Patent Publication Number: US-2013253571-A1

Title: Apparatus and methods for filtering emboli during percutaneous aortic valve replacement and repair procedures with filtration system coupled in-situ 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. 61/613,890, 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 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, are shaped to avoid dislodging additional occlusive material from the vessel walls 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 configured to couple 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 plurality of tensioning lines are each coupled to the frame of the filter with the proximal portion secured to the sheath at an anchor point. In other embodiments, these tensioning lines may pass through the length of the body of the sheath and be retractable from outside of the body to draw the outlet of the filter into contact with the distal end of the sheath. A plurality of grooves may be defined in the lumen of the sheath, each groove configured to receive a corresponding tensioning line. 
     In some embodiments, a snare is coupled to the frame of the filter and passes out of the body through the lumen. The snare 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. A leverage member may be disposed between the frame of the filter and the lumen, with the snare passing through the leverage member. The leverage member may be configured to close the filter when the snare is retracted from outside the body before the filter is drawn 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 inner diameter that is greater than the outer 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 then may be crimped into the recess during the manufacturing process, and as the introducer is retracted the filter then is tucked into the sheath, leaving only the distal nosecone of the introducer visible out the distal end of the sheath, while retaining the filter in the compressed state within the recess and between the introducer and the sheath. 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 keep the proximal ring of the filter coupled to the introducer while the sheath is retracted, allowing for slow deliberate expansion of the filter and avoiding traumatic sudden expansion and advancement out the end of the sheath. Alternatively, or additionally, the introducer may include a raised segment defining a secondary proximal recess of such a diameter as to secure the filter&#39;s proximal ring to the introducer by matching the thickness tolerance in between the stepped-up region to the thickness of the filter segment above the proximal ring. In such embodiments, retraction of the sheath will allow the filter to expand from the compressed state to the deployed state. 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 if needed. 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 capture mechanism on the end for coupling with a filter that is placed separately. 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 filter may be advanced through the previously positioned sheath via an introducer with a recess that will accommodate the filter and release wire mechanism to control expansion during exit of the filter and counterpart locking mechanism to attach to the distal sheath coupling mechanism, thus coupling the outlet of the filter 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. Alternatively, the filter and introducer may be disposed at the distal end of the sheath before inserting the distal end of the sheath into the body. 
    
    
     
       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. 1C  illustrates a cross-sectional view of the embolic filter and sheath assembly of  FIG. 1A , also in an expanded configuration. 
         FIGS. 2A-2E  illustrate various cross-sectional views of a sheath that may be used in the embolic filter and sheath assembly of  FIGS. 1A-1C . 
         FIGS. 3A-3B  illustrate perspective views of an introducer that may be used with the embolic filter and sheath assembly of  FIGS. 1A-1C . 
         FIG. 3C  illustrates a perspective view of a pre-curved sheath that may be used in the embolic filter and sheath assembly of  FIGS. 1A-1C  and the introducer of  FIGS. 3A-3B . 
         FIG. 4  illustrates steps in a method of using the embolic filter and sheath assembly of  FIGS. 1A-1C  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-1C  in an aortic arch during various steps of the method of  FIG. 4 . 
         FIGS. 6A-6D  illustrate perspective views of the removal of the embolic filter and sheath assembly of  FIGS. 1A-1C . 
         FIG. 7  illustrates a perspective view of an alternative embolic filter and sheath assembly that may be used with the embolic filter and sheath assembly of  FIGS. 1A-1C . 
         FIGS. 8A-8B  illustrate cross-sectional views of another alternative embolic filter and sheath assembly that may be used with the embolic filter and sheath assembly of  FIGS. 1A-1C . 
     
    
    
     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 compressed to a size suitable for percutaneous delivery into the aorta using a relatively small diameter sheath, e.g., an 18 F sheath, mounted on an introducer having a tapered nose, and disposed in the distal end of the sheath. The sheath containing the introducer and compressed filter then is 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 retracting the sheath relative to the introducer such that the filter expands to a deployed configuration at a location upstream of the great arteries, and the introducer then removed. The filter is configured to securely dock onto the distal end of the sheath in such a manner that the full lumen of the sheath then 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. Tensioning lines may be used to maintain secure coupling of the filter to the distal end of the sheath during such procedures, so as to prevent emboli from escaping through gaps between the filter and the sheath and to insure symmetrical coupling while also reducing the risk of uncoupling or separation. Then, when the percutaneous procedure is complete and any other devices have been removed from the lumen of the sheath, 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 retracting 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 an outer diameter suitable for percutaneous use, e.g., is 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 tensioning lines  131  via which filter  120  may be retracted into secure engagement with distal end  112  of sheath  110  while deployed, ratchet  134  which may be used to secure tensioning lines  131  in a retracted position, 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  133 , 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 . Or, for example, second ring  124  may have an inner diameter that is larger than the outer diameter of sheath  110 , so that second ring  124  seats over the outer surface of sheath  110  when retracted by tensioning lines  131  described further below with respect to  FIG. 1C . 
     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. 1C  illustrates additional structural detail of the coupling between distal end  112  of sheath  110  and second ring  124  of filter  120 . Second ring  124  is coupled to a plurality of tensioning lines  131  that pass out of the patient&#39;s body through sheath  110  via ports  114  and into handle  130  as illustrated in  FIG. 1A . For example, in the illustrated embodiment, each tensioning line  131  is respectively coupled to a minimum  128  of sinusoid  126  of second ring  124 , for example via a knot or hinge. Tensioning lines  131  may be retracted to cause second ring  124  to securely seat against distal end  112 . For example, each tensioning line  131  may be individually retractable via port  114  and handle  130  so as to enhance control over the seating of second ring  124  and compensate for any torque that may be placed on filter  120  due to blood flow; that is, each tensioning line  131  may be individually refracted via handle  130  to seat the portion of second ring  124  to which it is coupled against a respective portion of distal end  112  of sheath  110 . Alternatively, the proximal ends of tensioning lines  131  all may be coupled to a single control line in handle  130  that may be used to uniformly retract tensioning lines  131 . Preferably, tensioning lines  131  may be releasably secured once retracted so as to maintain contact between ring  124  and distal end  112 , e.g., using a ratchet  134  on handle  130  illustrated in  FIG. 1A  or other suitable mechanism. In still another alternative embodiment described further below with reference to  FIGS. 8A-8B , tensioning lines  131  may be anchored to sheath  110  at a position proximal of distal end  112 . 
     In some embodiments, tensioning lines  131  are formed of a relatively stiff material such as stainless steel, such that tensioning lines  131  may be pushed to move filter  120  distally relative to sheath  110 , as well as pulled to move filter  120  proximally relative to sheath  110 . Such material is particularly useful in embodiments where the inner diameter of second ring  124  is greater than the outer diameter of sheath  110 , because tensioning lines  131  may be pulled to seat second ring  124  over the outer surface of sheath  110  and later pushed to move second ring  124  off of the outer surface of sheath  110  so that filter  120  may be retracted into the lumen of sheath  110 , e.g., using snare  132  described further below. In other embodiments, tensioning lines  131  may be formed of a relatively flexible material such as fiber or polymer, so that tensioning lines  131  may be pulled to seat second ring  124  against distal end  112  but pushing tensioning lines  131  has no material effect on the relative position of second ring  124  and distal end  112 . In still other embodiments, tensioning lines  131  may be formed of an elastic material, e.g., an elastic polyurethane, silicon copolymer, latex, or polysiloxane modified ethylene/butylene/styrene (SEB) block copolymer or the like. Examples of materials and configurations suitable for such elastic tensioning lines may be found in U.S. Pat. No. 5,728,131, the entire contents of which are incorporated herein by reference. 
     As illustrated in  FIG. 1C , second ring  124  also is coupled to snare  132  that passes through leverage member  133 , which is positioned between second ring  124  and distal end  112  of sheath  110 . Snare  132  loops about second ring  124  and passes out of the patient&#39;s body through lumen  113  and port  114  and into handle  130  as illustrated in  FIG. 1A . Retracting snare  132  via handle  130  first causes second ring  124  to radially contract as a result of leverage applied by leverage member  133 , 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-6D . Alternatively, instead of providing leverage member  133  and disposing snare  132  in groove  117 , leverage member  133  may be omitted and snare  132  instead disposed in a separate hypotube (not illustrated) that extends within lumen  113  of sheath  110 . The distal end of the hypotube is adjacent second ring  124  and performs a similar function to that of leverage member  133 . Other suitable configurations for snare  132  and leverage member  133  may be found in U.S. Pat. No. 5,713,948, the entire contents of which are incorporated herein by reference. 
     Tensioning lines  131  may be disposed within grooves  116  and snare  132  may be disposed within groove  117  defined in the inner surface  118  of sheath  110 . Such an arrangement may inhibit interference between lines  131  or snare  132  and any devices that may be percutaneously introduced to the patient via sheath  110 . In particular, the grooves  116 ,  117  may be of such a depth that lines  131  and snare  132  do 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. 
       FIGS. 2A-2E  illustrate an exemplary arrangement of grooves  116 ,  117  on inner surface  118  of sheath  110 .  FIG. 2A  illustrates a cut-away view of the inner surface  118  of sheath  110 , in which two tensioning line grooves  116  and the snare groove  117  may be seen to run substantially parallel to lumen  113  of sheath  110 .  FIG. 2B  illustrates a cross-section of sheath  110  through plane  2 B, at distal end  112  of the sheath. Grooves  116 ,  117  may be seen to be defined on inner surface  118  of sheath  110 , with groove  117  being somewhat larger than grooves  116  because snare  132  may have a larger diameter than do tensioning lines  131 .  FIG. 2C  illustrates a cross-section of sheath  110  through plane  2 C, at a location proximal to plane  2 B. Here, it may be seen that groove  117  has transitioned to lumen  117 ′ defined within the wall  119  of sheath  110 , while grooves  116  continue along the inner surface  118  of sheath  110 .  FIG. 2D  illustrates a cross-section of sheath  110  through plane  2 D, at a location proximal to plane  2 C, Here, it may be seen that port  115  is connected to lumen  117 ′ so as to allow passage of snare  132  out of sheath  110  and into handle  130  such as illustrated in  FIG. 1A .  FIG. 2E  illustrates a cross-section of sheath  110  through plane  2 E, at a location proximal to plane  2 D. Here, it may be seen that ports  114  are connected to respective grooves  116  so as to allow passage of tensioning lines  131  out of sheath  110  and into handle  130  such as illustrated in  FIG. 1A . Note that tensioning line ports  114  and snare port  115  alternatively may be in the same plane as one another, or tensioning line ports  114  may be distal relative to snare port  115 . Other configurations for passing tensioning lines  131  and snare  132  along the length of, and out of sheath  110  may alternatively be used. Alternatively, as described below with reference to  FIGS. 8A-8B , tensioning lines  131  may be anchored to sheath  110  at points proximal of distal end  112  instead of passing along the length of sheath  110  and into handle  130 . 
       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. Recess  304  is configured to receive filter  120  in a compressed state. For example, as illustrated in  FIG. 3A , compressed state filter  120 ′ may include radially compressed first ring  123 ′, radially compressed second ring  124 ′, and folded mesh  122 ′, a portion of which is tucked underneath the compressed first ring so as to reduce the compressed length and diameter of compressed state filter  120 ′. Recess  304  of introducer  300  may be configured to have a length approximately equal to the length of compressed state filter  120 ′. Optionally, recess  304  also may include a raised segment  305  configured to engage a gap in filter  120 ′ between first and second rings  123 ′,  124 ′ so as to inhibit sliding of filter  120 ′ in the proximal or lateral directions. Such raised segment  305  may define a first proximal recess  304 ′ of such a diameter as to secure radially compressed first ring  123 ′, and a second proximal recess  304 ″ of such a diameter as to secure radially compressed second ring  124 ′. Preferably, recess  304  has a depth sufficient to accommodate the diameter of compressed state filter  120 ′ such that introducer  300  may be inserted within lumen  113  at the distal end  112  of sheath  110 , where recess  304  retains compressed state filter  120 ′ within the recess and between introducer  300  and sheath  110 . Radiopaque markers 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 so inserted into sheath  110 , tapered nose  301  extends past distal end  112  of sheath  110  so as to 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 retain introducer  300  in place while sheath  110  is retracted so as to allow compressed state filter  120 ′ to expand into the deployed state, e.g., filter  120  illustrated in  FIGS. 1A-1B . 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. 
     Optionally, sheath  110  is pre-curved to follow the curve of the patient&#39;s aortic arch, such as illustrated in  FIG. 3C  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  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. 
     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-2E . 
     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-1C  and  3 A. 
     The distal end of the sheath then may be introduced into the aortic arch (step  430 ). For example, compressed state filter  120 ′ first may be crimped into recess  304  of introducer  300  illustrated in  FIG. 3A , and introducer  300  inserted into lumen  113  at distal end  112  of sheath  110 . Then, as illustrated in  FIG. 5A , assembly  300 ,  120 ′,  112  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  440 ). For example, as illustrated in  FIG. 5B , distal end  112  of sheath  110  may be refracted from outside the patient&#39;s body while the position of introducer  300  is maintained, e.g., using control line  306  described above with reference to  FIG. 3A . Such refraction of distal end  112  of sheath  110  exposes recess  304  of introducer  300  in which compressed state filter  120 ′ is disposed, allowing the filter 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. 
     Referring again to  FIG. 4 , the outlet of the deployed filter then is coupled to the distal end of the sheath within the aortic arch, without leaving gaps through which emboli could pass and without obstructing the lumen at the distal end of the sheath (step  450 ). For example, retraction of tensioning lines  131  from outside the body such as described above with reference to FIGS.  1 C and  2 A- 2 E may securely seat second ring  124  of deployed filter  120  against distal end  112  of sheath  110 , 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 ( 460 ). 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. 
     Note that introducer  300  and filter  120  alternatively may be introduced into the aortic arch via the proximal end  111  of sheath  110  during the percutaneous procedure, rather than via the distal end  112  before the percutaneous procedure as described above. For example, distal end  112  of sheath  110  may be introduced to aortic arch  510  over a guidewire. Filter  120  may be crimped onto recess  304  of introducer  300 , and the compressed filter/introducer assembly  120 ′/ 300  may be introduced into lumen  113  of sheath  110  via proximal end  111 , and then advanced to distal end  112  by pushing control line  306 . Filter  120  then may be deployed in the aortic arch and introducer  300  may be removed as described above and a percutaneous procedure performed via lumen  113 . 
     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 , snare  132  may be looped around second ring  124  defining the outlet of filter  120 , e.g., adjacent to proximal end  129  of second ring  124 . Snare  132  then may pass through leverage member  133  and out of the body via groove  117 , lumen  117 ′, and port  115  defined in sheath  110  as described further above with reference to FIGS.  1 C and  2 A- 2 E. Retraction of snare  132  in the proximal direction radially compresses proximal end  129  of second ring  124 , resulting in partially compressed second ring  124 ″ having a generally conical shape as illustrated in  FIG. 6B . Preferably, compressed proximal end  129 ″ of partially compressed second ring  124 ″ has an outer diameter that is less than the inner diameter of lumen  113  of sheath  110 , so that further retraction of snare  132  in the proximal direction pulls proximal end  129 ″ of second ring  124 ″ into lumen  113  of sheath  113  as illustrated in  FIG. 6C . Leverage member  133 , if present, also may be pulled into lumen  113 . As illustrated in  FIG. 6D , further refraction of snare  132  in the proximal direction further compresses second ring  124 ′″ into a fully compressed removal state and pulls the ring deeper within lumen  113 ; pulls mesh  122 ′″ and any emboli therein into a compressed removal state within lumen  113 ; and pulls first ring  123 ′″ into a fully compressed removal state and pulls the ring into lumen  113 . 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 mesh  122 ′″ advantageously remain within lumen  113  during the removal process, so as to further reduce the patient&#39;s chance of stroke due to embolization. 
       FIG. 7  illustrates an alternative filter  720  that may be used in place of filter  120  in the above-described embodiments. Filter  720  includes frame  721  which, like frame  121  of filter  120 , may be formed of a shape memory alloy. Filter  720  further includes mesh  722  disposed over frame  721 , and attached to frame  721  with sutures  725  or other suitable attachment mechanism. Frame  721  defines an inlet  723  and an outlet  724  of filter  720 . Like ring  123  of filter  120 , inlet  723  of filter  720  preferably is configured to span the aortic arch in a region between the aortic valve and the great arteries, so that mesh  722  may filter emboli from substantially all of the blood passing through the aortic arch. Like ring  124  of filter  120 , outlet  724  of filter  710  preferably is configured to couple securely to distal end  112  of sheath  110  without leaving any gaps through which emboli could pass. Additionally outlet  724  of filter  710  preferably has an inner diameter that is equal to or greater than the inner diameter of lumen  113  of sheath  110 , or that is equal to or greater than the outer diameter of sheath  110 , so that percutaneous procedures may be performed via lumen  113  without interference from filter  720 . 
       FIGS. 8A-8B  illustrate an alternative filter/sheath/introducer configuration in which modified tensioning lines  131 ′ do not pass into handle  130  via lumen  113  and ports  115 , as described above with reference to  FIGS. 1A-2E , but instead each are anchored to sheath  110  at a point proximal of distal end  112 . Specifically,  FIG. 8A  illustrates compressed filter  120 ′ crimped onto introducer  300  and disposed within modified sheath  110 ′ having modified ports  115 ′ defined therethrough at a point proximal of distal end  112 , but at a location relatively close to distal end  112 . Modified tensioning lines  131 ′ are coupled to minima  128  of compressed second (proximal) ring  124 ′, and pass through modified ports  115 ′ where anchors  810  anchor the ends of lines  131 ′ to modified sheath  110 ′. Modified lines  131 ′ are slack when filter  120 ′ is in the compressed configuration. As illustrated in  FIG. 8B , when filter  120  is expanded by retracting modified sheath  110 ′ relative to introducer  300 , modified tensioning lines  131 ′ are drawn taut by proximal movement of ports  115 ′ and anchors  810 , thus securing filter  120  against distal end  112 ′ of modified sheath  110 ′. Modified tensioning lines  131 ′ have a length approximately equal to the distance between distal end  128 ′ and anchor  810 , so that there is substantially no slack in lines  131 ′ when filter  120  is in the deployed configuration. In this embodiment, modified sheath  110 ′ may lack grooves  116  described above with references to  FIGS. 1C-2E . 
     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.