Abstract:
Apparatuses and methods are disclosed for reducing the size of openings within a heart valve or other opening in the wall of a body lumen by implanting an elastically expanded member around the opening and then permitting the expandable member to contract. The expandable member may encircle a portion of an inflatable member, the distal end of which is inserted through the opening along with the expandable member. The inflatable member is inflated to expand the expandable member and then drawn proximally form the opening to drive projections formed on the expandable member into the valve or wall. The inflatable member is then withdrawn, allowing the expandable member to elastically contract. The inflatable member may have first and second stages, where the second stage is distal of the first stage and has a larger inflated diameter.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. The Field of the Invention 
         [0002]    This application relates generally to systems and method for percutaneously associating adjacent tissue, and more particularly for repairing mitral valve abnormalities. 
         [0003]    2. The Relevant Technology 
         [0004]    Referring to  FIGS. 1A and 1B , the mitral valve  10  of the heart  12  prevents the flow of blood from the left ventricle  14  into the right atrium  16  during ventricular systole. The mitral valve  10  includes two leaflets  18   a ,  18   b  that spread to permit blood flow into the left ventricle  14  during ventricular diastole and are forced together by pressure within the left ventricle  14  during ventricular systole. Degeneration of the mitral valve  10  or surrounding tissue may result in a gap  20  between the leaflets  18  during ventricular systole, resulting in regurgitation of blood into the left atrium. When severe, mitral regurgitation can lead to heart failure and abnormal heart rhythms. 
         [0005]    Current methods of repairing the mitral valve  10  include the joining of the valve leaflets  18   a ,  18   b  at one or more locations to decrease the flow cross section and prevent valve regurgitation. This method is generally referred to as the Alfieri method. Currently known devices that permit the Alfieri method to be practiced percutaneously include devices for gripping the valve leaflets  18   a ,  18   b  and suturing them together. However, these percutaneous methods face considerable drawbacks due to the difficulty in grasping the valve leaflets due to their rapid movement. The methods also require adequate visualization of the valve which is difficult to achieve. Available visualization techniques using fluoroscopy can be difficult to use, since a sufficient bolus of contrast is difficult to administer. Echocardiography is likewise unable to provide adequate visualization of the mitral valve. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    These and other limitations are overcome by embodiments of the disclosure, which relates to apparatuses and methods for repairing a mitral valve, patent foramen ovale, or a puncture site in a blood vessel or wall of another body lumen are disclosed. In particular, apparatuses and methods are disclosed for inserting a portion of an inflatable member encircled by an elastically expandable member through the mitral valve, or other opening in a wall of a body lumen. The elastically expandable member bears projections adapted to penetrate the wall or valve. The inflatable member may be inflated to expand the expandable member. The inflatable member may then be drawn through the valve or opening such that the projections are driven into the valve or opening. The inflatable member may then be withdrawn and the expandable member allowed to contract in order to reduce the size of the opening in the valve or wall. The inflatable member may be deflated either before or after withdrawal. 
         [0007]    In one aspect of the invention, the elastically expandable member includes a thin circuitous member defining a base line lying in a plane and circumscribing the inflatable member. The thin circuitous member may be bent to define a first plurality of peaks extending a first distance measured from the base line parallel to the inflatable member and a second plurality of peaks extending a second distance measured from the base line parallel to the inflatable member, the second distance being substantially greater than the first distance. 
         [0008]    In another aspect of the invention, a catch is secured adjacent the inflatable member and has a diameter greater than that of an adjacent portion of the elastically expandable member when the inflatable member is not inflated. 
         [0009]    In another aspect of the invention, the inflatable member includes a first portion and a second portion, the elastically expandable member encircling the first portion and the second portion having an inflated diameter substantially greater than the first portion. 
         [0010]    Additional features and advantages of the disclosure will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the disclosure. The features and advantages of the disclosure may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    To further clarify some of the advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is appreciated that these drawings depict only illustrated embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
           [0012]      FIG. 1A  is a partial cutaway view of a heart; 
           [0013]      FIG. 1B  is an illustration of a mitral valve; 
           [0014]      FIG. 2  is a side view of a device for implanting an elastically expandable member in accordance with an embodiment of the present invention; 
           [0015]      FIG. 3  is an isometric view of the device for implanting an elastically expandable member positioned within a mitral valve in accordance with an embodiment of the present invention; 
           [0016]      FIG. 4  is a schematic diagram of an inflation system for use with the device for implanting an elastically expandable member in accordance with an embodiment of the present invention; 
           [0017]      FIGS. 5A and 5B  are isometric views of an elastically expandable member in accordance with an embodiment of the present invention; 
           [0018]      FIG. 6  is a partial side view of the device for implanting an elastically expandable member in accordance with an embodiment of the present invention; 
           [0019]      FIG. 7  is a front end view of the device for implanting an elastically expandable member in accordance with an embodiment of the present invention; 
           [0020]      FIGS. 8A through 8F  illustrate a method for implanting an elastically expandable member in accordance with an embodiment of the present invention; 
           [0021]      FIG. 9  is a side view of a device for implanting an elastically expandable member having multiple inflatable portions in accordance with an embodiment of the present invention; 
           [0022]      FIG. 10  is a schematic diagram of an inflation system for use with the device of  FIG. 9  in accordance with an embodiment of the present invention; 
           [0023]      FIGS. 11A through 11C  illustrate another method for implanting an elastically expandable member in accordance with an embodiment of the present invention; 
           [0024]      FIGS. 12A through 16B  illustrate a method for implanting an elastically expandable member in an opening within a wall of a body lumen in accordance with an embodiment of the present invention; 
           [0025]      FIG. 17  illustrates an alternative embodiment of an elastically expandable member in accordance with an embodiment of the present invention; and 
           [0026]      FIGS. 18A through 18C  illustrate a method for implanting the elastically expandable member of  FIG. 17 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    Embodiments of the invention relate to associating adjacent tissue including joining adjacent tissue. Tissue can be brought together by an expandable medical device that can be expanded during deployment. The device includes attachment means to grasp or connect to the adjacent tissue. The medical device then collapses to reduce in profile and bring adjacent tissue together. By way of example only, embodiments of the invention can be used to repair mitral valves, perform vessel closure, perform PFO (Patent Foramen Ovale) closure, and repair other septal defects. 
         [0028]    Referring to  FIG. 2 , an apparatus  30  for repairing a mitral valve may include an inflatable member  32 , an elastically expandable member  34  encircling or disposed around the inflatable member  32 , and a catheter  36 . The inflatable member  32  includes a distal end  40  and a proximal end  38  secured to the catheter. An inflation medium may be delivered through the catheter  36  to the inflatable member through the proximal end  38 . The inflatable member  32  may have an uninflated diameter less than that of the lumen of the catheter  36 . 
         [0029]    A safety catch  42  may be secured near the distal end of the inflatable member  32  and prevent the expandable member  34  from sliding off of the inflatable member before placement as described hereinbelow. In some embodiments, the safety catch may cover a distal end  40  of the inflatable member  34 . The safety catch  42  may include a structure having an outer diameter greater than an undeformed outer diameter of the immediately adjacent portion of the inflatable member  34  to which it secures, such as near the distal end  40  thereof. For example, at least a length of the inflatable member  32  immediately adjacent the safety catch  42  may have a relaxed outer diameter less than the outer diameter of the safety catch. The length may be at least half as wide as the expandable member  34  along the longitudinal axis of the inflatable member  32 . The safety catch  42  preferably includes a structure having an outer diameter greater than an undeformed inner diameter of the expandable member  34 . Alternatively, the safety catch  42  has an outer diameter greater than an uninflated diameter of the inflatable member  32 . In the illustrated embodiment, the safety catch  42  is a cylindrical structure. However, other shapes having different cross section may be used having at least a portion therefore with a diameter greater than either the undeformed inner diameter of the expandable member  34  or the uninflated diameter of the inflatable member  32 . 
         [0030]    The inflatable member  32  may define a lumen for receiving a guide wire  44 . The guide wire  44  may be guided to an operation site as known in the art. The catheter  36  and inflatable member  32  may then be guided along the guide wire  44  to the operation site. In some embodiments, the inflatable member  32  is positioned within the catheter  36  during insertion proximate the distal end  40  thereof during insertion of the catheter. In other embodiments, the catheter  36  is first inserted to the operation site after which the inflatable member  32  and expandable member  34  are fed through the catheter  36  to the operation site. 
         [0031]    Referring to  FIG. 3 , while still referring to  FIG. 2 , the inflatable member  32  may bear markers  46  including a radiopaque material. Examples of biocompatible radiopaque materials include platinum, iridium, tungsten, tantalum, gold, and alloys thereof. In an alternative embodiment, the markers  46  are designed to be highly visible using echocardiography, such as by forming the markers  46  of a very dense material. The markers  46  may be elongate in shape having a direction of elongation extending parallel to a distal direction  48  in which the inflatable member  32  is moved during placement in the operation site as described hereinbelow. 
         [0032]    During placement in a mitral valve  10  the radiopaque markers  46  are approximately aligned with a midline  50  of the mitral valve  10  using fluoroscopy or other visualization technique. For example, the inflatable member  32  may be inserted within the mitral valve  10  and then rotated into the position shown in  FIG. 3 . Alternatively, the markers  46  may be positioned on or adjacent the midline  50  prior to insertion such that rotation is not necessary. 
         [0033]    As is readily apparent, the high visibility of the markers  46  using fluoroscopic or echocardiographic imaging enables ready positioning of the inflatable member  32  without the need for detailed imaging of the mitral valve  10 . The opening between the leaflets  18   a ,  18   b  of the mitral valve  10  may be readily apparent using echocardiography or fluoroscopy equipment. The high visibility of the markers  46  therefore enables them to be readily aligned such that they both lie on a midline  50  perpendicular to the opening between the leaflets  18   a ,  18   b.    
         [0034]    Referring to  FIG. 4 , inflatable member  32  may be inflated by means of a pressure source  52  external to the patient&#39;s body and coupled to the inflatable member  32  by means of a tube  54  extending from the pressure source  52 , through the catheter  36 , and to the inflatable member  32 . In some embodiments, the lumen  36  of the catheter provides a seal with the proximal end  38  of the inflatable member, such that a separate tube  56  is not needed within the catheter  36 . An inflation medium supplied from the source  52  may be controlled by a valve  56  that is selectively opened by the operator to inflate the inflatable member according to the method described hereinbelow. The valve  56  may also control selective release of the inflation medium from the inflation member  32 . In accordance with this invention, the inflation medium provided by pressure source  52  may be a gas or a liquid. For example, it may be any biocompatible gas, such as carbon dioxide, that is typically used in medical procedures, or it may be a fluid, such as saline, which also is also widely used in medical procedures such as those contemplated in this disclosure. 
         [0035]    Referring to  FIG. 5A , the expandable member  34  encircles the inflatable member  32  and elastically deforms as the inflatable member  32  is inflated. The expandable member  34  includes one or more projections  60  adapted to pierce the leaflets  18   a ,  18   b  of the mitral valve  10 . Accordingly, the projections  60  may have a converging profile such that the ends  62  of the projections  60  or of selected projections  60  are sharp enough to readily penetrate the leaflets  18   a ,  18   b.    
         [0036]    In the illustrated embodiment, the expandable member  34  is formed from a thin elastic material bent or shaped to form first peaks  64  and second peaks  66 . For example, the expandable member  34  may be formed from a resilient wire including a material such as nitinol. 
         [0037]    Referring to  FIG. 5B , in some embodiments the peaks  66  are not themselves expandable in order to reduce tissue spreading when the expandable member  34  is inserted into the leaflets  18   a ,  18   b . As shown in  FIG. 5B , in such embodiments, the peaks  66  may be secured to the expandable member due to monolithic formation therewith or by means of welding. Alternatively, peaks  66  may be formed by undulations in the expandable member that have been welded or otherwise fastened to prevent spreading of the peaks  66  when the expandable member  34  is expanded. 
         [0038]    Referring to  FIG. 6 , the second peaks  66  may be longer than the first peaks  64  and serve as the projections  60  for piercing the leaflets  18   a ,  18   b  of the mitral valve or of the tissue to be closed, joined, or associated. The second peaks  66  may include one or more beveled edges  70  at their ends to provide a sharper point for penetrating the leaflets  18   a ,  18   b  or for penetrating other tissue, such as vessel walls by way of example only. The second peaks  66  may be separated from one another by means of one or more first peaks  64 . The expandable member  34  may define a base line  68 , which is a base circle  68  in the illustrated embodiment. However, the base line  68  may have any shape forming a closed loop. The base line  68  lies in a plane perpendicular to the longitudinal axis of the inflatable member  32 , or in other words perpendicular to the distal direction  48 . 
         [0039]    The first peaks  64  may extend up to a first distance  72  from the base circle  68  and the second peaks  66  may extend at least a second distance  74  from the base circle  68 . The second distance  74  may be substantially greater than the first distance  72 . For example, the second distance  74  may be between 1.1 and 2 times the first distance  72 , or between about 1.2 and 1.6 times the first distance  72 . The second distance  74  may also be measured relative to the diameter of base circle  68 . For example, second distance  74  may be between about 0.3 and 0.8 of the diameter of base circle  68 , although any ratio may be contemplated within this invention. 
         [0040]    The second peaks  66  may also project away from the inflatable member  32  with distance from the base circle  68 . For example, the second peaks  66  may define an angle  76  with respect to the inflatable member that is between 5 and 25 degrees, or between about 5 and 15 degrees. The angled second peaks  66  enable the member to engage the tissue to be joined by providing a separation between the second peaks  66  and the inflatable member  32 . The angle  76  may also change as the expandable member is expanded by the inflatable member. 
         [0041]    Referring to  FIG. 7 , in the illustrated embodiments, the second peaks  66  are positioned an angular distance  78  from the markers  46  such that they will be adjacent to the leaflets  18   a ,  18   b  when the markers  46  are aligned with the midline  50  of the mitral valve  10 . For example, projections  60  may be within an angular distance  78  from the marker  46  equal to between about 5 and 30 degrees, or between about 5 and 15 degrees. In the illustrated embodiment, at least two of the projections  60  engage each leaflet  18   a ,  18   b . However, in other embodiments, at least three or more projections  60  may engage each leaflet  18   a ,  18   b . In some embodiments, some of the first peaks  64  may also engage the tissue in certain instances. 
         [0042]    For example, the device  30  illustrated in  FIGS. 2-7  depict an expandable medical device  30  in both an expanded an unexpanded state. In an unexpanded state, the device is positioned at an operational site, such as at a mitral valve. The device  30  can include a generally tubular body formed from a material such as a shape memory material as described below. The device  30  may comprise a ring that may be circular in shape. One will appreciate that the device  30  can include a pattern or configuration that permits the device  30  to be placed into a delivery configuration having a first diameter and radially expanded to at least a deployment configuration having a second, larger diameter as explained in greater detail below. In one embodiment, the first diameter corresponds to an unconstrained configuration of the device  30  and the device  30  may be configured to return to the unconstrained configuration after being subject to a deforming force, such as applied by the inflatable member to expand the device  30  during deployment. 
         [0043]    The device  30  can have a serpentine or undulating configuration formed from a plurality of peaks and corresponding valleys. As previously described, some of the peaks are longer than other peaks. As illustrated in  FIG. 5 , for example, the projections  60  may correspond to peaks that are longer that other peaks. These peaks are also configured to engage tissue in order to bring adjacent tissue closer together. The serpentine or undulating configuration can be sinusoidal, triangular, square, and the like. In some instances, the serpentine or undulating configuration can include multiple shapes that are repeated in series and/or have a similar shape that varies in size. 
         [0044]    A device  30  such as is described with respect to  FIGS. 2 through 7 , may be used in accordance with a method illustrated in  FIGS. 8A through 8F . Referring specifically to  FIG. 8A , a portion of the inflatable member  32  encircled by the expandable member  34  is urged through the mitral valve  10  into the left ventricle  14  along the distal direction  48  such that the proximal end  38  and distal end  40  of the inflatable member  32  are positioned on opposite sides of the mitral valve  10 . In some embodiments, the inflatable member  32  is extended from the catheter  36  prior to insertion through the mitral valve  10 . In other embodiments, the catheter  36  is inserted through the mitral valve  10  and then withdrawn as the inflatable member  32  is forced out of the catheter  36 , leaving the inflatable member in the position shown in  FIG. 8A . 
         [0045]    Referring to  FIG. 8B , the inflatable member  32  may then be inflated in order to expand the expandable member  34 . Expansion of the inflatable member  32  may also aid in positioning of the leaflets  18   a ,  18   b  of the mitral valve  10 , which would otherwise be prone to rapid movement responsive to beating of the heart  12 . In some embodiments inflation of the inflatable member  32  results in an inflated diameter that is between 1.5 and three times either the uninflated diameter of the inflatable member  32  or the inner diameter of the lumen of the catheter  36 . In one embodiment, the inflated diameter is between about two and three times either the uninflated diameter of the inflatable member  32  or the inner diameter of the catheter  36 . 
         [0046]    Referring to  FIG. 8C , the inflatable member  32  and expandable member  34  may then be urged in proximal direction  80  such that at least some of the projections  60  penetrate the leaflets  18   a ,  18   b  of the mitral valve  10 . In some embodiments, only the second peaks  66  penetrate into the leaflets  18   a ,  18   b . In other embodiments, some of the first peaks  64  also penetrate the leaflets  18   a ,  18   b.    
         [0047]    Referring to  FIG. 8D , the inflatable member  32  may then be urged further along the proximal direction  80  such that the expandable member  34  is moved off of the inflatable member  32 . The inflatable member  32  may be partially or completely deflated prior to urging the inflatable member  32  away from the expandable member  34 . For example, the inflatable member  32  may remain partially inflated such that the partially inflated diameter is greater than a largest outer diameter of the safety catch  42  such that the expandable member  34  is able to slide over the catch  42 . 
         [0048]    Referring to  FIG. 8E , following removal of the inflatable member  32 , the expandable member  34  may contract due to biasing forces within the expandable member  34 . As shown in  FIG. 8F , contraction of the expandable member  34  tends to draw the leaflets  18   a ,  18   b  together, thereby reducing mitral valve regurgitation. In some embodiments, two or more expandable members  34  may be placed within a mitral valve according to the method illustrated in  FIGS. 8A through 8F  in order to further reduce regurgitation. 
         [0049]    Referring to  FIG. 9 , in an alternative embodiment, the inflatable member  32  includes a first portion  90  and a second portion  92 . The first portion  90  is located nearer the proximal end  38  and the second portion  92  is located nearer the distal end  40  of the inflatable member  32 . The second portion  92  has an inflated diameter  94  that is larger than the inflated diameter  96  of the first portion. For example, the inflated diameter  94  of the second portion  92  may be between 1.3 and four times, or between about 1.4 and two times, the inflated diameter  96  of the first portion  90 . Inasmuch as the left ventricle has a profile that is considerably larger than the mitral valve diameter a device may be used with a second portion  92  having diameter that is considerably larger than the ranges specified above. 
         [0050]    The uninflated diameters of both the first portion  90  and second portion  92  may both be less than an inner diameter of the lumen of the catheter  36 . In the illustrated embodiment, the second portion  92  also has a longer length  98  along the distal direction  48  than the length  100  of the first portion. For example, the inflated length  98  of the second portion  92  may be between 1.3 and four times, or between about 1.4 and two times the length  100  of the first portion. However, it will be appreciated that the left ventricle has a length that is considerably greater than the left atrium length and therefore a device may be used with a second portion  92  diameter that is considerably larger than the ranges specified above. The first portion  90  and second portion  92  may be in fluid communication with one another or may be isolated from one another and filled by means of separately controlled inflation channels extending through the catheter  36 . 
         [0051]    Referring to  FIG. 10 , in embodiments where the first portion  90  and second portion  92  are separate chambers, each portion  90 ,  92 , may be coupled to a separate inflation line  54   a ,  54   b  coupled to the pressure source  52  and controlled by separate valves  56   a ,  56   b , respectively to allow inflation medium to enter and leave the portions  90 ,  92 . By selectively opening and closing one or both of the valves  56   a ,  56   b , the diameters of the portions  90 ,  92  may be independently controlled in order to deploy the expandable member  34  according to the methods described hereinbelow. 
         [0052]    Referring to  FIG. 11A , following insertion of the apparatus  30  into the mitral valve  10 , such as is shown in  FIG. 8A , the portions  90  and  92  may be inflated such that the diameter of the second portion  92  is substantially greater than that of the first portion  90 . The difference in the diameters of the first portion  90  and second portion  92  may be sufficiently large to prevent the expandable member  34  from sliding toward the distal end  40 . 
         [0053]    Referring to  FIG. 11B , the inflatable member  32  and expandable member  34  may then be drawn in the proximal direction  80  a sufficient distance that the projections  60  of the expandable member  34  penetrate the leaflets  18   a ,  18   b  of the mitral valve  10 . The portions  90  and  92  may then be deflated as shown in  FIG. 11C  and the inflatable member  32  drawn in the proximal direction  80 , leaving the expandable member in the position shown in  FIG. 8F . In some instances, the second portion  92  can be used to push the projections  60  into the leaflets  18   a  and  18   b  prior to being deflated. This can ensure that the device  30  is securely engaged with the tissue to be brought together. 
         [0054]    Referring to  FIG. 12A through 15B , the apparatus  30  may also be used for associating other types of tissue. For example, the apparatus may be used to close a patent foramen ovale (PFO), a septal defect, or a puncture site in a wall of a body lumen, such as a blood vessel. 
         [0055]    Referring to  FIGS. 12A and 12B , an opening  110  in a wall  112  of tissue may be irregular in shape, particularly if formed as the result of accidental trauma. The wall  112  may represent the wall of a blood vessel, organ, the atrial or ventricular septum of the heart, or other structure. The inflatable member  32  and expandable member may be inserted through the opening  110 , as shown in  FIG. 12B , such that the distal end  40  and expandable member  34  are located on an opposite side of the wall  112  than the proximal end  38 . 
         [0056]    Referring to  FIGS. 13A and 13B , the inflatable member  32  may then be inflated to substantially and/or partially occupy the entire opening  110  (e.g. between 70% and 100%, preferably greater than 90%, of the opening). Where the inflatable member  32  has a first portion  90  and second portion  92  with different inflated diameters, inflating the inflatable member may include inflating both portions  90  and  92 . 
         [0057]    Referring to  FIG. 14 , the inflatable member  32  may then be urged in the proximal direction  80  such that the peaks  60  of the expandable member  34  are urged into the wall  112 . The expandable member  34  may be the same as in other embodiments described herein. In some embodiments, where the expandable member is used for closing apertures other than the mitral valve, the projections  60 , such as the second peaks  66 , may be distributed along the entire circumference of the expandable member at regular intervals (e.g. between 15 and 45 degrees). In some embodiments, after the expandable member  34  is urged into the wall  112 , the inflatable member  32  may be further inflated (as shown by the dotted lines in  FIG. 14 ) in order to prevent bleeding through the opening  110 . 
         [0058]    Referring to  FIG. 15 , after the expandable member  34  is implanted in the wall  112 , the inflatable member  32  may then be deflated and withdrawn along the proximal direction  80  to leave the expandable member  34  in the configuration shown in  FIGS. 16A and 16B . As is readily apparent, the expandable member  34  is able to significantly decrease the size of the opening  110 , despite the irregular shape of the opening  110 . 
         [0059]    The expandable member  34 , of the present invention can be made of a variety of materials, such as, but not limited to, those materials which are well known in the art of medical device manufacturing. Generally, the materials for the expandable member  34  can be selected according to the structural performance and biological characteristics that are desired. Materials well known in the art for preparing medical devices (e.g., endoprostheses), such as polymers and metals, can be employed in preparing the expandable member  34 . 
         [0060]    In one embodiment, the medical device can include a material made from any of a variety of known suitable materials, such as a shaped memory material (“SMM”) or superelastic material. For example, the SMM can be shaped in a manner that allows for restriction to induce a substantially tubular, linear orientation while within a delivery shaft (e.g., delivery catheter or encircling an expandable member), but can automatically retain the memory shape of the medical device once extended from the delivery shaft. SMMs have a shape memory effect in which they can be made to remember a particular shape. Once a shape has been remembered, the SMM may be bent out of shape or deformed and then returned to its original shape by unloading from strain or heating. SMMs can be shape memory alloys (“SMA”) or superelastic metals comprised of metal alloys, or shape memory plastics (“SMP”) comprised of polymers. 
         [0061]    An SMA can have any non-characteristic initial shape that can then be configured into a memory shape by heating the SMA and conforming the SMA into the desired memory shape. After the SMA is cooled, the desired memory shape can be retained. This allows for the SMA to be bent, straightened, compacted, and placed into various contortions by the application of requisite forces; however, after the forces are released, the SMA can be capable of returning to the memory shape. The main types of SMAs are as follows: copper-zinc-aluminium; copper-aluminium-nickel; nickel-titanium (“NiTi”) alloys known as nitinol; and cobalt-chromium-nickel alloys or cobalt-chromium-nickel-molybdenum alloys known as elgiloy. The nitinol and elgiloy alloys can be more expensive, but have superior mechanical characteristics in comparison with the copper-based SMAs. The temperatures at which the SMA changes its crystallographic structure are characteristic of the alloy, and can be tuned by varying the elemental ratios. 
         [0062]    For example, the primary material of the expandable member  34  can be of a NiTi alloy that forms superelastic nitinol. Nitinol materials can be trained to remember a certain shape, straightened in a shaft, catheter, or other tube, and then released from the catheter or tube to return to its trained shape. Also, additional materials can be added to the nitinol depending on the desired characteristic. 
         [0063]    An SMP is a shape-shifting plastic that can be fashioned into the expandable member  34  in accordance with the present invention. When an SMP encounters a temperature above the lowest melting point of the individual polymers, the blend makes a transition to a rubbery state. The elastic modulus can change more than two orders of magnitude across the transition temperature (“T tr ”). As such, an SMP can be formed into a desired shape of expandable member  34  by heating it above the T tr , fixing the SMP into the new shape, and cooling the material below T tr . The SMP can then be arranged into a temporary shape by force and then resume the memory shape once the force has been applied. Examples of SMPs include, but are not limited to, biodegradable polymers, such as oligo(ε-caprolactone)diol, oligo(ρ-dioxanone)diol, and non-biodegradable polymers such as, polynorborene, polyisoprene, styrene butadiene, polyurethane-based materials, vinyl acetate-polyester-based compounds, and others yet to be determined. As such, any SMP can be used in accordance with the present invention. 
         [0064]    Also, it can be beneficial to include at least one layer of an SMA and at least one layer of an SMP to form a multilayered body; however, any appropriate combination of materials can be used to form a multilayered medical device. 
         [0065]    The expandable member  34  can be comprised of a variety of known suitable deformable materials, including stainless steel, silver, platinum, tantalum, palladium, cobalt-chromium alloys such as L605, MP35N, or MP20N, niobium, iridium, any equivalents thereof, alloys thereof, and combinations thereof. The alloy L605 is understood to be a trade name for an alloy available from UTI Corporation of Collegeville, Pa., including about 53% cobalt, 20% chromium and 10% nickel. The alloys MP35N and MP20N are understood to be trade names for alloys of cobalt, nickel, chromium and molybdenum available from Standard Press Steel Co., Jenkintown, Pa. More particularly, MP35N generally includes about 35% cobalt, 35% nickel, 20% chromium, and 10% molybdenum, and MP20N generally includes about 50% cobalt, 20% nickel, 20% chromium and 10% molybdenum. 
         [0066]    Also, the expandable member  34  can include a suitable biocompatible polymer in addition to or in place of a suitable metal. The polymeric expandable member  34  can include a biocompatible material, such as biostable, biodegradable, or bioabsorbable materials, which can be either plastically deformable or capable of being set in the deployed configuration. If plastically deformable, the material can be selected to allow the medical device (e.g., stent) to be expanded in a similar manner using an expandable member so as to have sufficient radial strength and scaffolding and also to minimize recoil once expanded. If the polymer is to be set in the deployed configuration, the expandable member  34  can be provided with a heat source or infusion ports to provide the required catalyst to set or cure the polymer. Biocompatible polymers are well known in the art, and examples are recited with respect to the polymeric matrix. Thus, the expandable member  34  can be prepared from a biocompatible polymer. 
         [0067]    Moreover, the expandable member  34  can include a radiopaque material to increase visibility during placement. Optionally, the radiopaque material can be a layer or coating any portion of the expandable member  34 . The radiopaque materials can be platinum, tungsten, silver, stainless steel, gold, tantalum, bismuth, barium sulfate, or a similar material. 
         [0068]    Referring to  FIG. 17 , in some embodiments the expandable member  34  may be embodied as a ring member  120  having a single projection  122  with a sharpened distal tip  124 . The ring member  120  may include an elastic material that can expand upon inflation of the inflatable member  32 . The ring member may also be formed of an undulating wire or other thin member in order to facilitate expansion upon inflation. The single projection  122  may have a relaxed of shape-memory shape that is curved in shape. 
         [0069]    As shown in  FIGS. 18A and 18B , the expandable member  34  of  FIG. 17  may be placed on an inflatable member  32 , such as any of the inflatable members illustrated herein. Upon inflation of the inflatable member  32 , the projection  122  is urged into a straightened configuration such that the sharpened distal tip  124  may be urged in the distal direction  40  through one of the leaflets  18   a . Referring to  FIG. 18C , upon deflation of the inflatable member  32 , the projection  122  is allowed to relax to its circular configuration, causing the sharpened distal tip  124  to be driven through the opposing leaflet  18   b . The inflatable member  32  may then be removed. 
         [0070]    The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.