Abstract:
Devices, systems and methods for treating diseases and disorders effecting the cardiovascular system of the human body are disclosed. An exemplary blood vessel in accordance with this disclosure comprises a shaft, tip member fixed to the shaft, and a probe extending beyond a distal surface of the tip member. In some useful embodiments, the tip member is relatively atraumatic and the probe is shaped so as to be more likely to produce trauma than the tip member.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of application Ser. No. 12/320,792, filed Feb. 4, 2009 now U.S. Pat. No. 8,202,246, which claims the benefit of U.S. Provisional Application No. 61/063,756, filed Feb. 5, 2008. This Application claims the right to priority based on Provisional Application No. 61/104,868, filed Oct. 13, 2008. The contents of the above-noted applications are expressly incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The inventions described herein relate to devices and associated methods for the treatment of chronic total occlusions. More particularly, the inventions described herein relate to devices and methods for crossing chronic total occlusions and establishing a pathway blood flow past the chronic total occlusions. 
     BACKGROUND OF THE INVENTION 
     Due to age, high cholesterol and other contributing factors, a large percentage of the population has arterial atherosclerosis that totally occludes portions of the patient&#39;s vasculature and presents significant risks to patient health. For example, in the case of a total occlusion of a coronary artery, the result may be painful angina, loss of cardiac tissue or patient death. In another example, complete occlusion of the femoral and/or popliteal arteries in the leg may result in limb threatening ischemia and limb amputation. 
     Commonly known endovascular devices and techniques are either inefficient (time consuming procedure), have a high risk of perforating a vessel (poor safety) or fail to cross the occlusion (poor efficacy). Physicians currently have difficulty visualizing the native vessel lumen, can not accurately direct endovascular devices toward the visualized lumen, or fail to advance devices through the lesion. Bypass surgery is often the preferred treatment for patients with chronic total occlusions, but less invasive techniques would be preferred. 
     BRIEF SUMMARY 
     Devices, systems and methods for treating diseases and disorders effecting the cardiovascular system of the human body are disclosed. An exemplary blood vessel in accordance with this disclosure comprises a shaft, tip member fixed to the shaft, and a probe extending beyond a distal surface of the tip member. In some useful embodiments, the tip member is relatively atraumatic and the probe is shaped so as to be more likely to produce trauma than the tip member. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a somewhat stylized representation of a human heart. The heart includes a plurality of coronary arteries, all of which are susceptible to occlusion. 
         FIG. 2  is an enlarged view further illustrating a portion of the heart shown in the previous figure. In  FIG. 2 , a total occlusion is shown within a coronary artery. 
         FIG. 3  is a perspective view of a blood vessel (e.g., a coronary artery). In  FIG. 3 , the wall of the blood vessel is shown having three layers (the intima, the media, and the adventitia). 
         FIG. 4  is a lateral cross-sectional view of the artery shown in the previous figure. In  FIG. 4 , an orienting device is shown disposed between the adventitia and the intima of the artery. 
         FIG. 5  is a longitudinal cross-sectional view of an artery having an occlusion blocking the true lumen. 
         FIG. 6  is an additional cross-sectional view of the artery shown in the previous figure. In the embodiment of  FIG. 6 , a crossing device has been advanced over a guidewire so that a distal portion of crossing device is disposed in proximal segment of the true lumen. 
         FIG. 7  is a plan view showing an assembly including crossing device shown in the previous figure. 
         FIG. 8  is an additional view of an artery. In the embodiment of  FIG. 8 , the distal end of the crossing device has been advanced in a distal direction so that the tip of the crossing device is adjacent an occlusion that is blocking the true lumen of the artery. 
         FIG. 9  is an additional view of the artery and the crossing device shown in the previous figure. In the embodiment of  FIG. 9 , the distal end of the crossing device has been advanced between the intima and the adventitia of the wall of the artery. 
         FIG. 10  is an additional view of the artery shown in the previous figure. In the embodiment of  FIG. 10 , the crossing device has been withdrawn and a guidewire remains in the position formerly occupied by the crossing device. 
         FIG. 11  is an additional view of the artery and the guidewire shown in the previous figure. In the embodiment of  FIG. 11 , an orienting device  100  been advanced over the guidewire. 
         FIG. 12  is an additional view of the artery and the orienting device shown in the previous figure. 
         FIG. 13  is an enlarged partial cross-sectional view showing a portion of the orienting device shown in the previous figure. In the embodiment of  FIG. 13 , a re-entry device has been advanced into the central lumen of orienting device. 
         FIG. 14  is an additional partial cross-sectional view showing a portion of the re-entry device and the orienting device shown in  FIG. 13 . For purposes of illustration,  FIG. 14  is enlarged and simplified relative to the items shown in  FIG. 13 . 
         FIG. 15  is an enlarged partial cross-sectional view showing a portion of the re-entry device and the orienting device shown in the previous figure. In the embodiment of  FIG. 15 , the re-entry device has been positioned so that a distal portion of the re-entry device has entered the first aperture of the orienting device. 
         FIG. 16  is an enlarged partial cross-sectional view showing a portion of a re-entry device and the intima of a blood vessel. In the embodiment of  FIG. 16 , a probe of the re-entry device is contacting the intima. 
         FIG. 17  is an enlarged partial cross-sectional view showing a portion of the re-entry device shown in the previous figure. In the embodiment of  FIG. 17 , the probe of the re-entry device has pierced the intima of the blood vessel. When this is the case, the probe may anchor the distal tip of the re-entry device to the intima. Additionally, the piercing of the intima with the probe may serve to weaken the intima. 
         FIG. 18  is an enlarged partial cross-sectional view showing a portion of the re-entry device shown in the previous figure. In the embodiment of  FIG. 18 , the distal end of the re-entry device has been advanced through the intima of a blood vessel and is disposed in the true lumen of the blood vessel. 
         FIG. 19  is a partial cross-sectional view of the re-entry device shown in the previous figure.  FIG. 19  has a different scale than the previous figure so that more of the surrounding context is visible in  FIG. 19 . In  FIG. 19 , the distal end of the re-entry device can be seen residing in the true lumen of the blood vessel. 
         FIG. 20  is an additional view of the blood vessel shown in the previous figure. In the embodiment of  FIG. 20 , the orienting device has been withdrawn leaving the re-entry device in the position shown in  FIG. 20 . Devices such as balloon angioplasty catheters, atherectomy catheters, and stent delivery catheters may be advanced over the re-entry device. In this way, these devices may be used in conjunction with the re-entry device to establish a blood flow path between around an occlusion in a blood vessel. 
         FIG. 21  is a partial cross-sectional view of an exemplary re-entry device. 
         FIG. 22  is a plan view of an exemplary re-entry device. 
         FIG. 23  is a partial cross-sectional view of an exemplary re-entry device. 
         FIG. 24  is a partial cross-sectional view of an exemplary re-entry device. 
         FIG. 25  is a plan view of an exemplary re-entry device. 
         FIG. 26  is a cross-sectional view of an exemplary re-entry device. 
         FIG. 27  is a cross-sectional view of an exemplary re-entry device. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention. 
       FIG. 1  is a somewhat stylized representation of a human heart  50 . Heart  50  includes a plurality of coronary arteries  52 , all of which are susceptible to occlusion. Under certain physiological circumstances and given sufficient time, some occlusions may become total or complete, such as total occlusion  36  shown in  FIG. 1 . 
     As used herein, the terms total occlusion and complete occlusion are intended to refer to the same or similar degree of occlusion with some possible variation in the age of the occlusion. Generally, a total occlusion refers to a vascular lumen that is ninety percent or more functionally occluded in cross-sectional area, rendering it with little to no blood flow therethrough and making it difficult or impossible to pass a conventional guide wire therethrough. Also generally, the older the total occlusion the more organized the occlusive material will be and the more fibrous and calcified it will become. According to one accepted clinical definition, a total occlusion is considered chronic if it is greater than two weeks old from symptom onset. 
       FIG. 2  is an enlarged view further illustrating a portion of heart  50  shown in the previous figure. In  FIG. 2 , a total occlusion  36  is shown within a coronary artery  52 . Generally, the proximal segment  32  of artery  52  (i.e., the portion of artery  52  proximal of total occlusion  36 ) has adequate blood flow to supply the surrounding cardiac muscle and may be easily accessed using endovascular devices. In contrast, the distal segment  34  of artery  52  (i.e., the portion of artery  52  distal of total occlusion  36 ) is not easily accessed with interventional devices. Additionally, distal segment  34  has significantly reduced blood flow as compared to proximal segment  32 . 
       FIG. 3  is a perspective view of an artery  20  having a wall  22 . In  FIG. 3 , wall  22  of artery  20  is shown having three layers. The outermost layer of wall  22  is the adventitia  24  and the innermost layer of wall  22  is the intima  26 . Intima  26  defines a true lumen  30  of artery  20 . The tissues extending between intima  26  and adventitia  24  may be collectively referred to as the media  28 . For purposes of illustration, intima  26 , media  28  and adventitia  24  are each shown as a single homogenous layer in  FIG. 3 . In the human body, however, the intima and the media each comprise a number of sub-layers. The transition between the external most portion of the intima and the internal most portion of the media is sometimes referred to as the subintimal space  40 . 
     With reference to  FIG. 3 , it will be appreciated that the subintimal space  40  has a generally annular shape with its radial center at the center of the true lumen. Some of the devices and methods discussed in this detailed description may take advantage of the position and geometry of the subintimal space  40  relative to the true lumen of the blood vessel. For example, some orienting devices described herein may be adapted to orient themselves within that space. Once the orientation of the orienting device is established, the orienting device may be used to direct a re-entry device toward the true lumen. 
       FIG. 4  is a lateral cross-sectional view of artery  20  shown in the previous figure. In  FIG. 4 , an orienting device  100  is shown disposed between adventitia  24  and intima  26  of artery  20 . Orienting device  100  comprises a distal shaft  102  having an outer wall  128  defining a central lumen  104 . Orienting device  100  comprises an orienting element  120  that is coupled to distal shaft  102 . 
     In the embodiment of  FIG. 4 , orienting element  120  comprises an inflatable member  126 . The top of inflatable member  126  may be fixed to distal shaft  102 , for example, at a first interface  190 A. The bottom of inflatable member  126  may be fixed to distal shaft  102 , for example, at a second interface  190 B. 
     Orienting element  120  comprises a first portion  106  and a second portion  108 . First portion  106  of orienting element  120  extends in a first direction away from distal shaft  102 . Second portion  108  of orienting element  120  extends away from distal shaft  102  in a second direction that is generally opposite the first direction. 
     Distal shaft  102  defines a first aperture  130  and a second aperture  132 . First aperture  130  extends in a third direction through distal shaft  102 . Second aperture  132  extends through distal shaft  102  in a forth direction that is generally opposite the third direction. First aperture  130  and second aperture  132  are generally oriented at a right angle to a tangent plane TP. In  FIG. 4 , tangent plane TP is tangent to subintimal space  40 . 
     When inflatable member  126  is inflated, the number of directions that first aperture  130  and second aperture  132  may be facing is reduced. This may be conceptualized in terms of degrees of freedom. When inflatable member  126  of orienting element  120  is inflated, the number of directions that an aperture may be facing is reduced from 360 degrees of freedom to two degrees of freedom, 180 degrees apart. 
     When inflatable member  126  of orienting element  120  is inflated between adventitia  24  and intima  26  of artery  20  orienting device  100  will orient itself within artery  20  so that either first aperture  130  or second aperture  132  opens toward a true lumen  30  of artery  20 . In the embodiment of  FIG. 4 , orienting device  100  has been positioned so that first aperture  130  opens toward intima  26  of artery  20  and second aperture  132  opens toward adventitia  24 . In  FIG. 4 , a re-entry device  180  is shown extending through first aperture  130  and intima  26 . A distal end of re-entry device  180  is disposed in true lumen  30  of blood vessel  20 . Orienting device  100  and re-entry device  180  may be used to establish fluid communication between a proximal segment and a distal segment that are separated by an occlusion. Exemplary methods for establishing this fluid communication will be described below. 
       FIG. 5  is a longitudinal cross-sectional view of an artery  20  having an occlusion  36  blocking true lumen  30  thereof. Occlusion  36  divides true lumen  30  into a proximal segment  32  and a distal segment  34 . In  FIG. 5 , a distal portion of a guidewire  60  is shown extending into proximal segment  32  of true lumen  30 . The methods described in this document may include the step of advancing a guidewire to a location proximate an occlusion in a blood vessel. The exemplary methods described in this document may also include the step of advancing guidewire  60  between occlusion  36  and adventitia  24  of wall  22 . In some cases, however, the nature of the occlusion and the blood vessel will be such that the guidewire is unlikely to advance beyond the occlusion. When this is the case, the guidewire may be used to guide additional endovascular devices to a location proximate occlusion  36 . 
       FIG. 6  is an additional cross-sectional view of artery  20  shown in the previous figure. In the embodiment of  FIG. 6 , a crossing device  70  has been advanced over guidewire  60  so that a distal portion of crossing device  70  is disposed in proximal segment  32  of true lumen  30 . Crossing device  70  of  FIG. 6  comprises a tip  74  that is fixed to a distal end of a shaft  72 . Crossing device  70  may be used in conjunction with a method for establishing a channel between proximal segment  32  and distal segment  34 . The methods described in this document may include the step of advancing a crossing device over a guidewire. 
     In some useful methods in accordance with the present disclosure, crossing device  70  may be rotated about it&#39;s longitudinal axis and moved in a direction parallel to it&#39;s longitudinal axis simultaneously. When this is the case, rotation of crossing device  70  may reduce resistance to the axial advancement of crossing device  70 . These methods take advantage of the fact that the kinetic coefficient of friction is usually less than the static coefficient of friction for a given frictional interface. Rotating crossing device  70  assures that the coefficient of friction at the interface between the crossing device and the surround tissue will be a kinetic coefficient of friction and not a static coefficient of friction. 
       FIG. 7  is a plan view showing an assembly including crossing device  70  shown in the previous figure. In the embodiment of  FIG. 7 , a handle assembly  76  is coupled to crossing device  70 . In  FIG. 7 , handle assembly  76  is shown disposed about a proximal portion of a shaft  152  of crossing device  70 . In  FIG. 7 , a portion of handle assembly  76  is positioned between the thumb and forefinger of a left hand LH. A second portion of handle assembly  76  is disposed between the thumb and forefinger of a right hand RH. With reference to  FIG. 7 , it will be appreciated that handle assembly  76  is long enough to receive the thumb and forefingers of a physician&#39;s right and left hands. When this is the case, a physician can use two hands to rotate handle assembly  76 . 
     Rotation of crossing device  70  can be achieved by rolling handle assembly  76  between the thumb and forefinger of one hand. Two hands may also be used to rotate handle assembly  76  as shown in  FIG. 7 . In some useful methods, crossing device  70  can be rotated and axially advanced simultaneously. 
     In some useful methods in accordance with the present disclosure, crossing device  70  is rotated at a rotational speed of between about 2 revolutions per minute and about 200 revolutions per minute. In some particularly useful methods in accordance with the present disclosure, crossing device  70  is rotated at a rotational speed of between about 50 revolutions per minute and about 150 revolutions per minute. 
     Crossing device  70  may be rotated by hand as depicted in  FIG. 7 . It is also contemplated that a mechanical device (e.g., an electric motor) may be used to rotate crossing device  70 . Rotating crossing device  70  assures that the coefficient of friction at the interface between the crossing device and the surround tissue will be a kinetic coefficient of friction and not a static coefficient of friction. 
       FIG. 8  is an additional longitudinal cross-sectional view of artery  20 . In the embodiment of  FIG. 8 , the distal end of crossing device  70  has been advanced in a distal direction so that tip  74  is adjacent occlusion  36 . With reference to  FIG. 8 , it will be appreciated that tip  74  has passed beyond intima  26  and is disposed between occlusion  36  and adventitia  24  of artery  20 . Some methods described in this document may include the step of advancing a crossing device between an occlusion and the adventitia of an artery. 
       FIG. 9  is an additional view of artery  20  and crossing device  70  shown in the previous figure. In the embodiment of  FIG. 9 , the distal end of crossing device  70  has been advanced in an axial direction past occlusion  36 . Methods described herein may include the step of advancing a crossing device beyond an occlusion. In the embodiment of  FIG. 9 , crossing device has crossed occlusion  36  by advancing between occlusion  36  and adventitia  24  of wall  22 . 
     It is to be appreciated that other methods of crossing an occlusion are within the spirit and scope of this disclosure. For example, the crossing device  70  may pass through occlusion  36  while remaining disposed inside true lumen  30 . In  FIG. 9 , tip  74  of crossing device  70  is shown residing between intima  26  and adventitia  24  of artery  20 . As tip  74  moves in an axial direction between intima  26  and adventitia  24 , tip  74  may cause blunt dissection of the layers forming wall  22  of artery  20 . Alternatively, tip  74  may cause blunt dissection of the materials comprising the occlusion  36 . 
     In the embodiment of  FIG. 9 , tip  74  of crossing device  70  is disposed between intima  26  and adventitia  24 . When this is the case, fluid communication between proximal segment  32  and distal segment  34  may be achieved by creating an opening through intima  26 . Such an opening may be created, for example, using a re-entry device and an orienting device that directs the advancement of the re-entry device toward intima  26 . 
       FIG. 10  is an additional view of artery  20  shown in the previous figure. In the embodiment of  FIG. 10 , crossing device  70  has been withdrawn from true lumen  30  of artery  20 . With reference to  FIG. 10 , it will be appreciated that guidewire  60  remains in the position formerly occupied by crossing device  70 . 
     The position of guidewire  60  shown in  FIG. 10  may be achieved using crossing device  70 . Guidewire  60  may be positioned, for example, by first placing crossing device  70  in the position shown in the previous figure, then advancing guidewire  60  through lumen  122  defined by shaft  72  of crossing device  70 . Alternately, guidewire  60  may be disposed within lumen  122  while crossing device  70  is advanced beyond occlusion  36 . 
     With guidewire  60  in the position shown in  FIG. 10 , guidewire  60  may be used to direct other devices between occlusion  36  and adventitia  24 . For example, a catheter may be advanced over guidewire  60  until the distal end of the catheter extends between an occlusion and the adventia. After reaching this location, the catheter may be used to dilate the tissue surrounding the catheter. Examples of catheters that may be used to dilate tissue include balloon angioplasty catheters, atherectomy catheters, and stent delivery catheters. 
       FIG. 11  is an additional view of artery  20  and guidewire  60  shown in the previous figure. In the embodiment of  FIG. 11 , an orienting device  100  has been advanced over guidewire  60 . Orienting device  100  includes a distal shaft  102  comprising a outer wall  128  defining a central lumen  104 . A first aperture  130  and a second aperture  132  are also defined by outer wall  128 . In the embodiment of  FIG. 11 , first aperture  130  and second aperture  132  are both in fluid communication with central lumen  104 . 
     In the embodiment of  FIG. 11 , orienting device  100  has been positioned so that first aperture  130  opens toward intima  26  of artery  20  and second aperture  132  opens toward adventitia  24 . In the embodiment of  FIG. 11 , first aperture  130  and second aperture  132  are longitudinally separated from one another. Orienting device  100  includes a first radiopaque marker that is located between first aperture  130  and second aperture  132 . A second radiopaque marker of orienting device  100  is located distally of second aperture  132 . 
       FIG. 12  is an additional view of artery  20  and orienting device  100  shown in the previous figure. In the embodiment of  FIG. 12 , guidewire  60  has been withdrawn leaving orienting device  100  in the position shown in  FIG. 12 . With reference to  FIG. 12 , it will be appreciated that orienting device  100  extends beyond occlusion  36 . In  FIG. 12 , occlusion  36  is shown blocking true lumen  30 . Occlusion  36  divides true lumen  30  into a proximal segment  32  and a distal segment  34 . When an orienting device in accordance with some embodiments disclosed herein is advanced between the adventitia and the intima of an artery, the orienting device may be used to direct a re-entry device toward true lumen  30 . Fluid communication between proximal segment  32  and distal segment  34  may be achieved by re-entering the true lumen with a re-entry device. 
       FIG. 13  is an enlarged partial cross-sectional view showing a portion of orienting device  100  shown in the previous figure. In the embodiment of  FIG. 13 , a re-entry device  180  has been advanced into central lumen  104  of orienting device  100 . With reference to  FIG. 13 , it will be appreciated that re-entry device  180  includes a bend  134  near distal end  136  of re-entry device  180 . 
       FIG. 14  is an additional partial cross-sectional view showing a portion of re-entry device  180  and orienting device  100 . For purposes of illustration,  FIG. 14  is enlarged and simplified relative to the items shown in the previous figure. In the embodiment of  FIG. 14 , re-entry device  180  is biased to assume a bent shape including a bend  134 . Also in the embodiment of  FIG. 14 , distal shaft  102  of orienting device  100  is holding re-entry device  180  in a somewhat compressed state. When this is the case, re-entry device  180  can be inserted through first aperture  130  by positioning distal end  136  over first aperture  130  and allowing bend  134  to assume it&#39;s natural state (i.e., bent at a sharper angle). Re-entry device  180  can be inserted through first aperture  130  until it comes into contact with intima  26 . 
     It the embodiment of  FIG. 14 , distal end  136  of re-entry device  180  is axially aligned with first aperture  130 , however, bend  134  is causing distal end  136  to point away from first aperture  130 . When this is the case, distal end  136  may be positioned over first aperture  130  by rotating re-entry device  180  central lumen  104  of orienting device  100 . 
       FIG. 15  is an enlarged partial cross-sectional view showing a portion of re-entry device  180  and orienting device  100  shown in the previous figure. In the embodiment of  FIG. 15 , re-entry device  180  has been positioned so that a distal portion of reentry device  180  has entered first aperture  130 . Intima  26  is shown below first aperture  130  in  FIG. 15 . 
       FIG. 16  is an enlarged partial cross-sectional view showing a portion of re-entry device  180  and intima  26 . In  FIG. 16 , re-entry device  180  is shown extending through central lumen  104  and first aperture  130 . With reference to  FIG. 16 , it will be appreciated that re-entry device  180  comprises a distal surface  144  and a probe  146  extending beyond distal surface  144 . In the embodiment of  FIG. 16 , probe  146  of re-entry device  180  is contacting intima  26 . 
       FIG. 17  is an enlarged partial cross-sectional view showing a portion of re-entry device  180 . In the embodiment of  FIG. 17 , probe  146  of re-entry device  180  has pierced intima  26 . When this is the case, probe  146  may anchor the distal tip of re-entry device  180  to intima  26 . Additionally, the piercing of intima  26  with probe  146  may serve to weaken intima  26 . 
       FIG. 18  is an enlarged partial cross-sectional view showing a portion of re-entry device  180 . In the embodiment of  FIG. 18 , the distal end  136  of re-entry device  180  has been advanced through intima  26 . With reference to  FIG. 18 , it will be appreciated that distal end  136  of re-entry device  180  is disposed in true lumen  30  defined by intima  26 . 
       FIG. 19  is a partial cross-sectional view of re-entry device  180  shown in the previous figure.  FIG. 19  has a different scale than the previous figure so that more of the surrounding context is visible in  FIG. 19 . In  FIG. 19 , distal end  136  of re-entry device  180  can be seen residing in true lumen  30 . 
       FIG. 20  is an additional view of artery  20  shown in the previous figure. In the embodiment of  FIG. 20 , orienting device  100  has been withdrawn leaving re-entry device  180  in the position shown in  FIG. 20 . Devices such as balloon angioplasty catheters, atherectomy catheters, and stent delivery catheters may be advanced over re-entry device  180 . In this way, these devices may be used in conjunction with re-entry device  180  to establish a blood flow path between proximal segment  32  of true lumen  30  and distal segment  34  of true lumen  30 . This path allows blood to flow around occlusion  36 . 
       FIG. 21  is a partial cross-sectional view of an exemplary re-entry device  280  in accordance with the present detailed description. Re-entry device  280  comprises a tip member  242  that is fixed to a shaft  240  and a coil  248  that is disposed about a distal portion of the shaft  240 . Shaft  240  comprises a proximal segment  250  that extends between a proximal end PE and a first tapered segment  252 . In the embodiment of  FIG. 21 , coil  248  extends between first tapered segment  252  and tip member  242 . 
     A first intermediate segment  262  of shaft  240  extends between first tapered segment  252  and a second tapered segment  254 . A second intermediate segment  264  of shaft  240  extends between second tapered segment  254  and a third tapered segment  256 . A distal segment  260  of shaft  240  extends between third tapered segment  256  and tip member  242 . With reference to  FIG. 21 , it will be appreciated that tip member  242  is fixed to distal segment  260  of shaft  240 . In the embodiment of  FIG. 21 , a probe  246  of re-entry device  280  extends distally beyond a distal surface  244  of tip member  242 . 
       FIG. 22  is a plan view of an exemplary re-entry device  380  in accordance with the present detailed description. Re-entry device  380  comprises a tip member  342  having a distal surface  344 . In the embodiment of  FIG. 22 , distal surface  344  of tip member has a generally convex shape. In some cases, tip member  342  may have a generally hemispherical shape. A probe  346  of re-entry device  380  extends distally beyond distal surface  344 . Probe  346  terminates at a distal face  358 . In  FIG. 22 , distal face  358  is shown as a straight line representing a substantially flat surface. With reference to  FIG. 22 , it will be appreciated that distal face  358  is substantially perpendicular to the longitudinal axis of probe  346 . 
     A number of exemplary dimensions associated with probe  346  are illustrated in  FIG. 22 . In the embodiment of  FIG. 22 , probe  346  extends beyond distal surface  344  of tip member  342  by a distance L. Also in the embodiment of  FIG. 22 , probe  346  has a diameter DA and tip member  342  has a diameter DB. With reference to  FIG. 22 , it will be appreciated that diameter DB of tip member  342  is generally greater than diameter DA of probe  346 . 
     In some useful embodiments, diameter DA of probe  346  is between about 0.0020 inches and about 0.0055 inches. In some useful embodiments, diameter DB of tip member  342  is between about 0.008 inches and about 0.035 inches. In some useful embodiments, length L of probe  346  is between about 0.003 inches and about 0.032 inches. In  FIG. 22 , a coil  348  is shown extending between tip member  342  and a first tapered segment  352 . Shaft  340  comprises a proximal segment  350  that extends between a proximal end PE and a first tapered segment  352 . 
       FIG. 23  is a partial cross-sectional view of an exemplary re-entry device  480  in accordance with the present detailed description. Re-entry device  480  comprises a tip member  442  that is fixed to a distal segment  460  of a shaft  440 . In the embodiment of  FIG. 23 , tip member  442  comprises a distal surface  444  and a probe  446  extending distally beyond distal surface  444 . In the embodiment of  FIG. 23 , distal surface  444  of tip member has a generally hemispherical shape and probe  446  has a generally cylindrical shape terminating at a flat distal face  458 . With reference to  FIG. 23 , it will be appreciated that distal face  458  is substantially perpendicular to the longitudinal axis of probe  446 . 
     Various processes may be used to fabricate a tip member having a shape similar to tip member  442  shown in  FIG. 23 . A tip member may be formed, for example, using various manufacturing processes such as, for example, casting and molding. A tip member may also be fabricated by a manufacturing process comprising removing material from a piece of stock material to produce a desired profile. Examples of processes that may be used to remove material from a piece of stock material include grinding and machining (e.g., turning on a lathe). 
     In the embodiment of  FIG. 23 , probe  446  extends beyond distal surface  444  of tip member  442  by a distance L. Also in the embodiment of  FIG. 23 , probe  446  has a diameter DA and tip member  442  has a diameter DB. In some useful embodiments, the these dimensions fall with the numerical ranges mentioned in the detailed description of  FIG. 22 . 
       FIG. 24  is a partial cross-sectional view of an exemplary re-entry device  580  in accordance with the present detailed description. Re-entry device  580  comprises a shaft  540  and a tip member  542  that is fixed to a distal segment  560  of shaft  540 . A probe  546  of re-entry device  580  extends distally beyond a distal surface  544  of tip member  542 . In the embodiment of  FIG. 24 , probe  546  comprises a portion of distal segment  560  that extends beyond distal surface  544 . A coil  548  of re-entry device  580  extends between tip member  542  and a first tapered segment  552  of shaft  540 . Coil  548  is fixed to first tapered section  552  at a joint  566 . Joint  566  and tip member  542  may comprise, for example, silver (e.g., silver solder and/or silver braze). Joint  566  and tip member  542  may be formed using various manufacturing processes (e.g., soldering, brazing, and welding). 
     In the embodiment of  FIG. 24 , distal segment  560  of shaft  540  terminates at a substantially flat distal face  558 . Probe  546  comprises a portion of distal segment  560  that extends beyond distal surface  544  of tip member  542  by a distance L. Also in the embodiment of  FIG. 24 , probe  546  has a diameter DA and tip member  542  has a diameter DB. In some useful embodiments, the these dimensions fall with the numerical ranges mentioned in the detailed description of  FIG. 22 . 
       FIG. 25  is a plan view of an exemplary re-entry device  680  in accordance with the present detailed description. Re-entry device  680  comprises a tip member  642  having a distal surface  644 . In the embodiment of  FIG. 25 , distal surface  644  of tip member has a generally convex shape. In some cases, tip member  642  may have a generally hemispherical shape. A probe  646  of re-entry device  680  extends distally beyond distal surface  644 . Probe  646  terminates at a distal face  658 . In  FIG. 25 , distal face  658  is shown as a straight line representing a substantially flat surface. 
     In  FIG. 25 , re-entry device  600  is shown being bent at an angle A. Accordingly, it can be said that re-entry device  600  includes a bend  630 . In some useful embodiments of re-entry device  600 , angle A is between about 90 degrees and about 180 degrees. In some particularly useful embodiments of re-entry device  600 , angle A is between about 120 degrees and about 150 degrees. Re-entry device  680  has a distal leg  668  disposed distally of bend  634  and a proximal leg  670  disposed proximally of bend  634 . 
       FIG. 26  is a cross-sectional view of an exemplary re-entry device  780  in accordance with the present detailed description. Re-entry device  780  comprises a core wire  772  and a jacket  774  that is disposed about a portion of core wire  772 . Jacket  774  terminates at a distal surface  744 . A probe  746  of re-entry device  780  extends distally beyond distal surface  744 . In the embodiment of  FIG. 26 , probe  746  comprises a distal segment  760  of core wire  772 . 
       FIG. 27  is a cross-sectional view of an exemplary re-entry device  780  in accordance with the present detailed description. Re-entry device  780  comprises a core wire  772  and a jacket  774  that is disposed about a portion of core wire  772 . With reference to  FIG. 27 , it will be appreciated that re-entry device  780  includes a bend  734  near its distal end. Re-entry device  780  has a distal leg  768  disposed distally of bend  734  and a proximal leg  770  disposed proximally of bend  734 . Distal leg  768  and proximal leg  770  define an angle A. In some useful embodiments of re-entry device  700 , angle A is between about 90 degrees and about 180 degrees. In some particularly useful embodiments of re-entry device  700 , angle A is between about 120 degrees and about 150 degrees. Jacket  774  of re-entry device  780  terminates at a distal surface  744 . A probe  746  of re-entry device  780  extends distally beyond distal surface  744 . In the embodiment of  FIG. 27 , probe  746  comprises a distal segment  760  of core wire  772 . 
     From the foregoing, it will be apparent to those skilled in the art that the present invention provides, in exemplary non-limiting embodiments, devices and methods for the treatment of chronic total occlusions. Further, those skilled in the art will recognize that the present invention may be manifested in a variety of forms other than the specific embodiments described and contemplated herein. Accordingly, departures in form and detail may be made without departing from the scope and spirit of the present invention as described in the appended claims.