Abstract:
A system including a longitudinally elongated housing, a member for incremental rotation of a screw, which moves the screw longitudinally, and a longitudinal sheath connected to the screw. The system has a delivery configuration in which a sheath covers a stent bed, and a deployed configuration in which the sheath does not cover the stent bed because manipulation of the member has rotated the screw, which has moved the screw longitudinally, pulling the sheath off of the stent bed.

Description:
PRIORITY 
       [0001]    This application is a continuation of U.S. application Ser. No. 11/581,645, filed Oct. 16, 2006, now U.S. Pat. No. 8,852,266, which is a continuation of U.S. application Ser. No. 10/357,985, filed Feb. 4, 2003, now U.S. Pat. No. 7,122,050, which is a continuation of U.S. application Ser. No. 09/409,210, filed Nov. 30, 1999, now U.S. Pat. No. 6,514,261, which claims the benefit of U.S. Provisional Application No. 60/102,498, filed Sep. 30, 1998, each of which are incorporated by reference into this application as if fully set forth herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to implantable medical devices. More particularly, the present invention relates to mechanisms for implanting a self-expanding stent graft which is used to sustain a weakened body vessel. 
       BACKGROUND 
       [0003]    Various diseases of blood vessels or hollow organs cause a stenosis or complete occlusion of their lumen, which results in a decrease or complete loss of their functional attributes. Various implantable prosthetic devices for sustaining a blood vessel or hollow organ lumen typically have a tubular-shaped frame body which is introduced into the vessel or hollow organ and fixed in the necessary location to sustain the lumen. 
         [0004]    A commonly used implant is a tubular-shaped wire frame known as a stent graft. In one type of stent graft, the wire frame is made of self-expanding nickel-titanium (nitinol) shape memory alloy which is laser cut and encapsulated within two layers of expanded polytetrafluoroethylene (ePTFE). The layers of ePTFE are processed such that the material forms a monolithic structure, fully enclosing the metallic stent where the cover is present. The encapsulation is intended to prevent restenosis of the vessel. The inner blood contacting lumen of the stent graft is impregnated with carbon. Typically, one or both ends of the stent graft is flared and free of encapsulation in order to facilitate anchoring within the vessel. The nitinol alloy is placed into the body during surgery at room temperature. As it increases to body temperature, it expands to its desired size. Balloon angioplasty may be done after implantation of the stent to set its final shape. 
         [0005]    In order to introduce the stent into the body vessel, it is placed within a tubular sheath catheter. When the device is positioned at the desired location, it is released from the tubular sheath and permitted to expand radially against the wall of the vessel. When the outer sheath is removed, the physician must be careful to avoid migration of the stent away from the desired location. Typical prior art devices employ a simple ratchet mechanism in conjunction with the outer sheath and an inner lumen. The inner lumen is maintained stationary to fix the stent in position and the outer lumen is drawn away from the stent by means of the ratchet mechanism actuated by a spring loaded trigger. Each pull on the trigger causes the outer sheath to retract by an amount corresponding to the stroke of the trigger. An anchor to which the outer sheath is attached includes a tooth which engages with each tooth of the ratchet mechanism. This mechanism has drawbacks in that it is awkward to operate and difficult to maintain steady so that the stent graft does not migrate away from its desired position during sheath retraction. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The present invention is directed to a stent delivery mechanism which is both easy to operate and facilitates extremely precise stent positioning. Several different configurations are described. For example, in a first embodiment, a simple V-shaped grip aligned generally longitudinally with the catheter to be deployed is utilized. A mechanical advantage gear mechanism is employed, which operates in conjunction with a ratchet to smoothly retract a sheath hub to which the outer sheath of the catheter is attached. The mechanism is easy to grasp and actuate in any rotational configuration. The V-shaped mechanism includes a body which contains the ratchet and a drive gear lever handle. The lever handle interacts with a drive pinion to drive the ratchet by a predetermined amount, thus retracting the sheath hub by a corresponding amount. The drive gear lever handle mechanism provides both the mechanical advantage, which results in movement of the outer sheath by a relatively small amount for a large displacement of the lever handle, and a much smoother operation than the direct ratchet operation of the prior art device. 
         [0007]    In a second embodiment of the invention employs a hydraulic mechanism to both provide the mechanical advantage and achieve extremely smooth retraction operation. In addition, the use of hydraulics, as opposed to other systems, creates positive positioning so that the actuator will not cause any unexpected motion. The hydraulic system may be actuated by means of a drive plunger similar to the operation of a syringe, or may be equipped with a lever handle to allow a gripping action to be employed for actuation. 
         [0008]    In a third embodiment, a rack and pinion drive system operated by a thumb wheel is employed. The rack and pinion drive system also provides a desirable mechanical advantage and promotes smooth operation. 
         [0009]    In a fourth embodiment, a power screw drive system is employed. This drive system is actuated by a thumb driven concentric drive knob which rotates to retract an internal power screw to which the outer sheath is secured. Again, a mechanical advantage is provided to promote smooth retraction of the outer sheath. 
         [0010]    In order to further facilitate the stent deployment, the inner lumen of the delivery system may be formed of a metal spring, which is contained in its fully compressed state. The use of such a spring for the inner lumen provides significant advantages in that it is extremely flexible, enabling introduction of the catheter into the body and proper positioning of the stent, and yet is very rigid and non-compressible so as to maintain the stent in the desired position during outer sheath retraction. 
         [0011]    These and other embodiments, features and advantages of the present invention will become more apparent to those skilled in the art when taken with reference to the following more detailed description of the invention in conjunction with the accompanying drawings that are first briefly described. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a cross-sectional view of the end of a catheter illustrating a stent to be implanted; 
           [0013]      FIG. 2  is a cross-sectional view of a first embodiment of the stent delivery mechanism of the present invention incorporating a moving rail mechanism; 
           [0014]      FIGS. 3-6  are cross-sectional views illustrating the retraction operation of the moving rail system; 
           [0015]      FIG. 7  is an exploded view of a preferred embodiment of the stent delivery mechanism shown in  FIG. 2 . 
           [0016]      FIG. 8  is a cross-sectional view of a second embodiment of the stent delivery mechanism of the present invention incorporating a hydraulic mechanism 
           [0017]      FIGS. 9-12  are cross-sectional views illustrating the operation of the embodiment of  FIG. 7 ; 
           [0018]      FIG. 13  is a cross-sectional view of a third embodiment of the stent delivery mechanism of the present invention employing a rack and pinion thumb actuated drive system; 
           [0019]      FIG. 14  is a view of the system of  FIG. 13  along line  14 - 14 ; 
           [0020]      FIGS. 15 and 16  are cross-sectional views illustrating the operation of the drive system of  FIG. 13 ; 
           [0021]      FIG. 17  is a cross-sectional view of a fourth embodiment of the stent delivery mechanism of the present invention employing a power screw drive system; 
           [0022]      FIG. 18  is an end plan view illustrating the drive knob and collar configuration of the system of  FIG. 17 ; and 
           [0023]      FIGS. 19 and 20  are cross-sectional views illustrating the operation of the power screw drive system of  FIG. 17 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    The following detailed description should be read with reference to the drawings, in which like elements in different drawings are identically numbered. The drawings, which are not necessarily to scale, depict selected preferred embodiments and are not intended to limit the scope of the invention. 
         [0025]    The detailed description illustrates by way of example, not by way of limitation, the principles of the invention. This description will clearly enable one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what is presently believed to be the best mode of carrying out the invention. 
         [0026]      FIG. 1  illustrates the distal end of a catheter  11  having a stent  16  carried within it for implantation into the body of a patient. The proximal end of the catheter  11  is connected to any of the delivery mechanisms to be described, and the catheter  11  is of sufficient length to reach the point of implantation of the stent  16  from the introduction point into the body. The catheter  11  includes an outer sheath  10 , a middle tube  12  which in the preferred embodiment is formed of a compressed spring, and a flexible (e.g., polyamide) inner tube  14 . The outer sheath  10  preferably has an ePTFE liner with a polyether blocked amide plastic (pebax) basecoat with reinforced braid, and an external layer of pebax. A stent  16  for implantation into a patient is carried within the outer sheath  10 . The stent  16  includes a nitinol memory metal alloy frame  18  which is formed in a criss-cross pattern which may be laser cut. Most or all of the length of the stent is encapsulated within two layers of ePTFE to form a monolithic body structure  20 , fully enclosing the metallic stent  16  both internally and externally where the cover  20  is present. One or both ends of the stent  16  may be left uncovered as illustrated at  22  and  24  to provide anchoring within the vessel where the stent  16  is to be implanted. 
         [0027]    A radiopaque atraumatic tip  26  is secured to the end of the inner tube  14  of the catheter. The atraumatic tip  26  has a rounded end and is gradually sloped to aid in the movement of the catheter through the body vessel. The atraumatic tip  26  is radiopaque so that its location may be monitored by appropriate equipment during the surgical procedure. The inner tube  14  is hollow so as to accommodate a guide wire, which is commonly placed in the vessel prior to insertion of the catheter, although the invention may employ a solid inner section and be used without a guide wire. Inner tube  14  has sufficient kink resistance to engage the vascular anatomy without binding during placement and withdrawal of the delivery system. In addition, inner tube  14  is of sufficient size and strength to allow saline injections without rupture. 
         [0028]    A generally cup-shaped element  28  is provided within the catheter  11  adjacent the rear end of the stent  16  and is attached to the end of the spring  12  by appropriate means, e.g., the cup element  28  may be plastic wherein the spring  12  is molded into its base, or the cup element  28  may be stainless steel wherein the spring  12  is secured by welding or the like. The open end of the cup element  28  serves to compress the end  24  of the stent  16  in order to provide a secure interface between the stent  16  and the spring  12 . Alternatively, instead of a cup shape, the element  28  could be formed of a simple disk having either a flat or slightly concave surface for contacting the end  24  of the stent  16 . 
         [0029]    In order to deploy the stent  16  inside a body vessel during a surgical procedure, the catheter  11  is introduced into the designated vessel via an introducer positioned at the skin of the patient. As mentioned above, a guide wire may have previously been introduced into the vessel, in which case the catheter  11  is introduced by passing the tip  26  over the end of the guide wire outside of the patient and moving the catheter  11  along the path within the vessel which has been established by the guide wire. 
         [0030]    The position of the catheter  11  is tracked by monitoring the tip  26  by means of a fluoroscope. When the catheter  11  is at the desired location i.e., when the stent  16  is positioned at the location where it is be implanted, the movement of the catheter  11  is halted. The catheter  11  must then be removed, leaving the stent  16  in place at the desired location within the vessel. This is accomplished by initially retracting the outer sheath  10 , i.e., towards the left in  FIG. 1 , until it no longer covers the stent  16 . The spring  12  is maintained in a fixed position and, in conjunction with the cup element  28 , serves to maintain the stent  16  in its desired position during the retraction of the outer sheath  10 . After the outer sheath  10  has been retracted such that it no longer covers the stent  16  and the stent  16  is expanded, the tip  26  can be pulled back through the stent  16  until the tip  26  abuts the outer sheath  10 . As illustrated, the diameter of the tip  26  is slightly greater than the inner diameter of stent  16  when it is inside the outer sheath  10 . The stent  16  will expand as it heats up to body temperature as a result of its memory metal characteristics. The tip  26  is then pulled through the center of the stent  16  after the stent  16  has expanded following withdrawal of the sheath  10 . Once the tip  26  has been pulled back against the outer sheath  10 , the catheter  11  can be removed from the vessel of the patient. This retraction procedure ensures that the tip  26  does not get caught on or embedded in any body vessel when being pulled out of the patient. 
         [0031]    As discussed above, the tube spring  12  is maintained stationary during the withdrawal of the outer sheath  10  and serves to keep the stent  16  in its desired location. The tube spring  12  is very well suited for this task since it has extremely low compression in a longitudinal direction once it is fully compressed. It is also well suited for the introduction of the catheter  11  into the body vessel, since it is extremely flexible. Alternatively, other materials, such as various plastics materials, could be employed as the middle tube  12 , so long as the compression is low to maintain stent positioning and the necessary flexibility is provided for moving through the vessel. In order to properly deploy the stent  16 , the outer sheath  10  must be smoothly retracted while the tube spring  12  maintains its position. The present invention provides a number of mechanisms intended to perform this operation with maximum ease of use and minimal stent migration. 
         [0032]      FIG. 2  illustrates a first embodiment of a delivery mechanism for implanting the stent  16 . This mechanism is generally in the form of a V-shaped lever device having a housing shell  30  from which the outer sheath  10  extends. The sheath  10  is secured to a pawl/sheath hub  32 . A spring pawl  34  attached to the hub  32  engages a ratchet  36  which is integrated into the housing shell  30 . Movement of the sheath hub  32  within the housing shell  30  is thus constrained to moving to the right as shown in  FIG. 2 . The tube spring  12  is secured in a fixed position to a guide wire port  38 . The interior of the device may be flushed by means of a flush stop cock  40 . A ratchet rail  42  is provided at the bottom of the housing shell  30  and is reciprocal back and forth within the shell  30 . The rail  42  includes ratchet teeth  44  on the upper side which engage with the spring pawl  34  and a rack gear  46  on the bottom surface thereof which engages a pinion  48 . The pinion  48  is rotated by means of a lever handle  50  which includes a drive gear  52 . The lever handle  50  is spring biased by means of a spring  54  to its open position. Other types of springs, such as a spring contained within the pivot point  56  of the lever handle could alternatively be employed. 
         [0033]    The operation of the device of  FIG. 2  will be described with reference to  FIGS. 3-6 . Initially, as illustrated in  FIG. 3 , the handle  50  is in its open position, which forms an angle of approximately twenty-five degrees with the housing shell  30 . When the handle is squeezed, bringing it adjacent to the housing shell as indicated by arrow  58  in  FIG. 4 , the drive gear  52  rotates the pinion  48  in a clockwise direction as illustrated by arrow  60 . The pinion  48  drives the rail  42  to the right, which in turn drives the sheath hub  32  to the right, thus extracting the outer sheath  10  by an incremental distance illustrated at  62 . In the described device, the incremental distance is approximately 1 cm. Referring to  FIG. 5 , when the handle  50  is released, the spring action returns it to the open position, thus rotating the pinion  48  counterclockwise and returning the rail  42  to its leftward position. The sheath hub  32  is maintained stationary by the ratchet  36 . 
         [0034]    The described device is intended for use with stents of approximately 40-100 mm in length. In order to fully retract the outer sheath  10 , the lever handle  50  must be closed and opened a number of times.  FIG. 6  illustrates the mechanism in which the handle  50  has been operated to move the hub  32 , and therefore the outer sheath  10 , back to its completely rightmost position. In this position (or sooner depending upon the length of the stent) the outer sheath  10  will be completely away from the stent  16 , allowing the stent  16  to expand. As described above, once the stent  16  expands, the inner tube  14  and tip  26  are pulled back through the middle of the stent  16  until the tip  26  is tight against the outer sheath  10 . The entire catheter  11  can then be removed, leaving the stent  16  in place at the desired location. 
         [0035]    A preferred embodiment of the device shown in  FIG. 2  is illustrated by the exploded view in  FIG. 7 . In this view, a left housing assembly  31  and a right housing assembly  33  can be seen. An inner catheter assembly  37  is disposed between the housing assemblies  31  and  33  to support the tube spring  12  as well as the spring pawl  34 . A strain relief member  51  fits over the end of housing shell  30  to reduce any potential pressure caused in the actuation of the mechanism. A safety pin  53  is insertable into the lever handle  50  for additional protection. Upon completion of the deployment of the stent  16  and the retraction of outer sheath  10 , a retractor sleeve  49  is pulled back slightly, releasing a retractor latch  47  from its locked position on the inner catheter assembly  37 . The inner catheter assembly  37 , which is coupled to the inner tube  14 , is pulled back away from the housing assemblies  31  and  33  in order to retract the inner tube  14  far enough so that tip  26  is snuggly against the outer sheath  10 . The catheter  11 , including the outer sheath  10 , the inner tube  14  and the tip  26  can then be removed from the body. Retraction of the catheter  11  in this manner ensures that the tip  26  can not get caught on anything outside of the body or inside the delivery mechanism. 
         [0036]    The gear mechanism including the lever gear  52 , pinion  48  and rack  46  is designed to provide a mechanical advantage of approximately 4:1. The mechanical advantage along with the rotating pinion configuration provides very smooth and linear operation with minimal fly back during the return stroke. In addition, the lever handle configuration is extremely convenient, as it can be easily operated in almost any rotational orientation. This is important due to the fact that when a catheter is introduced into the patient, it is often necessary to rotate the catheter in order for it to most easily follow the desired path through the vessel to the stent location. Therefore, the final orientation when the stent is to be deployed is variable. The configuration of the V-shaped lever handle mechanism enables a simple gripping action to be applied, and is easily gripped by the surgeon regardless of its final orientation. Generally, approximately ten cycles (i.e., squeezing and releasing) of the lever handle  50  are necessary to fully remove the outer sheath  10  from the stent. The configuration of this embodiment enables retraction to be done in a very smooth and linear fashion. 
         [0037]    A second embodiment of the stent delivery mechanism is illustrated in  FIG. 8 . This delivery mechanism employs a hydraulic system to achieve extremely smooth operation. A housing  62  defines a reservoir chamber  64  within which is carried a piston  66 . The outer sheath  10  is connected to the piston  66  to be moved therewith. A V-cup seal  68  prevents leakage of the hydraulic fluid carried within the housing. A piston displacement chamber  70  is defined between the piston  66  and the opening through which the sheath  10  exits. 
         [0038]    Conduits  72  and  74  are coupled to opposite ends of the piston housing  62 . Directional check valves  76  and  78  are contained within the conduits  72  and  74 , respectively. A drive plunger  80  is contained within a plunger housing  82 . Hydraulic fluid, such as saline solution, is provided through a port  84 . 
         [0039]    The operation of the hydraulic mechanism will be described with reference to  FIGS. 9-12 . In  FIG. 9 , the reservoir  64  is filled with fluid and the system is ready for operation. In  FIG. 10 , the plunger  80  is pulled rearward and transfers saline from the reservoir  64  through the conduit  72  via valve  76 . The valve  76  is open in this state and the valve  78  is closed. 
         [0040]    Referring to  FIG. 11 , the plunger  80  is pressed inward to open the valve  78  and move fluid through the conduit  74  into the piston chamber  70 , thus moving the piston  66  to the right by a fixed amount and, in turn, retracting the outer sheath  10  from the stent. In the present embodiment, one stroke of the plunger  80  provides approximately 1 cm of travel of the piston  66 . The plunger and piston are sized to provide a mechanical advantage of approximately 4:1. By repeatedly operating the plunger, the piston  66  will be drawn back to its fully deployed position as illustrated in  FIG. 12 . At this point, the outer sheath  10  is fully withdrawn from the stent  16 , and the catheter  11  can be pulled out of the patient as described above. 
         [0041]    Although the described embodiment employs a plunger which is manually operated, a lever or trigger mechanism could be employed to actuate the plunger  80 . Such mechanism would include a spring return or the like to bias the plunger to the extended position. The use of a lever mechanism (in which case the plunger orientation would be reversed and a lever handle coupled to it) would allow grip pressure to be utilized as opposed to finger or thumb pressure. 
         [0042]    Referring to  FIGS. 13-16 , a third embodiment of the invention will be described. This embodiment employs a rack and pinion mechanism actuated by means of a thumb knob. In  FIG. 13 , the device includes a housing  82  within which is carried a rack  84 , movable from left to right as illustrated in  FIGS. 15 and 16 . The rack  84  interacts with a rack drive gear  86  coupled to a reduction drive gear  88 , which in turn is driven by a knob  90  having a gear  92 . The outer sheath  10  is coupled to the rack  84  to be movable therewith.  FIG. 14  is a cross-sectional view of  FIG. 13  along line  14 - 14 , showing a different perspective of knob  90  in relation to housing  82 . 
         [0043]    In operation, the knob  90  is rotated counterclockwise as illustrated in  FIG. 15 , causing the gear  92  to move in the same direction. This action causes the reduction drive gear  88  and the rack drive gear  86  to move in a clockwise position, which in turn causes the rack  84  to retract within the housing by a distance of approximately 1 cm per revolution of the knob as indicated at  94 . The mechanical advantage is controlled by appropriate sizing of the gears which drive the rack  84 . After a sufficient number of rotations, the rack  84  will be fully retracted, as illustrated in  FIG. 16  and the outer sheath  10  will be completely removed from the stent  16  so that the catheter  11  can be removed from the patient as described above. 
         [0044]    Referring to  FIGS. 17-20 , a fourth embodiment of the delivery system will be described. In this embodiment, a power screw drive system is employed. A drive knob  96  is carried within a collar  98  of a housing  100 . The drive knob  96  is fixed to a power nut  102  having a threaded interior surface which mates with the threaded surface of a power screw  104  which is slidably carried within the housing  100 . The outer sheath  10  is coupled to the power screw  104  to move in conjunction therewith. By rotating the drive knob  96 , the power nut  102  rotates and drives the power screw  104  to the right as shown in the  FIGS. 19 and 20 .  FIG. 18  is an end plan view, illustrating the drive knob  96  within the collar  98 . The mechanical advantage of this fourth embodiment is determined by the pitch of the power screw  104  and the size of the knob  96 . 
         [0045]    As shown in  FIG. 19 , a single rotation of the knob  96  achieves a movement of the power screw  104  of approximately 1 cm, as indicated at  106 . The high mechanical advantage provided by the configuration facilitates smooth retraction of the outer sheath  10 . After a number of rotations of the knob  96 , the power screw  104  will be fully retracted, as illustrated in  FIG. 20 , and the outer sheath  10  will be completely withdrawn from the stent  16 . The catheter  11  can then be removed as described above. 
         [0046]    In summary, each of the disclosed systems provides a significant mechanical advantage which facilitates smooth retraction of the outer sheath  10  which covers the stent  16 . This minimizes migration of the stent  10  during sheath retraction, thus ensuring that the stent  16  will remain in its desired location. In addition, various configurations are provided which are operable in numerous orientations, thus providing convenient and simple use during surgery. 
         [0047]    This invention has been described and specific examples of the invention have been portrayed. While the invention has been described in terms of particular variations and illustrative figures, those of ordinary skill in the art will recognize that the invention is not limited to the variations or figures described. In addition, where methods and steps described above indicate certain events occurring in certain order, those of ordinary skill in the art will recognize that the ordering of certain steps may be modified and that such modifications are in accordance with the variations of the invention. Additionally, certain of the steps may be performed concurrently in a parallel process when possible, as well as performed sequentially as described above. Therefore, to the extent there are variations of the invention, which are within the spirit of the disclosure or equivalent to the inventions found in the claims, it is the intent that this patent will cover those variations as well. Finally, all publications and patent applications cited in this specification are herein incorporated by reference in their entirety as if each individual publication or patent application were specifically and individually put forth herein.