Abstract:
A rapid exchange balloon catheter has a short rapid exchange length for faster catheter exchanges the balloon catheter includes a balloon structure having a balloon leg connected to a catheter shaft. Marker bands may be provided in the balloon leg for facilitating measurement of a dimension of physiological features. A stiffening wire extending longitudinally at least partially into the balloon leg may be provided to supplement and control the flexibility characteristics of the balloon leg.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to interventional catheters, and more particularly, a rapid exchange stent delivery catheter. 
         [0003]    2. Brief Description of the Related Art 
         [0004]    Stent delivery catheters are known in the art. They generally comprise an elongated tubular device having a distal portion that carries a stent for delivery to a site in a patient&#39;s vasculature. The stent may be medicated and is used to prop open and support a constricted or otherwise compromised section of the blood vessel, due for example to arterial sclerosis. The stent is delivered in a contracted state so that it can be maneuvered through the vasculature. Once it is at the desired location, it is expanded and decoupled from the catheter. The delivery catheter is then withdrawn. 
         [0005]    The delivery catheter is provided with a balloon on which the stent is securely seated during delivery. When the stent reaches its destination, the balloon is inflated, causing the stent to expand in the lumen. The balloon is then deflated so that it disengages from the stent, allowing withdrawal of the catheter. 
         [0006]    Stents have many different configurations and sizes, and proper selection of the stent is an integral part of the procedure. Often, the determination of whether a particular stent is suitable can only made after the stent is delivered to the lesion site. Then, if the determination is that the stent is not suitable—for example because it is of the wrong length—then before inflation the stent must be withdrawn and replaced with a different stent. Alternatively, if a stent which is too short is implanted, an additional overlapping stent may be needed. Therefore there is a long-felt need to improve the ability to pre-assess the suitability of a particular stent, before it is expanded. This task is complicated by limitations of imaging technology. In most cases, imaging or visualization of a lesion is compromised by limitations of the viewing angle because the visualization system may not be positioned to provide a direct side view of the vessel. The view in this instance is foreshortened because of the orientation of the visualization system relative to the vessel, making a determination of lesion length even more difficult. This issue is further aggravated when curved vessels are involved, making length determination even more problematic. 
         [0007]    The rapid exchange stent delivery catheter itself is designed so that it can be quickly withdrawn and replaced if it is determined that its stent payload is of the wrong configuration for that particular application. As seen in  FIG. 1 , the generally tubular structure  10  defining the rapid exchange stent delivery catheter  11  is provided with a secondary tube  12  enclosed within the tubular structure. Secondary tube  12  provides a guidewire lumen which extends through the balloon  14 . Balloon  14  is in fluid communication with lumen  15  of tubular structure  10  such that the balloon can be inflated or deflated as necessary. Secondary tube  12  communicates with the exterior of the catheter by way of a distal port  16  located at the tip of the catheter, and a proximal port  18  located proximally of the balloon. 
         [0008]    With reference to  FIG. 2 , secondary tube  12  is designed to accommodate a guidewire  20  used to guide the catheter to the delivery site. During operation, the guidewire  20 , along with a guiding catheter  22 , are used to direct the rapid exchange stent delivery catheter  111  to the delivery site in the patient. When the distal end of the guidewire  20  is properly situated at the delivery site, loading of the rapid exchange stent delivery catheter  11  and introduction thereof into the patient can commence. This involves passing the proximal end of the guidewire  20 , which protrudes from the patient, into the catheter&#39;s distal guidewire port  16 , through secondary guidewire tube  12 , and out proximal guidewire port  18 . The catheter  11  is then guided along the guidewire  20 , through the length of the guiding catheter  22  in the patient, and then out distal end  24  of the guiding catheter and further to the delivery site. The stent  26  is then decoupled from the balloon  14  and the delivery catheter  11  is withdrawn. 
         [0009]    An example of a device having a configuration similar to that described above is the angioplasty-type balloon catheter described in U.S. Pat. No. 5,061,273 (Yock). In the Yock patent, it was recognized that important advantages can accrue from maintaining a transition region associated with the proximal guidewire port of the balloon catheter within the guiding catheter during the angioplasty procedure. The transition region is the region from which the guidewire emerges from the balloon catheter at the proximal guidewire port, and it was found to be important to maintain this region within the guiding catheter during the procedure. Accordingly, the balloon catheter was dimensioned such that the distance between the distal end of the balloon catheter and the transition region and/or the proximal guidewire port was at least 10 cm. However, such a dimension has been found to be problematic for several reasons. For catheters which are designed for stent delivery, the distal portion of the catheter in the vicinity of the balloon and proximal thereof should be simultaneously very flexible to navigate the coronary arteries, have good column strength to provide pushability, and have good kink resistance. By comparison, the remaining, proximal portion of the catheter generally requires good column strength and less flexibility. Flexibility of the distal portion of the catheter is important for maneuverability and deliverability of the catheter. However, flexibility must be balanced so as not to compromise the ability of the catheter to track over the guidewire, or permit bowing or looping of the catheter or other movement of the catheter away from the guidewire, resulting in loss of pushability. Extending the distance between the end of the catheter and the proximal guidewire port detracts from some of these desired characteristics, for example by reducing pushability. 
         [0010]    Another issue relating to the flexibility of the distal portion of the catheter is due to the composition of the catheter. Known rapid exchange balloon catheters and over-the-wire balloon catheters are formed by blowing a balloon from a length of suitable tubing, trimming the ends of the tubing close to the balloon and bonding the balloon onto a catheter shaft. However, the bond between the balloon and the shaft at a location close to the balloon proximal end forms a thickened and stiffer portion at a location where high flexibility and trackability are desired. 
       SUMMARY OF THE INVENTION 
       [0011]    In accordance with the invention, the afore-mentioned deficiencies in the prior art are addressed by providing a stent delivery balloon catheter including a balloon leg having an extended length so that the bonding junction between the balloon and the catheter shaft is move proximally. In addition, a distance between a proximal guidewire ports and the distal end of the catheter is reduced from traditional rapid exchange catheters to achieve a move rapid termed super rapid exchange. In this manner, pushability of the distal portion of the balloon catheter and trackability over the guidewire are improved, while at the same time more rapid exchanged are possible. Improved pushability of the distal portion of the balloon catheter and trackability over the guidewire, and reduced possibilities of shaft bowing away from the guidewire, or guidewire looping can also be achieved by providing a stiffening wire, having several possible configurations, that extends at least partially along the length of the balloon leg and catheter shaft. In addition, to provide lesion dimension measurements, radiopaque marker bands are provided on the guidewire tube such that a visual frame of reference is available against which lesion measurements can be made in order to assist with proper stent or balloon selection. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The invention of the present application will now be described in more detail with reference to embodiments of the apparatus and method exemplifying principles of the invention, given only by way of example, and with reference to the accompanying drawings, in which: 
           [0013]      FIG. 1  is a cross-sectional view of a distal portion of a stent delivery catheter; 
           [0014]      FIG. 2  is a schematic view showing placement of a stent in a vascular lesion during a stent delivery procedure; 
           [0015]      FIG. 3  is a schematic view of a rapid exchange stent delivery assembly; 
           [0016]      FIG. 4  is a cross-sectional view of a distal portion of a rapid exchange stent delivery catheter; 
           [0017]      FIG. 5  is a more detailed cross-sectional view of the distal portion of  FIG. 4  showing the balloon leg and connection region; 
           [0018]      FIG. 6  is a cross-sectional view showing a stiffening wire; 
           [0019]      FIG. 6A  is a more detailed view of the stiffing wire; 
           [0020]      FIG. 7  is a cross-sectional view showing the use of marker bands; and 
           [0021]      FIG. 8  is a cross-sectional schematic view showing the marker bands in use against a lesion. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0022]      FIG. 3  shows an assembly  30  including a rapid exchange stent delivery catheter  32 , a guidewire  34 , and a stent  36 . The stent  36  is seated over an expandable portion  38  of a balloon  50  disposed in the distal portion of the catheter. The stent  36  is shown in an expanded state. In the unexpanded or delivery configuration, the expandable portion  38  of the balloon  50  and stent  36  will have an outer diameter close to the outer diameter of the shaft of the catheter  32  for easy maneuverability through the patient&#39;s vasculature. 
         [0023]    As seen in  FIG. 4 , the expandable portion  38  is in fluid communication with a primary lumen  40  of the stent delivery catheter  32  defined by the generally tubular nature of the catheter shaft over substantially its entire length. The primary lumen  40  serves to deliver fluid, such as saline, to and from the expandable portion  38  to inflate or deflate the balloon. A secondary, guidewire tube  42  defining a secondary lumen  44  through which a guidewire (not shown) passes is disposed within the catheter  32 . Secondary tube  42  extends through the interior of expandable portion  38  and is bonded to the catheter  32  at both ends of the secondary tube. Secondary lumen  44  of secondary tube  42  is in communication with the exterior of the catheter  32  at a proximal guidewire port  46  and a distal guidewire port  48 . 
         [0024]    In order to control the flexibility and maneuverability of the stent delivery catheter  32 , portions of the shaft of the catheter may advantageously include a structure or features that alter its structure and behavior in response to forces exerted during manipulation. According to an advantageous embodiment of the present invention, a portion of the shaft includes one or more lengths of hypotubing, one or more overlayers or exterior jackets, or both. Further, the hypotubing may include features that modify its flexibility characteristics, such as suitably-oriented (circumferential, longitudinal, helical, etc.) and pitched cuts or grooves or other modifications to its structure that commensurately change its flexibility characteristics, particularly at a distal portion of the catheter in the vicinity of the expandable portion  38 , where increased flexibility may be desired. 
         [0025]      FIG. 5  illustrates a cross-sectional view of a distal portion of the stent delivery catheter  32  according to an embodiment of the invention. The expandable portion  38  is formed as part of a balloon  50 , which balloon also includes a proximal balloon leg  52  extending in the proximal direction from the expandable portion  38  and defining a balloon leg lumen  53 . Between the expandable portion  38  and the balloon leg  52  is the balloon proximal shoulder. Unlike expandable portion  38 , balloon leg  52  is not expandable, but rather maintains its shape and dimensions under operating pressures. The length of balloon leg  52  is at least about 2 cm measured from the edge of the balloon proximal sholder (?) The catheter  32  includes features such as hypotube  54  and helical cuts  56  formed in the hypotube to thereby modify the flexibility characteristics of the distal portion of the catheter. An outer polymer jacket  58  surrounds hypotube  54 . By forming the jacket  58  of a biocompatible material, e.g., a biocompatible polymer, the catheter  32  can be made fluid tight to the inflation fluid passing through primary lumen  40 , relatively low friction to assist in passing the catheter  32  through the vasculature of a patient, and the flexibility of the catheter can further be modified. 
         [0026]    Expandable portion  38  is depicted in an inflated or expanded state in  FIG. 5 . Expandable portion  38  is inflated or expanded by injecting fluid to its interior region. As explained above, balloon leg  52  is structured to essentially retain its shape and dimensions irrespective of the inflation state of expandable portion  38 , to the extent permissible. In other words, balloon leg  52  is not intended to be inflatable in the sense that balloon expandable portion  38  is, even though it is preferably made of the same material as the expandable portion and is made as a unitary piece integral therewith. This difference in behavior can be achieved by providing a different thickness profile for the balloon leg  52  than for the expandable portion  38 . A greater thickness reduces deformability, making the balloon leg  52  less likely to inflate under fluid pressures that would inflate expandable portion  38 . Proximal balloon leg  52 , along with a shorter distal balloon leg on the opposite side of expandable portion  38 , are formed by a balloon blowing process within a mold in which the mold ensures that the kg portions do not expand when the expandable portion  38  is formed. A distal tip portion  60  of a different (more flexible) material than balloon  50  is bonded to the distal balloon leg. 
         [0027]    Balloon  50  is coupled to the remainder of catheter  32  at a connection region  62  by way of a sleeve  64  providing a strong, fluid-tight seal between balloon leg  52  and a shaft  65  of catheter  32 . Sleeve  64  couples the distal opening  45  of primary lumen  40  with the proximal opening  55  of balloon leg lumen  53 . This coupling provides a bonding region between the proximal leg  52 , secondary tube  42  and catheter shaft  65 . Sleeve  64  also provides reinforcement for the connection point of secondary guidewire tube  42  in the vicinity of proximal guidewire port  46 . Secondary guidewire tube  42  extends at least partially through balloon leg portion  52 . Alternatively, coupling of balloon  50  to the remainder of the balloon catheter  32  may be achieved by overlying balloon leg  52  over the shaft  65  of the balloon catheter and bonding these two components together, either by heat shrinking and/or melting, adhesive, or other expedients. 
         [0028]    The connection region  62  includes several components, such as sleeve  64  and a proximal portion of secondary guidewire tube  42 . The presence of different catheter components at this connection region  62  impacts the flexibility characteristics of this portion of the catheter. Specifically, the additional structures detract from the flexibility of the catheter  32  in that region. Moving the connection region to a distance of at least 2 cm from the balloon shoulder improves flexibility of the catheter distal end providing improved performance. 
         [0029]    Balloon leg  52  is provided in order to distance the connection region  62  from expandable portion  38 , since the flexibility of the balloon leg can be better managed than that of the multi-layer connection region. 
         [0030]    Thus optimally, the distance from distal the end of the catheter, and specifically from distal guidewire port  48 , to proximal guidewire port  46  is preferably in the range of about 5 cm to about 8 cm, and more preferably, is about 7 to about 8 cm. Selection of the materials and structure of balloon leg  52  takes into account the desired flexibility of this portion of the catheter. Typically, the flexibility of the balloon leg  52  of the catheter  32  should be greater than that of shaft  65 , and even of the distal portion of shaft  65 , which may be more flexible than the proximal portion of the shaft. Suitable materials for the balloon  50  and balloon leg  52 , taking these flexibility requirements into account, include, but are not limited to, known balloon materials such as nylon  12 . 
         [0031]    In order to further modify or control the flexibility of the region of catheter  32  proximal to expandable portion  38 , a stiffening wire may be provided. With reference to  FIG. 6 , a stiffening wire  70  is shown disposed longitudinally within catheter  32 . Stiffening wire  70 , also shown in greater detail in  FIG. 6A , has a proximal portion  74 , a distal portion  76 , and a transition portion  78 . Transition portion  78  is in the form of a gradual inward taper from proximal portion  74  to distal portion  76 . The distal portion  76  is narrower and more flexible than the proximal portion  74 . The diameter d of distal portion  76  is about one half or less of the diameter D of proximal portion  74 . Materials from which stiffening wire  70  may be constructed include, but are not limited to, stainless steel, NiTi, and CoCr. 
         [0032]    Stiffening wire  70  is preferably free-floating at its ends, and is only attached to the catheter  32  in a region between the two ends, preferably in connection region  62 . A preferred attachment method is by way of sleeve  64  to which stiffening wire  70  is bonded. Bonding can be achieved by placing a small polymer sleeve over the wire  70  and bonding the small polymer sleeve into the connection region  62 . Wire  70  extends at least partially into lumen  53  of balloon leg  52 , and preferably into the entire length of the lumen  53 , but ends proximally of the balloon proximal shoulder. Wire  70  also extends proximally at least partially into lumen  40  of shaft  65 . An advantage of stiffening wire  70  is that it improves trackability over the guidewire by providing resistance to bending to both balloon leg  52  and shaft  65  at the shaft&#39;s distal and most flexible portion. This compensates for the increased length provided by balloon leg  52  and required to maintain the connection region  62  and proximal guidewire port  46  within the guiding catheter during stent delivery. The stiffening wire  70  thus can reduce bowing of the shaft  65  of the catheter  32  away from the guidewire, kinking of the catheter or looping of the guidewire. In addition, the increase in length afforded by the balloon leg  52  is limited in order to avoid introducing too much flexibility and pushability problems. 
         [0033]    Another advantageous feature that can be provided with catheter  32  can be referred as a radiopaque measuring stick and is described with reference to  FIG. 7 . Three or more radiopaque marker bands  80  are disposed in balloon leg  52 , preferably annularly around secondary guidewire tube  42 . The maker bands  80  are evenly spaced apart, for example every 1 cm or every 5 mm measured center-to-center. The length of each marker band  60  is about 0.1 to about 1.0 mm. Use of marker bands in this configuration provides a visual indication of the length of a lesion or other physiological feature of the patient against which is useful in situations where length is difficult to determine. Suitable radiopaque materials for the marker bands  60  include, but are not limited to, barium, platinum, iridium, gold or combinations thereof. 
         [0034]    In use, the expandable portion  38  is passed beyond the physiological feature to be measured and the measuring stick is aligned within the feature. A lesion that is 3 cm long for example would extend over three marker bands spaced 1 cm apart, enabling a physician to select a suitably dimensioned stent based on such a determination, or to determine if a selected stent is of an appropriate size. 
         [0035]    Although the foregoing describes aspects of the present invention in the context of a rapid exchange stent delivery catheter, the present invention is not limited to such devices. Accordingly, additional embodiments exemplifying principles of the present invention include rapid exchange and non-rapid exchange catheters, balloon and non-balloon catheters including, but not limited to, infusion catheters, angioplasty catheters, angiography catheters, thermal and/or RF and/or laser ablation catheters, and fixed-wire vascular catheters. 
         [0036]    With reference to the drawing figures, an exemplary method of stent implantation embodying further principles of the present invention will now be described. Preferably a stenosed region of a blood vessel a mammalian, preferably human, patient is first predilated with an angioplasty balloon catheter. A catheter in accordance with the present invention is then inserted into the vasculature optionally over a guidewire, and is advanced through a guide catheter to a vascular location of interest. The balloon of the catheter may then be inflated or expanded in a manner well appreciated by the skilled artisan, for example by increasing the pressure applied to an inflation fluid, and the balloon&#39;s diameter increases. When a stent is positioned on the exterior surface of the balloon, the stent is thus expanded, in a well know manner. Thus, the balloon and/or the stent can be expanded against the interior surface of the blood vessel. Due to the relative short rapid exchange length of about 8 cm or less the proximal guidewire port  46  may be positioned outside of the guide catheter during a procedure. 
         [0037]    With reference to  FIG. 8 , a procedure for determining the size of a lesion, for example in order to select an appropriate stent size balloon size, or determine whether a selected stent is appropriate, is described. The balloon  50  of catheter  32  is shown in the vicinity of lesion  82  of vessel  86 . Balloon  50  is introduced into this vicinity in the manner described above. Proximal balloon leg  52  is disposed such that radiopaque marker bands  80  can be visualized inside the lesion  82 , and the dimensions of the lesion  82  can be compared with the position and number of marker bands  88 . In the illustrated example, the length dimension of the lesion  82  corresponds to about three marker bands  88 , making its length about 1 cm assuming 0.5 cm separation between marker bands. This can assist the physician to determine whether the stent selected is of a correct size. If the stent is not of a correct size, it can be withdrawn and a more suitable stent the lesion can then be selected. 
         [0038]    While the invention has been described in detail with reference to exemplary embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention. Each of the aforementioned documents is incorporated by reference herein in its entirety.