Abstract:
The present invention provides an occluder with a self centering system that keeps the occluder properly centered in a defect which allows the center of the occluder to remain properly positioned within the defect so that the left and right sides cover the entire defect which reduces the chance of blood shunting through the defect and increases the effectiveness of the occluder. The self centering system is comprised of a series of arms that provide tension to hold the right and left sides in place. The arms are shaped to provide a flexible intermediate zone comprising a left and a right conical shaped network, wherein each network extends from the right and left sides and narrows at the center section. The flexible intermediate zone centers the occluder and helps to hold it in place.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to an occlusion device for the closure of physical apertures, such as vascular or septal apertures. More specifically, this invention relates to an occlusion device for the heart that centers itself in the defect to ensure that the defect is properly sealed.  
         [0002]     The heart is generally comprised of four chambers: the left and right atrium, and the left and right ventricle. Separating the left and right sides of the heart are two walls, or septa. The wall between the two atria is the interatrial septum, and the wall between the two ventricles is the interventricular septum. There are several defects which can affect the septa of both children and adults, including patent ductus arteriosus, patent foramen ovale, atrial septal defects (ASDs), and ventricular septal defects (VSDs). Although the causes and physical aspects of these defects vary by type, each of these defects is generally an aperture, flap, or hole, in the septum which allows blood to shunt between chambers in the heart where there is no blood flow in a normal, healthy heart. This abnormal shunt can cause a variety of health problems.  
         [0003]     Normally, permanently repairing certain cardiac defects in adults and children requires open heart surgery, which is a risky, painful, and expensive procedure. Surgery for closure of a heart defect is major heart surgery, which requires the patient to undergo general anesthesia and opening of the chest cavity. The patient must spend several days in the hospital and thereafter may take several weeks to be able to return to normal levels of activity.  
         [0004]     To avoid the risks and discomfort associated with open heart surgery, modern occlusion devices have been developed that are small, implantable devices capable of being delivered to the heart through a catheter. These devices effectively seal the defect but do not require surgery. Rather than surgery, a catheter inserted into a major blood vessel allows an occlusion device to be deployed at the defect by moving the device through a catheter to the treatment site. This procedure is performed in a cardiac cathlab and avoids the risks and pain associated with open heart surgery.  
         [0005]     These modern occlusion devices can repair a wide range of cardiac defects, including patent foramen ovale, patent ductus arteriosus, atrial septal defects, ventricular septal defects, and may occlude other cardiac and non-cardiac apertures. One form of an occlusion device generally has a left side, a right side, and a center section. Once the occluder is deployed, the occluder&#39;s center section extends through the center of the defect. The left and right sides occlude the aperture on the respective sides of the patient&#39;s septum.  
         [0006]     As mentioned, several types of septal defects exist. In addition, the size of each defect varies from patient to patient. If the defect is large, the center section of the occluder must remain in the center of the defect so that the left and right sides of the occluder cover the entire aperture. If the occlusion device moves or is not properly centered in the defect, the occlusion device may not properly occlude the defect. If the defect is not properly occluded, blood will continue to shunt through the defect, which lessens the effectiveness of the occluder.  
         [0007]     Thus, there is a need in the art for an occlusion device which has a centering system to keep the device properly centered in the defect.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     The present invention provides an occluder with a self centering system that keeps the occluder properly centered in a defect. The self centering system allows the center of the occluder to remain properly positioned within the defect so that the left and right sides cover the entire defect, which reduces the chance of blood shunting through the defect and increases the effectiveness of the occluder. The self centering system is comprised of a series of arms that provide tension to hold the right and left sides in place. The arms are shaped to provide a flexible intermediate zone comprising a left and a right conical shaped network, wherein each network extends from the right and left sides and narrows at the center section. The flexible intermediate zone centers the occluder and helps to hold it in place.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a perspective view of an occlusion device.  
         [0010]      FIG. 2  is a side perspective view of the right side of an occlusion device frame.  
         [0011]      FIG. 3  is a perspective view of the structure of the left side of an occlusion device frame.  
         [0012]      FIG. 4  is a diagrammatic side view of an occlusion device.  
         [0013]      FIG. 5A  is a heat shaped wire arm.  
         [0014]      FIG. 5B  is a heat shaped stranded cable wire arm.  
         [0015]      FIG. 5C  is a block for heat shaping wire arms.  
         [0016]      FIG. 6  is a perspective view of an end cap in place on a hoop.  
         [0017]      FIG. 7A  is a top view of an end cap which demonstrates one method of closing a hoop.  
         [0018]      FIG. 7B  is a top view of a coupler which demonstrates one method of closing a hoop.  
         [0019]      FIG. 8  is a top view of an occlusion device having a hoop which demonstrates how a sail is attached to the support frame and hoop.  
         [0020]      FIG. 9  is a perspective view of a foam patch in place on an occlusion device.  
     
    
     DETAILED DESCRIPTION  
       [0021]      FIG. 1  is a perspective view of an occlusion device  10 . The occlusion device  10  comprises a center post  12 , a right set of arms  14 , a left set of arms  16 , individual wire arms  18  which make up the left and right sets  14 ,  16 , end caps  20 , a right sheet  22 , a left sheet  24 , and two wire hoops  26 . The right set of arms 14  is connected to the center post  12  and comprises the six wire arms  18  which are capped with the end caps  20 . The hoops  26  surround the perimeter of the right and left sheets  22 ,  24  and pass through holes  28  in the end caps  20 . A grasping knob  30  is located near the tip of the center post  12 . Both sets of arms  14 ,  16  are located on the inner sides of the sheets  20 ,  22 .  
         [0022]     The sheets  22 ,  24  are connected to the device  10  at the hoops  26 . The sheets  22 ,  24  may attach to the hoops  26  by folding each sheet  24 ,  26  over the perimeter of the hoop  26  and securing the sheets  22 ,  24  in place. A variety of securing methods may be used such as suturing, heat treating, or laminating. Methods of attaching the sheets  22 ,  24  to the hoops  26  are described more fully in  FIGS. 8 and 9 .  
         [0023]     The sheets  22 ,  24  are preferably formed of a medical grade polymer. One suitable material is DACRON®. Preferably, the sheets  22 ,  24  are formed of a high density polyvinyl alcohol (PVA) foam, such as that offered under the trademark IVALON®. To minimize the chance of the device  10  causing a blood clot, the sheets  22 ,  24  may be treated with a thrombosis-inhibiting material. One such suitable material is heparin.  
         [0024]     The size of the sheets  22 ,  24  may vary to accommodate various sizes of defects. In some instances, it may be desirable to form the sheets  22 ,  24  so that they are not both the same size. For instance, one sheet and its associated set of arms can be made smaller than the corresponding sheet and its associated set of arms. This is particularly useful in situations where the occlusion device  10  is to be placed at a location in the heart which is close to other nearby cardiac structures. Making the sheets  22 ,  24  different sizes may assist in providing optimal occlusion of a defect, without affecting other structures of the heart which may be nearby.  
         [0025]      FIG. 2  is a perspective view of the occlusion device  10  without the sheets  22 ,  24  attached so that the frame of the device  10  may be more easily observed. Shown in  FIG. 2  is the center post  12 , the right set of arms  14 , the left set of arms  16 , end caps  20 , two wire hoops  26  and the grasping knob  30 . The left and right sets of arms  14 ,  16  are comprised of six arms  18  which are capped by end caps  20 .  
         [0026]     The right and left sets of arms  14 ,  16  are connected to the center post  12 . The center post  12  has holes drilled into the center post  12  on both ends, or sides. One method of connecting the right and left sets of arms  14 ,  16  to the post  12  is to provide the center post  12  with drill holes through which the right and left sets of arms  14 ,  16  pass. When connected to the center post  12  using holes drilled through the center post  12 , the right and left sets of arms  14 ,  16  may be formed of three wires. The three wires create the six arms  18  because the post  12  divides each wire into two arms  18  when the wire passes through the center post  12 . The end caps  20 , located at the distal ends of the arms  18 , are rounded to minimize damage to the surrounding tissue when the device is deployed. The right set of arms  14  is threaded through holes located on the left side of the center post  12 . Likewise, the left set of arms  16  is threaded through holes located on the right side of the center post  12 . Each individual arm  18  of the left and right sets of arms  14 ,  16  is offset from adjacent arms  18  by 60°. In addition, the left and right sets of arms  14 ,  16  are offset from one another by 30°. This offsetting serves to more evenly space the arms  18  which helps to create a uniform seal around the defect.  
         [0027]     The hoops  26  attach to the device at the end caps  22 . The end caps  22  are provided with drilled holes through which the hoops  26  can pass for attachment. The hoops  26  are constructed of a single, heat shaped wire which is threaded through the end caps  22  and then secured. Methods of securing the ends of the hoops  26  are described more fully in  FIGS. 7A and 7B .  
         [0028]     The knob  30  on the center post  12  is configured to allow the device  10  to be grasped by a delivery device as the device  10  is guided through the catheter. However, the method of attachment to a delivery device is not so limited. The knob  30  may be modified as needed to attach to any delivery device. For instance, the knob  30  may be fitted with threads so that it may be screwed onto a delivery device that is outfitted with threads.  
         [0029]     The device  10  is configured to be deployed through a catheter, and more specifically, the device  10  is constructed so that the sets of arms  14 ,  16  are easily collapsible about the center post  12  to allow the device  10  to be inserted through a catheter. Due to this construction, the device  10  can be folded such that the right set of arms  14  is folded in the axial direction A and the left set of arms  16  is folded in an opposite axial direction B, which allows the folded device  10  to fit into a small diameter catheter. The right and left sheets  22 ,  24  that attach to the sets of arms  14 ,  16  collapse as the sets of arms  14 ,  16  are folded. Likewise, the hoops  26  and the sheets  22 ,  24  are also flexible and are configured to collapse.  
         [0030]     Once the device  10  is deployed across a defect in the heart, the sets of arms  14 ,  16 , the hoops  26 , and the sheets  22 ,  24  unfold to form a seal around each side of the defect. To ensure the device  10  returns to a shape capable of exerting enough pressure to seal the defect, the sets of arms  14 ,  16  are made of a suitable material capable of shape memory, such as nickel-titanium alloy, commonly called Nitinol. Nitinol is preferably used because it is commercially available, very elastic, non-corrosive and has a fatigue life greater than that of stainless steel. To further ensure that the sets of arms  14 ,  16  do not suffer from fatigue failures, one embodiment of the present invention comprises making the wire sets of arms  14 ,  16  of stranded wire or cables.  
         [0031]     The wire arms  18  are preferably subjected to precise pre-shaping to give them a “shape memory.” The pre-shaping can be done either by machining, heat treating, or both. The shape memory helps to hold the strands together when the arms  18  are formed of stranded wire or cable, and can be used to add pretension to the arms  18  so that they “remember” their shape even after undergoing a strong deformation when the device  10  is passed through a catheter. The end caps  22  may further serve to prevent potential unraveling of the arms  18  when the arms  18  are formed of stranded wire or cable.  
         [0032]     The support hoops  26  are also made of a suitable material capable of shape memory, such as nickel-titanium alloy, like Nitinol. The hoops  26  maybe constructed of a single wire or stranded wire. The diameter of the wire that is used to form the support hoops  26  must be small enough so that the hoops  26  are flexible enough to collapse when the device  10  is being loaded or retrieved. However, the wire must be stiff enough to allow the hoops  26  to lie as flat as possible against the patient&#39;s septum to create an effective seal. Similar to the wire arms, the support hoops  26  may also be heat shaped or machine shaped so that they have shape memory to ensure that the hoops  26  resume the proper shape once the hoops  26  leave the catheter.  
         [0033]     Another advantage of pre-shaping the hoops  26  using heat is to ensure that the hoops  26  are properly sized. If the hoops  26  are too large or too small for the device  10 , the hoops  26  may cause the sheets  22 ,  24  to pucker. If the hoops  26  cause the sheets to pucker, the sheets  24 ,  26  cannot lie flat against the septum and therefore do not seal as effectively as if the sheets  22 ,  24  lie flat and hug the septum.  
         [0034]     The support hoops  26  allow the device  10  to hug the tissue surrounding the defect to create a uniform seal around the opening of the defect, which improves the sealing capabilities of the occlusion device  10 . The support hoops  26  further reduce the potential for increased pressure on surrounding tissue in any one area. More specifically, once deployed, the individual arms  18  that make up the sets of arms  14 ,  16  exert pressure on the hoops  26  and sheets  22 ,  24  to form a seal around the defect. Without the hoops  26 , the highest points of pressure are the six or eight pressure points where the tips of the arms  18  may press against the tissue surrounding the defect. Given the uneven topography of the heart, some arms  18  put more pressure on surrounding tissue than others. Thus, instead of having six or eight pressure points, the support hoop  26  can more evenly distribute pressure around a continuous circle, decreasing the possibility that increased pressure will be exerted at any one contact point. By distributing pressure more evenly, the risk that one or more tips of the arms  18  will poke through the tissue, or poke through the defect, is greatly reduced.  
         [0035]     The other parts of the stabilization device  10  are likewise formed of suitable materials. More specifically, the center posts  12 ,  14  may be formed of platinum-iridium and the end caps  22  may be formed of titanium. However, the invention is not limited to these materials and any suitably biocompatible material will suffice.  
         [0036]     Though not immediately evident in  FIGS. 1 and 2 , the arms  18  vary slightly in length. This is so that when the device  10  is folded, the device  10  fits more easily into a catheter. To allow the device  10  to be retrievable, as well as ensure that the device  10  fits into as small a diameter catheter as possible, it is important to ensure that the arms  18  are not of a length that results in the end caps  22  clustering at the same location when loaded inside the catheter. If the end caps  22  all occur at the same location when the device  10  is inside the catheter, the device  10  may become too bulky to allow it to be easily moved through the catheter. In addition, though shown with six arms  18 , the device  10  is not so limited. Rather, the device  10  may be comprised of four arms, or may be comprised of anywhere from five, six, eight, ten, or even more arms.  
         [0037]     Another feature of the occlusion device  10  is that it is fully retrievable. In situations where the occlusion device  10  is not properly deployed and must be retrieved into a catheter, it is possible to withdraw the occlusion device  10  back into a catheter by grasping either the center section  12  or by grasping any one of the arms  16 . As mentioned, it is important that the arms  18  are not of a length that results in the end caps  20  clustering at the same location. If the end caps  20  cluster at the same location when the device  10  is inside a catheter, the device  10  will become too bulky to easily move through a catheter. To make the device  10  retrievable, it is possible to vary the length of the upper arms  18  from the length of the lower arms  18  so that when the device  10  is retrieved, the end caps  20  on the upper arms  18  do not cluster at the same location as the end caps  20  on the lower arms  18 .  
         [0038]      FIG. 3  is a perspective view of a portion of the occlusion device  10  shown without the sheets  22 ,  24  again, for clarity.  FIG. 3  illustrates the left side frame of the device to demonstrate how the sets of arms  14 ,  16  connect to the center post  12  and to the hoop  26 . Shown is the center post  12 , three wire arms  18 , which comprise the left set of arms  16 , end caps  20 , and a hoop  26 . Although  FIG. 3  depicts the left side of the device  10 , the same construction method applies to the right side of the device  10 .  
         [0039]     To assemble the device, the arms  18  are threaded through holes drilled through the right portion of the center post  12  to create three sets of arms  16 . The end caps  20  are threaded onto the hoop  26  and the ends of the hoop  26  are joined together inside an end cap  20 , which is described more fully in  FIG. 7A . The ends of the set of arms  16  are then inserted into the end caps  20 . Thus, the arms  16  are connected to the hoop  26  via the end caps  20 .  
         [0040]     The individual wire arms  18  that create the sets of wire arms  14 ,  16  are shaped to form a self centering portion of the occlusion device. One suitable shape for the arms  18  is a bell shape. This shape allows the device  10  to maintain a low profile once the device  10  is deployed, and also allows the set of arms  16  to center the device  10  within the defect.  
         [0041]     After the hoop  26  is threaded through the end caps  20 , the arms  18  acquire slight tension, which allows the device  10  to self center in the defect. Before the hoop  26  is added, the arms  18  splay outward and upwards. Once the hoop  26  is added, the arms  18  can no longer splay because the arms  18  are attached to the hoop  16 . Tension is created in the arms  18 , however, because the arms  18  still have the tendency to splay but cannot because the hoop  26  secures the ends of the arms  18 . The tension causes the hoop  26  to be pulled slightly towards the arms  18  and also causes the curved portion of the arms  18  to push outward, away from the center post  12 .  
         [0042]     When the device  10  is deployed, the tension in the arms  18  allows the device to seal the defect and to center the device  10 . As mentioned, the arms  18  slightly pull the hoop  26  toward the arms  18 . Once the device  10  is in place, the arms pull the hoop  26  toward the septum so that the defect is sealed. Also, the ends of the set of arms  16  no longer splay out and thus, are compressed slightly to allow the arms  18  to be inserted in the end caps  20  and attached to the hoop  26 . In response to the compression, the curved top portion of the set of arms  16  has slight tension. The tension allows the device  10  to self center because, if there is room in the defect for the upper portion of the set of arms to widen, the set of arms  16  widen and expand to accommodate the defect. Because the widening is symmetrical around the center at the device, the device centers itself within the defect.  
         [0043]      FIG. 4  is a diagrammatic side view of the device  10 . Shown are hoops  26 , sets of arms  14 ,  16  comprised of individual arms  18 , a center post  12 , a grasping knob  30 , and end caps  20 . The set of arms  14 ,  16  form a flexible intermediate zone D at the device&#39;s center. Because the sets  14 ,  16  are made of wire arms  18  which remain somewhat flexible, the diameter of the zone D adjusts to the size of the defect but does not exert enough force to widen the diameter of the defect. If, however, the defect is large, the set of arms  16  may expand to be the same diameter of the defect and center the device  10  because of the tension mentioned previously.  
         [0044]     The size of the device  10  is variable and should correspond to the rough size of the defect so that the device  10  fits the defect properly. The ability of the self centering occlusion device  10  to center itself within the defect is improved when the size of the device  10  is appropriate. If the device  10  is properly sized and centered, the likelihood that the defect will be sealed is increased and the likelihood of blood shunting is reduced.  
         [0045]      FIGS. 5A and 5B  show a wire arm  18  after it has been heat shaped. In  FIG. 5A  the wire arm  18  is constructed of a single wire. In  FIG. 5B  the wire arm is constructed of a stranded cable. Also shown are end caps  20 . The wire arm  18  has a bell shape, as mentioned previously. This shape allows the device  10  to maintain a low profile but also exerts enough pressure to cause the device to hug the septum and to center the device. The wire may be heat shaped or shaped by another suitable method. One method of heat shaping the wire is to wrap it around a plate having three cylinders mounted to it. The wire may be wrapped around the cylinders so that it has the appropriate curvature and heated while it remains wrapped around the cylinders. Preferably, the wire is stranded, as in  FIG. 5B , to both increase strength and decrease the potential for breakage.  
         [0046]      FIG. 5C  demonstrates one method of heat shaping the wire arms  18 . Shown is a block  32  having  3  cylinders  34 , which are mounted to the block  32 , and a wire arm  18 . The wire arm  18  is wrapped around the cylinders  34  and then heated. After the wire arm  18  cools, the arm  18  is removed from the block  32  and can then be attached to the device.  
         [0047]      FIG. 6  shows an enlarged perspective view of an end cap  20  in place on a hoop. Shown is an end cap  20 , a portion of a support hoop  40 , a portion of a wire support arm  44 , a hole  46 , and an end cavity  48 . The support hoop  40  passes through holes  46  drilled crosswise through the end cap  20 . The wire support arm  16  is inserted into an end cavity  48  located at the base of the end cap  20 .  
         [0048]     The end caps  20  cap the wire support arms  18  to protect tissue and prevent unraveling of the wire support arms  18  if the arms  18  are stranded. The tip of the end cap  20  is rounded to reduce the potential for trauma to the tissue surrounding a defect. The end caps  20  also serve as a location for the support hoop  40  and the arms  18  to attach to the occlusion device  10 . By providing a link between the wire support arms  18  and the support hoop  40 , the end caps  20  assist in providing better distribution of pressure once the device  10  is deployed and exerting pressure on the tissue surrounding a defect.  
         [0049]      FIGS. 7A and 8B  are top plan views of a portion of the support hoop  40 .  FIGS. 7A and 7B  show enlarged views of two examples of how a support hoop  26  can be closed so that it forms a circle.  FIG. 7A  shows a portion of a support hoop  40  which has been closed inside an end cap  20 . Shown is an end cap  20 , a portion of a support hoop  40 , ends of the support hoop  50 , and an end cavity  48 .  
         [0050]     The support hoop  26  is typically formed of a single wire. To form the hoop  26 , the wire must be closed in order to provide a 360° seal around the defect and evenly distribute pressure. The support hoop  26  may be closed after it has been threaded through the end caps  20 . In  FIG. 7A , the ends of the support hoop  50  meet after passing through holes  46  in the end cap  20  so that the ends  50  are connected inside the end cap  20 . The ends of the support hoop  50  are secured in the end cap  20  using any suitable method, such as crimping, welding, or through the use of adhesives. By joining the ends of the support hoop  50  inside an end cap  20 , no additional material must be added to the occlusion device  10 , thereby keeping the size and weight of the device  10  to a minimum.  
         [0051]      FIG. 7B  shows a second example of how a support hoop  26  may be closed.  FIG. 7B  shows a portion of a support hoop  40  which has been closed inside a coupler  52 . Shown is a portion of a support hoop  40 , ends of the support hoop  50  and a coupler  52 . In this example, the coupler  52  is a small hollow tube with a diameter slightly larger than that of the wire used to construct the support hoop  26 . The ends of the support hoop  50  are inserted in the coupler  52  where they meet. The coupler  52  can then be crimped or welded so that the ends of the support hoop  50  remain inside the coupler  52 .  
         [0052]     Other possible methods of joining the ends of the support hoop  50  may include crimping the ends  50  together or welding the ends  50  together without the use of an end cap  20  or coupler  52 .  
         [0053]      FIG. 8  is a top view of an occlusion device  10  which demonstrates how the right and left sheets  22 ,  24  may be attached to the device  10 . Shown is the center post  12 , set of arms  14 ,  16 , wire arms  18 , end caps  20 , the right sheet  20 , and the support hoop  26 . Also shown is a reinforcement edge  60 .  
         [0054]     The diameter of the right sheet  20  is slightly larger than that of the support hoop  26 . The larger diameter of the sheet  20  extends beyond the support hoop  26  after it is attached to the wire arms  18  and constitutes the reinforcement edge material  60 . The reinforcement edge material  60  allows this portion of the sheet to be folded over the support hoop  26  to form a reinforced edge of double material around the perimeter of the device  10 . Once the reinforcement edge material  60  has been folded over the support hoop  26 , it can be held in place though suturing, bonding, adhesives, heat treating, laminating, or any other suitable method.  
         [0055]     Alternatively, the reinforced edge material  60  is created using a separate sheet of foam formed in a ring. The foam ring is sized to allow it to fold over the perimeter of the device  10  and support hoop  26 . The foam ring may be attached to the sheet  20  using any suitable method such as suturing, bonding, adhesive, heat treating, or laminating.  
         [0056]     Once attached, the reinforcement edge material  60  covers the exposed edges of the occlusion device  10 . The reinforcement edge material  60  acts as a cushion between the exposed metal edges of the occlusion device  10  and the tissue surrounding the defect, providing extra protection from pressure that the device  10  exerts on the tissue.  
         [0057]     The reinforced edge  60  also secures the sheets  20 ,  22  to the device  10 . Often, in order to adequately seal the defect, the wire arms  18  must bend to accommodate the contours of the heart. Because the sheets  20 ,  22  are sewn to the wire arms  18 , the sheets  20 ,  22  must accommodate the bending of the wire arms  18 . In locations where some of the wire arms  18  are bent by the contours of the heart, a portion of the sheets  20 ,  22  may be stretched so that it experiences constant tension. This tension may cause the sheets  20 ,  22  to tear, especially where the sutures  62  are located. If the sheets  20 ,  22  tear, the sealing ability of the occlusion device  10  may be compromised. The reinforced edge  60  helps to prevent the first and second sheets  20 ,  22  from tearing at the areas where the sheets  20 ,  22  are attached to the device  10  or are sutured. Because the reinforcement edge  60  overlaps the hoop  26  and is then affixed to the rest of the sheet  20 ,  22 , it adds an additional 360° of continuous attachment of the sheets  20 ,  22  to the frame of the device  10  reducing the likelihood of tearing or detachment. The additional foam material along the perimeter of the device helps to distribute the tension on the sheets  20 ,  22  along a continuum, instead of focusing tension at discrete attachment sites like the suture points.  
         [0058]      FIG. 9  demonstrates an alternative method of reinforcing attachment of the foam sheets to the occlusion device  10 . Shown is a patch  70 , a portion of a support hoop  40 , a portion of a wire arm  42 , and an end cap  22 . The patch  70  is constructed of foam and is configured to fit over the end cap  22 . In this example, the patch  70  is shaped like a cross which enables it to cover both sides of the end cap  22  and a small portion of the support hoop  40  where the hoop  40  extends out of the end cap  22 . The patch  70  may be secured by sutures, heat treatment, laminating, or another suitable method.  
         [0059]     In addition to reinforcing the sheets, the patch  70  also acts as a cushion between the metal end caps  22  of the occlusion device  10  and the tissue surrounding the defect, providing extra protection from pressure that the device  10  exerts on the tissue. The patch  70  also reduces the amount of metal to tissue contact.  
         [0060]     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.