Abstract:
A delivery system for implanting medical devices within a lumen or body cavity of a patient, the delivery system having a wire formed from a plurality of layered strands yielding a reduced bending stiffness for improved maneuverability with no reduction in overall tensile strength compared to delivery systems using a single wire and of comparable diameter. The physical properties of the delivery system permit optimal placement and retrieval of an intracardiac occluder within a patient.

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/317,117, filed Sep. 6, 2001, the entire disclosure of which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention generally relates to a delivery system for a medical device. More particularly, this invention relates to a system for the delivery and retrieval of a prosthetic occluder in the cardiovascular system of a patient. 
     DESCRIPTION OF THE RELATED ART 
     Numerous systems for percutaneous catheter delivery of implants have been devised over the years in order to assist physicians in delivering and positioning implants within the human body in a minimally invasive manner. A classic problem with many of these percutaneous delivery systems is that they can often adversely effect the position of the device that is being implanted. Many devices are released in stages and consequently, if the position of the device is not acceptable, the device can be removed or repositioned. If the delivery system, however, adversely influences the positioning of the implant, the physician is forced to estimate the effect of this on the implant position and take such effect into consideration when assessing final implant position prior to release. The final released position of the implant may be different from its position when still attached to the delivery system. Additionally, the movement of the implant that occurs following release from the delivery system can adversely effect the final position resulting in a less desirable final result (such as a residual leak in the case of septal occluders) or even embolization of the implant device. 
     Modern medical technology has produced a number of medical devices which are designed for compression into a small size tube or catheter to facilitate introduction into the vasculature and which are subsequently expandable for either occlusion of defects or holes in the heart, such as septal occluders (discussed in more detail below), or which contact the walls of the passageway or blood vessel, in the case of vena cava filters or stents. Among these devices are septal occluders such as the occluder shown in U.S. Pat. No. 5,425,744, the entire disclosure of which is hereby incorporated by reference. While the occluder noted above is a permanent implant which, when implanted is designed to remain in place, it can be recovered at a variety of stages during the implantation procedure. The most critical stage is following implant deployment but prior to release from the delivery system. To date, ball to ball (or pin to pin) attach/release mechanisms have been employed to implant and position such septal occluders within the heart. 
     Either congenitally or by acquisition, abnormal openings, holes or shunts can occur between the chambers of the heart or the great vessels, causing shunting of blood through the opening. These holes or shunts may develop between the left and right atria along the muscular wall which separates the two: the interatrial septum, a wall between the right and left ventricles which are separated by the interventricular septum. Such deformities are usually congenital and result from the incomplete formation of the septum, or wall, between chambers during fetal life when the heart forms from a folded tube into a four chambered, two unit system. These deformities can cause significant problems. Ultimately, the ill effects of these defects cause added strain on the heart which may result in heart failure if the defects are not corrected. One such defect, a patent foramen ovale (PFO), is a persistent, one-way, usually flap-like opening in the wall between the right atrium and left atrium of the heart. Since left atrial (LA) pressure is normally higher than right atrial (RA) pressure, the flap typically stays closed. Under certain conditions, however, RA pressure can exceed LA pressure creating the possibility for right to left shunting that can allow blood clots to enter the systemic circulation. This is of particular importance with patients who are prone to forming venous thrombus such as those with deep vein thrombosis or clotting abnormalities. 
     Nonsurgical (percutaneous) closure of PFOs has become possible using a variety of mechanical closure devices, allowing patients to avoid the potential side effects often associated with standard anticoagulation therapies or surgery. An example of an intracardiac medical implant is provided herein. Generally, these devices typically consist of a metallic structural framework combined with a synthetic tissue scaffold material. Similar intracardiac defects also currently treated with such devices include atrial septal defects (ASDs), ventricular septal defects (VSDs), and, left atrial appendages (LAAs). While standard synthetic tissue scaffolds are quite effective in most ASD and VSD indications, such thrombogenicity can be disastrous in both the PFO and the left atrial appendage (LAA) indications. 
     Unlike many other implantable medical devices, intracardiac occluders present special challenges for a medical device delivery system. First, the occluder must be very carefully and precisely deployed within the of the center defect to assure proper closure. Second, the tortuous anatomy of the heart and vascular system necessitate a delivery system capable of traversing the small radii of curvature and the confines of the heat chambers for delivery of the occluder to the deployment site. 
     Typical delivery systems for medical implant devices such as a septal occluder must satisfy a number of requirements to be effective. A common requirement is a predetermined tensile strength and stiffness in order for the delivery system to function properly. Often, at odds with this requirement for high tensile strength and stiffness, there is a need for bending flexibility so the delivery system can safely be guided to the intended target. Consequently, there is normally a design tradeoff in balancing these two needs. The delivery system may be required to be steerable through body lumens or cavities and be positionable or aimable with respect to organs or tissue within the body by an operator at a position external to the body. For example, a single 0.013 inch core wire imparts a significant stiffness to a device which reduces flexibility and can impede maneuverability through a body lumen or cavity. 
     Examples of delivery systems commonly in use within tortuous anatomy consist of an elongate spring type guide tube through which a single elongate core wire passes. A metal ball is formed on the distal end of the core wire. Delivery systems employing such spring type guide tubes require the use of a safety wire to keep the spring compressed when a tensile load is applied to the delivery system. Further, the use of spring type delivery systems generally require the use of separate guidewire catheters to help negotiate the implant to the deployment site. This requirement requires both the use of additional equipment and often taxes space limitations during a catherization procedure. The bending stiffness of the system formed by the spring guide and core wire is dominated by the relatively stiff core wire. Certain medical implant devices, such as intracardiac occluders, when implanted in a defect, may be required to remain attached to the delivery system for a period of time during which the clinician assesses the defect closure result. 
     SUMMARY OF THE INVENTION 
     A delivery system according to the present invention provides a device and method for implanting and removing medical devices. In one aspect, the invention relates to a medical device for implanting an intracardiac occluder within the heart of a patient. The medical device includes an elongate body member having a distal end and a proximal end and a longitudinal axis extending therethrough. The elongate body member includes a plurality of layered strands extending along the longitudinal axis. An attachment device is connected to the distal end of the elongate body member for releasable coupling to the intracardiac occluder. In one embodiment of the invention, the medical device includes a ball connected to the distal end of the elongate body member for releasable coupling to the intracardiac occluder. In another embodiment, the attachment device provides a pivoting connection between the implant and the delivery device in order to minimize any bending of the delivery device while inserting and positioning the implant. In a further embodiment of the invention, the medical device includes a catheter defining a lumen and that is slideably disposed along the longitudinal axis of the elongate body member. In various embodiments, the elongate body member includes multiple strands arranged in various configurations to provide the desired combination of material properties including high tensile strength and reduced bending stiffness. 
     This construction provides improved maneuverability in clinical applications with no reduction in overall tensile strength. High tensile strength is desirable in a medical delivery system for proper removal of a medical device from the body of a patient without elongation of one or more components of the device or breakage due to material failure. The physical properties of the delivery system may permit optimal placement and retrieval of medical devices including an intracardiac occluder within the heart of a patient. 
     In one embodiment, the strands of the medical device include stainless steel coated with a biocompatible material. In other embodiments strands include a nickel cobalt alloy. 
     It is an object of the invention to provide a delivery system having high tensile strength and low stiffness for implanting and removing medical devices. 
     It is another object of the invention is to provide a delivery system which retains the high tensile stiffness and strength required by its application while providing a significantly reduced bending stiffness relative to single core wire devices. 
     It is a further object of the invention to provide a delivery system for medical implant devices which replaces a single, elongate core wire with a wire rope formed from a plurality of layered strands. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which: 
         FIG. 1  depicts a schematic view of one embodiment of the flexible delivery system according to the invention; 
         FIG. 2  depicts a schematic view of another embodiment of the flexible delivery system according to the invention; 
         FIG. 3A  depicts a schematic view of the distal end of the flexible delivery system of  FIG. 1 ; 
         FIGS. 3B and 3C  depict cross-sectional views of two embodiments of the flexible delivery system of  FIG. 3A  along section B-B; 
         FIG. 4A  graphically depicts the relationship between wire diameter and tensile stiffness for varying embodiments according to the invention; 
         FIG. 4B  graphically depicts the relationship between wire diameter and bending stiffness for varying embodiments according to the invention; 
         FIG. 5  depicts a detailed perspective view of the distal end of the embodiment of the flexible delivery system depicted in  FIG. 1 ; 
         FIGS. 6A to 6C  depict longitudinal cross-sectional views of the distal end of the embodiment of the flexible delivery system of depicted in  FIG. 1 ; and 
         FIGS. 7A to 7C  depict a clinical application of the embodiment of the flexible delivery system depicted in  FIG. 1 . 
     
    
    
     DESCRIPTION 
     Delivery systems embodying the invention may include a wide variety of constructions. The delivery system according to the invention includes a plurality of helically layered strands providing reduced bending stiffness without compromising high tensile strength for delivery of a medical device to a body lumen or cavity. This combination of reduced bending stiffness and high tensile strength in a delivery system is advantageous when used with any medical implant, and particularly advantageous for implants requiring a tether, such as an intracardiac prosthetic occluder, either permanently or temporarily. 
     Embodiments of the present invention are described below. It is, however, expressly noted that the present invention is not limited to these embodiments, but rather the intention is that variations, modifications, and equivalents that are apparent to the person skilled in the art are also included. 
       FIGS. 1 and 2  show generally a delivery system  100  having a coaxial elongate construction extending along a longitudinal direction including a wire  110 , substantially enclosed by a catheter  120 , the catheter being substantially enclosed by a sheath  130 . Located at a distal end  135  of the delivery system  100  is an attachment device  140  which, in the embodiment depicted in  FIG. 1 , comprises a ball  140 , and in the embodiment depicted in  FIG. 2 , comprises an alternative embodiment of an attachment device  140 , for example, a hook  140 , either of which are coupled to the wire  110  at attachment point  150 . Other attachment device configurations are contemplated and are not limited to those depicted in the illustrations. In one embodiment, the ball  140  depicted in  FIG. 1  has a diameter between 0.0016 and 0.025 inches. There are a variety of ways to secure the attachment device to the wire  110 , e.g., welding, adhering, and threading. The connection of the attachment device  140  to the wire  110 , permits relative movement with respect to the catheter  120  via the handle  155  and actuator  160  located at a proximal end of the delivery system  100 . The distal end  135  of the delivery system  100  may be coupled to a medical device, for example, a prosthetic occluder (not shown) and is capable of being advanced through the vascular system and into a heart chamber of a patient. The wire  110  typically has a length in the range of 10 to 140 inches and preferably between 20 and 120 inches. The wire  110  has an outside diameter in the range of 0.0008 to 0.042 inches. Translational movement of the actuator  160  and rotational movement of the handle  155  are communicated along the longitudinal length of the delivery system  100  to the distal end  135  for manipulation, delivery, implantation, and/or removal of the occluder from within the body of a patient. 
     As shown in  FIGS. 3A to 3C , the wire  110  is formed of a plurality of twisted strands. In one embodiment, shown in cross-section in  FIG. 3B , the wire  110  is formed of 7 strands, each of which is approximately 0.005 inches in diameter. The strands may be formed of extruded filaments, twisted filaments, or braided filaments or any of their combination. In a particular embodiment, a central strand  200  is bounded by helically-wrapped outer strands  210   a  to  210   f.  The wire  110  may be formed by a plurality of strands in different patterns and include strands of different diameters. For example,  FIG. 3C  depicts an alternative embodiment wherein the wire  110  may be formed of nineteen twisted strands, each of which is approximately 0.003 inches in diameter. A central strand  220  is bounded by helically-wrapped outer strands  230 . The wire  110  according to the invention may be designed to match the tensile stiffness of a single core wire while reducing the bending stiffness of a delivery system for a medical implant device. 
     As shown graphically in  FIGS. 4A and 4B , it has been found that when the wire  110  is formed from a plurality of 7 strands, as depicted in  FIG. 3B , it has substantially the same tensile stiffness as one 0.013 inch single core wire, but only approximately 16 percent of the bending stiffness of the same single core wire. By replacing a single core wire with a plurality of strands having the same approximate aggregate diameter, the wire  110  is formed having all the tensile stiffness of the single core wire having a 0.013 inch outer diameter, but which is significantly more flexible than the single core wire. The helically bundled configuration determines that the outer diameter of a wire formed from a plurality of 7 strands is approximately 3 times the diameter of an individual strand. Moreover, the outer diameter of a wire formed from a plurality of nineteen strands is approximately 5 times the diameter of an individual strand. 
       FIG. 5  depicts a detailed perspective view of the distal end  135  of the delivery system  100 . Relative movement between the wire  110  and the catheter  120  permits coupling and decoupling of a medical device. The catheter  120  is moveable with respect to the wire  110  and the ball  140  attached thereto, and the sheath  130  is moveable with respect to the catheter  120 . Alternatively, the wire  110  and the ball attached thereto is moveable with respect to the catheter  120 . A distal sleeve  165  is attached to the distal end  135  of the catheter  120 . In one embodiment, the distal sleeve  165  is comprised of stainless steel and has a diameter of about 2 to 3 times the diameter of the ball  140 . 
       FIGS. 6A to 6C  schematically depict the distal end  135  of the delivery system  100  including the wire  110  engaging and coupling a prosthetic occluder  250 . A ball  260  similar to the ball  140  of the delivery system is connected to the occluder  250  by the linkage  270 . The occluder  250  is attached to the distal end  135  of the delivery system  100  as follows. The ball  140  of the delivery system  100  is placed proximate to the ball  260  of the occluder  250  such that the ball  140  is adjacent but located longitudinally distal to the ball  260 . The catheter  120  is moved relative to the wire  110  toward the ball  140  as shown in  FIG. 6B . The catheter is slid over both the ball  140  of the delivery system  100  and the ball  260  of the occluder, locking ball  140  and  260  together and within the inner diameter of the catheter  120 , thereby preventing longitudinal movement of the occluder  250  as shown in  FIG. 6C . In this way, the occluder  250  may be releasable secured to the distal end  135  of the delivery device during implantation of the occluder  250  within the patient. The distal sleeve  165  provides the catheter  135  with sufficient hoop strength for coupling the ball  140  of the wire  110  to the ball  260  of the occluder  250  within the catheter  120 . After implantation, the delivery system  100  may remain tethered to the occluder  250  at the ball-to-ball connection to permit the clinician to asses the closure result. After the occluder  250  is coupled to the delivery system  100  via the connection of ball  140  to ball  260 , the low bending stiffness of the wire  110  facilitates improved maneuverability of the occluder  250  for insertion, positioning, and implantation within the vascular system of a patient. The high tensile strength of the wire  110  enables removal of the occluder  250  while minimizing elongation of the delivery system  100  and the risk of failure to breakage 
     The general deployment of the septal occluder  250  in a clinical application is depicted schematically in  FIGS. 7A to 7C . The distal end  135  of the delivery system  100  including the wire  110  according to the invention is positioned proximate to a wall defect  400  in the heart. As shown in  FIG. 7A , a distal sealing membrane  410  of the occluder  250  is extracted out of the catheter  120  permitting the distal sealing membrane  410  to expand to the deployed shape. As shown in  FIG. 7B , the distal end  135  of the delivery system  100  is withdrawn away from the wall defect  400 , the occluder  250  is further extracted out of the catheter  120 , permitting the proximal sealing membrane  420  to expand to the deployed shape. As shown in  FIG. 7C , when the occluder  250  is properly positioned, the catheter  120  is retracted from the attachment mechanism (as shown in  FIGS. 6A to 6C ) and the ball  260  disengages from the distal end  135  of the delivery system  100  thereby releasing the occluder  250 , now implanted in a wall of the heart. The schematic depiction of the human heart, the chambers therein, and the surrounding vascular system demonstrate the tortuous anatomy necessitating the low bending stiffness provided by the wire  110  of the delivery system  100 . As the representative curvature of the distal end  135  of the delivery system  100  shows, the low bending stiffness of the wire  110  permits improved maneuverability of the delivery system  100 , and minimizes any adverse effect the delivery system  100  may have on the final position of the occluder  250  within the wall defect  400 . 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.