CLAIM OF PRIORITY 
       [0001]    The present application is based on and a claim of priority is made under 35 U.S.C. Section 119(e) to a provisional patent application that is currently pending in the U.S. Patent and Trademark Office, namely, that having Ser. No. 61/729,152 and a filing date of Nov. 21, 2012, and which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention is directed to an instrument assembly and method of use and application in the treatment of heart valve malfunction. In more specific terms the instrument assembly is specifically adapted to treat mitral regurgitation by means of a direct entry of the instrument through the atrial wall rather than through the vascular system, in order to apply sufficient tension to a prolapsing leaflet, including the anterior leaflet and/or the posterior leaflet of the mitral valve, in order to overcome mitral regurgitation. 
         [0004]    2. Description of the Related Art 
         [0005]    The human heart is a four chambered pump that moves blood efficiently through the vascular system. During normal operation, blood enters the heart through the vena cava and flows into the right atrium. Thereafter, blood flows from the right atrium through the tricuspid valve and into the right ventricle. Upon contraction of the right ventricle, blood is forced through the pulmonic valve and into the lungs for oxygenation. The oxygenated blood returns from the lungs and enters the heart through the left atrium and passes through the mitral valve into the left ventricle. Upon contraction of the left ventricle the blood therein flows through the aortic valve and into the aorta and throughout the vascular system. 
         [0006]    The mitral valve is disposed in flow regulating communication between the left atrium and the left ventricle. It is composed of two valve leaflets, the mitral valve annulus, which forms a ring that supports the valve leaflets; papillary muscles, which tether the valve leaflets to the left ventricle wall, by preventing them from prolapsing back into the left atrium. Chordae tendineae serve to connect the mitral valve leaflets to the papillary muscles thereby further preventing the leaflets from prolapsing back into the left atrium. A dysfunction of any of these components of the mitral valve can cause “mitral regurgitation”. Mitral regurgitation is a disorder of the heart in which the mitral valve does not close properly when the heart pumps out blood. This abnormal leaking of blood from the left ventricle, through the mitral valve and, into the left atrium when the left ventricle contracts, results in the “regurgitation” of blood back into the left atrium. It is generally recognized in the medical profession that mitral regurgitation is the second most common form of valvular heart disease. 
         [0007]    As generally set forth above, when properly functioning, the anterior and posterior valve leaflets of the mitral valve overlap during contraction of the left ventricle and prevent blood from flowing back into the left atrium. This overlap of the 2 leaflets leaning upon each other is called the coaptation and absorbs most of the strain on the mitral apparatus during the ventricular contraction. However, when the mitral valve malfunctions, due to various cardiac diseases, the leaflets are no longer coapting resulting in the mitral valve remaining partially open during ventricular contraction. In turn this allows the “regurgitation” of the blood back into the left atrium, as generally set forth above. When the mitral valve does not close hermetically during the ventricular contraction, the aforementioned back flow of blood to the atrium and the pulmonary vasculature, results in a deleterious condition. More specifically, this condition increases the work load to the heart and may lead to heart failure. 
         [0008]    Methods of treating conditions relating to the malfunctioning of the heart valve specifically including valve incompetencies, mitral valve leakage and other heart failure conditions may be in various stages of development such as the extending of an elongate member transverse across a corresponding or affected heart chamber. Each end of the elongate member extends through a wall of the heart such as the septum wall and an oppositely disposed wall portion, wherein first and second anchoring members are connected to corresponding ends of the elongate member but are disposed external of the heart chamber. Connecting clips or the like are applied to the corresponding exterior ends of the elongate member, resulting in the papillary muscles within the chamber to be effectively repositioned. A predetermined force is applied to the heart itself and/or the affected portions of the heart chamber. 
         [0009]    Other specific treatments associated with mitral regurgitation sometimes may include the replacement of the mitral valve, resulting in traumatic and frequently dangerous surgical procedures being performed on a patient. 
         [0010]    Accordingly, there is a need in the medical arts for appropriate instrumentation and attendant methods of overcoming heart valve malfunctions, specifically including mitral regurgitation. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention is directed to an instrument assembly and attendant method for treating heart valve malfunction. In more specific terms, the instrumentation and method are specifically, but not exclusively, adapted for the treatment of mitral regurgitation. However, for purposes of clarity and in order to emphasize the versatility of the various embodiments of the present invention, the subject instrument assembly and method will be described generically regarding treatment of a predetermined heart valve. In addition, the present invention will be more specifically described in regard to a procedure involving correction of a prolapsing mitral valve leaflet, which may include the anterior mitral valve leaflet and/or the posterior valve leaflet correcting of mitral regurgitation. 
         [0012]    Accordingly, the instrument assembly of the present invention includes an introductory sheath formed of a material of sufficient rigidity to facilitate the penetration and passage through various portions of the heart and mitral valve. As such, the introductory sheath may be said to be formed of at least a “semi-rigid” material. However, this term is to be understood to include material having sufficient flexibility to be manipulated or “steered” through and/or along a predetermined path during the delivery of the sheath and associated components of the instrument assembly to predetermined portions of the heart. Moreover, in one preferred embodiment the sheath will be sufficiently maneuverable to pass through the atrial wall into interior portions of the heart such as the left atrium and left ventricle. In addition and as described in greater detail hereinafter, an introduction assembly and a delivery catheter will be used to facilitate the positioning the introductory sheath into the thoracic cavity and through the atrial wall or other preferred exterior locations of the heart wall. 
         [0013]    Additional structural operative features of the instrument assembly include the provision and utilization of at least one, or under required circumstances, more than one elongated chord formed of a biocompatible material and being at least partially flexible. The material from which the chord is formed should have sufficient and/or predetermined tensile strength to exert a predetermined tension on the predetermined, prolapsing valve leaflet as the chord extends between a corresponding portion of the heart wall, such as the ventricular wall, as also more fully described hereinafter. The chord is initially housed concentrically within the interior of the introductory sheath, wherein the sheath and the chord are concurrently movable relative to the heart as well as throughout a portion of the interior thereof. As set forth above, the introductory sheath is formed of a material having physical characteristics that allow it to be accurately manipulated so as to be steerable in such a manner that its tip can aim towards the different designated portions of the anterior or posterior mitral valve leaflets that are in the siege of the prolapse. 
         [0014]    Also, the exteriorly concentric introductory sheath is movable relative to and along the length of the chord so as to accommodate proper and intended placement and anchoring of the chord within the heart chamber. Therefore, the sheath is movable with the chord into and through predetermined portions of the heart chamber and movable relative to the chord after proper anchoring, securing and/or intended placement of the chord within the heart chamber. Accordingly, the instrument assembly of the present invention also includes an anchor secured to an outer or distal end of the chord. The anchor may also be sufficiently sharpened, pointed or otherwise configured to penetrate an intended heart valve leaflet, such as a prolapsing leaflet of the mitral valve. Further, the penetration and passage of the anchor, the chord, and the introductory sheath substantially through the predetermined valve leaflet may thereby be facilitated. 
         [0015]    When properly positioned, the anchor is structured to be secured to a substantially opposing portion of the heart wall, such as the ventricular wall associated with the left ventricle and/or the papillary muscles associated therewith. In order to assure secure anchoring of the distal end of the chord with the corresponding ventricular wall, a gripping structure may be operatively attached to a remainder of the anchor and disposable into an outwardly and/or radially extending orientation. When so disposed, the gripping structure, in combination with the remainder of the anchor, eliminates or significantly restricts the inadvertent detachment of the anchor, and the distal end of the chord attached thereto, from the corresponding ventricular wall portion. In at least one preferred embodiment of the present invention, the anchor and the gripping structure are disposed and applied so as to penetrate the corresponding portion of the ventricular wall but not extend there through. Therefore, the anchored relation of the gripping structure, anchor and the connected distal end of the chord may be defined by a penetration into the interior of the ventricular wall rather than a passage completely there through. Complications associated with sealing and exterior attachment of the chord to the exterior of the ventricular wall are thereby eliminated. 
         [0016]    As provided, the present invention further comprises a method of treating heart and valve malfunction utilizing the instrument as generally set forth above. Accordingly, the attendant method comprises, at least in more generic terms, the passing of a portion of the instrument assembly into an intended heart chamber and into penetrating relation to a predetermined valve leaflet, such as a prolapsing leaflet. The sheath, with the chord concentrically disposed on the interior thereof, is passed through the predetermined valve leaflet. Therefore, by virtue of the enclosed disposition of the chord, the chord and sheath will concurrently enter and extend through the predetermined valve leaflet. By manipulation and the application of a positioning force on the sheath, the sheath and the chord will extend across a corresponding heart chamber and into an anchored relation with a substantially opposing portion of the heart wall. 
         [0017]    Once the anchor and the connected distal end of the chord are secured to the opposing heart wall portion, the sheath, still concentrically mounted exteriorly of and in enclosing relation to the chord, is withdrawn from heart chamber in which the chord is anchored. More specifically, the sheath is withdrawn by moving relative to and back along the length of the anchored chord in a direction away from the anchor and connected distal end of the chord. The introductory sheath is further withdrawn back through the predetermined valve leaflet while the proximal portion of the chord remains within the valve leaflet. Once the sheath is disposed exteriorly of the valve leaflet and possibly on the exterior of the heart itself, a securing assembly is operatively disposed within the heart chamber in interconnecting relation between a proximal extremity of the chord and the predetermined valve leaflet. 
         [0018]    In more specific terms, the securing assembly may include a securing member, which will be mounted on or connected to a proximal portion of the chord and moved along the length thereof into a predetermined, interconnecting position relative to the prolapsing valve leaflet. The position of the securing member will be tailored to and disposed at the exact position needed to achieve correction of the mitral regurgitation, which may be determined by preoperative transoesopageal echography or other preoperative manner, to quantify the occurring mitral regurgitation preoperatively. The securing member then securely interconnects the proximal extremity of the chord to the predetermined valve leaflet and any excess length of the chord will be severed or detached from the proximal extremity of the chord, which is secured to the surface of the leaflet associated with the atrium. The chord is thereby properly tensioned between the opposing, interior corresponding wall portion of the heart and the predetermined valve leaflet so as to overcome the malfunction of the predetermined valve leaflet as explained in more specific details hereinafter. 
         [0019]    As emphasized throughout this description, the instrument assembly and attendant method of the present invention is specifically adapted for the treatment of mitral regurgitation. As such, the introductory sheath and the chord, substantially concurrently enter the atrial wall of the left atrium and pass into the interior thereof. Further, the sheath and the chord penetrate and are passed, substantially concurrently, through a prolapsing (flail) anterior or posterior leaflet of the mitral valve into the left ventricle of the heart chamber. Thereafter the sheath and chord are concurrently extended transversely across the left ventricle, wherein the anchor penetrates and is thereby secured in an anchored relation with a substantially opposing portion of the ventricular wall and/or corresponding papillary muscles. The distal end of the chord is connected to the anchor and is thereby secured in an anchored relation to the ventricular wall, by virtue of the penetrating anchor. 
         [0020]    Once the distal end of the chord and anchor are in the anchored relation to the ventricular wall, the sheath is withdrawn back along the length of the chord, away from the anchor and the ventricular wall to which the distal portion of the chord is secured. Moreover, the introductory sheath continues to travel back along the length of the chord through the prolapsing anterior or posterior mitral valve leaflet to a location at least exterior to the leaflet, such as within the left atrium and possibly exteriorly of the heart itself. 
         [0021]    A securing assembly is then operatively associated with the instrument and is movably disposed along the length of a proximal portion of the chord. In even more specific terms, the movement of the securing assembly and its associated securing member are disposed into an interconnecting position between a proximal extremity of the chord and the mitral valve leaflet penetrated by the chord. As indicated above, proper tensioning is thereby placed on the prolapsing mitral valve leaflet in order to restore a sufficient surface of coaptation between its counterpart, opposing leaflet and maintain the suppressed leaflet in an operative position sufficient to overcome the mitral regurgitation. 
         [0022]    These and other objects, features and advantages of the present invention will become clearer when the drawings as well as the detailed description are taken into consideration. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    For a fuller understanding of the nature of the present invention, reference should be had to the following detailed description taken in connection with the accompanying drawings in which: 
           [0024]      FIG. 1  is a perspective view of one preferred embodiment of the instrument assembly of the present invention used in the treatment of heart valve malfunction. 
           [0025]      FIG. 1A  is a perspective view of the instrument assembly of the embodiment of  FIG. 1  in an initially introductory position. 
           [0026]      FIGS. 2 through 9  are schematic representations of successive steps in the attendant method of utilizing and applying the instrument assembly of the embodiment of  FIGS. 1 and 1A  specifically for the treatment and correction of mitral regurgitation. 
       
    
    
       [0027]    Like reference numerals refer to like parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0028]    As represented in the accompanying drawings and with specific reference to  FIGS. 1 and 1A , the instrument assembly of the present invention is schematically and generally indicated as  10  and is used for the treatment of heart valve malfunction generally and more specifically for the treatment of mitral regurgitation. As such, the instrument assembly  10  includes an elongated delivery catheter or tube  12  having a hollow interior and structured to deliver operative portions of the instrument assembly  10  to the treatment site within the heart of a patient. As such, the elongated delivery catheter or tube  12  is dimensioned and configured to enter the chest cavity through appropriate introduction instrumentation. The delivery tube  12  is formed of a material and/or includes positioning structure or linkage incorporated therein which facilitates the maneuvering or steering thereof to a point at least generally exterior the heart and more specifically the atrial wall of the left atrium. However, the at least semi-rigid material of the delivery tube  12  should be sufficient to also facilitate proper manipulation so as to position or “steer” the remainder of the instrument assembly  10  to the intended location within the interior thereof, as well as facilitate penetration of and anchoring to intended tissue portions. 
         [0029]    The instrument assembly  10  also includes an introductory sheath  14  movable within the delivery tube  12  and an elongated flexible material chord  16 . The introductory sheath  14  is concentrically and movably enclosed within the delivery tube  12  and the sheath  14  is movably disposed concentrically about the chord  16 . It is emphasized that  FIG. 1  represents a completely assembled instrument assembly  10 . However, as will be described in detail with the schematic representations of  FIGS. 1 through 9 , the various portions of the instrument assembly  10  are used in successive steps to accomplish installation relative to the affected portions of the heart valve being treated. 
         [0030]    Accordingly, the instrument assembly  10  further includes the elongated flexible material chord  16  which may be formed of a synthetic, biocompatible material. An anchor  18  is fixedly secured to the outer or distal end of the chord  16  and is movable therewith relative to the introductory sheath  14 . As clearly represented in  FIG. 1A  chord  16  is at least initially enclosed concentrically within the interior of the introductory sheath  14 , wherein the sheath  14  is movable along the length of the chord  16 . Further, the sheath includes an open distal end  14 ′ serving to at least partially encloses or be registered alignment with the anchor  18 . Therefore,  FIG. 1A  represents cooperative portions of the instrument assembly  10  at least upon initial entry of the introductory sheath  14  and anchor  18  into the interior of the heart  30 , as specifically described in detail in  FIGS. 2 through 9 , hereinafter described. 
         [0031]    Therefore, with further regard to  FIG. 1A , the positioning of the anchor  18 , the introductory sheath  14  and the chord  16  is such that the chord  16  is disposed within the interior of the introductory sheath  14 . Further, the anchor  18  is disposed at least partially within and/or in an exposed relation to the open distal end  14 ′ of the sheath  14 . In addition, the anchor  18  has a sharpened, pointed or other appropriate configuration for penetrating portions of the heart. The anchor  18  may also include a gripping structure  20  which may be initially disposed in a collapsed position when the anchor  18  is in registry with the distal opening  14 ′ of the sheath  14 . However, upon removal or exposure of the anchor  18  and a length of the chord  16  from an interior of the sheath  14 , the gripping structure  20  may include an inherent bias causing it to expand outwardly and/or radially from the remainder of the anchor  18 . This gripping structure  20  is provided to facilitate a secure engagement of the anchor  18  with predetermined heart wall portions, when the instrument assembly  10  is properly applied in the treatment of the heart valve malfunction. 
         [0032]    With further reference to  FIG. 1  the assembled representation of the instrument assembly  10  further includes the provision of a securing member  22  which may travel along the length of the chord  16 . The securing member may be forcibly positioned into an intended interconnecting location relative to a heart valve leaflet in order to accomplish a secure attachment of the chord  16  to the leaflet as will be explained in greater detail hereinafter. Such an interconnecting placement of the securing member  22  relative to both the chord  16  and the affected valve leaflet serves to establish and maintain a sufficient tension and/or positioning force on the predetermined valve leaflet to suppress movement thereof, as explained hereinafter with regard to  FIGS. 2 through 9 . 
         [0033]    As schematically represented in  FIGS. 2 through 9 , the heart is generally indicated as  30  and includes the representative portions including the left atrium  32 , the left ventricle  34  and the mitral valve  36 , including the anterior and posterior mitral valve leaflets  38  and  38 ′, respectively. As additionally represented, the left ventricle  34  is at least partially bordered or surrounded by ventricular wall  40  which may be directly associated with corresponding papillary muscles (not shown) facilitating the proper positioning of the mitral valve leaflets  38  and  38 ′ through organic tissue tethering, as generally outlined above. 
         [0034]    For purposes of clarity,  FIGS. 2-9  schematically represent the instrument assembly  10  used on the anterior leaflet  38  of the mitral valve  30  in order to treat and correct mitral regurgitation. However, it is emphasized the instrument assembly  10  and the attendant method of the present invention may be applied to an anterior and/or the posterior prolapsing leaflet in the manner described herein, in correcting a mitral regurgitation condition of the heart. Moreover, while the various embodiments of the present invention are described using a single chord  16 , a plurality of chords  16  may be used with the cooperative instrument components of the instrument assembly  10 . 
         [0035]    With initial reference to  FIGS. 2 and 3 , the instrument assembly  10  is introduced into the interior of the heart  30  and more specifically into the left atrium  32 , through the atrium wall  33 , using an appropriate introduction assembly  42 . Therefore, the introductory sheath  14  and the chord  16  located concentrically within the sheath  14  will concurrently pass through the atrial wall  33  of the heart into the left atrium  32 , as it is directed towards the anterior leaflet  38  of the mitral valve  36 . It should be further noted that the anchor  18  is at least initially in the position generally represented in  FIG. 1A . Due to its predetermined configuration the anchor  18  will serve to approach and penetrate the anterior leaflet  38  of the mitral valve  36  as clearly represented in  FIG. 3 . 
         [0036]    In addition, the penetration of the anterior leaflet  38  initially by the anchor  18  will facilitate the penetration and passage, substantially concurrently, of the chord  16  and the introductory sheath  14  through the anterior leaflet  38  as schematically represented. As further represented in  FIG. 3 , a continued force will be applied to the introductory sheath  14  causing the sheath  14  and interiorly disposed chord  16 , as well as the anchor  18  to continue concurrent passage through the anterior valve leaflet  38  until the anchor  18  reaches, penetrates and is secured to the ventricular wall  40  and/or correspondingly disposed papillary muscles associated therewith. 
         [0037]    As best represented in  FIGS. 4 and 5 , once the anchor  18  is secured to the ventricular wall  40  and/or the corresponding papillary muscles, the distal end of the chord  16  will be affixed to the ventricular wall  40  and remain in place as the introductory sheath  14  is withdrawn back along the length of the chord  16 , as indicated by the directional arrows. As the introductory sheath  14  is withdrawn back along the length of the chord  16 , the aforementioned gripping structure  20  will have been expanded into a gripping orientation. When the gripping structure  20  is so oriented, the anchor  18  and the distal end of the chord  16  connected thereto will be reliably anchored or connected to the ventricular wall  40 . Continued withdrawal of the introductory sheath  14  will result in its passage back through the initially penetrated and suppressed mitral valve leaflet  38 , as clearly represented in  FIG. 5 . As such, the majority of the length of the chord  16  will thereby be exposed and maintained in the represented position within the left ventricle and between the ventricular wall  40  and the penetrated (suppressed) leaflet  38 , while the introductory sheath  14  passes back through the introduction assembly  42  and out of the interior of the left atrium  32 , through the atrium wall  33 . Therefore, the proximal portion  16 ′ of the chord  16  remains in place, within the left atrium  32 , and may serve effectively as a guide or otherwise facilitate the placement of the securing member  22 , as represented in  FIGS. 6 through 9 . 
         [0038]    More specifically, once the introductory sheath  14  is removed from the left atrium  32 , through the introduction assembly  42 , the securing assembly, including securing member  22 , will move along the length of the chord  16  as it is introduced into the left atrium  32  such as through the atrium wall via, the introduction assembly  42 . As schematically represented, the securing member  22  will be forced, moved, positioned, etc. along the proximal portion or length  16 ′ of the chord  16  by any appropriate technique and/or appropriate positioning instrument/device, which may be incorporated or operatively associated with the chord  16 . Positioning of the securing member  22  will continue until it is disposed in engaging, interconnecting and at least partially protective or sealing engagement with an exterior surface portion of the suppressed anterior mitral valve leaflet  38  located within the left atrium  32 . The position of the securing member  22  will be disposed in the exact position, on and along the length of the chord  16  needed to position and or suppress movement of the leaflet  38  to achieve correction of the mitral regurgitation. Such exact positioning may be determined by preoperative transoesopageal echography or other preoperative manner to quantify online mitral regurgitation preoperatively. 
         [0039]    With further regard to the positioning of the securing member  22  into the interconnecting relation between the proximal extremity of chord  16  and the anterior leaflet  38 . One embodiment may also include a guiding element or sleeve  25 , as represented in  FIG. 1 . When utilized, the element  25  will be disposed at a predetermined position along the length on the artificial chord  16  and be mounted concentrically about and/or along a portion of the chord  16 . As applied, the guiding element  25  may assume and or be at least partially defined by a variety of different structures, devices and/or mechanisms other than, but possibly including, the schematically represented sleeve. Accordingly, the guiding element is operative to accurately center or otherwise dispose the securing member  22  in sealing and/or covering relation to the aperture or area where the chord  16  remains in its extended position through the anterior leaflet  38 . Further, the securing member  22  securely connects the proximal extremity  16 ″ of the chord  16  to the valve leaflet  38  and any excess length of the proximal portion  16 ′ of the chord  16  will be severed or detached from the extremity  16 ″ of the chord  16  and the securing member  22 , which interconnects the proximal extremity  16 ″ to the “exterior” surface of the leaflet  38  exposed to the left atrium  32 . 
         [0040]    With continued reference to  FIGS. 5 through 8 , manipulation of the instrument of the assembly  10 , such as by medical personnel manipulating the delivery catheter  12  causes a severing of the proximal extremity from a remainder of the chord  16 . As a result, the securing member  22  serves to securely connect and fasten the chord  16  to the exterior of the anterior leaflet  38 , disposed within the left atrium  32 . Upon a secure connection of the securing member  22  to the exterior side or surface of the anterior leaflet  38 , the introductory sheath  14  passes back through the introduction assembly  42  so as to exit the left atrium  32  and the remainder of the heart. Thereafter, the introduction assembly  42  is also removed from its initial operative position. 
         [0041]    Therefore, as represented in  FIG. 9  the heart  30  is represented with the synthetic chord  16  properly anchored between the ventricular wall  40  and the penetrated anterior leaflet  38 . In this position, proper tensioning or positioning forces are applied to the anterior leaflet  38  causing it to be positioned in a manner which effectively overcomes mitral regurgitation, as set forth above. 
         [0042]    Since many modifications, variations and changes in detail can be made to the described preferred embodiment of the invention, it is intended that all matters in the foregoing description and shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents. 
         [0043]    Now that the invention has been described,
An assembly and method for treating heart valve malfunction typically including treating of mitral regurgitation wherein an instrument assembly includes an elongated chord movably disposed within an introductory sheath and including an anchor secured to a distal end thereof. An attendant method includes concurrently introducing the sheath and the chord into the heart chamber through an exterior wall and penetrating and passing the sheath and the chord through the anterior mitral valve leaflet. The sheath and the chord are then extended transversely across the heart chamber and the distal end of the chord is anchored to an opposing portion of the heart wall. The sheath is then withdrawn back along the length of the anchored chord and through the anterior mitral valve leaflet and a securing member connects the proximal end of the chord to the valve leaflet. The chord is secured between the valve leaflet and the opposing heart wall under sufficient tension to maintain an intended positioning of the valve leaflet to overcome mitral regurgitation.