Abstract:
A multi-sheath delivery catheter and method for introducing a prosthesis into a body lumen involving use of (a) an outer sheath adapted to contain a portion of the prosthesis and having an inner surface with a non-round cross-section; (b) a middle sheath slideably disposed at least partly within the outer sheath and adapted to contain another portion of the prosthesis, the middle sheath having a distal end with a first handle attached to it that has a non-round cross-section corresponding to and engaging the non-round cross-section of the inner surface of the outer sheath; and (c) a pusher slideably disposed at least partly within the middle sheath and adapted to engage the prosthesis, whereby relative rotational movement between the outer sheath and the middle sheath is prevented by virtue of the engagement of the non-round cross-section of the first handle with the non-round cross-section of the inner surface of the outer sheath. In another aspect, the invention provides a delivery catheter having a mechanism for sequentially retracting concentric tubes to deploy the prosthesis. In another aspect, the invention provides a mechanism for preventing relative axial movement of concentric tubes. In another aspect, the invention provides a delivery system for introducing a prosthesis to a body lumen including a nose cone having a hole formed through it that is adapted to communicate with both the interior of the catheter and the ambient environment before insertion of the nose cone into the body lumen, whereby said hole allows flushing of the catheter to remove air bubbles therefrom before insertion into the body lumen. In another aspect, this invention provides a method for preventing leakage of fluid from an interior of a delivery catheter by disposing the outer tube on a mandrel having a cross-sectional area substantially equivalent to that of the inner tube, applying a compressive force to a portion of the outer tube, heating the outer tube to shrink it around the mandrel, and assembling the outer tube concentrically over the inner tube such that a seal is created between the portion of the outer tube and the inner tube.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to the deployment of endoluminal prostheses and, more particularly, to an improved multi-sheath delivery catheter for such deployment.  
         BACKGROUND OF THE INVENTION  
         [0002]    Endoluminal prostheses are used for reinforcing or repairing blood vessels and other lumens within the body. For example, arteries narrowed or occluded by stenosis, thrombosis, or aneurysm may be reinforced, with or without additional surgical procedures such as angioplasty, by placing a prosthesis in the diseased portion of the artery. Such prostheses may be deployed within a body lumen by minimally invasive endoluminal insertion techniques. These include “surgical cut-down” procedures in which a small incision is made in the vasculature, for example in the femoral artery in the leg or in an artery in the shoulder of a patient, and a catheter is inserted at that location into the vessel. The catheter is maneuvered to the desired point of deployment, and the prosthesis is advanced through the catheter to that point. During this insertion process, the prosthesis is in a reduced diameter configuration, smaller than its intended diameter for use in repairing the vessel. The prosthesis is then expelled from the catheter into the vessel and expanded, with or without additional manipulation, into its intended use diameter within the vessel. The catheter is then removed from the body. Alternatively, percutaneous access may be used, wherein a needle puncture rather than a surgical incision is used to gain access to the vasculature. Percutaneous techniques are used for inserting relatively small prostheses; surgical cut-down techniques are used for relatively large ones.  
           [0003]    A typical known insertion catheter consists of an outer sheath having a pusher slidably disposed within it. See, for example, U.S. Pat. No. 5,405,377 to Cragg. Once the catheter is inserted in the vessel and the prosthesis is advanced to the desired location within the vessel, the pusher is held in place while the outer sheath is retracted. This effectively discharges the prosthesis from the catheter.  
           [0004]    For some prostheses, this simple pusher-in-sheath catheter arrangement is insufficient. An example of such a prosthesis is one having multiple diameters along its axis, such as the bifurcated prosthesis described in U.S. Pat. No. 5,609,627 to Goicoechea et al. The bifurcated prosthesis described in that patent has a stent portion having a first diameter adapted to be disposed in an aorta, and a branch portion having a second diameter, smaller than the first diameter, that extends into one of the iliac arteries. To insert such a multi-diameter stent, a multi-sheath delivery catheter is required.  
           [0005]    It is also occasionally necessary to use a multi-sheath catheter to deliver a conventional straight prosthesis. With some prostheses, significant frictional forces exist between the prosthesis and the outer sheath of the catheter in which it is contained for transport to the delivery location and deployment. This may be the case with relatively long prostheses because friction increases as the outer surface area of the prosthesis increases.  
           [0006]    A known multi-sheath delivery catheter  10  is illustrated in FIG. 1. Multi-sheath catheter  10 , similar to that disclosed in Goicoechea &#39;627, comprises outer sheath  11 , middle sheath  12 , and pusher  13 . Outer sheath  11  and middle sheath  12  are designed to be of an optimum diameter for containing the aortic portion and one bifurcated leg portion, respectively, of the bifurcated stent described above.  
           [0007]    Outer sheath  11 , middle sheath  12 , and pusher  13  are concentrically slidably disposed relative to one another and are diametrically sized such that the prosthesis does not buckle against pusher  13  during deployment. In order to deploy a prosthesis contained within outer sheath  11  and middle sheath  12 , catheter  10  is first percutaneously inserted to the desired delivery location within a body lumen according to methods known in the art. Outer sheath  11  is then retracted while middle sheath  12  and pusher  13  are held stationary. This action releases the first portion of the prosthesis that had been contained by outer sheath  11  because stationary middle sheath  12  and pusher  13  effectively prevent the first and second portions, respectively, of the prosthesis from moving as outer sheath  11  is retracted. Outer sheath  11  and middle sheath  12  are then retracted together while pusher  13  is held stationary to complete deployment of the prosthesis.  
           [0008]    During this deployment, it is important that the tubes do not rotate with respect to one another. Rotation of any one of the tubes independently along its axis will not rotate the others. Such rotation could cause twisting or misalignment of the prosthesis being delivered. This also makes it difficult to gauge the twist or orientation of the prosthesis within the catheter, which is critical for aligning bifurcated prostheses with the anatomy. In addition, if the concentric tubes described above are not withdrawn in the proper order, the system will not properly deploy the prosthesis. Care must thus be exercised by a physician using a multi-sheath catheter to implant a prosthesis to retract the tubes in proper order.  
           [0009]    An improved multi sheath delivery catheter for deployment of endoluminal prostheses is desired.  
         SUMMARY OF THE INVENTION  
         [0010]    In a first aspect, the present invention provides a multi-sheath delivery catheter for introducing a prosthesis into a body lumen that has (a) an outer sheath adapted to contain a portion of the prosthesis and having an inner surface with a non-round cross-section; (b) a middle sheath slideably disposed at least partly within the outer sheath and adapted to contain another portion of the prosthesis, the middle sheath having a distal end with a first handle attached to it that has a non-round cross-section corresponding to and engaging the non-round cross-section of the inner surface of the outer sheath; and (c) a pusher slideably disposed at least partly within the middle sheath and adapted to engage the prosthesis; whereby relative rotational movement between the outer sheath and the middle sheath is prevented by virtue of the engagement of the non-round cross-section of the first handle with the non-round cross-section of the inner surface of the outer sheath. The pusher has a distal end with a second handle attached to it that has a non-round cross-section corresponding to and engaging the non-round cross-section of the first handle, whereby relative rotational movement between the pusher and the middle sheath is prevented by virtue of the engagement of the non-round cross-section of the second handle with the non-round cross-section of the first handle.  
           [0011]    In another aspect, the invention provides a method for introducing a prosthesis to a body lumen using a multi-sheath delivery catheter having an outer sheath with an inner surface, a middle sheath having a distal end and being slideably disposed at least partly within said outer sheath, and a pusher having a distal end and being slideably disposed at least partly within said middle sheath. The method includes the steps of (a) forming a non-round cross-section in the inner surface of the outer sheath; and (b) attaching to the distal end of the middle sheath a handle that has a non-round cross-section corresponding to and engaging the non-round cross section formed in the inner surface of the outer sheath. The method also includes the step of attaching to the distal end of the pusher a handle that has a non-round cross-section corresponding to and engaging the non-round cross section of the middle sheath.  
           [0012]    In another aspect, the invention provides a delivery catheter having a plurality of concentric tubes including an outer tube with an inner surface and an inner tube with an outer surface, at least one of which tubes is adapted to contain at least a portion of the prosthesis, and a first protrusion on the inner surface of the outer tube and a second protrusion, adapted to engage the first protrusion, on the outer surface of the inner tube, wherein the outer tube is adapted to be retracted over the inner tube before engagement of the first and second protuberances, and the outer tube and the inner tube are adapted to be retracted together upon the engagement.  
           [0013]    In another aspect, the invention provides a delivery catheter having a plurality of concentric tubes including an outer tube having a distal end and an inner surface and an inner tube having a periphery, at least one of which tubes is adapted to contain at least a portion of the prosthesis during introduction to the body lumen, and (a) at least one notch on the inner tube; (b) a prong assembly disposed on the periphery of the inner tube and abutting the distal end of the outer tube, the prong assembly having at least one prong adapted to engage the notch in the inner tube; (c) a lock ring having a first portion adapted to be disposed over the distal end of the outer tube and a second portion adapted to be disposed over the prong assembly abutting the distal end; and (d) a protrusion on the inner surface of the outer tube; wherein the second portion of the lock ring is adapted to exert a force on the prong assembly sufficient to maintain the engagement of the prong with the notch and thereby prevent relative axial movement of the inner and outer tubes.  
           [0014]    In another aspect, the invention provides a delivery catheter having a plurality of concentric tubes including an outer tube having a distal end and an inner tube having a periphery. The catheter also has (a) at least one notch on the inner tube; (b) a cam-lock assembly having (i) a hub fixedly attached to the distal end of the outer tube; and (ii) a cam-lock knob rotationally attached to the hub around the periphery of the inner tube; (iii) the cam-lock knob having a detailed inner cam surface adapted to engage the notch in a first position, thereby preventing relative axial motion between the inner and outer tubes, and disengaging the notch in a second position, thereby permitting relative axial motion between the inner and outer tubes.  
           [0015]    In another aspect, the invention provides a delivery system for introducing a prosthesis to a body lumen including (a) a guidewire; (b) a catheter with a lumen adapted to slide over said guidewire, a proximal end, an interior, and a plurality of concentric tubes, at least one of which is adapted to contain at least a portion of the prosthesis during introduction to the body lumen; and (c) a nose cone disposed around the guide wire at the proximal end of the catheter, the nose cone having a hole formed through it that is adapted to communicate with both the interior of the catheter and an ambient environment before insertion of the nose cone into the body lumen; whereby the hole allows flushing of the catheter to remove air bubbles from the catheter before insertion into the body lumen.  
           [0016]    In another aspect, this invention provides a method for preventing leakage of fluid from an interior of a delivery catheter by disposing the outer tube on a mandrel having a cross-sectional area substantially equivalent to that of the inner tube, applying a compressive force to a portion of the outer tube, heating the outer tube to shrink it around the mandrel, and assembling the outer tube concentrically over the inner tube such that a seal is created between the portion of the outer tube and the inner tube.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0017]    [0017]FIG. 1 is a side view of a portion of a prior art multi-sheath delivery catheter.  
         [0018]    [0018]FIG. 2 is a side view of component portions of an exemplary multi-sheath delivery catheter according to this invention.  
         [0019]    [0019]FIG. 3 is a side view of the component portions illustrated in FIG. 2 assembled into an exemplary multi-sheath delivery catheter according to this invention.  
         [0020]    [0020]FIG. 4 is a isometric view of a portion of another exemplary multi-sheath delivery catheter according to this invention.  
         [0021]    [0021]FIG. 5 is a partially cut-away isometric view of a portion of an exemplary multi-sheath delivery catheter according to this invention.  
         [0022]    [0022]FIG. 6 is a isometric view of a component used in another exemplary multi-sheath delivery catheter according to this invention.  
         [0023]    [0023]FIG. 6A is a isometric view of a portion of an exemplary multi-sheath delivery catheter according to this invention.  
         [0024]    [0024]FIG. 7 is a isometric view of a portion of an exemplary multi-sheath delivery catheter according to this invention.  
         [0025]    [0025]FIG. 8 is a partially cut-away isometric view of a portion of an exemplary multi-sheath delivery catheter according to this invention.  
         [0026]    [0026]FIG. 9 is a isometric view of another exemplary multi-sheath delivery catheter according to this invention.  
         [0027]    [0027]FIG. 10 is a side section view of a portion of the exemplary multi-sheath delivery catheter illustrated in FIG. 9.  
         [0028]    [0028]FIG. 11 is an end view of the portion of the exemplary multi-sheath delivery catheter shown in FIG. 10.  
         [0029]    [0029]FIG. 12 is a sectional detail view of a portion of the multi-sheath delivery catheter illustrated in FIG. 11.  
         [0030]    [0030]FIG. 13 is a sectional detail view of the exemplary multi-sheath delivery catheter shown in FIG. 11.  
         [0031]    [0031]FIG. 14 is a side view of a portion of another exemplary multi-sheath delivery catheter according to this invention.  
         [0032]    [0032]FIG. 14A is a side view of a portion of another exemplary multi-sheath delivery catheter according to this invention.  
         [0033]    [0033]FIG. 15 is a side view of a portion of another exemplary multi-sheath delivery catheter according to this invention.  
         [0034]    [0034]FIG. 16 is a side view of a portion of another exemplary multi-sheath delivery catheter according to this invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]    As shown in FIG. 1 discussed above, the basic components of a known multi-sheath delivery catheter include an outer sheath  11 , adapted to hold a first portion of a prosthesis to be delivered, a middle sheath  12 , adapted to hold a second portion of the prosthesis to be delivered, and a pusher  13  for engaging, typically abutting, the distal end of the prosthesis contained within the catheter. Throughout this specification, the term “distal” shall mean “furthest from the heart,” and the term “proximal” shall mean “closest to the heart.” In addition, although two sheaths and one pusher are typically illustrated in the exemplary embodiments of the multi-sheath delivery catheter of this invention, additional sheaths or pushers may be included and are intended to be encompassed within the scope of the invention described herein. The sheaths and pushers may generally be referred to as tubes.  
         [0036]    In a first aspect of this invention, the inventors have added features to a multi-sheath delivery catheter that prevent the sheaths and pusher from rotational motion relative to one another, while permitting the sheaths and pusher to slide axially relative to one another. As shown in FIG. 2, the anti-rotation feature involves attachment of a non-round profile handle  20  to pusher  13  and a non-round profile handle  21  to middle sheath  12 . Preferably, handles  20  and  21  have the same non-round profile. The same non-round profile is also formed on at least a portion  31  (as shown in FIG. 5) of the inner surface of outer sheath  11 . Non-round portion  31  may be integral with outer sheath  11  or formed by a separate member attached to it, such as by molding onto the inner surface. The non-round profile of handles  20  and  21  and of portion  31  on the inner surface of outer sheath  11  are shown in the illustrated embodiment to be square. Any non-round profile is suitable for purposes of this invention, however, such as triangular, ovular, creased (a “collapsed” circled), or D-shaped by way of example only. Alternatively, another non-round profile handle (not shown) may be attached to outer sheath  11  rather than forming the non-round profile on portion  31 . In such an alternative embodiment, the handle is attached to outer sheath  11  as described below.  
         [0037]    The tubes of the multi-sheath delivery catheter of this invention are typically made of polyethylene or other suitable thermoplastic material. Handles  20  and  21  may also be made of polyethylene or other suitable thermoplastic material, or of stainless steel. In the event that handles  21  and  20  are formed of the same material as middle sheath  12  and pusher  13 , respectively, handles  21  and  20  may either be separately formed and attached to middle sheath  12  and pusher  13  or formed integrally therewith, such as by molding processes known in the art. As an alternative, pusher  13  and middle sheath  12  may be formed entirely in the non-round profile, such that handles  20  and  21  are effectively simply the distal ends of pusher  13  and middle sheath  12 .  
         [0038]    Preferably, handles  20  and  21  are formed of stainless steel and attached to pusher  13  and middle sheath  12 , respectively, which are formed of polyethylene. To attach such stainless steel handles to polyethylene tubes, small notches are formed in the proximal end of the handle to be attached to the distal end of a tube. The proximal end of the handle is then inserted into the distal end of the tube and Teflon heat shrink tubing, known to those skilled in the art, is placed around the overlapping portions of the handle inside the tube. Upon heating, typically with a heat gun or a lap-welder, to a temperature and for a time period that may be easily optimized by those skilled in the art, the heat shrink tubing shrinks, thereby causing the tube to shrink down into tight engagement with the steel handle. In addition, the polyethylene of the tube melts and flows into the notches formed on the handle. Upon cooling this forms a tight interlocking bond between the tube and the handle. The heat shrink tubing may be removed and discarded.  
         [0039]    Because pusher  13  typically has a very small internal diameter, it may be necessary to bore out the distal end of pusher  13  before insertion of handle  20  and attachment of the two as described above. Other modular attachment methods may also be used to attach handles  21  and  20  to middle sheath  12  and pusher  13 , as will be understood by those skilled in the art.  
         [0040]    [0040]FIG. 3 illustrates the multi-sheath catheter of this invention formed from the components of FIG. 2 which have been coaxially assembled. In the arrangement shown in FIG. 3, pusher  13  is contained within middle sheath  12 , and handle  20  is contained within handle  21 . All of the tubes and handles are contained within outer sheath  11 . In one final configuration used by a physician to implant a prosthesis, tube  21  attached to middle sheath  12  is entirely covered by outer sheath  11 . Handle  20  may protrude from the distal end of outer sheath  11  for manipulation by the physician. In another final configuration, handle  21  may also protrude from the distal end of the outer sheath  11  for manipulation by the physician. The tubes are all dimensioned such that they can all slide axially with respect to one another but, because of the non-round profile of handles  20  and  21  and portion  31  of the inner surface of outer sheath  11 , the tubes cannot rotate relative to one another. Rotation of any of the tubes cause the other tubes to rotate with it.  
         [0041]    Another advantage of this invention is that non-round handles  20 ,  21  attached to pusher  13  and middle sheath  12 , respectively, prevent pusher  13  from falling out of middle sheath  12  distally, and middle sheath  12  from falling out of outer sheath  11  distally.  
         [0042]    A visual indicator  25  may optionally be added to the outside of outer sheath  11  (or anywhere else along the catheter handles adapted to remain outside the body into which the catheter is inserted) to illustrate the rotational orientation of the endoprosthesis within the delivery catheter. As shown in FIG. 3, the disposition of a “long leg-short leg” bifurcated endoprosthesis contained within the catheter is visually depicted. Absent such visual indicator  25 , the only way to determine prosthesis orientation is by interpretation of the position of radiopaque markers using fluoroscopy. Visual indicator  25  allows the catheter to be introduced into the body in approximately the correct rotation, requiring less adjustment once inside the patient. Radiopaque markers may or may not be used in conjunction with this insertion.  
         [0043]    The non-round profile of handle  20 , which may be exposed to a physician, provides both tactile and visual feedback to the physician when the catheter is rotated. The described system makes deployment of the endoprosthesis easier and more controlled by adding stiffness and stability to the handle region where forces are applied. The co-axial handles  20  and  21  of the system maintain a low profile for the catheter and do not add unnecessary weight or bulk. Using the anti-rotation system described above prevents twisting of the endoprosthesis within the delivery catheter by preventing the sheaths from rotating relative to one another, thus preventing deployment of the prosthesis in a twisted configuration.  
         [0044]    With a multi-sheath delivery catheter such as that described in connection with this invention, it is important that sheaths are withdrawn in the proper order. Otherwise, the system will not deploy the prosthesis. Accordingly, another aspect of this invention automatically ensures that the retraction of the tubes of the catheter during deployment of the prosthesis is performed in the proper sequence; namely, outer sheath  11  is first retracted to release the first, typically larger, portion of the prosthesis, then middle sheath  12  retracted to release the second, typically smaller, portion. Without such a system, middle sheath  12  may be inadvertently retracted before outer sheath  11 , rendering the delivery catheter inoperable.  
         [0045]    This aspect of the invention also allows the physician to perform only a single, uninterrupted motion to deploy the prosthesis. This helps prevent deployment errors by allowing the physician to devote more attention to other aspects of the procedure. Rather than performing a first retraction motion, removing a lock (for example), and then performing a second retraction motion, only a single motion is required.  
         [0046]    Sheath sequencing is achieved according to this aspect of the invention in combination with either an internal or an external locking mechanism, or a combination of internal and external mechanisms, that lock adjacent tubes to one another to prevent relative axial movement until the tubes are unlocked from one another. FIGS. 4 and 5 illustrate a first embodiment of this aspect of the invention. In this embodiment, the frictional forces between pusher  13  and middle sheath  12  (and their associated handles), and between middle sheath  12  and the prosthesis, are sufficient to prevent undesirable sliding of middle sheath  12  over pusher  13  as outer sheath  11  is being retracted.  
         [0047]    [0047]FIG. 4 shows the portion of the catheter of this invention where handle  20  attached to pusher  13  extends out of handle  21  attached to middle-sheath  12 . Handle  21  has a protrusion  30  on its outer surface. During deployment, outer sheath  11  (FIG. 5) is retracted over middle sheath  12  and associated tube  21  to deploy a first portion of a prosthesis. During this retraction of outer sheath  11 , the frictional forces between middle sheath  12  and pusher  13  and between middle sheath  12  and the prosthesis are sufficient to prevent any relative axial motion between them.  
         [0048]    According to this aspect of the invention, non-round portion  31  of the inner surface of outer sheath  11  is positioned such that upon deployment of the first portion of the prosthesis, portion  31  (which itself is effectively a protrusion from the inner surface of outer sheath  11 ) of outer sheath  11  engages protrusion  30  on the outer surface of handle  21 . By virtue of this engagement, the physician can overcome the frictional forces between pusher  13  and middle tube  12 , and between middle sheath  12  and the prosthesis, by continuing to retract outer sheath  11 . This causes relative motion between middle sheath  12  and pusher  13 . As a result, both outer sheath  11  and middle sheath  12  are retracted simultaneously after the engagement of portion  31  with protrusion  30  to complete deployment of the endoluminal prosthesis.  
         [0049]    Single motion sequenced retraction is thus achieved using this aspect of the invention. The physician need only retract one tube (outer sheath  11 ) and proper sequenced tube retraction is automatically ensured using by virtue of the engagement of portion  31  and protrusion  30 .  
         [0050]    FIGS.  6 - 8  illustrate sequenced sheath retraction using a separate prong assembly  40  as an internal lock mechanism in the event that the frictional forces between the tubes is not sufficient to prevent undesirable relative axial movement. As shown in FIG. 6, a prong assembly  40 , formed of a thermoplastic material such as polyethylene, or of stainless steel, or of other suitable material, has a cross-sectional profile that matches that of handle  20 . Prong assembly  40  is adapted to be disposed around the periphery of handle  20 . Prong assembly  40  has slits  42  formed in the sides thereof and prongs  41  disposed in each inside corner thereof in the illustrated embodiment. As shown in FIG. 6A, notches  49  are formed in the corners of handle  20 . Prongs  41  of the prong assembly  40  are adapted to fit into notches  49  when prong assembly  40  is disposed on handle  20 .  
         [0051]    [0051]FIG. 7 illustrates the use of prong assembly  40  in accordance with an exemplary embodiment of this aspect of this invention. Prong assembly  40  is placed on handle  20  attached to pusher  13  such that prongs  40  fit into notches  49 . A lock ring  43  is then placed over both prong assembly  40  and a distal portion of handle  21  attached to middle sheath  12 . Lock ring  43  serves to maintain the engagement of prongs  41  with notches  49  in handle  20 . Absent lock ring  43 , prongs  41  are easily disengaged from notches  49 . Lock ring  43  includes a slot  44  which is adapted to allow protrusion  30  in tube  21  to remain uncovered and to slide relative to lock ring  43  as lock ring  43  is retracted off handle  21  as described below. In the configuration illustrated in FIG. 7, middle sheath  12  is locked from retracting relative to pusher  13  because handle  21  cannot slide over the locked prong assembly  40  attached to handle  20 . This prevents relative movement between middle sheath  12  and pusher  13 .  
         [0052]    Lock ring  43  preferably has two portions of separate cross-sectional areas. The larger cross-sectional area portion is disposed over the periphery of handle  21 , and the smaller cross-sectional area portion is disposed over the periphery of prong assembly  40 . Both prong assembly  40  and lock ring  43  must have a wall thickness such that they will fit easily within outer sheath  11 .  
         [0053]    [0053]FIG. 8 illustrates the use of this internal locking mechanism during deployment of a prosthesis according to an embodiment of this invention wherein the mechanism is used in combination with the sequenced sheath retraction aspect of the invention described above. Outer sheath  11  is retracted until the first, larger diameter portion of the prosthesis is deployed. At that point, the distal end of portion  31  has engaged the proximal end of lock ring  43  and pushed the small diameter portion of lock ring  43  off prong assembly  40 . Because the large diameter portion of lock ring  43  now covers prong assembly  40 , there is no forced engagement of prongs  41  with notches  49  (the large diameter portion of lock ring  43  being sized such that there is space for prongs  41  to become disengaged within the large diameter portion of lock ring  43 ). Prongs  41  are thus released from notches  49  in handle  20 . Middle sheath  12  is thus unlocked from pusher  13 , and these two portions of the catheter can move relative to one another. Also at this point during retraction, portion  31  engages protrusion  30  on handle  21 , causing the sequenced sheath retraction described above.  
         [0054]    [0054]FIG. 9 illustrates another embodiment of this aspect of the invention for locking tubes together to prevent axial movement relative to one another. FIG. 9 shows an assembled catheter according to this invention where the distal end of handle  20  protrudes from the distal end of handle  21 , which in turn protrudes from the outer end of outer sheath  11 , which extends into the body of a patient into whom a prosthesis is to be inserted. In this embodiment, cam lock assemblies  50  are disposed at the portions of the catheter where one tube protrudes from another. Cam lock assemblies  50  allow locking and unlocking of the tube from which another tube protrudes and the protruding tube (generally referred to as an outer tube and an inner tube).  
         [0055]    [0055]FIG. 10 is a side view of one of the cam-lock assemblies  50 . Although illustrated and described in connection with the locking and unlocking of handles  20  and  21  (and hence pusher  13  and middle sheath  12 , any of the adjacent tubes may be locked and unlocked using the cam-lock assembly design described below.  
         [0056]    As shown in FIG. 10, cam-lock assembly  50  includes a cam lock knob  51  and a hub  52 . Cam-lock knob  51  is attached to, and pivots on, hub  52  which is glued or press-fit (or otherwise fixedly mounted) onto the distal end of handle  21 .  
         [0057]    [0057]FIG. 11 is an end view of the cam-lock assembly  50  shown in FIG. 10. As illustrated in FIG. 11 (and in FIG. 9) cam-lock assembly  50  includes indents  59  provided for easy handling and gripping by a physician using the device to insert a prosthesis. Also as shown in FIG. 11, and as shown in detail in FIG. 12, cam-lock knob  51  has a detailed inner cam surface  58  that allows respective engagement and disengagement of cam-knob  51  with notches  57  formed in handle  20 .  
         [0058]    In the situation illustrated in FIG. 12, inner surface  58  of cam-lock knob  51  extends into notch  57  at A. Inner cam surface  58  then extends out away from handle  20  at B, creating an open space C between inner cam surface  58  and handle  20 . Inner cam surface  58  then contours to the corner of handle  20  at D, extends away from handle  20  at E, creating inner space F, then extends into notch  57  in handle  20  at G, extends back out away from handle  20  at H, creating space I, contours around another corner of handle  20  at J, and extends away from handle  20  at K, creating space L.  
         [0059]    By virtue of inner cam surface  58  extending into the notches  57  of handle  20  at points A and G, handles  20  and  21  (and hence pusher  13  and middle sheath  12 ) are prevented from axial movement relative to one another.  
         [0060]    To unlock cam-lock assembly  50  and allow relative movement between tubes  20  and  21 , cam lock assembly  51  is rotated by a physician (for example) 45° counter clockwise from the illustration shown in FIG. 12. The result is the situation illustrated in FIG. 13. Inner surface  58  of cam-lock knob  51  in FIG. 13 is contoured such that no part of inner surface  58  extends into notches  57  of handle  20 . Corresponding lettered points along inner surface  58  are shown in FIG. 13 relative to their position in FIG. 12. As can be seen, each lettered point has rotated 45° counter clockwise such that there is no engagement with notches  57  of handle  20 . Accordingly, handle  20  is free to slide axially relative to handle  21 , and hence pusher  13  can move axially relative to middle sheath  12 .  
         [0061]    Using cam-lock assembly  50 , middle sheath  12  and pusher  13  may be selectively rigidly fixed and unlocked with respect to one another. The illustrated embodiment shows handles  20  and  21  having the same cross-sectional shape, but cam-lock assembly  50  can be used when the cross sectional shapes are different. The locking function of cam-lock assembly  50  is accomplished by the detailed inner cam surface  58  of cam-lock knob  51  which, when locked, engages premachined notches  57  in handle  20 . When cam-lock knob  51  is in the locked position, the two handles  20  and  21  cannot move axially, or slide, relative to one another. Cam-lock assembly  50  becomes unlocked when cam-lock knob  51  is turned counter clockwise approximately 45° in this embodiment, thereby disengaging inner cam surface  58  from notches  57  in inner tubing  20 .  
         [0062]    Cam-lock knob assembly  50  provides several advantages. First, handles  20  and  21  may be rigidly locked with absolutely no axial motion relative to one another by non-frictional means. This is important in an operating environment where contact with bodily fluids could easily disable frictional locking devices by reducing the coefficient of friction. Thus, accidental unlocking of the device is very unlikely. Second, cam-lock assembly  50  has a “positive feel” in both the locked and unlocked positions and is not easily placed in an intermediate position. Cam-lock knob assembly  50  may be a semi-rigid thermoplastic material, and handles  20  and  21  may be thermoplastic or metallic material, which allows slight deformations of cam-lock knob  50  to provide user feedback with a click or snap when locked. This, along with visual confirmation, lets the user, typically a physician, know whether the device is locked or not. Third, cam-lock assembly  50  is easy to use and intuitive, which is critical to the physician operating the device. Cam lock knob  51  may also be manufactured with a large grip to provide grip for gloved hands. The intuitive clockwise-lock and counter clockwise-unlock motions are nearly universal and describe a vast majority of screws and fasteners. Lastly, cam-lock assembly  50  has the ability to lock handle  20  in more than one position if multiple sets of notches  57  are provided. This may be useful when deploying different sizes of prostheses, for example. Notches  57  in handle  20  may be machined, by methods known to those skilled in the art, before the device is assembled. Notches  57  may also be molded instead of machined, or cut after assembly but before locking.  
         [0063]    According to another aspect of this invention, a seal may be provided between outer sheath  11  and middle sheath  12  and between middle sheath  12  and pusher  13 . Such a seal is desired, for example, to prevent saline solution from leaking out of the catheter during flushing of the device to remove air bubbles. The sealing also prevents blood from escaping from the catheter when it is inserted into the patient&#39;s body.  
         [0064]    The seal is created by applying a radial compressive force to the periphery of an outer tube while heating it over an inner tube or an appropriately sized mandrel. FIG. 14 illustrates the use of a Teflon heat shrink tubing  60  to provide the radial compressive force during heating (heat illustrated at  61 ), which is typically done with a heat gun or a lap-welder. As shown in FIG. 14, tubing  60  is applied over outer sheath  11  which has middle sheath  12  (as opposed to a mandrel) disposed within it. As will be understood by those skilled in the art, the heating should be of sufficient time and temperature (for example, 450 degrees F. for 15 seconds) to allow softening of the thermoplastic material of which the outer tube is formed in order to allow it to form a seal with the inner tube as tubing  60  shrinks.  
         [0065]    Forming a seal in this manner creates a local region  62  (the region where tubing  60  and heat  61  are applied) where the inside diameter of outer sheath  11  is very closely sized to the outer diameter of outer sheath  12 . As shown in FIG. 14A, this creates the desired seal. The same technique may be used to form a seal between middle sheath  12  and pusher  13  contained within it.  
         [0066]    This aspect of the invention provides an efficient, reliable seal between the respective parts of the catheter. This is an improvement over simply attempting to manufacture the sheaths of appropriately sized dimensions. Extrusion, or other formation, to such precise dimensions throughout the entire length of the sheaths is not feasible. Because of manufacturing variations, the tubes would either be too loose (no sealing) or too tight (excessive sliding friction). This invention overcomes these manufacturing and use limitations.  
         [0067]    According to another aspect of the invention illustrated in FIG. 15, a guide tip  73  with a through-hole  70  for a guidewire is connected to an inner shaft  76  to be contained within pusher  13  of the catheter of this invention. Passage of the guide tip  73  followed by the remainder of the catheter is facilitated by tracking over a guidewire previously introduced into the vessel.  
         [0068]    Guide tip  73  is formed of a thermoplastic material, preferably flexible. Front portion  74  of guide tip  73  extends proximally out from outer sheath  11  (not shown), while back portion  75  is contained within outer sheath  11 . A through-hole  72  is formed in guide tip  73 . Through-hole  72  provides fluid communication between the inside of outer sheath  11  and the environment.  
         [0069]    When the fully assembled catheter is ready for insertion into a patient, immediately before use, the system is typically flushed with saline solution to remove air from the catheter and prosthesis. Through-hole  72  allows the saline solution to be ejected from the inside of outer sheath  11  to the environment to insure that the air is removed. Rather than through-hole  72 , a groove  79  may be used for the same purpose as shown in the alternative embodiment illustrated in FIG. 16.  
         [0070]    Although this invention has been described in connection with certain specific embodiments, the scope of the invention is not intended to be limited thereto.