Patent Publication Number: US-2005137696-A1

Title: Apparatus and methods for protecting against embolization during endovascular heart valve replacement

Description:
REFERENCE TO RELATED APPLICATION  
      This application is a continuation-in-part application of Ser. No. 10/746,280, filed Dec. 23, 2003, which is incorporated herein by reference in its entirety and to which application we claim priority under 35 USC § 120. 
    
    
     BACKGROUND OF THE INVENTION  
      The present invention relates to methods and apparatus for protecting a patient from embolization during endovascular replacement of the patient&#39;s heart valve. More particularly, the present invention relates to methods and apparatus for providing embolic protection by filtering blood downstream of the valve during endovascular replacement.  
      Heart valve surgery is used to repair or replace diseased heart valves. Valve surgery typically is an open-heart procedure conducted under general anesthesia. An incision is made through a patient&#39;s sternum (sternotomy), and the patient&#39;s heart is stopped while blood flow is rerouted through a heart-lung bypass machine. The valve then is surgically repaired or replaced, blood is rerouted back through the patient&#39;s heart, the heart is restarted, and the patient is sewn up.  
      Valve replacement may be indicated when there is a narrowing of the native heart valve, commonly referred to as stenosis, or when the native valve leaks or regurgitates. When replacing the valve, the native valve is excised and replaced with either a biologic or a mechanical valve. Mechanical valves require lifelong anticoagulant medication to prevent blood clot formation, and clicking of the valve often may be heard through the chest. Biologic tissue valves typically do not require such medication. Tissue valves may be obtained from cadavers or may be porcine or bovine, and are commonly attached to synthetic rings that are secured to the patient&#39;s heart.  
      Valve replacement surgery is a highly invasive operation with significant concomitant risk. Risks include bleeding, infection, stroke, heart attack, arrhythmia, renal failure, adverse reactions to the anesthesia medications, as well as sudden death. 2-5% of patients die during surgery.  
      Post-surgery, patients temporarily may be confused due to emboli and other factors associated with the heart-lung machine. The first 2-3 days following surgery are spent in an intensive care unit where heart functions can be closely monitored. The average hospital stay is between  1  to  2  weeks, with several more weeks to months required for complete recovery.  
      In recent years, advancements in minimally invasive surgery and interventional cardiology have encouraged some investigators to pursue percutaneous, endovascular replacement of the aortic heart valve. See, e.g., U.S. Pat. No. 6,168,614, which is incorporated herein by reference in its entirety. The replacement valve may be deployed across the native diseased valve to permanently hold the native valve open, thereby alleviating a need to excise the native valve and to position the replacement valve in place of the native valve. Optionally, a valvuloplasty may be performed prior to, or after, deployment of the replacement valve.  
      Since the native valve may be calcified or stenosed, valvuloplasty and/or deployment of the replacement valve poses a risk of loosening and releasing embolic material into the patient&#39;s blood stream. This material may, for example, travel downstream through the patient&#39;s aorta and carotids to the cerebral vasculature of the brain. Thus, a risk exists of reduction in mental faculties, stroke or even death during endovascular heart valve replacement, due to release of embolic material.  
      In view of the foregoing, it would be desirable to provide methods and apparatus for protecting against embolization during endovascular replacement of a patient&#39;s heart valve.  
     SUMMARY OF THE INVENTION  
      One aspect of the invention provides apparatus for protecting against embolization during endovascularly replacement of a patient&#39;s heart valve, including: a replacement valve configured for endovascular delivery and deployment; and an embolic filter configured for disposal downstream of the replacement valve during endovascular deployment of the valve.  
      Another aspect of the invention provides a method for protecting a patient against embolization during endovascular replacement of the patient&#39;s heart valve, including the steps of: endovascularly delivering a replacement valve to a vicinity of the patient&#39;s heart valve; endovascularly deploying an embolic filter downstream of the heart valve; and endovascularly deploying the replacement valve. The method may also include the step removing the embolic filter from the patient after endovascular deployment of the replacement valve. In embodiments in which the heart valve is an aortic valve, the endovascular delivery step may include the step of endovasculary delivering the replacement valve along a retrograde approach, and the filter deployment step may include deploying the filter in the patient&#39;s aorta. The method may also include the step of endovascularly delivering an expandable balloon to the vicinity of the heart valve and performing valvuloplasty with the expandable balloon.  
      Yet another aspect of the invention provides apparatus for protecting against embolization during endovascularly replacement of a patient&#39;s heart valve, including: a delivery catheter having an expandable replacement valve disposed therein; and an embolic filter advanceable along the delivery catheter for diverting emboli released during endovascular deployment of the replacement valve.  
     INCORPORATION BY REFERENCE  
      All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which:  
      FIGS.  1 A-F are side views, partially in section, illustrating a method and apparatus for protecting a patient against embolization during endovascular replacement of the patient&#39;s diseased aortic valve.  
       FIG. 2  is a side view, partially in section, illustrating an alternative embodiment of the apparatus and method of  FIGS. 1 .  
      FIGS.  3 A-D are schematic side-sectional views illustrating another alternative method and apparatus for protecting against embolization during endovascular valve replacement.  
      FIGS.  4 A-D are side-views, partially in section, illustrating yet another method and apparatus for protecting against embolization, wherein an embolic filter is coaxially advanced over, or coupled to, an exterior of a replacement valve delivery catheter.  
      FIGS.  5 A-F are schematic isometric views illustrating alternative embodiments of the apparatus of  FIGS. 4 .  
      FIGS.  6 A-D are side views, partially in section, illustrating another method and apparatus for protecting against embolization.  
       FIG. 7A -B are cross- and side-sectional detail views, respectively, along section lines A-A and B-B of  FIG. 6A , respectively, illustrating an optional method and apparatus for enhancing blood flow to the patient&#39;s coronary arteries while utilizing the apparatus of  FIGS. 6 .  
       FIG. 8  is a schematic view of an embodiment of the apparatus of FIGS.  6  comprising a measuring element.  
      FIGS.  9 A-I are schematic views of exemplary alternative embodiments of the apparatus of  FIGS. 6 .  
      FIGS.  10 A-B are detail schematic views illustrating a spiral wound support structure.  
       FIG. 11  is a detail schematic view illustrating longitudinal supports for maintaining a length of the apparatus.  
      FIGS.  12 A-C are detail schematic views illustrating alternative deployment and retrieval methods for the apparatus.  
      FIGS.  13 A-G are schematic views and side views, partially in section, illustrating a method and apparatus for protecting a patient against embolization during endovascular valvuloplasty and replacement of the patient&#39;s diseased aortic valve. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      While preferred embodiments of the present invention are shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.  
      The present invention relates to methods and apparatus for protecting a patient against embolization during endovascular replacement of the patient&#39;s diseased heart valve. More particularly, the present invention relates to methods and apparatus for providing embolic protection by filtering blood downstream of the valve during endovascular replacement. Applicant has previously described methods and apparatus for endovascularly replacing a patient&#39;s diseased heart valve, for example, in co-pending U.S. patent application Ser. No. 10/746,280, filed Dec. 23, 2003, from which the present application claims priority and which previously has been incorporated herein by reference.  
      Referring now to  FIGS. 1 , a first embodiment of a method and apparatus for protecting a patient against embolization during endovascular replacement of the patient&#39;s diseased aortic valve is described. In  FIGS. 1 , replacement valve apparatus  10  illustratively comprises replacement valve  20  disposed within and coupled to expandable anchor  30 . Apparatus  10  is provided only for the sake of illustration, and any other replacement valve apparatus may alternatively be provided.  
      Replacement valve  20  preferably is from biologic tissues, e.g. porcine valve leaflets or bovine or equine pericardium tissues. Alternatively, it can be made from tissue-engineered materials (such as extracellular matrix material from Small Intestinal Submucosa (SIS)). As yet another alternative, the replacement valve may be prosthetic from an elastomeric polymer or silicone, or a Nitinol or stainless steel mesh or pattern (sputtered, chemically milled or laser cut). Replacement valve  20  may comprise leaflets that may also be made of a composite of the elastomeric or silicone materials and metal alloys or other fibers, such Kevlar or carbon. Anchor  30  may, for example, dynamically self-expand; expand via a hydraulic or pneumatic force, such as expansion of a balloon catheter therein; expand via a non-hydraulic or non-pneumatic force; and/or be foreshortened in order to increase its radial strength.  
      Replacement valve apparatus  10  is reversibly coupled to delivery system  100 , which illustratively comprises sheath  110  having lumen  112 , as well as control wires  50  and control rods or tubes  60 . Delivery system  100  may further comprise leaflet engagement element  120 , as well as filter structure  61 A. Engagement element  120 , which may be releasably coupled to the anchor, is disposed between the anchor and tubes  60  of the delivery system. Filter structure  61 A may, for example, comprise a membrane or braid, e.g., an expandable Nitinol braid, circumferentially disposed about tubes  60 . Structure  61 A preferably comprises a specified porosity, for example, preferably comprises a plurality of pores on the order of about 100 μm or less to facilitate blood flow therethrough while filtering dangerously sized emboli from the blood. Structure  61 A may be used independently or in combination with engagement element  120  to provide embolic protection during deployment of replacement valve apparatus  10 .  
      Replacement valve apparatus  10  is configured for disposal in a delivery configuration within lumen  112  of sheath  110  to facilitate percutaneous, endoluminal delivery thereof. Wires  50 , tubes  60 , element  120  and/or sheath  110  of delivery system  100  may be utilized to deploy apparatus  10  from the delivery configuration to an expanded deployed configuration.  
      In  FIG. 1A , sheath  110  of delivery system  100 , having apparatus  10  disposed therein, may be endovascularly advanced over guide wire G, preferably in a retrograde fashion (although an antegrade or hybrid approach alternatively may be used), through a patient&#39;s aorta A to the patient&#39;s diseased aortic valve AV. A nosecone  102  precedes sheath  110  in a known manner. In  FIG. 1B , sheath  110  is positioned such that its distal region is disposed within left ventricle LV of the patient&#39;s heart H.  
      After properly aligning the apparatus relative to anatomical landmarks, such as the patient&#39;s coronary ostia or the patient&#39;s native valve leaflets L, apparatus  10  may be deployed from lumen  112  of sheath  110 , for example, under fluoroscopic guidance. Anchor  30  of apparatus  10  illustratively self-expands to a partially deployed configuration, as in  FIG. 1C . Leaflet engagement element  120  of delivery system  100  preferably self-expands along with anchor  30 .  
      Element  120  initially is deployed proximal of the patient&#39;s native valve leaflets L, such that the element sealingly engages against the patient&#39;s aorta A to capture or otherwise filter emboli E that may be released during maneuvering or deployment of apparatus  10 . Element  120  may also direct emboli E into filter structure  61 A and out through sheath  110 , such that the emboli do not travel downstream through the patient&#39;s aorta or into the patient&#39;s cerebral vasculature. Suction optionally may be drawn through lumen  112  of sheath  110  during placement of apparatus  10  to facilitate aspiration or removal of emboli E from the patient&#39;s blood stream to further reduce a risk of embolization.  
      As seen in  FIG. 1D , apparatus  10  and element  120  may be advanced, and/or anchor  30  may be foreshortened, until the engagement element positively registers against valve leaflets L, thereby ensuring proper positioning of apparatus  10 . Upon positive registration of element  120  against leaflets L, element  120  precludes further distal migration of apparatus  10  during additional foreshortening or other deployment of apparatus  10 , thereby reducing a risk of improperly positioning the apparatus. Once expanded to the fully deployed configuration of  FIG. 1D , replacement valve apparatus  10  regulates normal blood flow between left ventricle LV and aorta A.  
      As discussed, emboli can be generated during manipulation and placement of apparatus  10 , e.g., from the diseased native leaflets or from surrounding aortic tissue. Arrows  61 B in  FIG. 1E  show blood flowing past engagement element  120  and through porous filter structure  61 A. While blood is able to flow through the filter structure, emboli E are trapped in the delivery system and removed with it at the end of the procedure or aspirated via suction during the procedure.  FIG. 1E  also details engagement of element  120  against the native leaflets and illustrates locks  40 , which optionally may be used to maintain apparatus  10  in the fully deployed configuration.  
      As seen in  FIG. 1F , delivery system  100  may be decoupled from apparatus  10  and removed from the patient, thereby removing the embolic filter provided by element  120  and filter structure  61 A, and completing protected, beating-heart, endovascular replacement of the patient&#39;s diseased aortic valve.  
      With reference to  FIG. 2 , an alternative embodiment of the apparatus of FIGS.  1  is described, wherein leaflet engagement element  120  is coupled to anchor  30  of apparatus  10 , rather than to delivery system  100 . Engagement element  120  remains implanted in the patient post-deployment of apparatus  10 , and leaflets L of native aortic valve AV are sandwiched between the engagement element and anchor  30 . In this manner, element  120  positively registers apparatus  10  relative to the leaflets and precludes distal migration of the apparatus over time. Furthermore, since element  120  may act as an embolic filter during deployment of apparatus  10 , any emboli E captured against element  120  may harmlessly remain sandwiched between the element and the patient&#39;s native leaflets, thereby reducing a risk of embolization.  
      Referring now to  FIGS. 3 , another alternative method and apparatus for protecting against embolization is described. In  FIG. 3A , replacement valve apparatus  10  is once again disposed within lumen  112  of sheath  110  of delivery system  100 . As seen in  FIG. 3B , the apparatus is deployed from the lumen and expands to a partially deployed configuration across the patient&#39;s native aortic valve AV. A separate, expandable embolic filter  200  is also deployed from lumen  112  downstream of apparatus  10  within the patient&#39;s aorta A, such that the filter sealingly engages the aorta. Any emboli generated during further expansion of apparatus  10  to a fully deployed configuration would be filtered out of the patient&#39;s blood stream via the filter and/or lumen  112  of sheath  110 . Filter  200  preferably is porous to allow for uninterrupted blood flow through aorta A during use of the filter. The filter may, for example, be fabricated from a porous polymer membrane, or from a braid or mesh, e.g. a braided Nitinol structure.  
      As seen in  FIG. 3C , balloon catheter  130  may be advanced through sheath  110  and filter  200  into apparatus  10 . The balloon may be inflated to further expand apparatus  10  to the fully deployed configuration. Emboli E generated during deployment of apparatus  10  then may be captured or otherwise filtered by filter  200 . As seen in  FIG. 3D , balloon catheter  130  then may be deflated and removed from the patient, filter  200  may be collapsed within lumen  112  of sheath  110 , and delivery system  100  may be removed, thereby completing the protected valve replacement procedure.  
      It should be understood that balloon catheter  130  alternatively may be used to perform valvuloplasty prior to placement of apparatus  10  across the diseased valve. In this configuration, filter  200  may be utilized to capture emboli generated during the valvuloplasty procedure and prior to placement of apparatus  10 , as well as to provide embolic protection during placement and deployment of the replacement valve apparatus. After the valvuloplasty procedure, apparatus  10  may be deployed with or without balloon catheter  130 .  
      Referring now to  FIGS. 4 , yet another method and apparatus for protecting against embolization is described, wherein an embolic filter is coaxially advanced over, or is coupled to, an exterior of a replacement valve delivery catheter. In  FIG. 4A , replacement valve apparatus, e.g., apparatus  10 , is disposed for delivery within the lumen of a delivery sheath, e.g., delivery sheath  110  of delivery system  100 . Expandable embolic filter  300  is either coupled to, or is advanceable over, an exterior surface of the delivery sheath.  
      When filter  300  is advanceable over the delivery sheath, sheath  110  may be positioned in a vicinity of a patient&#39;s diseased heart valve, as shown, and filter  300  may be advanced along the exterior of delivery sheath via coaxially-disposed pusher sheath  310 . Delivery sheath  110  preferably comprises a motion limitation element, such as a cross-section of locally increased diameter (not shown), which limits advancement of filter  300  relative to the delivery sheath.  
      When filter  300  is coupled to the exterior of delivery sheath  110 , the filter may be collapsed for delivery by advancing pusher sheath  310  over the filter, such that the filter is sandwiched in an annular space between delivery sheath  110  and pusher sheath  310 . Replacement valve apparatus  10 , delivery system  100 , filter  300  and pusher sheath  310  then may be endovascularly advanced to the vicinity of the patient&#39;s diseased heart valve AV. Once properly positioned, the pusher sheath may be retracted, such that filter  300  dynamically expands into sealing contact with the patient&#39;s aorta A, as in  FIG. 4A .  
      Regardless of whether filter  300  is coupled to, or is advanceable over, delivery sheath  110 ; once properly positioned, the filter sealingly contacts the patient&#39;s aorta and filters blood passing through the aorta to remove any harmful emboli (arrows illustrate blood flow in  FIG. 4A ). Thus, the replacement valve apparatus may be deployed while the filter protects against embolization. As seen in  FIG. 4B , once embolic protection is no longer desired, e.g., after endovascular replacement of the patient&#39;s diseased heart valve, filter  300  may be collapsed for removal by advancing pusher sheath  310  relative to delivery sheath  110  and filter  300 .  FIG. 4B  illustrates the filter after partial collapse, while  FIG. 4C  shows the filter nearly completely collapsed. In  FIG. 4D , filter  300  is fully enclosed within the annular space between delivery sheath  110  and pusher sheath  310 . Any dangerous emboli generated during deployment of the replacement valve apparatus are trapped between filter  300  and the exterior surface of delivery sheath  110 . Delivery system  100 , filter  300  and pusher sheath  310  then may be removed from the patient to complete the procedure.  
      With reference to  FIGS. 5 , alternative embodiments of the embolic protection apparatus of FIGS.  4  are described. In  FIG. 5A , filter  300  is substantially the same as in  FIGS. 4 , but a proximal control region of the embolic protection apparatus, which is disposed outside of the patient, is also described. Region  400 , which generally is shown as useable with any of the embodiments of  FIG. 5 , comprises proximal handle  115  of delivery sheath  110 , as well as proximal handle  315  of pusher sheath  310 . A medical practitioner may grasp handle  115  with a first hand and handle  315  with a second hand for relative movement of pusher sheath  310  and delivery sheath  110 .  
      In  FIG. 5B , filter  300  comprises first filter  300   a  and second filter  300   b.  As with the unitary filter of  FIGS. 4 and 5 A, filters  300   a  and  300   b  may be coupled to, or advanceable over, the exterior of sheath  110 . As another alternative, filter  300   a  may be coupled to the delivery sheath, while filter  300   b  is advanceable over the sheath. Filters  300   a  and  300   b  may be deployed and retrieved as described previously with respect to  FIGS. 4 . Specifically, one or both of the filters may be advanced along delivery sheath  110  via pusher sheath  310 , or may be expanded from the annular space between the delivery and pusher sheaths. Likewise, the filters may be collapsed for retrieval within the annular space.  
      Providing multiple filters may reduce a risk of embolization via emboli inadvertently bypassing the first filter, for example, due to an imperfect seal between the filter and the patient&#39;s anatomy. Additionally, each of the filters may have a different porosity; for example, filter  300   a  may provide a rough filter to remove larger emboli, while filter  300   b  may comprise a finer porosity to capture smaller emboli. Filtering the emboli through multiple filters may spread the emboli over multiple filters, thereby reducing a risk of impeding blood flow due to clogging of a single filter with too many emboli. The embodiment of  FIG. 5C  extends these concepts: filter  300  comprises first filter  300   a,  second filter  300   b  and third filter  300   c.  As will be apparent, any number of filters may be provided.  
      The filters of  FIGS. 5A-5C  generally comprise expandable baskets having self-expanding ribs  302 , e.g., Nitinol or spring steel ribs, surrounded by a porous and/or permeable filter membrane  304 .  FIG. 5D  provides an alternative filter  300  comprising a self-expanding wire loop  306  surrounded by membrane  304 . Deployment and retrieval of filter  300  of  FIG. 5D  is similar to that of filters  300  of  FIGS. 5A-5C .  
       FIGS. 5E and 5F  illustrate yet another embodiment of filter  300 . In  FIG. 5E , filter  300  is shown in a collapsed delivery configuration against the exterior surface of delivery sheath  110 . Filter  300  is proximally coupled to pusher sheath  310  at attachment point  308   a,  and is distally coupled to, or motion limited by, delivery sheath  110  at attachment point  308   b.  Filter  300  comprises proximal braid  310   a  and distal braid  310   b,  e.g., proximal and distal Nitinol braids. The proximal braid preferably comprises a tighter weave for filtering smaller emboli, and may also be covered by a permeable/porous membrane (not shown). Distal braid  310   b  comprises a more open braid to facilitate expansion, as well as capture of larger emboli.  
      In  FIG. 5F , pusher sheath  310  has been advanced relative to delivery sheath  110 , thereby expanding filter  300  for capturing emboli. Once embolic protection is no longer desired, e.g., after endovascular replacement of the patient&#39;s diseased heart valve, pusher sheath  310  may be retracted relative to the delivery sheath, which collapses the filter back to the delivery configuration of  FIG. 5E  and captures emboli between the filter and the delivery sheath. As another alternative, pusher sheath  310  may be further advanced relative to the delivery sheath, thereby collapsing the filter into a retrieval configuration wherein the proximal braid covers the distal braid (not shown).  
      Referring now to  FIGS. 6 , another method and apparatus for protecting against embolization is described. In  FIG. 6A , guidewire G has been percutaneously advanced through a patient&#39;s aorta A, past the patient&#39;s diseased aortic valve AV and into the left ventricle. Coronary guidewires CG may also be provided to facilitate proper positioning of elements advanced over guidewire G.  
      Embolic protection system  500  has been endovascularly advanced over guidewire G to the vicinity of the patient&#39;s aortic valve AV. System  500  includes exterior sheath  510  and embolic filter  520 . The embolic filter may be collapsed for delivery and/or retrieval within lumen  512  of the sheath. As seen in  FIGS. 6A and 6B , exterior sheath  510  may be withdrawn relative to filter  520 , such that the filter self-expands into contact with the patient&#39;s anatomy. The open mesh of the braid, e.g. Nitinol braid, from which the filter is fabricated, provides filtered perfusion: filtered blood continues to flow through the filter and through the patient&#39;s aorta, as well as through side-branchings off of the aorta. Optionally, filter  520  may also comprise a permeable/porous membrane to assist filtering.  
      As shown in  FIG. 6A , filter  520  optionally may comprise a scalloped distal edge  522  that fits behind the valve leaflets and over the leaflet commissures of aortic valve AV. The depth, number and/or shape(s) of distal edge  522  may be specified, as desired. Furthermore, marking indicia I (see  FIG. 6B ) may be provided on or near the edge to facilitate proper alignment of the edge with the patient&#39;s coronary ostia O.  FIG. 6B  illustrates an alternative embodiment of the filter wherein distal edge  522  is substantially planar. This may simplify placement of the filter without requiring complicated alignment with the patient&#39;s coronary ostia O, and the planar distal edge may simply rest on or near the valve leaflet commissures.  
      In addition to providing embolic protection, filter  520  may aid delivery of replacement valve apparatus. As seen in  FIG. 6B , filter  520  contacts the inner wall of aorta A over a significant distance, thereby providing a non-slip protective layer for guiding additional catheters past blood vessel branches without damaging the vessel walls. As seen in the cutaway view of  FIG. 6C , delivery system  100 , having replacement valve apparatus  10  disposed therein, may then be advanced through embolic protection system  500 ; and endovascular, beating-heart replacement of the patient&#39;s diseased aortic valve AV may proceed in an embolically protected manner. As will be apparent, any alternative replacement valve apparatus and delivery system may be used in combination with embolic protection system  500 . Furthermore, as seen in the detail view of  FIG. 6D , all or part of filter  520  may be detachable and remain as part of the implanted replacement valve apparatus, e.g., as an anchor for the replacement valve.  
      Referring now to  FIGS. 7 , optional end geometry for filter  520  is described. As seen in  FIG. 7B , distal edge  522  of filter  520  may distally extend into the cusps of the patient&#39;s diseased valve, for example, as a means to reference distances and/or to ensure full engagement. In order to guarantee adequate blood flow to the patient&#39;s coronary arteries, filter  520  may comprise heat-set or otherwise-formed indentations  524  that increase surface area flow through the filter to the patient;s coronary arteries. The indentations may also aid proper alignment of the replacement valve apparatus, e.g., may be used in conjunction with coronary guidewires CG.  
      With reference to  FIG. 8 , an embodiment of embolic protection apparatus  500  is described comprising a measuring element. Embolic filter  520  may, for example, comprise a pair of opposed thin wires  530  that are anchored to the distal end of the filter and extend out the other end to provide a measuring element. The wires optionally may be radiopaque to facilitate visualization. Wires  530  comprise measurement indicia  532  on their proximal ends that give the distance between the indicia and the distal end of the wire. The average distance measured between the two wires provides the center axis distance through the patient&#39;s aorta to the valve commissures.  
      Referring now to  FIGS. 9 , various exemplary alternative embodiments of embolic protection system  500  are described. In  FIG. 9A , a shorter version of embolic filter  520  is shown. The filter is disposed in the annular space between exterior sheath  510  and delivery system  100 /replacement valve apparatus  10 . The filter may be fabricated in a shorter length, or may be only partially deployed to a desired length.  
       FIG. 9B  illustrates another optionally short-necked version of filter  520 . However, unlike the filter of  FIG. 9A , the proximal end of filter  520  in  FIG. 9B  is at least partially disconnected from sheath  510 . Thus, filter  520  is a diverter that diverts emboli past the primary upper circulatory branchings of aorta A, e.g., those leading to the patient&#39;s carotid arteries, thereby protecting the patient from cerebral embolization. The emboli then may be allowed to continue downstream to less critical and/or dangerous regions of the patient&#39;s anatomy.  
      Optionally, suction may be applied through the lumen of sheath  510  to remove at least a portion of the emboli from the patient. Alternatively, a stand-alone suction catheter (not shown) may be advanced over, through or alongside sheath  510  to the vicinity of, or within, filter  520 ; suction then may be drawn through the suction catheter to aspirate the emboli. The suction catheter optionally may be part of delivery system  100 , e.g., sheath  110 .  
      The proximal end of filter  520  illustratively comprises a tapered or angled opening to facilitate collapse and removal of the filter from the patient. The distal end of the filter may likewise be tapered or angled in any desired direction or configuration.  
      In  FIG. 9B , replacement valve apparatus optionally may be deployed directly through sheath  510  without an intervening delivery sheath. Alternatively, a delivery sheath, such as sheath  110 , may be provided, as described previously. The delivery sheath may be advanced through or adjacent to filter sheath  510 ; alternatively, sheath  510  may be removed during placement of the replacement valve apparatus.  
       FIG. 9C  illustrates an alternative embodiment of filter  520  wherein the filter comprises a permeable or porous membrane, web, film, etc., as opposed to a braid. The membrane may comprise a specified porosity, for example, pores of about 100 μm or less. In  FIG. 9C , the proximal opening of filter  520  has been squared off.  FIG. 9D  illustrates an embodiment wherein sheath  510  is disposed along the opposing side of the patient&#39;s aorta A, as compared to the embodiment of  FIG. 9C .  
      In  FIG. 9E , filter  520  comprises membrane M with reinforcing, spiral-wound support S. The support optionally may be disposed within a guide track of the membrane and may be advanced or retracted within the membrane, as desired.  FIG. 9E  illustratively shows the proximal end of filter  520  tapered or angled in two different configurations; in  FIG. 9E (a), the taper distally extends towards the lesser curvature of the aorta, while in  FIG. 9E (b), the taper distally extends towards the greater curvature. Additional configurations will be apparent.  
       FIG. 9F  illustrates a membrane embodiment of filter  520 , which is similar to the braid embodiment of  FIG. 9B .  FIG. 9G  illustrates another membrane/spiral-wound embodiment of filter  520 . However, the filter of  FIG. 9G  is proximally attached to sheath  510 , such that embolic particles are captured and removed from the patient, rather than diverted.  FIG. 9H  provides another proximally attached embodiment of the filter having one or more regions of specially designed porosity P. For example, the size and/or density of the pores may be varied as desired in the vicinity of vessel branchings, e.g., to enhance blood flow and/or to more finely filter particles.  
      Filter  520  may have a biased profile, e.g., such that it naturally assumes the curve of the patient&#39;s aorta. Alternatively, the filter may comprise a non-biased or straight profile as in  FIG. 9I , which may be urged into a curved configuration. In  FIG. 9I , filter  520  comprises membrane M strung between longitudinal support structure S.  
      Referring now to  FIGS. 10 , a spiral wound structure for use with any of the previously described filters is described. Structure S acts as a radially-expansive support when torqued in a first direction, as seen in  FIG. 10A . When torqued in the opposing direction, the structure loosens and contracts in diameter, as seen in  FIG. 10B . The torque characteristics of structure S may be utilized to expand and contract an embolic filter, as well as to capture emboli disposed within the filter.  
      As shown in  FIG. 11 , filter  520  may comprise multiple longitudinal supports wound in long spirals. The supports may increase hoop strength. They may also help maintain a desired length of the filter.  
      FIGS.  12  illustrate alternative deployment and retrieval methods for filter  520 . In  FIG. 12A , the proximal end of filter  520  is attached to the distal end of sheath  510 . The filter and sheath may be advanced and withdrawn together with the filter conforming to the patient&#39;s anatomy as it is it repositioned. Alternatively, an additional over-sheath may be provided for collapsing the filter to a reduced delivery and retrieval configuration.  
      As seen in  FIG. 12B , filter  520  alternatively may be collapsed within sheath  510  during delivery and retrieval, e.g. via a pullwire coupled to a proximal end of the filter (see  FIGS. 13 ). As seen in  FIG. 12C , embolic protection system  500  optionally may comprise pullwire  540  attached to the distal outlet of filter  520 . By keeping the wire taut during retrieval of filter  520 , it is expected that a risk of snagging, or otherwise hanging up, filter  520  on sheath  510  will be reduced.  
      Prior to implantation of a replacement valve, such as those described above, it may be desirable to perform a valvuloplasty on the diseased valve by inserting a balloon into the valve and expanding it, e.g., using saline mixed with a contrast agent. In addition to preparing the valve site for implantation, fluoroscopic viewing of the valvuloplasty will help determine the appropriate size of replacement valve implant to use. During valvuloplasty, embolic protection, e.g., utilizing any of the embolic filters described previously, may be provided.  
      Referring now to  FIGS. 13 , a method of replacing a patient&#39;s diseased aortic valve utilizing replacement valve apparatus  10  and delivery system  100 , in combination with a diverter embodiment of embolic protection system  500 , is described. Although a retrograde approach via the femoral artery illustratively is utilized, it should be understood that alternative approaches may be utilized, including, but not limited to, radial or carotid approaches, as well as trans-septal antegrade venous approaches.  
      As seen in  FIG. 13A , arteriotomy puncture site Ar is formed, and introducer sheath  600  is advanced in a minimally invasive fashion into the patient&#39;s femoral artery. The introducer preferably initially comprises a relatively small sheath, for example, an introducer sheath on the order of about 6 Fr-compatible. Guidewire G is advanced through the introducer sheath into the femoral artery, and is then further advanced through the patient&#39;s aorta and across the patient&#39;s diseased aortic valve.  
      Additionally, imaging may be performed to determine whether the patient is a candidate for valvuloplasty and/or endovascular valve replacement. For example, angiographic imaging, per se known, may be performed via an angiography catheter (not shown) advanced from a femoral, radial, or other appropriate entry site. The angiography catheter may, for example, have a profile on the order of about 5 Fr to 8 Fr, although any alternative size may be used.  
      If it is determined that the patient is not a candidate for valvuloplasty and/or endovascular valve replacement, the guidewire and introducer sheath (as well as any imaging apparatus, e.g., the angiography catheter) may be removed from the patient, and the arteriotomy site may be sealed. If it is determined that the patient is a candidate, the arteriotomy site may be expanded, and, upon removal of any imaging apparatus, introducer sheath  600  may be exchanged with a larger introducer sheath  602  (see  FIG. 13C ), for example, an introducer sheath on the order of about 14 Fr compatible, to facilitate endovascular valvuloplasty and/or valve replacement.  
      As seen in  FIG. 13B , embolic protection system  500  then may be advanced over guidewire G to the vicinity of the patient&#39;s diseased valve. Sheath  510  may be retracted relative to diverter filter  520 , such that the diverter filter, which preferably comprises a self-expanding wire braid, expands into contact with the wall of aorta A downstream of aortic valve AV. Sheath  510  of embolic protection system  500  then may be removed from the patient.  
      Filter  520  is configured to divert emboli, generated during endovascular treatment of valve AV, away from the patient&#39;s cerebral vasculature. The filter illustratively comprises optional proximal and distal interfaces  521  of enlarged diameter that contact the wall of aorta A, while a central section of the filter disposed between the interfaces moves freely or ‘floats’ without engaging the aorta. This may reduce friction during deployment and/or retrieval of the filter, and may also reduce damage caused by the filter to the wall of the aorta. Filter  520  alternatively may contact aorta A along its length, as in  FIGS. 13D-13G . Filter  520  also optionally may comprise internal rails R that may be used to guide endovascular treatment tools through the filter. Filter  520  illustratively is coupled proximally to pullwire  540 , which extends from the proximal end of the filter to the exterior of the patient. Pullwire  540  allows a medical practitioner to maneuver filter  520 , as desired.  
      As seen in  FIG. 13C , upon removal of sheath  510  from the patient, guidewire G and pullwire  540  extend through introducer sheath  602 . Advantageously, with filter  520  positioned as desired within the patient&#39;s aorta and with slack removed from pullwire  540 , the filter may be maintained at the desired position by reversibly maintaining the position of pullwire  540 , e.g., by reversibly attaching the pullwire to the exterior of the patient via surgical tape T. In this manner, a medical practitioner may properly position diverter filter  520 , then leave it in the desired position without requiring significant manipulation or monitoring during endovascular treatment of the patient&#39;s diseased aortic valve AV. The open proximal end of diverter filter  520  allows additional endovascular tools, such as valvuloplasty catheter  700  and/or replacement valve apparatus  10  disposed within delivery system  100 , to be advanced through the diverter.  
      In  FIGS. 13C and 13D , optional valvuloplasty catheter  700 , having expandable balloon  702 , is advanced over guidewire G and through introducer sheath  602  into the patient&#39;s vasculature. Catheter  700  preferably comprises a delivery profile on the order of about 8-16 Fr, while balloon  702  preferably comprises an expanded diameter on the order of about 18 mm to 30 mm, more preferably about 20 mm to 23 mm. Proper sizing of balloon  702  optionally may be determined, for example, via angiographic imaging of aortic valve AV.  
      Balloon  702  is endovascularly advanced through aorta A and diverter filter  520  across diseased aortic valve AV. Diverter filter  520  advantageously guides catheter  700  past the arterial branches of aorta A as the catheter passes through the filter. In this manner, filter  520  facilitates proper placement of balloon  702 , while reducing a risk of injury to the arterial branches.  
      In  FIG. 13E , once positioned across the aortic valve, balloon  702  is expanded to break up or otherwise crack calcification and/or lesion(s) along the valve. Expansion may, for example, be achieved using saline mixed with a contrast agent. In addition to preparing the valve site for implantation, fluoroscopic viewing of the contrast agent and the valvuloplasty may help determine the appropriate size of replacement valve apparatus  10  to use. Balloon  702  is then deflated, and valvuloplasty catheter  700  is removed from the patient. Emboli E generated during valvuloplasty travel downstream through aorta A, where they are diverted by filter  520  away from the patient&#39;s cerebral vasculature.  
      Optionally, multiple catheters  700  may be provided and used sequentially to perform valvuloplasty. Alternatively or additionally, multiple catheters  700  may be used in parallel (e.g., via a ‘kissing balloon’ technique). The multiple catheters may comprise balloons  702  of the same size or of different sizes.  
      After optionally performing valvuloplasty, aortic valve AV may once again be imaged, e.g. via fluoroscopy and angiography, to determine whether the patient is a candidate for endovascular valve replacement. If it is determined that the patient is not a candidate, embolic protection system  500 , as well as guidewire G and introducer sheath  602 , may be removed from the patient, and arteriotomy site AR may be sealed. A suction catheter optionally may be positioned within filter  520  prior to retrieval of the filter to ‘vacuum out’ any emboli caught therein.  
      In order to collapse filter  520  for retrieval, sheath  510  of embolic protection system  500  optionally may be re-advanced through introducer  602  and over pullwire  540  (optionally, also over guidewire G) to contact a proximal region of the filter (see  FIGS. 12 ). The tapered proximal region may function as collapse element that facilitates sheathing of filter  520  for delivery and/or retrieval, e.g., by distributing forces applied to the filter by sheath  510  along a greater longitudinal length of the filter, as compared, for example, to embodiments of the filter that are not proximally tapered. Additional and alternative collapse elements may be provided with filter  520  or with sheath  510 . The collapse element may collapse the filter, e.g., by collapsing the filter braid.  
      Filter  520  alternatively may be retrieved by proximally retracting pullwire  540  without collapsing the filter within a retrieval sheath, thereby proximally retracting filter  520  directly through the patient&#39;s vasculature. As yet another alternative, a specialized retrieval sheath, e.g., a sheath of larger or smaller profile than sheath  510 , may be utilized. The retrieval sheath optionally may comprise a distally enlarged lumen to accommodate the collapsed filter.  
      In  FIG. 13F , if it is determined that the patient is a candidate for endovascular valve replacement, delivery system  100 , having replacement valve apparatus  10  disposed therein in a collapsed delivery configuration, may be endovascularly advanced over guidewire G through the introducer sheath, through filter  520  and across the patient&#39;s aortic valve AV. As during advancement of balloon catheter  700 , diverter filter  520  advantageously guides delivery system  100  past arterial branches of aorta A, while the delivery system is advanced through the filter. In this manner, filter  520  facilitates proper positioning of apparatus  10 , while protecting the aortic side branches from injury.  
      As it is expected that delivery system  100  may have a delivery profile on the order of about 18-21 Fr, preferably about 19 Fr, introducer sheath  602  optionally may be exchanged for a larger introducer sheath in order to accommodate the delivery system. Alternatively, in order to reduce the size of arteriotomy site AR, it may be desirable to remove the introducer sheath and to advance delivery system  100  directly through the arteriotomy site without an intervening introducer sheath, such that sheath  110  of the delivery system acts as the introducer sheath. Delivery system  100  optionally may comprise a rapid-exchange lumen for advancement over guidewire G.  
      If introducer sheath  602  is exchanged or removed, pullwire  540  temporarily may be disconnected from the exterior of the patient, e.g., by removing tape T. The introducer sheath then optionally may be removed or exchanged, and pullwire  540  may be re-affixed to the patient. During removal and/or exchange of introducer sheath  602  (i.e., while pullwire  540  is not affixed to the patient), a medical practitioner preferably grasps pullwire  540  and maintains its position relative to arteriotomy site AR, thereby maintaining the position of filter  520  deployed within the patient.  
      In  FIG. 13G , once replacement valve apparatus  10  has been properly positioned across the patient&#39;s diseased aortic valve AV, sheath  110  of delivery system  100  may be retracted, and apparatus  10  may be deployed as described previously, thereby endovascularly replacing the patient&#39;s diseased valve. Emboli E generated during deployment of apparatus  10  are diverted away from the patient&#39;s carotid arteries and cerebral vasculature by filter  520 . Delivery system  100  then may be removed from the patient.  
      Filter  520  optionally may be vacuumed out via a suction catheter, e.g., suction drawn through sheath  110 . Filter  520  and guidewire G then may be removed from the patient as discussed previously, and arteriotomy site AR may be sealed to complete the procedure. Guidewire G may retrieved and removed before, during or after retrieval and removal of filter  520 . Retrieval and removal of the filter may comprise reintroduction of sheath  510  (e.g., over pullwire  540  and directly through the arteriotomy site, through an introducer sheath or through sheath  110  of delivery system  100 ) and collapse of filter  520  within the sheath. Alternatively, removal of filter  520  may comprise retraction of pullwire  540  without collapse of the filter in an intervening retrieval sheath. Sealing of the arteriotomy site may comprise any known sealing method, including, but not limited to, application of pressure, introduction of sealants, suturing, clipping and/or placement of a collagen plug.  
      In  FIGS. 13 , although diversion and/or filtering of emboli illustratively has been conducted during both valvuloplasty and endovascular deployment of replacement valve apparatus, it should be understood that such diversion/filtering alternatively may be performed only during valvuloplasty or only during endovascular valve replacement. Furthermore, it should be understood that embolic protection may be provided during deployment of any endovascular replacement valve apparatus and is not limited to deployment of the specific embodiments of such apparatus described herein.