Abstract:
A system for delivering a stent from a catheter sheath in a longitudinal direction comprising: a thumbwheel mounted on an axle, the axle being supported by opposite walls of a housing; a first pinion mounted on the axle; a second pinion mounted on the axle, whereby rotation of the thumbwheel causes rotation of the first pinion and rotation of the second pinion; a first rack, enageable with the first pinion at a first surface of the first pinion, the first rack being operably connected with a stent-engaging member; a second rack, engageable with the second pinion at a second surface of the second pinion, the second surface being disposed in a direction diametrically opposite the first surface, the second rack being operably connected with a sheath configured to confine the stent.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is related to U.S. application Ser. No. 13/118,325, filed May 27, 2011, which is incorporated by reference herein. 
     BACKGROUND 
     This application relates to the field of delivering self-expanding stents into a body lumen of a patient. More specifically, the invention relates to providing a system for continuous stent advancement during delivery, and also for retraction of a sheath that confines the stent. 
     The broad concept of delivering a self-expanding stent into a body lumen of a patient is known in the art. Typically, self-expanding stent delivery involves pushing a stent so that the stent moves distally out of a confined condition within a sheath of a delivery catheter, into an expanded condition in the patient&#39;s body lumen. Typically, a delivery device is configured to push the stent distally. 
     However, various problems arise when this action is carried out by a delivery device that hooks (via a stent-engagement member) into the mesh of a stent before a distal force is applied to the stent-engagement member and hence to the stent. 
     First, a stent-engagement member that is positioned towards the rear (proximal) end of the stent may have the effect, when it is moved distally, of compressing the proximal end of the stent rather than moving the entire stent distally. This may be caused by the fact that friction against the sheath holds the distal end of the stent stationary in relation to the delivery catheter. 
     Second, if a stent-engagement member is positioned to engage the stent towards the front end of the stent in order to avoid the problem of compression identified above, then the stent engagement member must be made to oscillate backwards and forwards in short strokes in order to keep the stent-engagement member in contact with the mesh of the stent. (It will be appreciated that that the expansion of the stent will cause the stent-engagement member to disengage from the stent.) This oscillation requirement introduces further complexity in that the user physician must keep track of how many times he has moved the stent, and the distance of each oscillation. 
     Thus both methods of forcing a stent distally out of a confining sheath during deployment of a self expanding stent from a catheter are beset by problems. There is accordingly a need for a self expanding stent delivery system that address the problems in the art. The present invention addresses these and other needs. 
     SUMMARY OF THE INVENTION 
     In some embodiments, the invention is a system for delivering a stent from a catheter sheath in a longitudinal direction comprising a thumbwheel mounted on an axle, the axle being supported by opposite walls of a housing. A first pinion is mounted on the axle, and a second pinion is mounted on the axle, whereby rotation of the thumbwheel causes rotation of the first pinion and rotation of the second pinion. A first rack is provided, enageable with the first pinion at a first surface of the first pinion. The first rack is operably connected with a stent-engaging member. A second rack is provided, engageable with the second pinion at a second surface of the second pinion, the second surface being disposed in a direction diametrically opposite the first surface. The second rack is operably connected with a sheath configured to confine the stent. In further embodiments, the axle is mounted in a circular bearing in each of opposite walls of the housing, wherein the first rack and the second rack are spaced apart to allow the first pinion to be engaged with the first rack at the same time as the second pinion is engaged with the second rack. In yet further embodiments, the first pinion has a first diameter and the second pinion has a second diameter, the first diameter being different from the second diameter. In some embodiments, the axle is mounted in an elongated slot in each of opposite walls of the housing, the slot having an elongate direction that extends between the first surface and the second surface, wherein the first rack and the second rack are spaced apart to allow the first pinion to be engaged with the first rack while the second pinion is disengaged from the second rack, and separately, to allow the second pinion to be engaged with the second rack while the first pinion is disengaged from the first rack. A biasing element may be provided, and configured to bias the axle to a first end of the elongated slot, such that the second pinion is engaged with the second rack. A lever may be attached to the housing and configured to be operable by a user to urge the axle, against the biasing element, to a second end of the elongated slot opposite the first end, such that the first pinion is engaged with the first rack. Preferably, the lever is rotatably pinned to the housing. 
     In a different embodiment, the invention is a method of delivering a stent from a catheter sheath, the catheter being of a kind that includes a stent-engagement member, and a sheath surrounding the stent. The method comprises rolling a thumbwheel in one direction and, simultaneously with rolling the thumbwheel in one direction, both advancing the stent-engagement member and retracting the sheath. In some embodiments, advancing the stent-engagement member and retracting the sheath includes advancing the stent-engagement member by a first distance and retracting the sheath by a second distance, wherein the first distance is different from the second distance, where the first distance may be larger than the second distance. 
     In yet another embodiment, the invention is a method of delivering a stent from a catheter sheath, the catheter being of a kind that includes a stent-engagement member, and a sheath surrounding the stent. The method comprises engaging the stent-engagement member to be operably connected with a thumbwheel. The thumbwheel is rolled, thereby advancing the stent-engagement member. The stent-engagement member is disengaged from the thumbwheel, the sheath is engaged to be operably connected with the thumbwheel, and the thumbwheel is rolled, thereby retracting the sheath. In some embodiments, engaging the stent-engagement member includes disengaging the sheath. In some embodiments, engaging the sheath includes disengaging the stent-engaging member. In some embodiments, rolling the thumbwheel to advance the stent-engaging member, and rolling the thumbwheel to retract the sheath includes rolling the thumbwheel in the same direction in each instance of rolling the thumbwheel. In some embodiments, engaging the stent-engaging member includes operating a trigger attached to a housing of the catheter. Preferably, engaging the sheath includes operating a trigger attached to a housing of the catheter. 
     These and other advantages of the invention will become apparent when the specification is read in conjunction drawings and the detailed descriptions of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present disclosure are described with reference to the drawings of certain embodiments, which are intended to illustrate certain embodiments and not to limit the invention. 
         FIG. 1  is a schematic top view, partially cut away, of a handle for a stent delivery catheter in which features of the invention are exemplified. 
         FIG. 2  is a schematic sectional side view, partially cut away, taken substantially along line B-B of  FIG. 1 , in which further features of the embodiment of  FIG. 1  are exemplified. 
         FIG. 3  is a schematic sectional end view, taken substantially along line A-A in  FIG. 2 . 
         FIG. 4  is a schematic sectional view of a distal end of the stent delivery catheter of which the handle is shown in  FIG. 1 , and in which further features of the invention are exemplified. 
         FIGS. 5A-5C  show schematic views of a stent emerging from a sheath inside a body lumen, following features of the invention. 
         FIG. 6  is a schematic top view, in partial cut away, of a handle for a stent delivery catheter showing a different embodiment of the invention. 
         FIG. 7  is a schematic sectional view, in partial cutaway, taken substantially along the line B-B in  FIG. 6 . 
         FIG. 8  is a schematic side view of the embodiment shown in  FIG. 6 . 
         FIG. 9  is a sectional end view, taken substantially along the line A-A in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     Although certain embodiments and examples are described below, those of skill in the art will appreciate that the invention extends beyond the specifically disclosed embodiments and/or uses and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the invention herein disclosed should not be limited by any particular embodiments described below. 
     Certain general aspects of stent delivery systems are described in U.S. patent application Ser. No. 13/118,325, published as U.S. Patent Pub. No. 2011/0295354, which is incorporated herein by reference in its entirety. The novel features of the invention are described in the present application. 
     In one embodiment, the invention is configured to provide advantageous control over both stent delivery, and sheath retraction. 
     In furtherance of enabling the stated result, reference is first made to  FIGS. 1-3 , where there is exemplified a handle  700  of a deployment catheter, preferably formed from two mirror image half sections of plastic or polymer to form a housing  701 , joined down a center line in a known fashion. The handle has a cavity  703  into which certain actuation elements are inserted. The actuation elements of one embodiment may include a thumbwheel  702 , mounted on an axle  704  so as to be rotationally fixed to the axle. The ends of the axle may be mounted in circular bearings  705  in sidewalls of the housing  701 , so that the thumbwheel is suspended inside the cavity  703 . On each side of the thumbwheel, and also mounted on the axle  704  within the cavity  703 , are two pinions, or gears  706 ,  708 . Both pinions are also rotationally fixed to the axle  704  so that they rotate in unison with the thumbwheel  702 . As explained in more detail below, the pinions may have different diameters, to produce different mechanical advantages when the thumbwheel is rotated. 
     Inside the cavity  703 , two racks are provided. A first rack  710  is positioned to slide axially within the cavity. To this end, upper and lower tracks (not shown in the figures) may be provided to protrude from side walls of the housing and to confine and limit the passage of the two racks to a backward and forward sliding motion. The first rack  710 , having a set of teeth, is positioned to be in geared connection with the teeth of the first pinion  706 , so that rotation of the thumbwheel  702  imparts a rotation to the first pinion, and hence a linear motion to the first rack  710 . A second rack  712  is similarly provided to be in geared connection with the second pinion  708 . Notably, however, the first rack  710  is positioned to be on the top of the first pinion  706 , while the second rack  712  is positioned to be on the bottom of the second pinion  708 . Thus, it will be appreciated that a single rotation of the thumbwheel  702  will cause the two racks to move in opposite directions from each other. For example, in the exemplary  FIGS. 1-3 , an anti-clockwise rotation of the thumbwheel will result in a backward (proximal) motion of the first rack  710 , but it will also result in a forward (distal) motion of the second rack  712 . It will also be appreciated that, due to the difference in diameter between the first pinion  706  and the second pinion  708 , the mechanical advantage imparted to the two racks will be different, and the speed of their motions (besides being in opposite directions) will be different under a uniform motion of the thumbwheel. This aspect of the configuration of the embodiment may be utilized to advantageous effect as will be more fully explained below. 
     Attached to each rack is a tie. Thus, a first tie  714  is attached to the first rack  710 . A second tie  716  is attached to the second rack  712 . Thus, linear movement of each rack imparts an equivalent movement to each associated tie. Each tie, in turn extends through a central portion of the catheter according to known principles. The central portion of the catheter is not shown in the figures, but will be readily envisaged by those of ordinary skill. 
     Turning to  FIG. 4 , this figure shows, schematically in section, the distal end portion of the stent delivering catheter. It shows the relationship between a stent engaging member  45 , a sheath  20 , and the two ties  714  and  716  which have been previously described in the context of the handle. As noted, the ties extend as linear elements all the way from the handle  700  of the catheter to the distal end portion shown in  FIG. 4 . As seen in  FIG. 4 , a self expanding stent  30  is confined within the sheath  20 . A stent engaging member  45  (which may comprise a pair of opposite stent engaging members  45 ) is positioned within the internal lumen of the stent  30 . The stent engaging members comprise sharp forwardly pointing hooks, and are mounted on spring loaded arms or biasing elements  40  that are shaped to urge the stent engaging members radially outwardly, so as to engage with the fabric of the self expanding stent. Distal movement of the stent engaging members  45  will cause the stent engaging members to lodge in the fabric of the stent, and move the stent distally, as may be envisaged with reference to  FIG. 4 , which shows the sharp points of the stent engaging member  45  partially distorting the proximal fabric of the stent. As the stent is forced distally to emerge from the sheath  30 , the distal tip  31  of the stent expands radially outwardly, as seen in  FIG. 4 . The stent-engaging member  45  of  FIG. 4  may be similar to that exemplified and described with reference to  FIG. 8 , of application Ser. No. 13/118,325 (incorporated by reference). 
     Also shown in  FIG. 4  is a chord  70  that may be used to pull the stent back into the sheath in the event of a mishap, and the surgeon elects to abort the procedure. The chord  70  is known in the art and is not further described herein. 
     In the present invention, the second tie  716  is operably connected to a stent-engaging member  45  via a biasing element  40 . It will be appreciated that linear movement of the second rack  712  via the thumbwheel will be followed by a corresponding and equal linear movement of the stent-engaging member  45 . 
     The first tie  714  is operably connected to the sheath  20  which surrounds the stent  30 . The connection between first tie  714  and sheath  20  is exemplified in  FIG. 4 . It will be appreciated that linear movement of the first rack  710  via the thumbwheel will be followed by a corresponding and equal linear movement of the sheath  20 . 
     In further description of  FIG. 4 , an outside guide catheter  750  may be provided to enclose the stent and its delivery mechanism during delivery of the catheter to the desired location in the vasculature of the patient. 
     It will be appreciated with reference to  FIG. 4  in combination with  FIGS. 5A-5C  that a distal movement of, let us say, X units of length by the stent-engaging element  45  will advance the stent in its collapsed configuration by X units of distance. However, when that length of stent emerges from the sheath  20 , the expanding stent will shorten in length so that the net increment in the length of the expanded portion of the stent is less than X units, say Y units. Thus, if the physician wishes for the stent that has emerged from the sheath to (a) remain anchored by its distal tip  31  in a fixed position within the vessel of the patient and, (b) at the same time, the physician wants to keep the proximal end of the catheter stationary, then he will need to ensure that the sheath is retracted by a distance equal to Y units. 
     This feature is demonstrated schematically in  FIG. 5A-5C .  FIG. 5A  shows the stent  30  and the sheath  20  are initially aligned at their distal tips before any advancement of the stent or retraction of the sheath. A reference point “R” is shown in the figures to indicate a schematic reference point in relation to the vessel wall “V” where the stent and sheath are in initial alignment with each other. Then, moving to  FIG. 5B , there is exemplified how if the stent  30  is advanced at the proximal end by a stent-engagement member  45  by a distance of X units, then the sheath must be withdrawn by Y units if the catheter as a whole is to be maintained motionless in relation to the body of the patient while, at the same time, maintaining the contact point of the stent tip  31  against the vessel wall “V” at a motionless point “P”. Significantly, because the stent expands as it emerges from the sheath, the distance Y must be less than the distance X. Then, moving to  FIG. 5C , there is exemplified how if the stent  30  is advanced at the proximal end by a stent-engagement member  45  by a distance of 2X units, then the sheath must be withdrawn by 2Y units if the catheter as a whole is to be maintained motionless in relation to the body of the patient while, at the same time, maintaining the contact point of the stent tip  31  against the vessel wall “V” at the motionless point “P”. 
     In one embodiment, the invention introduces a solution to automatically satisfy the geometric requirement described above. The solution is to provide first and second pinions that have differently sized diameters so that the ratio of the diameter of the first pinion  706  to the diameter of the second pinion  708  is Y:X. 
     It will be appreciated by those of ordinary skill that under these conditions, rolling the thumb wheel backward (anti-clockwise) as indicated in  FIG. 2  will result in the first rack  710  retracting a first distance, and the second rack  712  advancing a second distance, such that the ratio of the first distance to the second distance is Y:X. By corollary, under the structure described, the sheath  20  will retract by the first distance, and the stent engagement member  45  will advance by the second distance, in the same ratio. Thus, it will be apparent that if the surgeon holds the catheter in a stationary position in relation to the body of the patient, and rolls the thumbwheel  702  anti-clockwise, then the stent  30  will advance and the sheath  20  will retract by amounts respectively that conveniently allow the surgeon to hold the catheter stationary, while the stent emerges from the sheath without dislodging the connection between the distal tip  31  of the stent and the vessel wall “V” as seen in  FIGS. 5A-5C . 
     The foregoing is an advantageous result, because the physician user may confidently move the thumbwheel and hold the catheter stationary in relation to the patient&#39;s body, knowing that the tip of the stent will remain in stationary contact with the vessel wall, and will not slide against the vessel wall with potentially catastrophic effects in the form of dislodging plaque from the wall. 
     In another embodiment, features of the previous embodiment may be utilized, along with additional or modified structure that will now be described. Elements of  FIG. 6 - FIG. 9  exemplify these additional or modified structural features, and they may be utilized to give the physician a different type of control over the advancement of the stent and retraction of the sheath than that described above. In this embodiment, the axle  704  may be mounted within an elongate slot  718  (seen in  FIGS. 8, 9 ), which extends vertically, in opposite walls of the housing  701 . Thus, the assembly that includes the axle with the thumbwheel and two pinions mounted on the axle can be elevated or depressed by a small distance in relation to the housing. In this embodiment, the first rack  710  and the second rack  712  are spaced slightly further apart from each other in a vertical direction than in the previous embodiment, so that only one pinion can be placed in contact with one rack at any given moment. In order to allow the physician to elect which rack should be engaged via the thumbwheel, a trigger  730  is provided. The trigger comprises a “Y” shaped structure with arms  732  that flank the housing  701 . The arms are fixed with pins  734  to the housing ( FIGS. 8 and 9 ), allowing the trigger to rotate beneath the housing. On each side of the housing, a vertically extending rod  736  is provided. At a lower end, each rod is fixed with a pin  738  to the trigger. At an upper end of each rod, the rod abuts the axle  704 . Above each end of the axle a biasing element  740 , preferably a spring, is located to bias the axle in a downward direction. Under this configuration, the physician user may pull the trigger  730  proximally with his forefinger. This action will elevate each rod  736 , and thus elevate the ends of the axle against the bias of the biasing elements  740 . Elevating the axle will urge the first pinion  706  into contact with the first rack  710 , but will disengage the second pinion  708  from the second rack  712 . Conversely, if the physician user releases his pull on the trigger, the biasing elements  740  will bias the axle downward in the absence of any force opposing such bias. Downward movement of the axle  704  results in engagement of the second pinion  708  with the second rack  712 , but disengagement of the first pinion  706  from the first rack  710 . 
     Thus, it will be appreciated that this modified structure gives the physician user a choice in which he may select to engage the thumb wheel  702  with either the stent-engaging member  45  for advancement of the stent, or alternatively the sheath  20  for retraction of the sheath. It will be understood that by providing an election to the physician user results in a delivery mechanism that operates under a different principle than the foregoing embodiment. Here, the physician may wish to follow more closely the actual rate of delivery of the stent through the sheath using conventional means such as radiopaque markers, and if his observation causes him to conclude, for example, that the stent is in fact becoming compressed within the sheath rather than emerging from the end of the sheath, he may decide to pull the sheath back a little faster. Additionally, the structure of this embodiment allows the user to repeatedly advance the stent without retracting the sheath, but to subsequently retract the sheath without advancing the stent. The present invention gives the user this option, which may be required by the user under conditions in which the geometry of the vasculature requires a repeated advancement of the stent rather than a single forward movement of the stent. 
     Thus there is described a delivery system that provides advantages over prior art delivery systems, and addresses needs in the art. 
     Although this invention has been disclosed in the context of certain embodiments and examples, it will be understood by those skilled in the art that the invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. In addition, while several variations of the embodiments of the invention have been shown and described in detail, other modifications, which are within the scope of this invention, will be readily apparent to those of skill in the art based upon this disclosure. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the invention. It should be understood that various features and aspects of the disclosed embodiments can be combined with, or substituted for, one another in order to form varying modes of the embodiments of the disclosed invention. Thus, it is intended that the scope of the invention herein disclosed should not be limited by the particular embodiments described above.