Abstract:
An occlusion device with stranded wire support arms for the closure of atrial or ventricular septal defects, for the closure of patent ductus arteriosus, patent foramen ovale, or other vascular defects. The occlusion device comprises a center section extending in an axial direction, with upper and lower stranded wire fixation devices emanating from the center section. The stranded wire fixation devices have been heat treated and formed with a shape memory. The stranded wire fixation devices are formed of multiple wire strands and have atraumatic tips. Attached to the fixation devices are sheets, which serve to occlude the opening.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     None. 
     BACKGROUND OF THE INVENTION 
     This invention relates to an occlusion device for the closure of physical anomalies like vascular or septal apertures, such as patent ductus arteriosus, patent foramen ovale, atrial septal defects, or ventricular septal defects. The invention comprises a center section extending in an axial direction, upper and lower stranded wire elastic shape memory fixation devices emanating from the center section, with first and second sheets of polyvinyl alcohol foam attached to the fixation devices. The stranded wire elastic shape memory fixation devices are formed from multiple wire strands. This formation greatly increases the resistance to fatigue of the fixation devices and significantly extends the life of the devices after implantation in a patient. 
     Normally, permanently repairing certain cardiac defects in adults and children requires open heart surgery. Open heart surgery is risky and painful. To avoid it, modern occlusion devices have been developed are that small, implantable devices capable of being delivered through a catheter. Rather than surgery, an occlusion device is deployed by a catheter inserted into a major blood vessel, a procedure that is performed in a cardiac cathlab and avoids the risks and pain associated with open heart surgery. These modem occlusion devices can repair patent ductus arteriosis, patent foramen ovale, atrial septal defects, ventricular septal defects, and other cardiac and non-cardiac apertures. 
     One such device, disclosed in PCT application PCT/US98/15961, entitled  Occlusion Device for the Closure of a Physical Anomaly Such as a Vascular Aperture or an Aperture in a Septum , filed on Jul. 31, 1998 by Bernhard Schneidt, discloses a non-thrombogenic occlusion device that is insertable into an anomaly via a catheter. In addition, a similar device filed as German Appln. 297 14 242.9 on Aug. 8, 1997, discloses an occlusion device which can be inserted via a catheter. 
     The new occlusion devices that are inserted via a catheter include button devices, collapsible umbrella-like structures, and plug-like devices. One major draw back is that the intent of some of these occlusion devices is to fill the ductus and stimulate thrombosus, or a blood clot. Once the blood has clotted around the device, tissue begins to grow thus ensuring that the ductus is permanently closed. Blood clots, however, are potentially dangerous in that they may dislodge, get carried to the brain and cause a stroke. 
     Occlusion devices with umbrella-like structures use a system of small metal wires to hold the occlusion device in place. 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, the wires may develop fatigue failure problems. With each pulse, the wires are strained and eventually may fracture or break, giving rise to potential complications and patient anxiety. In addition to the stress caused by the beating of the heart, metal wires may also be strained when a device is inserted into an irregularly shaped opening. For instance, one side of the opening may only be a few millimeters thick, but another side may be many more millimeters thick. Thus, one side of the occluding device may be bent open ether than the other side, putting more stress on the wires used on that side. This stress from being deformed and bent may also lead to fatigue failures. 
     Efforts to alleviate the fatigue failures described above include varying the shape and diameter of the wires used in occlusion devices. However, increasing the diameter of the wire can actually result in the wires becoming more brittle and more susceptible to fatigue failure and fracturing. Another effort to prevent failure of the wire is to use coils or hinges. The coils and hinges attempt to distribute the forces acting upon the wires, and prevent the problems with fatigue failures. However, the coils and hinges do not significantly decrease fractures or failures in the wires. So far, nothing has dealt satisfactorily with the fatigue failures in the wires. 
     Thus, there is a need in the art for an occlusion device that is collapsible enough to fold into a small catheter and constructed of materials that will not cause blood clots. In addition, there is a need for an occlusion device that is durable enough to withstand the heart&#39;s pulsing without experiencing fatigue failure. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is an occlusion device for closure of a physical anomaly. The occlusion device is more durable and will not suffer from fatigue failures caused by the continuous pulsing of the human heart. This is because the fixation devices, which hold the device in place, are constructed of stranded wire. The stranded wire configuration greatly increases the strength and cycle life of the fixation devices without increasing the size of the device. Attached to the fixation devices are sheets (e.g. polyvinyl foam sheets) which serve to occlude the anomaly. The occlusion device is collapsible and capable of being inserted into an anomaly by means of a catheter. 
     The occlusion device is comprised of a center section to which the stranded wire elastic shape memory fixation devices are attached. The fixation devices hold the occlusion device in place once it is inserted into an aperture. In addition, the sheets attached to the fixation devices act to occlude the aperture. To prevent any damage to surrounding tissue, the fixation devices are fitted with atraumatic tips. 
     Each of the fixation devices are made of multiple wire strands or cables. Using multiple wire strands or a cable serves to greatly extend the cycle life of the fixation devices and prevent any fatigue failure caused by the severe environment the human heart presents for an occlusion device. Once attached to the center section, the fixation devices are collapsible so that the entire occlusion device can be moved through a catheter. The fixation devices have a shape memory, which allows the fixation devices to return to their original shape, or “remember” their shape even after being bent or deformed for passage through a catheter. In setting the shape, the deformation caused by passage through a catheter is taken into account. 
     A material suitable for the sheets is a polyvinyl alcohol foam, such as IVALON®. A first sheet is attached to the upper fixation devices and a second sheet is attached to the lower fixation device. The shape of the foam sheets can either be a square or a circle or any other such suitable shape. The sheet on the upper fixation device may be originated asymmetrically from the sheet on the lower fixation device. This is advantageous in that a wider variety of anomalies can be closed using such an arrangement, including anomalies of different sizes and shapes. 
     A method of inserting an occlusion device begins by using a guide catheter introduced through the femoral vein and lower vena cava and placed in the right ventricle of the heart. After passing through the defect in the atrial septum, the distal portion of the device is forced out of the catheter and unfolded in the left atrium, much like unfolding an umbrella. The unfolded portion is drawn back against the septum due to the pre-tensioning of the fixation devices. Then, the proximal parts of the implant are likewise pushed out of the catheter and independently unfolded in the right atrium. The insertion forceps used to guide the occlusion device through the catheter are then separated from the center piece. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top perspective view of an occlusion device with stranded wire support arms. 
     FIG. 2 is a bottom perspective view of an occlusion device with stranded wire support arms. 
     FIG. 3 is a greatly enlarged side view of a portion of the stranded wire support arm and atraumatic tip. 
     FIG. 4 is a perspective view of a cable comprised of wire strands. 
     FIG. 5 is a graphical illustration of wire strands. 
     FIG. 6 is a graphical representation of cables. 
     FIG. 7 is a side diagrammatic view of the occlusion device inserted into a catheter. 
     FIG. 8 is a side diagrammatic view of a stranded wire elastic shape memory fixation device. 
     FIG. 8A is a side view of an alternate embodiment of an stranded wire elastic shape memory fixation device. 
     FIG. 9 is a side diagrammatic view of an occlusion device inserted into septal anomaly. 
     FIG. 10 is a bottom view of a portion of the occlusion device taken along line A. 
     FIG. 11 is a top view of the occlusion device with stranded wire support arms. 
     FIG. 12 is an enlarged view of a portion of the stranded wire elastic shape memory arm and atraumatic tip. 
     FIG. 13 is an alternate embodiment of an atraumatic tip formed from a stranded wire elastic shape memory arm. 
     FIG. 14 shows a side view of a center piece of an occlusion device. 
     FIG. 15 shows a detail of a center piece of an occlusion device. 
     FIG. 16 is a top view of one embodiment of the occlusion device wherein the elastic shape memory fixation devices are shaped in an “S” form. 
     FIG. 17 is a top view of one embodiment of the occlusion device wherein the elastic shape memory fixation devices are not centered about the sheets. 
     FIG. 18 is a side view of a collapsible frame occlusion device. 
     FIG. 19 is a side view of a mesh type fabric constructed of multiple wire strands or cable. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a top perspective view of an occlusion device with stranded wire support arms. The occlusion device  10  is comprised of a center section  12  extending in the axial direction. The center section  12  has attached an upper stranded wire elastic shape memory fixation device  14  comprising four upper stranded wire arms  16 . The stranded wire arms  16  are exaggerated views to illustrate the individual wires that comprise the strand; the individual wires are not clearly visible to the naked eye. Attached to the end of each stranded wire arm  16  is affixed an atraumatic tip  18 . The occlusion device  10  also comprises a first sheet  20  attached to the atraumatic tips  18  via sutures  24 . 
     FIG. 2 is a bottom view of the same occlusion device  10 . Visible in FIG. 2 is the bottom of the center section  12  with a groove  26 . Attached through the bottom of center section  12  is the lower stranded wire elastic shape memory fixation device  28  comprising four bottom stranded wire arms  30 . Once again, the stranded wire aims  30  are capped with atraumatic tips  18  and are exaggerated to show the individual wires that comprise the strands. The second sheet  22  is attached to the lower stranded wire elastic shape memory fixation device  28  via sutures  24  sewn through the tips  18 . 
     The occlusion device  10  is constructed so that the upper and lower stranded wire elastic shape memory fixation devices  14 ,  28  are easily collapsible about the center section  12 . Due to this construction, the occlusion device  10  can be folded so that the upper stranded wire elastic shape memory fixation device  14  is folded upwards in the axial direction and the lower stranded wire elastic shape memory fixation  28  device is folded downwards in the axial direction. The first and second sheets  20 ,  22  attached to the upper and lower stranded wire elastic shape memory fixation devices  14 ,  28  are made of a flexible material, such as polyvinyl alcohol (PVA) foam, and likewise collapse as the upper and lower fixation devices  14 ,  28  are folded. 
     A human heart pulses up to 5 billion times over the lifetime of a human. In the past, occlusion devices have suffered from fatigue failures, such as cracks or breaks, due to the constant pulsing and extreme environment the human heart poses. The present invention alleviates these fatigue failure problems due to a novel design. FIG. 3 is a greatly enlarged detail of a portion of the stranded wire shape memory fixation device  32 . Visible is multi-wire strand  34  comprised of a 1×7 strand. The 1×7 strand is comprised of six individual wires,  38 - 48  laid about a center wire (not shown). An atraumatic tip  36  caps the strand  34  and serves to prevent potential unraveling of the strand  34  while at the same time preventing damage to surrounding tissue. Each wire  38 - 48  of the multi-wire strand  34  is made of a suitable material capable of shape memory, such as 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. Nitinol is known to those skilled in the art. 
     The multi-wire strand  34  has been subjected to a precise pre-shaping to give it a “shape memory”. This pre-shaping can be done by means of machining or heat treatment or both. The shape memory helps to hold the strands together, prevent unraveling, and can be used to add pretension to the wire so that the wires can return to (or remember) their shape even after the strong deformation that occurs when the occlusion device is passed through a catheter. 
     Of particular benefit to the invention is the significant extension of cycle life the multi-wire strand  34  adds to the fixation devices. While an individual wire, when subjected to the repeated pulsing of a human heart, may likely suffer a fatigue failure and either fracture or break, a multi-wire strand greatly decreases the chances of such a failure. The reason being that when formed in a strand or a cable, the resulting cycle life of the strand or the cable approximates the cycle life of each individual wire. Small diameter wires have the greatest resistence to fatigue failure, and thus have the longest cycle life, because they are extremely elastic. However, this elasticity also means that the small diameter wires do not have enough stiffness to perform the function required of the fixation device, that is to occlude an anomaly and hold the device in place. When stranded, the small diameter wires retain the elasticity and resistance to fatigue failure, and yet also obtain the necessary stiffness required to allow the device to function. Thus, the resulting strand benefits from significantly increasing its cycle life while not greatly increasing in size. There are several options for either strands or cables to be used in the present invention. 
     A cable refers to two or more strands laid together, and a strand refers to two or more wires laid together. FIG. 4 is a perspective view of a multi-wire cable  50 . The cable  50  is made of several strands  52  laid about a core  54 . Each strand  52  is made of several individual wires  56  laid about a center  58 . Also visible in FIG. 4 is the lay of the cable, which is a right regular lay. The lay refers to the direction, length, and general pattern that the wires  56  are laid in strand  52  and the strands  52  are laid in cable  50 . 
     A left lay is when the wire  56  or strands  52  are laid in a helix having a left-hand pitch, similar to a left hand screw. Similarly, a right lay is when the wire  56  or strands  52  are laid in a helix having a right-hand pitch, similar to a right hand screw. Regular lay refers to cable  50  in which the wires  56  in the strands  52 , and the strands  52  in the cable  50  are laid in opposite directions. A regular lay is standard, affording good flexibility and kink resistance. A lang lay refers to a cable  50  in which the wires  56  in the strands  52  and the strands  52  in the cable  50  are laid in the same direction. A lang lay is more flexible than the regular lay, but is also more susceptible to kinks. In addition, the lang lay cable, should only be used in applications where the cable  50  is not allowed to turn, or the cable  50  will unwind itself. 
     The length of the lay also provides information regarding the cable or strand. The length of the lay is the distance, in a straight line, in which a wire will make one complete spiral around the strand&#39;s center core, or in the case of a cable, the distance in which a strand will make one complete spiral around the cable&#39;s core. Generally, the longer the lay, the stronger the strand or cable, and the shorter the lay, the more flexible the strand or cable. Good combinations of flexibility and strength can be obtained by using a length of lay factor of 10 times the finished strand diameter for strand, and 7 times the finished cable diameter for cable. 
     A variety of strand options are illustrated in FIG.  5 . The construction of a strand is normally referred to as 1×the number of wires involved. Thus, a 1×3 strand  60  comprises three wires  61  laid together. Similarly, a 1×7 strand  62  comprises six wires  63  laid about a single wire. Likewise, a 1×19 strand  64  comprises a 1×7 strand with twelve wires  65  laid about it. The 1×3 strand  60  is the simplest construction of a strand with symmetrical balance. The 1×3 strand  60  is very flexible when the individual wires  61  have extremely small diameters. The 1×7 strand  62  is stronger than the 1×3 strand  60 , but has essentially the same flexibility range. A 1×7 strand  62  is more symmetrical in configuration and affords better flexibility when made of small diameter wires  63 . The 1×19 strand  64  is likewise stronger than a 1×7 strand  62  and more symmetrical in configuration, affording still better properties as far as flexibility and strength than the 1×7 strand  62 . Because the fatigue resistance and cycle life of a strand approximates the fatigue resistance and cycle life of each individual wire, it is possible to use much smaller diameter wires to achieve a desired cycle life, while keeping the outer diameter of the strand within a desired size. 
     Any of the strands shown in FIG. 5 can be used in connection with the present invention. Preferably, the individual wires  61 ,  63 ,  65  used to form either a 1×3, 1×7, or 1×19 strand  60 ,  62 ,  64  have a diameter of less than 0.008 inch, more preferably the wires  61 ,  63 ,  65  have a diameter of less than 0.005 inch. At this size, the outer diameter of the strand can be kept within a desired diameter, but a significant increase in cycle life is gained. For instance, using 0.005 inch wires  63  in a 1×7 strand  62  results in the outer diameter of the strand  62  being 0.015 inch (because the strand is three wires  63  across). This 0.015 inch diameter strand has similar strength but significantly more resistance to fatigue than a solid 0.015 inch diameter wire would, yet retains many of the desirable properties, such as flexibility, as a 0.005 inch wire. When 0.001 inch wires  63  are used in a 1×7 strand  62 , the resulting outer diameter is 0.003 inches. 
     When using a 1×19 strand  64 , the outer diameter is five times the diameter of the individual wires  65  used (because the strand is five wires  65  across). Thus, if 0.005 inch wires  65  are used, the outer diameter becomes 0.025 inch. If 0.001 inch diameter wires  65  are used, the outer diameter of the strand  64  is 0.005 inch. 
     However, it is not necessary for all wires in the strand to have the same diameters. For instance, a 1×7 strand  62  comprises six wires  63  laid about a center. The center wire  63  can have a diameter different from the six wires  63  laid about it. For example, the diameter of the center wire may be 0.001 inch and the diameters of the outer wires may be 0.005 inch. Further, the center wire  63  may be made of a strand of wires rather than being a solid wire. Similarly, in a 1×19 strand  64 , twelve wires  65  are laid about a 1×7 strand center. The twelve wires  65  laid about the center can have a different diameter than the wires  65  used to make the 1×7 strand center. 
     FIG. 6 illustrates several configurations of cable. As mentioned above, a cable is two or more strands laid together. The construction of a cable is normally referred to as the number of strands×number of wires in each strand. For instance, a 3×7 cable  66  is a combination of three 1×7 strands  67 . A 3×7 cable  66  is very flexible when made with small diameter wires. A 7×3 cable  68  is a combination of seven 1×3 strands  69 , and has properties essentially the same as a 3×7 cable  66 , but results in a much smoother strand. A 7×7 cable  70  is a combination of seven 1×7 strands  71 , which allows for abrasion resistance and flexibility through a wide range of wire diameters. A 7×19 cable  72  is a combination of seven 1×19 strands  73  producing a combination of strength and very good flexibility. 
     With any of the cables or strands, it is possible to coat the cable or strand, as illustrated by the 7×19 cable  72  with a coating  74 . Much like the benefits of strands, the benefits of a cable are increased strength. The strength of a cable is about 83% of the aggregate strength of each individual wire. Thus, it is possible to use a much smaller diameter wire to create a cable of a desired diameter, strength, and flexibility. 
     Cables, much like strands, are suitable for use in connection with the present invention. Varying configurations of cable can be used, including 3×7, 7×3, 7×7, 7×19, or any other suitable configuration. Most preferably, the diameter of the cable used in the present invention is less than about 0.025 inch. The cable may be laid on either a solid core or laid about a core comprised of multiple wires or strands of wires. 
     Though discussed in terms of cables and strands, stranded wire may also refer to other configurations of wires. For instance, stranded wire also includes braided or woven wire. Further, stranded wire may simply be several individual wires laid together, affixed at points along the length of the wires to keep the bundle together. 
     The occlusion device is foldable so that it can be inserted into a catheter for implantation in or retrieval from a patient. FIG. 7 is a side diagrammatic view of an occlusion device  80  inserted into a catheter  82 . The center section  84  extends in the vertical direction. Attached to the center section  84  is the upper stranded wire elastic shape memory fixation device  86  to which a first sheet  88  is attached. The upper stranded wire elastic shape memory fixation device  86  and first sheet  88  are folded upwards in such a way as to fit inside the catheter  82 . Likewise, the lower stranded wire elastic shape memory fixation device  90  and the second sheet  92  attached thereto are folded downwards to fit inside the catheter  82 . 
     Visible once again on the center section  84  is groove  94 . The center section  84 , also referred to as a center strut or center piece, preferably has an axial length of about 20 mm or less. In particular, center section  84  preferably has a length between about 1 mm and about 10 mm. Though shown as having a solid center section  84 , the center section  84  may be articulated or constructed of stranded wire so that it is flexible. 
     Having a flexible center section  84  is advantageous because often when implanted, an occlusion device may be located in an irregularly shaped anomaly. Having a flexible center section  84  allows the occlusion device  80  to fit in a wider variety of anomalies, despite the shape or size of the anomaly. For instance, one side of the anomaly may be only a few millimeters thick, but another side may be many more millimeters thick. In such cases, one side of the occluding device  80  may be bent open further than the other side, putting more stress on the fixation device  86 ,  90  used on that side. If the center section  84  is flexible, the center section  84  can bend such that the upper or lower fixation device  86 ,  90  need not be the only location where the occlusion device adjusts to fit the anomaly. 
     The groove  94  allows for a guide forceps  96  to manipulate the occlusion device  80  as it is pushed through the catheter  82 . Likewise, the guide forceps  96  can be used to position the occlusion device  80  once it reaches the desired location, or used to retrieve the occlusion device  80  should it not be placed properly. The groove  94  may additionally have a cross-sectional area which allows a forceps  96  to rotatably move the device  80  while the device is inserted into an anomaly. The groove  94  is grasped by a forceps  96  so that there is at least some play between the forceps  96  and the groove  94  when pushing the device  80  through a catheter  82 . In particular, the guide forceps  96  engages the groove  94  by means of a claw-like or hook-like end. 
     Because the relative movement between the forceps  96  and the device  80  results in a relatively short rigid unit, the occlusion device  80  can be passed through sharply curved positions. In addition, because the device  80  is foldable, it can easily be retrieved if deployed or implanted imperfectly simply by grasping any part of the device  80 . Because the stranded wire fixation devices are so flexible, grasping one part of a fixation device  86 ,  90  and pulling on it will cause the remaining portions of the device  80  to be folded in the axial direction along the center section  84  so that the device  80  can be removed. 
     Due to the small diameter of catheter  82 , the upper and lower fixation devices  86 ,  90  undergo a strong deformation which can have an adverse effect on an implanted occlusion device  80  by causing the ends of the fixation devices  86 ,  90  to retain some of the deformation caused by being folded and thus project away from the septal wall after insertion. For this reason, the upper and lower stranded wire elastic shape memory fixation devices  86 ,  90  are formed of stranded wire that has been formed by mechanical means and heat treated to retain its shape or “remember” its configuration. 
     One reason for giving the fixation devices  86 ,  90  a shape memory is to prevent any unraveling of the individual strands. But more importantly, the shape memory ensures that the fixation devices  86 ,  90  will hold the PVA foam  88 ,  92  sheets next to the walls of the area to be occluded. Thus, the pre-shaping takes the form of a convex curve which urges the fixation devices  86 ,  90  toward the septum wall. FIG. 8 is one illustration of a suitable configuration for the shape memory of the fixation devices. Shown is a first multi-wire strand arm  100  threaded through the center section  102 . The holding arms  100  need not necessarily lay flat against a vascular wall. As shown, the arms  100  are curved to form a convex shape. In this way, the desired contact with the septal wall takes place. In addition, other suitable shapes are possible as illustrated in FIG.  8 A. In FIG. 8A, one holding arm  104  is divided into two legs  106 ,  108  in which each leg raises as it emanates from the center piece  102  only to slope downwards after reaching a maximum. In this manner, the desired contact with the wall of the area to be occluded still takes place. 
     The shape memory feature is further illustrated in FIG. 9, which is a side view of an occlusion device inserted into a septal anomaly. The occlusion device  110  is used to close an occlusion in the septal wall  112 . In doing so, the upper stranded wire fixation device  114  is used to hold the first sheet  116  essentially flush against the septal wall  112 . In like manner, the lower stranded wire fixation device  118  is used to hold the second sheet  120  essentially flush against the other side of the septal wall  112 . Also shown in FIG. 9, is an optional foam plug  122  which further serves to fill the occlusion or septal anomaly. As mentioned before, the stranded wire fixation devices  114 ,  118  are formed so that they are pre-shaped or pre-tensioned. Due to this pre-tensioning or pre-shaping, the fixation devices  114 ,  118  urge the attached sheets  116 ,  118  toward the septal wall  112 . In this manner, the occlusion device  110  is held securely against both sides of the septal wall  112 . 
     Also shown in FIG. 9 are atraumatic tips  126 , which are affixed to the ends of the fixation devices  114 ,  118 . The center section  124  is also fitted with an atraumatic tip  128 . The atraumatic tips  124 ,  128  ensure that there is a minimum of tissue damage caused by the occlusion device  110  when inserted. 
     FIG. 10 is a view taken along line A in FIG. 9 showing a bottom view of second sheet  120 . As evidenced in FIG. 10, the second sheet  120  is attached to the fixation device  118  via sutures  130 . Likewise, the second sheet  120  is attached to the center section  128  via sutures  132 . Though described as being attached via sutures  130 ,  132 , the sheet  120  can also be attached by cementing, joining to, or molding over the fixation device  118  in other suitable manners. The sheet  120  is comprised of a medical grade polymer in the form of film, foam, gel, or a combination thereof Preferably, a material is used which is offered under the trade name IVALON® and is a high density foam. 
     The thickness of the sheet  120  when dry is between about 0.2 mm and 2.0 mm. Preferably, the thickness of foam when dry is between about 0.3 mm and about 0.8 mm. PVA foam sheets  120  are preferably formed to these thicknesses by slicing thin sheets of foam from a thicker foam block. When the foam sheets  120  are generally square, the sheets  120  preferably have a diagonal dimension of between about 5 mm and about 50 mm. Preferably, the diagonal dimension is between about 18 mm and about 30 mm. After exposure to blood or other moisture, the PVA foam sheet  120  expands on the order of about 10% in thickness. 
     An important advantage of the present invention is that the PVA foam sheets  120  immediately block blood flow as soon as they are unfolded during implantation. The physician therefore can test the effectiveness of the occlusion device  110  immediately after placement by injecting x-ray contrast fluid through the catheter. If the occlusion device  110  is for any reason not positioned so that it is properly blocking the aperture, the physician can use the forceps to reposition or remove the occlusion device  110 . In contrast, prior art devices using DACRON® do not initially block blood flow, but rather require clotting to take place in the DACRON® over a period of days or weeks. This “residual shunting” makes it much more difficult to ascertain whether an effective deployment of an occlusion device has occurred. 
     It is also significant that PVA foam does not rely on clotting as the mechanism for occluding the anomaly. PVA foam is apparently non-thrombogenic, which reduces the risk of clot formations associated with implantation of occlusion devices which may embolize, causing a stroke. Another advantage is that PVA foam may be formulated in a radiopaque form, which allows the physician to see the device more clearly during deployment. This ensures proper positioning of the device  110 . 
     PVA foam is a proven bio-compatible material. The cellular nature of PVA foam promotes rapid end othelialization. In addition, PVA foam sheets  120  expand considerably when wetted. The softness and expandability allow the PVA foam sheets  120  to expand and conform as needed to occlude or fill a defect. This is particulary advantageous because current techniques for determining the size and shape of septal defects are not precise. 
     PVA foam can be shaped in a wide variety of sizes and configurations. It is easily handled and worked in its dry, rigid state, yet is soft and highly compressible after it has been wetted. This permits the fabrication of devices of a wide variety of shapes, both simple and complex. For example, device  110  can be custom formed to fit a particular patients defect. Likewise, though the preferred embodiment shown has the sheet shaped as a square, it is also possible for this sheet to be shaped in a circle or other suitable shape. 
     The occlusion device  110  may be used in a variety of physical anomalies of a variety of sizes and shapes. To accomplish this, the device  110  is comprised of two parts that are offset from one another by 45°. FIG. 11 is a top plan view of the occlusion device  140  with an upper stranded wire elastic shape memory fixation device  142 . Visible is the center section  144  through which the fixation device  142  extends. The fixation device  142  comprising a first multi-wire strand shape memory arm  146  and a second multi-wire strand shape memory arm  148 . Attached to the arms  142 ,  146  is a first sheet  152 . A second sheet  154  is placed asymmetrically below first sheet  152 , offset by 45°. This asymmetric configuration allows for more precise insertion of the occlusion device  140 . Likewise, the asymmetric configuration allows for the occlusion device  140  to be used in a wider variety of anomalies, such as those with irregular shapes. At the end of each arm  142 ,  146 , are atraumatic tips  150 . 
     FIG. 12 offers a greatly enlarged view of an atraumatic tip  160  attached to a multi-wire strand shape memory fixation device  162 . The tip  160  can be joined with the fixation device  162  by pressing, welding, or cementing. The tip  160  is a molded, elongated metal body having a rounded distal end  164  and a beveled proximal end  166 . The tip  160  also has a hole drilled  168  into which a filament can be passed through to join the tip  160  to a PVA foam sheet. Blind hole  170  in the proximal end  166  of tip  160  receives the distal end of multi-wire strand  162 . 
     The atraumatic tip  160  shown in FIG. 12 is particularly advantageous because its elongated shape makes it easy to crimp the tip  160  onto the distal end of the multi-wire strand  162 . The elongated shape also makes its easier to drill a hole  168  through the tip  160 . However, such a tip  160  can be made from a spherical object as well. The bevel of the proximal end  166  is also important in that it provides a smooth surface when pulling the device into a guide catheter or introducer. With other embodiments of atraumatic tips, a more abrupt junction between the tip  160  and wire strand  162  can cause the device to hang up on that junction when the occlusion device is being loading into a catheter. 
     FIG. 13 shows another embodiment of an atraumatic tip  172  located at the end of the multi-wire strand  174 . In FIG. 13, the atraumatic tip  172  is formed at the end of a multi-wire strand  174  by rounding and polishing the strand  174  at its distal end. Tip  172  is circular, and includes an aperture  176  through which a filament can be extended for suturing a PVA foam sheet to the tip  172 . 
     FIG. 14 is a side view of one embodiment of center section  180 . The center section  180  may be made from ceramic, plastic, or metals (such as platinum, iridium, titanium) or combination thereof. Center section  180  has a center bridge  182 , a contacting piece  184 , and a head piece  186 . The contacting piece  184  with the center bridge  182  can be telescopically pushed toward headpiece  186  in order to easily adapt to different septal or vessel wall thicknesses. Thus, center bridge  182  is supported in relation to head piece  186  by means of spring  188 . Other well known adjustable options for varying the length of center section  180  may also be used, or center section  180  may be of a fixed length. 
     FIG. 15 is a side view of a detail of a center section  190 . As mentioned, the elastic shape memory fixation device  192  passes through the center section  190  and the fixation device  192  is capable of being deformed in the axial direction. In order to ensure that the fixation device  192  is not kinked or severed by a sharp edge, any holes  194  used for the fixation device  192  are rounded off. Thus, when the fixation device  192  passes through the hole  194  and is strongly deformed, it is much less likely to be sheared off or permanently kinked since the edges of the hole  194  are beveled or rounded off. Another benefit of the beveled hole  194  is that the fixation device  192  can be bent in closer proximity to the center section  190 , thus allowing the use of a smaller diameter catheter. Such a configuration occurs on holes  197  on both the center section  190 , and also on any holes drilled in the atraumatic tips to allow sutures to pass therethrough. In this manner, it can be assured that the suture thread will not be sheared off by a sharp edge. 
     FIG. 16 shows an alternate embodiment of an occlusion device  210 . The device  210  is configured with holding arms  212  and  214 , which rather than being formed straight, are shaped in the form of an “S” and are bent in such a way that the arms  212 ,  214  are enclosed by a circle  216  in the form of an envelope. The free ends of the holding arms  212 ,  214  are located within the respective envelope  216 . The advantage of such a configuration is that in the event of forces acting from outside the holding arms  212 ,  214  which, for instance, can occur with the shrinkage of a heart upon aging, the free ends will not lead to injuries of the septa. FIG. 17 illustrates another configuration with an off center arrangement. In FIG. 17, the center section  218  is not located in the center of the device  210 . This configuration makes it possible to close septal defects of irregular shape. 
     Though discussed in terms of support arms, the multiple wire strands and cables are suitable for use with other embodiments of occlusion devices. The stranded wire design may replace any stainless steel single wire occlusion device designs, including those utilizing hinges or coils. One such device that would benefit from stranded wire is U.S. Pat. No. 5,451,235 , Occluder and Method for Repair of Cardiac and Vascular Defects . The multiple wire stands and cables are also suitable for use with collapsible frame configurations of occlusion devices. 
     FIG. 18 is a side view of a collapsible frame occlusion device  220  comprised of a multiple wire strand mesh fabric type material. The material, more fully illustrated in FIG. 19, is comprised of several wire strands or cables interwoven to form a hollow tube-like structure  222 . As shown in FIG. 18, the mesh can be formed into an occlusion device  220  with a first collapsible frame  224  and a second collapsible frame  226  separated by a center section  228 . 
     In creating the device  220 , the mesh is formed into the desired shape, either through use of a mold or other suitable method, and heat treating the wires to give them a “shape memory”. In this manner, even after being elongated to move through a catheter, the device  220  will return to its preformed shape once inserted into an anomaly. Though the present embodiment shows the first frame  224  as being smaller than the second frame  226 , the frames  224 ,  226  can be the same size. In the present embodiment, the larger frame  226  is placed on the side of the septum against which the most pressure is exerted. The smaller frame  224  serves to hold the device  220  in place. 
     Because the mesh material may unravel, the ends  230  of the device  220  are crimped to hold the material together. The crimped area  230  can be topped with atraumatic tips  232 . Due to the device  220  being made of the collapsible mesh, the device  220  can be elongated in the axial direction and stretched into a narrow tube capable of being loaded into a catheter. The tips  232  may be configured so that a forceps can be engaged to guide the device  220  through the catheter for implantation. To further aid in occluding a septal defect, the device  220  may have fiber inserted into the mesh. Likewise, a PVA foam sheet can be attached to the collapsible frames  224 ,  226  to aid in occlusion. 
     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. For instance, though discussed in terms of closing cardiac anomalies, the present invention is not so limited and may be used to occlude other cardiac or non-cardiac apertures.