Abstract:
A guidewire navigable through body vessels of a human subject for delivery of a catheter or the like is provided. The guidewire has a tube which receives a corewire that protrudes beyond a distal portion of the tube. The protruding portion of the corewire is surrounded by a spring and shapeable into a curve or arc. The cross-sectional shape of the spring may be varied in order to promote bending flexibility and curvature or to favor curvature of a chosen type. The corewire is axially movable with respect to the tube, which compresses or stretches the spring to change the stiffness of the spring. The tube has a proximal portion comprised of a relatively rigid material, such as stainless steel, while a distal portion is comprised of a more flexible material, such as a nitinol.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention generally relates to medical devices that are navigable through body vessels of a human subject. More particularly, this invention relates to guidewires used to position a catheter or the like within a body vessel.  
       DESCRIPTION OF RELATED ART  
       [0002]     Vessel defects, such as blockages and stenoses, within the human vasculature system are often treated by the intraluminal delivery of treatment fluids or expansion devices and stents. Expansion devices can take any of a number of forms, but are all generally delivered by a flexible catheter that, once properly positioned, deploys the expansion device. The path to the diseased site is typically tortuous and may additionally pass through other constricted lumens, so catheters cannot be used to define their own path through the vasculature. As such, a more rigid guidewire is first passed through the vasculature to the desired site, and then the catheter is passed over the guidewire.  
         [0003]     The different body environments in which guidewires must operate create several design complications. For example, it is desirable for the guidewire to be somewhat flexible so that it can pass through tortuous portions of the vasculature. On the other hand, it is also desirable for the guidewire to be somewhat rigid so that it may be forced through constricted body vessels and lesions or used to perforate the fibrocalcific cap of chronic total coronary artery occlusions. More rigid guidewires also provide tactile feedback to the operator. Most guidewires have a fixed stiffness, so the surgeon must select a guidewire based on the predicted body environment. Of course, if the guidewire is not properly selected, then multiple guidewires with different stiffness values must be used. Even proper guidewire selection cannot obviate the need for multiple guidewire usage for some body environments.  
         [0004]     In recognition of this problem, a number of variable stiffness guidewires and stylets have been suggested. Examples can be seen in U.S. Pat. No. 3,854,473 to Matsuo; U.S. Pat. No. 4,215,703 to Wilson; U.S. Pat. No. 5,762,615 to Weier; U.S. Pat. No. 5,957,903 to Mirzaee et al.; U.S. Pat. No. 6,113,557 to Fagan et al; U.S. Pat. No. 6,183,420 to Douk et al.; and U.S. Pat. No. 6,755,794 to Soukup, all of which are hereby incorporated herein by reference.  
         [0005]     Generally speaking, these variable stiffness devices include a tube which receives a corewire that protrudes distally beyond the tube. A coiled spring surrounds the protruding portion and is connected at opposite ends to the corewire and the tube, such that axial movement of the corewire with respect to the tube will compress or stretch the spring. When the tip of the corewire is moved away from the tube using a handle outside of the body, the separation gaps between the coils of the spring enlarge and the tip become more flexible and better suited for being fed through tortuous body vessels. In the event that the guidewire encounters a constricted body vessel through which it must pass, the corewire is moved toward the tube, which compresses the spring and causes the separation gaps to diminish and the tip to become more rigid.  
         [0006]     While these known variable stiffness guidewires are an improvement over previous fixed stiffness guidewires, there are still several possible areas of improvement. For example, the described tubes are comprised of a relatively rigid material, typically stainless steel. Stainless steel is well-suited for procedures requiring the guidewire to be forced through a constricted vessel, but it is not sufficiently flexible for procedures requiring the guidewire to define a tortuous path.  
         [0007]     Another problem with known variable stiffness guidewires is that they use springs having a uniform cross-sectional shape. Most often, the coil spring has a round or circular cross-sectional shape, which performs well for operations requiring flexibility, but not as well for operations requiring more stiffness. The other known alternative is to use a flat coil spring, which is typically stronger than a spring having a round cross-sectional shape and performs better in operations requiring a relatively stiff guidewire tip. However, flat coil springs are not as flexible as would be desired in operations involving a tortuous vessel pathway.  
         [0008]     Accordingly, a general aspect or object of the present invention is to provide a variable stiffness guidewire having a tube which provides increased flexibility without sacrificing stiffness.  
         [0009]     Another aspect or object of this invention is to provide a guidewire with a spring having regions of differing stiffness.  
         [0010]     Other aspects, objects and advantages of the present invention, including the various features used in various combinations, will be understood from the following description according to preferred embodiments of the present invention, taken in conjunction with the drawings in which certain specific features are shown.  
       SUMMARY OF THE INVENTION  
       [0011]     In accordance with one aspect of the present invention, a variable stiffness guidewire is provided with a tube, an elongated corewire received by the tube and protruding from both ends of the tube, and a coiled spring surrounding the distally protruding portion of the corewire. The corewire is movable with respect to the tube in order to compress or stretch the spring, which contributes to varying the stiffness of the tip of the guidewire. The tube has a composite structure, wherein a proximal portion is relatively rigid and a distal portion is more flexible. In a preferred embodiment, the proximal portion is stainless steel and the distal portion is comprised of a shape memory material, such as a nitinol material. A tube according to the present invention is sufficiently rigid to be pushed through constricted vessels and the like, but also has a more flexible distal portion for pre-shaping and improved navigability through tortuous body vessels.  
         [0012]     According to another aspect of the present invention, a spring is provided for use with a guidewire. The spring has different cross-sectional shapes at different locations. In a preferred embodiment, selected sections of the spring are substantially flat for providing improved stiffness and tip shape retention during stiffening. Other sections of the spring have a substantially round or circular cross-sectional area for improved bending flexibility. The pitch and/or length of the spring may be varied in order to impart different performance characteristics, as dictated by the subject body environment.  
         [0013]     Special application for the present invention has been found for guidewire delivery of catheters to vessels of the human vascular system. However, the present invention is also applicable to guidewire delivery of catheters to other body lumens, such as in gastrointestinal procedures, so it will be understood that the products described herein are not limited to particular medical devices or particular surgical applications. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a front elevational view of a guidewire according to an aspect of the present invention, shown at a typical in-use location;  
         [0015]      FIG. 2  is a cross-sectional view of the guidewire of  FIG. 1 , in a maximum stiffness configuration;  
         [0016]      FIG. 3  is a cross-sectional view of the guidewire of  FIG. 1 , in a minimum stiffness configuration;  
         [0017]      FIG. 4  is a cross-sectional view of a guidewire according to another aspect of the present invention, in a minimum stiffness configuration;  
         [0018]      FIG. 4   a  is a transverse cross-sectional view through a guidewire embodiment having a non-rotation feature;  
         [0019]      FIG. 5  is a cross-sectional view of the guidewire of  FIG. 4 , in a maximum stiffness configuration; and  
         [0020]      FIG. 6  is a cross-sectional view of another embodiment of a guidewire according to the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriate manner.  
         [0022]      FIG. 1  illustrates a guidewire  10  in a body vessel V. The guidewire  10  includes a hypotube or tube  12  with a proximal portion  14  and a distal portion  16 , which are best shown in  FIGS. 2 and 3 . The proximal portion  14  and distal portion  16  are made of different materials, typically being separate tubes that are joined at joint  18 . The respective proximal and distal portions  14  and  16  preferably have substantially equal respective outer and inner diameters at their location of contact, which facilitates the creation of a smooth joint  18 . The joint  18  is preferably smooth or atraumatic in order to prevent damage to the surrounding vessel V, corewire  20 , or to a catheter slid over the guidewire  10 .  
         [0023]     The proximal and distal portions  14  and  16  are comprised of different materials, because they serve different functions. The proximal portion  14  extends from the joint  18  to outside of the body and is manipulated by the operator to feed the guidewire  10  through the vasculature. Accordingly, it is preferable for the proximal portion  14  to be made of a relatively rigid, biocompatible material. In a preferred embodiment, the proximal portion  14  is comprised of stainless steel.  
         [0024]     In contrast to the proximal portion  14 , it is important for the distal portion  16  to be relatively flexible in order to follow the vasculature path, especially if the path is tortuous. Furthermore, it is often useful to pre-shape the distal portion  16  in anticipation of the body environment, so the distal portion  16  should be suitable for repeated shaping without weakening, permanent deformation, or failure. Accordingly, the distal portion  16  is preferably made of a material having shape memory properties. When used herein, the term “shape memory” is intended to refer to materials capable of recovering from an apparent inelastic deformation and returning to a default geometry. In a preferred embodiment, the distal portion  16  is made of a nitinol material having a tubular default geometry illustrated in  FIGS. 1-3 . Of course, the distal portion  16  may have any other default geometry without departing from the scope of the present invention. An example is a curved or bent geometry, as illustrated in  FIG. 6 , of a distal portion  16   b . A curved or bent protruding portion  28   b  of the distal end  24   b  of a corewire  20   b  also is shown.  
         [0025]     The distal portion  16  is most preferably made of a nitinol composition having a transformation temperature greater than body temperature, such that the nitinol material is in a martensitic state at room temperature and when in vivo. In use, the austenitic shape of the distal portion  16  is heat treated and initially set to the substantially tubular shape of  FIGS. 1-3 . Thereafter, the distal portion  16  is brought below the heat treatment temperature and to a temperature below the transformation temperature. For example, when not in use, the distal portion  16  will typically be stored in a martensitic state at room temperature. When the guidewire  10  is to be used, the operator may pre-shape the distal portion  16  to a generally curved configuration that would be useful in navigating the anticipated path. After the operation, the distal portion  16  may be heated above the transformation temperature in order to reset it to the default geometry.  
         [0026]     The nature of the joint  18  depends on the materials used to form the proximal and distal portions  14  and  16 . Mechanical methods, such as crimping or swaging, are typically the most reliable ways to join the proximal and distal portions  14  and  16 . Welding, brazing, and soldering may also be used, but special care must be taken to remove the oxide layer when practicing such methods with nitinol. The shape memory properties of nitinol and similar materials may be exploited by expanding or contracting the martensitic distal portion  16 , then returning it to its austenitic state to tightly engage the proximal portion  14 . Other joining methods are possible and it is well within the skill of one in the art to select an appropriate method.  
         [0027]     The tube  12  movably receives an elongated corewire  20  extending between a proximal end  22  and a distal end  24 . The corewire  20  is generally constructed in accordance with known devices and may be made of stainless steel or, most preferably, a nitinol material. Other materials and combinations of materials, such as a stainless steel proximal end and a nitinol material distal end, are also possible. Furthermore, rather than using a single corewire, it is instead possible to use a plurality of smaller corewires for improved flexibility.  
         [0028]     The proximal end  22  of the corewire  20  terminates in a handle, not illustrated, that remains outside of the body for manipulation by an operator, as will be described herein. Intermediate the handle and the distal portion  14  of the tube  12  is a tapered stopping mechanism or diameter ramp-up  26 . The stopping mechanism  26  has a larger diameter than the tube inner diameter, so it limits distal or downstream movement of the corewire  20  with respect to the tube  12  by coming into contact with the proximal portion  14 . Downstream movement of the corewire  20  can be understood by comparing  FIG. 2  to  FIG. 3 , while proximal or upstream movement can be understood as moving the corewire  20  from the orientation of  FIG. 3  to the orientation of  FIG. 2 .  
         [0029]     The distal end  24  of the corewire  20  includes a tapered protruding portion  28  that extends at least partially beyond the distal portion  16  of the tube  12  and terminates at an atraumatic weld  30 . The protruding portion  28  is tapered in order to increase its flexibility for improved navigability through tortuous body cavities. At least the protruding portion  28  of the corewire  20  is preferably made of a nitinol or another material having shape memory properties in order to allow for repeatable pre-shaping without weakening the corewire  20 .  FIGS. 4 and 5  provide another example of a pre-shaped protruding portion  28 .  
         [0030]     The protruding portion  28  is surrounded by a coiled spring  32  that extends from the distal portion  16  of the tube  12  to the weld  30  of the corewire  20 . Preferably, a proximal end  34  of the spring  32  is connected to the distal portion  16  and a distal end  36  of the spring  32  is connected to the weld  30 , such that the spring  32  is movable with the tube  12  and with the corewire  20  between the maximum stiffness configuration of  FIG. 2  and the minimum stiffness configuration of  FIG. 3 .  
         [0031]     In the maximum stiffness configuration, there is preferably no separation gap between adjacent coils. This configuration imparts increased stiffness to the guidewire tip  38 . When used herein, the term “tip” or “guidewire tip” refers to the protruding portion  28  of the corewire  20  and any other component extending beyond the distal portion  16  of the tube  12 , such as the portion of the spring  32  surrounding the protruding portion  28 . The separation gap G between adjacent coils is preferably about 0.010 inch in the minimum stiffness configuration of  FIG. 3 , which gap decreases the stiffness of the tip  38 . The maximum stretching of the spring  32  is regulated by the location of the diameter ramp-up  26  at the proximal end  22  of the corewire  20 , which contacts the tube proximal portion  14  to prevent further downstream movement.  
         [0032]     The corewire  20  is preferably axially slideable with respect to the tube  12 , but other modes of axial advancement, such as rotation, are within the scope of the present invention. Typically, the spring  32  is also rotatably mounted to at least one of the distal portion  16  and/or weld  30 , which allows the corewire  20  to be rotated with respect to the tube  12  without torsional resistance from the spring  32 . Alternatively, a non-rotation feature can be included, such as by incorporating a longitudinal pathway such as a flat slot or channel  61  along corewire  20   c  and a complementary protrusion or follower  62  of tube  12   c , as shown in  FIG. 4   a . Instead, the pathway can be along the tube and the protrusion on the corewire.  
         [0033]     The guidewire  10  is preferably provided with a ratcheting or locking mechanism, not illustrated, associated with the handle in order to allow controlled movement of the corewire  20  with respect to the tube  12  and/or to prevent unintentional movement of the corewire  20  with respect to the tube  12 . A suitable mechanism is illustrated in U.S. Pat. No. 3,854,437 to Matsuo, which is hereby incorporated herein by reference. Of course, other mechanisms are possible and within the scope of the present invention.  
         [0034]     The spring  32  of  FIGS. 1-3  is illustrated as having a round or circular cross-sectional shape, but other shapes, such as a flat coiled spring, are within the scope of the present invention. According to an aspect of the present invention, shown in  FIGS. 4 and 5 , the spring  32   a  has a heterogeneous combination of cross-sectional shapes, which promotes bending flexibility and curvature. The embodiment of  FIGS. 4 and 5  includes a single spring  32   a  with a cross-section that varies between a substantially circular or round shape  40  and a substantially flat or rectangular shape  42 . The respective round and flat shapes  40  and  42  have different properties, which can be used for enhanced performance, as will be described herein. Regardless of the cross-sectional shape of the coils, the spring may have a varying pitch along its length in order to provide differing flexibility characteristics. For example,  FIG. 6  shows a spring  32   b  having an increasing pitch; that is, the separation gap increases from G 1  to G 2  and from the proximal end  34   b  to the distal end  36   b  of the spring.  
         [0035]     The spring is preferably surrounded by a sheath  44  of lubricating and/or sealing material. Typically, the sheath  44  is more lubricious than the spring  32 . The spring is made of any suitable guidewire spring material, preferably a material that is radiopaque, typically by being a high density metal. Spring materials include platinum, tungsten, and alloys such as tungsten iridium alloys, as well as stainless steel. Also, the sheath  44  preferably is fluid-tight and prevents body fluids, contrast dye, and the like from seeping into the interior of the guidewire  10 . In a preferred embodiment, the sheath  44  is polytetrafluoroethylene (PTFE), which is heat-shrunk over the spring  32  and weld  30 . A similar sheath  44   a  is illustrated for encapsulating spring  32   a.    
         [0036]     In use, the guidewire tip  38  and/or distal portion  16  of the tube  12  are pre-shaped by the operator, if necessary, in anticipation of the expected body environment. If the tip  38  is to be pre-shaped, then the guidewire embodiment of  FIGS. 4 and 5  can be provided to enhance the preshaping action. As illustrated, the round sections  40  of the spring  32   a  may be diametrically opposed by the flat sections  42 , which causes the spring  32   a  to better conform to the pre-shaped protruding portion  28  in the compressed or maximum stiffness configuration of  FIG. 5 , due to the greater length of the flat sections  42 . Such flat sections that are illustrated have a greater axial length than the illustrated round sections, and are thereby less bendable. Also, this effect is achieved because the gap between same is less than the gap between the coils with a round cross-section. Alternative distributions of round and flat spring sections  40  and  42 , such as alternating adjacent round and flat sections, may be employed for different performance characteristics and it is to be understood that the illustrated embodiment of  FIGS. 4 and 5  only shows one possible spring configuration. Generally, the less rigid the section, whether by shape, size or material, the easier for the spring and thus the tip to flex and typically bend to follow a change in shape of the vessel through which it is fed.  
         [0037]     When the guidewire  10  has been pre-shaped, it is then inserted into a body vessel through an incision in the skin. The guidewire  10  may be inserted with the tip  38  in a maximum stiffness or minimum stiffness configuration, or in an intermediate stiffness configuration, depending on the expected body environment. The guidewire  10  is fed through the vasculature and may be adjusted to a stiffer tip configuration for constricted vessel sites and to a more flexible tip configuration for twisting and tortuous sites. Of course, this is only an exemplary method of using a guidewire according to the present invention and should not be considered limiting.  
         [0038]     It will be understood that the embodiments of the present invention which have been described are illustrative of some of the applications of the principles of the present invention. Numerous modifications may be made by those skilled in the art without departing from the true spirit and scope of the invention, including those combinations of features that are individually disclosed or claimed herein.