Abstract:
An occlusion device having at least five arms. Though the number of arms is increased, the diameter of each arm is reduced. As a result, the increased number of arms provides the desired tension as the occlusion device is deployed and provides the desired strength to hold the occlusion device in place and properly occlude the defect. At the same time, the reduced diameter of the arms improves the cycle life of the occlusion device. Furthermore, the increased number of arms provides for better sealing across the defect and reduces residual shunting.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
   This application is related to U.S. Patent application entitled Articulated Center Post, Ser. No. 10/348,856, U.S. Pat. application entitled Hoop Design for Occlusion Device, Ser. No. 10/349,118, Septal Stabilization Device, Ser. No.10/349,744, and U.S. Pat. application entitled Laminated Sheets for Use in a Fully Retrievable Occlusion Device, Ser. No. 10/348,864, all filed on even date herewith. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a method of occluding an aperture in a body. More specifically, the present invention relates to an occlusion device for occluding a septal defect having five or more arms. 
   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 ovate, atrial septal defects (ASDs), and ventricular septal defects (VSDs). 
   Normally, permanently repairing septal or other cardiac defects in adults and children requires open heart surgery, a high risk, painful, and costly procedure. In response to these concerns, modern occlusion devices have been developed are that small enough to be delivered through a catheter. Rather than surgery, these occlusion devices are deployed by inserting a catheter into a major blood vessel and moving the occlusion device through the catheter. This type of procedure can be performed in a cardiac cathlab, and avoids much of the risks, cost, and pain associated with open heart surgery. These modern occlusion devices can be used to treat a wide range of cardiac defects, including patent ductus arteriosis, patent foramen ovale, atrial septal defects, ventricular septal defects, and can be used to occlude other cardiac and non-cardiac apertures. 
   Occlusion devices that can be inserted via a catheter include button devices, collapsible umbrella-like structures, and plug-like devices. Occlusion devices with umbrella-like structures use a system of small metal wires to hold the occlusion device in place. When designing such occlusion devices, there are several design constraints due to the severe environment the human heart presents, including a continuous cycling of up to 5 billion pulses over the lifetime of a human. 
   First, the occlusion device must be stiff enough and have enough tension so that the occlusion device will remain in place even as the heart pulses. Second, the occlusion device must have a high cycle life, so that it does not develop fatigue failure problems due to the constant flexing of portions of the occlusion device caused by the beating heart. Lastly, the device must have a suitable tactile response so that when it is deployed, the physician can “feel” whether or not the device has been successfully deployed at the defect. 
   Each of these constraints competes with the other, making it difficult to design an occluder which adequately addresses all of them. Increasing stiffness may increase the tactile response, but may also lead to a decreased cycle life. This is because increasing the stiffness typically involves varying the shape and increasing the diameter of the wires used in occlusion devices. However, increasing the diameter of the wire to improve its stiffness or strength often reduces the cycle life because a larger diameter wire is often more brittle, and thus more susceptible to fatigue failure. Conversely, using smaller, thinner wires may result in increase fatigue life, but may also reduces the ability of the occlusion device to successfully occlude the defect, and may adversely affect the tactile response felt by the physician. 
   Yet another design criteria for designing an occlusion device is to ensure that the occluder seats properly. Because every patient&#39;s heart is different, and because it is extremely rare for the surfaces of the heart to be smooth and even, it is difficult to ensure that the occlusion device properly matches the contours of the defect to be occluded. 
   Thus, there is a need in the art for an occlusion device with a high fatigue life that has enough tension so that the occlusion device stays in place and provides the desired feel to a physician. There is also a need in the art for improved conformance to the defect to be occluded. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is an improved occlusion device for occluding a septal defect. The occlusion device is comprised of a center section to which upper and lower wire fixation devices are attached. Attached to the upper and lower fixation devices are polyvinyl alcohol sails which serve to further occlude the defect. To prevent any damage to surrounding tissue, the fixation devices are fitted with atraumatic tips. When deployed, the center post extends through the defect, and the upper fixation device and upper sheet are positioned one side of a defect, and the lower fixation device and lower sails are located on the other side of the defect. The upper and lower fixation devices are formed to bias the sails toward the wall of the defect so that the sails occlude the defect. 
   The upper and lower fixation devices comprise at least five arms. Forming the upper and lower fixation devices with at least five arms improves the tension and “feel” of the device as it is deployed across the defect. At the same time, the diameter of each of the arms is decreased to make them more flexible and increase their fatigue life. As a result, increasing the number of arms provides the desired tension as the occlusion device is deployed, provides the desired strength to hold the occlusion device in place and properly occlude the defect, but yet also provides the desired fatigue life of the occlusion device. Furthermore, the increased number of arms on the upper and lower fixation devices provides for better sealing across the defect and reduces residual shunting. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an occlusion device according to the present invention. 
       FIG. 2  is a top view of a six-arm occlusion device. 
       FIG. 3  is a plan view of a portion of a five-arm occlusion device. 
       FIG. 4  is a plan view of a portion of an occlusion device having eight arms. 
       FIG. 5  is a plan view of a occlusion device having ten arms. 
       FIG. 6  is a side view of an occlusion device with six arms when the device is inserted into a catheter. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a top perspective view of one embodiment of an occlusion device  10 . The occlusion device  10  comprises a center section  12  having a groove  14 , an upper wire fixation device  16 , and an upper sail  18 . The upper wire fixation device  16  comprises six wire arms  20  which terminate in atraumatic tips  22 . The atraumatic tips  22  are covered by reinforcement patches  24 . Also visible in  FIG. 1  is a bottom sail  26  and wire arms  28 , which likewise terminate in atraumatic tips  22  covered by patches  24 . 
     FIG. 2  is a bottom perspective view of the occlusion device  10 . Shown in  FIG. 2  is the center post  12 , bottom sail  26  and lower fixation device  30 . The lower fixation device  30  likewise comprises six wire arms  32  which terminate in atraumatic tips  22  covered by reinforcement patches  24 . Also shown in  FIG. 2  is the upper sail  18 , portions of the wire arms  20  and the atraumatic tips  22  covered by reinforcement patches  24 . 
   Unlike the upper fixation device  16  which is located on an outer side of the upper sail  18 , the lower fixation device  30  is located on an inner side of the lower sail  26 . However, the device is not so limited, and the fixation devices  16 ,  30  may be located on the outer side of the sails  26 ,  18 , on the inner side of the sails  26 ,  18 , or any combination thereof. 
   The upper and lower fixation devices  16 ,  30  are connected to the center post  12  using any suitable method, including welding, soldering, or adhesives. One method of connecting upper and lower fixation devices  16 ,  30  to the center post  12  is to provide the center post  12  with drill holes through which the upper and lower fixation devices  16 ,  30  extend. To hold the fixation devices  16 ,  30  more securely, the fixation devices  16 ,  30  may additionally be welded, soldered, or otherwise attached to the center post  12  in a more permanent manner. 
   When connected to the center post  12  using holes drilled through the center post  12 , the fixation devices  16 ,  30  may be formed of three wires. The three wires create the six arms  20 ,  32  because each wire forms two arms  20 ,  32  when the wire passes through the center post  12 . The atraumatic tips  22  are located at the distal end of each arm  20 ,  32  and serve to minimize damage to the surrounding tissue. Though not shown, the center post  12  may comprise an articulation to allow the device  10  to conform to a wider variety of defects. 
   The sails  18 ,  26  are connected to the occlusion device  10  at the center post and at the upper and lower fixation devices  16 ,  30 . The sails  18 ,  26  may be connected to the fixation devices  16 ,  30  using any suitable method. One method of attaching the sails  18 ,  20  to the fixation devices  16 ,  30  is to suture the sails  18 ,  20  to the fixation devices  16 ,  30  along the length of the arms  20 ,  32 . Alternatively, the sheets  18 ,  20  may be sewn to device  10  at the atraumatic tips  22 . To do so, the atruamatic tips  22  may be provided with drilled holes through which sutures can pass to sew the sheets  18 ,  20  to the tips  22 . 
   The reinforcement patches  24  are configured to fit over the atraumatic tips  22 . The reinforcement patches  24  are placed at the end of an tips  22  and are folded over the tips  22  so that the tips  22  are covered on both their top and bottom sides. The patches  24  may be secured to the sheets  18 ,  26  using any suitable method, including sutures, heat treatment, or laminating. 
   The reinforcement patches  24  serve to reinforce the foam sheets  18 ,  26  near the ends of the wire arms  20 ,  32 . This reinforcement helps strengthens the sails  18 ,  26  at the locations they are likely to tear or wear. The reinforcement patches also act as a cushion between the metal tips  22  of the occlusion device  10  and the tissue surrounding the defect. The patches provide extra protection of the tissue from the pressure that the device  10  exerts on the tissue at the atraumatic tips  22 . 
   The occlusion device  10  is configured to be deployed through a catheter, and the groove  14  on the center section  12  is configured to allow the occlusion device  10  to be grasped by a forceps as it is guided through the catheter. More specifically, the occlusion device  10  is constructed so that the upper and lower fixation devices  16 ,  30  are easily collapsible about the center section  12 . Due to this construction, the occlusion device  10  can be folded so that the upper fixation device  16  is folded upwards in the axial direction and the lower fixation device  30  is folded downwards in the axial direction. The upper and lower sails  18 ,  26  attached to the upper and lower fixation devices  16 ,  30  are also flexible, and can likewise collapse as the upper and lower devices  16 ,  30  are folded. 
   The occlusion device  10  is preferably made from bio-compatible materials with the desired properties. More specifically, the wire fixation devices  16 ,  30  are preferably formed of a material that is capable of shape memory. One such suitable material is a 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. Similarly, the center post  12  may be formed of platinum iridium, the atraumatic tips  22  may be formed of titanium, and any sutures may be formed of polypropylene, all of which are bio-compatible. 
   The sails  18 ,  26 , also called sheets  18 ,  26 , are comprised of a medical grade polymer in the form of film, foam, gel, or a combination thereof. One suitable material is DACRON®. Preferably, a high density polyvinyl alcohol (PVA) foam is used, such as that offered under the trademark IVALON®. To minimize the chance of the occlusion device  10  causing a blood clot, the foam sails  18 ,  26  may be treated with a thrombosis inhibiting material. One such suitable material is heparin. 
   In some instances, it may be desirable to form the sheets  18 ,  26  so that they are not both the same size. For instance, one sheet and its associated fixation device can be made smaller than the corresponding sheet and its associated fixation device. 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 sails  18 ,  26  different sizes may assist in providing optimal occlusion of a defect, without affecting other structures of the heart which may be nearby. 
   To ensure the occlusion device  10  is effective at closing a septal defect even after it has been passed through a catheter, the wire arms  20 ,  32  are preferably subjected to a precise pre-shaping to give them a “shape memory.” The pre-shaping can be done either by machining, heat treatment, or both. The shape memory helps to hold the strands together and can be used to add pre-tension to the wire arms  20 ,  32  so that they remember their shape even after the strong deformation that occurs when the occlusion device  10  is passed through the catheter. 
   In the past, occlusion devices have suffered from fatigue failures, such as cracks or breaks, due to the extreme environment the human heart poses. The human heart may pulse up to 5 billion times over its lifetime, and with each pulse, the wire fixation devices  16 ,  30  of the occlusion device  10  may undergo flexing or bending. This flexing and bending may eventually lead to the wires experiencing fatigue failure. To avoid fatigue failure of the fixation devices  16 ,  30 , one embodiment of the present invention relies on making the wire fixation devices  16 ,  30  of stranded wire or cables. The stranded wire or cable improves the fatigue life of the fixation devices  16 ,  30  without increasing their size or decreasing their strength. The atraumatic tips  22  cap the wire arms  20 ,  32  and can serve to prevent potential unraveling of the strands in addition to preventing damage to surrounding issue. 
   A more significant feature of the invention is the number of arms  20 ,  32  provided on the upper and lower fixation devices  16 ,  30 . The occlusion device  10  is provided with an increased number of arms  20 ,  32 , but the stiffness and tension of each arm  20 ,  32  is decreased. One method of decreasing the stiffness and tension of each arm is to decrease the diameter of the wire, stranded wires, or cable that form each arm  20 ,  32 . When formed of stranded wire or cables, the individual strands which make up the stranded wire or cable may range in diameter from about 0.001 inches to about 0.15 inches. The overall diameters of the arms  20 ,  32 , even when formed of stranded wire, may range from as small as about 0.003 inches to about 0.050 inches. 
   In the past, occlusion devices were typically made having only four arms. Each arm had to be flexible enough to be inserted into a catheter, yet stiff enough to firmly occlude the defect. In addition, the arms had to be thin enough to allow the device to fit into a catheter, yet thick enough to provide the desired stiffness. One continuing challenge faced in making the four arm devices was ensuring that the arms did not reach fatigue failure and break. Efforts to prevent fatigue failure involved increasing the diameter of the wire. However, this often led to more brittleness in the arms, and thus a decrease in cycle life. Finally, if the arms were made too flexible, to improve their fatigue life, the device was more difficult to deploy because the tension was low and it was difficult for a physician to “feel” the point where the device was deployed. In addition, if the arms were too flexible, it was possible for the device to embolize. 
   The present invention addresses all these issues. Increasing the number of arms  20 ,  32  on the occlusion device  10  ensures that the fixation devices  16 ,  30  have the required strength or stiffness to hold the sails  18 ,  26  firmly against the defect. Increasing the number of arms  20 ,  32  also improves the tension and “feel” of the device as it is inserted, which in turn assists the physician and ensures the device is properly inserted on the first try. At the same time, the diameter of each of the arms  20 ,  32  has been decreased to make them more flexible and  10  increase their cycle life. Decreasing the diameter of each arm  20 ,  32  ensures that even though the device  10  has more arms  20 ,  32 , the device  10  can still fit in to small diameter catheters for deployment. 
   Another benefit of the invention is that the device  10  improves the closing ability of the occlusion device  10 . Increasing the number of arms  20 ,  32  on the device  10  allows the device  10  to better conform to the complex surfaces present at many septal defects. Better conformance of the device  10  to the defect not only improves the functioning of the device, it can also reduce the stress placed on any one of the arms  20 ,  32 . Reducing the stress on the arms  20 ,  32  also improves the cycle life of the occlusion device  10 . 
   Each arm  20 ,  32  may be equally spaced from an adjacent arm in the six arm device  10 , each arm  20 ,  32  is located 60° from the adjacent arm. In addition, to assist in maximizing the occlusion ability of the six arm device  10 , the upper sail  18  may be offset from the bottom sail  26 . The amount one sail is offset from the other may vary based on the desired performance of the device  10 . In one embodiment, the upper sail  18  is offset from the bottom sail  26  at an angle of about 30°. 
     FIG. 3  is a top plan view of another example of an occlusion device  40  according to the present invention. The occlusion device  40  comprises a center post  42 , sail  44 , stranded wire arms  46 , end caps  48 , and reinforcement patches  50  placed over the tips  48 . For simplicity, the occlusion device  40  is shown with only one sail  44 . Similar to the occlusion device of  FIGS. 1 and 2 , the sail  44  is connected to the occlusion device  40  using any suitable method, such as sutures along the arms  46 . End caps  48  serve to prevent tissue damage and reinforcement patches  50  both provide extra protection to surrounding tissue and reinforce the sail  44  at the location it is most likely to tear. 
   The occlusion device  40  of  FIG. 3  comprises five arms  46 . When forming a five arm device  40 , rather than using a single long wire to form two arms by passing the wires through holes in the center post, the five arm device may be formed of five separate short wires. Or, the arms  46  may be formed with a combination of long wires which form two arms and short wires which form single arms. This holds true for all occlusion devices having greater than five arms. For occlusion devices having an odd number of arms, the arms may likewise be created using an odd number of shorter single wires, or may be formed using a combination of long wires which form two arms and short wires which form single arms. Conversely, forming an occlusion device having an even number of arms can be accomplished by using long wires which form two arms, as described with reference to  FIGS. 1 and 2  above. The arms  46  are affixed to the center post  42  using any suitable method, such as welding, soldering, adhesive, or other. 
   Each arm  46  of the device  40  is formed of a small enough diameter so that each arm  46  has an increased cycle life, yet the increased number of arms  46  ensures that the device  40  has enough strength and stiffness to properly occlude a defect. The increased number of arms  46  also ensures that the tension felt by a physician is adequate to detect proper deployment of the device. Increasing the number of arms  46  on the device  40  allows the device  40  to better conform to the complex surfaces present at many septal defects. In this manner, the five arm device  40  achieves the same goals as the six arm device  10  of  FIGS. 1 and 2 . 
   Once again, each arm  46  may be spaced equally from an adjacent arm  46 . In addition, the number of arms  46  may affect the shape of the sail  44 . For example, as shown in  FIG. 3 , it may be preferable to make the sail  44  so that it has the same number of sides as there are arms  46  on the device  40 . 
     FIG. 4  is a top plan view of yet another example of an occlusion device  60  according to the present invention. The occlusion device  60  comprises a center post  62 , sail  64 , stranded wire arms  66 , end caps  68 , and reinforcement patches  70  placed over the tips  68 . Just as in  FIG. 3 , the occlusion device  60  is shown with only one sail  64 . Similar to the previously described occlusion devices, the sail  64  is connected to the occlusion device  60  using any suitable method, Such as sutures along the arms  66 . End caps  68  serve to prevent tissue damage and reinforcement patches  70  both provide extra protection to surrounding tissue and reinforce the sail  64  at the location it is most likely to tear. 
     FIG. 5  is a top plan view of a final example of an occlusion device  80 . The occlusion device  80  comprises a center post  82 , sail  84 , stranded wire arms  86 , end caps  88 , and reinforcement patches  90  placed over the tips  88 . Just as above, the occlusion device  80  is shown with only one sail  84  for simplicity. Similar to the previously described occlusion devices, the sail  84  is connected to the occlusion device  80  using any suitable method, such as sutures along the arms  86 . End caps  88  serve to prevent tissue damage and reinforcement patches  90  both provide extra protection to surrounding tissue and reinforce the sail  84  at the location it is most likely to tear. 
   The occlusion devices  60 ,  80  of  FIGS. 4 and 5  comprises eight and ten arm devices  60 ,  80 . Though the number of arms  66 ,  86  is increased, the occlusion devices  60 ,  80  achieve the same goals as the previously described examples of the invention. Specifically, each arm  66 ,  86  of the devices  60 ,  80  are formed of a small enough diameter stranded wire so that each arm  66 ,  86  has an increased cycle life. At the same time, the increased number of arms  66 ,  86  ensures that the devices  60 ,  80  have enough strength and stiffness to properly occlude a defect. The increased number of arms  66 ,  86  also ensures that the tension felt by a physician is adequate to detect proper deployment of the device. Further, the increased number of arms  66 ,  86  improves the ability of the devices  60 ,  80  to conform to the complex surfaces present at many septal defects. In this manner, the devices  60 ,  80  achieve the same goals as the six arm device  10  of  FIGS. 1 and 2 . 
   Once again, each arm  66 ,  86  may be spaced equally from an adjacent arm  66 ,  86 . In addition, the number of arms  66 ,  86  may affect the shape of the sails  64 ,  84 . As shown in  FIGS. 4 and 5 , the sails  64 ,  84  have the same number of sides as there are arms  66 ,  86  on the device  60 ,  80 . 
     FIG. 6  is a side view of an occlusion device  100  inserted into a catheter  102 . The occlusion device  100  comprises a center post  104 , six upper arms  106 , six lower arms  108 , and tips  110 . For simplicity, the occlusion device  100  is shown without sails. The upper and lower arms  106 ,  108  are connected to the center post  104  at holes  112  drilled through the post  104 . When inserted into the catheter  102 , the upper arms  106  are folded against the catheter  102  in the axial direction of the center post  104 . Similarly, the lower arms  108  are folded against the catheter  102  in an opposite direction in the axial direction of the center post  104 . 
   When the occlusion device  100  is inserted into the catheter  102  it is important to ensure that the arms  106 ,  108  are not of a length that results in the tips  110  clustering at the same location. If the tips  110  all occur at the same location when the device  100  is inside the catheter  102 , the device will become too bulky to allow it to be easily moved through the catheter. 
   One solution for avoiding this problem is to insert the arms  106 ,  108  at different locations along the length of the center post  104 . When connecting the arms  106 ,  108  to the center post using holes  112 , it is possible to space the holes to minimize the clustering of the tips  110  at one location when the arms  106 ,  108  are folded. Another way to avoid this problem is to make the arms  106 ,  108  of varying lengths. As is greatly exaggerated in  FIG. 6 , each set of arms  106 ,  108  can be made of a different length, allowing all the arms  106 ,  108  to easily fold and fit into the catheter  102 . 
   In some situations, the occlusion device  100  is not properly deployed and must be retrieved into the catheter  102  after both the upper and lower arms  106 ,  108  have been pushed out of the catheter  102 . The occlusion device  100  may be retrieved by grasping the center post  104  or by grasping any one of the arms  106 ,  108 . When the device  100  is retrieved into the catheter  102 , both the upper arms  106  and the lower arms  108  will be folded in the same direction. In such an instance, it is likewise important to vary the length of the upper arms  106  from the length of the lower arms  108  so that when the device is retrieved, the tips  110  on both the upper arms  106  do not cluster at the same location as the tips  110  on the lower arms  108 . Thus, though not readily apparent from  FIG. 6 , the upper arms  106  are of a different length than the lower arms  108 . 
   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. In particular, any of the applicable features disclosed in related applications U.S. patent application entitled Articulated Center Post, Ser. No. 10/348,856, U.S. Pat. application entitled Hoop Design for Occlusion Device, Ser. No. 10/349,118, Septal Stabilization Device, Ser. No. 10/349,744, and U.S. Pat. application entitled Laminated Sheets for Use in a Fully Retrievable Occlusion Device, Ser. No. 10/348,864, filed on even date herewith, may be of use in the present invention. Each of these applications is hereby incorporated by reference.