Background
A wide variety of intracardiac repair devices are used in different medical procedures. For example, certain intravascular devices, such as catheters and guide wires, are generally used only to deliver fluids or other medical devices to specific locations within a patient's heart, such as selective coronary arteries in the vascular system. More sophisticated other devices are often used to treat specific conditions, such as devices for removing vascular emboli or for treating septal defects and the like.
In some cases, it may be desirable to occlude a patient's blood vessel, such as to prevent blood flow through an artery into a tumor or other wound site. Currently, this is usually accomplished only by inserting coil springs, such as Ivalon pellets (a commercial name for vasoocclusive pellets) and short sections, at the desired location within the vessel. These "embolic agents" will accumulate in the vessel, often floating downstream of the site, where they are loosened prior to occluding the vessel. This process often limits its utility, in part, due to the inability to accurately place the embolic agent. These embolic agents are not commonly used as intracardiac occlusion devices.
The physician may temporarily occlude the septal defect until the patient is sufficiently stable to undergo an open heart surgical procedure and use a balloon catheter similar to that disclosed in U.S. patent 4,836,204 to Landymore et al. When using such a catheter, an inflatable balloon is carried on the distal end of the catheter. When the catheter is introduced to the desired location, the balloon is inflated with fluid until it substantially fills the vessel and is contained therein. A resin that will harden in the bladder (e.g., acrylonitrile) may be used to permanently fix the size and shape of the bladder. The balloon may be detached from the end of the catheter and left in place. If the balloon is not sufficiently filled, it will not be adequately contained within the septal defect and may rotate and loosen from the septal wall, thereby releasing into the blood flow from either the right or left ventricular chambers. Overfilling of the balloon, which may result in rupture of the balloon and release of resin into the patient's bloodstream, is also undesirable.
Typical examples of mechanical embolization devices, filters and traps have been proposed in the past and are disclosed in U.S. patent 3,874,388 to King et al (patent '388), U.S. patent 5,334,217 to Das (patent' 217), U.S. patent 4,917,089 to Sideris (patent '089) and U.S. patent 5,108,420 to Marks (patent' 420). The '388,' 217, '089 and' 420 instruments are typically preloaded into the introduction or delivery catheter and are not typically loaded by the physician during the medical procedure. Retraction of these devices into the delivery catheter is difficult, if not impossible, during deployment, thereby limiting the effectiveness of these devices.
Notably, the size of these instruments is inherently limited by the configuration and form of the instrument. When occluding a septal defect using an occlusion instrument such as '089,' 388, '217, or' 420, the change in pressure, and thus the movement of the instrument, increases as the size of the defect increases. Thus, these devices must have a large retention skirt that seats on each side of the defect. Oftentimes, the location of the septal defect dictates the size of the retention skirt. In membranous type septal defects, it is difficult, if not impossible, to effectively place the instruments of '388', 217 ', 089, and' 420 without less local occlusion of the aorta. Also, these disclosed devices tend to be expensive and time consuming to manufacture. Accordingly, there is a need to provide a small instrument that is recoverable and can be retracted into the delivery system without increasing the overall thickness of the instrument. The ideal instrument can also be manufactured with a relatively small retention skirt to fit in a membranous type septal defect without occluding the aorta.
Also, prior art device shapes (e.g., square, triangular, pentagonal, hexagonal, and octagonal) require a larger contact area with corners extending to the free wall of the atrium. The inner lead in prior art devices (as described in the Das 217 patent) was bent each atrial contraction (approximately 100,000 per day), which resulted in fatigue failure of the structure in about thirty percent of all cases. The sharp corners of these instruments have resulted in a high percentage of cardiac perforations, and they have therefore exited the market. In addition, the prior devices required 14-16French introduction catheters, making these devices impossible to use in treating children with congenital defects.
It would therefore be desirable to provide a reliable occluding device that is both easily deployed through a 6-7French catheter and that can be accurately placed within a vessel or organ. It is also desirable to provide a small, reconfigurable instrument for use in an organ of a patient's body.
A reliable, small-scale, intracardiac occlusion device is described in us patent 5,846,261 to Kotula et al, which may be configured for the treatment of, for example, Ventricular Septal Defects (VSDs) and atrial septal defects (hereinafter ASDs) and patent ductus arteriosus (hereinafter PDAs). When these intravascular devices are constructed with an elastic metal fabric composed of a plurality of elastic strands, the strands are constructed into an elastic material by weaving. The woven fabric is then deformed into substantial conformity with the molding surface of the molding element and the woven fabric in contact with the surface of the molding element is heat treated at an elevated temperature. The heat treatment time and temperature are selected to substantially place the woven fabric in its deformed state. After heat treatment, the fabric is removed from the contacting molding elements and will substantially retain its shape in the deformed state. The woven fabric so treated defines a deployed state of the medical device, which may be deployed through a catheter into a tract in a patient.
Embodiments of the Kotula et al invention provide a medical device with a specific shape that can be manufactured according to the invention to meet medical needs and long-term treatment procedures. The device has a deployed compact configuration and may include a female clip that collects and retains the braided metal fabric tip and is attached to the tip of a delivery or guide wire so that the device may be restored after placement. In use, a guide catheter is placed into a patient such that the distal end of the catheter is adjacent to a location requiring treatment to treat a physiological condition. A preselected medical device manufactured according to Kotula et al and having a predetermined shape is then collapsed (collapse) by longitudinal stretching and inserted into the lumen of the catheter. The instrument is advanced through the catheter and extends from its distal end, which, due to its memory properties, will tend to return substantially to its deployed state adjacent the treatment site. The guide wire or delivery catheter is then released from the clip and removed.
According to a first embodiment, a substantially elongate medical device has a substantially tubular middle portion and a pair of deployed diameter portions, one deployed diameter portion being disposed at either end of the middle portion. The width of the intermediate portion is similar to the wall thickness of the tissue to be occluded, e.g., the thickness dimension of the septum and the diameter of the size of the defect to be occluded. The center of at least one of the expanded diameter portions may be concentric with or offset from the center of the intermediate portion to enable occlusion of various septal defects including membranous-type ventricular septal defects, while providing a retention skirt of sufficient size to reliably occlude abnormal openings in the septal. As described above, the ends of each braid of the device are held together with a clip. The clip can be recessed into the expanded diameter portion of the instrument, thereby reducing the overall length dimension of the instrument and creating a small obturator.
In another embodiment of the Kotula et al invention described in the' 261 patent, the medical device is substantially bell-shaped, having an elongated body, a tapered first end, and a larger second end. The second end has a fabric disk oriented substantially perpendicular to the axis of the tube when deployed in the tube. The clip holding the ends of the braided wire together is recessed toward the center of the "bell", providing a small instrument with a reduced overall height dimension.
The ability of the device described in the Kotula et al' 261 patent to occlude abnormal openings in vascular tissue depends on the weft (pick) size of the braided structure, which in turn depends on the number of metal strands used in the braid. However, a practical limitation is precisely how much such thread can be woven. For example, if 72 spools of thread are used on the knitting machine, the resulting weft yarn size is such that all thrombus formation and total occlusion of blood flow through the device must occur over an extended period of time. Even with 144 spools of line, blood flow is not immediately prevented. If the size of the weft yarn is effectively halved by doubling the number of yarn axes on the knitting machine to 288, occlusion will occur instantaneously when the medical device is placed in an abnormal opening. However, the mechanical dimensions of the resulting braiding machine are impractical from a size and cost standpoint.
As a method for reducing the time required to complete the total occlusion, the Kotula et al' 261 patent teaches the concept of filling the interior of the medical device with an occlusive fiber or fabric (e.g., polyester fabric). The occlusive fiber material or fabric is essentially hand sewn in place, which significantly increases the manufacturing cost of the medical device. Perhaps more importantly, the addition of polyester fibers or fabric within the device hinders the ability of the device to reduce the effective diameter as it is stretched prior to loading into the lumen of the delivery catheter. It should be appreciated that the delivery catheter may be used with smaller patients by reducing its size.
Accordingly, there is a need for a method of manufacturing a collapsible medical device for occluding an abnormal opening in vascular tissue that provides rapid occlusion with delivery and placement thereof and does not require the incorporation of occluding fibers within the medical device as taught by the prior art. The present invention provides an easily manufacturable solution to the aforementioned problems inherent in the prior art as demonstrated by the' 261 patent to Kotula et al.
Detailed Description
The present invention provides an occlusion device for percutaneous catheterization for occluding abnormal openings in a patient, such as Atrial Septal Defects (ASD), Ventricular Septal Defects (VSD), Patent Ductus Arteriosus (PDA), Patent Foramen Ovale (PFO), and the like. It may also be used to construct a flow restrictor or aneurysm bridge or other type of occluder for placement into the vascular system. In the manufacture of the medical device by the method of the invention, a planar or tubular metal fabric is provided. The planar and tubular fabrics are made of a large number of metal strands (wire strands) with a predetermined mutual orientation between the strands. The tubular fabric has metal strands divided into two substantially parallel, usually helical, sets of strands, one of which has a "hand-held", i.e. the direction of rotation is opposite to that of the other set. The tubular fabric is also known in the textile industry as a tubular braid.
The pitch of the metal strands (i.e. the angle defined between one turn of wire and the axis of the braid) and the weft of the fabric (i.e. the number of turns per unit length) and other factors such as the number of wires used in the tubular braid and their diameter are important in determining many of the characteristics of the device. For example, the greater the pick and pitch of the fabric, and therefore the greater the density of the metal strands in the fabric, the stiffer the device. The greater the wire density, the greater the wire surface area of the device can also be provided, which generally increases the tendency of the device to occlude when deployed in a blood vessel. The thrombosis (thrombosis) can be enhanced, for example, by coating with thrombolytic agents, or can be attenuated, for example, by coating with unstable antithrombotic compounds. When a tubular braid is used to make the device of the Kotula' 261 patent, a tubular braid having a diameter of about 4mm, a draft of about 50 °, and a fill yarn of about 74 (per linear inch) appears suitable for making devices capable of occluding abnormal openings having an inner diameter of about 2mm to about 4 mm. However, the occlusion is not formed instantaneously.
Metal flat fabrics are the more common fabrics and may take the form of woven sheets, knitted sheets or the like. Typical in woven fabrics are two sets of wires, one set of wires oriented at an angle, for example, substantially perpendicular (with approximately 90 ° weft) to the other. As mentioned above, the pitch and weft of the fabric (or, in the case of a knitted fabric, the pattern of weft and knit, such as a jersey or double knit) can be selected to optimize the desired properties of the resulting medical device.
The metal strands of the planar or tubular metal fabric are preferably made of a so-called shape memory alloy. Such alloys tend to have a temperature that causes a phase change, which results in a material having a preferred structure that can be fixed by heating the material above a particular transition temperature to cause a change in the phase of the material. When the alloy cools down, the alloy will "remember" its shape during the heat treatment and tend to assume the structure unless limited thereto.
Without any limiting intent, suitable metal wire strand materials may be selected from the group consisting of cobalt-based low thermal expansion alloys referred to, for example, in the ELGELOY field, Nickel-based high temperature high strength "superalloys" commercially available from Haynes International under the trade designation HASTELLOY, Nickel-based heat treatable alloys sold by International Nickel under the designation INCOLOY, and various grades of stainless steel. An important factor in choosing a suitable material for the metal strands is that the metal wire will retain a suitable degree of deformation caused by the mould surface (as described below) when subjected to a predetermined heat treatment.
In a preferred embodiment, the metal strands are made of a shape memory alloy, NiTi (commonly known as nitinol) is a near stoichiometric alloy of nickel and titanium, and may also include small amounts of other metals to achieve the desired properties. The processing requirements and variations of the composition of NiTi alloys are well known in the art and therefore a detailed discussion of such alloys is not necessary here. The teachings of U.S. patents 5,067,489(Lind) and 4,991,602(Amplatz et al) discussed the use of shape memory NiTi alloys in guidewires are incorporated herein by reference. Such NiTi alloys are at least partially preferred because they are commercially available and the processing of such alloys is more well known than the processing of other shape memory alloys. NiTi alloys also have good elasticity and are referred to as "superelastic" or "pseudoelastic". This resiliency allows the device of the present invention to return to the preset, deployed configuration when in use.
When manufacturing a medical device according to the invention, a plurality of tubular or planar metal fabric sheets of suitable dimensions, except for having a single knitted fabric layer, are suitably layered with respect to each other and inserted into the same mould, which thus deforms the fabric layers to substantially conform to the shape of the inner cavity of the mould. The shape of the lumen is such that the plurality of metallic fabric layers are substantially deformed into the shape of the desired medical device. The ends of the metal strands of the tubular or planar metal fabric layer should be fastened to prevent the metal fabric from unraveling. Clips or welds may be used to secure the ends of the metal strands, as will be described further below. The advantages of the present invention can also be achieved by heat treating the inner and outer fabric layers separately and then inserting the inner layer or layers within the outer limits. It is further desirable that the inner and outer fabric layers be heat set to different geometries and then assembled one into the other.
In the case of a tubular braid, a molding element may be placed into the inner lumen of the braid prior to insertion into the mold, thereby further defining the molding surface. If the ends of the tubular metal fabric have been fixed by clips or welding, the moulding element can be inserted into the cavity by manually removing the metal strands of the fabric layer and inserting the moulding element into the cavity of the innermost tubular fabric. By using such a molding element, the size and shape of the processed medical device can be controlled with considerable precision and the fabric is ensured to conform to the internal cavity of the mold.
The molding element is optionally made of a material that can be broken or removed from the interior of the metal fabric. For example, the molded element may be made of a brittle, breakable, or breakable material. Once the material is heat treated to contact the mold cavity and the molded component, the molded component can be broken into small pieces that can be easily removed from the metal fabric. For example, if the material is glass, the molding element and metal fabric can be struck against a hard surface, causing the glass to shatter. These glass fragments can then be removed from the metal fabric casing.
Alternatively, the molding element may be made of a material that can be chemically dissolved or decomposed with a chemical agent that does not substantially affect the characteristics of the metal strands. For example, the molding member may be made of a heat-resistant plastic resin that is soluble with a suitable organic solvent. In this case, the fabric and the molding element may be subjected to a heat treatment to substantially conform the shape of the fabric to the mold cavity and molding element, and then the molding element and metal fabric may be immersed in a solvent. Once the molding element is substantially dissolved, the metal fabric can be removed from the solvent.
Care is taken to ensure that the material from which the molding element is made is selected to be able to withstand heat treatment without losing its shape, at least before the shaping of the layers of fabric. For example, the molding element may be made of a material having a melting point higher than the temperature required for the setting of the metal strands, but lower than the melting point of the strands forming the metallic fabric layer. The molded element and the layers of metal fabric that ultimately make up the medical device are then heat treated to set the metal material, and the temperature can then be raised to substantially completely melt the molded element, thereby removing the molded element from the metal fabric. It will be appreciated by those of ordinary skill in the art that the shape of the mold cavity and the molding elements may be varied in order to produce the medical device having a predetermined size and shape.
It will be appreciated that a particular molding element of a particular shape produces a particular shape, and other molding elements having different shaped configurations may be used if desired. The moulding element and mould may have additional parts including a cam arrangement if a more complex shape is required, but the mould may have fewer parts if the shape to be produced is simpler. The number of parts and the shape of those parts in a given mold is almost entirely determined by the shape of the desired medical device that substantially conforms to the metal fabric.
For example, when the multilayered tubular braid is in its relaxed configuration, the metal strands forming the tubular braid have a first predetermined relative orientation with respect to one another. Since these tubular braids are compressed along their axes, the fabric layers tend to splay outward from their axes, conforming to the shape of the mold. When so deformed, the relative orientation of the metal strands of the metal fabric layer will change. When the mold is assembled, the outside and inside metal fabrics will substantially conform to the mold surface of the internal cavity. The medical device has a preset deployed configuration and a retracted configuration that allows the device to be passed through a catheter or other similar delivery device. The shape of the fabric layers substantially defines the deployed configuration when they are deformed to substantially conform to the molding surface of the mold.
Once the tubular or planar metallic fabric layer is fully seated in the preselected mold and the metallic fabric layer substantially conforms to the molding surface of the cavity therein, the fabric layers may be subjected to a heat treatment while remaining in contact with the molding surface. Heat treating the metal fabric comprising the plurality of layers of metal strands substantially sets the shape of the metal strands from their woven reoriented relative position when the fabric layer conforms to the molding surface. The fabric layer maintains the shape of the molding surface of the mold cavity as the medical device is removed from the mold, thereby defining the desired shape of the medical device. The heat treatment depends in large part on the material from which the metal strands of the metallic fabric layer are made, but the time and temperature of the heat treatment should be selected to substantially bring the fabric layer into their deformed state, i.e., with the metal strands in their reoriented opposed configuration, and with the fabric layer substantially conforming to the molding surface.
After heat treatment, the device is removed from the molding surface in contact therewith and will substantially retain its shape in the deformed state. If a molded element is used, the molded element can be removed as described above.
The time and temperature of the heat treatment may depend to a large extent on the material from which the metal wire strands are made. As mentioned above, one preferred class of materials for making the metal strands is shape memory alloys, with nitinol (a nickel titanium alloy) being particularly preferred. If nitinol is used to make the metal strands of the fabric layer, the metal strands will tend to be very elastic when the metal is in its austenitic phase; this phase state of good elasticity is often referred to as the superelastic or pseudoelastic phase state. By heating the nitinol above a certain phase transition temperature, the crystalline structure of the nitinol metal will tend to "set" the shape of the fabric layer and the relative structure of the metal strands in the position they maintain during the heating process.
Suitable heat treatments to set the nitinol into the desired shape are well known in the art. For example, helically coiled nitinol coils are used in many medical devices, such as coils that are typically made to attach around the distal end of a guide wire and made into other medical products as is known in the art. There is a wide range of knowledge regarding nitinol in such devices, and therefore a more detailed description of the thermal treatment parameters of nitinol preferably used in the present invention is not required herein.
Briefly, however, it was found that maintaining the nitinol fabric at about 500 to about 550 degrees celsius for a period of about 1 to 30 minutes, depending on the size of the mold and the stiffness of the device to be manufactured, would place the fabric layers in their deformed state, i.e., where they conform to the molding surface of the mold cavity. At lower temperatures, the heat treatment will be longer, while at higher temperatures, the time will be shorter. These parameters may be varied as necessary to accommodate the exact composition of the nitinol prior to heat treating the nitinol, the characteristics of the nitinol desired in the final product, and other factors known to those of ordinary skill in the art.
It is also known in the art to apply an electrical current to the nitinol to heat it, other than by convection heating or the like. For example, in the present invention, this can be achieved by connecting electrodes at opposite ends of the metallic fabric layer. To achieve the desired heat treatment, resistance heating can heat the wire without the need to heat the entire mold to the desired heat treatment temperature. Materials, molding elements, and methods of molding medical devices from tubular or planar metal fabrics are further described in U.S. patent nos. 5,725,552, 5,944,738, and 5,846,261, assigned to the same assignee as the present invention, the entire disclosures of which are incorporated herein by reference.
Once the device is formed having the preselected shape, the device may be used to treat a physiological condition of a patient. A medical device suitable for treating the condition is selected, substantially in accordance with one of the embodiments outlined below. Once the appropriate medical device is selected, a catheter or other suitable delivery device may be placed in a conduit within the patient to place the distal end of the delivery device adjacent to the site requiring treatment, such as in close proximity to (or even within) a shunt such as an abnormal opening in the patient's tissue.
The delivery instrument (not shown) may have any suitable shape, but desirably includes an elongated flexible metal rod having a threaded distal end for engaging a threaded hole formed in the clip of the medical instrument. The delivery device may be used to push the medical device through the lumen of the catheter for deployment within a conduit of a patient's body. The delivery device may still constrain the medical device as it is deployed from the distal end of the catheter. Once the medical instrument is properly positioned within the shunt of the abnormal opening, the shaft of the delivery instrument may be rotated about the delivery instrument axis to release the medical instrument from the delivery device.
By keeping the medical device attached to the delivery device, the operator can retract the device to reposition it relative to the abnormal opening if it is determined that the device is not properly positioned within the shunt. A threaded clamp attached to the medical instrument allows the operator to control the medical instrument in a distal catheter configuration. When the medical device exits the catheter, it will tend to resiliently return to the preferred deployed shape, which is set upon heat treatment of the fabric. When the instrument springs back to this shape, it tends to react against the distal end of the catheter, effectively pushing itself forward over the tip of the catheter. It is envisaged that if the position of the instrument in the duct is critical, for example it is seated in a shunt between two vessels, the resilient action will result in improper seating of the instrument. Since the threaded clamp allows the operator to continue to hold the instrument during deployment, the elastic action of the instrument can be controlled by the operator to ensure proper placement during deployment.
The medical device may be collapsed to its reduced diameter configuration and inserted into the lumen of the catheter. The collapsed configuration of the device may be any shape suitable for easy passage through the lumen of the catheter and proper deployment from the distal end of the catheter. For example, ASD occluding devices may have a relatively elongated contracted configuration in which the devices are stretched along their axes. The constriction may be achieved simply by stretching along the axis of the instrument, for example by grasping the clips by hand and pulling them apart, which tends to constrict the expanded diameter portion of the instrument inwardly towards the axis of the instrument. PDA occlusion devices can also be operated in a very similar manner and can be collapsed to their collapsed configuration by applying tension substantially along the axis of the device for insertion into a catheter. In this regard, these instruments, unlike "Chinese handcuffs" (Chinese handcuffs), tend to compress in diameter under axial tension.
If the device is used to permanently occlude a conduit in a patient, the catheter may simply be withdrawn and removed from the patient. This leaves the medical device deployed in the patient's vascular system so that it can occlude a blood vessel or other conduit in the patient's body. In some cases, the medical instrument may be coupled to the delivery system in a manner that secures the instrument to the distal end of the delivery device. Prior to removal of the catheter in such systems, it may be necessary to separate the medical instrument from the delivery device prior to removal of the catheter and delivery device.
Although the device will tend to spring back to its original deployed configuration, i.e. its shape prior to being collapsed for passage through the catheter, it will be appreciated that it may not always return fully to that shape. For example, it may be desirable for the instrument, in its deployed configuration, to have a maximum outer diameter that is at least as large as, and preferably larger than, the inner diameter of the lumen of the abnormal opening in which the instrument is disposed. If such an instrument is deployed in a vessel or abnormal opening having a smaller lumen, engagement with the lumen will limit the instrument from fully returning to its deployed configuration. Nonetheless, the instrument will be properly deployed as it will engage the inner wall of the lumen to secure the instrument thereto.
When the device is deployed in a patient, thrombus will tend to collect on the surface of the wire. As with the multilayer structure of the present invention providing a greater density of metal wires, the total surface area of the wires will increase, thereby increasing the thrombogenicity of the device and allowing it to occlude the vessel in which it is deployed relatively quickly. It is believed that the outermost tubular braid formed from strands about 0.004 inches in diameter with at least about 40 picks and a pitch of at least about 30 deg. has a diameter of 4mm and that the occluding device is manufactured around an inner tubular braid formed from strands about 0.001 inches with the same picks and pitch that will provide sufficient surface area to substantially completely occlude an abnormal opening or a blood vessel of 2mm to about 4mm inner diameter in a relatively short period of time. If it is desired to increase the rate of occlusion of the device, a third or fourth layer of fabric, which is concentrically disposed, may be added.
Referring now to the drawings, embodiments of the medical device of the present invention will be discussed next. Fig. 1-4 illustrate a first preferred embodiment of a medical device 10 constructed in accordance with the present invention for compensating for an Atrial Septal Defect (ASD). Referring to fig. 1-4, the device 10 is greatly enlarged to illustrate the layers that make up the medical device. The ASD instrument is in its relaxed, unstretched state with the two aligned discs 12 and 14 connected together by a short intermediate cylindrical portion 16 (fig. 3). The purpose of this is that the instrument 10 may also be well suited for occluding defects known in the art as patent foramen ovale (hereinafter PFO). Those skilled in the art will appreciate that devices of this configuration may also be suitable for closure of ductal tracts during Fenestrated defective Fontan's. ASD is a congenital abnormality of the atrial septum characterized by a deletion of the atrial septum structure. A shunt may occur within the interatrial septum, allowing communication between the right atrium and the left atrium of the heart. In the larger notch, with significant left-to-right shunting through the notch, the right atrium and right ventricle volume is overloaded, and this increased volume is injected into the pulmonary vascular bed of low resistance.
Pulmonary vascular occlusive disease and pulmonary arterial hypertension (atrial hypertension) develop in adulthood. ASD patients with significant shunting (as determined by a ratio of pulmonary to systemic blood flow greater than 1.5) ideally undergo surgery between the ages of two and five or later when diagnosed. With the advent of two-dimensional echocardiography and Doppler (Doppler) color flow mapping, the precise anatomical anatomy of the defect can be visualized. The size of this absence as determined by balloon measurements corresponds to the selected size of the ASD instrument 10 being used.
The device 10, shown in its free or relaxed state in figures 1 and 2, is adapted for deployment in a shunt site including an ASD or PFO. For purposes of example, the instrument 10 used during ASD occlusion is described in the Kotula' 261 patent mentioned above, and further reference is made to those required information of that patent. Returning to the structural features of the original instrument 10, the size of the ASD obturator is proportional to the shunt site to be occluded. In the relaxed orientation, the metal fabric is shaped as two disks 12 and 14 that are axially aligned and joined together by a short cylindrical section 16. The length of the cylindrical section 16 when not stretched is preferably approximately the thickness of the atrial septum, which ranges between 3 and 5 mm. The proximal disc 12 and distal disc 14 preferably have slightly larger outer diameters than the shunt to prevent movement of the instrument. The proximal disc 14 has a relatively flat configuration, while the distal disc 12 is preferably cupped toward the proximal end and slightly overlaps the proximal disc 14. In this manner, the resilient action of the device 10 will cause the peripheral edge 18 of the distal disc to substantially engage the side wall of the septum and likewise the outer edge of the proximal disc 14 will substantially engage the opposite side wall of the septum.
In accordance with the present invention, the device 10 includes an outer braid layer 20, a first inner layer 22, and possibly an optional third and innermost layer 24, thereby substantially increasing the density of the wire without unduly increasing the stiffness of the device or its ability to exhibit a reduction in outer diameter when stretched in length. Multiple inner layers may be used if desired.
The ends of the tubular braided metal fabric device 10 are welded or clamped together as at 26 by clips to prevent fraying. The ends of all layers may be brought together and secured by two clips, one for each end or separate clips may be applied at each end of each layer. Of course the ends may alternatively be held together in other ways that are already known to those of ordinary skill in the art. The clip 26 which ties the layers of metal strands together at one end also serves to connect the device to a delivery system, and in the embodiment shown in figure 1, the clip 26 is generally cylindrical in shape and has a recess (not shown) for receiving the ends of the metal fabric to substantially prevent the metal wires making up the woven fabric from moving relative to each other. The clip 26 also has a threaded hole 28. The threaded bore is adapted to receive and engage a threaded distal end of a delivery instrument, such as a pushwire.
The ASD occluding device 10 of this embodiment of the present invention may be advantageously manufactured according to the methods described above. The outer layer 20 of the device 10 is preferably made of a nitinol metal wire strand having a diameter of.004-. 008 inches, but could equally be made with smaller or larger diameter wires. The weaving of the wire mesh including the outer layer may be performed by using a Maypole weaving machine (braider) having 72 wire guides (wire carrier) with a shielding angle (shield) of about 64 degrees and 28 picks per inch. The braided layers 22 and 24 each comprise 144 strands of nitinol wire having a diameter in the range of 0.001 inches to 0.002 inches, braided at the same pitch. The stiffness of the ASD instrument 100 may be increased or decreased by varying the wire size, shielding angle, weft ratio, and number of wire guides or heat treatment processes. One of ordinary skill in the art will appreciate from the foregoing discussion that the shape of the mold cavity must conform to the shape of the desired ASD device. Likewise, it should be understood that some desired configurations may require some portion of the lumen to be convex. Fig. 3 illustrates the ASD instrument 10 in a slightly longitudinally stretched condition. The distance separating the distal and proximal discs 12 and 14 is preferably equal to or slightly less than the length of the cylindrical section 16. The cup-like shape of each of the disks 12 and 14 ensures adequate contact between the outer edge of each of the disks 12 and 14 and the atrial septum. With proper placement, a new endocardial layer of endothelial cells forms on the occluding device 10, thereby reducing the chance of bacterial endocarditis and thromboembolism.
The distance separating the discs 12 and 14 of the occluding device 10 may be increased to provide an occluding device suitable for occluding a conduit within a patient's body with unique advantages in use like a vaso-occlusive device. The instrument 10 includes a generally tubular middle portion 16 and a pair of deployed diameter portions 12 and 14. The flared diameter portions are disposed at both ends of the substantially tubular middle portion. The relative sizes of the tubular intermediate portion 16 and the flared diameter portions 12-14 can be varied as desired. The medical device may be used as a vaso-occlusive device to substantially prevent blood flow through a patient's blood vessel. When the device 10 is deployed in a patient's blood vessel, it is positioned within the blood vessel such that its long axis substantially coincides with the axis of the vessel segment into which it is inserted. It is desirable to limit the ability of the vaso-occlusive device to rotate at an angle relative to the axis of the vessel with a dumbbell shape to ensure that it maintains substantially the same position as the operator deploys it within the vessel.
For relatively firm engagement with the vessel lumen, the maximum diameter of the deployed diameter portions 12-14 should be selected to be at least as large as, and preferably slightly larger than, the diameter of the vessel lumen in which the device is deployed. When deployed in the patient's vessel, the vasculature closure device will engage the lumen at two spaced apart locations. It is desirable that the instrument be longer in dimension along its axis than its maximum diameter. This will substantially prevent the vessel closing device 10 from rotating an angle about its axis within the lumen, essentially preventing the device from moving in the blood flow through the vessel and tumbling along the vessel.
The relative sizes of the generally tubular intermediate portion 16 and the expanded diameter portions 12-14 of the vaso-occlusive device can be varied as desired for any particular application by appropriate selection of the mold used in the heat setting of the device. For example, the outer diameter of intermediate portion 16 may be in the range of about 1/4 to about 1/3 percent of the maximum diameter of the deployed diameter portion, and the length of intermediate portion 16 may comprise about 20 to about 50 percent of the overall length of the instrument 10. While these dimensions are appropriate if the device is used solely to occlude a vascular vessel, it should be understood that these dimensions may vary if the device is used in other applications, such as an obturator for Ventricular Septal Defects (VSDs).
The aspect ratio of the instrument 10 shown in this embodiment (i.e., the ratio of the length of the instrument to its maximum diameter or width) is desirably at least about 1.0, preferably in the range of about 1.0 to about 3.0, and a particularly preferred aspect ratio is about 2.0. Having a larger aspect ratio will tend to prevent the instrument 10 from rotating substantially perpendicular to its axis, which is known as end-over-end roll. As long as the outer diameter of the deployed diameter portions 12-14 of the device 10 is large enough to hold the device fairly firmly against the lumen of the conduit in which it is deployed, the device cannot roll over, which will help keep the device properly deployed and positioned in the vasculature of the patient or other conduit within the patient. Alternatively, the deployed diameter portions 12-14 have a natural relaxed diameter substantially larger than the lumen of the vessel in which the device is deployed, and should also be sufficient to wedge the device into position in the vessel without being overly related to the aspect ratio of the device.
Referring now to fig. 5-9, there is shown generally an occluding device 100 suitable for use with a Patent Ductus Arteriosus (PDA). PDA is actually two blood vessels: the aorta and the pulmonary artery, which adjoin the heart, have a shunt condition between their respective lumens. Blood can flow directly between these two vessels through the shunt site, resulting in heart failure and pulmonary vascular disease. The PDA device 100 has a generally bell-shaped body 102 and an outwardly flared forward end 104. The bell-shaped body 102 is adapted to be placed within the aorta to help secure the body of the device in the shunt site. The size of the body 102 and end 104 may be varied during manufacture as needed to accommodate different sized shunt sites. For example, the body 102 may have a diameter of about 10mm along its substantially elongated middle portion and a length of about 25mm along its axis. In such a medical device 100, the bottom of the body may be flared generally radially outward to an outer diameter equal to the leading end 104, which may be on the order of about 20mm in diameter.
The base 106 needs to flare relatively quickly outward to define a shoulder 108 that tapers radially outward from the body 102. When the instrument 100 is deployed in a vessel, the shoulder 108 will abut the periphery of the lumen to be treated with a high pressure. The leading end 104 remains within the vessel and pushes the bottom of the body 102 open to ensure that the shoulder 108 engages the wall of the vessel to prevent movement of the instrument within the shunt site.
The PDA occluding device 100 of an embodiment of the present invention may be advantageously manufactured in the manner described above by deforming a plurality of layers 110, 112 and 114 (fig. 7) of substantially concentrically oriented tubular metallic fabric to conform to the molding surface of a mold, and heat treating the fabric layers to place the fabric layers in their deformed state. Still referring to the greatly enlarged view of fig. 7, the outer layer 110 includes a frame (frame) that defines the outer shape of the medical instrument 100. It is preferably made of 72 or 144 braided wires having a diameter in the range of 0.003 to about 0.008 inches. The slope of the braid may vary. Within this frame is a layer 112 which forms an outer jacket (outer liner). It may also prove advantageous to incorporate the third layer 114 as an inner liner. The jacket and liner may be braided using 144 bundles of shape memory wire having a diameter of 0.001 to 0.002 inches. The slope of the weave in layers 112 and 114 may be the same. As mentioned above, the ends 116 and 118 of the braid should be fixed to prevent the braid from coming loose. In a preferred embodiment, clips 120 are used to tie the respective ends of the metal strands together at each end 116 and 118 of the tubular braided article forming the occluding device 100. Alternatively, the ends of the metal strands of the outer braid layer may be secured using different clips than those used to secure the ends of each of the inner metal strands. It will be appreciated that other suitable securing means may be attached to the ends in other ways, for example by welding, soldering, brazing, using a biocompatible adhesive material or in any other suitable manner. One or both of the outer clips 120 may include a threaded hole 122 (not shown) for attaching the instrument 100 to a delivery system. In the embodiment shown, the clip 120 is substantially cylindrical and has a crimped recess to receive the ends of the metal strands, thereby substantially preventing the wires from moving relative to each other.
When using raw NiTi fabric, the strands will tend to return to their unwoven configuration, and the braid layers 110, 112 and 114 can be released fairly quickly unless the ends of the braid length of the device are cut to form a constraint relative to each other. The clips 120 effectively prevent the layers of braid from loosening at either end. Although soldering and brazing of NiTi alloys has proven to be rather difficult, the ends may be welded together, for example by spot welding with a laser welder. When cutting a fabric comprising a plurality of layers 110, 112 and 114 to the desired size, care should be taken to ensure that the fabric layers do not come loose. For example, in the case of a tubular braid made of a NiTi alloy, unless constrained, the individual wires will tend to return to their heat set configuration. If the braid is heat treated to set the threads in the braid structure, they will tend to remain in the braided shape and only the ends will be worn. However, it may be more economical to form the braid only without heat treating the braid, as the braid will be heat treated again when forming the medical device.
Once the fabric is compressed to conform to the walls defining the interior of the mold, the fabric layer may be subjected to a heat treatment as described above. When the mold is reopened, the fabric will substantially retain its deformed, compressed configuration. The resulting instrument 100 may be contracted, for example, by pushing the clips 120 away from each other in a substantially axial direction, which will tend to contract the instrument 100 toward its axis. The collapsed instrument can then be coupled to a delivery instrument, such as an elongated flexible pusher wire, and passed through a delivery catheter for deployment at a predetermined location within the patient. The use of the resulting device to occlude the PDA is the same as described in the Kotula' 261 patent and need not be repeated here.
Since the number of metal strands is significantly increased in the composite multilayer structure, the introduction of a stitched-in polyester material is no longer required to reduce the time required to establish a total occlusion of the PDA. This not only reduces manufacturing costs, but also facilitates loading of the resulting device into a reduced French size delivery catheter. Reduced French size means the ability to treat smaller patients, which has great benefits.
The present invention has been described herein in considerable detail in order to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use embodiments as required. However, it will be appreciated that the invention may be carried out with a variety of different instruments and that various changes may be made without departing from the scope of the invention.