropriate size to filter emboli having diameters of, e.g., 20 μm or greater, or 50 μm or greater, or 100 μm or greater, or 150 μm or greater, or 200 μm or greater. In one illustrative embodiment, mesh  122  is a polyurethane film of thickness 0.0003 inches to about 0.0030 inches and having holes defined therethrough, e.g., circular, square, or triangular holes in a suitable size and density to permit substantially the entire aortic blood flow to pass therethrough without a detrimental amount of resistance. 
       FIG. 2A  illustrates an exemplary coupling/release mechanism that may be used to couple and subsequently detach filter  120  from distal end  112  of sheath  110  and pull the filter into lumen  113  of the sheath. Second ring  124  of filter  120  is coupled to a release line  131  that passes out of the patient&#39;s body through sheath  110  via lumen  135  and into handle  130  as illustrated in  FIG. 1A . Release line  131  is coupled to, or includes, a wire or suture  133  that loops through sinusoids  126  of second ring  124 , as well as through sheath elements  134  which are embedded in distal end  112  of sheath  110 . Tension in wire/suture  133  causes second ring  124  to securely seat against distal end  112 . As described in greater detail below with reference to  FIGS. 6A-6C , retraction of release line  131  from outside the body may break wire/suture  133 , releasing such tension and detaching ring  124  from distal end  112 . In some embodiments, wire/suture  133  and/or release line  131  is formed of a relatively stiff material such as stainless steel or a shape memory alloy, so as to maintain a relatively large amount of tension to retain second ring  124  against distal end  112 . In other embodiments, wire/suture  133  and/or release line  131  may be formed of a relatively flexible material such as fiber or polymer, so that wire/suture  133  may easily be broken, thus detaching ring  124  from distal end  112 . Sheath elements  134  may be formed of a relatively stiff material such as stainless steel or a shape memory alloy. Other possible configurations for sheath elements  134  are described further below with reference to  FIGS. 7B-7C . Note also that instead of looping wire/suture  133  through sinusoids  126  as described with reference to  FIG. 2A , a fabric ring may be coupled to second ring  124  and wire/suture  133  woven therethrough instead, such as described further below with reference to  FIGS. 7A-7I . 
     As illustrated in  FIG. 2A , second ring  124  also is coupled to snare  132 , which is coupled to, or includes, wire  135  that loops about second ring  124  and passes out of the patient&#39;s body through groove  136  and into handle  130  as illustrated in  FIG. 1A . Retracting snare  132  via handle  130  first causes wire  135  to radially contract second ring  124 , and then pulls filter  120  into lumen  113  sheath  110  for removal from the body. Such a process is described further below with reference to  FIGS. 6A-6C . In some embodiments, wire  135  and/or snare  132  is formed of a relatively stiff material such as stainless steel or a shape memory alloy, so as to impose relatively large compressive forces on second ring  124 . 
       FIG. 2B  illustrates distal end  112  of sheath  110  in greater detail. Release line  131  (not shown in  FIG. 2B ) may be disposed within lumen  135 , and snare  132  (not shown in  FIG. 2B ) may be disposed within groove  136  defined in the inner surface  118  of sheath  110 . Such an arrangement may inhibit interference between release line  131  or snare  132  and any devices that may be percutaneously introduced to the patient via sheath  110 . In particular, groove  136  may be of such a depth that snare  132  does not reduce the effective inner diameter of lumen  113 , thus allowing the physician to make full use of lumen  113  without obstruction during a percutaneous procedure. Alternative embodiments described below with reference to  FIGS. 8A-9D  use a combined snare/release mechanism that uses only a single groove through which filter  120  may be detached from distal end  112  of sheath  110  and pulled into lumen  113 , thus further simplifying construction of sheath  110  and reducing the possibility of interference with instruments during the percutaneous procedure. 
     Optionally, sheath  110  is pre-curved to follow the curve of the patient&#39;s aortic arch, such as illustrated in  FIG. 2C  where bend  119  is disposed proximal of distal end  112 . Pre-curving sheath  110  as such may help to reduce tension the aortic arch may otherwise place on sheath  110  and/or filter  120  when deployed therein. Preferably, inserting introducer  300  (described further below with reference to  FIGS. 3A-3F ) into sheath  110  temporarily straightens bend  119 ; later, when introducer  300  is removed from sheath  110 , bend  119  returns and generally follows the curve of the patient&#39;s aortic arch. 
       FIG. 3A  illustrates an introducer  300  that may be used to introduce and deploy filter  120  into a patient&#39;s aortic arch. Introducer  300  includes tapered distal nose  301 , proximal end  302 , a guidewire lumen  303  configured to receive a guidewire (not illustrated in  FIG. 3A ), and a recess  304  between the distal nose and proximal end having cover  305  disposed thereover. Recess  304  is configured to receive filter  120  in a compressed state. For example, as illustrated in  FIG. 3B , compressed state filter  120 ′ may include radially compressed first ring  123 ′, radially compressed second ring  124 ′, folded mesh  122 ′, and compressed struts  127 ′. Section  302  of introducer  300  may be tapered as shown to accommodate tilting of compressed second ring  124 ′ caused by coupling of that ring to distal end  112  of sheath  110 . Recess  304  of introducer  300  may be configured to have a length approximately equal to the length of compressed state filter  120 ′, and an outer diameter (defined by the outer surface of cover  305 ) suitable for percutaneous insertion. Cover  305  may retain sliding of filter  120 ′ in the proximal or lateral directions. Radiopaque markers (not shown) may be provided on introducer  300  and/or on filter  120 / 120 ′ so as to assist the physician in properly positioning introducer  300  and filter  120 / 120 ′ in the aortic arch. 
     As illustrated in  FIG. 3B , when introducer  300  is inserted into lumen  113  of sheath  110 , tapered nose  301  and cover  305  provide a smooth surface when introducer  300 , compressed state filter  120 ′, and distal end  112  of sheath  110  are percutaneously advanced into the aortic arch by pushing introducer  300  over the guidewire (not illustrated) via sheath  110 . Preferably, introducer  300  also includes control line  306  which is coupled to proximal end  302  and which passes out of the body via lumen  113  of sheath  110  and an appropriate port (not illustrated). Control line  306  may be used to advance introducer  300  while sheath  110  is held in place so as to allow compressed state filter  120 ′ to expand into the deployed state, e.g., filter  120  illustrated in  FIGS. 1A-1B . 
     For example,  FIG. 3C  illustrates the relative positioning of introducer  300 , filter  120 , and sheath  110  when introducer  300  is partially advanced out of lumen  113  of sheath  110  by advancing control line  306  relative to sheath  110 . As introducer  300  is moved distally, partially deployed struts  127 ″ of partially deployed filter  120 ″ bow outwardly as the struts are no longer retained beneath cover  305 . At the illustrated stage of deployment, first ring  123 ′ of filter  120 ″ is retained in the compressed state within recess  304  and beneath cover  305 . However, second ring  124  of filter  120 ″ is no longer in the compressed state because it is no longer within recess  304  or beneath cover  305 . 
     As illustrated in  FIG. 3D , when introducer  300  is further advanced out of lumen  113  of sheath  110  via control line  306 , first ring  123  of filter  120  opens to a fully deployed state, as do struts  127 , because first ring  123  is no longer within recess  304  or beneath cover  305 . Then, as illustrated in  FIG. 3E , introducer  300  may be removed via lumen  113  by retracting control line  306 . Further details on the use of introducer  300  to deploy filter  120  are described in greater detail below with reference to FIGS.  4  and  5 A- 5 C. 
     A method of percutaneously deploying filter  120  and distal end of sheath  112  in the aortic arch for filtering emboli during a percutaneous procedure will now be described with reference to  FIG. 4 , which illustrates steps in method  400 , and  FIGS. 5A-5C , which illustrate the relative positions of components of apparatus  100  and a patient&#39;s heart. 
     Method  400  includes providing a sheath having proximal and distal ends and a lumen therebetween (step  410 ), for example sheath  110  illustrated in  FIGS. 1A-2C . 
     A filter is also provided having a compressed state and a deployed state, a frame having an inlet sized to span the aortic arch in the deployed state and an outlet, and an emboli-filtering mesh attached to the frame (step  420 ), for example filter  120 / 120 ′ illustrated in  FIGS. 1A-1B . 
     The filter then may be coupled to the distal end of the sheath (step  430 ), e.g., with a wire/suture such as illustrated in  FIG. 2A . The filter then may be compressed within the recess of an introducer (step  440 ), e.g., as described above with reference to  FIGS. 3A-3F . 
     The introducer, the filter, and the distal end of the sheath then may be introduced into the aortic arch (step  450 ). For example, introducer  300  may be inserted into lumen  113  at distal end  112  of sheath  110 , and compressed state filter  120 ′ may be crimped into recess  304  of the introducer and covered with cover  305 . Then, as illustrated in  FIG. 5A , assembly  300 ,  120 ′,  112  (filter  120 ′ not shown in  FIG. 5A ) may be percutaneously advanced into aortic arch  510  of a patient&#39;s heart  500  over guidewire  510  through guidewire lumen  303  of introducer  300 , by pushing on the proximal end  111  of sheath  110  from outside the patient&#39;s body. Assembly  300 ,  120 ′,  112  (filter  120 ′ not shown in  FIG. 5A ) is preferably pushed to a location in aortic arch  501  that is between aortic valve  502  and great arteries  503 . 
     Referring again to  FIG. 4 , the filter then may be expanded from the compressed state to the deployed state within the aortic arch (step  460 ). For example, as illustrated in  FIG. 5B , introducer  300  may be advanced from outside the patient&#39;s body, e.g., using control line  306  described above with reference to  FIGS. 3A-3F , while the position of sheath  110  is maintained. Such advancement of introducer  300  allows compressed state filter  120 ′ to expand to deployed state filter  120  which, as illustrated in  FIG. 5B , substantially spans the aortic arch between aortic valve  502  and the great arteries  503 . In particular, control line  306  maintains the relative positioning of compressed second (proximal) ring  124 ′ of compressed filter  120 ′ and introducer  300 , thus facilitating slow, deliberate expansion of filter  120  as sheath  110  is retracted and avoiding traumatic sudden expansion of filter  120  out of sheath  110 . Introducer  300  then may be removed via lumen  113 , e.g., by retracting control line  306  from outside the body, leaving the lumen of sheath  110  unobstructed, as illustrated in  FIG. 5C . 
     Referring again to  FIG. 4 , a percutaneous procedure may be performed on the aortic valve through the lumen of the sheath ( 470 ). Such percutaneous procedures may involve, for example, percutaneously introducing a guidewire, introducer, balloon, cutter, and/or prosthetic valve to the heart through sheath  110  and filter  120  as illustrated in  FIG. 5C . For example, the physician may implant a prosthetic aortic valve that is specifically configured for percutaneous delivery via an 18 French sheath, such as the COREVALVE™ device manufactured by Medtronic, or the SAPIEN™ device manufactured by Edwards Lifesciences. Advantageously, filter  120 , tensioning lines  131 , and snare  132  do not obstruct lumen  113  of sheath  110 , so that the physician may perform any desired percutaneous procedure using the full diameter of sheath  110 . Filter  120  captures any emboli that may be freed from the region surrounding the aortic valve during such procedure, thus reducing the patient&#39;s risk of stroke from embolization. 
     An illustrative method of removing filter  120  and any filtered emboli from the body will now be described with reference to  FIGS. 6A-6D . As illustrated in  FIG. 6A , release line  131  may be retracted from outside the body, causing breakage of suture/wire  133 ′ and allowing free end  133 ″ of broken suture/wire  133 ′ to come loose from sheath elements  134  and sinusoids  126  of second ring  124 , thus detaching filter  120  from sheath  110 . Then, as illustrated in  FIG. 6B , retraction of snare  132  in the proximal direction causes wire  135  to radially compress proximal end  129  of second ring  124 , resulting in partially compressed second ring  124 ′ having a generally hourglass shape as illustrated in  FIG. 6B , and to begin to retract partially compressed second ring  124 ′ into lumen  113  of sheath  110 . Further retraction of snare  132  in the proximal direction pulls proximal end  129  of second ring  124 ″&#39; fully into lumen  113  of sheath  110  as illustrated in  FIG. 6C . Further retraction of snare  132  in the proximal direction retracts the entirety of filter  120 , including any emboli therein, into a compressed removal state within lumen  113  of sheath  110 . Sheath  110  then may be withdrawn from the body by pulling the sheath in the proximal direction. Advantageously, sheath  110  does not have any sharp corners that would potentially loosen emboli during such removal. Additionally, any emboli within filter  120  advantageously remain within lumen  113  during the removal process, so as to further reduce the patient&#39;s chance of stroke due to embolization. 
       FIGS. 7A-7I  illustrate an alternative mechanism that may be used to release filter  120  from sheath  110  prior to retraction with snare  132  into lumen  113 . Referring to  FIG. 7A , second ring  124  of filter  120  is coupled via sutures, adhesive, or the like to fabric ring  701 , which is a ring of flexible, biocompatible fabric having a length sufficiently short to avoid folding-in of the fabric during device or introducer retraction. Wire/suture  733  is stitched or woven through fabric ring  701  and sheath elements  734 , which secures filter  120  to distal end  112  of sheath  110 . Sheath elements  734  may be closed arches having both ends embedded in distal end  112  of sheath  110 , such as illustrated in  FIGS. 7A-7B , or may have a construction similar to the eye of a needle, with an aperture spaced some distance away from distal end  112 , such as illustrated in  FIG. 7C . 
     The two ends of wire/suture  733  are coupled to locking mechanism  732 , which in the illustrated embodiment includes a “J”-shaped hook  735  that is coupled to release line  731  within lumen  736 . Hook  735  may be formed of a shape memory alloy such as described above. As can be seen in  FIG. 7A , a first end of wire/suture  733  is coupled to one side of hook  735 , which is disposed within pocket  737  defined within distal end  112  of sheath  110 , while the second end of wire/suture  733  is coupled to the other side of hook  735 . As such, hook  735  securely retains the ends of wire/suture  733  and thus maintains coupling between filter  120  and sheath  110  until hook  735  is retracted via release line  731 . Further details on coupling wire/suture  733  to hook  735  are provided further below with reference to  FIGS. 7D-7G , and further details on detaching filter  120  from sheath  110  using wire/suture  711 , hook  735 , and release line  731  are provided further below with reference to  FIGS. 7H-7I . 
     Referring now to  FIG. 7D , hook  735  includes short end  738 , and long end  739 . Short end  738  may be moved relative to distal end  112  of sheath  110  by pushing or retracting release line  731 , which may be integrally formed with hook  735 , e.g., using a shape memory alloy. As illustrated in  FIG. 7E , first end  741  of wire/suture  733  may include a loop through which short end  738  of hook  735  fits, while second end  742  of wire/suture  733  may include a loop through which long end  739  of hook  735  fits.  FIG. 7F  illustrates motion of hook  735  in the proximal direction when release line  731  is partially retracted, during which short end  738  of hook  735  becomes disposed in pocket  737  defined at distal end  112  of sheath  110 . As illustrated in  FIG. 7G , such motion of hook  735  secures the first and second ends  741 ,  742  of wire/suture  733 , which as discussed above securely couples filter  120  to sheath  110 .  FIG. 7H  illustrates further motion of hook  735  in the proximal direction when release line  731  is more fully retracted, during which short end  738  of hook  735  is pulled out of pocket  737  and drawn into release line lumen  736 . As illustrated in  FIG. 71 , such motion of hook  735  releases the first and second ends  741 ,  742  of suture, which as discussed above detaches filter  120  from sheath  110 . 
       FIGS. 8A-8C  illustrate another alternative mechanism that may be used to release filter  120  from sheath  110  prior to retraction into lumen  113 . In this embodiment, a combined release/retraction mechanism permits both functions to be performed using only a single mechanism, thus simplifying the design of sheath  110  by obviating the need to provide multiple separate grooves or lumens to control release and retraction of filter  120 . Referring to  FIG. 8A , second ring  124  of filter  120  is coupled via sutures, adhesive, or the like to fabric ring  801 , which is a ring of flexible, biocompatible fabric having a length sufficiently short to avoid folding-in of the fabric during device or introducer retraction. Wire/suture  833  is stitched or woven through fabric ring  801  and sheath elements  834 , which secures filter  120  to distal end  112  of sheath  110 . Wire/suture  833  passes through locking mechanism  832 , which in the illustrated embodiment includes an release segment  835  configured to break wire/suture  833  by applying electrical current or voltage thereto. 
     As illustrated in  FIGS. 8B-8C , in which filter  120  and sheath  110  are not shown, electrical current or voltage may be passed to release segment  835  along modified snare line  132 ′, which is coupled to current generator  836 . Current generator  836  may include a safety latch or cover  837  to protect against inadvertent application of electrical current to release segment  835 . Release segment  835  includes first and second terminals  838 ,  839 , across which electrical current or voltage may be applied by disabling safety latch or cover  837  and actuating current generator  836  such as illustrated in  FIG. 8C . The resulting breakage of wire/suture  833 ′ detaches filter  120  from sheath  110  and allows filter  120  to be retracted into lumen  113  of sheath  110  by retracting modified snare line  132 ′ in a similar manner as described above. 
     Materials suitable for use in wire/suture  833 , e.g., materials that may be formed into wires or sutures and that break when electrical current or voltage is applied thereto, are known in the relevant art. 
       FIGS. 9A-9D  illustrate another alternative mechanism that may be used to release filter  120  from sheath  110  prior to retraction into lumen  113 . In this embodiment, a combined release/retraction mechanism permits both functions to be performed using only a single mechanism, thus simplifying the design of sheath  110  by obviating the need to provide multiple separate grooves or lumens to control release and retraction of filter  120 . Referring to  FIG. 9A , second ring  124  of filter  120  is coupled via sutures, adhesive, or the like to fabric ring  901 , which is a ring of flexible, biocompatible fabric having a length sufficiently short to avoid folding-in of the fabric during device or introducer retraction. Wire/suture  933  is stitched or woven through fabric ring  901 , and the first and second ends  941 ,  942  of wire/suture  933  are looped around pull pin  935 . Pull pin  935  is disposed in pouch  936  attached to fabric ring  901 . The combination of elements  901 ,  933 ,  935 , and  936  secures filter  120  to the distal end of sheath  110 . 
     As illustrated in  FIG. 9B , modified snare line  132 ″ passes through loop  937  of pin  935 , and is attached to segment  938  which has a larger outer diameter than the inner diameter of loop  937 . Modified snare line  132 ″ also includes slack portion  939  that facilitates detachment of filter  120  from sheath  110  before the filter is retracted into lumen  113  of sheath  110 . Specifically, as illustrated in  FIG. 9C , initial retraction of modified snare line  132 ″ pulls segment  938  in the proximal direction, causing segment  938  to engage loop  937  of pin  935  while slack portion  939  is drawn taut. Such motion pulls pin  935  proximally out of pouch  936 , which frees the first and second ends  941 ,  942  of wire/suture  933  and detaches filter  120  from sheath  110 . Further retraction of modified snare line  132 ″ draws filter  120  into lumen  113  of sheath  110 , such as described above and as illustrated in  FIG. 9D . 
     While various illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the invention. For example, although the embodiments above have been described primarily with respect to configurations suitable for use in the aortic arch, it should be appreciated that the apparatus and methods suitably may be modified for percutaneous use in other blood vessels and for other applications including but not limited to: treatment of atherosclerotic arterial disease, aneurysmal disease and venous thrombosis. The appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.