Abstract:
An intravascular catheter such as a dilatation catheter for angioplasty procedures having a removable distal shaft section. The catheter construction allows the original distal shaft section of the catheter to be removed and a replacement distal shaft section to be secured to the proximal section which is useful with angioplasty catheters when the dimensions of the balloon on the original distal shaft section are inappropriate for dilating a particular stenotic region. Such catheter construction is also useful when there is a need to implant a stent into a dilated stenotic region to maintain its patency.

Description:
BACKGROUND OF THE INVENTION 
     This invention generally relates to the field of intravascular catheters which are advanceable over a guidewire into a desired region of a patient&#39;s vasculature, and particularly to an intravascular catheter which is advanceable into a patient&#39;s coronary arteries for therapeutic or diagnostic procedures therein. 
     In percutaneous transluminal coronary angioplasty (PCTA) procedures, a guiding catheter having a preshaped distal tip is percutaneously introduced by a Seldinger techniques into the cardiovascular system of a patient and advanced within the system until the preshaped distal tip of the guiding catheter is disposed within the ascending aorta adjacent the ostium of the desired coronary artery. The guiding catheter is relatively stiff and when it is twisted or torqued from its proximal end, which extends outside the patient, the distal tip of the guiding catheter may be guided into the desired coronary ostium. With the distal end of the guiding catheter well seated within the ostium of the desired coronary artery, a balloon dilatation catheter is introduced into and advanced through the guiding catheter and out the distal tip thereof into the patient&#39;s coronary artery until the balloon on the distal extremity of the dilatation catheter is properly positioned across the lesion to be dilated. Once properly positioned, the balloon is inflated one or more times to a predetermined size with radiopague liquid at relatively high pressures (e.g., generally 4-12 atmospheres) to dilate the stenotic region of the diseased artery. When the dilatations have been completed, the balloon is finally deflated so that the dilatation catheter can be removed from the dilated stenosis to allow the resumption of increased blood flow through the dilated artery. 
     One frequently used type of angioplasty catheter is an over-the-wire type catheter which has an inner lumen extending within the catheter shaft which is configured to slidably receive a guidewire which facilitates advancement of the catheter over the guidewire to the desired location within the patient&#39;s coronary arteries. The guidewire receiving inner lumen may extend the entire length of the catheter as in conventional over-the-wire catheters or only in the distal portion of the catheter between a distal guidewire port and a proximal guidewire port which is spaced a short distance proximally from the distal guidewire port and a substantial distance from the proximal end of the catheter as in rapid exchange type catheters. 
     It is not uncommon during an angioplasty procedure to exchange the dilatation catheter once the dilatation catheter has been advanced within the patient&#39;s arterial system. For example, if the physician determines that the inflated size of the balloon or the length of the balloon is inappropriate for the stenosis to be dilated, the dilatation catheter will be withdrawn and another, more appropriately sized dilatation catheter will be advanced into the coronary artery over the guidewire which remains in-place to dilate the stenosis. However, if the catheter is a conventional over-the-wire catheter, before the catheter is withdrawn either the guidewire in place must be replaced with an exchange wire, which is similar to the in-place guidewire except about twice as long, e.g. about 300 cm, as the normal guidewire or an extension wire about the same length as the in-place guidewire must be secured to the proximal end of the in-place guidewire to facilitate the withdrawal of the catheter from the patient&#39;s vasculature without loss of the distal position of the guidewire. The reason that it is important to maintain the position of the distal tip of the guidewire across the stenosis, is that, if the guidewire is withdrawn, it may take the attending physician a substantial amount of time, e.g. from about 15 minutes up to about two hours or more, to advance a replacement guidewire into the patient&#39;s coronary artery and across the stenosis to be dilated and to then advance the dilatation catheter until the dilatation balloon thereof crosses the stenotic region. The original unsuitable catheter is usually discarded. 
     In some instances, after a dilatation is complete, it is necessary or at least desireable to implant a stent in the dilated stenotic region to provide long term patency thereto. In these cases the dilatation catheter which has performed the dilatation is removed and another balloon catheter having an unexpanded stent mounted about the balloon is advanced over the in-place guidewire to the stenotic region where the balloon is inflated to expand and thus implant the stent in the stenotic region. In this case the original angioplasty catheter is also discarded. 
     What has been needed and heretofore unavailable is a system for easily changing a shaft section of an intravascular catheter without the need to discard the entire catheter. The present invention satisfies these and other needs. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an intraluminal catheter with an exchangeable shaft section. 
     The intraluminal catheter of the invention has an elongated shaft having a proximal shaft section with at least one inner lumen extending therein and a distal shaft section with an inner lumen extending therein which is in communication with the inner lumen of the proximal shaft section. Means are provided to releasably secure the proximal end of the distal shaft section to the distal end of the proximal shaft portion, The proximal end of the distal shaft section is provided with releasable connecting means which is configured to be connected to connecting means on the distal end of the proximal shaft section which allows the distal section to be readily exchanged for another distal section. The preferred releasable connecting means are matching threads, male threads on the exterior of one shaft section member and female threads on the interior of another shaft section member which are configured to receive shaft section member with the male threads. 
     In one aspect of the invention, the intraluminal catheter is a dilatation catheter for performing angioplasty procedures with a dilatation balloon on the distal shaft section thereof. This allows the original distal shaft section to be exchanged for another distal shaft section when, for example, the dilatation balloon is of inappropriate size, either in length or in inflated diameter, for a particular stenotic region of the patient&#39;s artery. 
     The distal shaft section  42  of the above dilatation catheter may also be replaced when it is necessary or desireable to instal a stent in a dilated stenotic region of the patient&#39;s artery to ensure that the region remains patent after the dilatation. In this case, the original distal shaft section is removed after the dilatation has been performed and a replacement distal shaft section having an inflatable balloon or other expandable means thereon with a stent mounted about the inflatable balloon or other expandable means. The catheter with the replacement distal shaft section is advanced within the arterial system of the patient until the inflatable balloon or other expandable means is disposed within the stenosis so expansion thereof expands the stent to secure the stent within the arterial passageway. The expanded balloon may then be deflated and the catheter removed from the patient with the expanded stent maintaining within the arterial passageway to maintain its patency. 
     In a presently preferred embodiment, the exchangeable catheter shaft section has an inner and an outer tubular member with the threaded connections on an end of either the outer tubular member or the inner tubular member or both which engage the matching treads on the mating ends of the tubular members of the shaft section which is not to be replaced when the threaded connections are made. 
     The above described advantages of the invention as well as others will become more apparent from the following detailed description of the invention when taken in conjunction with the accompanying exemplary drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevational view, partially in section, of an over-the-wire balloon dilatation catheter embodying features of the invention. 
         FIG. 2  is a transverse cross-sectional view of the catheter shown in  FIG. 1  taken along the lines of  2 — 2 . 
         FIG. 3 , is an elevational view, partially in section, of a rapid exchange type balloon dilatation catheter embodying features of the invention. 
         FIG. 4  is an elevational view of a distal portion of a balloon catheter embodying features of the invention with an expandable stent mounted on the balloon of the catheter with the balloon and the stent in expanded conditions within a stenotic region of a patient&#39;s artery. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIGS. 1 and 2 , dilatation catheter  10  embodying features of the invention includes an elongated catheter shaft  11  with a proximal section  12  and a replaceable distal section  13 . The proximal section  12  has an outer tubular member  14  and an inner tubular member  15  with the distal end of the outer tubular member having male threads  16  for connection to the distal section  13 . The distal section  13  has an outer tubular member  17  and an inner tubular member  18  with proximal end of the outer tubular member  17  having female threads  19  which are configured to engage the male threads  16  on the distal end of the outer tubular member  14 . The distal end of the inner tubular member  15  of the proximal section  12  is tapered so as to sealingly fit into the inner passageway of the inner tubular member  18  of the distal section  13  when the outer tubular members  14  and  16  are threadably connected (as shown in phantom in FIG.  1 ). The outer tubular member  17  may be provided with webs or spacers (not shown) to centrally position the inner tubular member  18  within the outer tubular member  17  to ensure appropriate entry of the distal end of the inner tubular member  15  into the inner tubular member  18 . 
     A dilatation balloon  22  is provided on the replaceable distal section  13  which has an interior in fluid communication with the annular inner lumen  23  defined between the inner and outer tubular members  18  and  17  and the annular lumen  24  defined between the outer and inner tubular members  14  and  15  of the proximal section  12 . 
     A multiarm adaptor  25  is provided on the proximal end of the proximal section  12  to facilitate delivery of inflation fluid to the interior of dilatation balloon  22  through side arm  26  and annular lumens  23  and  24 . The inner tubular members  15  and  18  define a guidewire receiving lumen  27  which extends from the adapter  25  through the length of the catheter to a distal guidewire port  28  in the distal end of the distal placeable section  13  and is configured to slidably receive a guidewire  30 . 
     Due to strength requirements for the threaded connection between the outer tubular members  14  and  17 , it is usually preferable to form the threaded portions  31  and  32  of these members of a high strength material (e.g. stainless steel, NiTi alloys and the like). In this instance, the separate threaded connecting elements  31  and  32  would be formed independently of the other portions of the outer tubular members  14  and  17  and then secured to these members by a suitable adhesive or other means such as a fusion or solvent bond, depending upon the nature of the material from which the separate connecting elements  31  and  32  are formed. Other materials which are suitable for forming the connecting elements  31  and  32  include high strength polymers such as polycarbonate polymers and the like. 
     The dilatation catheter  10  depicted in  FIGS. 1-2  may be used in a typical fashion whereby it is advanced over guidewire  30  previously disposed across the stenosis to be dilated until the balloon  22  extends across the lesion to be dilated. In the event the balloon&#39;s size, e.g. its inflated diameter or its length, is found to be inappropriate for the lesion to be dilated, the catheter  10  is withdrawn from the patient over the guidewire  30  and once outside of the patient, the removable distal section  13  and the proximal section  12  can be separated by twisting one or both so that the threaded members  31  and  32  can disengage. Another distal section of essentially the same construction, but with a balloon with a more appropriately sized length or inflated diameter, may then be threadably secured onto the distal end of the proximal section  12  and the reconstructed dilatation catheter may then be mounted onto the in-place guidewire and advanced over the guidewire until the more appropriately sized dilatation balloon crosses the stenosis. An extension wire is usually secured to the proximal end of the guidewire  30  to facilitate the withdrawal of the original catheter  10  and the introduction and advancement of the replacement catheter with a new distal shaft section through the patient&#39;s arterial system until the more appropriately sized replacement balloon extends across the stenosis. The replacement balloon may then be inflated one or more times in a conventional manner to dilate the stenotic region of the patient&#39;s artery and then be withdrawn as the original catheter  10 . 
       FIG. 3  illustrates a rapid exchange type dilatation catheter  40  embodying features of the invention which has a proximal shaft section  41 , a distal shaft section  42 , a dilatation balloon  43  on the distal shaft section and an adaptor  44  on the proximal end of the proximal shaft section. The proximal shaft section  41  is preferably hypotubing formed of metal such as stainless steel (e.g.  304 ) or pseudoelastic NiTi alloy provided with male threads  46  which are configured to threadably engage the female threads  47  on connector element  48  secured to the proximal end of distal shaft section  42 . As shown in  FIG. 3 , the distal shaft section  42  is provided with a guidewire receiving inner lumen  50  which extends from proximal guidewire port  51  to the distal guidewire port  52  provided in the distal end of the catheter. A dual lumen portion  53  extends from the connector element  48  to just within the proximal end of the balloon  43  and a tubular extension  54  thereof extends through the interior of the balloon  43  and out the distal end thereof. A guidewire  55  is slidably disposed within the guidewire receiving inner lumen  50 . A radiopague marker  56  is provided on the tubular extension  54  at the midpoint between the two ends of the balloon  43  to facilitate the fluoroscopic observation thereof within the patient. 
     The distal shaft section  42  of the catheter  40  may be replaced as in the previously described embodiment, the only major difference being that there is no need for an extension wire to facilitate withdrawal of the original catheter  40  and the introduction of the replacement catheter with a different distal section. 
       FIG. 4  illustrates a replacement distal section  60  similar to the distal section  42  shown in  FIG. 3  but adapted to deliver an expandable stent  61  to a stenotic region of a patient&#39;s artery to provide long term patency. Once the stent  61  is properly expanded, the balloon  63  may be deflated and the catheter withdrawn from the patient. This particular embodiment may be utilized after dilatation of the stenotic region by means of a catheter of the invention such as shown in FIG.  3 . In this instance, after the dilatation, the dilatation catheter may be withdrawn, the distal section  42  removed from the proximal shaft section  41  by disengaging the threaded ends of the proximal shaft section and connector element  48  and securing the replacement distal section  60  to the threaded end of proximal shaft section by threadably engaging the connector element  64  with female threads  65  to the distal end of the proximal shaft section with male threads  46 . The replacement catheter with the distal section  60  may then be advanced into and through the patient&#39;s arterial system over the guidewire  66  until the balloon  63  is disposed across the stenosis. Expansion of the balloon  63  within the stenosis expands the stent  61  to hold open the stenotic region of the patient&#39;s artery. The catheter can then be removed with the stent remaining within the dilated arterial passageway to maintain its patency. 
     The catheter construction and the materials of the various portions thereof may be conventional. Moreover, while the invention is described herein in terms of certain preferred embodiments, a variety of modification can be made. For example, threaded connections are described between the proximal and distal shaft sections to facilitate separation of the distal shaft section from the proximal shaft section. However, other types of connections are contemplated with the present invention, the threaded connection being a presently preferred embodiment. Other connections include projections and corresponding detentes. Additionally, while replacement of the distal shaft section is primarily described herein, those skilled in the art will recognize that the proximal shaft section may be the replaceable shaft section. Other modifications and improvements may be made to the invention without departing from the scope thereof.