Abstract:
Occluded vasculature such as occluded arterial vasculature can be recanalized using a device that is configured to penetrate an occlusion, while limiting a distance that said penetration structure can extend in order to limit inadvertent vascular damage. The device can include an elongate shaft of a guidewire and a stylet disposed within a lumen of the elongate shaft such that the stylet is selectively actuatable within the elongate shaft.

Description:
CROSS REFERENCE 
       [0001]    This is a continuation of U.S. application Ser. No. 11/354,377, filed on Feb. 15, 2006, which is a continuation-in-part of U.S. application Ser. No. 10/877,340, filed on Jun. 24, 2004, the entire disclosure of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates generally to medical devices and more specifically to medical devices configured for recanalization of occluded vasculature. 
       BACKGROUND 
       [0003]    A number of patients suffer from vascular occlusions. Vascular occlusions can occur in the coronary arteries as well as in peripheral arteries such as those found in a patient&#39;s legs. Occlusions can be partial occlusions that reduce blood flow through the occluded portion of an artery. Occlusions can also be total occlusions, which substantially reduce or even completely eliminate blood flow through the occluded portion of the artery. Total occlusions such as chronic total occlusions can be difficult to traverse with existing catheters and guidewires, as they can include stiff or tough portions at their proximal and distal limits. 
         [0004]    Physicians have attempted to cross or recanalize chronically totally occluded blood vessels such as arteries using a variety of devices and techniques. Unfortunately, many of these devices and techniques have relatively low rates of success and relatively high rates of complications. A particular issue is penetrating a proximal cap of an occlusion without damaging the surrounding blood vessel, as proximal caps can have a curved or angled configuration that guides devices into the vessel wall or perhaps into a branch vessel. 
         [0005]    Therefore, a need remains for a safe and effective way to penetrate and traverse occlusions such as chronic total occlusions. A need remains for a safe and effective way to penetrate and traverse difficult portions of an occlusion such as a proximal cap, which then allows traversing of the remainder of the occlusion with a conventional guidewire, catheter or other device. 
       SUMMARY 
       [0006]    The invention is directed to apparatus and methods for recanalizing occluded vasculature such as occluded arterial vasculature. The invention provides a device that includes structure that is configured to penetrate an occlusion while limiting a distance that the penetration structure can extend in order to limit inadvertent vascular damage. Further, a preferred embodiment of the device provides means for centering the penetration into the proximal cap or other difficult portion of an occlusion. In preferred embodiments, the device provides means for advancement through the center of the occlusion. 
         [0007]    Accordingly, an example embodiment of the invention can be found in an apparatus that includes an elongate sheath having a distal region, a proximal region and an inner surface defining a lumen extending therebetween. A stylet is disposed within the elongate sheath. The stylet includes a lumen extending from a distal region to a proximal region of the stylet. The elongate sheath and the stylet include, in combination, an engagement section that is configured to limit relative axial movement between the elongate sheath and the stylet. 
         [0008]    Another example embodiment of the invention can be found in a recanalization assembly that includes a catheter having a distal region, a proximal region and a lumen extending therebetween. An elongate sheath is disposed within the catheter lumen and has a distal region, a proximal region and an inner surface defining a lumen extending therebetween. A stylet is disposed within the elongate sheath and has a distal region comprising a cutting surface, a proximal region and a lumen extending therebetween. The elongate sheath and the stylet include, in combination, an engagement section that is configured to limit relative axial movement between the elongate sheath and the stylet. 
         [0009]    Another example embodiment of the invention can be found in an assembly that is configured for traversing a chronic total occlusion. The assembly includes an elongate shaft that has a distal region, a proximal region and a lumen extending therebetween. The assembly also includes a penetrating structure that is disposed within the elongate shaft lumen. The penetrating structure is disposed within the lumen such that relative axial movement between the elongate shaft and the penetrating structure is limited. 
         [0010]    Another example embodiment of the invention can be found in a method of traversing a vascular occlusion. An apparatus including an elongate shaft and a stylet disposed within the elongate shaft is positioned such that a distal region of the apparatus is proximate an occlusion. The stylet is advanced distally such that a distal region of the stylet that includes a cutting surface extends distally beyond a distal region of the elongate shaft and contacts a surface of the occlusion. The stylet is moved such that its cutting surface contacts and penetrates the occlusion. Provision is also made for injecting contrast media to aid in visualization. Additional medical devices may be advanced over the elongate shaft during a medical procedure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: 
           [0012]      FIG. 1  is a perspective view of a recanalization apparatus for penetrating a vascular occlusion in accordance with an embodiment of the invention; 
           [0013]      FIG. 2  is a plan view of a catheter in accordance with an embodiment of the invention; 
           [0014]      FIG. 3  is a cross-sectional view of the catheter of  FIG. 1  taken along 3-3 line; 
           [0015]      FIG. 4  is a plan view of a balloon catheter in accordance with an embodiment of the invention; 
           [0016]      FIG. 5  is a partially sectioned view of the distal portion of a recanalization apparatus for penetrating a vascular occlusion in accordance with an embodiment of the invention; 
           [0017]      FIG. 6  is a partially sectioned view of the distal portion of a recanalization apparatus for penetrating a vascular occlusion in accordance with an embodiment of the invention; 
           [0018]      FIG. 7  is a partially sectioned view of the distal portion of a recanalization apparatus for penetrating a vascular occlusion in accordance with an embodiment of the invention; 
           [0019]      FIG. 8  is a partially sectioned view of the distal portion of a recanalization apparatus for penetrating a vascular occlusion in accordance with an embodiment of the invention; 
           [0020]      FIG. 9  is a partially sectioned view of the distal portion of a recanalization apparatus for penetrating a vascular occlusion in accordance with an embodiment of the invention; 
           [0021]      FIG. 10  is a partially sectioned view of the distal portion of a recanalization apparatus for penetrating a vascular occlusion in accordance with an embodiment of the invention; 
           [0022]      FIG. 11  is a partially sectioned view of the distal portion of a recanalization apparatus for penetrating a vascular occlusion in accordance with an embodiment of the invention; 
           [0023]      FIG. 12  is a partially sectioned view of the distal portion of an apparatus for penetrating a vascular occlusion in accordance with an embodiment of the invention; 
           [0024]      FIG. 13  is a partially sectioned view of the distal portion of an apparatus for penetrating a vascular occlusion in accordance with an embodiment of the invention; 
           [0025]      FIGS. 14-21  illustrate a particular use of the apparatus for penetrating a vascular occlusion; 
           [0026]      FIGS. 22A and 22B  are cross-sectional views illustrating another exemplary apparatus for penetrating a vascular occlusion; 
           [0027]      FIGS. 23A and 23B  are cross-sectional views illustrating another exemplary apparatus for penetrating a vascular occlusion; and 
           [0028]      FIGS. 24A and 24B  are cross-sectional views illustrating another exemplary apparatus for penetrating a vascular occlusion. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    For the following defined terms, these definitions shall be applied, unless a different definition is given in the claims or elsewhere in this specification. 
         [0030]    All numeric values are herein assumed to be modified by the term “about”, whether or not explicitly indicated. The term “about” generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (i.e., having the same function or result). In many instances, the terms “about” may include numbers that are rounded to the nearest significant figure. 
         [0031]    The recitation of numerical ranges by endpoints includes all numbers within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). 
         [0032]    As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
         [0033]    The following description should be read with reference to the drawings wherein like reference numerals indicate like elements throughout the several views. The drawings, which are not necessarily to scale, depict illustrative embodiments of the claimed invention. 
         [0034]      FIG. 1  is a perspective view of a recanalization assembly  10  in accordance with an embodiment of the present invention. The recanalization assembly  10  includes an elongate shaft  12  that has a distal region  14  defining a distal end  16 . An inner surface  18  defines a shaft lumen  20 . A sheath  22  is at least partially disposed within the shaft lumen  20 . The sheath  22  includes a distal region  24  defining a distal end  26 . An inner surface  28  defines a sheath lumen  30 . A stylet  32  is at least partially disposed within the sheath lumen  30 . The stylet  32  includes a distal region  34  defining a distal end  36 . The distal end  36  includes an aperture  38  suitable to accommodate a guidewire as will be discussed in greater detail hereinafter. In the illustrated embodiment, the distal region  34  is defined at least in part by a needle tip  40  that can be configured for penetration into an occlusion. 
         [0035]    In use, as will be discussed in greater detail hereinafter, the sheath  22  can be moved axially with respect to the elongate shaft  12 . In some embodiments, the elongate shaft  12  can be advanced through a patient&#39;s vasculature before the sheath  22  has been deployed within the shaft lumen  20 . Once the elongate shaft  12  has reached an appropriate position, the sheath  22  can be advanced distally through the shaft lumen  20 . In other embodiments, the elongate shaft  12  can be advanced through the patient&#39;s vasculature with the sheath  22  already positioned within the shaft lumen  20 . 
         [0036]    The sheath  22  can be advanced distally so that its distal end  26  extends distally beyond the distal end  16  of the elongate shaft  12 . The stylet  32  can move with respect to the sheath  22 . In some embodiments, the stylet  32  can be moved axially such that its distal end  36  extends distally beyond the distal end  26  of the sheath  22 . In some embodiments, the stylet  32  can undergo reciprocal motion so that the needle tip  40  can penetrate into an occlusion. In some embodiments, the stylet  32  can also rotate to aid in occlusion penetration. The stylet  32  can be made to move axially and/or rotationally using any known technique or method, both manual and mechanical means included. 
         [0037]      FIG. 2  is a plan view of a catheter  42  in accordance with an embodiment of the invention. In some embodiments, the shaft  44  can be any of a variety of different catheters, but is preferably an intravascular catheter and will be discussed with respect to a catheter  42 . Examples of intravascular catheters include balloon catheters, atherectomy catheters, drug delivery catheters, diagnostic catheters and guide catheters. Except as described herein, the catheter  42  can be manufactured using conventional techniques and materials. 
         [0038]    The catheter  42  can be sized in accordance with its intended use. The catheter  42  can have a length that is in the range of about 50 centimeters to about 100 centimeters and can have a diameter that is in the range of about 4 F (French) to about 9 F. 
         [0039]    In the illustrated embodiment, the catheter  42  includes an elongate shaft  44  that has a proximal region  46 , a distal region  48  and a distal end  50 . A hub and strain relief assembly  52  can be connected to the proximal region  46  of the elongate shaft  44 . The hub and strain relief assembly  52  includes a main body portion  54 , a pair of flanges  56  designed to improve gripping, and a strain relief  58  that is intended to reduce kinking. The hub and strain relief assembly  52  can be of conventional design and can be attached using conventional techniques. 
         [0040]      FIG. 3  is a cross-sectional view of one example of the elongate shaft  44  taken along line  3 - 3  of  FIG. 2 . The elongate shaft  44  includes an outer layer  60  and an inner layer  62 . Each of the outer layer  60  and the inner layer  62  can extend from the proximal region  46  of the elongate shaft  44  to the distal region  48  of the elongate shaft  44 . The inner layer  62  defines a lumen  64  that extends through the elongate shaft  44 . 
         [0041]    In some embodiments, the elongate shaft  44  can include a reinforcing braid or ribbon layer  66  to increase particular properties such as kink resistance. The reinforcing braid or ribbon layer  66  can be positioned between the outer layer  60  and the inner layer  62  and can provide adequate kink resistance without substantially increasing the overall profile of the elongate shaft  44 . Alternatively, a single layer shaft can be utilized. An inflation lumen can also be provided, whether coaxial or in a multi-lumen co-extrusion, for example. 
         [0042]    In some embodiments (not illustrated), the elongate shaft  44  can include one or more shaft segments having varying degrees of flexibility. For example, the elongate shaft  44  can include a proximal segment, an intermediate segment and a distal segment. In some embodiments, the elongate shaft  44  can also include a distal tip segment that can be formed from a softer, more flexible polymer. The elongate shaft  44  can include more than three segments, or the elongate shaft  44  can include fewer than three segments. 
         [0043]    If the elongate shaft  44  has, for example, three segments such as a proximal segment, an intermediate segment and a distal segment, each segment can include an inner layer  62  that is the same for each segment and an outer layer that becomes increasingly more flexible with proximity to the distal end  50  of the elongate shaft  44 . For example, the proximal segment can have an outer layer that is formed from a polymer having a hardness of 72 D (Durometer), the intermediate segment can have an outer layer that is formed from a polymer having a hardness of 68 D and the distal segment can be formed from a polymer having a hardness of 46 D. 
         [0044]    If the elongate shaft  44  has three segments, each of the segments can be sized in accordance with the intended function of the resulting catheter  42 . For example, the proximal segment can have a length of about 35 inches, the intermediate segment can have a length that is in the range of about 2 inches to about 3 inches, and the distal segment can have a length that is in the range of about 1 inch to about 1.25 inches. 
         [0045]    The inner layer  62  can be a uniform material and can define a lumen  64  that can run the entire length of the elongate shaft  44  and that is in fluid communication with a lumen (not illustrated) extending through the hub assembly  52 . The lumen  64  defined by the inner layer  62  can provide passage to a variety of different medical devices such as the sheath  22  (see  FIG. 1 ), and thus the inner layer  62  can include, be formed from or coated with a lubricious material to reduce friction within the lumen  64 . An exemplary material is polytetrafluoroethylene (PTFE), better known as TEFLON®. The inner layer  62  can be dimensioned to define a lumen  64  having an appropriate inner diameter to accommodate its intended use. In some embodiments, the inner layer  62  can define a lumen  64  having a diameter of about 0.040 inches to about 0.058 inches, and the inner layer  62  can have a wall thickness of about 0.001 inches. 
         [0046]    The outer layer  60  can be formed from any suitable polymer that will provide the desired strength, flexibility or other desired characteristics. Polymers with low durometer or hardness can provide increased flexibility, while polymers with high durometer or hardness can provide increased stiffness. In some embodiments, the polymer material used is a thermoplastic polymer material. Some examples of some suitable materials include polyurethane, elastomeric polyamides, block polyamide/ethers (such as PEBAX®), silicones, and co-polymers. The outer layer  60  can be a single polymer, multiple layers, or a blend of polymers. By employing careful selection of materials and processing techniques, thermoplastic, solvent soluble, and thermosetting variants of these materials can be employed to achieve the desired results. 
         [0047]    In particular embodiments, a thermoplastic polymer such as a co-polyester thermoplastic elastomer such as that available commercially under the ARNITEL® name can be used. The outer layer  60  can have an inner diameter that is about equal to the outer diameter of the inner layer  62 . 
         [0048]    In some embodiments, the outer layer  60  can have an inner diameter in the range of about 0.014 inches to about 0.060 inches and an outer diameter in the range of about 0.018 inches to about 0.0690 inches. Part or all of the outer layer  60  can include materials added to increase the radiopacity of the outer layer  60 , such as 50% bismuth subcarbonate. 
         [0049]    In particular embodiments, the catheter  44  can be a balloon catheter such as the balloon catheter  68  illustrated in  FIG. 4 .  FIG. 4  is a plan view of a balloon catheter  68  that is similar in construction to the catheter  42 , but includes a balloon  70  and an inflation lumen. As illustrated, the balloon  70  has a proximal waist  72 , a distal waist  74  and an intermediate portion  76 . The balloon  70  is seen in an expanded or inflated configuration. Construction of the balloon catheter  68  is conventional. Use of the balloon catheter  68  as the shaft  14  can have advantages that will be discussed in greater detail hereinafter. 
         [0050]      FIGS. 5 through 11  illustrate particular embodiments of recanalization assemblies employing a balloon catheter  68  (see  FIG. 4 ) in accordance with the invention. Turning to  FIG. 5 , a distal portion of a recanalization assembly  78  is illustrated. The balloon catheter  68  defines a lumen  80  that is sized to accept an elongate sheath  82  that has a proximal region  84 , a distal region  86  and a distal end  88 . The lumen  80  can have an inner diameter that is in the range of about 0.014 to about 0.035 inches, which corresponds to typical guidewire dimensions. 
         [0051]    The sheath  82  has an inner surface  90  defining a sheath lumen  92 . The sheath  82  can be formed of any suitable polymeric material such as those discussed above with respect to the catheter  42  (see  FIG. 2 ). The sheath  82  can also be formed of a suitable metallic material, such as nitinol, stainless steel, Elgiloy® and other alloys, that has been slit or otherwise processed to provide suitable flexibility and other desired characteristics. The sheath  82  can have an outer diameter of about 0.010 inches to about 0.035 inches, preferably about 0.014 inches to about 0.020 inches and an inner diameter of about 0.006 inches to about 0.030 inches, preferably about 0.008 inches to about 0.014 inches. The sheath  82  can have a length that is in the range of about 80 cm to about 150 cm, preferably about 135 cm. 
         [0052]    A stylet  94  is disposed within the sheath lumen  92 . The stylet  94  has a proximal region  96 , a distal region  98  and a distal end  100 . The distal region  98  can have an outer diameter that is in the range of about 0.004 to about 0.014 inches in order to minimize inadvertent tissue damage. The stylet  94  can have a length that is in the range of about 80 cm to about 150 cm. The distal region  98  includes a cutting surface  102  that as illustrated can be a needle tip. The stylet  94  can be formed of any suitable material. Exemplary materials include metals such as stainless steel, nitinol, Elgiloy®, titanium or other alloys. Although not shown in  FIG. 5 , the stylet can include a lumen therethrough in some preferred embodiments, as shown in  FIG. 1 . The lumen allows passage of a guidewire after the occlusion is penetrated. 
         [0053]    As can be seen, the stylet  94  can be moved axially within the sheath  82 , and the sheath  82  can be moved axially within the balloon catheter  68 . In other embodiments, the recanalization assembly  78  can include structure that limits relative axial travel between the sheath  82  and the stylet  94 . The stylet in  FIGS. 5-11  can pierce the proximal or distal cap of the occlusion via application of a forward pushing force, alone or in combination with a turning action imparted to the stylet. The turning action can be applied to the stylet as shown in  FIG. 1  by digital manipulation or mechanical means (not shown). These embodiments are shown, for example, in  FIGS. 6-11 . 
         [0054]    Turning now to  FIG. 6 , a recanalization assembly  104  is illustrated as including the balloon catheter  68 . A sheath  106  having a proximal region  108 , a distal region  110  and a distal end  112  is disposed within the lumen  80 . The sheath  106  includes an inner surface  114  defining a sheath lumen  116 . A stylet  118  having a proximal region  120 , a distal region  122  and a distal end  124  is disposed within the sheath lumen  116 . The distal region  122  can define a cutting surface  126 . The sheath  106  and the stylet  118  can be formed of any suitable materials and have any suitable dimensions as discussed with respect to  FIG. 5 . 
         [0055]    The recanalization assembly  104  includes an engagement section  128  that is configured to limit relative axial movement between the sheath  106  and the stylet  118 . The engagement section  128  can be positioned anywhere along the sheath  106  and the stylet  118 . In some embodiments, as illustrated, the engagement section  128  can be positioned proximate the distal region of the sheath  106  and the stylet  118  for greater control and accuracy. 
         [0056]    In the illustrated embodiment, the sheath  106  includes a stop  130  that can be a cylindrical stop having an inner diameter that is less than an inner diameter of the sheath  106  on either side of the stop  130 . The stop  130  can be integrally formed with the sheath  106  or can be independently formed and subsequently secured using any suitable technique. In some embodiments, the stop  130  can continue for an entire circumference (360 degrees) of the sheath  106 . In other embodiments, the stop  130  can include one or more distinct sections spaced apart along the circumference of the sheath  106 . 
         [0057]    The stylet  118  includes an engagement portion  132  that has a proximal end  134  and a distal end  136 . The engagement portion  132  can have an outer diameter that is reduced with respect to an outer diameter of the stylet  118  on either side of the engagement portion  132 . As can be seen, distal movement of the stylet  118  is limited by the stop  130  contacting the proximal end  134  of the engagement portion  132 . Similarly, proximal movement of the stylet  118  is limited by the stop  130  contacting the distal end  136  of the engagement portion. 
         [0058]    In some embodiments, the stylet  118  can be withdrawn proximally such that the cutting surface  126  is completely within the sheath lumen  116 . This permits extending the sheath  106  distally through the balloon catheter lumen  80  without contacting the vasculature distal of the balloon catheter  68 . In some embodiments, the distal end  124  of the stylet  118  can extend beyond the distal end  112  of the sheath  106  even when withdrawn. 
         [0059]    Turning now to  FIG. 7 , a recanalization assembly  138  is illustrated as once again including the balloon catheter  68 . A sheath  140  having a proximal region  142 , a distal region  144  and a distal end  146  is disposed within balloon catheter lumen  80 . The sheath  140  includes an inner surface  148  that defines a sheath lumen  150 . A stylet  152  having a proximal region  154 , a distal region  156  and a distal end  158  is disposed within the sheath lumen  150 . The distal region  158  includes a cutting surface  160  that can in some embodiments be a needle tip. The sheath  140  and the stylet  152  can be formed of any suitable materials and have any suitable dimensions as discussed with respect to  FIG. 5 . As with prior embodiments, the stylet  152  can include a lumen therethrough (now shown) for passage of a guidewire. 
         [0060]    The recanalization assembly  138  includes an engagement section  162  that is configured to limit relative axial movement between the sheath  140  and the stylet  152 . The sheath  140  includes an engagement portion  164  having a proximal end  166  and a distal end  168 . The engagement portion  164  has an inner diameter that is greater than an inner diameter of the sheath  140  on either side of the engagement portion  164 . The engagement portion  164  can be integrally formed with the sheath  140 , or the sheath  140  can be formed and material can subsequently be removed using any suitable technique to form the increased inner diameter engagement portion  164 . 
         [0061]    The engagement section  162  also refers to a portion of the stylet  152 . The stylet  152  includes a stop  170  that has an outer diameter that is greater than an outer diameter of the stylet  152  on either side of the stop  170 . In some embodiments, the stop  170  can continue for an entire circumference (360 degrees) of the stylet  152 . In other embodiments, the stop  170  can include one or more distinct sections spaced apart along the circumference of the stylet  152 . As can be seen, proximal movement of the stylet  152  is limited by the stop  170  contacting the proximal end  166  of the engagement portion  164 . Similarly, distal movement of the stylet  152  is limited by the stop  170  contacting the distal end  168  of the engagement portion  164 . 
         [0062]    In some embodiments, the distal end  158  of the stylet  152  can remain proximal of the distal end  146  of the sheath  140 , while in other embodiments, the distal end  158  of the stylet  152  can extend distally beyond the distal end  146  of the sheath  140  when the stylet  152  is completely refracted. 
         [0063]    In comparing  FIG. 6  to  FIG. 7 , it is clear that the stylet  152  of  FIG. 7  is narrower than the stylet  118  of  FIG. 6 . In some embodiments, a thinner stylet can be advantageous as this can provide for additional flexibility. In other embodiments, a stronger or stiffer stylet can permit application of additional force in attempting to break through an occlusion. The sheath  140  of  FIG. 7  has thicker walls than the sheath  106  of  FIG. 6 . In some embodiments, a thicker-walled sheath can be advantageous as this can provide for additional pushability. In other embodiments, a thinner-walled sheath may be more flexible. 
         [0064]    Turning now to  FIG. 8 , a recanalization assembly  172  is illustrated as including the balloon catheter  68 . A sheath  174  having a proximal region  176 , a distal region  178  and a distal end  180  is disposed within balloon catheter lumen  80 . The sheath  174  includes an inner surface  182  that defines a sheath lumen  184 . A stylet  186  having a proximal region  188 , a distal region  190  and a distal end  192  is disposed within the sheath lumen  184 . The distal region  190  includes a cutting surface  194  that can in some embodiments be a needle tip. The sheath  174  and the stylet  186  can be formed of any suitable materials and have any suitable dimensions as discussed with respect to  FIG. 5 . Further, the stylet can include a lumen therethrough for guidewire passage. 
         [0065]    The recanalization assembly  172  includes an engagement section  196  that is configured to limit distal travel of the stylet  186  with respect to the sheath  174 . The sheath  174  includes an engagement portion  198  having an inner diameter that is reduced with respect to an inner diameter of the sheath  174  proximal of the engagement portion  198 . The engagement portion  198  terminates at a distal stop  200 . 
         [0066]    The engagement section  196  also pertains to the distal region  190  of the stylet  186 , which terminates at a proximal stop  200 . The distal region  190  has a reduced outer diameter with respect to an outer diameter of the stylet  186  proximal of the engagement section  196 . As can be seen, distal travel of the stylet  186  is limited by the proximal stop  202  of the stylet  186  contacting the distal stop  200  of the sheath  174 . In this embodiment, the stylet  186  can be completely removed proximally from the sheath  174 , should there be a need to inject contrast fluid or deploy a different device. 
         [0067]    In some embodiments, the distal end  192  of the stylet  186  can remain proximal of the distal end  180  of the sheath  174 , while in other embodiments the distal end  192  of the stylet  186  can extend distally beyond the distal end  180  of the sheath  174  when the stylet  186  is completely retracted. 
         [0068]    In some embodiments, such as illustrated in  FIG. 9 , a second sheath  204  can be deployed inside the balloon catheter lumen  80  but exterior to the sheath  174 . The second sheath  204  has a proximal region  206 , a distal region  208  and a distal end  210 . The second sheath  204  can be used in situations in which the sheath  174  has an outer diameter that is somewhat less than an inner diameter of the balloon catheter lumen  80  in order to reduce the size differential between the balloon catheter  68  and the sheath  174  and to provide for easier exchange for other devices. The second sheath  204  can extend across the opening in the distal cap and hold in position to allow the sheath and stylet to be exchanged for a guidewire. In some embodiments, the second sheath  204  can have an inner diameter that is about 0.010 to about 0.014 inches and an outer diameter that is about 0.014 to about 0.018 inches in order to account for standard guidewire sizes. The second sheath  204  can be formed of any suitable material as discussed with respect to the catheter  42  (see  FIG. 2 ). 
         [0069]    In some embodiments, the second sheath  204  can be employed in order to move the sheath  174  and the stylet  186  distally further from the balloon  76 . While  FIG. 9  shows the second sheath  204  deployed with the recanalization assembly  172  illustrated in  FIG. 8 , it is important to note that the second sheath  204  can also be used with the embodiments illustrated in the previous Figures. 
         [0070]    In a similar embodiment, shown in  FIG. 10 , recanalization assembly  172  includes a balloon catheter  212  having a balloon  214 . The balloon  214  has a proximal waist  216 , a distal waist  218  and an intermediate portion  220 . The balloon catheter  212  differs from the balloon catheter  68  previously described herein by virtue of having a shaft  222  that extends distally beyond the balloon  214 . The shaft  222  includes a distal region  224  that can function to allow the shaft  222  to extend across the opening that is made in the proximal cap and then allow the shaft and stylet to be withdrawn and replaced by a guidewire suitable for extending further through the occlusion. While  FIG. 10  shows the elongated balloon catheter shaft  222  deployed with the recanalization assembly  172 , it is important to note that the elongated balloon catheter shaft  222  can be used with the embodiments illustrated in the previous Figures. 
         [0071]      FIG. 11  shows another embodiment related to that of  FIG. 6 .  FIG. 11  illustrates a recanalization assembly  226  deployed within the balloon catheter  68  previous described. In this embodiment, however, the engagement section  228  includes biasing structure that can be used to forcibly move the stylet  118  distally with respect to the sheath  106 . Any suitable biasing structure, such as a resilient material or spring, can be used. 
         [0072]    In the illustrated embodiment, the biasing structure includes one or more proximal springs  230  that are positioned between the stop  130  and the proximal end  134  of the engagement portion  132  and one or more distal springs  232  that are positioned between the stop  130  and the distal end  136  of the engagement portion  132 . In some embodiments, the biasing structure can include only the proximal springs  230 , with the distal springs  232  being absent. In other embodiments, the biasing structure can include only the distal springs  232 , with the proximal springs  230  being absent. 
         [0073]    In use, the stylet  118  can be moved proximally. In the illustrated embodiment, moving the stylet  118  proximally can compress the proximal springs  230  from their equilibrium length with extending the distal springs  232  from their equilibrium length. Letting go of the stylet  118  will permit the proximal springs  230  and the distal springs  232  to release the potential energy stored therein as a result of their displacement from their equilibrium lengths. As a result, the stylet  118  can be driven forcibly in a distal direction such that the cutting surface  126  can contact and penetrate an occlusion. 
         [0074]      FIGS. 12 and 13  illustrate other embodiments of the invention that employ a piercing catheter. In particular,  FIG. 12  shows a piercing catheter  234  having a proximal region  236 , a distal region  238  and a distal end  240 . The piercing catheter  234  includes an elongate shaft  242  that has an inner surface  244  defining a shaft lumen  246 . A stylet  248  is disposed within the shaft lumen  246 . The stylet  248  has a proximal region  250 , a distal region  252  and a distal end  254 . The stylet  248  has a stylet lumen  259  that extends from the proximal region  250  through the distal region  252 . The distal region  252  of the stylet  248  includes an angled cutting needle surface  254 . 
         [0075]    The piercing catheter  234  can be formed of any suitable materials such as those discussed above with respect to the catheter  42  (see  FIG. 2 ). Exemplary materials for forming the shaft  242  include nylon, PEBAX®, polyethylene, polyurethane and copolymers thereof. Further, the shaft can be metallic, with or without slots. The shaft  242  can have a length that is in the range of about 80 cm to about 150 cm. The shaft  242  can have an outer diameter that is in the range of about 0.012 inches to about 0.035 inches and an inner diameter that is in the range of about 0.008 inches to about 0.030 inches. The stylet  248  can be formed of any suitable material including stainless steel, nitinol, Elgiloy®, other alloys or polymers and can have a length that is in the range of about 80 cm to about 150 cm, an outer diameter that is in the range of about 0.007 inches to about 0.031 inches and an inner diameter that is in the range of about 0.005 inches to about 0.027 inches. 
         [0076]    The piercing catheter  234  includes an engagement section  257  that is configured to limit relative axial movement between the elongate shaft  242  and the stylet  248 . The inner surface  244  of the elongate shaft  242  includes an engagement portion  258  that has an inner diameter that is less than an inner diameter of the elongate shaft  242  on either side of the engagement portion  258 . The engagement portion  258  has a proximal end  260  and a distal end  262 . The engagement portion  258  can have a length between the proximal end  260  and the distal end  262  that is in the range of about 2 mm to about 10 mm, preferably about 3 mm to about 6 mm. 
         [0077]    The engagement section  257  also pertains to the stylet  248 . The stylet  248  has a stop  264  that has a larger outer diameter than an outer diameter of the stylet  248  on either side of the stop  264 . In some embodiments, the stop  264  can be a cylindrical stop that extends circumferentially all the way around the stylet  248  while in other embodiments the stop  264  can include one or more distinct sections that are circumferentially spaced around the stylet  248 . As can be seen, proximal travel of the stylet  248  is limited by the stop  264  contacting the proximal end  260  of the engagement portion  258  while distal travel of the stylet  248  is limited by the stop  264  contacting the distal end  262  of the engagement portion  258 . 
         [0078]    In some embodiments, the stylet  248  can extend proximally through the elongate shaft  242 . In other embodiments, as illustrated, the stylet  248  can be shorter than the elongate shaft  242 . A pushing tube  266  can have a proximal region  268 , a distal region  270  and a distal end  272 . The distal end  272  of the pushing tube  266  can contact a proximal end  274  of the stylet  248 . In some embodiments, there may be advantages in having a shortened stylet  248  disposed in the distal region  238  of the piercing catheter  234  while a pushing tube  266  having different strength and flexibility characteristics is disposed proximally thereof. The stylet lumen  259  can, in some embodiments, allow for passage of a guidewire through the surface  254  after the stylet  248  has crossed the proximal cap. The angled cutting surface  254  allows the stylet  248  to be rotated within the sheath and allows the tip  265  of the stylet to be centered on the proximal cap via fluoroscopic imaging techniques. 
         [0079]      FIG. 13  shows a similar embodiment in which the distal region  252  of the stylet  248  includes a cylindrical cutting edge  268  rather than the angled cutting needle surface  256  shown in  FIG. 12 .  FIG. 13  shows a stylet  248  that extends proximally and thus inclusion of a pushing tube  266  is not necessary. The embodiment shown in  FIG. 13  also adds an optional second sheath  270  to the piercing catheter  234  to function similar to the second sheath  204  shown in  FIG. 9 . The stylet  248  can be rotated to assist in crossing the proximal cap. 
         [0080]      FIGS. 14 through 17  illustrate a possible use of the recanalization assemblies described herein. In  FIG. 14 , an introducer sheath  276  having a proximal region  278  and a distal region  280  has been introduced through a patient&#39;s tissue  282  into the patient&#39;s vasculature  284  as is well known in the art. A catheter  286  that in some embodiments can be a balloon catheter has been inserted into the proximal region  278  of the introducer sheath  276  and has been advanced to a position near a desired treatment site, such as an occlusion  288  having a proximal cap  308 , distal cap  290  and side branch  291 . The catheter  286  has a proximal region  290  and a distal region  292 . 
         [0081]    Turning now to  FIG. 15 , a sheath  294  having a proximal region  296  and a distal region  298  can be deployed within the catheter  286 . The catheter  286  includes a balloon  314  that can be inflated prior to deploying the sheath  294 . The balloon can be a dilating balloon or a gentle elastomeric centering balloon made from, for example, latex or polyurethane. In some embodiments, there may be advantages in deploying the sheath  294  prior to inflating the balloon  314 . The balloon  314 , once inflated, can aid in centering the sheath  294  and thus can assist the sheath  294  and enclosed stylet  300  in properly contacting the occlusion  288  without damaging the vessel wall. The stylet  300  has a proximal region  302  and a distal region  304 . The distal region  304  includes a needle tip  306  that is positioned (as illustrated) proximate the occlusion  288 . 
         [0082]    As seen in  FIG. 16 , the stylet  300  can be moved distally such that the distal region  304  of the stylet  300  penetrates at least partially into the occlusion  288 . The stylet  300  can be axially moved back and forth to aid in penetrating the occlusion  288 . In some embodiments, the stylet  300  can be rotated and in other embodiments the stylet  300  can be both rotated and moved reciprocally. In some embodiments, the occlusion  288  can have a stiff or otherwise tough proximal cap  308  and a relatively softer central portion  310 . In some embodiments, forcing the stylet  300  to penetrate the proximal cap  308  of the occlusion  288  is sufficient to permit a guidewire  312  to be extended through the stylet  300 , and then into and through the occlusion  288 , as illustrated in  FIG. 17 . After the stylet has extended through the proximal cap  308 , a guidewire  312  can cross through the second sheath as in  FIG. 18  or the shaft extension  222  as in  FIG. 19  or through the hollow stylet  248  as in  FIG. 20 . The recanalization assembly can be further advanced through occlusion  288  and the balloon  70  placed near the distal cap  290  and the stylet centered and passed across the distal cap  290  as in  FIG. 21 . Contrast in section can be made either through the dilation catheter, the second sheath, or the hollow stylet to provide visualization. 
         [0083]    Referring to  FIGS. 22A and 22B , another recanalization assembly, illustrated as a guidewire assembly  400 , is disclosed. The guidewire assembly  400  includes an elongate shaft  405  having a proximal end  412 , a distal end  414 , and a lumen  416  extending therethrough. The guidewire assembly  400  may be sized to allow additional medical devices to be inserted over the guidewire assembly  400  and advanced distally, such that the guidewire assembly may facilitate navigation of additional medical devices within an anatomical region, such as the vasculature of a patient. For example, in some embodiments, the guidewire assembly  400  may have an outer diameter of about 0.20 mm (0.008 inch), about 0.25 mm (0.01 inch), about 0.36 mm (0.014 inch), about 0.46 mm (0.018 inch), about 0.64 mm (0.025 inch), about 0.89 mm (0.035 inch), about 0.97 mm (0.038 inch), or other desired size. In some embodiments the guidewire assembly  400  may have a length of about 50 cm to about 300 cm, or more. Although some suitable dimensions are disclosed, one of skill in the art would understand that the guidewire assembly  400  may have dimensions which deviate from those expressly disclosed. 
         [0084]    The elongate shaft  405  may comprise any suitable material. Some examples of suitable materials include metals, metal alloys, polymers, or the like, or combinations, blends, or mixtures thereof. Some examples of suitable metals and metal alloys include, but are not limited to, stainless steel, such as 304V, 304L, and 316L stainless steel; alloys including nickel-titanium alloy such as linear elastic or superelastic (i.e., pseudoelastic) nitinol; nickel-chromium alloy; nickel-chromium-iron alloy; cobalt alloy; tungsten or tungsten alloys; MP35-N (having a composition of about 35% Ni, 35% Co, 20% Cr, 9.75% Mo, a maximum 1% Fe, a maximum 1% Ti, a maximum 0.25% C, a maximum 0.15% Mn, and a maximum 0.15% Si); hastelloy; monel 400; inconel 625; or the like; or other suitable material or combinations or alloys thereof. Some examples of suitable polymeric materials may include, but are not limited to, polyurethane, polyamide, high density polyamide (HDPE), low density polyamide (LDPE), polyether block amide (PEBA), polyethylene, polytetrafluoroethylene (PTFE), and their copolymers, combinations, blends, and mixtures thereof. However, other materials not expressly disclosed may be used in forming the elongate shaft  405 , or portions thereof. 
         [0085]    As illustrated in  FIGS. 22A and 22B , the elongate shaft  405  may comprise a metallic tubular member  410  having a tubular wall  418  including a plurality of apertures  420 , such as grooves, cuts, slits, slots, or the like, processed therein. The apertures  420  may be processed in a portion of, or along the entire length of, the metallic tubular member  410 . Such a structure may be desirable because it may allow the metallic tubular member  410 , or select portions thereof, to have a desired level of lateral flexibility as well as have the ability to transmit torque and pushing forces through the metallic tubular member  410 . The apertures  420  may be formed in essentially any known way. For example, the apertures  420  can be formed by methods such as micro-machining, saw-cutting, laser cutting, grinding, milling, casting, molding, chemically etching or treating, or other known methods, and the like. In some such embodiments, the structure of the metallic tubular member  410  is formed by cutting and/or removing portions of the metallic tubular member  410  to form the apertures  420 . Some such metallic tubular members  410  are commonly referred to as hypotubes, and some such apertures can be referred to as slots or openings. 
         [0086]    In some embodiments, the apertures  420  can extend entirely through the wall  418  of the metallic tubular member  410 , or the apertures  420  can extend only partially into the wall  418  of the metallic tubular member  410 . Other embodiments may include combinations of both complete and partial apertures  420  through the wall  418  of the metallic tubular member  410 . Additionally, the quantity, size, spacing, distribution, and/or orientation of the apertures  420  can be varied to achieve desired characteristics. For example, the quantity or density of the apertures  420  along the length of the metallic tubular member  410  may be constant or may vary, depending upon desired characteristics. For example, the density of the apertures  420  in the distal portion of the metallic tubular member  410  may be greater than the density of the apertures  420  in the proximal portion of the metallic tubular member  410 . In such embodiments, the flexibility of the distal portion of the elongate shaft  405  may be greater than the flexibility of the proximal portion of the elongate shaft  405 . One of skill in the art would recognize that other arrangements of the apertures  420  may be imparted in the metallic tubular member  410  to achieve desired characteristics. 
         [0087]    Some additional examples of shaft constructions and/or arrangements of cuts or slots formed in a tubular member are disclosed in U.S. Pat. Nos. 6,428,489 and 6,579,246, which are each incorporated herein by reference. Additionally, U.S. Publication No. 2004/0193140, which is incorporated herein by reference, illustrates additional arrangements of apertures providing a degree of lateral flexibility formed in a medical device. 
         [0088]    In some embodiments, such as illustrated in  FIGS. 22A and 22B , the inner surface  424  of the metallic tubular member  410  may also include an inner coating or layer of a lubricious, hydrophilic, hydrophobic, and/or protective material. For example, lubricious coatings can aid in insertion and steerability of devices within the lumen  416  of the metallic tubular member  410 . One suitable lubricous coating is polytetrafluoroethylene (PTFE). However, one of skill in the art would recognize other materials having desirable characteristics. 
         [0089]    The distal end  414  of the elongate shaft  405  may include an atraumatic tip  428 . The atraumatic tip  428  may be adapted to reduce or prevent damage to a vessel wall during insertion and/or manipulation of the elongate shaft  405  within a vasculature. For example, the atraumatic tip  428  may include a polymer material having a relatively small durometer of hardness. However, other suitable materials may be used to form the atraumatic tip  428 . 
         [0090]    A stylet  450  is disposed within the lumen  416  of the metallic tubular member  410 . The stylet  450  has a proximal end  452  and a distal end  454 . The distal end  454  of the stylet  450  includes a cutting surface  456  illustrated as a needle tip. However, in other embodiments, the distal end  454  may include other suitable cutting and/or penetrating means. For example, in some embodiments, the distal end  454  of the stylet  450  may include a tapered, beveled, pointed, rounded, or flat tip. In other embodiments, the distal end  454  of the stylet  450  may include a machining element, such as an end mill, a spade mill, a fluted drill, a drill point, hard grit, grinding surfaces, or the like. The stylet  450  and/or the cutting surface  456  may comprise any suitable material. Some examples include metal or metal alloys, glass, ceramic material, or polymeric materials, including those materials disclosed elsewhere herein. 
         [0091]    The proximal end of the guidewire assembly  400  may include a control means for selectively controlling the position of the stylet  450  within the lumen  416  of the elongate shaft  405 . For example, the proximal end of the guidewire assembly  400  may include a hub assembly  460  configured to limit axial movement of the stylet  450  within the elongate shaft  405 . The hub assembly  460 , as shown in  FIGS. 22A and 22B  includes a hub element  462  coupled to the proximal end  452  of the stylet  450 . The hub element  462  may be coupled to the proximal end  452  of the stylet  450  in any known may. For example, the hub element  462  may be removably coupled to the stylet  450 , or the hub element  462  may be permanently coupled to the stylet  450 . As shown in the illustrative embodiment, the hub element  462  may include a threaded portion configured for mating engagement with a complementary threaded portion of the proximal end  452  of the stylet  450 . Thus, the hub element  462  may be variably positioned at one of multiple longitudinal positions of the stylet  450 . However, in other embodiments, the hub element  462  may be coupled to the stylet  450  with mechanical fasteners, crimping, adhesive or other bonding material, welding, thermal bonding, chemical bonding, an interference or frictional fit, an interlocking or snap fit, or the like. Movement of the stylette  450  with respect to the metallic tubular member  410  can be controlled or limited in a manner that is similar to that shown in  FIGS. 6-8 . 
         [0092]    The hub element  462  may be configured to have radial extents greater than the lumen  416  of the elongate shaft  405  such that the hub element  462  may limit longitudinal movement of the stylet  450  within the lumen  416 . For instance abutment of the hub element  462  against the proximal end  412  of the elongate shaft  405 , as shown in  FIG. 22B , prevents further longitudinal movement of the stylet  450  in the distal direction. 
         [0093]    Actuation of the stylet  450  may be accomplished by relative longitudinal movement between the stylet  450  and the elongate shaft  405  and/or rotational movement of the stylet  450  within the elongate shaft  405 . For example, the stylet  450  may be slidably actuated between a first, or retracted, position shown in  FIG. 22A  and a second, or extended, position shown in  FIG. 22B . In the second or extended position of  FIG. 22B , the cutting surface  456  of the stylet  450  is extended distally of the distal end  414  of the elongate shaft  405 . In the first or retracted position, the cutting surface  456  of the stylet  450  is retracted within the lumen  416  of the elongate shaft  405 . Thus, the hub assembly  460  may be manipulated in order to selectively extend the stylet  450  distal of the distal end  414  of the elongate shaft  405  and retract the stylet  450  within the elongate shaft  405 . However, in some embodiments, the distal end  454  of the stylet  450  can extend beyond the distal end  414  of the elongate shaft  405  even in the retracted position. 
         [0094]    Referring to  FIGS. 23A and 23B , another recanalization assembly, illustrated as a guidewire assembly  500 , is disclosed. The guidewire assembly  500  includes an elongate shaft  505  having a proximal end  512 , a distal end  514 , and a lumen  516  extending therethrough. The guidewire assembly  500  may be sized to allow additional medical devices to be inserted over the guidewire assembly  500  and advanced distally, such that the guidewire assembly  500  may facilitate navigation of additional medical devices within an anatomical region, such as the vasculature of a patient. For example, in some embodiments, the guidewire assembly  500  may have an outer diameter of about 0.20 mm (0.008 inch), about 0.25 mm (0.01 inch), about 0.36 mm (0.014 inch), about 0.46 mm (0.018 inch), about 0.64 mm (0.025 inch), about 0.89 mm (0.035 inch), about 0.97 mm (0.038 inch), or other desired size. In some embodiments the guidewire assembly  500  may have a length of about 50 cm to about 300 cm, or more. Although some suitable dimensions are disclosed, one of skill in the art would understand that the guidewire assembly  500  may have dimensions which deviate from those expressly disclosed. 
         [0095]    The elongate shaft  505  may be substantially similar to the elongate shaft  405  of  FIGS. 22A and 22B , thus for the sake of repetitiveness, similarities of the elongate shaft  505  with the elongate shaft  405  will not be repeated. For example, the elongate shaft  505  may be formed of any suitable material, such as those disclosed above regarding the elongate shaft  405 . For example, the elongate shaft  505  may include a metallic tubular member  510  having a tubular wall  518  including a plurality of apertures  520 , such as grooves, cuts, slits, slots, or the like, processed therein. The apertures  520  may be desirable as the apertures  520  may impart a desired level of lateral flexibility to the metallic tubular member  510 , or select portions thereof. The apertures  520  may be formed in essentially any known way. 
         [0096]    Additionally, an inner tubular member, such as a polymeric tubular member  525  may be positioned within the metallic tubular member  510 . The inner tubular member  525  may provide a fluid passageway and/or reduce frictional forces within the elongate shaft  505 . In some embodiments, the inner surface  524  of the metallic tubular member  510  may additionally or alternatively include an inner coating or layer of a lubricious, hydrophilic, hydrophobic, and/or protective material, such as a polytetrafluoroethylene (PTFE) coating, or the like. However, one of skill in the art would recognize that the metallic tubular member  510  may be coated or combined with other materials to impart desired characteristics to the elongate shaft  505 . 
         [0097]    The distal end  514  of the elongate shaft  505  may include an atraumatic tip  528 . The atraumatic tip  528  may be adapted to reduce or prevent damage to a vessel wall during insertion and/or manipulation of the elongate shaft  505  within a vasculature. For example, the atraumatic tip  528  may include a polymer material having a relatively small durometer of hardness. However, other suitable materials may be used to form the atraumatic tip  528 . 
         [0098]    A stylet  550  is disposed within the lumen  516  of the metallic tubular member  510 . The stylet  550  has a proximal end  552  and a distal end  554 . The distal end  554  of the stylet  550  includes a cutting surface  556  illustrated as a needle tip. However, in other embodiments, the distal end  554  may include other suitable cutting and/or penetrating means. For example, in some embodiments the distal end  554  of the stylet  550  may include a tapered, beveled, pointed, rounded, or flat tip. In other embodiments, the distal end  554  of the stylet  550  may include a machining element, such as an end mill, a spade mill, a fluted drill, a drill point, hard grit, grinding surfaces, or the like. The stylet  550  and/or the cutting surface  556  may comprise any suitable material. Some examples include metal or metal alloys, glass, ceramic material, or polymeric materials, including those materials disclosed elsewhere herein. 
         [0099]    The stylet  550 , as illustrated in  FIGS. 23A and 23B , may include a plurality of apertures  555 , such as grooves, cuts, slits, slots, or the like, processed therein. The apertures  555  may be substantially similar to the apertures  520  processed in the metallic tubular member  510 . The apertures  555  may be desirable as the apertures  555  may impart a desired level of lateral flexibility to the stylet  550 , or select portions thereof, yet retain sufficient rigidity to the stylet  550  to permit longitudinal actuation of the stylet  550  through the elongate shaft  505 . The apertures  520  may be formed in essentially any known way. 
         [0100]    The proximal end of the guidewire assembly  500  may include a control means for selectively controlling the position of the stylet  550  within the lumen  516  of the elongate shaft  505 . For example, the proximal end of the guidewire assembly  500  may include a hub assembly  560  configured to limit axial movement of the stylet  550  within the elongate shaft  505 . The hub assembly  560 , as shown in  FIGS. 23A and 23B  includes a hub element  564  coupled to the proximal end  512  of the elongate shaft  505 . The hub element  564  may be coupled to the proximal end  512  of the elongate shaft  505  in any known may. For example, the hub element  564  may be removably coupled to the elongate shaft  505 , or the hub element  564  may be permanently coupled to the elongate shaft  505 . In some embodiments, the hub element  564  may be coupled to the elongate shaft  505  with mechanical fasteners, a threaded connection, crimping, adhesive or other bonding material, welding, thermal bonding, chemical bonding, an interference or frictional fit, an interlocking or snap fit, or the like. 
         [0101]    The hub assembly  560  includes an engagement section  566  providing selective engagement between the stylet  550  and the elongate shaft  505 . The engagement section  566  includes an engagement portion  568  of the hub element  564 . In the illustrative embodiment, the engagement portion  568  is a portion of the hub element  564  having greater inner dimensions from an adjacent portion of the hub element  564 . For example, the engagement portion  568  may be a recessed area, such as a cavity, groove, bore, slot, or the like. The engagement portion  568  includes a proximal end  571  and a distal end  572 . 
         [0102]    The engagement section  566  of the hub assembly  560  also refers to a portion of the stylet  550 . The stylet  550  includes a stop  558  that has an outer periphery that is greater than the outer periphery of the stylet  550  on either side of the stop  558 . For example, in some embodiments, the stop  558  may be an annular ring extending around the circumference of the stylet  550 . In other embodiments, the stop  558  may include one or more distinct sections extending from the periphery of the stylet  550 . As shown in  FIG. 23A , proximal movement of the stylet  550  is limited by the stop  558  contacting the proximal end  571  of the engagement portion  568 . Similarly, distal movement of the stylet  550  is limited by the stop  558  contacting the distal end  572  of the engagement portion  568 . 
         [0103]    Additionally, the hub assembly  560  may include a biasing structure, such as a helical spring  563 . In the illustrated embodiment, the helical spring  563  is positioned between the distal end  572  of the engagement portion  568  of the hub element  564  and the stop  558 . Thus, the helical spring  563  may bias the stop  558 , and thus the stylet  550  proximally. In other words, the helical spring  563  may bias the stylet  550  in a first, or retracted position shown in  FIG. 23A . Thus, an actuation force greater than the biasing force of the helical spring  563  is necessary to actuate the stylet  550  to an extended position. However, in other embodiments, the helical spring  563 , or another biasing structure, may be positioned between the stop  558  and the proximal end  571  of the engagement portion  568  of the hub element  564 , biasing the stylet  550  in a second, or extended position shown in  FIG. 23B . 
         [0104]    Actuation of the stylet  550  may be accomplished by relative longitudinal movement between the stylet  550  and the elongate shaft  505  and/or rotational movement of the stylet  550  within the elongate shaft  505 . The stylet  550  may be actuated by manipulating the proximal end  552  of the stylet  550  extending proximal of the hub assembly  560 . For example, the stylet  550  may be slidably actuated between a first, or retracted, position shown in  FIG. 23A  and a second, or extended, position shown in  FIG. 23B . In the second or extended position of  FIG. 23B , the cutting surface  556  of the stylet  550  is extended distally of the distal end  514  of the elongate shaft  505 . In the first or retracted position, the cutting surface  556  of the stylet  550  is retracted within the lumen  516  of the elongate shaft  505 . Thus, the hub assembly  560  may be manipulated in order to selectively extend the stylet  550  distal of the distal end  514  of the elongate shaft  505  and retract the stylet  550  within the elongate shaft  505 . However, in some embodiments, the distal end  554  of the stylet  550  can extend beyond the distal end  514  of the elongate shaft  505  even in the retracted position. 
         [0105]    Referring now to  FIGS. 24A and 24B , another recanalization assembly, illustrated as a guidewire assembly  600 , is disclosed. The guidewire assembly  600  includes an elongate shaft  605 , having a proximal end  612 , a distal end  614 , and a lumen  616  extending therethrough. The guidewire assembly  600  may be sized to allow additional medical devices to be inserted over the guidewire assembly  600  and advanced distally, such that the guidewire assembly  600  may facilitate navigation of additional medical devices within an anatomical region, such as the vasculature of a patient. For example, in some embodiments, the guidewire assembly  600  may have an outer diameter of about 0.20 mm (0.008 inch), about 0.25 mm (0.01 inch), about 0.36 mm (0.014 inch), about 0.46 mm (0.018 inch), about 0.64 mm (0.025 inch), about 0.89 mm (0.035 inch), about 0.97 mm (0.038 inch), or other desired size. In some embodiments the guidewire assembly  600  may have a length of about 50 cm to about 300 cm, or more. Although some suitable dimensions are disclosed, one of skill in the art would understand that the guidewire assembly  600  may have dimensions which deviate from those expressly disclosed. 
         [0106]    The elongate shaft  605  may include a single-layer or multi-layer tubular member. For example, the elongate shaft  605  may include an inner tubular member  606 , an outer tubular member  607  and a reinforcement layer  608  interposed between the inner tubular member  606  and the outer tubular member  607 . The inner tubular member  606  and the outer tubular member  607  may be formed of any suitable material including, but not limited to, those materials disclosed elsewhere herein. For instance, the inner tubular member  606  and the outer tubular member  607  may each include a polymeric material, such as, but not limited to, any of the polymer materials described herein. For example, in some embodiments the inner tubular member  606  may include a lubricious polymeric material, such as high density polyethylene (HDPE) or polytetrafluoroethylene (PTFE), thus imparting lubricity to the inner surface  624  of the elongate shaft  605 . In some embodiments, the outer tubular member  607  may include a polyamide, or a polyether block amide (PEBA). Different portions or segments of the elongate shaft  605  may include dissimilar materials and/or materials having different durometers and/or flexibilities, thus imparting a plurality of regions having dissimilar flexibilities along the length of the elongate shaft  605 . For example, in some embodiments, the outer tubular member  607  may include multiple tubular segments, having dissimilar flexibility and/or hardness properties. 
         [0107]    In some embodiments, the reinforcement layer  608  may include one or more filaments, such as ribbon members, helically wound or coiled around the inner tubular member  606 . In other embodiments, the reinforcement layer  608  may include one or more braid members, such as one or more braids having interwoven opposingly helically wound filaments disposed on the inner tubular member  606 . The reinforcement layer  608  may provide the elongate shaft  605  with a desired degree of kink resistance, yet provide sufficient flexibility for navigation through a tortuous anatomy. 
         [0108]    The distal end  614  of the elongate shaft  605  may include an atraumatic tip  628 . The atraumatic tip  628  may be adapted to reduce or prevent damage to a vessel wall during insertion and/or manipulation of the elongate shaft  605  within a vasculature. For example, the atraumatic tip  628  may include a polymer material having a relatively small durometer of hardness. However, other suitable materials may be used to form the atraumatic tip  628 . 
         [0109]    A stylet  650  is disposed within the lumen  616  of the elongate shaft  605 . The stylet  650  has a proximal end  652  and a distal end  654 . The distal end  654  of the stylet  650  includes a cutting surface  656  illustrated as a needle tip. However, in other embodiments, the distal end  654  may include other suitable cutting and/or penetrating means. For example, in some embodiments the distal end  654  of the stylet  650  may include a tapered, beveled, pointed, rounded, or flat tip. In other embodiments, the distal end  654  of the stylet  650  may include a machining element, such as an end mill, a spade mill, a fluted drill, a drill point, hard grit, grinding surfaces, or the like. The stylet  650  and/or the cutting surface  656  may comprise any suitable material. Some examples include metal or metal alloys, glass, ceramic material, or polymeric materials, including those materials disclosed elsewhere herein. 
         [0110]    The stylet  650  may include a radiopaque marker  659  imparting a degree of radiopacity to the stylet  650 . In other embodiments, all or portions of the elongate shaft  605  and/or the stylet  650  may be made of, impregnated with, plated or clad with, or otherwise include a radiopaque material and/or structure to facilitate radiographic visualization. Radiopaque materials are understood to be materials capable of producing a relatively bright image on a fluoroscopy screen or another imaging technique during a medical procedure. Some examples of radiopaque materials can include, but are not limited to, gold, platinum, palladium, tantalum, tungsten alloy, polymer material loaded with radiopaque filler, and the like. 
         [0111]    The proximal end of the guidewire assembly  600  may include a control means for selectively controlling the position of the stylet  650  within the lumen  616  of the elongate shaft  605 . For example, the proximal end of the guidewire assembly  600  may include a hub assembly  660  configured to limit axial movement of the stylet  650  within the elongate shaft  605 . The hub assembly  660 , as shown in  FIGS. 24A and 24B  includes a hub element  664  coupled to the proximal end  612  of the elongate shaft  605 . The hub element  664  may be coupled to the proximal end  612  of the elongate shaft  605  in any known may. For example, the hub element  664  may be removably coupled to the elongate shaft  605 , or the hub element  664  may be permanently coupled to the elongate shaft  605 . In some embodiments, the hub element  664  may be coupled to the elongate shaft  605  with mechanical fasteners, a threaded connection, crimping, adhesive or other bonding material, welding, thermal bonding, chemical bonding, an interference or frictional fit, an interlocking or snap fit, or the like. In the illustrative embodiment, the hub element  664  includes an annular projection  667  extending into the proximal end  612  of the elongate shaft  605 . Thus, the annular projection  667  may be coupled to the proximal end  612  of the elongate shaft  605 . For example, the annular projection  667  may be bonded to the elongate shaft  605  with adhesive, UV bonding, thermal bonding, chemical bonding, RF welding, laser welding, or the like. 
         [0112]    As shown in the illustrative embodiment, the outer extents of the hub element  664  may be substantially similar to the outer diameter of the proximal end  612  of the elongate shaft  605 . Thus, the inclusion of the hub element  664  at the proximal end  612  of the elongate shaft  605  does not significantly hinder the ability of other medical devices of conventional sizes of being disposed about the guidewire assembly  600  and advanced distally over the elongate shaft  605  through a tortuous vasculature. However, in other embodiments, the hub element  664 , and/or other portions of the hub assembly  660 , may be removed from the elongate shaft  605  prior to disposing and advancing additional medical devices over the guidewire assembly  600 . 
         [0113]    The hub assembly  660  includes an engagement section  666  providing selective engagement between the stylet  650  and the elongate shaft  605 . The engagement section  666  includes an engagement portion of the hub element  664 . In the illustrative embodiment, the engagement portion of the hub element  664  is an opening  668 , or a plurality of openings  668  extending through the wall of the hub element  664 . For example, the opening  668  may be a slot, gap, or the like, allowing access to the interior of the hub element  664 . The opening  668  includes a proximal end  671  and a distal end  672 . In some embodiments, the opening  668  may be a portion of a bayonet style coupling mechanism for coupling the stylet  650  with the elongate shaft  605 . Thus, the stylet  650  may be selectively retained with the opening  668 . 
         [0114]    The engagement section  666  of the hub assembly  660  also refers to a portion of the stylet  650 . The stylet  650  includes a stop  658  that extends at least partially into the opening  668 . For example, in some embodiments, the stop  658  may be a projection extending into or through the opening  668 . As shown in  FIG. 24A , proximal movement of the stylet  650  is limited by the stop  658  contacting the proximal end  671  of the engagement portion  668 . Similarly, distal movement of the stylet  650  is limited by the stop  658  contacting the distal end  672  of the engagement portion  668 . In embodiments where the hub assembly  660  includes a bayonet style coupling mechanism, the stop  658  may be passed from the distal end of the hub element  664 , rotated, and positioned in the opening  668  of the hub element  664 . 
         [0115]    Actuation of the stylet  650  may be accomplished by relative longitudinal movement between the stylet  650  and the elongate shaft  605  and/or rotational movement of the stylet  650  within the elongate shaft  605 . The stylet  650  may be actuated by moving the stop  658  along the opening  668 . For example, the stylet  650  may be slidably actuated between a first, or retracted, position shown in  FIG. 24A  and a second, or extended, position shown in  FIG. 24B . In the second or extended position of  FIG. 24B , the cutting surface  656  of the stylet  650  is extended distally of the distal end  614  of the elongate shaft  605 . In the first or retracted position, the cutting surface  656  of the stylet  650  is retracted within the lumen  616  of the elongate shaft  605 . Thus, the hub assembly  660  may be manipulated in order to selectively extend the stylet  650  distal of the distal end  614  of the elongate shaft  605  and retract the stylet  650  within the elongate shaft  605 . However, in some embodiments, the distal end  654  of the stylet  650  can extend beyond the distal end  614  of the elongate shaft  605  even in the retracted position. 
         [0116]    In use during a medical procedure, the guidewire assembly  400 ,  500 ,  600  may be advanced through a vasculature to a distal location. When the distal end of the guidewire assembly  400 ,  500 ,  600  is proximate an occlusion, such as a chronic total occlusion of the vasculature, the stylet  450 ,  550 ,  650  may be actuated from the proximal end of the guidewire assembly  400 ,  500 ,  600 . For example, the stylet  450 ,  550 ,  650  may be actuated by advancing the stylet  450 ,  550 ,  650  distally and/or proximally, with a longitudinal back and forth (e.g., reciprocal) motion, a tapping motion, a rotational motion, and the like. Actuation of the stylet  450 ,  550 ,  650  may allow the distal end  454 ,  554 ,  654  of the stylet  450 ,  550 ,  650  to penetrate the occlusion, such as the proximal cap of a chronic total occlusion. Once penetration of the occlusion has occurred, the guidewire assembly  400 ,  500 ,  600  may be advanced further distally into or across the occlusion to a desired location in the vasculature. Once properly positioned, additional medical devices, such as a balloon catheter, a cutting device, or the like, may be advanced over the guidewire assembly  400 ,  500 ,  600  and navigated through the vasculature to a target location, such as the occlusion and/or a location distal of the occlusion. Thus, the guidewire assembly  400 ,  500 ,  600  may facilitate crossing an occlusion, such as a chronic total occlusion, within the vasculature with conventional medical devices. A similar procedure can be followed to allow passage of the guidewire assembly through the entire vessel lesion including passage through the distal cap of a chronic total occlusion. A balloon catheter such as an angioplasty catheter or other diagnostic or therapeutic catheter can be used to help center the guidewire assembly and the stylette in the vessel and allow the stylette to enter more closely to the central region of a proximal cap of a chronic total occlusion, for example, prior to advancing the guidewire assembly across the proximal cap. The stylette can be removed from the tubular member if desired to allow delivery of contrast medium through the tubular member lumen. 
         [0117]    As noted, the medical devices in accordance with the present invention can be of conventional materials and construction, except as described herein. The medical devices described herein can be partially or completely coated with a lubricious or other type of coating. Hydrophobic coatings such as fluoropolymers provide a dry lubricity that can improve handling and device exchanges. An example of a suitable fluoropolymer is polytetrafluoroethylene (PTFE), better known as TEFLON®. 
         [0118]    Lubricious coatings can improve steerability and improve lesion crossing capability. Examples of suitable lubricious polymers include hydrophilic polymers such as polyarylene oxides, polyvinylpyrolidones, polyvinylalcohols, hydroxy alkyl cellulosics, algins, saccharides, caprolactones, and the like, and mixtures and combinations thereof. Hydrophilic polymers can be blended among themselves or with formulated amounts of water insoluble compounds (including some polymers) to yield coatings with suitable lubricity, bonding, and solubility. In some embodiments, a distal portion of a composite medical device can be coated with a hydrophilic polymer as discussed above, while the more proximal portions can be coated with a fluoropolymer. 
         [0119]    The medical devices described herein can include, or be doped with, radiopaque material to improve visibility when using imaging techniques such as fluoroscopy techniques. Any suitable radiopaque material known in the art can be used. Some examples include precious metals, tungsten, barium subcarbonate powder, and the like, and mixtures thereof. In some embodiments, radiopaque material can be dispersed within the polymers used to form the particular medical device. In some embodiments, the radiopaque materials distinct from the ferromagnetic materials are dispersed. 
         [0120]    It should be understood that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of steps without exceeding the scope of the invention. The invention&#39;s scope is, of course, defined in the language in which the appended claims are expressed.