Abstract:
A method of securing a prosthesis atraumatically to body tissue can include one or more of the following steps. A prosthesis can be delivered into a patient. The prosthesis may include an expandable frame. The frame can be expanded within a body cavity of the patient. Expansion of the frame can causes respective ends of both proximal prongs and distal prongs to draw closer together to grasp native tissue between the respective ends of the proximal prongs and distal prongs.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 12/084,586, filed Apr. 13, 2009, now U.S. Pat. No. 8,092,520, which is a national stage of PCT/US2006/043526, filed Nov. 9, 2006, which claims the benefit of priority of U.S. Provisional Application No. 60/735,221, filed Nov. 10, 2005, all of which are hereby incorporated herein by reference in their entirety and are to be considered a part of this specification. 
    
    
     BACKGROUND 
     Field of the Invention 
     The present invention relates to a vascular balloon-expandable and/or self-expanding stent that can be used as a connecting/attaching mechanism for various kinds of vascular grafts or other prostheses in the vascular system of the human body. 
     SUMMARY OF THE INVENTION 
     It is a primary object of the present invention to provide a vascular balloon-expandable and/or self-expanding stent to facilitate efficient execution of simple and more complex vascular and cardiac procedures by less invasive and/or percutaneous techniques. 
     This and other objects of the present invention are achieved by an expandable vascular stent comprising an m×n array of ovals formed into a cylinder having a diameter, a circumference, an axis, and a length in the direction of the axis, where m is the number of columns of ovals in the circumferential direction and n is the number of rows of ovals in the axial direction. Connecting means located at rows 1 and n of the m×n array connect the cylinder to a surrounding body. The array of ovals can be of any size and number in a given stent. 
     The ovals have a short axis and a long axis, the short axis of the ovals extending in the circumferential direction and the long axis of the ovals extending in the axial direction. The cylinder is expandable from an initial diameter to a pre-determined final diameter, wherein an increase in the diameter of the stent results in a substantial decrease in the length of the stent to bring the prongs together to produce a connection to the body surrounding the stent. 
     The connecting means comprise a plurality of prongs extending inwardly from the outer ends of respective ovals in rows 1 and n of the m×n array. The prongs are arranged in facing pairs extending from ovals that are in alignment in the axial direction, and are approximately collinear in ovals having a common long axis, and approximately parallel in ovals having a common short axis. 
     Prior to expansion of the cylinder, the prongs substantially conform to the shape of the cylinder. As the stent expands, the distance between the prongs decreases and the prongs extend outwardly from the cylinder to engage the surrounding tissue. 
     Circumferential connectors connect adjacent ovals to each other in the circumferential direction and axial connectors connecting adjacent ovals to each other in the axial direction. The circumferential connectors and the axial connectors are positioned between the ovals coincident with the common short and long axes of the ovals, respectively. 
     The tube and the prongs can be made of surgical stainless steel, the tube being expandable using an angioplasty balloon; or the tube and the prongs can be made of a memory metal and the tube is self-expanding. 
     Other objects, features, and advantages of the present invention will be apparent to those skilled in the art upon a reading of this specification including the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is better understood by reading the following Detailed Description of the Preferred Embodiments with reference to the accompanying drawing figures, in which like reference numerals refer to like elements throughout, and in which: 
         FIG. 1  shows a first embodiment of a stent form stamped from a piece of metal. 
         FIG. 2  shows the stent form of  FIG. 1  stretched width-wise. 
         FIG. 3  shows the stent form of  FIG. 1  rolled into a stent. 
         FIGS. 4A-4C  show the progression of deformation of the stent of  FIG. 3  as it is stretched radially along its diameter. 
         FIGS. 5A-5Q  show the steps in the expansion of the stent of  FIG. 3  in an artery or other body cavity. 
         FIG. 6A  is a perspective view, partially cut away, of a collapsed prosthetic heart valve loaded in an undeployed stent in accordance with the present invention. 
         FIG. 6B  is a perspective view, partially cut away, of the prosthetic heart valve and stent of  FIG. 6A  in their expanded conditions. 
         FIGS. 7A-7C  show the progression of deformation of a second embodiment of the stent as it is stretched radially along its diameter. 
         FIG. 8A  is a side elevational view of a third embodiment of the stent. 
         FIG. 8B  is a perspective view of the stent of  FIG. 8A . 
         FIG. 8C  is a side elevational view of the stent of  FIG. 8A  in a deformed state after being stretched radially along its diameter. 
         FIG. 8D  is an enlarged view of a prong of the stent of  FIG. 8A . 
         FIG. 8E  is a plan view of the stent form of  FIG. 8A . 
         FIGS. 9A-9G  show the steps in the expansion of the stent of  FIG. 8A  in an artery or other body cavity. 
         FIG. 10A  is a perspective view of a fourth embodiment of the stent. 
         FIG. 10B  is a plan view of the stent form of  FIG. 10A . 
         FIG. 10C  is an enlarged view of the prong of the stent of  FIG. 10A . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In describing preferred embodiments of the present invention illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. 
     As shown in  FIGS. 3 and 4A-4C , a first embodiment of the device is a balloon expandable stainless steel stent  100  that can be expanded from an initial diameter (shown in  FIG. 4A ) to a pre-determined final diameter (shown in  FIG. 4C ) depending on the set dimensions of the balloon used to expand it. The configuration of the stent  100  is such that, with reference to  FIG. 3 , an increase in the diameter (D) of the stent will result in a substantial decrease in the length (L) of the stent. 
     To achieve this change in the shape and dimension of the stent  100 , an m×n array  100   a  of ovals  105  is formed as shown in  FIG. 1 , where m is the number of columns of ovals in the circumferential direction C and n is the number of rows of ovals in the axial, or lengthwise, direction A, and where the short axis of the ovals  105  extends in the circumferential direction C and the long axis of the ovals  105  extends in the axial direction A. The array  100   a  shown in  FIG. 1  is a 2×5 array. However, the array  100   a  can be any size greater than 1×1, depending on the desired size of the circumference and the length of the stent. 
     With reference to  FIGS. 1 and 2 , the array  100   a  of ovals  105  can be formed by stamping or electrical discharge machining from a sheet or tube of metal, preferably stainless steel. Adjacent ovals  105  are connected to each other in the circumferential direction C by connectors  115   a  and in the axial direction A by connectors  115   b  positioned between the ovals coincident with their common short and long axes, respectively. 
     At least some of the ovals  105  at the ends of the stent  100  (that is, the ovals  105  in rows 1 and n in the axial direction) have a prong  120  extending inwardly from their outer ends in approximate alignment with their longitudinal axes. The prongs  120  are placed in facing pairs extending from ovals  105  that are in alignment in the axial direction A. Thus, for ovals  105  having a common long axis, the prongs  120  are approximately collinear; while for ovals  105  having a common short axis, the prongs  120  are approximately parallel. 
     There may be intervening “blank” ovals  105  without any prongs  120 , and which serve merely as spacers. The blank ovals  105  are utilized in some situations where more space is required between the connecting prongs  120 . 
     If the array  100   a  of ovals  105  is formed from a sheet of metal, then the array  100   a  is rolled into a cylinder. The rolled cylinder and the stamped or machined tube have the general configuration of a stent  100 , as shown in  FIG. 4A , with the longitudinal axis of the cylinder being parallel to the long axes of the ovals  105 . 
     In this embodiment, the prongs  120  are pre-bent. That is, at the time the stent  100  is formed, the prongs  120  are bent outwardly relative to the longitudinal axis of the cylinder, adjacent their attached ends, and also are bent inwardly relative to the longitudinal axis of the cylinder at a point offset from their free ends, in a reverse curve, so as to have a hook configuration. 
     An angioplasty balloon  130  is used to expand the undeployed stent  100  and to post the expanded stent  100  in the wall of an artery or other body cavity. When the balloon  130  is inflated, the ovals  105  expand in the direction of their short axes and contract along the direction of their long axes, deforming the ovals  105  into diamonds and causing a reduction in the length of the stent  100 , as shown in  FIGS. 4B and 4C . As also shown in  FIGS. 4B and 4C , the deformation of the ovals  105  also causes the approximately collinear prongs  120  to draw closer together to engage the surrounding tissue and the approximately parallel prongs  120  to spread farther apart. This deformation of the ovals  105  and movement of the prongs  120  provide the connecting mechanism of the stent  100 . 
     As illustrated in  FIGS. 4B and 4C , when the frame is in an expanded configuration, there are a plurality of distal anchors, each of the distal anchors extending proximally to a proximal most portion that is positioned radially outward from the frame. There are also a plurality of proximal anchors, each of which extend distally to a distal most portion that is positioned radially outward from the frame. The proximal most portions of the distal anchors extend in a direction that is more parallel with a longitudinal axis of the frame than with a transverse axis perpendicular to the longitudinal axis of the frame, and the distal most portions of the proximal anchors extend in a direction that is more parallel with the longitudinal axis than with a transverse axis perpendicular to the longitudinal axis of the frame. The proximal anchors are connected to the frame only at locations on the frame proximal to the distal most portions, and the distal anchors are connected to the frame only at locations on the frame distal to the proximal most portions. The distal most portions of the proximal anchors and the proximal most portions of the distal anchors are spaced apart by less than two cell lengths or less than one cell length when the frame is in an expanded configuration. When the frame is in an expanded configuration, at least some of the anchoring portions of at least one of the pluralities of proximal anchors and distal anchors curve radially outward before extending respectively, distally or proximally, in an axial direction approximately parallel with each other and with the longitudinal axis. 
     The angioplasty balloon  130  is the correct size and shape to expand the stent  100  to the desired size and shape. The undeployed stent  100  is loaded over the balloon  130  of a conventional balloon catheter  132  and inserted into the artery or other body cavity according to conventional medical procedure. Inflating the balloon  130  deploys (opens) the stent  100  (that is, causes an increase in its diameter and a decrease in its length), which remains expanded to keep the artery or body cavity open. A high-pressure balloon  130  allows the physician to fully expand the stent  100  until it is in full contact with the wall of the artery or body cavity. A low compliance balloon  130  is used so that the stent  100  and the artery or body cavity will not be over-expanded, and so that the balloon  130  will not dog-bone and over-expand the artery or body cavity on either end of the stent  100 . The stent  100  stays in position after the balloon  130  is deflated and removed from the body. 
     In instances when the stent  100  is self-expanding, i.e. made from memory metal, then upon deployment the stent  100  takes its predetermined configuration. 
       FIGS. 5A-5Q  show the steps in the expansion of the stent of  FIG. 3  in an artery or other body cavity. 
     The stent  100  in accordance with the present invention can also be of use as a versatile connector in clinical settings in which it can be pre-attached to a side wall of another prosthesis, such as an endo-luminal graft. It can also be used as a connector to connect main and branch endo-aortic grafts for branch graft repair, as described in my co-pending U.S. patent application Ser. No. 10/960,296, filed Oct. 8, 2004. 
     The stent  100  in accordance with the present invention can further be used in conjunction with percutaneous heart valve technology. In a percutaneous heart valve procedure, a collapsed percutaneous heart valve  125  is mounted on a balloon-expandable stent  100  and threaded through the patient&#39;s circulatory system via a catheter to the aortic valve from either an antegrade approach (in which the patient&#39;s septum and mitral valve are crossed to reach their native aortic valve) or a retrograde approach (in which the percutaneous heart valve  125  is delivered directly to the aortic valve through the patient&#39;s main artery). Once in the aortic valve, the percutaneous heart valve  125  is expanded by a balloon catheter to push the patient&#39;s existing valve leaflets aside and anchor inside the valve opening. 
     As shown in  FIG. 6A , the percutaneous heart valve  125  in a collapsed state can be seated inside the undeployed stent  100  in accordance with the present invention, which in turn is loaded over the balloon of a conventional balloon catheter, as previously described. Once the valve  125  and stent  100  are positioned in the desired location, the balloon  130  is inflated, causing the valve  125  and the stent  100  to expand, as shown in  FIG. 6B . The valve  125  is fixed in position by the mechanism provided by the stent  100 . 
     A second embodiment of the stent  100 ′, and the progression of its deformation as it is stretched radially along its diameter, is shown in  FIGS. 7A-7C . In this alternate embodiment, the stent  100 ′ is similar to the stent  100 , but has additional prongs  135  extending from and perpendicular to the connectors  115   a  positioned between the ovals  105 , and parallel to the longitudinal axis of the stent  100 ′. These prongs  135  are for the purpose of attaching the stent  100 ′ to, for example, a branch graft or a valve. 
     A third embodiment of the stent  300  is shown in its undeployed state in  FIGS. 8A and 8B , and in its deployed state after being stretched radially along its diameter in  FIG. 8C . In the third embodiment, the stent  300  is formed of an m×n array  300   a  of ovals  305  formed as shown in  FIG. 8E . With reference to  FIG. 8D , the array  300   a  of ovals  305  can be formed by laser-cutting a sheet or tube of metal, preferably stainless steel or a memory metal. Adjacent ovals  305  are connected to each other in the circumferential direction C by connectors  315   a  and in the axial direction A by connectors  315   b  positioned between the ovals coincident with their common short and long axes, respectively. 
     At least some of the ovals  305  at the ends of the stent  300  (that is, the ovals  305  in rows 1 and n in the axial direction) have a prong  320  extending inwardly from their outer ends in approximate alignment with their longitudinal axes. The prongs  320  are placed in facing pairs extending from ovals  305  that are in alignment in the axial direction A. Thus, for ovals  305  having a common long axis, the prongs  320  are approximately collinear; while for ovals  305  having a common short axis, the prongs  320  are approximately parallel. The prongs  350  are bifurcated, providing two point penetration for better purchase. 
     Referring now to  FIGS. 8D and 8E , in the embodiment of  FIGS. 8A-8C , each prong  320  includes a spine  320   a  extending the length of the long axis of the oval  305  and a furcation  320   b  on either side of the spine  320   a  at a location between the ends of the spine  320 . The spine  320   a  has two end hinge points  320   c  at the ends thereof and one intermediate hinge point  320   d  at the base of the furcations  320   b . The amount by which the ovals  305  are foreshortened and the angle of the prongs  320  (that is, the angle of the furcations  320   b ) can be adjusted by varying the location of the furcations  320   b  and the intermediate hinge point  320   d  relative to the ends of the spines  320  and the end hinge points  320   c.    
     There may be intervening “blank” ovals  305  without any prongs  320 , and which serve merely as spacers. The blank ovals  305  are utilized in some situations where more space is required between the connecting prongs  320 . At least some of the ovals  305  at one end of the stent  300  can include a docking socket  360  (shown in  FIG. 8C ) for mating to the cardiac locking pin of a valve frame. 
       FIGS. 9A-5Q  show the steps in the expansion of the stent of  FIGS. 8A-8C  in an artery or other body cavity, using an angioplasty balloon. The undeployed stent  300  is loaded over the balloon  130  of a conventional balloon catheter  132  and inserted into the artery or other body cavity according to conventional medical procedure. As the balloon  130  inflates, the ovals  305  foreshorten in the axial direction, causing the spines  320   a  of the prongs  320  to bend at the hinges  320   c  and  320   d  and the consequent activation of the prongs  320 . As the balloon  130  continues to inflate, the angles assumed by the spines  320   a  at their hinges reach their maximums, bringing opposing furcations  320   b  together to engage the tissue therebetween. 
     Referring now to  FIGS. 10A and 10B , there is shown a fourth embodiment of the stent  400 . In the fourth embodiment, the stent  400  is formed of an m×n array  400   a  of ovals  405 . With reference to  FIG. 10B , the array  400   a  of ovals  405  can be formed by laser-cutting a sheet or tube of metal, preferably stainless steel. Adjacent ovals  405  are connected to each other in the circumferential direction C by connectors  415   a  and in the axial direction A by connectors  415   b  positioned between the ovals coincident with their common short and long axes, respectively. 
     At least some of the ovals  405  at the ends of the stent  400  (that is, the ovals  405  in rows 1 and n in the axial direction) have a prong  420  extending inwardly from their outer ends in approximate alignment with their longitudinal axes. The prongs  420  are placed in facing pairs extending from ovals  405  that are in alignment in the axial direction A. 
     As shown in  FIG. 10C , each prong  420  has substantially the same configuration as an oval  305  and a prong  320  of the third embodiment, described above. That is, each prong  420  includes an oval frame  420 ′, a spine  420   a  extending the length of the long axis of the oval frame  420 ′, and a furcation  420   b  on either side of the spine  420   a  at a location between the ends of the spine  420 . The spine  420   a  has two end hinge points  420   c  at the ends thereof and one intermediate hinge point  420   d  at the base of the furcations  420   b.    
     The oval frames  420 ′ are connected at their short axes to the ovals  405  by connectors  420   e , and are connected at one end of their long axes to the ovals  405  by a connector  420   f . Thus, as the ovals  405  foreshorten, the oval frames  420 ′ also foreshorten. The amount by which the oval frames  420 ′ are foreshortened and the angle of the furcations  420   b  can be adjusted by varying the location of the furcations  420   b  and the intermediate hinge point  420   d  relative to the ends of the spines  420  and the end hinge points  420   c . Preferably, the prongs  420  are formed by laser cutting. 
     As with stent  300 , stent  400  is loaded over the balloon  130  of a conventional balloon catheter  132  and inserted into the artery or other body cavity according to conventional medical procedure. As the balloon  130  inflates, the ovals  405  and the oval frames  420 ′ foreshorten in the axial direction, causing the spines  420   a  of the prongs  420  to bend at the hinges  420   c  and  420   d  and the consequent activation of the prongs  420 . As the balloon  130  continues to inflate, the angles assumed by the spines  420   a  at their hinges reach their maximums, bringing opposing furcations  420   b  together to engage the tissue therebetween. 
     There may be intervening “blank” ovals  405  without any prongs  420 , and which serve merely as spacers. The blank ovals  405  are utilized in some situations where more space is required between the connecting prongs  420 . At least some of the ovals  405  at one end of the stent  400  can include a docking socket (not shown) similar to the docking socket  360  shown in  FIG. 8C , for mating to the cardiac locking pin of a valve frame. 
     Modifications and variations of the above-described embodiments of the present invention are possible, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described.