Abstract:
The present disclosure is directed to a method of facilitating treatment via a vascular wall defining a vascular lumen containing an occlusion therein. The method may include providing an intravascular device having a distal portion and a longitudinal axis and inserting the intravascular device into the vascular lumen. The method may further include positioning the distal portion in the vascular wall, rotating the intravascular device about the longitudinal axis, and advancing the intravascular device within the vascular wall.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a continuation application of U.S. patent application Ser. No. 12/289,154, filed Oct. 21, 2008, which claims the benefit of U.S. Provisional Application No. 60/999,879, filed Oct. 22, 2007, the complete disclosures of which are herein incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    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 
       [0003]    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. 
         [0004]    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. 
         [0005]    Described herein are devices and methods employed to exploit the vascular wall of a vascular lumen for the purpose of bypassing a total occlusion of an artery. Exploitation of a vascular wall may involve the passage of an endovascular device into and out of said wall which is commonly and interchangeable described as false lumen access, intramural access, submedial access or in the case of this disclosure, subintimal access. 
       BRIEF SUMMARY 
       [0006]    Described herein are devices and methods employed to exploit the vascular wall of a vascular lumen for the purpose of bypassing a total occlusion of an artery. Exploitation of a vascular wall may involve the passage of an endovascular device into and out of said wall which is commonly and interchangeable described as false lumen access, intramural access, submedial access or in the case of this disclosure, subintimal access. 
         [0007]    In one aspect, the present disclosure is directed to a method of facilitating treatment via a vascular wall defining a vascular lumen containing an occlusion therein. The method may include providing an intravascular device having a distal portion and a longitudinal axis and inserting the intravascular device into the vascular lumen. The method may further include positioning the distal portion in the vascular wall, rotating the intravascular device about the longitudinal axis, and advancing the intravascular device within the vascular wall. 
         [0008]    In another aspect, the present disclosure is direct to a device for facilitating treatment via a vascular wall defining a vascular lumen containing an occlusion therein. The device may include a shaft having a distal end and a proximal end. The shaft may include a coil having a plurality of filars wound in a helical shape, the coil extending from the distal end of the shaft to the proximal end of the shaft, and a sleeve, having a proximal end and a distal end, the sleeve extending from the distal end of the shaft and covering a portion of the coil. The device may further include a tip fixed to the distal end of the shaft, and a hub fixed to the proximal end of the shaft. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0009]      FIG. 1  is a cross-sectional view of an artery. 
           [0010]      FIG. 2  is an additional view of the artery shown in the previous figure. 
           [0011]      FIG. 3  is an additional view of the artery shown in the previous figure. 
           [0012]      FIG. 4  is an additional view of the artery shown in the previous figure. 
           [0013]      FIG. 5  is a cross-sectional view of an artery. 
           [0014]      FIG. 6  is an additional view of the artery shown in the previous figure. 
           [0015]      FIG. 7  is a partial cross-sectional view of an exemplary crossing device. 
           [0016]      FIG. 8  is a plan view showing an assembly including the crossing device shown in the previous figure. 
           [0017]      FIG. 9  is a plan view of the assembly shown in the previous figure. 
           [0018]      FIG. 10  is a cross-sectional view of the assembly shown in the previous figure. 
           [0019]      FIG. 11  is a cross sectional view of the handle assembly shown in the previous figure. 
           [0020]      FIG. 12  is a partial cross-sectional view showing a guidewire that is disposed in a lumen defined by a shaft of a crossing device. 
           [0021]      FIG. 13  is an additional view of the guidewire and crossing device shown in the previous figure. 
           [0022]      FIG. 14  is a plan view showing a heart including a coronary artery. 
           [0023]      FIG. 15A  is an enlarged view showing a portion of the heart shown in the previous figure. 
           [0024]      FIG. 15B  is an enlarged plan view of a crossing device shown in  FIG. 15A . 
           [0025]      FIG. 16A  is an additional view showing a crossing device disposed in a heart. 
           [0026]      FIG. 16B  is an enlarged plan view of a crossing device shown in  FIG. 16A . 
           [0027]      FIG. 17A  is an enlarged view showing a portion of a heart and a crossing device that is extending into a proximal segment of a coronary artery of the heart. 
           [0028]      FIG. 17B  is a representation of a fluoroscopic display produced when radiopaque fluid has been injected into the body from the distal end of a crossing device while the distal end of the crossing device is disposed in the true lumen of a coronary artery. 
           [0029]      FIG. 18A  is an enlarged view showing a portion of a heart and a crossing device that is extending into a proximal segment of a coronary artery of the heart. 
           [0030]      FIG. 18B  is a representation of a fluoroscopic display produced when radiopaque fluid has been injected into the body from the distal end of a crossing device while the distal end of the crossing device is disposed in the subintimal space of a coronary artery. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0031]    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. 
         [0032]      FIG. 1  is a cross-sectional view of an artery  102  having a wall  126 . In  FIG. 1 , wall  126  of artery  102  is shown having three layers. The outermost layer of wall  126  is the adventitia  105  and the innermost layer of wall  126  is the intima  107 . The tissues extending between intima  107  and adventitia  105  may be collectively referred to as the media  109 . For purposes of illustration, intima  107 , media  109  and adventitia  105  are each shown as a single homogenous layer in  FIG. 1 . 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. 
         [0033]    Intima  107  defines a true lumen  106  of artery  102 . In  FIG. 1 , an occlusion  108  is shown blocking true lumen  106 . Occlusion  108  divides true lumen  106  into a proximal segment  103  and a distal segment  104 . A crossing device  120  is disposed in proximal segment  103  of true lumen  106 . Crossing device  120  may be used to establish a channel between proximal segment  103  and distal segment  104 . Crossing device  120  of  FIG. 1  comprises a tip  124  that is fixed to a distal end of a shaft  122 . 
         [0034]      FIG. 2  is an additional view of artery  102  shown in the previous figure. In the embodiment of  FIG. 2 , the distal end of crossing device  120  has been advanced in a distal direction so that tip  124  is disposed in subintimal space  128 . With reference to  FIG. 2 , it will be appreciated that tip  124  has passed through intima  107  and is disposed between intima  107  and adventitia  105  of artery  102 . The embodiment of  FIG. 2  and other embodiments described herewithin show access to the subintimal space  128  by way of example, not limitation, as the crossing device  120  may alternatively pass through the occlusion  108  thus remaining disposed in the true lumen  106 . 
         [0035]    In the embodiment of  FIG. 2 , shaft  122  of crossing device  120  defines a lumen  130 . Lumen  130  may be used to deliver fluids into the body. For example, radiopaque fluid may be injected through lumen  130  and into subintimal space  128 . In some useful embodiments, lumen  130  is dimensioned to receive a guidewire. 
         [0036]      FIG. 3  is an additional view of artery  102  shown in the previous figure. In the embodiment of  FIG. 3 , the distal end of crossing device  120  has been advanced so that tip  124  has moved in an axial direction through subintimal space  128 . With reference to  FIG. 3 , it will be appreciated that tip  124  has moved distally past occlusion  108 . In  FIG. 3 , tip  124  is shown residing between intima  107  and adventitia  105  of artery  102 . Axial advancement of tip  124  may cause blunt dissection of the layers forming wall  126  of artery  102 . Alternatively, the tip may cause blunt dissection of the materials comprising the occlusion  108  (not shown). 
         [0037]    In some useful methods in accordance with the present disclosure, crossing device  120  is 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  120  may reduce resistance to the axial advancement of crossing device  120 . 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  120  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. 
         [0038]      FIG. 4  is an additional view of artery  102  shown in the previous figure. In the embodiment of  FIG. 4 , crossing device  120  has been withdrawn from true lumen  106  of artery  102 . With reference to  FIG. 4 , it will be appreciated that a guidewire  132  remains in the position formerly occupied by crossing device  120 . 
         [0039]    The position of guidewire  132  shown in  FIG. 4  may be achieved using crossing device  120 . Guidewire  132  may be positioned, for example, by first placing crossing device  120  in the position shown in the previous figure, then advancing guidewire  132  through lumen  130  defined by shaft  122  of crossing device  120 . Alternately, guidewire  132  may be disposed within lumen  130  while crossing device  120  is advanced through the vasculature of a patient. When this is the case, guidewire  132  may be used to aid in the process of steering crossing device  120  through the vasculature. 
         [0040]    With guidewire  132  in the position shown in  FIG. 4 , guidewire  132  may be used to direct other devices to subintimal space  128 . For example, a catheter may be advanced over guidewire  132  until the distal end of the catheter is disposed in subintimal space  128 . After reaching the subintimal space, the catheter may be used to dilate subintimal space  128 . Examples of catheters that may be used to dilate the subintimal space include balloon catheters and atherectomy catheters. 
         [0041]      FIG. 5  is a cross sectional view of an artery  202  having a wall  226 . In  FIG. 5 , a crossing device  220  is shown extending through subintimal space  228  and around an occlusion  208 . In  FIG. 5 , occlusion  208  is shown blocking a true lumen  206  defined by an intima  207  of wall  226 . Occlusion  208  divides true lumen  206  into a proximal segment  203  and a distal segment  204 . When a crossing member in accordance with some embodiments of the present disclosure is advanced through the subintimal space of an artery, the distal end of the crossing device may penetrate the intima and enter the distal segment of the true lumen after advancing beyond an occlusion. 
         [0042]    In the embodiment of  FIG. 5 , a tip  224  of crossing device  220  is disposed in distal segment  204 . Accordingly, it will be appreciated that crossing device  220  has pierced intima  207  distally of occlusion  208  and entered distal segment  204  of artery  202 . In  FIG. 5 , shaft  222  is shown extending through intima  207  and subintimal space  228 . Shaft  222  of crossing device  220  may define a lumen  230 . 
         [0043]      FIG. 6  is an additional view of artery  202  shown in the previous figure. In the embodiment of  FIG. 6 , crossing device  220  has been withdrawn leaving a guidewire  232  in the position shown in  FIG. 6 . 
         [0044]    The position of guidewire  232  shown in  FIG. 6  may be achieved using crossing device  220 . Guidewire  232  may be positioned, for example, by first placing crossing device  220  in the position shown in the previous figure, then advancing guidewire  232  through lumen  230  defined by shaft  222  of crossing device  220 . Alternately, guidewire  232  may be disposed within lumen  230  while crossing device  220  is advanced through the vasculature of a patient. When this is the case, guidewire  232  may be used to aid in the process of steering crossing device  220  through the vasculature of a patient. 
         [0045]    Devices such as balloon angioplasty catheters and atherectomy catheters may be advanced over guidewire  232  and into subintimal space  228 . In this way, these devices may be used in conjunction with guidewire  232  to establish a blood flow path between proximal segment  203  of true lumen  206  and distal segment  204  of true lumen  206 . This path allows blood to flow through subintimal space  228  and around occlusion  208 . 
         [0046]      FIG. 7  is a partial cross-sectional view of an exemplary crossing device  320 . Crossing device  320  of  FIG. 7  comprises a tip  324  that is fixed to a distal end of a shaft  322 . In the exemplary embodiment of  FIG. 7 , shaft  322  comprises a coil  334 , a sleeve  336 , a tubular body  338 , and a sheath  344 . 
         [0047]    Tip  324  is fixed to a distal portion of coil  334 . Coil  334  comprises a plurality of filars  342  that are wound in a generally helical shape. In some useful embodiments of crossing device  320 , coil  334  comprises eight, nine or ten filars wound into the shape illustrated in  FIG. 7 . Crossing device  320  includes a sleeve  336  that is disposed about a portion of coil  334 . Sleeve  336  may comprise, for example, PET shrink tubing, i.e. polyethylene terephthalate. 
         [0048]    Sleeve  336  and coil  334  both extend into a lumen defined by a tubular body  338 . Tubular body  338  may comprise, for example hypodermic tubing formed of Nitinol, i.e. nickel titanium. With reference to  FIG. 7 , it will be appreciated that a proximal portion of sleeve  336  is disposed between tubular body  338  and coil  334 . In some embodiments of crossing device  320 , a distal portion of tubular body  338  defines a helical cut. This helical cut may be formed, for example, using a laser cutting process. The helical cut may be shaped and dimensioned to provide an advantageous transition in lateral stiffness proximate the distal end of tubular body  338 . 
         [0049]    A proximal portion of coil  334  extends proximally beyond the distal end of tubular body  338 . A hub  346  is fixed to a proximal portion of coil  334  and a proximal portion of tubular body  338 . Hub  346  may comprise, for example, a luer fitting. Sheath  344  is disposed about a portion of tubular body  338  and a portion of sleeve  336 . In some embodiments of crossing device  320 , sheath  344  comprises HYTREL, a thermoplastic elastomer. 
         [0050]    With reference to  FIG. 7 , it will be appreciated that tubular body  338 , coil  334 , sleeve  336 , and sheath  344  each have a proximal end and a distal end. The proximal end of sheath  344  is disposed between the proximal end of tubular body  338  and the proximal end of sleeve  336 . The distal end of sleeve  336  is positioned proximate tip  324  that is fixed to the distal end of coil  334 . The distal end of sheath  344  is located between the distal end of tubular body  338  and the distal end of sleeve  336 . With reference to  FIG. 7 , it will be appreciated that sheath  344  overlays the distal end of tubular body  338 . 
         [0051]    With reference to  FIG. 7 , it will be appreciate that tip  324  has a generally rounded shape. The generally rounded shape of tip  324  may reduce the likelihood that crossing device  320  will penetrate the adventitia of an artery. Tip  324  may be formed from a suitable metallic material including but not limited to stainless steel, silver solder, and braze. Tip  324  may also be formed from suitable polymeric materials or adhesives including but not limited to polycarbonate, polyethylene and epoxy. In some embodiments of crossing device  320 , outer surface  340  of tip  324  comprises a generally non-abrasive surface. For example, outer surface  340  may have a surface roughness of  25  micrometers or less. A tip member having a relatively smooth outer surface may reduce the likelihood that the tip member will abrade the adventitia of an artery. 
         [0052]      FIG. 8  is a plan view showing an assembly  348  including crossing device  320  shown in the previous figure. In the embodiment of  FIG. 8 , a handle assembly  350  is coupled to crossing device  320 . In  FIG. 8 , handle assembly  350  is shown disposed about a proximal portion of shaft  322  of crossing device  320 . Handle assembly  350  comprises a handle body  352  and a handle cap  354 . 
         [0053]    In some useful embodiments in accordance with the present disclosure, handle assembly  350  is long enough to receive the thumb and for fingers of a physician&#39;s right and left hands. When this is the case, a physician can use two hands to rotate handle assembly  350 . In the embodiment of  FIG. 8 , grooves  356  are formed in handle body  352  and handle cap  354 . Grooves  356  may improve the physician&#39;s ability to grip handle assembly  350 . 
         [0054]      FIG. 9  is an additional plan view showing assembly  348  shown in the previous figure. In  FIG. 9 , a proximal portion of handle assembly  350  is positioned between the thumb and forefinger of a left hand  358 . A distal portion of handle assembly  350  is disposed between the thumb and forefinger of a right hand  360 . 
         [0055]    In some useful methods, crossing device  320  is rotated and axially advanced simultaneously. Rotation of crossing device  320  can be achieved by rolling handle assembly  350  between the thumb and forefinger one hand. Two hands can also be used as shown in  FIG. 9 . Rotating crossing device  320  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. 
         [0056]    In some useful methods in accordance with the present disclosure, crossing device  320  is rotated at a rotational speed of 2 to 200 revolutions per minute. In some particularly useful methods in accordance with the present disclosure, crossing device  320  is rotated at a rotational speed of 50 and 150 revolutions per minute. Crossing device  320  may be rotated by hand as depicted in  FIG. 9 . It is also contemplated that a mechanical device (e.g., an electric motor) may be used to rotate crossing device  320 . 
         [0057]      FIG. 10  is a cross-sectional view of assembly  348  shown in the previous figure. With reference to  FIG. 10  it will be appreciated that handle assembly  350  is disposed about sheath  344 , tubular body  338 , sleeve  336  and coil  334 . 
         [0058]      FIG. 11  is a cross sectional view of handle assembly  350  shown in the previous figure. With reference to  FIG. 11 , it will be appreciated that handle assembly  350  includes a plurality of grip sleeves  362  and a plurality of spacers  364 . In the embodiment of  FIG. 11 , handle cap  354  includes male threads  366  that engage female threads  368  in handle body  352 . 
         [0059]    When handle cap  354  is rotated relative to handle body  352 , the threads produce relative longitudinal motion between handle cap  354  and handle body  352 . In other words, handle cap  354  can be screwed into handle body  352 . As handle cap  354  is advanced into handle body  352 , the inner end of handle cap  354  applies a compressive force to grip sleeves  362 . Grip sleeves  362  are made from an elastomeric material. The compression forces applied to grip sleeves  362  by handle body  352  and handle cap  354  cause grip sleeves  362  to bulge. The bulging of grip sleeves  362  causes grip sleeves  362  to grip shaft  322  of crossing device  320 . 
         [0060]    The force that each grip sleeve  362  applies to the shaft is generally equally distributed about the circumference of the shaft. When this is the case, the likelihood that the shaft will be crushed by the grip sleeves is reduced. At the same time, the grip sleeves provide an interface that allows significant torque to be applied to the shaft when the handle is rotated. 
         [0061]      FIG. 12  is a partial cross-sectional view showing a guidewire  432  that is disposed in a lumen  430  defined by a shaft  422  of a crossing device  420 .  FIG. 13  is an additional view showing guidewire  432  and crossing device  420  shown in  FIG. 12 . In some embodiments of crossing device  420 , shaft  422  defines a lumen  430 . When this is the case, a guidewire may be inserted into the lumen. The guidewire may be used to steer the crossing device. The guidewire may remain inside the lumen until it is needed for steering. When steering is needed, the guidewire may be advanced so that a portion of the guidewire extends beyond the distal end of the crossing device. A distal portion of the guidewire may then be advanced in the direction that the physician wishes to advance crossing device  420 . 
         [0062]    In the embodiment of  FIG. 13 , guidewire  432  has been distally advanced (relative to the position shown in  FIG. 12 ). With reference to  FIG. 13 , it will be appreciated that a distal portion  470  of guidewire  432  is extending beyond the distal end of crossing device  420 . In the embodiment of  FIG. 13 , distal portion  470  of guidewire  432  is biased to assume a generally curved shape when it is unrestrained by crossing device  420 . 
         [0063]    In the embodiment of  FIG. 13 , there are at least two degrees of freedom between guidewire  432  and crossing device  420 . First, guidewire  432  and crossing device  420  are free to rotate relative to one another. Second, guidewire  432  and crossing device  420  are free to move in a longitudinal direction relative to one another. It is sometimes desirable to use guidewire  432  as an aid in directing crossing device  420  through the vasculature of a patient. When this is the case, distal portion  470  of guidewire  432  may be advanced beyond the distal end of crossing device  420 . Guidewire  432  may then be rotated until distal portion  470  of guidewire  432  assumes a desired orientation. 
         [0064]      FIG. 14  shows a heart  500  including a coronary artery  502 . An occlusion  508  is disposed in coronary artery  502 . Occlusion  508  divides a lumen of coronary artery  502  into a proximal segment  503  and a distal segment  504 . The proximal segment  503  may be easily accessed using endovascular devices and has adequate blood flow to supply the cardiac muscle. The distal segment  504  is not easily accessed with interventional devices and has significantly reduced blood flow as compared to proximal segment  503 . 
         [0065]      FIG. 15A  is an enlarged view showing a portion of heart  500  shown in the previous figure. In  FIG. 15A , a crossing device  520  is disposed in proximal segment  503  of coronary artery  502 .  FIG. 15B  is an enlarged plan view of crossing device  520  shown in  FIG. 15A . Crossing device  520  comprises a tip  524  and a shaft  522 . 
         [0066]      FIG. 16A  is an additional view showing crossing device  520  disposed in heart  500 .  FIG. 16B  is an enlarged plan view of crossing device  520  shown in  FIG. 16A . In  FIGS. 16A and 16B  crossing device  520  has been rotated approximately ninety degrees relative to the position shown in  FIGS. 15A and 15B . 
         [0067]    Some useful methods in accordance with the present disclosure include the step of rotating crossing device  520 . When the proximal portion of a crossing device is rotated, it may be desirable to confirm that the distal end of the crossing device is also rotating. 
         [0068]    Many physicians have experience using guidewires. These physicians are aware that twisting the proximal end of a guidewire when the distal end of the guidewire is fixed may cause the guidewire to break due to twisting. Accordingly, many physicians may be hesitant to rotate an intravascular device more than a few revolutions unless they are certain that the distal end of the device is free to rotate. 
         [0069]    One method for determining whether the tip of a crossing member is rotating may be described with reference to  FIGS. 15A ,  15 B,  16 A and  16 B. As shown in the figures, crossing member  520  comprises a tip  524  fixed to the distal end of a shaft  522 . Tip  524  comprises a radiopaque marker  572 . Radiopaque marker  572  has a face  574  and an edge  576 . Face  574  has a width W and a length L. Edge  576  has a length L and a thickness T. In some useful embodiments of crossing device  520 , thickness T of radiopaque marker  572  is smaller than both length L and width W. When this is the case, radiopaque marker  572  may be used to provide a physician with visual feedback indicating that tip  524  of crossing device  520  is rotating. 
         [0070]    During rotation of crossing device  520 , the shape of radiopaque marker provides visual feedback assuring the physician that the tip of the crossing member is rotating as the physician rotates the proximal portion of the crossing member. Radiopaque marker  572  provides two different appearances while it is being rotated and observed using fluoroscopic methods. When edge  576  of radiopaque marker is viewed on a fluoroscopic display a first appearance is achieved. When face  574  of radiopaque marker  572  is viewed, it provides a second appearance on the fluoroscopic display. With reference to the figures, it will be appreciate that the first appearance has a smaller footprint than the second appearance. When the appearance of radiopaque marker  572  is alternating between the first appearance and the second appearance, the physician can infer that tip  524  is rotating. This visual feedback allows the physician to confirm that the distal end of crossing member is rotating. 
         [0071]      FIGS. 17A and 18A  each show a crossing device  520  comprising a tip  524  fixed to a shaft  522 . Tip  524  comprises a radiopaque marker  572 . Tip  524  of crossing device  520  has been advanced through a proximal segment  503  of a coronary artery  502 . With reference to  FIGS. 17A and 18A , it will be appreciated that tip  524  is near wall  526  of coronary artery  502  and an occlusion  508  that is located in the true lumen of coronary artery  502 . When a surgical procedure is viewed on a fluoroscope, it may be difficult for the physician to determine whether or not tip  524  is disposed in the subintimal space of coronary artery  502 . Methods for determining whether the tip is disposed in the subintimal space may be described with reference to  FIGS. 17 and 18 . 
         [0072]    For example, one method in accordance with the present disclosure may include the steps of positioning the distal end of a crossing device in a position that may or may not be in the subintimal space of an artery and injecting radiopaque fluid into the body from the distal end of crossing device  520 . If the radiopaque fluid remains in a localized area (e.g., in the subintimal space) then a physician viewing the radiopaque fluid on a fluoroscopic display can infer that the distal end of the crossing device is disposed in the subintimal space. If the radiopaque fluid rapidly enters the bloodstream and is carried through the vasculature, then the physician can infer that the distal end of the crossing device is disposed in the true lumen of the artery. 
         [0073]      FIG. 17B  is a representation of a fluoroscopic display  578  produced when radiopaque fluid has been injected into the body from the distal end of crossing device  520  while tip  524  is disposed in the true lumen of coronary artery  502 . In  FIG. 17B , the radiopaque fluid  580  has rapidly entered the bloodstream and has cause the vasculature in fluid communication with proximal segment  503  to become illuminated on fluoroscopic display  578 . Radiopaque marker  572  is also visible in fluoroscopic display  578 . 
         [0074]      FIG. 18B  is a representation of a fluoroscopic display  578  produced when radiopaque fluid has been injected into the body from the distal end of crossing device  520  while tip  524  is disposed in the subintimal space of coronary artery  502 . In  FIG. 18B , the radiopaque fluid  580  is disposed in a localized area (i.e., in the subintimal space). Radiopaque marker  572  is also visible in fluoroscopic display  578 . 
         [0075]    Additional methods are also contemplated. For example, negative pressure (i.e., sub atmospheric pressure) may be applied to the lumen defined by crossing device  520 . The physician may observe the results of this application of negative pressure. If a partial vacuum is produced and little or no blood is drawn through the lumen, then the physician can infer that the distal end of the lumen is located in the subintimal space. If, on the other hand, blood is drawn through the lumen of the crossing member, then the physician can infer that the distal end of the crossing member is disposed in the true lumen of a blood vessel.