Abstract:
A balloon catheter having a radiopaque coil embedded in the catheter&#39;s body corresponding to a landmark of the balloon or other location on the catheter body. The radiopaque coil can be viewed under fluoroscopy to located the balloon or other structure of the catheter. The coil can be readily inserted in the manufacturing process by inserting it between two layers that form the catheter body, and then sealing the coil inside the catheter at the desired location. This facilitates both the manufacturing process and prevents the marker from being dislodged during the manufacturing, navigation, or inflation process.

Description:
BACKGROUND 
       [0001]    This invention generally relates to intravascular balloon catheters and systems for performing percutaneous transluminal coronary angioplasty (PTCA) and/or stent delivery, and more particularly to a catheter delivery system that uses a radiopaque coil in the catheter structure to provide a visual indicator in the system showing where a part of the catheter is located within a body lumen. 
         [0002]    PTCA is a widely used procedure for the treatment of coronary heart disease. In this procedure, a balloon dilatation catheter is advanced into the patient&#39;s coronary artery and the balloon on the catheter is inflated within the stenotic region of the patient&#39;s artery to open up the arterial passageway and thereby increase the blood flow there through. To facilitate the advancement of the dilatation catheter into the patient&#39;s coronary artery, a guiding catheter having a pre-shaped distal tip is first percutaneously introduced into the cardiovascular system of a patient by the Seldinger technique or other method through the brachial or femoral arteries. 
         [0003]    The catheter is advanced until the pre-shaped distal tip of the guiding catheter is disposed within the aorta adjacent the ostium of the desired coronary artery, and the distal tip of the guiding catheter is then maneuvered into the ostium. A balloon dilatation catheter may then be advanced through the guiding catheter into the patient&#39;s coronary artery over a guidewire until the balloon on the catheter is disposed within the stenotic region of the patient&#39;s artery. The balloon is inflated to open up the arterial passageway and increase the blood flow through the artery. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not over expand the artery wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed. 
         [0004]    In a large number of angioplasty procedures, there may be a restenosis, i.e. reformation of the arterial plaque. To reduce the restenosis rate and to strengthen the dilated area, physicians may implant an intravascular prosthesis or “stent” inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is then deflated to remove the catheter and the stent is left in place within the artery at the site of the dilated lesion. 
         [0005]    To accurately place the balloon, and also the stent, at the desired location, visual markers on the catheter are typically utilized that are read by machines outside the body. For example, in the case where a balloon catheter is used with an fluoroscope, a radiopaque marker incorporated into the catheter body may be observed visually on a screen while the procedure is taking place. In many cases, the markers must be precisely located to ensure accurate placement of the balloon in the affected area. Incorporating markers into the catheter&#39;s or balloon&#39;s structure can be expensive, and the markers can become dislodged when the catheter is torqued during delivery or when the catheter&#39;s balloon expands. For these reasons, a better and more economically feasible method of incorporating a radiopaque marker into a balloon catheter is needed. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is a catheter or catheter delivery system that incorporates a coil made from a radiopaque material that can be inserted between layers of a multi-layer catheter body. The coil is placed, for example, over a first layer of a multi-layer catheter body, and then a second layer of material is formed over the first, capturing the radiopaque coil between the two layers. Where the coil is disposed at, for example, the beginning or end of the working length of the balloon, the physician can accurately determine the precise location that the balloon needs to be positioned under fluoroscopy by locating the coil, which in turn identifies the beginning (or end) of the balloon&#39;s working length. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is an elevated, perspective view of a catheter delivery system of the present invention; 
           [0008]      FIG. 2  is a cross-sectional view of the catheter of  FIG. 1  taken along lines  2 - 2 ; 
           [0009]      FIG. 3  is a cross-sectional view of the catheter of  FIG. 1  taken along lines  3 - 3 ; 
           [0010]      FIG. 4  is a perspective view of the catheter as the outer layer is being peeled back for removal; 
           [0011]      FIG. 5  is a perspective view of the coil being placed over the inner layer of the catheter; 
           [0012]      FIG. 6  is an enlarged perspective view of the coil on the inner layer of the catheter; 
           [0013]      FIG. 7  is an enlarged view of the catheter with a new outer layer placed over the coil and the inner layer; 
           [0014]      FIG. 8  is an enlarged view, partially in shadow, of the catheter with the balloon showing the position of the coil in a first embodiment; and 
           [0015]      FIG. 9  is a perspective view of the catheter balloon showing the position of the coil in a second embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]      FIG. 1  illustrates a balloon catheter of the type that can benefit from the present invention. The catheter  10  of the invention generally comprises an elongated catheter shaft  11  having a proximal section,  12  a distal section  13 , an inflatable balloon  14  formed of one or more polymeric materials on the distal section  13  of the catheter shaft  11 , and an adapter  17  mounted on the proximal section  12  of shaft  11 . In  FIG. 1 , the distal portion of the catheter  10  is illustrated within a patient&#39;s body lumen  18 , prior to expansion of the balloon  14 . 
         [0017]    In the embodiment illustrated in  FIG. 1 , the catheter shaft  11  has an outer tubular member  19  and an inner tubular member  20  disposed within the outer tubular member defining, with the outer tubular member, an inflation lumen  21 . Inflation lumen  21  is in fluid communication with the interior chamber  15  of the inflatable balloon  14 . The inner tubular member  20  has an inner lumen  22  extending therein which is configured to slidably receive a guidewire  23  suitable for advancement through a patient&#39;s coronary arteries. The distal extremity  31  of the inflatable balloon  14  is sealingly secured to the distal extremity of the inner tubular member  20  and the proximal extremity  32  of the balloon  14  is sealingly secured to the distal extremity of the outer tubular member  19 . 
         [0018]      FIGS. 2 and 3  show transverse cross sections of the catheter shaft  11  and balloon  14 , respectively, illustrating the guidewire receiving lumen  22  of the guidewire&#39;s inner tubular member  20  and inflation lumen  21  leading to the balloon interior  15 . The balloon  14  can be inflated by a fluid introduced at the port in the side arm  24  into inflation lumen  21  contained in the catheter shaft  11 , or by other means, such as from a passageway formed between the outside of the inner tubular member  20  and the outer tubular member  11 , depending on the particular design of the catheter. The details and mechanics of balloon inflation vary according to the specific design of the catheter, and are well known in the art. 
         [0019]    Typically balloon catheters of the type shown in  FIG. 1  include radiopaque markers incorporated onto the inner tubular member. These markers must be formed onto the inner tubular member&#39;s surface, either through adhesives, mechanical attachment, or embedded into the inner tubular member&#39;s material. As explained above, there are shortcomings with incorporating radiopaque markers relating to reliability of adhering the markers to the catheter body as well as the fact that the procedure is expensive and reduces the manufacturing yield of the catheters. The present invention overcomes these shortcomings by implanting a radiopaque coil into the catheter body, preferably at a location of interest to the physician, so that the conventional balloon markers can be omitted.  FIGS. 4-7  illustrate the various steps of one method for constructing the catheter of the present invention. 
         [0020]    With reference to  FIG. 4 , a catheter body  11  is formed on a mandrel  130  and may be formed, for example, as a dual-layer hollow extrusion with a lubricious inner layer  100  of HDPE or ultra high molecular weight polyethylene (UHMWPE) and an outer layer  105  of nylon or Pebax, with or without the usual Primacor “tie layer” that binds the inner layer  100  to the outer layer  105 . To insert the radiopaque coil into the catheter body, the outer layer  105  is stripped away by peeling back tabs  115  until the scored portion  110  is readed, whereupon a coil placed over the inner layer  100 . Assembly begins with the following steps to remove a distal section of the outer Pebax or nylon layer  105 : 
         [0021]    Step  1 : At an appropriate distance from the distal end of the catheter body  11 , the outer layer of the HDPE/nylon or HDPE/Pebax extrusion is circumferentially scored  110  using a cutting instrument such as a razor blade or the like to create a break point of the outer layer  105  only ( FIG. 4 ). Care is called for to control the scoring blade in order to protect the inner layer  100 . 
         [0022]    Step  2 : A longitudinal slit is made at the distal end of the catheter body over a length of several millimeters or more using a cutting knife such as a razor blade or equivalent, creating two semi-circular halves at the distal end. 
         [0023]    Step  3 : To separate the outer layer  105  from the inner layer  100 , both halves of the bisected end are folded or rolled back, and a grasping tool such as tweezers or the like is used to grasp the outer layer  105  at the semi-circular halves and pull them away from the inner layer  100  of each half ( FIG. 4 ). The outer layer  105  is then peeled away from their respective inner layer to thus separate and remove the outer layer until the score mark  110  is reached, whereupon the outer layer halves  105   a,b  tear away from the catheter body  11 . The result is a stepped transition  140  between the exposed HDPE inner layer  100  and the intact proximal remainder of the extrusion&#39;s outer layer  105  ( FIG. 5 ). 
         [0024]    Next, a radiopaque coil  150  is slid over the exposed inner layer  100  of the catheter (see arrow  170  of  FIG. 5 ) and a second coil may be added to the first coil. The coils  150  may, but not need be, stacked, and a separation of the two (or more) coils can provide a gap where the outer tubular member and the inner tubular member make physical contact to help seal the coil therebetween. Once the coil or coils  150  are in place, a new, lower durometer coextrusion outer layer  180  is slid over the coil(s)  150  and the inner layer  100  as shown in  FIG. 7 . The coextrusion  180  may include an adhesive tie-layer (not shown) to help bond the new outer layer  180  to the inner layer  100 . Placing the outer layer  180  over the coil sandwiches the coil  150  inside the catheter&#39;s multi-layer construction. The new outer layer  180  is butted against the old outer layer  105 , and a suitable length of shrink tubing may be placed over the joint as is known in the art. A fluoropolymer shrink tube material, such as FEP, is preferable due to its non-stick nature. This region is then progressively heated to melt bond the various segments  180  and  100  together and, where present, allow a Primacor middle layer to adhere or “tie” the outer layer  180  to the underlying HDPE layer. Afterwards, the shrink tubing and mandrel  130  are removed to leave the finished catheter body with the radiopaque coil  150  embedded in the catheter body. 
         [0025]    The resultant catheter has the radiopaque coil  150  embedded in its construction and can be used to locate the balloon  14  or other part of the catheter under fluoroscopy. In  FIG. 8 , the catheter  11  can be seen with a balloon  14  mounted thereon such that the coil  150  terminates at the end of the working section  51  of the balloon  14 . Under fluoroscopy, a physician would be able to locate the coil  150  and immediately know where the working section  51  of the balloon ends. This feature allows the physician to locate the coil adjacent the lesion or obstruction and know with confidence that the balloon  14  will be applied at the precise location where the proximal end of the coil  150  begins. Alternatively, as shown in  FIG. 9 , the coil  150  or coils can be placed along and co-terminus with the working section of the balloon  14  (between  51  and  52 ). For the catheter balloon  14  of  FIG. 9 , the coil  150  corresponds to the beginning  52  and end  51  of the working portion of the balloon  14 , so the physician can locate the coil  150  under fluoroscopy and place the balloon  14  precisely where it needs to be to accomplish the greatest effectiveness. Other locations are also available, such as at the beginning of the working section of the balloon for example. 
         [0026]    The outer layer  105  can be any durometer polymer, as required by the application, and its inner layer  100  can be any extrudable lubricious material. However, preferably the layer materials should not adhere well to each other during extrusion, because peeling off the outer layer  105  at the distal end would be more difficult. The dual layer catheter may be E-beam irradiated, particularly if its inner layer is HDPE (or UHMWPE), as this promotes cross-linking and thus prevents undesirable material flow of the inner layer during subsequent melt bonding operations. 
         [0027]    The newly added outer layer segment  180  can be any durometer polymer, as the application requires, but it is preferred that it contain an inner surface of a “tie layer” material like Primacor in order to promote secure bonding to the inner layer  100 . The heat needed for such bonding is preferably achieved by equipment that provides localized and controllable heat with the ability to traverse or rotate, and the required radial pressure is preferably provided by shrink tubing which does not adhere well to the underlying materials. Although it would be possible to simply heat the assembly in an oven, this is less desirable because of a greater tendency to trap air beneath the shrink tubing leading to surface irregularities. 
         [0028]    This invention is also applicable to inner members whose inner layer  100  is a fluoropolymer such as PTFE. For example, the inner layer  100  can be a single-layer extrusion that is subsequently etched (e.g., sodium naphthalene or “Tetra Etch”) to promote bondability of its outer surface. An outer layer  105  is then extruded onto the fluoropolymer tubing in a semi-continuous (reel to reel) manner, with the extrusion parameters selected to prevent melt bonding of the two layers. Thus, the outer layer  105  can be subsequently peeled away at one end to make room for the installation of various durometers of outer jacket segments and radiopaque coils  150 . In this embodiment, the added segments do not require an inner “tie layer’ because they can be melt bonded directly to the etched fluoropolymer surface, again using heat and shrink tubing. 
         [0029]    While particular forms of the invention have been illustrated and described, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited except by the appended claims.