Patent Publication Number: US-2021186560-A1

Title: Endovascular devices and methods for exploiting intramural space

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 11/984,668, filed Nov. 20, 2007, which claims the benefit of U.S. Provisional Application No. 60/860,416, filed Nov. 21, 2006 under 35 U.S.C. § 119(e), the entire disclosures of which are incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The inventions described herein relate to endovascular devices and methods. More particularly, the inventions described herein relate to devices and methods for exploiting intramural (e.g., subintimal) space of a vascular wall to facilitate the treatment of vascular disease. For example, the inventions described herein may be used to cross a chronic total occlusion and facilitate treatment of the occluded vessel by balloon angioplasty, stenting, atherectomy, or other endovascular procedure. 
     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 risk to the patient&#39;s health. For example, in the case of a chronic total occlusion (CTO) of a coronary artery, the result may be painful angina, loss of functional cardiac tissue or death. In another example, complete occlusion of the femoral or popliteal arteries in the leg may result in limb threatening ischemia and limb amputation. 
     Commonly known endovascular devices and techniques for the treatment of chronic total occlusions (CTOs) are either inefficient (resulting in a time consuming procedure), have a high risk of perforating a vessel (resulting in an unsafe procedure), or fail to cross the occlusion (resulting in poor efficacy). Physicians currently have difficulty visualizing the native vessel lumen, cannot accurately direct endovascular devices toward the visualized lumen, or fail to advance devices through the occlusion. Bypass surgery is often the preferred treatment for patients with chronic total occlusions, but surgical procedures are undesirably invasive. 
     SUMMARY OF THE INVENTION 
     To address this and other unmet needs, the present invention provides, in exemplary non-limiting embodiments, devices and methods for exploiting intramural (e.g., subintimal) space of a vascular wall to facilitate the treatment of vascular disease. For example, the devices and methods disclosed herein may be used to (i) visually define the vessel wall boundary; (ii) protect the vessel wall boundary from perforation; (iii) bypass an occlusion; and/or (iv) remove an occlusion. Embodiments are described herein which perform these functions individually as well as collectively. These embodiments may be used in the treatment of a variety of vascular diseases such as chronic total occlusions in the coronary and peripheral arteries, but are not necessarily limited in terms of vascular site or disease state. 
     The embodiments presented herein are generally described in terms of use in the subintimal space between the intima and media for purposes of illustration, not necessarily limitation. It is contemplated that these embodiments may be used anywhere in the vascular wall (i.e., intramural) or between the vascular wall and an adjacent occlusion. It is also contemplated that these embodiments may operate at one or more intramural locations, and may operate within the outer limits of the vascular wall to avoid perforation out of the wall and into the pericardial space. 
     In one embodiment, devices and methods are disclosed herein which visually define the vessel wall boundary across an occlusion by placement of a circumferential radiopaque element in the subintimal space. In another embodiment, devices and methods are disclosed herein which protect the vessel wall boundary from perforation by a device passing through an occlusion by placement of a circumferential guard element in the subintimal space. In yet another embodiment, devices and methods are disclosed herein which bypass an occlusion by entering the subintimal space proximal of the occlusion, safely passing through the subintimal space past the occlusion, and reentering the native lumen distal of the occlusion. Other embodiments exploiting the subintimal space are also disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       It is to be understood that both the foregoing summary and the following detailed description are exemplary. Together with the following detailed description, the drawings illustrate exemplary embodiments and serve to explain certain principles. In the drawings: 
         FIG. 1  is a schematic illustration of a heart showing a coronary artery that contains a total occlusion; 
         FIG. 1A  is a detailed view of the coronary artery and total occlusion shown in  FIG. 1 ; 
         FIG. 1B  is a fluoroscopic representation of the view shown in  FIG. 1A ; 
         FIG. 2  is a schematic representation of a coronary artery showing the intimal, medial and adventitial layers; 
         FIG. 3A  is a longitudinal cross-section of an artery with a total occlusion showing a device deployed in the subintimal space; 
         FIG. 3B  is a fluoroscopic representation of the deployed subintimal device; 
         FIG. 4  is a schematic illustration of a device for deploying the subintimal device in a helical pattern; 
         FIG. 4A  is a cross-sectional view taken along line A-A in  FIG. 4 ; 
         FIG. 4B  is a cross-sectional view taken along line B-B in  FIG. 4 ; 
         FIG. 5  is a longitudinal cross-section of an artery with a total occlusion showing a delivery device deploying a subintimal device in a helical pattern within the subintimal space; 
         FIG. 6  is a schematic illustration of an alternative subintimal device that may assume a helical pattern itself; 
         FIGS. 7A-7D  schematically illustrate alternative subintimal device embodiments; 
         FIGS. 8A and 8B  schematically illustrate a system that utilizes fluid to achieve atraumatic passage and promote dissection in the subintimal space; 
         FIGS. 9A-9J  schematically illustrate various embodiments of torsionally rigid yet flexible designs for a subintimal device; 
         FIGS. 10A-10D  schematically illustrate various embodiments of threaded designs for a subintimal device; 
         FIGS. 11A-11C  schematically illustrate various over-the-wire embodiments for a subintimal device; 
         FIGS. 12A-12C  schematically illustrate various directing devices for directing a subintimal device to engage and penetrate the intimal layer and enter the subintimal space; 
         FIGS. 13A-13B  schematically illustrate a subintimal device capable of dissection by actuation; 
         FIGS. 13C, 13D, 13E and 13F  schematically illustrate alternative subintimal devices capable of dissection; 
         FIGS. 14A-14H  schematically illustrated the steps involved in bypassing a total occlusion via the subintimal space; 
         FIGS. 15A and 15B  schematically illustrate an embodiment for orienting and reentering the true lumen; 
         FIGS. 16A-16D  schematically illustrate an alternative embodiment for orienting and reentering the true lumen; 
         FIGS. 17, 17A and 17B  illustrate a subintimal device having a mating or keying feature for torque transmission; 
         FIG. 18  illustrates an alternative subintimal device; 
         FIGS. 19A and 19B  illustrate a subintimal device having a compound bend to facilitate orientation; 
         FIG. 20A  illustrates an alternative subintimal device capable of achieving a compound bend; 
         FIG. 20B  illustrates a laser cut pattern for a Nitinol tube for use in the device shown in  FIG. 20A ; 
         FIGS. 21A and 21B  illustrate another alternative subintimal device capable of achieving a compound bend; 
         FIGS. 22A-22C  illustrate yet another alternative subintimal device capable of achieving a compound bend; 
         FIGS. 23A-23E  illustrate various re-entry device embodiments; 
         FIGS. 24A-24C  illustrate various penetration mechanisms for a re-entry device; 
         FIG. 25  schematically illustrates a system for confirming true lumen re-entry; 
         FIGS. 26A and 26B  schematically illustrate a subintimal deployable element and delivery system therefor; 
         FIG. 27  illustrates the use of a subintimal deployable element for guarding against perforation; 
         FIG. 28  schematically illustrate an alternative subintimal deployable element; 
         FIGS. 29A-29D  illustrate a subintimal device including an accessory subintimal deployable element; 
         FIGS. 30A-30D and 31A-31B  illustrate various devices that facilitate occlusion removal after subintimal delamination; 
         FIGS. 32A-32E  illustrate an alternative system for bypassing a total occlusion; 
         FIGS. 33A-33E  schematically illustrate an embodiment using one or more subintimal guide catheters to introduce an orienting device; 
         FIGS. 34A-34H  schematically illustrate an embodiment using a subintimal crossing device or guide wire to introduce an orienting device; 
         FIGS. 35A-35C  schematically illustrate alternative methods for orienting toward the true lumen of the artery; 
         FIGS. 36A-36G  schematically illustrate alternative re-entry device embodiments; 
         FIG. 37  is a perspective view of a rotary drive unit for the re-entry devices illustrated in  FIGS. 36A-36G ; and 
         FIGS. 38A-38E  are schematic illustrations of alternative embodiments of orienting devices. 
     
    
    
     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. 
     Introduction 
     Generally, the various embodiments described herein exploit the subintimal space in a vascular wall for purposes of facilitating treatment of vascular disease. In the following detailed description, the embodiments have been organized in terms of their particular function: (i) visually defining the vessel wall boundary; (ii) guarding the vessel wall boundary from perforation; (iii) bypassing an occlusion; and (iv) alternative functions. This organizational approach is used for purposes of illustration and explanation, not for purposes of limitation, as some aspects of some embodiments may be utilized for more than one of the stated functions, and many embodiments have alternative functions not specifically stated or reflected by the organizational titles. 
     In order to understand the methods by which the embodiments described herein advantageously exploit the subintimal path, it is helpful to first understand the anatomical structures at hand. 
     Relevant Anatomy 
     With reference to  FIG. 1 , a diseased heart  100  is shown schematically. Heart  100  includes a plurality of coronary arteries  110 , 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  120 . 
     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 90% 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 (2) weeks old from symptom onset. 
     With reference to  FIG. 1A , a magnified view of total occlusion  120  within coronary artery  110  is shown schematically. Generally, the proximal portion  112  of artery  110  (i.e., the portion of artery  110  proximal of total occlusion  120 ) may be easily accessed using endovascular devices and has adequate blood flow to supply the surrounding cardiac muscle. The distal portion  114  of artery  110  (i.e., the portion of artery  110  distal of total occlusion  120 ) is not easily accessed with interventional devices and has significantly reduced blood flow as compared to proximal portion  112 . 
     A commonly performed diagnostic procedure called an angiogram involves the infusion of a radiopaque fluid into the arterial bloodstream through a percutaneously placed angiography catheter. Using an x-ray fluoroscope, two-dimensional images of the arterial pathways may be obtained and recorded.  FIG. 1B  shows a schematic example of an angiographic image of a chronic total occlusion  120 . It is common that the angiogram allows a physician to visualize the proximal segment  112  but does not allow visualization of the occlusion  120  or the distal segment  114 . 
     With reference to  FIG. 2 , a cut-away segment of coronary artery  110  is shown schematically. Coronary artery  110  includes a true or native lumen  116  defined by arterial wall  118 . The innermost layer of arterial wall  118  is called the intima or intimal layer  113  (for sake of clarity, the multi layer intima is shown as a single homogenous layer). Concentrically outward of the intima is the media or medial layer  115  (which also is comprised of more than one layer but is shown as a single homogenous layer). The outermost layer of the artery is the adventitia  117 . The transition between the outermost portion of the intima and the innermost portion of the media is referred to as the subintimal space, which may be delaminated to increase the space therebetween. The subintimal space is sometimes referred to as a false lumen, in contrast to true lumen  116 . 
     Visualization &amp; Perforation Guard Embodiments 
     As may be appreciated from  FIG. 1B , a total occlusion  120  prevents the occlusion and distal arterial segment  114  from being visualized using radiopaque contrast media injection fluoroscopy. In some instances, sufficient contrast media may pass through collaterals around the total occlusion  120  to achieve visualization of the distal segment  114 , but visualization of the distal segment  114  is often unclear and visualization of the occluded segment  120  is still not achieved. In some rare instances, sufficient radiopaque contrast may be injected retrograde through the venous system to achieve a fluoroscopic image of the distal segment  114 , but such images are often hazy and still do not illuminate the occluded segment  120 . 
     To achieve visualization of the occluded segment  120  and the distal segment  114 , a radiopaque subintimal device  300  may be introduced into the subintimal space as shown in  FIG. 3A . In this illustration, subintimal device  300  is intended to be relatively generic, as a variety of subintimal devices may be employed as will be described in more detail hereinafter. The subintimal device  300  exits the true lumen  116  and enters the subintimal space  130  at entry point  132  proximal of the total occlusion  120  somewhere in the proximal segment  112 . Within the subintimal space  130 , the subintimal device  300  may extend across and beyond the total occlusion  120  and into the distal segment  114 . With the subintimal device positioned as shown in  FIG. 3A , and due to the radiopaque nature of the subintimal device  300 , the occluded segment  120  and distal segment  114  may be fluoroscopically visualized as shown in  FIG. 3B . 
     Thus, subintimal device  300  may be used to enhance arterial visualization by placement within the subintimal space  130  concentrically around the total occlusion  120 . The subintimal device  300  defines the approximate inside diameter of the artery  110  and also defines axial bends or tortuosity in the vessel  110  across the occluded segment  120  and distal segment  114 , thereby defining the circumferential boundary of the artery  110  across the occluded segment  120  and distal segment  114 . Also, by placement within the subintimal space  130  concentrically around the total occlusion  120 , the subintimal device  300  may be used to protect or guard the wall  118  of the artery  110  from perforation of devices that attempt to penetrate the total occlusion  120  via the true lumen  116 . 
     As shown in  FIGS. 3A and 3B , the subintimal device  300  is deployed in a helical pattern within the subintimal space  130 . The helical pattern is shown for purposes of illustration, not limitation, as other patterns may be employed as well. Various other deployment patterns are described in more detail hereinafter, but the helical pattern is used herein to further illustrate the concept. 
     With reference to  FIGS. 4, 4A and 4B , a deployment device  400  is shown schematically. Deployment device  400  may be used to direct the subintimal device  300  into the subintimal space  130  at entry point  132  and deploy the subintimal device  300  in a helical pattern therein as shown in  FIG. 5 . The deployment device  400  may take the form of a balloon catheter including catheter shaft  402  and distal balloon  404 . Catheter shaft  402  includes an outer tube  406  and an inner tube  408  defining an inflation lumen  410  therebetween for inflation of balloon  404 . The inner wire tube  408  defines a guide wire lumen  412  therein for advancement of the device  400  over a guide wire (not shown). A delivery tube  414  extends along the outer tube  406  and around the balloon  404  in a helical (or other) pattern. The delivery tube  414  defines a delivery lumen  416  therein for advancement of the subintimal device therethrough. In this particular embodiment, the subintimal device  300  may have a straight configuration in its relaxed state and rely on the helical delivery tube  414  to achieve the desired helical pattern. 
     With reference to  FIG. 5 , the delivery device  400  is shown in position just proximal of the total occlusion  120 . In this position, the balloon  404  may be inflated within the vessel lumen  116  to direct the delivery tube  414  toward the vessel wall  118  at an orientation for the subintimal device  300  to penetrate through the intima  113  at an entry point and into the subintimal space. By virtue of the helical delivery tube  414 , the subintimal device  300  is sent on a helical trajectory as it is advanced through delivery tube  414  resulting in deployment of the subintimal device  300  in a helical pattern. As shown, the subintimal device  300  has been advanced through the delivery tube  414  and positioned concentrically outside the total occlusion  120 , outside the intimal layer  113 , and inside the medial layer  115  in the subintimal space. 
     With reference to  FIG. 6 , an alternative approach to achieving a helical pattern in the subintimal space is shown. Whereas the delivery device  400  described previously provided a helical delivery tube to deliver a subintimal device  300  that had a straight configuration in its relaxed state,  FIG. 6  schematically illustrates an alternative subintimal device  600  that may assume a helical shape itself. Subintimal device  600  includes an elongate tubular shaft  604 , at least a distal portion of which includes a helical interlocking gear  606  and a helical wire coil  608  disposed thereon. A helically shaped inner mandrel or tube  610  may be disposed in the tubular shaft  604  such that the shaft  604  rotates freely thereon. The shaft  604  may have a linear or straight configuration in a relaxed state and a helical configuration (shown) when the helically shaped inner member  610  is disposed therein. The device  600  may be disposed in a constraining sheath (not shown) and navigated to the intravascular site, such as the site of a total occlusion. When the device  600  is advanced distally out the end of the constraining sheath or when the sheath is pulled proximally relative thereto, the distal portion of the device  600  assumes a helical shape as shown. The shaft  604  may be rotated relative to the inner member  610  to cause rotation of the helical wire threads  608 , which may be used to engage the vessel wall and advance around the total occlusion in the subintimal path. A bearing (not shown) may be disposed on the inner member  610  to engage the proximal or distal end of the shaft  604  to enable the shaft  604  and the inner member  610  to be advanced in unison. Subintimal device  600  may include any of the variants described hereinafter, such as various gear shaft configurations, distal atraumatic tip configurations, fluidic dissection mechanisms, etc. 
     Generally, the subintimal devices described herein are designed for intravascular navigation and atraumatic subintimal passage. The subintimal devices  300  may be constructed similar to a guide wire and may include elements to atraumatically pass through the subintimal space. Such atraumatic elements may be employed to minimize damage to arterial wall and to minimize the likelihood of perforation therethrough. Examples of such atraumatic elements  310  are schematically illustrated in  FIGS. 7A-7C . The subintimal device may include a ball-shaped tip  310 A as shown In  FIG. 7A , a hook-shaped or loop-shaped tip  310 B as shown in  FIG. 7B , and/or a bent tip  310 C as shown in  FIG. 7C . These atraumatic elements distribute axial forces over larger areas of tissue and thereby reduce the chance of vessel perforation. An additional aspect of the bent tip  310 C is ability to torsionally direct the tip and control the path of the device through the subintimal space. The ball tip  310 A may be formed from a suitable metallic material including but not limited to stainless steel, silver solder, or braze. The ball tip  310 A may also be formed from suitable polymeric materials or adhesives including but not limited to polycarbonate, polyethylene or epoxy. Note that the ball tip  310 A may be bulbous and larger than the shaft proximal thereto. The loop tip  310 A and bent tip  310 C may be created during the manufacturing process (for example by heat setting or mechanical deformation) or the tip may be shaped (for example by mechanical deformation) by the physician. 
     As an alternative or in addition to the atraumatic tip elements  310  as described above, the subintimal device  300  may use a guide wire  700  to facilitate atraumatic passage as shown in  FIG. 7D . In this embodiment, the subintimal device  300  may include a lumen extending therethrough such that the device  300  may be advanced over the guide wire  700 . In this embodiment, the body of the subintimal device  300  has a hollow internal diameter defining a guide wire lumen therein. The guide wire lumen extends from a proximal opening to a distal opening and is sized to accept a guide wire  700  therethrough. The guide wire  700  provides an atraumatic element at its distal end and also provides a mechanism for rotationally steering the subintimal device  300  through the subintimal space. The guide wire  700  may be pushed forward by the subintimal device through a bearing element (not shown) at the proximal or distal end of the subintimal device. The bearing element may provide interference in the axial direction while allowing for relative rotation between the subintimal device and guide wire. An example of a bearing element may be a collar crimped to the distal end of the guide wire with an outside diameter larger in dimension than the guide wire lumen within the subintimal device. 
     Other techniques may be employed to facilitate atraumatic passage through the subintimal space. For example, pressurized fluid may be used to facilitate atraumatic passage and even promote atraumatic dissection of the layers defining the subintimal space.  FIGS. 8A and 8B  schematically illustrate a system  800  that utilizes fluid to achieve atraumatic passage and promote dissection. System  800  includes a subintimal device  810  and associated pumping system  820 . The fluidic system  800  is similar in certain aspects to the arrangements described elsewhere herein, the various aspects of which may be combined or used in the alternative as will be appreciated by those skilled in the art. System  800  includes a subintimal device  810  which may comprise any of the tubular subintimal devices described herein. Generally, subintimal device  810  includes a tubular shaft  812  having a proximal end connected to a pumping mechanism  820 . A plunger rod  814  is slidably disposed in the tubular shaft  812  as shown in  FIG. 8B  and its proximal end is connected to a linear actuator  822  of the pumping mechanism as shown in  FIG. 8A . The rod  814  extends through the tubular shaft  812  to a point proximal of the distal end thereof to define a pumping chamber  816 . A source of liquid  830  (e.g., saline bag) is connected to the proximal end of the subintimal device  810  via a fluid line  832  and optional valve  834  to supply liquid to the annular lumen between the rod  814  and the inner wall of the tubular shaft  812 . As the linear actuator moves the rod  814  back and forth in the tubular shaft  812 , liquid is caused to be expelled out of the chamber  816  in a pulsatile fashion, which may be used to hydraulically dissect tissues to define a subintimal path as described previously, for example. Optionally, a balloon may be disposed on the distal end of the device such that it is cyclically inflated and deflated with the pulsatile flow to cause controlled dissection. The stroke length, stroke rate and stroke volume may be adjusted to achieve the desired effect. For example, the stroke volume of the chamber  816  may be relatively small (0.01 cc-1.0 cc, for example) such that liquid exits the chamber  816  with high energy that dissipates quickly to minimize trauma to tissues as they are dissected. One example is a stroke volume of 0.25 cc and a stroke rate of 10 Hz which has been found to facilitate atraumatic passage and even promote atraumatic dissection in a bench-top model using animal tissues. 
     Another technique to facilitate or supplement atraumatic passage of the subintimal device is to reduce friction between the device and the surrounding tissues. The fluidic embodiment described above benefits from this technique in that saline acts to reduce friction. Friction may also be reduced by using coatings (e.g., PTFE, hydrophilic materials, etc.) which may be applied to the external surface of the subintimal device. Friction may also be reduced by taking advantage of the fact that the kinetic coefficient of friction is usually less than the static coefficient of friction for a given frictional interface. As applied to the subintimal devices described herein, the lower kinetic coefficient of friction may be utilized by rotating the device back and forth between tissues in the subintimal space. Such reciprocal rotational motion may be applied manually by rolling the proximal end of the device between the user&#39;s thumb and forefinger, or may be applied using automatically using a reciprocal motor drive, for example. 
     Whether it is to reduce friction, to facilitate steering, or to facilitate advancement, it may be desirable to incorporate enhanced torsional characteristics in the body  302  of the subintimal device  300  as schematically shown in  FIGS. 9A-9F . Generally, it is desirable to maintain flexibility of at least a distal portion of the body  302  to avoid compromising intravascular navigation in tortuous pathways.  FIG. 9A  schematically shows a generic subintimal device  300  with a distal body portion  302  and a proximal body portion  304 . Relative to the proximal body portion  304 , the distal body portion may be more flexible since it will frequently encounter a tortuous pathway. The proximal body portion may only encounter minimal bends in a guide catheter or the like, and therefore may be made more stiff yet torsionally rigid as with a metal tube (e.g., stainless steel hypotube). 
     One example of a flexible yet torsionally rigid distal body  302  design is shown in  FIGS. 9B and 9C . In this embodiment, distal body portion  302  is made of a multitude of independent coils  902 ,  904 ,  906  concentrically wound in opposing directions. These coils can diametrically interact (for example internal coil diametrically expands while the external coil diametrically contracts) with an applied torque. This interaction can provide torsional strength while maintaining axial flexibility. The core of the distal body  302  may be hollow or may contain a fixed wire  910  within its internal lumen. The fixed wire  910  may provide an increase in axial and/or torsional stiffness, and may also have a tapering cross-section to increase flexibility in the distal direction. A hollow core may be used for insertion of a guide wire. Coils  902 ,  904 ,  906  and core wire  910  may be made of suitable metallic or polymeric materials including but not limited to stainless steel, nickel titanium, platinum or ultra high molecular weight polyethylene. 
     Another example of a flexible yet torsionally rigid distal body  302  design is shown in  FIG. 9D  wherein a single coil  908  is wound over an internal core  910  surrounded by a thin polymeric sheath  920 . Yet another example of a flexible yet torsionally rigid distal body  302  design is shown in  FIGS. 9E and 9F  wherein the body simply comprises a single open wound coil  912 . 
     A further example of a flexible yet torsionally rigid distal body  302  design is shown in  FIG. 9G . The distal body  302  may be constructed in part or in to total of a single layer coil with geometric features along the coil length that allow adjacent coils to engage (for example mechanical engagement similar to the teeth of a gear).  FIG. 9G  shows coil  930  closely wound with a multitude of teeth  932  along the coil edges in contact such that the peaks of one coil falls within the valleys of the adjacent coil. A conventional coil (without teeth) reacts to an applied torsional load by diametrically expanding or contracting, thus forcing the wire surfaces within a turn of the coil to translate with respect to its neighboring turn. The construction of coil  930  resists the translation of wire surfaces within the coil thus resisting the diametric expansion or contraction (coil deformation). An increased resistance to coil deformation increases the torsional resistance of the device body while the coiled construction provides axial flexibility. 
     This design may be implemented in manner shown in  FIG. 9H . The subintimal device  300  includes a proximal body portion  304  that is formed of a continuous solid metallic tube and a distal body portion  302  that is formed of the same tube with a laser cut coil segment  930 , wherein the pattern of the laser cut defines the teeth  932 . Suitable materials for the metallic tube include but are not limited to stainless steel and nickel titanium. Alternatively, the coil  930  may be wound from a continuous wire. The wire may have a cross section that for example has been mechanically deformed (stamped) to form the teeth  932  and allow coil engagement. 
       FIG. 9I  shows one example of a laser cut pattern from the circumference of a tube that has been shown in a flat configuration for purposes of illustration. In the pattern shown in  FIG. 9I , the teeth  932  are generally trapezoidal and extend orthogonal to the coil turns  930 .  FIG. 9J  shows an alternative pattern wherein the teeth are generally rectangular (with a clipped corner) with a major (longer) length extending parallel to the axis of the body. The parallel orientation and longer length of the teeth  932  shown in  FIG. 9J  promote engagement and reduce slippage of adjacent coil turns  930 . 
     As mentioned previously, another application of a flexible yet torsionally rigid subintimal device is to facilitate advancement through the subintimal space using threads that rotationally engage vascular tissues similar to a threaded screw.  FIG. 10A  shows a subintimal device  300  wherein at least the distal body portion  302  includes threads  1000  on the exterior surface thereof. The threads  1000  act like an external corkscrew that has the ability to rotationally engage the arterial tissues and help drive the subintimal device  300  through the subintimal space.  FIGS. 10B-10D  are cross-sectional views taken along line A-A in  FIG. 10A  and show various alternative embodiments for the threads  1000 .  FIG. 10B  shows one or more round corkscrew members  1010  that are concentrically wound on the outside of the distal body  302 .  FIG. 10C  shows a multi-layer coil construction with coil layers  902 ,  904 ,  906  where corkscrew member  1020  comprises a wire element of larger cross sectional area wound within the external concentric coil  906 . The corkscrew members may have a rounded shape as shown in  FIGS. 10B and 10C , or other shape such as triangular, square, or other cross-sectional shape that may aid in tissue engagement and subintimal device advancement.  FIG. 10D  shows a polymer tube with a corkscrew profile  1030  formed therein and concentrically positioned around distal body portion  302 . In each of these embodiments, withdrawal of the subintimal device  300  may be achieved by rotating the device in the opposite direction thus driving the device back out of the subintimal space. 
     In some instances, it may be desirable to utilize an over-the-wire type subintimal device to facilitate advancement into and through the subintimal space. In addition to the embodiments described previously,  FIGS. 11A-11C  illustrate additional over-the-wire type embodiments of subintimal devices. These embodiments may also be used to facilitate guide wire advancement through a total occlusion, such as when it is desirable to stay in the true lumen. 
       FIG. 11A  shows an over-the-wire type subintimal device  1100  (or wire support device) having a coiled gear design  930  as described with reference to  FIGS. 9G-9J  and a thread design  1000  as described with reference to  FIGS. 10A-10D . The device  1100  has a hollow core and may be advanced over a guide wire  700 . The geared coils  930  provide axial flexibility and torsional rigidity and the external helical threads provide mechanical engagement with the lesion or arterial wall.  FIG. 11B  shows an over-the-wire type subintimal device  1110  (or wire support device) in longitudinal section, with an inner tube  1112  having a coiled gear design  930 , and an outer tube  1114  having a thread design  1000 . The inner tube  1112  contains a guide wire lumen capable of accepting a conventional guide wire  700 .  FIG. 11C  shows a partial enlarged view of an alternative inner tube  1112  where a gap  1116  between adjacent coils allow articulation of the inner tube  1112  upon proximal withdrawal of actuation wire  1118 . Outer tube  1114  may freely rotate with respect to inner tube  1112  when the inner tube  1112  is in both the straight and actuated positions. 
     In the foregoing embodiments, the subintimal device enters the subintimal space via an entry point. In other words, the subintimal device extends from the true lumen and into the subintimal space through the entry point. This may be accomplished by directing a subintimal device toward the intimal layer and penetrating therethrough. Alternatively, a guide wire may be used to penetrate the intimal layer and enter the subintimal space. This later approach may be more commonly employed since physicians often find themselves unintentionally entering the subintimal space with a guide wire. However, to facilitate definitive exploitation of the subintimal space, the embodiments described herein intentionally facilitate penetration of the intimal layer and entry into the subintimal space, which is contrary to conventional current practice. 
     It is contemplated that a bare guide wire (i.e., a guide wire without a directing catheter) using a bent tip at a length and angle sufficient to engage the intima away from the true lumen, may be used to intentionally penetrate the intima and enter the subintimal space. However, a directing catheter may be employed to consistently and predictably facilitate entry into the subintimal space. As illustrated in  FIGS. 12A-12C , various directing devices may be used to direct the subintimal device (or guide wire over which the subintimal device is advanced) to engage and penetrate the intimal layer and enter the subintimal space. 
       FIG. 12A  schematically illustrates a directing catheter  1200  substantially similar to an over-the-wire balloon catheter including a distal balloon  1220  with the addition of a delivery and directing tube  1210 . As shown, the directing catheter  1200  has been advanced over a conventional guide wire  700  and inflated proximal to the total occlusion  120 . For the sake of clarity,  FIG. 12A  shows a subintimal device path that is substantially parallel to the vessel lumen, but other orientations (e.g., helical) may also be employed. The delivery and directing tube  1210  may be positioned adjacent to and pointed slightly outward and toward the intimal layer  113  such that the subintimal device  300  may be advanced to perforate the subintimal layer  113 . A fluid source (e.g., syringe)  1230  may be connected to be in fluid communication with the delivery and directing tube  1210  via an infusion tube  1232 . Fluid may flow from the fluid source  1230  through the delivery and directing tube  1210  under a controlled pressure or a controlled volume. The infused fluid may enter the subintimal space  130  directly from the delivery and directing tube  1210  or from the true lumen  116  space defined between the distal end of the balloon  1220  and the proximal edge of the occlusion  120 . The fluid may be radiopaque contrast media to facilitate fluoroscopic visualization of the subintimal space, and/or may be used to delaminate the intimal layer  113  and medial layer  115  defining the subintimal space  130 .  FIG. 12B  schematically illustrates an alternative embodiment of directing catheter  1200  wherein the fluid source  1230  is in fluid communication with a lumen within the subintimal device  300  thereby directly infusing fluid into the subintimal space  130  via subintimal device  300 .  FIG. 12C  schematically illustrates another embodiment wherein the directing catheter  1250  is similar to a sub-selective guide catheter wherein the distal end  1252  has a predefined shape or an actuating element that allows manipulation by the physician intra-operatively to direct the subintimal device  300  toward the intimal layer for penetration therethrough. 
     Once the subintimal device is in the subintimal space, the intima may be delaminated from the media to open the subintimal space by blunt dissection as the subintimal device is being advanced. Alternatively, the intima may be delaminated from the media using pressurized fluid as described previously. As a further alternative, the layers may be delaminated by actuation as illustrated in  FIGS. 13A and 13B . Subintimal device  1300  may be actuated or self-expanded between a collapsed configuration shown in  FIG. 13A  and an expanded configuration shown in  FIG. 13B . The device  1300  may be advanced in a collapsed state until resistance is felt, and then expanded to delaminate layers in the expanded state in order to propagate the subintimal dissection. The subintimal device  1300  may comprise a shaft  1310  having a plurality of resilient expandable elements  1312  (e.g., heat set NiTi) and an atraumatic tip  1314  (shown bent). A sheath  1320  may be disposed about the proximal shaft  1310  and the expandable elements  1312  to retain the expandable elements  1312  in a collapsed configuration as shown in  FIG. 13A . Upon proximal retraction of the sheath  1320  (or distal advancement of the shaft  1310 ) the expandable elements  1312  elastically expand as shown in  FIG. 13B  to cause propagation of the dissection. The sheath  1320  may be advanced to collapse the expandable elements  1312  and the device  1300  may be advanced further into the subintimal space. Alternatively, the actuation mechanism may comprise an inflatable balloon that dissects when inflated and is advanceable when deflated. 
       FIGS. 13C and 13D  schematically illustrate an alternative subintimal crossing device  1330 . Subintimal device  1330  may be actuated or self-expanded between a collapsed configuration shown in  FIG. 13D  and an expanded configuration shown in  FIG. 13C  to delaminate the layers of the vascular wall. Alternatively, the subintimal device  1330  may be nominally in the expanded configuration and collapsible upon retraction. The device  1330  may be advanced in a collapsed state until resistance is felt, and then expanded to delaminate layers in the expanded state in order to propagate the subintimal dissection. The subintimal device  1330  may comprise a flexible shaft  1332  and an expandable element  1334 . The shaft may comprise a flexible superelastic metal tube (e.g., NiTi) or a composite polymeric shaft (e.g., braid reinforced polyether block amide). The expandable element  1334  may be connected to the distal end of the shaft  1332  using an adhesive or weld joint, for example. The expandable element  1334  may comprise a plurality of braided filaments formed of a resilient material such as NiTi, and may be heat set in the expanded state or the collapsed state. The distal end of the expandable element  1334  may comprise an atraumatic tip comprising, for example, a weld ball  1336  securing the individual braided filaments. The expandable element  1334  may be expanded by pushing on the shaft  1332  when resistance to advancement is encountered, thus delaminating adjacent tissue layers. Alternatively, the expandable element  1334  may be expanded by pushing on the shaft  1332  and pulling on a pull wire (not shown) attached to the distal end of the expandable element  1334  and extending proximally through the lumen of the shaft  1332 . A flexible polymeric sheath  1340  may be used to facilitate delivery of the crossing device  1330 , provide and maintain a crossing path within the vascular wall, and/or to facilitate removal of the crossing device  1330  as shown in  FIG. 13D . The polymeric sheath  1340  may alternatively comprise an orienting device as described herein or another intravascular device (e.g., balloon catheter) configured to be advanced over a guide wire or the like. 
       FIGS. 13E and 13F  schematically illustrate an alternative subintimal crossing device  1350 . Subintimal device  1350  includes an elongate flexible and torqueable shaft  1352  and a distal elastic loop  1354  formed of a superelastic metal alloy such as NiTi, for example. The loop  1354  may be self-expanded between a collapsed configuration shown in  FIG. 13F  and an expanded configuration shown in  FIG. 13E . The device  1350  may be advanced distally through sheath  1340  for delivery and pulled proximally into sheath  1340  for removal. When expanded, the loop  1354  may be substantially planar, and with rotation of the shaft  1352 , the loop  1354  rotates in the subintimal space forcing delamination of tissue layers. 
     Bypass Embodiments 
     The foregoing embodiments generally involve penetrating the intimal layer, placing a subintimal device in the subintimal space, and traversing across the occluded segment for purposes of defining the vascular boundary and/or for purposes of guarding against perforation. The following bypass embodiments also involve the initial steps of penetrating the intimal layer, placing a subintimal device in the subintimal space, and traversing across the occluded segment. To this end, the devices and methods described with reference to boundary definition and perforation guard embodiments have application to the following bypass embodiments. 
     In addition to penetrating the intimal layer, entering the subintimal space, and traversing the occluded segment, the following bypass embodiments generally involve orientation and re-entry into the true lumen. A general approach to the foregoing bypass embodiments is schematically illustrated in  FIGS. 14A-14H . A guide wire  700  may be advanced through the proximal segment  112  of the true lumen  116  of the occluded artery to the proximal edge of the total occlusion  120  adjacent the vessel wall  118  as shown in  FIG. 14A . By manipulating and directing the guide wire  700  to the proximal edge of the total occlusion  120  toward the wall  118 , the guide wire  700  may penetrate the intimal layer  113  and enter the subintimal space  130  between the intima  113  and the media/adventitia  115 / 117  as shown in  FIG. 14B . The manipulating and directing of the guide wire  700  as described above may be performed by using the guide wire alone or by using any of the directing devices described herein. With the guide wire  700  in the subintimal space  130 , a subintimal device  1400  may be advanced over the guide wire  700  as shown in  FIG. 14C . In the illustrated embodiment, the subintimal device  1400  includes a hollow elongate shaft  1402  and an atraumatic bulbous tip  1404 . However, any of the subintimal devices described herein may be employed, particularly the over-the-wire type subintimal devices. As shown in  FIG. 14D , the subintimal device  1400  may be further advanced over the guide wire  700  such that the tip  1404  resides in the subintimal space  130 . At this procedural stage, the guide wire  700  may be withdrawn, completely removing it from the subintimal device  1400 . Further manipulation of the subintimal device  1400  (both axial advancement and radial rotation) allows blunt dissection of the layers defining the subintimal space  130  and advancement of the device  1400  to the distal portion of the total occlusion  120  as shown in  FIG. 14E . Penetration of the intimal layer  113  and re-entry into the distal segment  114  of the true lumen  116  distal to the occlusion  120  may be achieved by various means described later in detail, which generally include the steps of orientation toward the center of the true lumen  116  and penetration of the intimal layer  113 . For purposes of illustration, not limitation,  FIG. 14F  shows a shaped re-entry device  1420  having a curled and sharpened tip exiting the lumen of the subintimal device  1400  distal of occlusion  120  and entering the distal segment  114  of the true lumen  116  through the intimal layer  113 . With re-entry device  1420  in the distal segment  114  of the true lumen  116 , the subintimal device  1400  may be advanced into the true lumen  116  over the re-entry device  1420  as shown in  FIG. 14G . The re-entry device  1420  may be withdrawn from the subintimal device  1400  and the guide wire  700  may be advanced in its place as shown in  FIG. 14H , after which the subintimal device  1400  may be withdrawn leaving the guide wire  700  in place. As such, the guide wire  700  extends from the proximal segment  112  of the true lumen  116  proximal of the occlusion  120 , traverses the occluded segment via the subintimal space  130 , and reenters the distal segment  114  of the true lumen  116  distal of the occlusion  120 , thus bypassing the total occlusion  120  without exiting the artery. With the guide wire  700  so placed, the subintimal space  130  may be dilated (e.g., by balloon angioplasty or atherectomy) and stented, for example, or otherwise treated using known techniques. 
     As mentioned above, re-entry into the true lumen from the subintimal space generally involves orientation toward the center of the true lumen and penetration of the intimal layer. Although fluoroscopy is a commonly available visualization tool used during interventional procedures, it only provides two-dimensional images which are typically insufficient, taken alone, to determine the proper direction for penetration from the subintimal space toward the center of the true lumen. As such, those skilled in the art may use visualization tools with greater accuracy or with the ability to show three dimensional data. For example, intravascular ultrasound (IVUS) or magnetic resonance imaging (MRI) may be used to determine the position and direction of true lumen re-entry from the subintimal space. However, such techniques are time consuming, expensive and often impractical, and therefore it would be desirable to facilitate orientation (i.e., direct a re-entry device from the subintimal space toward the true lumen distal of a total occlusion) without the need for such burdensome visualization techniques. 
     Various orientation and re-entry embodiments are described herein that take advantage of the position and geometry of the subintimal space relative to the true lumen to facilitate effective orientation of a re-entry device from the subintimal space toward the true lumen. This may be accomplished by recognizing that the subintimal space is generally annular with its radial center at the center of the true lumen. Thus, a curved device deployed in the subintimal space defines at least an arc and at most a full circle (in radial cross-section), the radial center of which must reside at the center of the true lumen. In other words, if a curved device that is deployed in the subintimal space such that the curvature of the device is aligned with the curvature of the subintimal space, then the true lumen is by necessity oriented toward the concave side of the curved subintimal device. A re-entry device may then be keyed or otherwise oriented to the concave side of the subintimal device, and is thus automatically oriented toward the true lumen without visualization. 
     One such embodiment that operates under this premise is shown schematically in  FIGS. 15A and 15B . In this embodiment, a helical subintimal device  1500  is shown generically, the features of which may be incorporated into other subintimal device embodiments described herein. Subintimal device  1500  generally includes an elongate tubular shaft  1502  having a lumen  1504  extending therethrough and a re-entry port  1506  disposed distally in the region of the helical shape. In this embodiment, the distal portion of the shaft  1502  may have a helical shape in its relaxed state such that the re-entry port  1506  is always oriented toward the concave side or center of the helix as shown in  FIG. 15A . The helical portion may be deployed in the subintimal space around the total occlusion as described elsewhere herein, resulting in the concave portion of the helix and the port  1506  being oriented toward the true lumen. With this arrangement, a re-entry device such as a guide wire  700  or flexible stylet with a tissue penetrating tip may be advanced through the lumen  1504  of the shaft  1502  to exit the re-entry port  1506  as shown in  FIG. 15B . This arrangement may be used to establish re-entry into the true lumen after the subintimal device  1500  has been deployed across an occlusion in the subintimal space. 
     Other orientation and re-entry embodiments are described herein that take advantage of the different properties of the layers of the artery wall to facilitate effective orientation of a re-entry device from the subintimal space toward the true lumen. In some instances, the intima  113  is more pliable than the composite of the media  115  and adventitia  117 . Thus, expansion of an element in the subintimal space  130  will result in more deflection of the intima  113  than the media  115  and adventitia  117 . 
     One such embodiment that operates under this premise is shown schematically in  FIGS. 16A-16D . In this embodiment, a subintimal device (not shown) as described elsewhere herein may be used to pass the total occlusion and place a guide wire  700  as shown in  FIG. 16A . The guide wire  700  extends across the occlusion  120  and is disposed in the subintimal space  130  between intima  113  and the media/adventitia  115 / 117  where re-entry into the true lumen  116  distal of the occlusion  120  is desired. A balloon catheter  1620  is then advanced over the guide wire  700  until the balloon portion  1622  is disposed adjacent the distal end of the occlusion  120  as shown in  FIGS. 16B and 16C . The guide wire  700  is pulled proximally and the balloon  1622  is then inflated causing radial displacement of the distal end of the balloon catheter  1620  as shown in  FIG. 16C . Inflating the balloon  1622  of the balloon catheter  1620  orients the tip of the catheter  1620  toward the intima  113 . The guide wire  700  may be removed from the balloon catheter  1620  and a sharpened stylet  1630  or the like may be advanced through the guide wire lumen of the catheter  1620  until the distal end of the stylet  1630  penetrates the intima  113  as shown in  FIG. 16D , thus establishing re-entry from the subintimal path  130  and into the true lumen  116 . 
     Detailed Examples of Bypass Embodiments 
     In the following embodiments, detailed examples of devices are described which facilitate one or more of the steps involved in visualizing, perforation guarding, and/or bypassing a total occlusion as generally described previously. These devices may, for example: (i) facilitate subintimal device tracking by transmitting sufficient axial force and radial torque (sometimes referred to as push and twist respectively) to enter the subintimal space, delaminate the intima from surrounding tissue layers, and traverse the total occlusion via the subintimal space; (ii) facilitate alignment of the subintimal device within the subintimal space with a favorable orientation for true lumen re-entry distal of the total occlusion; (iii) facilitate advancement of a re-entry element that takes advantage of the subintimal device alignment and orientation to direct itself toward the true lumen; (iv) facilitate penetration of the intimal layer to regain access to the true lumen distal of the total occlusion; and/or (v) facilitate confirmation that true lumen re-entry has been achieved. 
     Detailed Examples of Axial Push Force and Radial Torque Embodiments 
     The embodiments described with reference to  FIGS. 17 and 18  illustrate features of subintimal devices that facilitate the transmission of push and twist to enter the subintimal space and advance therein.  FIG. 17  shows an embodiment of a subintimal device  1700  where the properties of push and twist may be provided by an internal stylet  1703  slideably disposed within the central lumen  1701  of a tubular shaft  1702 . With stylet  1703  removed, the central lumen may also accept a guide wire (not shown). 
     The tubular shaft  1702  may be made from suitable polymeric materials such as polyethylene, nylon, or polyether-block-amide (e.g., Pebax™). The tubular shaft  1702  may also have composite structure where the inside layer may have a lubricious polymer such as polyethylene or a fluoropolymer such as PTFE (e.g., Teflon™), the middle layer may have a metallic or polymeric braided structure such as polyester or stainless steel, while the outside layer may also be made of a similar polymeric material. The outside of the subintimal device  1700  may also have a lubricious exterior coating. For example, coatings may include liquid silicone or a hydrophilic coating such as hyaluronic acid. The stylet  1703  may be made of suitable metallic materials including but not limited to stainless steel or nickel titanium alloys. The atraumatic tip  1704  may be made of suitable metallic or polymeric materials including, for example, stainless steel, titanium, polycarbonate, or polyether-block-amide (e.g., Pebax™). 
     As seen in  FIGS. 17A and 17B , which are cross sectional views taken along lines A-A and B-B, respectively, in  FIG. 17 , all or a portion (e.g., distal portion) of the stylet  1703  may interface with a feature  1706  within the tubular shaft  1702  and/or within the atraumatic tip  1704 . For example, the tubular shaft  1702  and/or the atraumatic tip  1704  may contain a lumen with a geometric feature  1706  intended to mate or key with distal tip of the stylet  1707  as shown in  FIG. 17B . This keying or mating feature  1706  allows torque to be transmitted from the operators hand to the distal tip of the subintimal device through twist of the subintimal device and stylet. For the purpose of illustration, the geometric feature  1706  is shown as a square in cross-section, but it is intended that any geometry other than round may be used to create engagement of the perimeter of the stylet  1703  with the internal lumen of the tubular shaft  1702  and/or atraumatic tip  1704 . 
       FIG. 18  shows an embodiment of a subintimal device  1800  having a proximal tubular shaft  1804 , a distal tubular shaft  1802 , and an atraumatic bulbous tip  1805 . In this embodiment, the desired properties of push and twist may be provided by constructing the proximal shaft  1804  of a rigid material (e.g., metallic hypotube) and contracting the distal shaft  1802  in a similar manner, for example, to the gear shaft previously described with reference to  FIG. 9  et seq. Distal gear shaft  1802  may be flexible yet torsionally and longitudinally rigid. The distal shaft  1802  may be disposed within an outer sheath  1801  and may have an internal sheath  1803  as well. The outer and inner sheaths may be made of suitable polymeric materials such as polyethylene, nylon, polyether-block-amide (e.g., Pebax™), or a fluoropolymer such as Teflon™. 
     Detailed Examples of True Lumen Orientation Embodiments 
     The embodiments described with reference to  FIGS. 19A-19B, 20A-20B, 21A-21B, and 22A-22C  illustrate features of subintimal devices that facilitate orientation toward the true lumen. Generally, by deploying a subintimal device around at least a portion of the circumference (sometimes referred to as radial bend or curve), the direction of the true lumen is toward the center (concave side) of the curve. To achieve a radial bend from a longitudinally positioned subintimal device, it may be necessary or desirable to initially impart an axial bend or curve in the subintimal device to act as a transitional geometry. Hence, some subintimal device embodiments described herein have both an axial bend (e.g.,  FIG. 19A ) and a radial bend (e.g.,  FIG. 19B ) when deployed in the subintimal space. Since the concave side of the radial bend is consistently toward the true lumen, a re-entry device may be predictably directed toward the true lumen (without employing complex visualization techniques) by aligning itself with respect to the radial curve of the subintimal device. Thus, in the following embodiments, various subintimal device designs are illustrated that accommodate radial bends (and axial bends) to establish the direction of the true lumen toward the concave side of the radial bend. 
       FIGS. 19A and 19B  show subintimal device  1900  that is capable of aiming a re-entry device (not shown) toward the true lumen  116  distal of a total occlusion with the aid of standard fluoroscopy. Subintimal device  1900  with atraumatic tip  1902  may be positioned within the subintimal space  130  between the intima  113  and media  115  layers. The subintimal device  1900  may be advanced using similar techniques previously described with reference to  FIGS. 14A-14E . Once the subintimal device  1900  is in the proper position within the subintimal space  130 , a distal portion of the subintimal device  1900  is configured to achieve a geometry having a bend in the longitudinal direction as shown in  FIG. 19A  and a bend in the radial direction as shown in  FIG. 19B . This three-dimensional geometry may be referred to as a compound bend. As will be described in more detail herein, the compound bend may be used to facilitate alignment of a re-entry device toward the true lumen  116  of the artery  110 . 
       FIG. 20A  illustrates a subintimal device  2000 , similar to the subintimal device  1800  described with reference to  FIG. 18 , that may be capable of achieving a compound bend. The subintimal device  2000  includes an elongate tubular shaft  2001  defining an internal lumen, an actuation (e.g., push or pull) member  2003  residing in the lumen of the shaft  2001  and having a distal end attached to the distal end of the shaft  2001 , and an atraumatic tip  2004  attached to the distal end of the shaft  2001 . The flexible yet torsionally rigid distal shaft  2001  has one or more open areas  2002  oriented along the actuation member  2003 . An external sheath  2005  may be disposed about the length of the shaft  2001  and actuation member  2003 , with its distal end attached to the atraumatic tip  2004 . For purpose of illustration only,  FIG. 20A  shows a single actuation member  2003  in the proximity of a single row of open areas  2002  in the shaft  2001 . The subintimal device may have one or more actuation members and may have one or more rows of open areas. For example, the shaft  2001  may have a laser cut geometry as shown in  FIG. 20B  with two rows of open areas  2002 . 
     With continued reference to  FIG. 20A , a bend may be achieved by pulling the longitudinal actuation member  2003 . Pulling the actuation member  2003  partially or completely closes the open spaces  2002  thus shortening the length of the shaft  2001  in proximity of the open areas  2002  and creating a bend in the device  2000 . A compound bend may be achieved through the use of multiple rows of open areas and/or multiple longitudinal members  2003 . Alternatively, a compound bend may also be achieved using a single row of open areas and a single longitudinal member by relying on device interaction with the adventitial layer. In this alternative, pulling the actuation member  2003  creates the axial curvature (see  FIG. 19A ) and interaction with the adventitia may force the subintimal device to accommodate a radial curvature (see  FIG. 19B ). 
       FIG. 21A  shows an alternative embodiment of a subintimal device  2100  that may also achieve a compound bend. The subintimal device  2001  generally includes an elongate tubular shaft  2102  defining an internal lumen  2101 , an actuation (e.g., push or pull) member  2105  having a distal end attached to the distal end of the shaft  2102 , and an atraumatic tip  2106  attached to the distal end of the shaft  2102 . The shaft  2102  may be constructed from a multitude of alternating wedge-shaped polymeric segments where segment  2103  may have a lower durometer and greater flexibility as compared to the adjacent segment  2104 . For example, segment  2103  may be made of 4033 Pebax while segment  2104  may be 6333 Pebax. These multiple segments may be assembled together to make a continuous shaft. For example, the edges of adjacent segments may be fused together using a process that heats the segments above their melt temperature. The application of heat to segments that is held in proximity may allow said segments to fuse together.  FIG. 21A  shows a series of wedged-shaped segments wherein the relatively stiff segment  2104  defines a larger percentage of one side along a line of the shaft  2102  while the relatively flexible segment  2103  defines a larger percentage of the opposing side of the same shaft. 
     As shown in  FIG. 21B , the side of the shaft  2102  with a greater percentage of relatively flexible segments  2103  allows more relative compression upon actuation of member  2105 , such that the shaft  2105  may have a predisposition to flex to the side with more flexible segment material  2103  and may have greater resistance to flex to the side with more stiff segment material  2104 . The longitudinal actuation member  2105  may be slideably disposed in a lumen within the wall of the shaft  2102  and may be attached to the atraumatic tip  2106 , extending the length of the shaft  2105  and out the proximal end. For purpose of illustration,  FIGS. 21A and 21B  show a single longitudinal member  2105  in the proximity of a line of relatively flexible segments  2103 . The subintimal device  2100  may have one or more longitudinal members and may have one or more lines of flexible segments  2103 . 
     With reference to  FIG. 21B  a compound bend may be achieved by pulling the actuation member  2105  relative to shaft  2102 . Pulling the actuation member  2105  may compress segments  2103  thus shortening the subintimal device length along the side of the of the shaft  2102  with more flexible segment material  2103 . A compound bend may be achieved by arranging the flexible segment material  2103  in the desired pattern and/or by using multiple longitudinal members  2105 . Alternatively, a compound bend may also be achieved using a single side of flexible segment material  2103  and a single longitudinal member by relying on device interaction with the adventitial layer as described previously. 
     With reference to  FIGS. 22A-22C , another embodiment of a subintimal device  2200  capable of achieving a compound bend is shown schematically.  FIG. 22A  only shows the distal portion of the subintimal device  2200  for purposes of illustration and clarity. In this embodiment, the tubular shaft of the subintimal device  2200  comprises an inner tube  2201  and an outer tube  2204  (shown cut away), between which is disposed a series of circumferential rings  2202  interconnected by longitudinal members  2203 . An atraumatic tip  2207  is connected to the distal end of the shaft, and a central lumen  2206  runs through the device  2200  for the acceptance of a guide wire and/or a re-entry device. Suitable materials for the circumferential rings  2202  and longitudinal members  2203  include but are not limited to nickel titanium, stainless steel, or MP35N. The inner tube  2201  and the outer tube  2204  may be made of suitable polymeric materials such as polyethylene, polyether-block-amide (e.g., Pebax™), or nylon. The distal portion of the subintimal device may have a pre-formed curved shape (e.g., compound bend) in its relaxed state as shown in  FIG. 22A . 
     The subintimal device  2200  may be slideably disposed within an external delivery sheath  2205  as shown in  FIGS. 22B and 22C . The sheath  2205  may be slightly stiffer then the subintimal device  2200  such that the subintimal device  2200  assumes a straight shape when the sheath  2205  covers the distal portion of the device as shown in  FIG. 22B , and assumes a curved shape when the sheath  2205  is retracted as shown in  FIG. 22A . Upon proximal retraction of the sheath  2205 , the subintimal device  2200  may assume a compound bend by virtue of its preformed shape, or it may assume axial curvature by virtue of its preformed shape and radial curvature by virtue of interaction with the adventitia as described previously. 
     Detailed Examples of Re-Entry Embodiments 
     As described above, the concave side of a subintimal device with a radial bend is consistently toward the true lumen. A re-entry device may thus be predictably directed toward the true lumen (without employing complex visualization techniques) by aligning itself with respect to the concave side of the radial curve of the subintimal device. Therefore, in the following embodiments, various re-entry devices are illustrated that align themselves relative to the concave side of a radial bend in a subintimal device to establish predictable re-entry into the true lumen (without employing complex visualization techniques). 
       FIGS. 23A-23E  show embodiments of re-entry devices that may be advanced through a lumen within a subintimal device  2300 . The subintimal device  2300  may be similar to the devices described previously to facilitate formation of a radial bend with a concave side oriented toward the true lumen  116  distal of a total occlusion. With reference to  FIG. 23A , subintimal device  2300  may be positioned within the subintimal space  130  between the intimal  113  and medial  115  layers. A radial curve may be formed in the subintimal device  2300  using any of the methods described previously, and the radial curve may be less than the radial curvature of the artery. A radial curvature with a diameter less than the inside diameter of the artery causes the tip of the subintimal device  2300  to be pointed toward the true lumen  116 . The re-entry device  2310  may comprise a guide wire, a sharpened stylet or the like to facilitate penetration through the intimal layer. Advancement of the re-entry device  2310  though the central lumen within the subintimal device  2300  and out the distal end results in penetration through the intimal layer  113  and into the true lumen  116 . 
     An alternative re-entry embodiment is shown in  FIG. 23B  wherein the subintimal device  2300  has a radial curvature approximating the inside curvature of the artery. The subintimal device may be placed within the arterial wall between intimal  113  and medial  115  layers as described previously. In this embodiment, the re-entry device  2310  may have a preformed bend that is less than the curvature of the subintimal device  2300  and less than the inside curvature of the artery. The re-entry device is longitudinally and rotationally movable with respect to the subintimal device  2300 , thus allowing the curvature of the re-entry device  2310  to self-align with the curvature of the subintimal device  2300 . Thus, with the concave side of the curved subintimal device oriented toward the true lumen, the concave side of the curved re-entry device  2310  will also be oriented toward the true lumen. Advancement of the re-entry device  2310  through the subintimal device  2300  and out the distal end thereof results in penetration through the intimal layer  113  and into the true lumen  116 . Because the curvature of the re-entry device is less than the inside curvature of the artery, the tip of the re-entry device remains in the true lumen and does not engage the opposite wall of the artery. 
     Another alternative re-entry device embodiment is shown in  FIG. 23C  wherein the re-entry device  2310  exits out a distal side port  2302  in the subintimal device  2300 . The side port  2302  may be located on the concave side of the curvature of the subintimal device  2300  thus orienting the tip of the re-entry device  2310  toward the true lumen  116 . In this embodiment, the re-entry device  2310  may have a slight bend at its distal end to bias the tip toward the port  2302  such that it exits the port upon advancement. 
     Another alternative re-entry device embodiment is shown in  FIGS. 23D and 23E .  FIG. 23E  is a cross sectional view taken along line A-A in  FIG. 23D . In this embodiment, the subintimal device  2300  and the re-entry device may be provided with radial curvature for orientation toward the true lumen  116  as described previously. In addition, a portion of the subintimal device  2300  such as the tip  2304  and a distal portion of the re-entry device  2310  may be provided with a mating or keying geometry to facilitate relative alignment. Various non-circular mating geometries may be used, including a rectangular cross section as shown in  FIG. 23E . 
       FIGS. 24A-24C  show various embodiments of penetrating tips for use on a re-entry device. As mentioned previously, the re-entry device  2310  may comprise a guide wire or the like to facilitate penetration through the intimal layer  113  from the subintimal space  130  to the true lumen  116 . Alternatively, the tip of the re-entry device  2310  may be designed to enhance penetration through the intimal layer  113 , particularly in the case where the intimal layer is diseased. If the intimal layer  113  is diseased, it will likely be tougher than healthy tissue because it may contain soft plaque, fibrous plaque and/or hard calcified plaque. The presence or absence of disease at the intended re-entry site and the nature of the disease may require a re-entry device capable of penetrating the various plaques within a non-homogenous diseased arterial wall. In the event the re-entry site is free from disease or contains relatively soft plaque, a conventional guide wire may be used as a re-entry device. Alternatively, if disease is encountered, the tip configurations illustrated in  FIGS. 24A-24C  may be employed. 
     As shown in  FIG. 24A , the re-entry device may have a rotational cutting or piercing element  2410  capable of penetrating the arterial wall. The rotational element  2410  may, for example, be similar to a fluted drill bit. Rotation of the re-entry device with rotational cutting element  2410  may be achieved through manual manipulation by the physician or through a powered mechanism such as an electric motor. 
     As shown in  FIG. 24B , the re-entry device may have a rotational abrasive element  2420 . The abrasive element  2420  may include an abrasive coating such as  220  grit diamond abrasive. The abrasive coating may be applied to the tip of the re-entry device through an electroplating process. Rotation of the re-entry device with rotational abrasive element  2420  may be achieved through manual manipulation by the physician or through a powered mechanism such as an electric motor. 
     As shown in  FIG. 24C , the re-entry device may have a tapered or sharpened tip  2430 . The sharpened tip  2430  may penetrate the intimal layer  113  through axial advancement or axial reciprocation. The end of the re-entry device, for example, may taper to a sharp point. Axial movement or reciprocation of the tapered or sharpened tip  2430  may be achieved through manual manipulation by the physician or through a powered mechanism such as an electric motor or a solenoid. 
     Confirmation of a re-entry device entering the true arterial lumen distal of the occlusion may be difficult through the sole use of two-dimensional images obtained via fluoroscopy. These two-dimensional images may allow a physician to determine if a re-entry device is in close proximity to the artery, but may not offer adequate resolution to determine precise position (i.e. within the artery wall vs. within the true arterial lumen). Confirmation of true lumen re-entry may be achieved by understanding when the re-entry and/or the subintimal device penetrate the intimal layer  113  and come in contact with the blood in the true lumen  116  distal to the total occlusion. 
     One method of determining if the true arterial lumen has been accessed is by drawing intra-arterial blood from the distal entry point proximally through a lumen within the re-entry device or a lumen within the subintimal device to the proximal end of the device where the presence of blood may be detected. This method takes advantage of the fact that there is typically blood in the true lumen distal of the occlusion but there is little to no blood in the subintimal space. Thus, the absence of blood indicates the device is subintimal and the presence of blood indicates the device is in the true lumen. This technique may also be used to indicate perforation of the device out of the artery and into the pericardial space by the presence of pericardial fluid. 
       FIG. 25  illustrates a re-entry device  2500  that facilitates confirmation of true lumen re-entry. The re-entry device  2500  may be passed through a subintimal device  2300 , oriented toward the true lumen  116 , and penetrate the intimal layer  113  from the subintimal space  130  to the true lumen  116  as described previously. In this embodiment, the re-entry device  2500  is provided with an internal lumen extending from its proximal end to a distal opening  2502 . The proximal end of the re-entry device  2500  is connected to an indicator  2504  which is in turn connected to a vacuum source. The indicator  2504  may be a flow indicator such as a collection vessel where the presence and type of fluid may be visually observed. With the vacuum source generating a negative pressure, entry of the re-entry device  2500  into the true lumen  116  allows blood to flow into the distal opening  2502  and through the internal lumen to the indicator  2504 . Alternatively, the vacuum source and indicator may be fluidly attached to the subintimal device where entry of the device into the true lumen results in similar blood flow into the indicator. Alternative indicators  2504  may be employed such as impedance sensors, oxygen sensors, optical sensors, etc. 
     Detailed Examples of Deployable Element Embodiments 
     Various devices have been previously described herein that are deployable in the subintimal space for a variety of purposes. The following embodiments are additional examples of such deployable devices that may be used in the same or similar manner. For example, the following embodiments provide a deployable element that when released within the subintimal space along the length and around the circumference of the total occlusion may serve as: (i) a visualization aid that may help define the arterial wall during fluoroscopy; (ii) a protective element that may guard the exterior vessel layer or layers from devices passing through the total occlusion within the true arterial lumen; and/or (iii) a protective element that may provide an indication of close proximity or contact between a device passed through the total occlusion within the true arterial lumen and the protective element. The deployable element may be readily released from and re-captured into an exterior containment sheath. The deployable element may also be released and remain deployed within a patient as a permanent implant. This permanent implant may serve as a stent and/or may also elute a drug. 
     An example of a deployable element  2600  is schematically illustrated in  FIG. 26A . The deployable element  2600  may be disposed about a subintimal device  2300  and contained thereon by a retractable containment sheath  2610 . In  FIG. 26A , the deployable element  2600  is shown in the process of release from its constrained position the proximal retraction of the containment sheath  2610 . The deployable element  2600  may comprise, for example, a collapsible lattice structure that is capable of expanding from a first collapsed configuration within the containment sheath  2610  to a second deployed configuration upon retraction of the sheath  2610  that allows it to expand within the arterial wall. In this embodiment, the deployable element  2600  is shown in the submedial space between the media  115  and adventitia  117 .  FIG. 26B  shows the deployable element  2600  completely released from the subintimal device  2300  by complete retraction of the exterior containment sheath  2610 . The deployable element  2600  may expand around the circumference and along the length of a total occlusion (not shown) thus concentrically surrounding a diseased segment. The lattice structure of the deployable element  2600  may be made of a material capable of withstanding strain between the collapsed configuration and the deployed configuration without significant permanent deformation. Suitable materials for the deployable element  2600  include but are not limited to nickel titanium, stainless steel, elgiloy, or MP35N. 
     The deployable element may be used to aid in defining the arterial wall in the area of a total occlusion. As known to those skilled in the art, a totally occluded artery may not allow sufficient radiopaque contrast solution to penetrate the diseased segment thus preventing a physician from visualizing the artery in the occluded area. Placing a deployable element of sufficient radiopacity (as seen via fluoroscopy) within the arterial wall around a total occlusion may allow a physician to visualize the occluded segment. Visualization of the artery in the area of occlusion may allow subsequent interventional devices (i.e. guide wires, balloons, stents, etc.) to be successfully passed within the confines of the deployable element. 
     The deployable element may alternatively provide mechanical protection for the arterial layers concentrically outward of the deployable element from crossing devices intended to penetrate the total occlusion such as guide wires, atherectomy devices, laser ablation devices, and radiofrequency ablation devices. For example,  FIG. 27  shows a rotational abrasive device  2700  with an abrasive cutting tip  2710  passing through a total occlusion  120  with the deployable element  2600  protecting the arterial wall from perforation. While the abrasive tip  2710  is effective at passing through the total occlusion  120 , the deployable element comprises a relatively harder material (e.g., metallic) with a lattice pattern having openings smaller than the tip  2710  to prevent perforation therethrough. 
     The deployable element may alternatively provide vessel wall protection by indicating when the occlusion crossing device (guide wire, atherectomy device, laser ablation device, and radiofrequency ablation device, etc.) is in close proximity to or in contact with the vessel wall. For example, either the distal end of the deployable element or the distal end of the crossing device may act as a transmitting antenna and the other of the two may act as a receiving antenna. The transmitting antenna may be electrically connected to a radiofrequency (RF) signal generator and the receiving antenna may be connected to an RF signal receiving or detection circuit via a lengthwise insulated and/or shielded lead disposed in each of the devices. As an alternative to RF proximity detection, impedance may be similarly used as an indicator of proximity. 
     With either an RF or impedance based approach, a relatively weak signal is indicative of the crossing device being further away from the deployable element, for example when the crossing device is in the center of the occluded artery. A relatively stronger signal is indicative of the crossing device being in close proximity to the deployable element, for example within the subintimal space. The physician may use this proximity information to safely and effectively direct the crossing device within the confines of the deployable element and across the total occlusion within the true arterial lumen. 
     As an alternative to a lattice structure described previously, the deployable element  2800  may comprise one or more continuous elastic members as shown in  FIG. 28 . The deployable element  2800  may be released from an exterior containment sheath (not shown) as described previously to expand circumferentially within the subintimal space. As shown in  FIG. 28 , the deployable element  2800  may comprise a single continuous preformed elastic wire with an atraumatic tip located at the distal end of the wire form to reduce the potential for unintended vessel wall damage. The wire may be made of suitable elastic materials that include but are not limited to nickel titanium, stainless steel, elgiloy, or MP35N. This wire form may include multi-axis bends approximating a sinusoidal pattern bent around a cylinder. The diameter of the cylindrical shape may be selected to match the inside diameter of the artery. The wire form may be restrained in a relatively straight configuration when placed within an exterior containment sheath for advancement through the vasculature to the intended deployment site. Upon withdrawal of the containment sheath, the wire form may assume the aforementioned multi-axis shape. 
     The deployable element may also be used to orient a re-entry device toward the true lumen distal of the total occlusion. For example, a subintimal device  2900  may have an accessory deployable element  2910  as shown in  FIGS. 29A-29D .  FIGS. 29B and 29D  are cross sectional end views of  FIGS. 29A and 29C , respectively. With reference to  FIGS. 29A and 29B , the subintimal device  2900  is shown positioned in the subintimal space with the accessory deployable element  2910  having an exposed portion disposed in a recess and a proximally extending portion in a lumen of the subintimal device  2900 . With reference to  FIGS. 29C and 29D , advancing the proximal portion of the deployable element causes the exposed portion to protrude from a side port  2904  and advance within the subintimal space. The geometry of the deployable element may be a preformed shape such as a U-shape to allow atraumatic expansion within the subintimal space as shown. With the accessory deployable element in the subintimal space as shown, it forms a radial curvature with a concave side that faces the true lumen  116 . With the concave side facing the true lumen, a re-entry device may be directed to penetrate the intimal layer into the true lumen as previously described with reference to  FIGS. 23A-23E, 24A-24C, and 25 . 
     Occlusion Removal Embodiments 
     Some of the devices described herein may also be used to facilitate complete or partial removal of a total occlusion, potentially including an inner portion of the arterial wall.  FIGS. 30A-30D  illustrate an example of this application wherein a delivery device  400  is used to deliver a subintimal device  300  around a total occlusion  120 , similar to what is shown and described with reference to  FIGS. 4, 4A, 4B and 5 . The occlusion is then removed as will be described in more detail. 
     With reference to  FIG. 30A , the delivery device  400  is positioned just proximal of a total occlusion  120 . In this position, the balloon  404  may be inflated within the vessel lumen  116  to direct the delivery tube  414  toward the vessel wall  118  at an orientation for the subintimal device  300  to penetrate through the intima  113  at an entry point and into the subintimal space. By virtue of the helical delivery tube  414 , the subintimal device  300  is sent on a helical trajectory as it is advanced through delivery tube  414  resulting in deployment of the subintimal device  300  in a helical pattern. As shown, the subintimal device  300  has been advanced through the delivery tube  414  and positioned concentrically outside the total occlusion  120 , outside the intimal layer  113 , and inside the medial layer  115  in the subintimal space. 
     With reference to  FIG. 30B , a subintimal device capture catheter  3010  is positioned across the chronic total occlusion  120  over a conventional guide wire  700  and within the subintimal device  300 . The proximal  301  and distal  303  ends of the subintimal device  300  have been captured and rotated by capture device  3010  so as to reduce the outside diameter and contain the lesion  120  and intima  113  within the coils of the subintimal device  300 . 
     With reference to  FIG. 30C , a tubular cutting device  3020  with a sharpened leading edge may be advanced over the subintimal device  300  and the capture device  3010  to engage and cut the intimal layer  113  with the total occlusion  120  therein. With reference to  FIG. 30D , further advancement of the cutting device  3020  cuts and separates the diseased portion including the total occlusion and surrounding intima from the remainder of the artery. Proximal withdrawal of the device from the artery results in removal of the total occlusion and a patent true lumen  116 . The occlusion  120  may be removed through the percutaneous intravascular access site or a surgical cut down may be performed to facilitate removal if the occlusion is too large for removal through the percutaneous access site. Alternatively, to reduce the size of the occlusion and thus facilitate removal through the percutaneous access site, a maceration mechanism may be employed to macerate the occlusion prior to removal. 
     In addition or as an alternative, a corkscrew-type device  3110  may be used to grasp and pull the total occlusion  120  for removal as shown in  FIGS. 31A and 31B . It is contemplated that corkscrew-type device  3110  may be used in combination with the devices described with reference to  FIGS. 30A-30D  which are not shown for sake of clarity. With reference to  FIG. 31A , the corkscrew device  3110  is shown with an exterior sheath  3120 . The corkscrew device  3110  is shown engaging occlusion  120  after delamination of the intimal layer  113  has been performed by the aforementioned methods and devices.  FIG. 31B  shows removal of the occlusion  120  and a portion of the intimal layer  113  through axial withdrawal of the corkscrew device  3110 . 
     Alternative Bypass Embodiment 
       FIGS. 32A-32E  illustrate an alternative system for bypassing a total occlusion. With reference to  FIG. 32A , a subintimal device  3200  is shown in the deployed configuration. The subintimal device  3200  includes an elastic wire  3210  with a distal form similar to the elastic wire form  2800  described with reference to  FIG. 28 , except with fewer sinusoidal turns. The subintimal device also includes a crescent-shaped or semi-circular delivery shaft  3220  and a retractable constraining sheath  3230 . As seen in  FIG. 32B , which is a cross-sectional view taken along line A-A in  FIG. 32A , the wire  3210  resides in the recess of the semi-circular delivery shaft  3220  over which the constraining sheath  3230  is disposed. As an alternative, the constraining sheath  3230  may be disposed about the wire  3210  only and may reside in the recess of the delivery shaft  3220 , provided that the constraining sheath  3230  is sufficiently stiff to at least partially straighten the formed wire  3210 . The distal end of the wire  3210  is connected to a blunt tip  3222  of the shaft  3220 . The wire  3210  and the semi-circular shaft  3220  may be formed of a resilient metallic material such as nickel titanium, stainless steel, elgiloy, or MP35N, and the sheath  3230  may be formed of a flexible polymeric material such as a polyether-block-amide (e.g., Pebax) lined with PTFE (e.g., Teflon). 
     Pulling the wire  3210  proximally relative to the shaft  3220  and advancing the sheath  3230  over the wire form constrains the wire form in the recess and renders the device  3200  suitable for atraumatic passage through the subintimal space. Once the device  3200  is positioned across the total occlusion within the subintimal space, the sheath  3230  may be retracted relative to the shaft  3220  to release the formed portion of the wire  3210 . Releasing the wire form causes it to extend circumferentially around the occlusion in the subintimal space as shown in  FIG. 32C . Once the wire form is fully deployed in the subintimal space, the sheath may be completely removed. 
     As shown in  FIG. 32D , with the wire form  3210  deployed in the subintimal space and with the sheath  3230  removed from the shaft  3220 , a dual lumen re-entry delivery catheter  3250  may be advance over the shaft  3220 . As seen in  FIG. 32E , which is a cross-sectional view taken along line A-A in  FIG. 32D , the delivery catheter  3250  includes a crescent-shaped or semi-circular lumen  3254  that accommodates the shaft  3220  extending therethrough. The delivery catheter  3250  also includes a circular lumen  3252  that accommodates a re-entry device  3240  extending therethrough. The delivery catheter  3250  may comprise a dual lumen polymeric extrusion such as polyether-block-amid (e.g., Pebax) and the re-entry device  3240  may be the same or similar to the re-entry devices described previously herein. 
     Alternatively, the delivery catheter  3250  may comprise two coaxial tubes including an elongate inner tube disposed in an elongate outer tube. The inner tube is configured to accommodate a re-entry device. The annular lumen defined between the inner tube and the outer tube is configured to accommodate semicircular delivery shaft  3220 . At the distal end of the delivery catheter  3250 , the inner tube may be tacked to the inside of the outer tube using a heating forming process where a portion of the outside circumference of the inner tube is thermally fused to the inside circumference of the outer tube thus creating a cross section similar to that shown in  FIG. 32E  over the heat formed area. Outside the heat formed area, the inner and outer tubes may remain coaxial and un-fused. 
     As described previously, the concave side of the wire form faces the true lumen, and with the fixed attachment of the wire  3210  to the tip  3222  of the shaft  3220 , the concave side of the semi-circular shaft  3220  also faces the true lumen. This feature may be used to facilitate orientation of a re-entry device toward the true lumen. For example, because lumen  3252  of the delivery catheter  3250  has a mating or keyed geometry with the semi-circular shaft  3220 , and because the concave side of the semi-circular shaft  3220  is oriented toward the true lumen, the re-entry device lumen  3252  may be oriented toward the true lumen as well. With this in mind, any of the re-entry device orientation methods described with reference to  FIGS. 23A-23E  may be employed. As shown in  FIG. 32D , the distal end of the semi-circular shaft  3220  has a curvature with a concave side facing the true lumen which may be used in concert with a curved re-entry device  3240 . Once orientation is established, the re-entry device  3240  may penetrate the intimal layer  113  and re-enter the true lumen as shown. 
     Orienting Device Introduced Through Subintimal Guide Catheter Embodiment 
       FIGS. 33A-33E  schematically illustrate an embodiment using one or more subintimal guide catheters  3310 / 3320  to introduce an orienting device  3330 . These Figures show a window cut-away in the outer layer of the vascular wall for purposes of illustration. In this embodiment, which is an alternative bypass embodiment in some aspects, as subintimal crossing device  300  with or without a guide wire lumen (shown) and having a bulbous tip  310  (e.g., 0.038 in. diameter olive shaped weld ball) is used to safely cross the subintimal space by blunt dissection as described elsewhere herein. 
     As shown in  FIG. 33A , a first (inner) sheath  3310  having an inside diameter (e.g., 0.018 inches) slightly larger than the outside diameter (e.g., 0.014-0.016 inches) of the shaft of the crossing device  300  may be advanced by pushing and back-and-forth rotation over the crossing device  300  and through the subintimal space up to the bulbous tip  310  located adjacent the distal end of the occlusion (not shown). Once in place, a second (outer) sheath  3320  having an outside diameter of 0.050 inches, for example, and an inside diameter (e.g., 0.040 inches) slightly larger than the outside diameter (e.g., 0.037 inches) of the inner sheath  3310  and slightly larger than the outside diameter of the tip  310  may be advanced by pushing and back-and-forth rotation over the inner sheath  3310  up to the bulbous tip  310  as shown in  FIG. 33B . In this Figure, a window cut-away is shown in the distal portion of the outer sheath  3320  for purposes of illustration. Once the outer sheath  3320  is in this position, the subintimal crossing device  300  and the inner sheath  3310  may be removed proximally through the outer sheath. Although the outer sheath  3320  may be advanced over the subintimal crossing device  300  without the need for inner sheath  3310 , the inner sheath  3310  provides step-wise increase in dissection diameter making traversal easier. The inner sheath  3310  may be formed of a braid reinforced polymeric construction (e.g.,  55 D polyether block amide) with an atraumatic tip (e.g., unreinforced  40 D polyether block amide). The outer sheath  3320  may be formed of a more rigid polymer (e.g.  72 D polyether block amide) and may optionally include a braid composite construction. Braid reinforced construction provides enhances push and torque, and it is believed that rotation of the sheaths  3310 / 3320  enhances the ability to cross and delaminate across the subintimal path. 
     With the outer sheath  3320  in place and providing a protected path across the occlusion within the subintimal space, an orienting device  3330  may be inserted into the sheath  3320  to the distal end thereof as shown in  FIG. 33C . In this Figure, a window cut-away is shown in the distal portion of the outer sheath  3320  for purposes of illustration.  FIG. 33C  shows the orienting device  3330  in the delivery configuration with the orienting element collapsed and  33 D shows the orienting device  3330  in the deployed configuration with the orienting element expanded. 
     The orienting device  3330  shown in  FIG. 33D  is similar to the orienting device  3200  shown in  FIG. 32A . The orienting device  3330  may include a tubular shaft  3332  with a wire  3334  disposed therein. The tubular shaft  3332  may comprise a polymeric tube with a wire ribbon (e.g., SST) embedded therein to add stiffness for pushability. The tubular shaft  3332  includes a lumen extending therethrough, and the distal end of the lumen is directed at an angle to a side facing exit port  3338  located proximate the orienting element  3336 . The distal end of the wire  3334  may include an orienting element  3336  comprising, for example, a preformed planar sinusoid, referred to as a wire form. The wire  3334  and the wire form  3336  may comprise a superelastic metal alloy such as NiTi, for example, and the wire form  3336  may be formed by heat setting. To deploy the orienting element  3336 , the outer sheath  3320  may be pulled proximally and the shaft  3332  may be pushed distally in an alternating fashion until the entire wire form  3336  is within the subintimal space. 
     The side port  3338  is oriented at a right angle to the plane of the orienting element  3336 . With this arrangement, the side port  3338  is either directed toward the vascular true lumen  116  or 180 degrees away from the vascular true lumen  116 . Radiographic visualization or other techniques as described elsewhere herein may be used to determine if the port  3338  is directed toward or away from the true lumen  116 . If the port  3338  is directed away from the true lumen  116 , the orienting device may be retracted, rotated 180 degrees, and re-deployed to point the port  3338  toward the true lumen  116 . A re-entry device as described elsewhere herein may then be advanced through the lumen of the tubular shaft  3332 , through the vascular wall and into the true lumen  116 . 
     As an alternative to orienting device  3330  shown in  FIG. 33D , orienting device  3340  shown in  FIG. 33E  may be employed in substantially the same manner. Orienting device  3340  includes an outer tube  3342  and an inner tube  3344 . The outer tube  3342  may be formed of a superelastic metal alloy (e.g., NiTi), and a distal portion of the outer tube  3342  may cut (e.g., using laser cutting techniques) to form slots to define two wings  3346  that hinge outward in a planar fashion as shown. The inner tube  3344  extends through the lumen of the outer tube  3342  and is attached distally to the distal end of the outer tube  3342 . Inner tube  3344  is similar in design and function as tubular shaft  3332 , and includes a distal side port  3348  to accommodate a re-entry device as described with reference thereto. Alternatively, a flap port may be used as will be described in more detail hereinafter. 
     Orienting Device Introduced Over Subintimal Crossing Device or Guide Wire Embodiment 
       FIGS. 34A-34H  schematically illustrate an embodiment using a subintimal crossing device or guide wire to introduce an orienting device  3400 . In this embodiment, the orienting device  3400  is designed to accommodate a subintimal crossing device or guide wire therein, thus negating the need for the subintimal guide catheters described previously. With specific reference to  FIG. 34A , a detailed view of a distal portion of the orienting device  3400  is shown.  FIG. 34B ( 1 ) is a cross-sectional view taken along line A-A in  FIG. 34A , and  FIG. 34B ( 2 ) is a cross-sectional view taken along line B-B in  FIG. 34A . The orienting device  3400  includes an elongate outer tubular shaft  3410  with a distal end connected to an orienting element  3440 . An elongate inner tubular shaft  3420  extends through the outer shaft  3410  and orienting element  3440 . The distal end of the inner shaft  3420  is connected to the distal end of the orienting element  3440 , as is a distal atraumatic tubular tip  3450 . A low friction liner  3430  may extend through the lumen of the inner shaft  3420  to facilitate smooth passage of devices therein. 
     The outer shaft  3410  may comprise, for example, a polymeric tube  3412  that may be reinforced with an embedded braid or wire ribbon. The inner shaft  3420  may comprise a metallic tube  3422  (e.g., NiTi) with a solid tubular proximal segment and a spiral cut  3424  distal segment for added flexibility and torqueability. The distal portion of the inner shaft  3420  may include an inwardly inclined flap  3426 . As seen in  FIG. 34B , the flap  3426  extends into the lumen of the inner shaft  3420  and operates to (1) direct front loaded devices (e.g., re-entry device) out the side port  3425  of the inner shaft  3420  adjacent the orienting element  3440 ; and (2) direct back loaded devices (e.g., subintimal crossing device or guide wire) down the lumen of the proximal segment  3422  of the inner shaft  3420  while preventing back loaded devices from exiting the side port  3425 . A semi-circular slot  3428  may be formed to accommodate the end of the flap  3426  to prevent the edge of the flap  3426  from snagging on devices passing by. The cuts may be formed by laser cutting or the like and the flap may be biased inwardly by heat setting. 
     With reference to  FIG. 34C , the inner shaft  3420  may have an overall length of approximately 135 cm for coronary applications, with a spiral cut  3424  distal segment length of approximately 35 cm, for example. With reference to  FIG. 34D , which is a detailed view of a distal portion of the inner shaft  3420 , the cut pattern is illustrated as if the tube were laid flat with dimensions given in inches unless otherwise noted. The spiral cut  3424  may terminate proximal of the side port  3425  and flap  3426 . A hinge slot  3427  may be provided to allow the flap  3426  to hinge when devices are back loaded as described previously. A semi-circular slot  3428  may be provided to accommodate the end of the flap as described previously. A hole  3429  may be used to provide connection to the distal end of the orienting element (not shown) by pinning or welding, for example. 
     With reference to  FIGS. 34A and 34E , the orienting element  3440  may comprise a metallic tube (e.g., NiTi) with cuts made to define two wings  3442 A and  3442 B. In  FIG. 34E , the cut pattern of the orienting element  3440  is shown as if the tube were laid flat with dimensions given in inches unless otherwise noted. The cuts are made to define two separate wings  3442 A and  3442 B, with three hinge points  3443 ,  3444  and  3445  per wing  3442 . The proximal end  3446  of the orienting element  3440  is connected to a flared end of the outer shaft  3410 , and the distal end  3448  is connected to the distal end of the inner shaft  3420  and the proximal end of the tubular tip  3450 . By contracting the proximal end  3446  toward the distal end  3448 , the proximal hinge  3445  and the distal hinge  3443  flex outwardly to extend each wing  3442  outwardly, with the center hinge  3444  at the apex of each wing  3442 . 
     The distal tip  3450  may comprise a relatively soft polymeric tube segment, optionally loaded with radiopaque material. The inner liner  3430  may comprise a tubular extrusion  3432  or internal coating made of a low friction material such as high density polyethylene (HDPE) or polytetrafluoroethylene (PTFE). 
       FIGS. 34F-34H  schematically illustrate a method of using the orienting device  3400  described above. As mentioned previously, orienting device  3400  is designed to be advanced over a subintimal crossing device or guide wire, but subintimal guiding catheters may be used in addition to or in place of a crossing device or guide wire. For sake of illustration, the orienting device  3400  is shown over subintimal crossing device  1330  having an expandable and collapsible tip  1334  at the distal end of an elongate shaft  1332 , but the orienting device  3400  may also be advanced over a conventional guide wire (not shown), another subintimal device, or another similarly sized device advanced across the occlusion within the subintimal space. Using a device with a collapsible tip (e.g., subintimal crossing device  1330 ) or a device without an enlarged tip allows it to be removed through the center lumen of the orienting device  3400  such that a re-entry device may be subsequently advanced through the same lumen, thus using a single lumen for dual purposes and conserving device profile. 
     With reference to  FIG. 34F , once the subintimal crossing device  1330  extends across the occlusion within the subintimal space such that the tip  1334  is adjacent the distal end of the occlusion, the orienting device  3400  may be back-loaded (direction shown in  FIG. 34B ( 1 )) over the subintimal crossing device  1330  such that the shaft  1332  of the crossing device  1330  deflects the flap  3426  outwardly and extends through the center lumen of the orienting device  3400 . The orienting device  3400  may then be advanced over the subintimal crossing device  1330  until the distal end of the orienting device is adjacent the distal end of the occlusion. The tip  1334  of the subintimal crossing device  1330  may then be collapsed and withdrawn proximally. 
     With reference to  FIG. 34G , the orienting element  3440  may be expanded to extend the wings  3442 A and  3442 B in a substantially planar manner as shown. To facilitate expansion and contraction of the orienting element  3440 , an actuation mechanism  3460  may be used to push the outer shaft  3410  and pull the inner shaft  3420  relative to each other to cause expansion, or pull the outer shaft  3410  and push the inner shaft  3420  relative to each other to cause retraction. The actuation mechanism may comprise, for example, a fixed handle  3462  fixedly connected to the proximal end of the outer shaft  3410 , a rotatable handle  3464  rotatably connected to the proximal end of inner shaft  3420 , and a threaded shaft fixedly connected to rotatable handle  3464  that engages internal threads (not visible) in the fixed handle  3462 . The rotatable handle  3464  may engage a collar (not visible) on the proximal end of the inner shaft  3420  that permits relative rotation but prevents relative axial motion and therefore causes axial displacement of the inner shaft  3420  upon rotation of the rotatable handle  3464 . 
     With continued reference to  FIG. 34G  and additional reference to  FIG. 34H , the side port  3425  is either directed toward the vascular true lumen  116  or 180 degrees away from the vascular true lumen  116 . Radiographic visualization or other techniques as described elsewhere herein may be used to determine if the port  3425  is directed toward or away from the true lumen  116 . If the port  3425  is directed away from the true lumen  116 , the orienting device  3400  may be retracted, rotated 180 degrees, and re-deployed to direct the port  3425  toward the true lumen  116 . A re-entry device  3600  may then be front-loaded (direction shown in  FIG. 34B ( 1 )) through the center lumen of the orienting device  3400 . Although re-entry device  3600  is shown for purposes of illustration, other re-entry devices may be used as described elsewhere herein. As the re-entry device  3600  is advanced into the center lumen of the orienting device  3400 , the flap  3426  causes the distal end of the re-entry device  3600  to be directed out the side port  3425 . Further advancement of the re-entry device  3600  causes it to engage the vascular wall, and by action of the tip of re-entry device  3600  (e.g., rotational abrasion), it may penetrate the vascular wall and enter into the vascular true lumen  116  distal of the occlusion  120 . 
     Orienting Methods Using Planar Orienting Elements 
     Some of the orienting devices (e.g.,  3330 ,  3340 ,  3400 ) described hereinbefore have substantially planar orientation elements with an associated side port for delivery of a re-entry device. The side port is generally oriented at a right angle to the plane of the orienting element. With this arrangement, the side port is either directed toward the vascular true lumen or 180 degrees away from the vascular true lumen. In essence, the orienting device reduces the number of directions the side port may be facing from 360 degrees of freedom to two degrees of freedom, 180 degrees apart. The following is a description of methods to determine if the port is directed toward or away from the true lumen, thus reducing two degrees of freedom to one degree of freedom. Generally, if the side port is directed away from the true lumen, the orienting device may be retracted, rotated 180 degrees, and re-deployed to direct the side port toward the true lumen. A re-entry device as described elsewhere herein may then be advanced through the side port, through the vascular wall and into the true lumen. 
     One method of directing the side port toward the true lumen involves taking advantage of the curvature of the heart  100 . Generally speaking, the coronary arteries including the left anterior descending artery  110  as shown in  FIG. 35A  will follow the outside curvature of the heart  100 . An orienting device (e.g.,  3330 ,  3340 ,  3400 ) inserted into the coronary artery  110  via a guide catheter  200  seated in the ostium of the artery  110  will generally follow the outside curvature of the artery  110  within the subintimal space and across the occlusion  120 . In this scenario, as seen in  FIG. 35B , the true lumen  116  will lie toward the inside of the curvature of the artery  110  and thus the inside curvature (i.e., concave side) of the orienting device  3400 . Thus, the side port of the orienting device  3400  may be directed toward the concave side of the curvature which will predictably direct the side port toward the true lumen  116 . Directing the side port in this fashion may be facilitated by using radiographic visualization to view one or more radiopaque markers on the orienting device associated with the side port or a radiopaque device (e.g., guide wire) inserted into the orienting device just as it exits the side port. In addition or as an alternative, the orienting device may be pre-curved such that it naturally orients or “keys” with the curvature of the artery with the side port arranged on the concave side of the pre-curve. In addition or as an alternative, a radiopaque device (e.g., guide wire  700 ) may be substantially advanced and bunched within the subintimal space via a subintimal device (e.g., crossing device  300  or orienting device  3400 ) as shown in  FIG. 35C  such that the radiopaque device extends at least partially circumferentially to assume the curvature of the artery with the true lumen oriented toward the concave side thereof. 
     Alternative Re-Entry Devices 
     With reference to  FIGS. 36A-36G , alternative re-entry devices are schematically illustrated. These embodiments may be used with any of the orienting devices described previously, but are particularly suited for use with orienting devices  3330 ,  3340 , and  3400  described hereinbefore. Generally, each of the foregoing re-entry devices may be sized like a conventional guide wire, having a 0.014 inch diameter profile for coronary applications, for example. Also generally, each of the foregoing re-entry devices utilizes rotary abrasion as a mechanism to penetrate the intimal layer and enter into the true vascular lumen. 
     With specific reference to  FIG. 36A , and to  FIG. 36B  which is a detailed cross-sectional view of the distal end, re-entry device  3610  includes a distally tapered drive shaft  3612  which may comprise a metallic alloy such as stainless steel or NiTi, for example. The re-entry device  3610  may have a nominal profile of 0.014 inches and a length of 150 cm for coronary applications. The shaft  3612  may have a proximal diameter of 0.014 inches and a distal taper from 0.014 inches to 0.006 to 0.008 inches over approximately 4.0 inches. An abrasive tip  3620  may be connected to the distal end of the shaft  3612  by brazing or welding techniques. The shaft  3612  just proximal of the tip  3620  is configured with sufficient flexibility to allow flexure of the tip  3620  after it penetrates the vascular wall into the true vascular lumen, thus preventing penetration of the opposite vascular wall. The abrasive tip  3620  may comprise a metallic alloy tube  3622  such as stainless steel, platinum or platinum-iridium with a weld ball cap  3624 . The tube  3622  may have an inside diameter of approximately 0.007 inches and an outside diameter of approximately 0.0105 inches. An abrasive coating such as a  600  grit diamond coating  3626  may be applied to the outer surface of the tube  3622  with a thickness of approximately 0.0015 inches using conventional techniques available from Continental Diamond Tool (New Haven, Ind.). 
     With reference to  FIG. 36C , and to  FIG. 36D  which is a detailed cross-sectional view of the distal end, re-entry device  3610  further includes a distal coil  3630  disposed over the distal tapered portion of the shaft  3612 . The helical coil  3630  may comprise a stainless steel, platinum or platinum-iridium wire having a diameter of approximately 0.003 to 0.004 inches. The helical coil  3630  generally imparts enhanced torqueability without compromising flexibility of the tapered portion of the shaft  3612 . 
     With reference to  FIG. 36E , and to  FIG. 36F  which is a detailed cross-sectional view of the distal end, re-entry device  3610  alternatively includes a cable shaft  3614  comprising a 1 by 7 or 1 by 19 construction having an outside profile diameter of 0.014 inches, for example. The cable shaft  3614  construction generally imparts enhanced torqueability in at least one direction while increasing flexibility. 
     With reference to  FIG. 37 , a rotary drive unit  3700  is shown in perspective view. Rotary drive unit  3700  is particularly suited for use with re-entry device  3610  shown in  FIGS. 36A-36G , but may be used with other re-entry devices described elsewhere herein. Generally, the rotary drive unit  3700  provides for independent rotation and advancement of a re-entry device, wherein the rotation is provided by a motor and advancement is provided by shortening or lengthening a partial loop of an advancement sleeve that is attached at only one end and may be advanced/retract without moving the motor drive. 
     The rotary drive unit  3700  includes a base  3710  with two vertical mounting plates  3712  and  3714  attached thereto. A motor  3720  is mounted to plate  3714  and is linked by offset gears  3722  to a hollow drive shaft  3724 . A lock mechanism  3726  such as a hollow pin vise or collet is secured to the hollow drive shaft  3724 . The proximal shaft  3612  of the re-entry device  3610  may be secured to the locking mechanism  3726  such that activation of the motor  3720  by a suitable power supply causes rotation of the re-entry device  3610 . An advancement sleeve  3730  may be fixedly attached to the back side of vertical plate  3714  and coaxially aligned with the hollow drive shaft  3724  to receive the re-entry device shaft  3612  therethrough. The advancement sleeve  3720  extends in a semi-loop around limiting block  3716  and slidably through holes in vertical plates  3714  and  3712 . The advancement sleeve  3730  does not rotate but rather supports the rotating shaft  3612  of the re-entry device  3610  and thus may be manually held by the treating physician. The advancement sleeve  3730  may be advanced or retracted thus shortening or lengthening, respectively, the semi-loop thereof and thus advancing or retracting the re-entry device  3610  as it rotates. The advancement sleeve  3730  thereby provides tactile feel of the distal tip  3620  of the re-entry device  3610  as it engages tissue without being hampered by the rotary drive thereof 
     Additional Orienting Embodiment and Methods Using Planar Orienting Element 
       FIGS. 38A-38E  schematically illustrate an embodiment of an alternative orienting device  3800 . In this embodiment, the orienting device  3800  is designed to accommodate a subintimal crossing device or guide wire therein, similar to device  3400 . In addition, device  3800  includes bi-directional distal tip  3880  for orienting a re-entry device toward the true vascular lumen distal of a chronic total occlusion. With specific reference to  FIGS. 38A and 38B , detailed views of a distal portion of the orienting device  3800  are shown.  FIG. 38A  shows the device  3800  in a collapsed delivery configuration and  FIG. 38B  shows the device  3800  in an expanded deployed configuration. 
     The orienting device  3800  includes an elongate shaft  3810  including an outer tubular layer  3812  and an inner tubular layer  3814 . The inner layer  3814  extends through the outer layer  3412  and through the orienting element  3840 . The inner layer  3814  of the shaft  3810  defines a guide wire and re-entry device lumen  3860  extending therethrough. The outer layer  3812  may comprise a polymeric sheath and the inner layer  3814  may comprise a metallic material. For example, the outer layer  3812  may comprise a polymeric sheath made of a suitable low friction polymer (e.g., HDPE or PTFE) that concentrically covers the inner layer  3814  and houses several tension members as will be described in more detail hereinafter. Also by way of example, the inner layer  3814  may comprise a flexible metallic construction such as a stainless steel coil adjacent to or proximal of the orienting element  3840 , transitioning to a super elastic alloy tube (e.g., nitinol) adjacent to or distal of the orienting element  3840 . 
     The orienting element  3840  may include oppositely opposed wings  3842  connected at the proximal end by proximal collar  3844  and connected at the distal end by distal collar  3846 . The proximal collar  3844  may be connected to the inner layer  3814  of the shaft  3810  by suitable attachment means (e.g., swaging, adhesive bonding, laser welding, etc.). The distal collar  3846  may be slidably disposed about the inner layer  3814 , and connected to a tension member  3820  by suitable attachment means (e.g., swaging, adhesive bonding, laser welding, etc.). The tension member  3820  may comprise a metallic ribbon or multifilament fiber that extends proximally to the proximal end of the shaft  3810  between the inner  3814  and outer  3812  layers thereof. The orienting wings  3842  may be parallel to the shaft  3810 , including the central guide wire/re-entry device lumen  3860 . The orienting element  3840  may be made of a suitable radiopaque metallic material such as stainless steel or super elastic alloy (e.g., nitinol). 
     The orienting element  3840  may have a substantially planar shape (shown) when expanded, or may have a curved shape (not shown) when expanded to at least partially conform to the curvature of the vascular wall. The orienting element  3840  may be actuated by longitudinal displacement of the tension member  3820 . Pulling on the tension member relative to the shaft  3810  causes the orienting element  3840  to expand. Conversely, releasing the tension member  3820  relative to the shaft  3810  causes the orienting element  3840  to collapse by elastic recovery of the wings  3842 . 
     A distal section of the inner layer  3814  may have material selectively removed therefrom to form an articulation zone  3835 . For example, material may be selectively removed from the inner layer  3814  in the articulation zone to form an open pattern that allows lateral flexibility of the tip  3880  and defines two directions of bending that are generally at a right angle to the plane of the wings  3842 . For example, material may be removed creating a pattern that consists of individual rings that are attached by two 180 degree circumferentially opposed longitudinal spines. This open pattern may be cut into the inner layer  3814  using, for example, a YAG laser. The articulation zone  3835  may be defined by other hinge-type mechanisms that selectively permit deflection in two directions orthogonal to the plane of the orienting element  3840  when expanded. 
     The bi-directional tip  3880  may direct the guide wire and re-entry lumen  3860  from its initial substantially axial orientation (e.g., 0 degrees) to a positively angled orientation (e.g., +30 to +90 degrees) or a negatively angled orientation (e.g., −30 to −90 degrees). The bi-directional tip  3880  may be generally oriented at a right angle to the plane defined by the wings  3842  of the orienting element  3840 . With this arrangement, when actuated to an angled orientation, the tip  3880  is either directed toward the vascular true lumen or 180 degrees away from the vascular true lumen. In essence, the orienting device reduces the number of directions the tip may be facing from 360 degrees of freedom to two degrees of freedom, 180 degrees apart. Two degrees of freedom are further reduced to one degree of freedom (directed toward the true lumen) through the use of fluoroscopy. Using a fluoroscope, a physician obtains views (e.g., orthogonal views) of the vascular and/or anatomic features of the heart and surrounding anatomy and compares these features with the position and radiopaque elements of the orienting element  3840  or tip  3880 . This comparison allows the physician to determine the direction the bi-directional tip is pointing with respect to the true vascular lumen. Once the direction of the vascular true lumen and catheter tip is determined, a re-entry device may be advanced through the central lumen  3860  of the shaft  3810 . This directs the re-entry device toward the true lumen. Any of the re-entry devices described herein may thus be used to penetrate the targeted vascular wall for the ultimate delivery of a guide wire as described previously. 
     Three radiopaque marker bands made from materials that are more visible under fluoroscopy (e.g., platinum, platinum-iridium, or gold) may be fixed to the shaft  3810  via a suitable attachment technique such as adhesive bonding, spot welding or laser welding. Two of the radiopaque marker bands may be positioned, for example, at or adjacent the proximal collar  3844  and the distal collar  3846  of the orienting element  3840 . Another of the radiopaque bands may be positioned at or adjacent the distal tip  3880  of the inner layer  3814  of the shaft  3810 . One of the functions of the distal most radiopaque mark is to show a physician the position of the distal end of the catheter as well as the orientation of the tip (positively or negatively angled) upon actuating the bi-directional tip. The radiopaque marks at either end of the wings may serve to indicate the position (expanded or collapsed) of the orienting wings. 
     Generally aligned in the center of the open pattern of the articulation zone  3835 , 180 degrees circumferentially opposed, are two tension members, one of which is visible, namely tension member  3850 , both of which run the length of the shaft  3810  between the inner layer  3814  and the outer layer  3812 . One of the tension members  3850  is visible on the top of the inner layer  3814  of the shaft  3810 , and the other is not visible but resides diametrically opposed on the bottom of the inner layer  3814  of the shaft  3810 . The tension members may be made from a suitable metallic material such as nitinol or stainless steel. Each tension member may be fixedly attached to the distal end of the tip  3880  of the inner layer  3814  of the shaft  3810  by collar  3870  via a suitable technique such as spot welding or laser welding, while the rest of each tension member is slidably disposed between the inner layer  3814  and the outer layer  3812  of the shaft  3810  over the length of the shaft  3810  to the proximal end thereof. By pulling on tension member  3850  residing on top of the inner layer  3814 , the tip  3880  may be actuated in one direction (e.g., up) as shown in  FIG. 38C . By releasing tension member  3850  and pulling on the other tension member (not shown), the tip  3880  may be actuated in the opposite direction (e.g., down) as shown in  FIG. 38D . The tension members may thus be selectively actuated to selectively deflect the tip  3880  and direct the lumen  3860  toward the true lumen as described herein. Those skilled in the art will recognize that the tension members may alternatively be replaced by push members for actuation of the tip  3880 . Actuation (e.g., pulling) of the tension members may be controlled by a suitable mechanism (not shown) located at a proximal end of the shaft  3810 . 
     Actuation of the orienting element  3840  as described above may be referred to as active actuation with passive return. In other words, active actuation (i.e., pulling on the tension member  3820  relative to the shaft  3810 ) causes the orienting element  3840  to expand, and passive return (i.e., releasing the tension member  3820  relative to the shaft  3810 ) causes the orienting element  3840  to collapse by elastic recovery of the wings  3842 . 
     As an alternative, actuation of the orienting element may comprise active actuation and active return. In this alternative embodiment, which is illustrated in  FIG. 38E , the orienting element  3840  is actively actuated and actively collapsed using a looped tension member  3890 . In this embodiment, the distal collar  3846  of the orienting element is fixed to the inner layer  3814  of the shaft  3810  by the aforementioned means, while the proximal collar  3844  is slidably disposed about the inner layer  3814  of the shaft  3810 . The flexible tension member  3890  may comprise, for example, a braided polymeric fiber such as Vectran™ or Dyneema™. One half of the looped tension member  3890  extends along the shaft  3810  from the proximal end thereof (not shown), under a proximal collar  3832 , and is fixedly connected to the proximal collar  3844 . The other half of the looped tension member  3890  extends along the shaft  3810  from the proximal end thereof (not shown), under the proximal collar  3832 , over the top of the bearing plate  3830 , and is fixedly connected to the proximal collar  3844  of the orienting element  3840 . At the distal end of the bearing plate  3830 , the tension member  3890  is looped around a 180 degree bend. Collar  3832  functions to contain the looped tension member  3890  and functions as a proximal mechanical stop for the proximal collar  3844  of the orienting element  3840 . The bearing plate  3830  may be a metallic or polymeric element that is fixedly attached (e.g., by adhesive bonding, spot or laser welding) to the inner layer  3814  of the shaft  3810  over a cut-out window. The bearing plate  3830  functions as a bearing surface or pulley for the tension member loop  3890  and functions as a distal mechanical stop for the proximal collar  3844  of the orienting element  3840 . The looped tension member  3890  along with an associated mechanical actuation mechanism at the proximal end of the catheter (not shown) allows the physician to actively and forcibly expand the orienting element  3840  by pulling on one end of the loop  3890 , and actively and forcibly collapse the orienting element  3840  by pulling on the other end of the loop  3890 . 
     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.