Abstract:
A delivery system has reduced profile in the catheter portion of the delivery system without compromising the pushability of the delivery system. The present invention also provides a structure which improves and simplifies the attachment of small catheter components to other structures forming the catheter portion the delivery system.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to delivery systems for deploying medical devices and, more particularly, to delivery systems to accurately deploy medical devices, such as a stent, a vascular stent-graft and the like, in a body vessel of a patient for the treatment of stenosis, aortic aneurysms and other afflictions which may strike body lumens. 
     Stents are generally cylindrically shaped devices which function to hold open and sometimes expand a segment of a blood vessel or other arterial lumen, such as coronary artery. Stents are usually delivered in a compressed condition to the target site and then deployed at that location into an expanded condition to support the vessel and help maintain it in an open position. They are particularly suitable for use to support and hold back a dissected arterial lining which can occlude the fluid passageway there through. Stents are particularly useful in the treatment and repair of blood vessels after a stenosis has been compressed by percutaneous transluminal coronary angioplasty, percutaneous transluminal angioplasty, or removed by atherectomy or other means, to help improve the results of the procedure and reduce the possibility of restenosis. Stents, or stent like devices, are often used as the support and mounting structure for implantable vascular grafts which can be used to create an artificial conduit to bypass the diseased portion of the vasculature, such as an abdominal aortic aneurism. 
     A variety of devices are known in the art for use as stents and have included coiled wires in a variety of patterns that are expanded after being placed intraluminally on a balloon catheter; helically wound coiled springs manufactured from an expandable heat sensitive metal; and self expanding stents inserted into a compressed state for deployment into a body lumen. One of the difficulties encountered in using prior art stents involve maintaining the radial rigidity needed to hold open a body lumen while at the same time maintaining the longitudinal flexibility of the stent to facilitate its delivery and accommodate the often tortuous path of the body lumen. 
     Prior art stents typically fall into two general categories of construction. The first type of stent is expandable upon application of a controlled force, often through the inflation of the balloon portion of a dilatation catheter which, upon inflation of the balloon or other expansion means, expands the compressed stent to a larger diameter to be left in place within the artery at the target site. The second type of stent is a self expanding stent formed from shape memory metals or superelastic nickel titanium alloys, which will automatically expand from a compressed state when the stent is advanced out of the distal end of the delivery, or when a restraining sheath which holds the compressed stent in its delivery position is retracted to expose the stent. 
     Some prior art stent delivery systems for delivery and implanting self-expanding stents include an inner member upon which the compressed or collapsed stent is mounted and an outer restraining sheath which is initially placed over the compressed stent prior to deployment. When the stent is to be deployed in the body vessel, the outer sheath is moved in relation to the inner member to “uncover” the compressed stent, allowing the stent to move to its expanded condition. Some delivery systems utilize a “push pull” type technique in which the outer sheath is retracted while the inner member is pushed forward. Another common delivery system utilizes a simple pull back delivery system in which the self expanding stent is maintained in its compressed position by an outer sheath. Once the mounted stent has been moved at the desired treatment location, the outer sheath is pulled back via a deployment handle located at a remote position outside of the patient, which uncovers the stent to allow it to self expand within the patient. Still other delivery systems use an actuating wire attached to the outer sheath. When the actuating wire is pulled to retract the outer sheath and deploy the stent, the inner member must remain stationary, preventing the stent from moving axially within the body vessel. 
     In certain applications, it is desirable to employ a delivery system which provides a low profile to allow the catheter portion of the system to reach tight distal lesions. For such applications, the stent delivery catheter is required to have a relatively low profile to facilitate positioning the operative distal end portion of the catheter at the desired treatment site in the patient&#39;s body lumen. Delivery system can attain a reduced overall profile by utilizing tubular components having a small diameter to create the catheter portion of the delivery system. However, the delivery system will still require the use of components that provide sufficient pushability or axial stiffness to allow the catheter portion to be delivered over a guide wire to the target location. For example, a catheter with a distal shaft section having a large wall thickness likely has sufficient catheter tensile strength to be pushed along a guide wire to a target location in a patient&#39;s vasculature, however, it may not have sufficient flexibility and low profile/lumen size to be practicable in all applications. If the catheter shaft does not possess sufficient pushability, then the physician may have a difficult time reaching the target lesion. The catheter profile must be balanced with competing considerations such as the catheter tensile strength and kink resistance, and other important characteristics such as those related to the nature of the materials used to form the catheter components. When downsizing catheter components to reduce the overall profile of the catheter, the size of the components must still be strong enough to supply the pushability and kink resistance needed for a given application. Accordingly, while it is desirable to reduce the profile of a delivery system, the delivery system&#39;s pushability should not be compromised. Therefore, what has been needed is a stent delivery catheter system with an improved balance of these catheter characteristics. 
     Some delivery systems which utilize an inner catheter member to support or carry a medical device obtain the necessary axial strength by rely on lengths of tubing having different axial strengths. In this regard, the more proximal sections of the inner catheter member utilize tubing which has increased axial strength to allow the physician to push the catheter portion of the delivery system through the body vessel. The more distal section of the inner catheter member is usually made from a much more flexible tubing to provide needed flexibility at the distal end which often is placed in tortuous and narrow body vessels. As a result, the inner catheter member is often made from a number of different tubular sections bonded together to create a composite unit. From a manufacturing standpoint, the bonding of different tubular sections together increases the overall cost of the product since such bonding steps can often be labor intensive. Additionally, there is always a possibility that the catheter could tear as the physician is pulling the catheter from the patient. 
     The manufacturing of stent delivery systems also often require the physical attachment of small components together to create a composite catheter. For example, atramatic catheter tips, often attached at the distal most end of the catheter portion of a delivery system, provide a soft component that helps to prevent trauma to the vessel walls as the catheter portion is being delivered through, for example, the patient&#39;s vasculature. Delivery systems that do not include a distal tip at the end of the catheter portion can cause a “snow-plowing” effect as the distal tip scrapes against the vessel walls. The scraping of the distal end of the catheter portion can cause significant damage to the vessel walls and could promote the formation of plaque at the damaged locations. Soft distal tips can prevent this from occurring and thus are quite useful to a stent delivery system or any delivery system which is delivered into a body vessel. However, the distal tip must remain permanently attached to the catheter portion. A catheter distal tip which becomes un-attached within the body lumen can cause extreme trouble to the physician performing the medical procedure. For example, a catheter design having insufficient tensile strength can result a catheter failure as the catheter is under tension while being proximally retracted from within the patient&#39;s body lumen, such that the catheter shaft partially or completely tears, which can result in the potentially lethal dislocation of the catheter distal tip. Therefore, there is also a need to maintain the distal tip permanently bonded to the catheter on any delivery system. 
     The present invention disclosed herein satisfies these and other needs. 
     SUMMARY OF THE INVENTION 
     Briefly and in general terms, the present invention is directed towards delivery systems and methods of their use for reducing the overall profile of the catheter portion of the delivery system without compromising the pushability of the delivery system. The present invention also provides a structure which improves and simplifies the attachment of small catheter components to other structures forming the catheter portion the delivery system. 
     In one particular embodiment, the delivery system utilizes an inner catheter member made from single wire having a distal flat wire portion that enhances the bonding of certain catheter components thereto. The use of a single, continuous wire for the inner portion also eliminates the need to bond various tubular components together to form a suitable inner member. The system includes a control handle and a catheter portion coupled to the control handle. The catheter portion including an inner member having a mounting region located near its distal end for carrying the medical device, such as a stent, stent-graft and the like. The proximal region of the single wire generally has a circular cross-section and is coupled to the handle. 
     An outer catheter member is coaxially disposed over at least a portion of the inner member and includes a retraining sheath adapted to cover the medical device. The retraining sheath is movable by the control handle. An inner guide wire lumen formed, for example, from a length of flexible tubing, extends proximally from the distal end of the inner member. This guide wire lumen can be partially or totally connected directly to the flat wire portion of the inner member. The flat wire portion of the inner member provides a solid structure for connecting the guide wire lumen to the inner member. This guide wire lumen has a first opening spaced apart from a second opening which can be located along the distal region of the inner member. In another aspect of the present invention, shrink wrapping can be used to wrap the flat wire portion of the inner member and the guide wire lumen together. 
     In one aspect of the present invention, a distal tip is coupled to the inner member by utilizing the flat wire portion of the inner member. In one aspect, the distal tip includes a bonding port extending through the wall of the distal tip to an inner lumen formed therein. This bonding port extends from the outer surface of the distal tip to the surface of the flat wire when the distal tip is to be attached to the inner member. This bonding port is adapted to receive a bonding material which fixedly attaches the distal tip to the flat wire portion. This structure allows for the simple and quick assembly of the distal tip to the inner member. 
     In one aspect, the shrink wrap used to connect the guide wire lumen to the flat wire portion is removed at the location where the bonding port overlies the flat wire portion. This structure allows the distal tip to be bonded directly to the surface of the flat wire portion to create a strong bond between these components. In an alternative embodiment, the shrink wrap extends entirely over the flat wire portion so that the bonding port is directly over the shrink wrap which surrounds the flat wire portion. The distal tip would then be bonded directly to the shrink wrap tubing, rather than directly to the surface of the flat wire portion. 
     In yet another aspect, the inner member includes a proximal section having a circular diameter which extends proximally from the flat wire portion. The single wire transitions from a circular diameter to the flat wire portion near the second opening of the guide wire lumen. The outer catheter member may include a guide wire opening located near the second opening of the guide wire lumen to allow a guide wire to extend therethrough. In this fashion, a “rapid-exchange” type delivery system can be attained. 
     In another aspect of the present invention, the handle includes a tubular support member having a distal end and a proximal end with a lumen extending therethrough. The proximal region of the inner member (single wire) is adapted to extend through the lumen and is attached to the proximal end of the tubular member to secure the inner member to the handle. A luer fitting could be utilized to attach the end of the tubular member and inner member to the handle. 
     These and other features of the present invention become apparent from the following detailed description and the accompanying exemplary drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an embodiment of a delivery system incorporating features of the present invention; 
         FIG. 2A  is a side, elevational view of the embodiment of a delivery system of  FIG. 1  including the catheter portion which extends from the deployment handle; 
         FIG. 2B  is a cross-sectional view of the catheter portion taken along line  2 B- 2 B; 
         FIG. 2C  is an exploded view of the catheter portion of the system along line  2 C; 
         FIG. 2D  is a cross-sectional view of the catheter portion taken along line  2 D- 2 D; 
         FIG. 3A  is a cross sectional view of the distal portion of the delivery system of  FIG. 1 ; 
         FIG. 3B  is a cross sectional view of the distal portion of the delivery system of  FIG. 3A  taken along line  3 B- 3 B; 
         FIG. 3C  is a cross sectional view of the distal portion of the delivery system of  FIG. 3A  taken along line  3 C-C; 
         FIG. 4  is a perspective view of a distal end of a delivery system incorporating features of the present invention; 
         FIG. 5  is a perspective view of the distal end shown in  FIG. 4  with an attached tapered tip component; 
         FIG. 6  is a perspective view partially in cross section of a distal end of a delivery system incorporating features of the present invention; 
         FIG. 7  is a perspective view, partially in cross section, of the distal end of a delivery system shown in  FIGS. 3A ,  3 B,  3 C,  4  and  5 ; 
         FIG. 8  is a perspective view, partially in cross section, of the distal end of a delivery system incorporating features of the present invention; 
         FIG. 9  is a perspective view, partially in cross section, of the distal end of a delivery system incorporating features of the present invention; 
         FIG. 10  is a cross sectional view of the delivery system of  FIG. 1  showing other features of the present invention; 
         FIG. 11  is a side, elevational view of a portion of the actuation mechanism shown in  FIG. 10 ; 
         FIG. 12  is a side, elevational view of the proximal end of the component shown in  FIG. 10  with the Luer valve removed; and 
         FIG. 13  is a cross sectional view of the Luer valve shown in  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention relates to a system that delivers and deploys a medical device at a target site within a patient&#39;s body, such as a body lumen. For illustration purposes, the following exemplary embodiments are directed to a system for delivering and deploying a self-expanding stent, although it is understood that the present invention is applicable to other medical devices which are implantable in a body lumen as well as other parts of the body. Additionally, the medical device can be either a self-expanding device or a non self-expanding device. 
     Referring now to  FIGS. 1-5 , a delivery system  20  incorporating features of the present invention is illustrated. The delivery system  20  includes a handle  22  with a catheter portion  24  coupled to the handle  22 . A medical device, such as a stent  26  ( FIG. 3A ), is to be delivered by the delivery system  20  in a target sight within the patient&#39;s vasculature. As can be seen in  FIGS. 1 and 2 , the handle  22  includes a gripping portion  28  which allows the physician to grasp the handle and actuate the actuating mechanism associated with the handle. 
     The catheter portion  24  includes an inner member  30  which extends from the handle  22  to the distal end  31  of the catheter portion. This inner member  30  is made from a single, continuous wire having unique features to help reduce the overall profile of the catheter portion  24 . The inner member  30  has a device mounting region  32  locating near the distal end  31  of the catheter portion  24 , upon which the stent  26  is mounted in a delivery position. An outer catheter member  34 , including a restraining sheath  36 , is coaxially disposed over the inner member  30 . In this particular embodiment, the restraining sheath  36  is designed to extend over the entire stent  26  to maintain the stent in a collapsed, delivery position. An actuating mechanism  38 , which includes a rotatable thumbwheel, can be rotated by the physician to retract the outer catheter member  34  and the restraining sheath  36  from the stent  26  to allow the stent to self expand into its fully expanded position. 
     The inner member  30  includes a distal region  40  and a proximal region  42  which extends substantially the entire length of the catheter portion  24 . This distal region  40  of the inner member  30  includes a flat wire portion  44  in which the inner member has a flat or ribbon shape to create a “support” structure which allows for the quick and easy assembly of components parts together. The advantages of this flat-wire portion  44  will be described in greater detail below. The inner member  30  has a generally round or circular diameter in the proximal region  42 . The diameter of the single wire in the proximal region  42  is sufficient to provide the needed axial strength to allow the catheter portion of the system to be pushed up along a guide wire into a target location in the patient&#39;s vasculature. The proximal region  42  of the inner member  30  can include transition regions where the diameter of the wire decreases in a proximal to distal fashion. Therefore, the single wire forming the inner member can have a smaller diameter near its distal region where more flexibility is needed and a larger diameter in a proximal portion where more strength may be needed to provide adequate pushability to the catheter portion  24  of the delivery system  20 . 
     A distal tip  46  is attached to the flat wire portion  44  of the inner member  30 . This distal tip  46  provides a soft, atraumatic component to the catheter portion  24  to help prevent a “snow plowing” effect as the distal end of the catheter portion is delivered through the patient&#39;s vasculature. The delivery system  20  includes a guide wire lumen  48  which can be made, for example, from a length of flexible tubing. This guide wire lumen  48  is attached directly to the flat wire portion  44  of the inner member  30 . This guide wire lumen  48  includes a first opening  50  located at the distal end of the tubing and a second opening  51  which extends along the length of the flat wire portion  44  to provide egress for a guide wire  52 . This guide wire lumen  48  thus provides a short segment which allows the catheter portion  24  to ride along the guide wire  52 . As can be see in  FIGS. 3A ,  3 B and  3 C, shrink wrap  54  can be utilized to attach the guide wire lumen  48  to the flat wire portion  44 . It will be appreciated those skilled in the art that other means for attaching the guide wire lumen  48  to the flat wire portion  44  could be utilized. For example, adhesives, crimping rings and similar fastening devices could be utilized as well. 
     The outer catheter member  34  also includes a guidewire opening  56  which allows the guidewire  52  to exit the guide wire lumen  48  and the outer catheter member  34 . As can be seen in  FIG. 2C , a short segment  53  of the guide wire lumen  48  is not encased by the shrink wrap  54  near the second opening  51  to allow the segment  53  to be easily positioned within the guide wire opening  56  of the outer catheter member  34 . This construction allows the guide wire lumen  48  to be easily aligned with the opening  56  during manufacturing. In use, the outer catheter member  34  is simply retracted proximally while the guide wire  52  remains in the guide wire lumen  48 . The guide wire  52  also extends through a lumen  58  formed within the distal tip  46 . Again, the atraumatic distal tip  46  helps to prevent trauma to the vessel wall as the catheter portion  24  is being advanced along the guidewire. 
     Generally, in a vascular procedure, a guide wire  52  has already been implanted in the patient&#39;s vasculature and the delivery system  20  is advanced over the implanted guide wire. This guide wire lumen  48  provides what is known as a rapid-exchange feature to the delivery system so that only the guide wire lumen actually slides over the guide wire, to help reduce the amount of friction between the catheter portion  24  and the guide wire  52 . 
     Referring specifically now to  FIG. 5 , the distal tip  46  is shown including a bonding port  60  which extends through the wall of the distal tip  46  into the lumen  58 . This bonding port  60  is adapted to receive a bonding material, such as an adhesive  62  (see  FIGS. 3A and 3B ) which couples the distal tip  46  to the flat wire portion  44  of the inner member  30 . As can be seen in  FIGS. 3A and 3B , in this particular embodiment, the adhesive material  62  actually bonds directly to the shrink wrap  54  which encases both the flat wire portion  44  and the guide wire lumen  48 . From a manufacturing standpoint, this bonding port  60  makes it quite easy to bond the distal tip  46  to the inner member  30  by using the flat wire portion  44 . This structure provides for easy set up since adhesive material  62  can be easily applied to achieve tip bonding. It should still be appreciated that other portions of the distal tip could also be bonded to other components, such as the guide wire lumen  48 , as well, to increase the overall strength of the tip attachment. A suitable adhesive for bonding the components together is Loctite 4306 which is a flashcure cyanacrylate adhesive manufactured by Loctite. 
       FIG. 6  shows the distal end  64  of a guide wire lumen  48  as it abuts against a shoulder  66  formed in the lumen  56  of the distal tip  46 . As can be seen in  FIG. 6 , the distal most end of the flat wire portion  44  extends to the distal end  64  of the guide wire lumen  48 . Other variations regarding the location of the distal end  64  of the guide wire lumen  56  will be discussed in greater detail. 
       FIG. 7  shows an alternative structure which allows the distal tip  46  to be directly attached to surface of the flat wire portion  44  of the inner member  30 . In this particular embodiment, a portion of the shrink wrap  54  has been removed to expose the surface of the flat wire portion  44 . This exposed region  65  of the flat wire portion  44  would be located directly beneath the bonding port  60  so that the adhesive (not shown in  FIG. 7 ) will come in direct contact with the surface of the flat wire portion  44 , rather than the shrink wrap  54 , as is shown in the previous embodiment. This particular embodiment of the present invention is desirable since it creates an extremely strong bond between the distal tip  46  and the flat wire portion  44  of the inner member  30 . 
     Referring now to  FIG. 8 , another alternative embodiment is shown in which the distal most end  68  of the flat wire portion  44  bents over a portion of itself in the area near the bonding portion  60 . The distal end  68  is bent over itself in order to take up any space which may exist between the lumen  58  of the distal tip  46  and the flat wire portion and guidewire lumen  48 . In this particular embodiment, the flat wire portion  44  is again fully exposed to allow the application of the adhesive material (not shown) to bond directly onto the surface of the flat wire portion  44  rather than the shrink wrap  54 . Shrink wrap  54  is still used in the particular embodiment, however, it terminates just proximal to the bonding port  60 , as is shown in  FIG. 8 . Also, as can be seen in  FIG. 8 , the distal end  64  of the guide wire lumen  48  is shown extending all the way to the distal most end  70  of the distal tip  46   
     Referring now to  FIG. 9 , still another embodiment of the present invention is shown with the distal end  64  of the guide wire lumen  48  extending fully to the distal most end  70  of the distal tip  46 . This particular embodiment is very similar to the one shown in  FIG. 6  except for the fact that the guide wire lumen  48  now extends fully through to the distal most end  70  of the distal tip  46 . It should be appreciated that this particular embodiment shown in  FIG. 9  can also have a configuration in which a portion of the shrink wrap  54  is removed directly under the bonding port  60  to allow the adhesive to bond directly onto the surface of the flat wire portion  44  of the inner member  30 . 
     Referring now to  FIG. 10 , the handle  22  is shown with the actuating mechanism  38  which causes the outer catheter member  34  and the restraining sheath  36  to be retracted proximally in order to remove the sheath  36  from the stent  26 . The actuating mechanism includes a thumbwheel  72  which is operative connected with a rack-in-pinion assembly  74 . The proximal end  76  of the outer catheter member  34  can be coupled to this rack-in-pinion assembly  74 , as is shown in  FIG. 10 . When the physician manipulates the thumbwheel  72  in a clockwise rotation, the rack-in-pinion assembly  74  moves proximally causing the outer catheter member  34  and restraining sheath  36  to move proximally as well. The handle  22  is shown including a tubular support member  78  upon which the rack portion of the rack and gear assembly is mounted. This tubular support member  78  extends from the proximal end  80  to the distal end  82  of the handle  22 . The proximal end  84  of the inner member  30  is designed to extend within a lumen  86  formed within this tubular member  78 . 
     As can be seen in  FIG. 12 , the proximal end  84  of the inner member  30  extends through this lumen  86  and is bent back against the outer surface  88  of the tubular member  78  to form a “hook” which helps to fasten the inner member  30  to the handle  22 . A luer fitting  90 , shown in  FIG. 13 , can be placed over the proximal end  84  of the tubular member  78 , along with the proximal end  86  of the inner member  30 , to securely fasten the inner member  30  onto the tubular member  78 . This luer fitting  90  is, in turn, fastened within a recess  92  formed at the proximal end  80  of the handle. In this fashion, the inner member  30  will remain securely attached to the handle  22 . It should be appreciated that the present embodiment shows just one manner in which the proximal end of the inner member  30  can be attached to a handle portion. Additionally, one particular handle is shown for purposes of explaining the present invention. It should be appreciated that other styles of handles could be used with the inner member described above. 
     The catheter components such as the outer tubular members and guide wire lumen can be formed of materials found useful in catheter construction. For example, the polymeric tubular members can be formed of materials such as polyamides (e.g., nylon), polyamide copolymers (e.g., polyether block amide), polyolefins (e.g., polyethylene), polyurethanes, polyesters, and the like. Generally speaking, the more proximal portions of the outer tubular member are usually stiffer than the distal portions, to provide the catheter sufficient pushability, and the catheter distal section is configured to provide flexibility and trackability to advance through the patient&#39;s vascular system by tracking on the guide wire. However, since a wire is utilized to create the inner member  30 , the strength of the catheter portion can be more strongly associated with the wire, than the other portion. Therefore, the diameter and stiffness of the outer member and restraining sheath can be decreased due to the increased strength supplied by the inner member  30 . 
     The wire forming the inner member  30  must have sufficient strength for the intended application. It will be understood that different strength material could be used for particular applications. The inner member  30  can be made from high strength metals and alloys, such as, for example, stainless steel, high tensile stainless steel such as hi-ten 304V, precipitation hardenable alloys, including precipitation hardenable stainless steel and other high strength alloys such as MP35N, L605, Elgiloy and metallic and high strength polymeric materials associated with medical grade devices. The inner member  30  may also be made from superelastic, pseudoelastic or shape memory alloys such as NiTi. High strength alloys used with medical grade devices can also be used. Also, the size of the diameter of the proximal portion of the wire can vary. It has been found that stainless steel wire having a diameter of about 0.012 to 0.014 inches is suitable. Larger diameter wires, e.g. up to 0.035 inch (0.89 mm) or more may be employed when the delivery device is to be used in peripheral arteries and other body lumens. The flat wire portion  44  can have generally rectangular shaped transverse cross-sections which usually have dimensions of about 0.008 to about 0.014 inches (0.2-0.36 mm) in width and about 0.0004 to about 0.008 inches (0.1-0.2 mm) in thickness. It should be appreciated that the width and thickness of the flat wire portion can be varied, as needed for a particular application. The above-listed ranges of widths and thickness have been found to provide sufficient flexibility for a delivery system to be used in a vascular system. However, these dimensions can vary, of course, depending upon the type of material chosen to create the inner member. 
     The overall length of the inner member  30  and the length of the flat wire portion  44  also will vary depending upon the procedure. For most percutaneous intravascular procedures, the overall length of the inner member would be generally about 100 to about 200 cm. The length of the distal flat wire portion  44  can range from about 5 to about 30 cm, depending upon the flexibility and other properties desired in the final product. 
     The inner member can be coated with a lubricious coating such as a fluoropolymer, e.g. TEFLON® available from DuPont, MICROGLIDE™ coating and other commercially available coatings which extends the length of the proximal section of the inner member  30 . A hydrophilic coating may also be employed. These coating help to reduce friction between the surface of the inner member  30  and the inner surface of the outer catheter member  34 . 
     It is to be understood that even though numerous characteristics and advantages of the present invention have been set forth in specific description, together with details of the structure and function of the invention, the disclosure is illustrative only and changes may be made in detail, such as size, shape and arrangement of the various components of the present invention, without departing from the spirit and scope of the present invention. It would be appreciated to those skilled in the art that further modifications or improvement may additionally be made to the delivery system disclosed herein without departing from the scope of the invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.