Abstract:
The invention relates to a delivery system for delivering a stent (S) into a body vessel of a patient, comprising a flexible catheter tube ( 3 ) having a proximal and a distal end for delivering the stent (S) to a predetermined location in the body vessel and a catheter tip ( 1 ) having a longitudinal direction, which is disposed at the distal end of the catheter tube ( 3 ). The catheter tip ( 1 ) has a stent chamber ( 150 ) to receive the stent ( 1 ). The catheter tip has a first pressure chamber ( 20, 22 ). In the catheter tube ( 3 ) a first fluid channel ( 31 ) extends from the proximal end to the first pressure chamber ( 20, 22 ) of the catheter tip ( 1 ). The volume of the first pressure chamber ( 20, 22 ) can be enlarged by delivering a first fluid from the first fluid channel ( 31 ) to the first pressure chamber ( 20, 22 ), such that the stent (S) is released from the stent chamber ( 150 ) at the predetermined location in the body vessel. According to the invention the catheter tip ( 1 ) has a second pressure chamber ( 21, 23 ), wherein in the catheter tube ( 3 ) a second fluid channel ( 32 ) extends from the proximal end to the second pressure chamber ( 21, 23 ) and wherein the volume of the second pressure chamber ( 21, 23 ) can be enlarged by delivering a second fluid from the second fluid channel ( 32 ) to the second pressure chamber ( 21, 23 ), such that a partially released stent (S) can be returned from the predetermined location in the body vessel into the stent chamber ( 150 ). This delivery system according to the invention makes it possible to release a stent (S) at a well-defined location and also to surround same again relatively atraumatically and to reposition same in situ.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a stent applicator, i.e. a delivery system for guiding a stent in a body of a patient in accordance with the preamble of patent claim  1 , and to a catheter head. 
       PRIOR ART 
       [0002]    Stents and applicators for inserting and unfolding stents are known with many different embodiments in the prior art. A stent is usually a cylindrical prosthesis, which is introduced into a vessel or a lumen of a patient and radially expanded there. Stents are employed in very different regions, for example as heart valve stents, coronary stents or peripheral stents. In preferred embodiments, the stents have a self-expanding embodiment, particularly by means of a spring force. For example balloon-expanded stents are also known. 
         [0003]    Catheters with a specifically embodied catheter tip are usually used as a delivery system, which is also referred to as a stent applicator. This tip surrounds the compressed stent and it is embodied in such a way that, as stipulated by the medical practitioner, it can release the stent at the desired position. It is necessary for this catheter, and in particular this tip, to have an external diameter which is as small as possible. 
         [0004]    Stent applicators which have a mechanism with pull and push rods are very widespread. 
         [0005]    However, the prior art has also disclosed stent applicators which are actuated by a fluid in order to release the stent. Examples for this include EP 0 746 375, EP 1 565 227, WO 2005/115524, EP 0 705 578, WO 2008/153765, U.S. Pat. No. 6,113,608, EP 1 208 816, U.S. Pat. No. 6,056,759, U.S. Pat. No. 6,027,474 and WO 2006/096229. 
         [0006]    Furthermore, WO 2009/011866 discloses a delivery system for stents with a double-acting cylinder arranged in the manipulation instruments of the catheter. This system is intended to simplify the unfolding of the stent. 
         [0007]    These stent applicators enable a release of a stent at the desired point within a body vessel. However, they are unsuitable for re-sheathing a partly or wholly released stent, repositioning it or completely removing it from the body again. 
         [0008]    However, such repositioning or removal of the stent is often desired. By way of example, the stent may be dislocated during the implantation on the beating heart, and so it once again has to be positioned anew. 
       SUMMARY OF THE INVENTION 
       [0009]    It is therefore an object of the invention to develop a delivery system for a stent which enables not only releasing, but also a re-sheathing of the stent. 
         [0010]    This object is achieved by a delivery system having the features of patent claim  1 . 
         [0011]    The delivery system according to the invention for delivering a stent in a body of a patient, for example in a vessel or a lumen, comprises a flexible catheter tube with a proximal and a distal end for delivering the stent to a predetermined point in the body vessel and a catheter tip with a longitudinal direction, which is arranged at the distal end of the catheter tube. The catheter tip has a stent chamber for receiving the stent. The catheter tip has a first pressure chamber. A first fluid channel extends in the catheter tube from the proximal end to the first pressure chamber of the catheter tip. A volume of the first pressure chamber is enlargeable by delivering a first fluid from the first fluid channel to the first pressure chamber, wherein, as a result thereof, the stent is releasable from the stent chamber at the predetermined point in the body vessel. According to the invention, the catheter tip has a second pressure chamber. A second fluid channel extends in the catheter tube from the proximal end to the second pressure chamber. A volume of the second pressure chamber is enlargeable by delivering a second fluid from the second fluid channel to the second pressure chamber, as a result of which a partly released stent is retractable into the stent chamber from the predetermined point in the body vessel. 
         [0012]    In this text, “proximal” and “back” mean facing the medical practitioner and facing away from the patient. In this text, “distal” and “front” mean facing away from the medical practitioner and facing the patient. 
         [0013]    The stent applicator according to the invention enables not only precise positioning of a stent in a vessel of a patient, but also the retraction thereof in situ. It is only possible to retract the stent under all circumstances in the partly released stage. Retracting and re-sheathing a completely released stent is dependent on the shape and type of the stent and the connection thereof to the stent applicator, but it is also possible using the mechanism according to the invention. 
         [0014]    Thanks to the system according to the invention, the stent can be positioned precisely at the position at which it already lay in a sheathed condition. Unlike what is conventional in the prior art, it is not displaced forward. Rather, the sheath thereof is pulled away to the back. This enables precise positioning of the stent within the body opening or the body channel. 
         [0015]    In preferred embodiments, the delivery system has a double-action hydraulic cylinder, which releases and re-sheaths the stent. Preferably, the two pressure chambers in the catheter tip are not connected to one another, i.e. they do not exchange fluids. Preferably, the whole system does not interchange the two fluids. 
         [0016]    The catheter tube is preferably embodied as a multi-lumen catheter tube which has at least two lines separate from one another and preferably one lumen for a guide wire. This tube at the same time serves as a flexible plunger rod for displacing the at least one catheter plunger arranged in the catheter tip or said tube acts as a plunger itself. 
         [0017]    In preferred embodiments, the catheter tube no longer moves during the release and re-sheathing of the stent after it has brought the catheter tip to the predetermined point in the body vessel. In other embodiments, only an inner part of the catheter tube remains immobile and an outer part moves during the release and/or during the re-sheathing of the stent. 
         [0018]    In preferred embodiments, the catheter tip has a first sleeve, in which the first pressure chamber is arranged, and a second sleeve, in which the second pressure chamber is arranged. 
         [0019]    Preferably, the catheter tube has a guide lumen for passing a guide wire therethrough, wherein the first sleeve and the second sleeve are displaceable relative to this guide lumen and wherein the guide lumen remains unchanged in terms of its location in respect of the predetermined point and the first and second sleeve move relative to the predetermined point. 
         [0020]    In a preferred embodiment, the first sleeve and the second sleeve are arranged in succession in the longitudinal direction, wherein, in the longitudinal direction, they are connected to one another in a non-displaceable manner relative to one another. 
         [0021]    Preferably, the first sleeve and the second sleeve are displaceable together relative to the catheter tube in the longitudinal direction. 
         [0022]    So that the catheter tip can also be pushed around tight bends without traumatizing the surrounding tissue when it is pushed through body channels, the catheter tip preferably has at least one flexible region such that it is flexible transverse to the longitudinal direction. This renders it possible to embody the catheter tip in a relatively long manner and, in particular, arrange the two pressure chambers in succession. 
         [0023]    In a preferred embodiment, a first catheter plunger which forms a distal end of the first pressure chamber is arranged at the distal end of the catheter tube, wherein the first sleeve is displaceable in the longitudinal direction in a sealing sliding manner relative to this first catheter plunger, wherein the first pressure chamber has a first sleeve base which forms a proximal end of the first pressure chamber, wherein the first sleeve base is securely connected to the first sleeve and arranged in a sealing sliding manner around the catheter tube, wherein a second catheter plunger which forms a proximal end of the second pressure chamber is arranged on the catheter tube, wherein the second sleeve is displaceable in the longitudinal direction in a sealing sliding manner relative to this second catheter plunger, wherein the second pressure chamber has a second sleeve base which forms a distal end of the second pressure chamber, and wherein the second sleeve base is securely connected to the second sleeve and arranged in a sealing sliding manner around the catheter tube. 
         [0024]    This embodiment can be embodied with a very narrow diameter. 
         [0025]    In another preferred embodiment, the second sleeve is arranged within the first sleeve and in a manner displaceable relative to the latter. Preferably, the catheter tube in this embodiment has an outer tube portion and an inner tube portion arranged therein, wherein the outer tube portion is displaceable in the longitudinal direction relative to the inner tube portion, wherein the first sleeve is securely connected to the outer tube portion and displaceable in the longitudinal direction in a sealing sliding manner in relation to the inner tube portion, wherein a catheter plunger is present, which plunger is securely connected to the inner tube portion and displaceable in the longitudinal direction in a sealing manner relative to the inner sleeve, wherein the second sleeve is sealed at the proximal end thereof by a sleeve base, which is securely connected to the former and which is displaceable in the longitudinal direction in a sealing sliding manner relative to the first sleeve, wherein the first pressure chamber is embodied between the sleeve base and the catheter plunger, and the second pressure chamber is embodied between a proximal end of the first sleeve and the sleeve base. This embodiment has a relatively short length. 
         [0026]    In both and further embodiments, the catheter plunger closest to the distal end of the catheter tube preferably forms a distal end of the stent chamber. That is to say the stent chamber is arranged in front of the two pressure chambers. 
         [0027]    In both and further embodiments, the catheter tip, at the distal end thereof, has a catheter head in the form of spring leaves, wherein the spring leaves are inclined with respect to one another in a petaloid or bud-shaped manner and at least partly close an opening to the stent chamber. Preferably, each spring leaf has an inwardly directed protrusion. It is also possible to use other shapes of atraumatic catheter heads. 
         [0028]    The delivery system preferably has a manipulation part which is arranged at the proximal end of the catheter tube, wherein, by means of the manipulation part, the stent can be released from, and returned back into, the stent chamber at the predetermined point in the body vessel. 
         [0029]    In a preferred embodiment, the manipulation part has a hydraulic apparatus with a first fluid chamber with a first plunger and a second fluid chamber with a second plunger, wherein a proximal end of the first fluid lumen is connected to the first fluid chamber and a proximal end of the second fluid lumen is connected to the second fluid chamber. Here, preferably, the first plunger is actuatable by means of an actuation lever and the second plunger is actuatable by means of a rotary knob. 
         [0030]    It is a further object of the invention to develop a catheter head which is as atraumatic as possible. 
         [0031]    This object is achieved by a catheter head having the features of claim  17 . 
         [0032]    The catheter head according to the invention has spring leaves which are inclined with respect to one another in a petaloid or bud-shaped manner and which open from the inside to the outside by pressure. 
         [0033]    Preferably, the spring leaves automatically spring back into the bud shape thereof after releasing a stent. 
         [0034]    In order to simplify the release of a stent and also, where applicable, a re-sheathing, the spring leaves preferably have inwardly directed protrusions. 
         [0035]    The risk of traumatization can be further reduced if the spring leaves are together surrounded by a flexible protection tube which extends outwardly when the spring leaves are opened and which is elastic enough to rest against the spring leaves again when these are closed again. 
         [0036]    This catheter head is suitable for various applications, but in particular for use in a delivery system as described in this text. 
         [0037]    Further embodiments are specified in the dependent claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0038]    Preferred embodiments of the invention are described below on the basis of the drawings, which merely serve for explanatory purposes and are not intended to be interpreted as being restrictive. In the drawings: 
           [0039]      FIG. 1  shows a perspective illustration of a stent applicator according to the invention in a first embodiment; 
           [0040]      FIG. 2  shows a longitudinal section through the stent applicator in accordance with  FIG. 1  with a partly released stent; 
           [0041]      FIG. 3  shows a longitudinal section through individual regions of the stent applicator in accordance with  FIG. 1  with a sheathed stent; 
           [0042]      FIG. 4  shows a longitudinal section through individual regions of the stent applicator in accordance with  FIG. 1  with a partly released stent; 
           [0043]      FIG. 5  shows a magnified illustration of the front region in accordance with  FIG. 3 ; 
           [0044]      FIG. 6  shows a magnified illustration of the front region in accordance with  FIG. 4 ; 
           [0045]      FIG. 7  shows a perspective illustration of a stent applicator according to the invention in a second embodiment; 
           [0046]      FIG. 8  shows a longitudinal section through a front region of the stent applicator with a sheathed stent in accordance with  FIG. 7 ; 
           [0047]      FIG. 9  shows a longitudinal section through a front region of the stent applicator in accordance with  FIG. 7  with a completely sheathed stent; 
           [0048]      FIG. 10  shows the stent applicator in accordance with  FIG. 9  with a partly released stent; 
           [0049]      FIG. 11  shows the stent applicator in accordance with  FIG. 9  with a stent in an advanced state of release; 
           [0050]      FIG. 12  shows the stent applicator in accordance with  FIG. 9  with a partly re-sheathed stent; 
           [0051]      FIG. 13  shows the stent applicator in accordance with  FIG. 9  with a stent in an advanced state of sheathing, analogous to  FIG. 7 ; 
           [0052]      FIG. 14  shows the stent applicator in accordance with  FIG. 9  when re-sheathing the inner sleeve and 
           [0053]      FIG. 15  shows the stent applicator in accordance with  FIG. 9  in the new initial position thereof. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0054]      FIGS. 1 to 6  depict a first exemplary embodiment of a stent applicator according to the invention. It has a manipulation instrument in the form of a pistol-shaped, rigid handheld part  4 . This handheld part  4  has a main body  40  with, formed thereon, a handle  41  for holding the instrument in the hand of the medical practitioner or user. An actuation lever  42  can be pulled towards the handle  41  by the fingers of the hand which holds the handle  41 . 
         [0055]    A flexible catheter tube  3  is fastened to the handheld part  4 . Preferably, it is detachably connected thereto. However, it can also be connected securely or in a manner not detachable in a nondestructive manner to the handheld part  4 . The catheter tube  3  is manufactured from a flexible material, in particular Pebax. It has a length matched to the field of application of the stent applicator. In the figures, it is depicted with an interruption in its length. 
         [0056]    At the free end thereof facing away from the handheld part  4 , the catheter tube  3  ends in a catheter tip  1 . In this example, this catheter tip  1  has a relatively long embodiment, as is identifiable in  FIG. 1 . Therefore, the catheter tip  1  preferably has one or more flexible regions  160 , at which it can be bent. As a result of this, the catheter tip  1  can also be guided around tight bends through body channels of the patient. 
         [0057]    A stent S which can be released by means of the handheld part  4  is arranged in the catheter tip  1 . In  FIG. 1 , the stent S is completely held within the catheter tip  1  and therefore not visible. In  FIG. 2 , it is practically completely released, wherein it is still held in the catheter tip  1  with the back end thereof facing the handheld part  4 . 
         [0058]    Here, the stent S is depicted schematically. Preferably, this is a self-expanding stent S. It can have any form. By way of example, it can consist of a flexible tube-shaped mesh. Various other forms are known from the prior art. By way of example, the stent can also be provided with a graft, wherein the graft may have flaps or no flaps. 
         [0059]    The stent is preferably held in the catheter tip, for example by virtue of being detachably hung in hooks (which are not depicted in this exemplary embodiment). Other types of retention means can also be used. 
         [0060]    As is identifiable in  FIG. 2 , the actuation lever  42  acts on a first plunger rod  421 . This plunger rod  421  is part of a hydraulic apparatus  46 , which is arranged in the handheld part  4 . A protruding lug is embodied at the upper end of the actuation lever  42 , which lug penetrates the housing of the main body  40  to the outside and moves as a display pin  420  along a display slit  45  depending on the movement of the actuation lever  42 . As a result, as is identifiable in  FIG. 1 , the current function of the handheld part  4  can be read from the outside. 
         [0061]    The rear end of the handheld part  4  is provided with a rotary knob  43 . This rotary knob  43  turns a second plunger rod  430  of the hydraulic apparatus  46 . This second plunger rod  430  is provided with a thread  431  or it is embodied over a portion as a circumferential toothed rack. A pickup  44  acts on this portion, which pickup engages into the thread  431  or the toothed rack and thus displaces the plunger rod forward in the direction of the catheter tip  1 . 
         [0062]    As is easily identifiable in  FIG. 3 , the hydraulic apparatus  46  has a first and a second fluid chamber  460 ,  461 , which are arranged next to one another. The first plunger rod  421  ends in the first fluid chamber  460  with a first plunger  470 ; the second plunger rod  430  ends in the second fluid chamber  461  with a second plunger  471 . In the respective fluid chamber  460 ,  461 , both plungers  470 ,  471  are displaceable in the longitudinal direction by means of the associated plunger rod  421 ,  430 , wherein they are mounted in a sealing manner in relation to an outer housing  464  of the hydraulic apparatus  46 . 
         [0063]    In the housing  464  of the hydraulic apparatus  46 , a first fluid channel  462  leads from the first fluid chamber  460  to a first entrance opening of a first fluid delivery lumen  31  of the catheter tube  3 . A second fluid channel  463  leads from the second fluid chamber  461  to a first entrance opening of a second fluid delivery lumen  32  of the catheter tube  3 . 
         [0064]    The catheter tube  3  furthermore has a central lumen  30 , through which a guide wire  5  can be guided from the handheld part  4  to the catheter tip  1  and therebeyond. As is identifiable in  FIG. 1 , the proximal end of the guide wire is guided out of the handheld part  4  such that it can be held manually by the user. 
         [0065]    The catheter tip  1  is easily identifiable in  FIG. 5 . It has two sleeves  15 ,  16  arranged in succession, which preferably have different external diameters. The two sleeves  15 ,  16  preferably have a non-elastic but flexible embodiment. They preferably consist of a fiber-reinforced plastic, e.g. reinforced Pebax. The first sleeve  15  forms a stent chamber  150  for receiving the stent S. The internal diameter of the first sleeve  15  is dimensioned in such a way that the stent S can be held in the stent chamber  150  in the radially compressed state. 
         [0066]    The front end of the first sleeve  15  facing away from the handheld part  4  merges into spring leaves  10 . They form a head part of the catheter. They are preferably embodied integrally with the first sleeve  15 . These spring leaves  10  close the front free end of the first sleeve  15  in a petaloid manner. Each spring leaf  10  preferably has an inwardly directed protrusion  100 . 
         [0067]    The first sleeve  15  is connected in a sealed and secured manner to the second sleeve  16  by way of a first sleeve base  12 . The second sleeve  16  preferably has a smaller external diameter than the first sleeve  15 . A second sleeve base  13  is arranged in a secure position inside the second sleeve  16 , preferably in the central region thereof as seen in the longitudinal direction. This second sleeve base  13  subdivides the inner space of the second sleeve into two chambers. This sleeve base  13  preferably penetrates the wall of the second sleeve  16 . 
         [0068]    The second sleeve base  13  is arranged at a distance from the first sleeve base  12 . The region lying therebetween is embodied as a flexible region  160 . It is preferably manufactured from an elastic material, for example silicone. 
         [0069]    The first and second sleeve base  12 ,  13  can also directly adjoin one another or be formed by a common, in particular integral, component. They preferably have a flexible embodiment in these variants such that they can themselves form the hinge or the flexible region  160 . 
         [0070]    The catheter tube  3  penetrates the second sleeve  16  and ends in the first sleeve  15 . A first catheter plunger is arranged securely at the free end thereof. The first catheter plunger  11  is situated in the interior of the first sleeve  15  and forms a handheld part-side wall of the stent chamber  150 . The first catheter plunger  11  is held in the first sleeve  15  in a manner displaceable thereto. Here, it is sealed with a first sealing ring  110  in relation to the inner wall of the first sleeve  15 . 
         [0071]    The space between the first catheter plunger  11  and the first sleeve base  12 , the size of which is changeable, forms a first pressure chamber  20 , the functionality of which will be explained below. The first fluid lumen  31  of the catheter tube  3  ends in this first pressure chamber  20 . The lumen opening leading into this first pressure chamber  20  is provided with the reference sign  310 . As a result, a line connection is provided from the first fluid chamber  460  in the handheld piece  4  to the first pressure chamber  20  via the catheter tube  3 . This system is filled with a first fluid, preferably a liquid. In particular, a saline solution, a contrast agent or other biocompatible liquids are suitable as a liquid. The liquid is preferably highly viscous in order to ensure the tightness of the system. 
         [0072]    Furthermore, a second catheter plunger  14  is securely arranged on the catheter tube  3 . It is held displaceably in the longitudinal direction within the second sleeve  16 , with it also being sealed in relation to the inner wall of the second sleeve  16  by way of at least one second sealing ring  140 . A second pressure chamber  21  is formed between this second catheter plunger  14  and the second sleeve base  13 . The second fluid lumen  32  of the catheter tube ends in a second lumen opening  320 , which leads into this second pressure chamber  21 . Therefore, a line is formed between the second fluid chamber  461  in the handheld part  4  and the second pressure chamber  21  by way of the catheter tube  3 . This system is likewise filled with a second fluid, preferably a liquid, in particular a highly viscous liquid. The same examples can be provided as above. Both systems are preferably filled with the same type of fluid. However, the fluids of the two systems do not mix with one another. 
         [0073]    The catheter tube  3  penetrates the first and the second sleeve base  12 ,  13  and is displaceable in the longitudinal direction relative to these. The first sleeve base  12  is sealed in relation to the outer jacket of the catheter tube  3  by way of a sealing ring  120 . 
         [0074]    The more precise mode of action of the hydraulic apparatus  46  with the double action cylinder is identifiable in the overview of  FIGS. 3 to 6 . In  FIGS. 3 and 5 , the stent S is arranged in the catheter tip and completely sheathed. The first plunger  470  is situated in the retracted position and the display pin  421  visible in  FIG. 2  is situated at the rear location, i.e. different to what is depicted in  FIG. 2 . The first fluid chamber  460 , which is formed by the first cylinder, is filled with the first fluid. The volume of the first pressure chamber  20  is reduced to a minimum. The first sleeve base  12  is preferably drawn near to the first catheter plunger  11  as far as a spacer  121  in the first pressure chamber  20 . 
         [0075]    In this position, the second piston  471  is situated at the front, catheter-side stop of the second fluid chamber  461 . The second fluid is predominantly in the second pressure chamber  21 . The latter is preferably extended to the maximum thereof, i.e. the second catheter piston  14  is situated at the handheld part-side end of the second sleeve  16  at the maximum distance from the second sleeve base  13 . 
         [0076]    This situation is referred to as “loaded”. The actuation lever  42  of the handheld part  4  is not actuated. 
         [0077]    If the actuation lever  42  now is actuated, i.e. pulled toward the handle  41 , the first plunger rod  421  pushes the first plunger  470  in the forward direction in the cylinder and the first fluid is guided into the first pressure chamber  20 . The display pin  420  is pushed forward together with the first actuation rod  421  and now shows, as depicted in  FIG. 2 , the “released” situation of the stent S. This situation is depicted in  FIGS. 4 and 6 . The first sleeve base  12  arranged in a displaceable manner around the catheter tube  3  is pushed backward in the direction of the handheld part  4  and pulls or pushes the first and second sleeve  15 ,  16  backward. 
         [0078]    Since the stent S rests on the first catheter plunger  11 , the spring leaves  10  impact on the latter and open outwardly. They then slide over the stent S such that the latter is released. The released region of the stent S thereupon unfolds, preferably independently, the material of the stent S relaxes and the stent S affixes itself in the anatomical structure of the region of use, preferably by residual compression or residual pretension. 
         [0079]    The second sleeve  16  slides over the second catheter plunger  14  and the second sleeve base  13  thus approaches said plunger  14  up to a spacer  131 . As a result, the volume in the second pressure chamber  21  is reduced and the second fluid is pressed back into the second fluid chamber  461  in the handheld part  4 . The second piston  471  is moved backward. To this end, the pickup  44  in the handheld part  4  is at a distance from the second actuation rod  430 , i.e. it is slightly pulled out of the main body  40  and therefore releases the toothed rack  431 . 
         [0080]    If the released or partly released stent S should now be retracted again into the catheter tip  1  and be repositioned or completely removed from the body of the patient, this is implemented by means of the rotary knob  43  of the handheld part  4 . To this end, the pickup  44  engages with the thread  431  of the second actuation rod  430 . If the rotary knob  43  is rotated manually, the second actuation rod  430  is displaced forwardly. The second piston  471  presses again the second fluid back into the second pressure chamber  21  of the catheter tip  1  and the two sleeves  15 ,  16  are pushed forward again. The spring leaves  10  slide over the stent and recapture the latter. If necessary, they open up for this purpose. 
         [0081]    Here, the first fluid is, in turn, guided back from the first pressure chamber  20  into the first fluid chamber  460  until the “loaded” situation in accordance with  FIGS. 3 and 5  has once again been reached. As soon as the stent S is largely or completely re-sheathed, the position within the body of the patient can be corrected as desired and the stent S can subsequently be released again. 
         [0082]    Since high compressive forces are required for this re-sheathing of the stent S, a flower-like structure, in this case the spring leaves  10 , was developed for reducing the forces. There are preferably two, three, four, five or more spring leaves  10 . They preferably have a flexible embodiment relative to the first sleeve and automatically assume their closed position in accordance with  FIGS. 3 and 5 . They preferably consist of nitinol. During opening, a funnel is generated, like in the case of an opening flower. This funnel eases the sliding out, but also the re-sheathing as the stent is not pressed back into its compressed form over a sharp edge but via this funnel geometry. 
         [0083]    When the stent S is placed correctly, the delivery system can be pulled out of the patient body. Here, the spring leaves  10  at the catheter tip  1  reduce the risk of traumatization. Since they automatically spring back into their closed position after the stent S is released, they do not form an increased resistance when pulling out the system. 
         [0084]    The closed petaloid structure formed by the spring leaves  10  is preferably coated by an elastic protection tube  8 . The protection tube is preferably manufactured from silicone. This protection tube  8  has an open embodiment in the proximal and distal direction and is preferably adhesively bonded at the proximal end. A shrinking tube can also be used as protection tube  8 . The protection tube  8  completely surrounds the spring leaves  10 . When the spring leaves  10  are opening, said protection tube can be stretched enough to allow the stent S to be released. Moreover, it is sufficiently elastic to likewise retract during the renewed closing of the spring leaves  10  and thus securely surround these again, at least in an approximate manner. 
         [0085]    Arranging the pressure chambers  20 ,  21  of the catheter tip in succession in the longitudinal direction is advantageous in that the catheter tip or the catheter head can have a relatively small external diameter. The size of the stent S and the wall strength of the sleeve define this external diameter. 
         [0086]    Variations of this embodiment are possible. Thus, a single sleeve or multipiece sleeve, which is preferably flexible and in which the two plungers and the two bases or the one base are arranged, can be used instead of two sleeves  15 ,  16 , for example. 
         [0087]      FIGS. 7 to 15  depict a second embodiment of the delivery system according to the invention. In contrast to the first exemplary embodiment, the two pressure chambers are now arranged concentrically with one another. This is advantageous in that the catheter tip can have a shorter embodiment and therefore can be passed more easily about tight bends in the body channels. 
         [0088]    The delivery system has a catheter tip  1  with an external sleeve  17 . This catheter tip  1 , more precisely the outer sleeve  17 , can be closed off at the front, distal end by a catheter head  7 . The outer sleeve  17  preferably has a non-elastic but flexible embodiment. It is preferably made of fiber-reinforced plastic, e.g. reinforced Pebax. 
         [0089]    As is identifiable in  FIG. 7 , a flexible catheter tube  3 , preferably made of Pebax, is securely connected to the catheter tip  1 . At the rear, i.e. proximal, end thereof, the catheter tube is connected to a connector unit, preferably to two Y-connectors  6 ,  6 ′ arranged in succession. A guide wire  5  passes through the connector unit  6 ,  6 ′, the catheter tube  3 , the catheter tip  1  and the catheter head  7 , wherein said guide wire protrudes from a first connection part  61  of the connector unit, more precisely from the first Y-connector  6 . The guide wire  5  usually serves to insert the catheter tube  3  into a body channel of the patient. 
         [0090]    A second connection part  62  of the first Y-connector  6  serves to introduce a fluid into an inner tube portion  34  of a catheter tube  3  up to the catheter tip  1 . This is for example implemented by a manually or motor-driven syringe. Suitable fluids have already been specified above. 
         [0091]    The inner tube portion  34  passes through the second Y-connector  6 ′, more precisely a third connection part  63  of same, and is held therein in a manner displaceable in the longitudinal direction. A fourth connection part of the second Y-connector  6 ′ serves to bring a second fluid through an outer tube portion  33  of the catheter tube  3  up to the catheter tip  1 . In this example, the second fluid also extends completely separately from the first fluid. However, it preferably consists of the same substance. 
         [0092]      FIG. 8  shows a longitudinal section through the distal region of the delivery system. In this case, the catheter tube  3  is also a multi-lumen flexible tube. It has an outer tube portion  33  and an inner tube portion  34 . The inner tube portion  34  is displaceable in the longitudinal direction relative to the outer tube portion  33 . 
         [0093]    The catheter tube  3  has a central lumen  30  for receiving the guide wire  5 , which is displaceable in the longitudinal direction relative thereto. Furthermore, the tube  3  once again has two fluid lumens  31 ,  32 , which in this case are arranged concentrically around the central lumen  30 . The first, inner fluid lumen  31  is situated in the inner tube portion  34 . The second, outer fluid lumen  32  is formed by the cavity between outer and inner tube portion  33 ,  34 . 
         [0094]    The outer jacket of the catheter tip  1  is formed by the outer sleeve  17 . At the rear, proximal end of the outer sleeve  17 , the outer tube portion  33  of the catheter tube  3  is securely connected to this outer sleeve  17 . At this end, the outer sleeve  17  is otherwise embodied in a closed manner. The second fluid lumen  32  ends in a rear, proximal cavity of the outer sleeve  17  which forms a second pressure chamber  23 . 
         [0095]    An inner sleeve  18  is held in the outer sleeve  17  in a manner displaceable in the longitudinal direction. Said inner sleeve is sealed in relation to the outer sleeve by one or more sealing rings  170 . At the rear proximal end thereof, it is closed by a sleeve base  19  which is securely connected thereto. This sleeve base  19  is penetrated by the inner tube portion  34  of the catheter tube  3 . In the longitudinal direction, it is displaceable relative to the inner tube portion  34 , wherein it is sealed in relation to the inner tube portion  34  by a sealing ring  190 . 
         [0096]    Distally from this sleeve base  19 , the inner tube portion  34  penetrates a catheter plunger  35  which is securely connected to the inner tube portion  34  and displaceable in the longitudinal direction relative to the inner, and therefore also to the outer, sleeve  18 ,  17 . This catheter plunger  35  is sealed in relation to the inner sleeve  18  by a sealing ring  350 . It is also possible, as is depicted here, for there to be a plurality of sealing rings, in particular two sealing rings  350 . The plunger  35  can have an integral or multi-part embodiment. 
         [0097]    A first pressure chamber  22  is formed between the sleeve base  19  and the catheter plunger  35 . The first fluid lumen  31  ends in this first pressure chamber  22 . 
         [0098]    A stent chamber  150  for receiving the stent S is formed distally from the catheter plunger  35  in the inner sleeve  18 . In this case, the stent S is also only depicted schematically. It can have the conventional embodiments known from the prior art. 
         [0099]    The distal end of the catheter plunger  35  forms a proximal rear wall of the stent chamber  150 . The distal wall is formed by the catheter head  7 , which is securely connected to the catheter tube  3  and displaceable together with the latter. The catheter head  7  is dimensioned in such a way that it closes the distal end of the inner sleeve  18 . 
         [0100]    The mode of action of this delivery system is identifiable in  FIGS. 9 to 15 . 
         [0101]    In  FIG. 9 , the stent S is loaded in the stent chamber  150 , wherein the catheter tip  1  is closed by the catheter head  7 . 
         [0102]    In  FIG. 10 , the first fluid is now introduced into the first pressure chamber  22  by the first fluid lumen  31 . As a result, the outer and inner sleeve  17 ,  18  move backward, i.e. in the proximal direction, together with the outer tube portion  33 . The distal access to the inner sleeve  18  and also the stent S are released. The stent S can unfold. 
         [0103]      FIG. 11  depicts the state in which the front end of the sleeves  17 ,  18  have reached the catheter plunger  35  and therefore the first pressure chamber  22  has a maximum extent. The stent S is practically exposed, but it is still held by the retention means, in this case hooks  351 , of the piston  35 . 
         [0104]    If the stent S should now be repositioned in situ or even completely re-sheathed, the second fluid is now introduced into the second pressure chamber  23  by the second fluid lumen  32 . The latter extends towards the distal end and pushes the sleeve base  19  toward the distal end together with the inner sleeve  18  and therefore out of the outer sleeve  17 . This is depicted in  FIG. 12 . The inner sleeve  18  slides over the stent S and recaptures the latter. 
         [0105]    In  FIG. 13 , the sleeve base  19  has reached the plunger  35 , i.e. the second pressure chamber  23  has the maximum extent. The first fluid was once again pressed out of the first pressure chamber  22 . The first pressure chamber  22  has once again reached minimum size. The first fluid can also be actively removed from the first pressure chamber  22 . The inner sleeve  18  has again completely shifted over the stent S and the catheter head  7  closes the inner sleeve  18 . 
         [0106]    In accordance with  FIG. 14 , the inner sleeve  18  can now, together with the stent S, be re-sheathed by the outer sleeve  17  by virtue of the second fluid being removed from the second pressure chamber  23 . The removal of the fluid is preferably once again implemented manually or by way of motor-driven syringes or pumps. 
         [0107]    The situation in accordance with  FIG. 15  corresponds to that in accordance with  FIG. 9 , i.e. the catheter tip is loaded again, i.e. the stent is sheathed, and the pressure chambers are more or less empty and minimized in terms of volume. 
         [0108]    Variations of this embodiment are possible. Thus, for example, the spring leaves and, preferably, also the protection tube in accordance with the first example can be arranged at the inner sleeve instead of the conventional catheter head in accordance with  FIGS. 7 to 15 . Moreover, a similar handheld part in accordance with the first exemplary embodiment can also be used in place of the Y-connector. 
         [0109]    Thanks to the delivery system according to the invention, a stent can be released at a well-defined point, but also be re-sheathed relatively atraumatically and repositioned in situ. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 LIST OF REFERENCE SIGNS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  1 
                 Sleeve 
               
               
                   
                  10 
                 Spring leaf 
               
               
                   
                 100 
                 Protrusion 
               
               
                   
                  11 
                 First catheter plunger 
               
               
                   
                 110 
                 First sealing ring 
               
               
                   
                  12 
                 First sleeve base 
               
               
                   
                 120 
                 Second sealing ring 
               
               
                   
                 121 
                 Spacer 
               
               
                   
                 13 
                 Second sleeve base 
               
               
                   
                 131 
                 Spacer 
               
               
                   
                  14 
                 Second catheter plunger 
               
               
                   
                 140 
                 Third sealing ring 
               
               
                   
                  15 
                 First sleeve 
               
               
                   
                 150 
                 Stent chamber 
               
               
                   
                  16 
                 Second sleeve 
               
               
                   
                 160 
                 Flexible region 
               
               
                   
                  17 
                 Outer sleeve 
               
               
                   
                 170 
                 Sealing ring 
               
               
                   
                  18 
                 Inner sleeve 
               
               
                   
                  19 
                 Sealing ring 
               
               
                   
                 190 
                 Sealing ring 
               
               
                   
                  20 
                 First pressure chamber 
               
               
                   
                  21 
                 Second pressure chamber 
               
               
                   
                  22 
                 First pressure chamber 
               
               
                   
                  23 
                 Second pressure chamber 
               
               
                   
                  3 
                 Catheter 
               
               
                   
                  30 
                 Central lumen 
               
               
                   
                  31 
                 First fluid lumen 
               
               
                   
                 310 
                 First lumen opening 
               
               
                   
                  32 
                 Second fluid lumen 
               
               
                   
                 320 
                 Second lumen opening 
               
               
                   
                  33 
                 Outer tube portion 
               
               
                   
                  34 
                 Inner tube portion 
               
               
                   
                  35 
                 Catheter plunger 
               
               
                   
                 350 
                 Sealing ring 
               
               
                   
                 351 
                 Hook 
               
               
                   
                  4 
                 Handheld part 
               
               
                   
                  40 
                 Main body 
               
               
                   
                  41 
                 Handle 
               
               
                   
                  42 
                 Actuation lever 
               
               
                   
                 420 
                 Display pin 
               
               
                   
                 421 
                 First plunger rod 
               
               
                   
                  43 
                 Rotary knob 
               
               
                   
                 430 
                 Second plunger rod 
               
               
                   
                 431 
                 Teeth 
               
               
                   
                  44 
                 Locking device 
               
               
                   
                  45 
                 Display slit 
               
               
                   
                  46 
                 Hydraulic apparatus 
               
               
                   
                 460 
                 First fluid chamber 
               
               
                   
                 461 
                 Second fluid chamber 
               
               
                   
                 462 
                 First fluid channel 
               
               
                   
                 463 
                 Second fluid channel 
               
               
                   
                 464 
                 Housing 
               
               
                   
                 470 
                 First plunger 
               
               
                   
                 471 
                 Second plunger 
               
               
                   
                  5 
                 Guide wire 
               
               
                   
                  6 
                 First Y-connector 
               
               
                   
                  6′ 
                 Second Y-connector 
               
               
                   
                  61 
                 First connection part 
               
               
                   
                  62 
                 Second connection part 
               
               
                   
                  63 
                 Third connection part 
               
               
                   
                  64 
                 Fourth connection part 
               
               
                   
                  7 
                 Catheter head 
               
               
                   
                  8 
                 Protection tube 
               
               
                   
                 S 
                 Stent