Abstract:
An intravascular device having a tubular shaft with an outer wall and an inner wall which divides the outer wall into two or more lumens. The shaft also includes one or more regions of modified flexibility extending longitudinally along the outer wall. Absent the regions of modified flexibility, the inner wall would create an imbalance of material and flexibility about the center axis of the shaft. The regions of modified flexibility are positioned to reduce any such imbalance, thereby providing more uniform flexibility. The regions of modified flexibility also provide for more uniform torque transmission, and thereby reduce whipping effects. The regions of modified flexibility may comprise one or more regions of decreased wall thickness in the outer wall, one or more spines extending longitudinally along the outer wall, or a combination thereof.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to intravascular medical devices. More specifically, the present invention relates to multi-lumen intravascular medical devices such as balloon catheters.  
         BACKGROUND OF THE INVENTION  
         [0002]    Intravascular devices are commonly used to diagnose and treat various types of vascular disease. For example, coronary artery disease (CAD) may be treated utilizing a procedure called percutaneous transluminal coronary angioplasty (PTCA). In a typical PTCA procedure, intravascular devices are inserted into the patient&#39;s vascular system at a remote access site such as the femoral artery near the groin. The intravascular devices are navigated through the femoral artery and the descending aorta, over the aortic arch, down the ascending aorta, and into the targeted coronary artery.  
           [0003]    The path from the remote access site to the targeted coronary artery is established and maintained utilizing a conventional guide catheter and guidewire. The guide catheter extends from a point outside the patient&#39;s body, through the remote access site, to the ostium of the targeted coronary artery. The guidewire extends from a point outside the patient&#39;s body, through the guide catheter, and across the treatment site of the targeted coronary artery. A balloon catheter may then be advanced over the guidewire through the guide catheter until the distally mounted balloon is positioned across the treatment site. The balloon is then inflated to dilate the vascular restriction, thereby opening the artery and restoring blood flow.  
           [0004]    Different types of balloon catheters are suitable for use in this type of procedure. Balloon catheters that are designed for use in combination with a guidewire as discussed above are typically referred to as over-the wire (OTW) or rapid exchange (RX) type balloon catheters. OTW and RX type balloon catheters include an elongate shaft having an inflation lumen and a guidewire lumen. In an OTW type balloon catheter, the guidewire lumen extends from the proximal end of the catheter to the distal end of the catheter. In an RX type balloon catheter, the guidewire lumen extends from a point distal of the proximal end to the distal end of the catheter. In both cases, at least a portion of the elongate shaft includes an inflation lumen and a guidewire lumen.  
           [0005]    In typical OTW and RX type balloon catheters, the guidewire lumen and the inflation lumen are defined by either a coaxial shaft structure or a dual lumen shaft structure. In a coaxial design, the elongate shaft includes an inner tube coaxially disposed in an outer tube such that the inner tube defines a circular guidewire lumen and the outer tube defines an annular inflation lumen. An example of a typical coaxial shaft design is disclosed in U.S. Pat. No. 4,323,071 to Simpson et al. In dual lumen shaft designs, a single tubular extrusion is used to define separate guidewire and inflation lumens extending side-by-side. An example of a dual lumen shaft design is disclosed in U.S. Pat. No. 4,782,834 to Maguire et al.  
           [0006]    One advantage provided by a coaxial type shaft design, as compared to a dual lumen type shaft design, is uniform flexibility due to the coaxial arrangement of parts. In other words, the coaxial type shaft design has the same flexibility in all planes of flexure, whereas the dual lumen type shaft design has non-uniform flexibility in differenct planes of flexure due to the imbalance of material relative to the longitudinal center axis of the catheter shaft. The non-uniformity in flexibility of the dual lumen type shaft design may compromise trackability and torqueability of the catheter, thereby reducing the ability of the catheter to navigate tortuous vasculature. One advantage provided by a dual lumen type shaft design is reduced frictional loss and less resistance to fluid flow in the inflation lumen as compared to a coaxial type shaft design having the same cross-sectional area. This provides better balloon inflation/deflation rates which are desirable for various clinical reasons.  
           [0007]    Accordingly, there is a need for a shaft design for an intravascular device such as a balloon catheter wherein the flexibility is uniform in all planes of flexure and the frictional loss in the inflation lumen is minimized.  
         SUMMARY OF THE INVENTION  
         [0008]    To address this need, the present invention provides an intravascular device, such as a balloon catheter, having a tubular shaft with an outer wall and an inner wall. The inner wall divides the outer wall into two or more lumens, such as a larger crescent-shaped lumen which may be used as an inflation lumen, and a smaller circle-shaped lumen which may be used as a guidewire lumen. The shaft also includes one or more regions of modified flexibility extending longitudinally along the outer wall. Absent the regions of modified flexibility, the inner wall would create an imbalance of material and flexibility about the center axis of the shaft. The regions of modified flexibility are positioned to reduce any such imbalance, thereby providing more uniform flexibility, without compromising the fluid dynamic capabilities of the lumens. The regions of modified flexibility also provide for more uniform torque transmission, and thereby reduce whipping effects.  
           [0009]    In one embodiment, the regions of modified flexibility comprise one or more regions of decreased wall thickness in the outer wall. In another embodiment, the regions of modified flexibility comprise one or more spines extending longitudinally along the outer wall. In yet another embodiment, the regions of modified flexibility comprise a combination of these features. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a plan view of an intravascular device in accordance with the present invention, shown in the exemplary form of a balloon catheter;  
         [0011]    [0011]FIG. 2A is a cross-sectional view and FIG. 3A is a partial isometric view of an embodiment of the elongate shaft of the intravascular device shown in FIG. 1;  
         [0012]    [0012]FIG. 2B is a cross-sectional view and FIG. 3B is a partial isometric view of another embodiment of the elongate shaft of the intravascular device shown in FIG. 1;  
         [0013]    [0013]FIG. 2C is a cross-sectional view of a further embodiment of the elongate shaft of the intravascular device shown in FIG. 1; and  
         [0014]    [0014]FIG. 2D is a cross-sectional view of yet another embodiment of the elongate shaft of the intravascular device shown in FIG. 1.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention.  
         [0016]    Refer now to FIG. 1, which illustrates a plan view of an intravascular device in the form of a balloon catheter  10 . Those skilled in the art will recognize that the present invention may be implemented in a wide variety of intravascular devices, such as infusion catheters, guide catheters, diagnostic catheters, atherectomy devices and balloon catheters such as balloon catheter  10 . Balloon catheter  10  includes an elongate shaft  12  having a proximal end and a distal end. A conventional manifold  14  is connected to the proximal end of the elongate shaft  12 . Manifold  14  facilitates connection to an inflation device to inflate and deflate a balloon  16  mounted to the distal end of the elongate shaft  12 . Fluid communication between the manifold  14  and the inflatable balloon  16  is provided by way of an inflation lumen  22  (visible in FIG. 2A) and an inflation port  18 . Manifold  14  also facilitates insertion of a guidewire (not shown) into the guidewire lumen  26  (visible in FIG. 2A) which extends to the distal end of the elongate shaft  12 . With the exception of the elongate shaft  12  and its features discussed hereinafter, intravascular balloon catheter  10  is substantially conventional. FIGS.  2 A- 2 D describe various embodiments ( 12 A, 12 B, 12 C, 12 D) of the elongate shaft  12  of the intravascular balloon catheter  10  illustrated in FIG. 1.  
         [0017]    Refer now to FIG. 2A, which illustrates a cross-sectional view of a first embodiment of the elongate shaft  12 A taken along line  2 - 2  in FIG. 1. Also refer to FIG. 3A, which illustrates an isometric view of a segment of the elongate shaft  12 A. In this particular embodiment, the elongate shaft  12 A includes an outer wall  20  and an inner wall  24 . As used herein for purposes of description, the outer wall  20  refers to the entire wall defining the circumference of the elongate shaft  12 A, and the inner wall  24  refers to the wall segment extending between two points inside the outer wall  20 .  
         [0018]    The outer wall  20  defines the majority of the inflation lumen  22 . The inner wall  24  and a portion of the outer wall  20  define the guidewire lumen  26 . In this particular example, the inflation lumen  22  is crescent-shaped and larger than the circle-shaped guidewire lumen  26 . Those skilled in the art will recognize that that size, shape and position of the inner wall  24  may be varied to change the size, shape and geometry of the inflation lumen  22  and the guidewire lumen  26 . In addition, those skilled in the art will recognize that the lumens  22 , 26  may be varied in number and function depending on the particular intravascular device implementing the concepts of the present invention.  
         [0019]    As seen in FIG. 2A, the portion of the outer wall  20  which defines the guidewire lumen  26  includes a thinned portion  28  extending longitudinally along the shaft  12 A. The thinned portion  28  of the outer wall  20  has a wall thickness T 1 , which is less than the wall thickness T 2  of the remainder of the outer wall  20 . The thickness T 1 , of the thinned portion  28  may also be less than the wall thickness T 3  of the inner wall  24 . The reduced wall thickness T 1  of the thinned portion  28  compensates for the imbalance of material and flexibility relative to the center longitudinal axis of the elongate shaft  12 A due to the inner wall  24 . In FIG. 2A, the center longitudinal axis of the elongate shaft  12 A appears as a point (not shown) positioned at the geometric center of the outer wall  20 . The provision of the inner wall  24  increases the amount of material on one side of the shaft  12 A when viewed in cross section. The increased amount of material due to the inner wall  24  increases the rigidity along that side of the elongate shaft  12 A, thereby causing non-uniformity in flexibility in different planes of flexure. By reducing the wall thickness T 1 , in the thinned outer wall portion  28 , the imbalance of material and flexibility due to the inner wall  24  is mitigated.  
         [0020]    Because the thinned portion  28  of the outer wall  20  does not define any portion of the inflation lumen  22 , the thinned portion  28  does not compromise the ability of the inflation lumen  22  to withstand high inflation pressures. In addition, the inner wall  24  may be shifted toward the thinned portion  28  of the outer wall  20  a distance approximately equal to T 2 −T 1  without compromising the size of the guidewire lumen  26 . Because the inner wall  24  may be shifted in the direction of the thinned portion  28  of the outer wall  20 , the inflation lumen  22  also benefits from a corresponding increase in cross-sectional area, thereby improving fluid flow therethrough.  
         [0021]    Refer now to FIG. 2B, which illustrates a cross-sectional view of an elongate shaft  12 B in accordance with another embodiment of the present invention. Also refer to FIG. 3B, which illustrates an isometric view of a segment of the elongate shaft  12 B. Except as illustrated and described herein, the elongate shaft  12 B is substantially the same as elongate shaft  12 A described with reference to FIGS. 2A and 3A.  
         [0022]    Elongate shaft  12 B includes an outer wall  20 , an inner wall  24 , an inflation lumen  22  and a guidewire lumen  26 . Elongate shaft  12 B may optionally include a thinned region  28  in the outer wall  20 . Elongate shaft  12 B further includes longitudinally extending spines  30  to further compensate for the imbalance of material and flexibility about the center longitudinal axis of the shaft  12 B that would otherwise occur due to the inner wall  24 . Relative to the center longitudinal axis, the longitudinal spines  30  are disposed on the opposite side of the inner wall  24  and the thinned portion  28  of the outer wall  20 .  
         [0023]    The longitudinal spines  30  may comprise discrete components connected to the outer wall  20 . Alternatively, the longitudinal spines  30  may comprise integral components of the outer wall  20  such as an increase in thickness of the outer wall  20 . Preferably, the longitudinal spines  30  are integrally formed with the outer wall  20  during extrusion. The longitudinal spines  30  may extend outwardly from the outer wall  20  (as shown) to maintain the size of the inflation lumen  22 . Alternatively, the longitudinal spines  32  (shown in phantom) may extend inwardly into the inflation lumen  22  to maintain the outside profile of the elongate shaft  12 B.  
         [0024]    The longitudinal spines  30  may be positioned, relative to the center longitudinal axis of the elongate shaft  12 B, opposite the inner wall  24  and the thinned portion  28  of the outer wall  20 . The longitudinal spines  30  may be positioned equidistant from the inner wall  24  and/or thinned portion  28  of the outer wall  20 . Preferably, the longitudinal spines  30  are uniformly spaced along the outer wall  20  opposite the inner wall  24  and thinned portion  28  of the outer wall  20  to increase the balance of material and flexibility about the center axis of the elongate shaft  12 B.  
         [0025]    Those skilled in the art will recognize that the size, shape and number of longitudinal spines  30  may be varied depending on the size, shape and position of the inner wall  24 . For example, it is contemplated that a single longitudinal spine  30  may be positioned immediately opposite the inner wall  24  and thinned portion  28  of the outer wall  20 . If two longitudinal spines  30  are utilized (as shown), the spines  30  may be positioned approximately one-third the radius of the outer wall  20  from the longitudinal center axis of the elongate shaft  12 B to properly counterbalance the material of the inner wall  24 .  
         [0026]    As mentioned previously, the size, shape and number of longitudinal spines  30  may be varied depending on the degree of counterbalance needed to balance the material and flexibility of the elongate shaft  12 . FIGS. 2C and 2D illustrate examples of variations in the size, number and position of the longitudinal spines  30 . FIG. 2C illustrates elongate shaft  12 C having two longitudinal spines  30  with a smoother outside surface than elongate shaft  12 B. FIG. 2D illustrates an elongate shaft  12 D having three longitudinal spines  30  uniformly spaced about the outer wall  20  opposite the inner wall  24  relative to the longitudinal center axis.  
         [0027]    Those skilled in the art will recognize that the present invention may be manifested in a variety of forms other than the specific embodiments described and contemplated herein. Accordingly, departures in form and detail may be made without departing from the scope and spirit of the present invention as described in the appended claims.