Abstract:
This present invention provides a surgical rivet, a rivet deployment actuator, a rivet cutting instrument and a method for securing a prosthetic valve to the heart which has the potential to substantially decrease the ischemic time required for valve implantation and allow larger prostheses to be inserted in small annuli. The surgical rivet is comprised of two flexible preformed elements capable of assuming a preconfigured shape once it is delivered and secured with the deployment actuator. The deployment actuator is a reusable instrument that lowers the prosthesis to the annulus, secures the prosthesis with an “O” ring and cuts and deploys the flexible elements so that they rest on the sewing ring of the prosthetic valve. The present invention eliminates the tedious and time-consuming tasks of tying sutures which may be particularly difficult in small annuli. It also automatically cuts the sutures to the appropriate length. The use of single rivets allows for expansion to the annulus and insertion of one full size larger (2 mm) prosthesis than what is possible using the classical horizontal pledget mattress technique. This feature is of particular importance in small annuli where prosthesis/patient mismatch can lead to suboptimal long term results.  1

Description:
FIELD OF INVENTION  
       [0001]     This invention relates generally to apparatuses and methods related to cardiac valve replacement. In particular, this invention pertains to a unique surgical fastener and its method of implantation to secure a prosthetic valve to the heart structures in a more efficient and less traumatic way.  
       BACKGROUND OF THE INVENTION  
       [0002]     When a cardiac valve malfunctions or becomes diseased and is beyond repair, the native valve is replaced with a biological or mechanical prosthesis in order to restore adequate hemodynamics. Traditionally valve replacement operations involve placing the patient on cardiopulmonary bypass, arresting the heart, removing the diseased valve leaflets and securing the prosthetic valve with sutures placed through the valve annulus. After placing the sutures through the annulus and the sewing ring of the prosthesis, the valve is lowered and each of the sutures, which may range from 12 to over 25, has to be individually tied with 4 to 6 surgical knots. This manual process of knotting and securing the sutures is the longest, slowest and perhaps the most difficult portion of valve replacement. It is particularly complicated in small aortic roots where the surgeon&#39;s fingers cannot adequately reach.  
         [0003]     Adding to the complication is the tension variability that can be applied to the sutures. If the surgeon applies too much tension, the sutures can cut through the tissues or if the surgeon applies too little tension, the sutures are not tied down sufficiently hard resulting in insecure fixations and leaks that require repairs. Thus, in placing each knot the surgeon must use his past experience to judge the optimal tension he applies to the sutures.  
         [0004]     Valve replacement surgery is a long, complicated procedure taking approximately 4 hours but even longer when combined with other necessary procedures including coronary bypasses, multi-valve replacement and resection of aneurysms. Although the time required for single valve replacement is well tolerated by patients, when the ischemic time is prolonged, myocardial dysfunction can ensue.  2  Additionally, mortality and morbidity increase considerably for lengthy procedures, especially in elderly patients.  
         [0005]     Because the classical suturing technique for valve implantation is a time consuming procedure, variations of fasteners have been developed to simplify all types of surgical operations. For cardiac valves in particular, U.S. patent application Ser. No. 09/007,4012 filed Apr. 10, 2002 discloses an annuloplasty, valve repair and valve replacement method employing an unshaped self-closing clip to eliminate the need for suture knotting and suture management. Examples of such clips are disclosed in U.S. patent application Ser. Nos. 09/089,884, 09/090,305, 09/259,705, and 09/260,623 and International Publication Nos. WO 99/12563 and WO 99/62406. While this novel valve replacement method eliminates suture knotting and suture management, reducing surgery time by 38%, all the aforementioned clips have size limitations.  3  Many of the clips are manufactured in various sizes and require the surgeon to predict the right size to use before inserting it into the body. However, before inserting any fastener through the annulus and sewing ring of the prosthesis, the surgeon cannot predict which clip size is needed. The clip size depends not only on the thickness of the annulus but also how the surgeon positions the clip. If the surgeon positions the clip with too much tissue in between the two ends, the clip will not close properly. In this case the surgeon must remove and place a larger one, leading to additional trauma to the tissues and operating room time. Additionally these clips are meant to be used as horizontal mattresses which like the conventional suturing technique, has the tendency to pinch the tissues together and thus decrease the annulus size. In small annuli, this pursestringing effect can lead to insertion of very small prostheses, resulting in patient/prosthesis mismatch and functionally stenotic valves.  4    
         [0006]     The present invention eliminates the inconveniences associated with the use of traditional suture techniques and currently available fasteners for valve replacement operations.  
       SUMMARY OF THE INVENTION  
       [0007]     The apparatuses and methods surrounding the present invention will simplify cardiac valve replacement procedure with a more efficient alternative of attaching a prosthetic valve. This invention involves a surgical rivet restrained by a protective sheath which aids in a smoother passage of the rivet through tissues, a deployment actuator that: correctly aligns the rivet with respect to the annulus, causes the rivet to assume its unrestrained position, further secures the rivet with an O ring, cuts the redundant length of rivet and causes the cut end to rest on the sewing ring.  
         [0008]     A surgical rivet, according to the present invention, comprises two memory preformed elements encased in a sheath causing the elements to be in a high tension or constrained state, a built-in pledget or stopper at one end and a piercing needle to pass the ensemble through the tissues and sewing ring at the other end. The two preformed elements are comprised of an alloy that is biocompatible and capable of retaining shape memory such as nitinol, although other materials may be used. The shape of the constrained rivet is similar to an inverted “T” whereas the released or unconstrained form resembles an “m” figure. At the point where the two rivet elements connect rests a pledget composed of a type of metal alloy that sits parallel to the annulus. The protective or constraining sheath serves to keep the two elements in a shape that allows them to pass through the tissues and sewing ring smoothly, thereby minimizing trauma. When the elements are released from the protective sheath via a deployment actuator, the elements assume their natural unrestrained position causing apposition of the prosthetic sewing ring and patient&#39;s annulus.  
         [0009]     In order to pass the rivet through the tissue of the annulus and sewing ring of the prosthesis, the clip is attached to a needle by a long element covered in a protective sheath. In aortic valve replacement, the rivets are placed through the annulus from the ventricular to the aortic side as in the classical suprannular technique. After all the rivets are placed through the annulus, the valve is sized and the needles are then placed through the sewing ring of the prosthetic valve. The valve is then lowered into position. Secure, less traumatic insertion is accomplished by using three appropriately placed deployment actuators without having to use fingers to lower the valve. Once the surgeon feels and sees that the annulus and sewing rings are in good apposition, an “O” ring is lowered and the deployment actuator is activated to strip the protective sheath and allows the elements to unfold onto the sewing ring in its natural unrestrained position. Upon activation, the actuator also flattens the “O” ring to secure the two elements in place, forcing the flexible elements to rest on the sewing ring.  
         [0010]     Should the need arise to remove the rivet, a specially designed tool is inserted between the annulus and sewing ring of the prosthesis. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The following detailed descriptions in conjunction with the accompanying drawings will illustrate the advantages and provide a better understanding of the present invention.  
         [0012]      FIGS. 1A-1B  are variations of views of a restrained surgical fastener according to the present invention, where  FIG. 1A  shows the front view of the restrained surgical fastener, and  FIG. 1B  shows the side view of the restrained surgical fastener.  
         [0013]      FIG. 2A-2B  are perspective views of the cross-section of the wire that compose the rivet where  2 A is circular and  2 B is non-circular.  
         [0014]      FIG. 3A-3B  are variations of views of the permanently attached pledget to the preformed elements, where  FIG. 3A  shows the front view,  FIG. 3B  shows the side view.  
         [0015]      FIG. 4  illustrates how the configuration of the built-in pledget in conjunction with the cross-sectional shape of the preformed elements forces the correct alignment of the rivet to the longitudinal axis of the annulus.  
         [0016]      FIG. 5A-5B  shows the preformed elements absent of the protective sheath in its natural unrestrained “m” configuration.  
         [0017]      FIG. 6  is a view of the instrument used on the fastener.  
         [0018]      FIG. 7  is a view of the “O” ring spirally coiled like a spring.  
         [0019]      FIGS. 8A-8E  are variations of views of the deployment actuator used to fix the “O” ring around the preformed elements to lock in the annulus and prosthesis between the “O” ring and the pledget, where  FIG. 8A  is a schematic view of the actuator with an undeployed “O” ring,  FIG. 8B  is a sectional view of  FIG. 8A ,  FIG. 8C  is a view of the actuator in the process of deploying the “O” ring,  FIG. 8D  is a sectional view of  FIG. 8C  to show the protective sheath being stripped off the preformed elements when the inner tube is removed after the “O” ring is deployed.  
         [0020]      FIG. 9A-9E  illustrate the valve replacement procedure of the present invention, where  FIG. 9A  shows the insertion of the rivet,  FIG. 9B  shows an alternative to single, separate fasteners,  FIG. 9C  show the protective sheath threaded through the inner tube,  FIG. 9D  shows the tightening of the connection between the prosthesis and annulus,  FIG. 9E  shows the unrestrained rivet holding the sewing ring and annulus together. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     This present invention relates to apparatuses and methods for simplifying cardiac valve replacement involving a unique surgical rivet  100  shown schematically in  FIGS. 1A-1B , used to attach a prosthesis sewing ring to a valvular annulus shown in  FIG. 9A . The following description in conjunction with the drawings explains the details of the invention.  
         [0022]     Referring to the drawings, and first to  FIG. 1A , is the surgical rivet  100  comprise of a metallic pledget or stopper  101 , two memory alloy preformed elements  102  encased in a protective sheath  103  causing the elements to be in a high tension or constrained state, attaching the memory alloy elements to a surgical needle  105 . The two preformed elements  102  are wire composed of nitinol or some other memory alloy that can have a circular cross-section shown in  FIG. 2A  or non-circular cross-section shown in  FIG. 2B  to resist rotation about the elongated direction, permitting the fastener to also resist rotation. The two preformed elements  102 , connected by a metallic pledget  101  as seen in  FIG. 3A-3B , are movable between a restrained position ( FIGS. 1A-1B ) and unrestrained position ( FIG. 5 ).  
         [0023]     The pledget  101  composed of a metallic material is permanently attached to the preformed elements  102  by welding or any other suitable means of connection.  FIG. 4  shows how the rectangular shape of the pledget  101  makes it natural for the pledget  101  to align its lengthier side parallel to the annulus  501 . However because of the rotational symmetry of the currently used sutures, the pledget  101  has a tendency to torque out of place at the time of suture placement. But, because the cross-sectional shape of the preformed elements  102  of the present invention is non-circular, which eliminates the rotational symmetry, the pledget  101  is held in place and does not torque. Thus, the configuration of the built-in pledget in conjunction with the shape of the preformed elements  102  forces the correct alignment of the rivet  100  to the longitudinal axis of the annulus  501  as illustrated by  FIG. 4 .  
         [0024]     In the pre-deployment state ( FIGS. 1A-1B ), the preformed elements  102  are parallel and held in tension in an inverted “T” shape by the protective sheath  103 . The protective sheath  103  is essentially a hollow elliptical cylinder that fits snugly around the preformed elements  102  and can slide over the preformed element. In the deployed state shown in  FIG. 5 , the elements  102 , absent of the protective sheath  103 , are free and assume its natural unrestrained configuration where the ends of the elements are preformed to curl assuming an “m” shape.  
         [0025]      FIG. 6  illustrates an “O” ring  201  holding the preformed elements  102  together and securing the connection between a prosthetic valve  500  and annulus  501 . The “O” ring  201  is spirally coiled like a spring shown in  FIG. 7  or some other configuration that serves the same function. When the ends of the preformed elements  102  are free of the protective sheath  103 , the ends curl in to assume the “m” shape which applies tension to the annulus/prosthesis junction. Said tension is further reinforced by the “O” ring  201  which further secures it in place. Since the shape of the “O” ring  201  is specially designed to apply a reaction force, it springs back against the ends of the preformed elements so there will always be the same constant net force sandwiching the valve  500  and annulus  501  between the “O” ring  201  and the pledget  101 . This eliminates the variability in tension associated with the current conventional suture technique as mentioned previously.  
         [0026]     Included in the present invention is the deployment actuator  200  of  FIG. 8A  and  FIG. 8C  used to deploy an “O” ring  201  and strip the protective sheath  103  off the elements  102 . The deployment actuator  200  comprises of an elongated shaft assembly  202  having a distal end  2021  and a proximal end  2022  with an outer tube  203  that can easily slide over a hollow inner tube  204 . The inner tube  204  is longer than the outer tube  203  and has a slit  205  down the middle for the protective sheath  103  to pass through. At the distal end  2021  portion of the inner tube  204 , which is slightly larger than the opening of the “O” ring  201 , the inner tube  204  holds the “O” ring  201  in radial tension. To deploy the “O” ring  201  the outer tube  203  slides over the inner tube  204 , pushing the “O” ring  201  off the inner tube  204  and transferring it onto the preformed elements  102 .  
         [0027]     Also at the distal end portion  2021  but on the inside of the inner tube  204  is a mechanism  206  ( FIG. 8B ) that strips the protective sheath  103  off the preformed elements  102 . This stripper mechanism  206  is constructed in such a way that when the protective sheath  103  slides into the mechanism  206  nothing is affected. But when the protective sheath  103  slides out, the mechanism  206  is activated and the protective sheath  103  is stripped off the preformed elements  102 . This occurs simultaneously ( FIG. 8D ) when the inner tube  204  is removed after the “O” ring  201  is deployed. Once the elements  102  are free of the protective sheath  103  they are no longer constrained and can assume their natural unrestrained “m” configuration ( FIG. 8F ).  
         [0028]     The valve replacement procedure visualized in  FIGS. 9A-9E  embodying this invention includes a surgical rivet  100  comprised of two memory alloy, preformed elements  102  encased in a protective sheath  103  causing the elements  102  to be in a high tension or constrained state, a pledget  101  or stopper at one end and a piercing needle  105  to pass through the tissues at the opposite end. All methods prior to and including trimming of the annular leaflets follow the current standard valve replacement surgical procedure. After the leaflets are trimmed, a surgical rivet  100  is inserted into the annulus  501  using the piercing needle  105  to puncture the annulus  501  and to pull the surgical rivet  100  through until the pledget  101  reaches the annulus ( FIG. 9A ). The appropriate number of rivets is inserted in the same fashion and the valve is sized. Alternative, the rivets  100  can be connected by long strands of flexible wire or other material  106  made of a type of biocompatible material as in  FIG. 9B . The surgeon can choose the appropriate number of rivets  100  by cutting off the excess after the rivets  100  are inserted into the annulus  501 . The protective sheath  103  of the rivet  100  is threaded through the inner tube  204  and exits from the slit  205  shown in  FIG. 9C .  FIG. 9D  illustrates how the connection between the prosthetic valve  500  and annulus  501  is tightened. With one hand the surgeon pushes the inner tube  204  down on the sewing ring  500  and with the other hand the surgeon pulls the protective sheath  103  in the opposite direction. The outer tube  203  is slid over the inner tube  204  to transfer the “O” ring  201  to the preformed elements  102 . While the outer tube  203  is held against the sewing ring  500 , the inner tube  204  is removed to strip the protective sheath  103  off the preformed elements  102 .  FIG. 9E  shows the elements  102  in its unrestrained “m” configuration sandwiching the prosthesis  500  and annulus  501  between the pledget  101  and the unrestrained preformed elements  102 . In the same picture, notice that the inverted “T” shape of the preformed elements  102  does not pinch the fibers together as sutures and other fasteners do, and thus does not decrease the native valve size.  
         [0029]     The description and examples are not meant to limit the invention. There can be variations as long as the functions remain within the details of the invention.  
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                 WO 03/88875 A1 
                 October 2003 
               
               
                   
                   
               
             
          
         
       
       
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