Abstract:
A method and systems for treating chronic total occlusions, particularly those that are difficult to treat, is disclosed. In this approach, recanalizing the CTO is achieved using a combined antegrade and retrograde approach. The proximal end of the occlusion is penetrated using an antegrade wire, using a traditional approach. Using collateral vessels, the distal end of the occlusion is crossed in a retrograde fashion. By appropriately maneuvering each member and applying radiofrequency energy between the proximal and distal ends of the occlusion, a continuous channel is created.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. application Ser. No. 12/753,844, filed Apr. 2, 2010, titled “Recanalizing Occluded Vessels Using Radiofrequency Energy”, which is a continuation-in-part of U.S. application Ser. No. 12/680,500, a national stage application under 35 U.S.C. §371, filed Mar. 26, 2010, titled “Recanalizing Occluded Vessels Using Radiofrequency Energy”, which claims priority from PCT Application No. PCT/US2008/077403, filed Sep. 23, 2008, which claims the priority benefit of U.S. Provisional Application No. 60/975,473, filed Sep. 27, 2007. U.S. application Ser. No. 12/753,844 also claims priority to U.S. Provisional Application Ser. No. 61/298,547, filed on Jan. 26, 2010, titled “Recanalizing Occluded Vessels Using Radiofrequency Energy”. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to dealing with occlusions of the lumen and more specifically to apparatus and methods for crossing severe or total chronic occlusions of lumens in the body using radiofrequency energy. 
       DESCRIPTION OF THE RELATED ART 
       [0003]    Chronic total occlusion (CTO) is the complete blockage of a vessel and may have serious consequences if not treated in a timely fashion. The blockage could be due to atheromatous plaque or old thrombus. One of the common procedures for treating CTOs of the coronary arteries is percutaneous transluminal coronary angioplasty (PTCA). During a PTCA procedure, a small incision is typically made in the groin. A guiding catheter over a guidewire is introduced into the femoral artery and advanced to the occlusion. At times, with gentle maneuvering, the guidewire is able to cross the occlusion. A balloon-tipped angioplasty catheter is then advanced over the guidewire to the occlusion. The balloon is inflated, separating or fracturing the atheroma. Often times, a stent is subsequently or simultaneously deployed. Some of the common steps involved in the PTCA procedure for CTOs are the simultaneous injection of a contrast agent in the contra-lateral vessel, securing backup force or stabilization for a guidewire (which could invoke additional personnel to handle the catheter), puncturing the plaque, drilling or rotating the guidewire to push it through the dense plaque, etc. Because of the stiff resistance sometimes offered by dense plaque, one could be forced to use stiff wires. Occasionally, the wires could puncture the vessel wall calling for remedial measures. 
         [0004]    The most common percutaneous coronary intervention (PCI) failure mode for CTOs is inability to successfully pass a guidewire across the lesion into the true lumen of the distal vessel. To date, there is no consensus on how best to treat CTO after attempts with conventional guidewires have failed. Different strategies for CTOs have been developed including the side branch technique, the parallel wire technique, and the IVUS guided technique. Mechanical and energy based devices have also been proposed for passing guidewires through hard calcified occlusions, such as mechanical cutting or oscillation and laser or ultrasound or radiofrequency (RF) energy ablation. Each of these devices works by strictly utilizing an antegrade approach and locally applying energy (typically in the form of heat) at the tip of the guidewire or catheter device in order to create a channel and hopefully enter the distal true lumen. 
         [0005]    RF energy is widely used to coagulate, cut or ablate tissue. In both modalities, monopolar and bipolar, conductive electrodes contact the tissue to be treated. In the monopolar mode, the active electrode is placed in contact with the tissue to be treated and a return electrode with a large surface area is located on the patient at a distance from the active electrode. In the bipolar mode, the active and return electrodes are in close proximity to each other bracketing the tissue to be treated. Sometimes an array of electrodes is used to provide better control over the depth of penetration of the RF field and hence control over the temperatures to which the tissue is heated. There are many disadvantages with each mode. For example, in the monopolar arrangement, because of the large physical separation between the electrodes there are frequent reports of local burning at the electrode sites. This would clearly be undesirable where one of the electrodes will be inside a blood vessel. The other serious issue is the likelihood of forming blood clots. The tissue that is in contact with the electrodes can be coagulated or ablated. In the case of the electrodes being present inside a blood vessel, the formation of dangerous blood clots would obviously be undesirable. 
         [0006]    In an attempt to overcome the issues described above, various device and electrode configurations are described in the following patents. U.S. Pat. Nos. 5,366,443 and 5,419,767 describe the use of RF electrodes on a catheter to cross a lesion. These patents describe a bipolar electrode assembly at the distal tip of a catheter that is in contact with the occlusion, and patentees state that application of RF energy ablates the occlusion and renders the occlusion susceptible for the guidewire to penetrate. This method has the drawback that careful tracking of the occlusion and the ablation process is necessary to avoid trauma to the vessel walls or healthy tissue, since the possibility of short-circuiting of current through healthy tissue instead of the occlusion is high. U.S. Pat. No. 5,419,767 overcomes this limitation to a certain extent through the use of a multiple electrode array. However, this device requires a channel to be pre-created through the occlusion so that the device can be passed through a guidewire traversing this channel, which is not always easy. 
         [0007]    U.S. Pat. No. 5,514,128 to Hillsman et al. describes a laser catheter device that enables ablation of an occlusion in the vasculature. This system has similar drawbacks to the ones described above—need for a guidance system, potential for healthy tissue to be ablated, complexity (and hence cost) of the device, etc. 
         [0008]    One major problem with the existing devices is the potential for the ablation energy to damage the walls of the vasculature, in the absence of a mechanism to track the orientation and position of the energy delivery member. Several devices exist in the prior art that address the issue of tracking and steering of the energy delivery element. U.S. Pat. No. 6,911,026 to Hall et al. describes a magnetic steering and guidance system to direct an ablation device that delivers RF energy at the tip in a unipolar configuration where the return electrode is placed externally in contact with the body or in a bipolar configuration where the return electrode is a ring surrounding the central wire electrode. 
         [0009]    U.S. Pat. No. 6,416,523 to Lafontaine discusses a mechanical cutting device where the guidance is provided by measuring impedance of the tissue in contact. The guidance system senses the difference in impedance between the stenotic tissue and the vessel wall and directs the cutting element to the occlusion. 
         [0010]    However, none of these alternate strategies have provided satisfactory results for the most challenging of the CTOs. In case of hard calcified occlusions, the revascularization procedure can be tedious and time consuming. Therefore, there is a need for improved methods of ablating or disrupting the occlusive material that are safe, efficacious and fast. It would be beneficial to have alternate techniques and devices that would recanalize a CTO without the shortcomings of the current techniques. 
         [0011]    CTOs that are hard to recanalize, either because of the tortuous anatomy of the diseased vessel, or because the proximal end of the stenosis is too hard for the guide wire to penetrate, or other characteristics of the CTO that would make the standard procedure vulnerable to failure would benefit from newer approaches to recanalize CTOs. Recently a combined antegrade-retrograde approach has been proposed for recanalizing chronic occlusions (U.S. application Ser. No. 11/706,041). The method disclosed in the co-pending application would benefit from the use of energy for crossing CTOs. 
       SUMMARY OF THE INVENTION 
       [0012]    Various methods and devices are provided to overcome some of the commonly encountered problems in treating chronic total occlusions. One aspect of this invention is to provide a method and systems for successfully recanalizing an occluded vessel by advancing, in combination, guidewires in an antegrade and retrograde fashion to the occlusion and applying RF energy between the proximal and distal ends of the occlusion. The RF energy application across the occlusion is accomplished using a bipolar arrangement, where one electrode is located on the antegrade guidewire and the other electrode that makes up the bipolar arrangement is located on the retrograde guidewire. In one aspect, the present invention discloses a method of recanalizing an occluded vessel comprising advancing in an antegrade fashion a first longitudinal member through a proximal end of an occlusion, advancing in a retrograde fashion a second longitudinal member through a distal end of the occlusion, applying RF energy between the distal ends of the antegrade and retrograde guidewires, ablating the tissue locally, and creating a channel through which a guidewire could be advanced. In another embodiment, the retrograde guidewire could have a deployable capture mechanism at its distal end and upon deployment could snare the antegrade guidewire. 
         [0013]    In another aspect, this invention relates to a catheter assembly for recanalizing an occluded vessel comprising an antegrade longitudinal member with a distal end containing an RF electrode and a retrograde longitudinal member with a distal end containing a second RF electrode; and the proximal end of the catheter assembly connected to an RF generator. Additionally, a temperature measuring element could be disposed on the distal ends of the antegrade or retrograde longitudinal member. The RF generator could also be programmed to treat the tissue for a pre-set time or until a set condition has been reached. One such condition could be till the occlusion has reached a pre-determined temperature. Another condition could be the impedance of the occlusion. 
         [0014]    In another aspect, the invention is a kit for recanalizing occluded vessels comprising one or more of the following: an antegrade guidewire, a retrograde guidewire, a dilating device, a capture device and an injection catheter, wherein at least one of these devices contains at least one electrode. Additionally, the proximal ends of this device are configured to be coupled with an RF generator. 
         [0015]    In another aspect, a system for recanalizing occluded vessels may comprise two antegrade longitudinal members, wherein at least one longitudinal member may comprise a distal end that is capable of being redirected. The redirected distal end may substantially position in a retrograde fashion towards the occlusion. Alternatively, the redirected distal end may be substantially positioned towards the distal end of another longitudinal member. In another aspect, at least one longitudinal member may comprise an interior lumen configured to deliver a fluid to the occlusion. 
         [0016]    In yet another aspect, the invention relates to a catheter positioning system with a balloon catheter comprising an inflatable balloon, a delivery catheter disposed within the balloon catheter, wherein upon inflation of the balloon, a position of the balloon catheter is substantially fixed, and wherein the delivery catheter is configured to advance through the balloon catheter without substantially altering the position of the balloon catheter. 
         [0017]    Other aspects of the invention include methods corresponding to the devices and systems described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The invention has other advantages and features which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which: 
           [0019]      FIG. 1  is a schematic showing an RF generator connected to the longitudinal members. 
           [0020]      FIG. 2  shows the features of the longitudinal members. 
           [0021]      FIGS. 2A-2B  show various embodiments of longitudinal members comprising insulators. 
           [0022]      FIGS. 3A and 3B  show the steps involved in recanalizing a CTO using bipolar RF and combined antegrade and retrograde approach. 
           [0023]      FIGS. 3C-3E  show embodiments of electrodes configured to expand outwardly. 
           [0024]      FIG. 4  shows an example embodiment of a longitudinal member comprising an embolic protection mechanism. 
           [0025]      FIGS. 5A-5C  show a longitudinal member structurally configured along at least part of the length of the catheter to enable advancement or alignment of the longitudinal member through a narrow diameter blood vessel or occlusion. 
           [0026]      FIG. 6  shows one embodiment of the recanalization system comprising a longitudinal member that is capable of being redirected. 
           [0027]      FIG. 7  shows a flow diagram of various steps involved in performing the recanalization of the body vessel according to the present embodiments. 
           [0028]      FIGS. 8A-8F  show various stages of recanalization of the body vessel according to the present embodiments. 
           [0029]      FIGS. 9A-9B  show one embodiment of the recanalization system comprising a delivery element. 
           [0030]      FIG. 10  shows one embodiment of the recanalization system utilizing radio frequency energy. 
           [0031]      FIG. 11  shows a flow diagram of various steps involved in performing the recanalization of the body vessel utilizing radio frequency energy. 
           [0032]      FIG. 12  shows one embodiment of the centering balloon catheter system. 
           [0033]      FIG. 13A-13B  show one embodiment of the centering balloon catheter system comprising helical groves. 
           [0034]      FIG. 14  shows one embodiment of longitudinal member comprising an lumen. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    Although the detailed description contains many specifics, these should not be construed as limiting the scope of the invention but merely as illustrating different examples and aspects of the invention. It should be appreciated that the scope of the invention includes other embodiments not discussed herein. Various other modifications, changes and variations which will be apparent to those skilled in the art may be made in the arrangement, operation and details of the method and apparatus of the present invention disclosed herein without departing from the spirit and scope of the invention as described here. 
         [0036]    The present embodiments combine the use of RF energy delivered through antegrade and retrograde members for recanalizing occluded lumens, particularly chronic total occlusions. The methods and systems described herein recanalize difficult to cross occlusions by taking advantage of an antegrade and retrograde approach to establish a bipolar electrode arrangement across the occlusion. This approach minimizes the potential of the vessel wall becoming perforated or injured, as may otherwise occur in a conventional bipolar RF treatment approach, where both RF electrodes are on the same side of the occlusion. Because the electrodes are distributed on opposite sides of the occlusion, the tissue that is ablated by the RF treatment (i.e., the occlusion) is well contained between the electrodes. This also allows the user to localize the treatment to the occlusion. 
         [0037]    As disclosed in the co-pending U.S. patent application Ser. No. 11/706,041 by the same inventors, which is incorporated herein in its entirety, in the controlled antegrade and retrograde tracking (CART) technique the retrograde approach takes advantage of an intercoronary channel. Such a channel may be an epicardial channel, an inter-atrial channel, an intra-septal channel (also referred to as septal collateral), or a bypass graft. The basic concept of the CART technique is to create a channel through an occlusion, preferably with limited dissections, by approaching the occlusion both antegradely and retrogradely. 
         [0038]    While the combined antegrade and retrograde approach has been effective in crossing difficult to cross lesions, it has been observed that using energy, for example RF energy, to ablate or alter the tissue in a controlled fashion is beneficial in crossing hard to cross lesions. Such controlled energy deployment is achieved using a bipolar arrangement of the electrodes, where one electrode is located on the antegrade element and the other electrode that constitutes the bipolar arrangement is located on the retrograde element. These electrodes can also be referred to as the return and active electrodes. They are also referred to as the anode and cathode, respectively. The electrodes could also be arranged in an array (multiple electrodes), where the electrode arrangement provides better control over the depth of penetration of the RF field and thereby provides the ability to control the tissue temperature. 
         [0039]      FIG. 1  shows a system for recanalizing occluded vessels using RF energy. The system comprises longitudinal members  100   a  and  100   b  for delivering RF energy to an occlusion. As indicated in  FIG. 1 , longitudinal member  100   a  serves as an antegrade member and longitudinal member  100   b  serves as a retrograde member. An RF generator  10  (also referred to as a controller) serves as the source of RF energy to be provided to longitudinal members  100   a  and  100   b . Optionally, the RF generator may be a hand-held battery-operated device. Longitudinal members  100   a  and  100   b  may be guidewires, catheters, micro-catheters, or dilating catheters. In a preferred embodiment, longitudinal members  100   a  and  100   b  are guidewires. Thus, while in the following description the term “guidewire” is used to refer to a longitudinal member  100   a  or  100   b , it is understood that the term “guidewire” as used herein is intended to include any other type of longitudinal member. 
         [0040]    To provide RF energy from the RF generator  10  to the guidewires  100   a  and  100   b , a pigtail  20  connects at its proximal end to the RF generator  10  and terminates at its distal end in a connector  30 . Connector  30  is a standard connector that couples the input and output signals of the RF generator  10  to the guidewires  100   a  and  100   b.    
         [0041]    One embodiment of the connector would be a locking tool or torque device which can be placed over the guidewire. In such a configuration, the locking tool or torque device is configured to make electrical contact with a portion of the guidewire (such as the guidewire corewire) that conducts radiofrequency energy to, or from, the one or more electrodes disposed on the guidewire. In such a configuration, the locking tool or torque device would also be configured to connect to a radiofrequency generator, thereby electrically connecting the generator to the guidewire and electrodes. Means of locking the connector to the guidewire may include compressible prongs, screws, sliding rings, or other mechanisms commonly utilized in torque devices. 
         [0042]    Guidewires  100   a  and  100   b  are configured to have sufficient torsional rigidity and longitudinal flexibility to advance through an occlusion, and to align their electrodes in a direction away from the vessel wall, towards the other guidewire, or any combination thereof. 
         [0043]    As shown in  FIG. 2 , the antegrade and retrograde guidewires  100   a  and  100   b  have conductive electrodes  105   a  and  105   b , respectively, at their distal ends. In one embodiment, the electrodes  105   a  and  105   b  are located on one side of their respective guidewires  100   a  and  100   b , thereby providing the operating physician with the freedom to allow the electrode-free side of the guidewire to touch the vessel wall (if needed) while still directing the RF energy away from the vessel wall. Additionally, this allows the configuration to direct the RF energy away from the vessel wall, thereby minimizing potential RF injury to the vessel wall. In one embodiment, one or more of the guidewires comprises a plurality of electrodes arranged in an array. 
         [0044]    Conductive wires (not shown) connect the electrodes  105   a  and  105   b  of the antegrade and retrograde guidewires, respectively, to connector  30  to deliver RF energy from the RF generator  10  to the electrodes  105   a  and  105   b . The exterior of the antegrade and retrograde guidewires are covered by non-conductive layers  115   a  and  115   b , respectively, which sandwich the conductive wires between the guidewires and the non-conductive layers. In one embodiment, the non-conductive layers  115   a  and  115   b  comprise a sheath or a coating. Example of materials may include Teflon, ceramic, polyimide, parylene, or other suitable materials. Examples of methods which could be employed for coating may include spraying, dipping, vapor deposition, or plasma deposition. In another embodiment, the conductive wires are insulated by using a heat resistant material on the guidewire to protect the device and surrounding tissue from excessive heat.  FIG. 2A  shows a cross-sectional view of a guidewire comprising an electrode and an insulator, in accordance with an embodiment of the present invention. A guidewire  200  comprises an electrode  210  as its distal tip. The electrode  210  is electrically coupled to the guidewire&#39;s corewire via an electrically conductive ribbon  220  or other such electrically conductive connector. An insulator  230  is disposed at a distal portion of the guidewire  200  to deflect some of the heat that is generated when the electrode  210  is energized with radiofrequency energy, thereby protecting the rest of the device from such heat. The insulator  230  may wrap around the distal portion of the guidewire  200 , as shown in  FIG. 2A , or it may be configured as a plurality of discrete pieces disposed at the distal portion of the guidewire  200 . The insulator may or may not directly contact electrodes. 
         [0045]    In another embodiment, the insulator may be configured to protrude forward so that the electrode is recessed. An example of this is shown in  FIG. 2B , showing a protruding insulator  240  configured to extend beyond the electrode  210 , thereby recessing the electrode  210 . This limits the exposure of the electrode  210  to surrounding tissue, while leaving the electrode sufficiently exposed to create the bipolar arrangement. 
         [0046]    In one embodiment, and as further shown in  FIG. 2 , the guidewires  100   a  and  100   b  comprise temperature measuring elements  110   a  and  110   b  at the distal tip of the antegrade and retrograde guidewires, respectively. In one embodiment, the temperature measuring elements  110   a  and  110   b  comprise thermocouples or thermistors that are connected to the connector  30 . In another embodiment, pressure measuring elements are placed on the distal ends of the guidewires to detect a change in pressure upon activation of the RF energy. 
         [0047]    RF generator  10  is configured to allow the user to set a maximum temperature, a treatment time period, a level of RF power, or a combination of these control parameters. The treatment time period indicates the period of time over which the RF energy will flow between the electrodes. The maximum temperature setting serves as a threshold temperature for the tissue that is in contact with the electrodes, and the RF generator  10  can be set to reduce or shut off power to one or both electrodes when one or more of the temperature measuring elements  110   a  and  110   b  indicate a tissue temperature at or near the threshold. 
         [0048]    In one embodiment, the generator  10  is capable of measuring the impedance of the tissue between the two electrodes  105   a  and  105   b . Based on the type of the occlusion (i.e., the nature of the calcified material), the user can choose the appropriate combination of temperature, treatment time, and the amount of RF energy to be provided to the tissue to achieve a safe and effective treatment. Alternatively, the treatment may proceed with the user manually controlling the parameters during the recanalization procedure, with the user treating the occlusion until recanalization is achieved. 
         [0049]    The sequence of the recanalization treatment steps are illustrated in  FIGS. 3A and 3B . As shown in diagram A of  FIG. 3A , the antegrade guidewire  100   a  and retrograde guidewire  100   b  are advanced to the proximal and distal ends  310   a  and  310   b  of the occlusion  310 , respectively. This can be accomplished using standard angioplasty techniques. As described in the above referenced co-pending U.S. patent application Ser. No. 11/706,041, the retrograde guidewire can be advanced to the distal end of the occlusion  310   b  using collaterals such as the septals. 
         [0050]    Once the user has confirmed that the guidewires  100   a  and  100   b  are in contact with the occlusion  310  and are not touching the vessel wall  300 , the RF treatment is initiated. 
         [0051]    Alternatively, the guidewires are advanced as deep into the occlusion as possible to minimize the distance between the electrodes and, consequently, minimize the length of the ablation zone. Confirmation that the guidewires  100   a  and  100   b  are in an appropriate position can be generated by impedance measurements and/or by using any of the standard imaging techniques employed during interventional procedures, such as fluoroscopy or intravascular ultrasound (IVUS), in which transducers are placed on the distal ends of the guidewire. When using tissue impedance measurements, the calcified occlusion  310  generally exhibits significantly higher impedance than the vessel wall  300 . If an impedance measurement indicates a low impedance value, it is likely that one or both guidewires are in contact with the vessel wall  300 , and appropriate repositioning of the guidewires may be warranted. 
         [0052]    Upon initiating the recanalization RF treatment, the occlusion  310  is ablated from the ends  310   a  and  310   b  of the occlusion  310  to the interior of the occlusion  310 , as shown in  FIG. 3A  diagram B. The user then slowly and carefully advances one or both guidewires  100   a  and  100   b  until a channel or path is created in the occlusion  310 , as shown in  FIG. 3A  diagram C. As shown in  FIG. 3A , the antegrade guidewire  100   a  may be kept stationary and the retrograde guidewire  100   b  may be advanced through the occlusion  310 . Once a channel has been created, the retrograde guidewire  100   b  may be withdrawn and the antegrade guidewire  100   a  may be advanced through the occlusion  310 , as shown in  FIG. 3A  diagram D, and standard interventional procedures, such as balloon angioplasty, can be performed. Alternatively, the retrograde guidewire  100   b  can be kept stationary during the RF treatment and the antegrade guidewire  100   a  can be advanced through the occlusion  310 . This is illustrated in  FIG. 3B  diagrams A-D. 
         [0053]    It is noted that energizing an electrode with radiofrequency energy causes the electrode to generate heat. In general, the amount of such heat is proportional to the amount of radiofrequency energy delivered to the electrode, and inversely proportional to the surface area of the electrode. This is because the smaller the surface area of an electrode, the higher the current density passing through that surface area (for a given total current), which in turn causes the electrode to reach correspondingly higher temperatures. In one embodiment, the system is configured to deliver sufficient radiofrequency energy to an electrode such that radiofrequency sparks are generated. 
         [0054]    While it is possible to have the surface areas of the active and return electrodes be of similar size, in a preferred embodiment an active electrode is configured to have a smaller surface area than a return electrode. This allows the active electrode to generate sufficient current or energy density to affect cutting or ablating and spark cover to the return electrode, while at the same time allowing the return electrode surface area to be sufficiently large so as to maximize its contact with the occlusion and act as a sink for the energy emitted from the active electrode. Another advantage of such an embodiment is that the return electrode will likely not reach as high temperatures as the active electrode. In one embodiment, the ratio of the return electrode surface area to the active electrode surface area is configured to be in the range of about 50:1 to about 1:1, and preferably about 10:1. In one embodiment, the return electrode is configured in a pigtail design to increase surface area contact with the occlusion. 
         [0055]    In another embodiment, a plurality of return electrodes may be configured to expand outwardly in order to spread out and increase surface area contact with the occlusion. Such an embodiment is shown in  FIG. 3C , where a plurality of ribs  310  are disposed on a distal end  320  of a guidewire  300 . The ribs  310  are configured to flare out, as shown in  FIG. 3D . In a collapsed state, the ribs  310  are kept under tension, for example by using a restraining sleeve (not shown), by twisting the ribs  310 , by exerting a stretching or pulling force on the proximal ends of the ribs  310 , etc. The guidewire  300 , with the ribs  310  in a collapsed state, is advanced into the occlusion. Upon releasing the tension or pulling back on the restraining sleeve, the ribs  310  flare open. 
         [0056]    In another embodiment, the ribs  310  comprise electrode areas  330  adjacent to insulator areas  340 , as shown in the cross-sectional view of  FIG. 3E . In such an embodiment, when the ribs  310  flare out into a basket-like configuration, the insulator areas  340  are on the outside and the electrode areas  330  are on the inside of the basket-like configuration. This configuration advantageously aids in directing radiofrequency energy inside the basket-like configuration while simultaneously providing protection to the surrounding tissue. Alternatively, it is contemplated that in other embodiments the placement of the electrode areas  330  and insulator areas  340  may be varied. In an optional embodiment, a capture device may be configured to comprise one or more electrode areas for use as return electrodes. Examples of capture devices are disclosed in the co-pending U.S. patent application Ser. No. 12/150,111 by the same inventors, which is incorporated herein in its entirety. 
         [0057]    Optionally, a centering balloon catheter can be utilized along with the guidewire to center the guidewire within the vessel prior to energizing the system. In such a configuration, it would be advantageous to have a heat resistant tip on the distal end of the balloon catheter. 
         [0058]    Optionally, the catheter comprises a means for removing or withdrawing debris resulting from the RF ablation. For example, a mechanism could be provided to capture and retrieve the debris, or a suction device could be provided to actively remove the debris near the ablation area. Examples of such embolic protection mechanisms are disclosed in the above referenced co-pending U.S. patent application Ser. No. 11/706,041.  FIG. 4  shows an exemplary embodiment of a longitudinal member  400  comprising an embolic protection mechanism  410 . The embolic protection mechanism  410  comprises a filter, mesh, net, or similar element, for capturing and retrieving ablation debris. As another example, the embolic protection may comprise a balloon for occluding the vessel and preventing the debris from circulating, and for subsequent aspiration of the debris through a longitudinal member. As another example, if a sheath is provided, such sheath may also be configured to be or to include a debris capture and retrieval mechanism or a suction device. In one embodiment, a longitudinal member may be retracted, and the remaining sheath may be used as a capture and retrieval mechanism or a suction device to remove ablation debris. In another embodiment, the longitudinal member comprises an ablating wire housed in the lumen of a dilating catheter. Upon ablation, the ablating wire may be retracted and the dilating catheter may be used to remove the debris. Alternatively, the system comprises a separate catheter to provide suction, or otherwise capture and remove the debris from the ablation site. 
         [0059]    Optionally, the device may be coupled to an electrocardiogram (EKG) machine to aid in timing energy emissions. For example, the rate of blood flow through the coronary arteries typically varies during the cardiac cycle. During systole when the heart is contracting, flow through the arteries is generally lower than during diastole. In one embodiment, energy emission is timed during diastole, for example using an algorithm to detect the R-wave of an EKG, and energy emission is timed to occur when flow is highest, thereby maximizing the cooling effect provided by blood flow and consequently minimizing the heat exposure to the vessel. Additionally, coronary artery dimensions can vary during the cardiac cycle and energy emission can similarly be timed to take advantage of this fact. 
         [0060]    Optionally, the device may be configured to perform an imaging function, such as intravascular ultrasound or optical coherence tomography (OCT). In one embodiment, this may be accomplished by adding a piezoelectric crystal to a longitudinal member of the device, wherein the piezoelectric crystal may be energized to transmit or receive ultrasonic waves. In another embodiment, an imaging core may be inserted into a longitudinal member of the device (e.g., in the case of a dilating catheter) and operated to transmit and receive ultrasonic waves. In another embodiment, an optical fiber may be used for performing OCT imaging. 
         [0061]    Optionally, the device comprises a mechanism for detecting or estimating the distance between the electrodes, and for decreasing the amount of delivered RF energy as the distance between the electrodes decreases, thereby minimizing potential RF injury to the vessel wall. 
         [0062]    In another embodiment, the device is an ablation catheter comprising a longitudinal member having a distal end, a proximal end, and a guidewire shaft there-between comprising a guidewire lumen. The longitudinal member is a dilating catheter and is structurally configured along at least part of the length of the catheter to enable advancement or alignment of the longitudinal member through a narrow diameter blood vessel or occlusion. Advancement is achieved, for example, by turning or twisting the longitudinal member.  FIGS. 5A-5C  show such an embodiment of the present invention. For example, as shown in  FIG. 5A , the longitudinal member  500  may comprise a helical exterior  501  that advances through the vessel and dilates the vessel as the member is being twisted or rotated. Helical exterior  501  comprises a plurality of grooves  502  carved into the outer body of the longitudinal member  500 . The distal tip of longitudinal member  500  optionally comprises a radiopaque marker  510 . An electrode  520  is located at or near the distal end of the catheter. Another example is shown in  FIG. 5B , the cross section of which is shown in  FIG. 5C . The longitudinal member  550  may comprise a plurality of wires  551  and  552  wound around a liner  565 . In one embodiment, the wires  551  and  552  comprise at least two different diameters. Longitudinal member  550  optionally terminates at a marker  570 . An electrode  580  is located at or near the distal end of the longitudinal member  550 . The ablation catheter additionally and optionally comprises conductive wires for transmitting energy between the electrode and an external energy source. Alternatively, the plurality of wires may be configured to act as the electrode or conductive wires. Additionally and optionally, the catheter comprises an insulating sheath  560  which is optionally retractable. 
         [0063]    The guidewires and electrodes may be made from any one or more suitable materials as is commonly known in the art. Examples of such suitable materials include stainless steel, Nitinol, Elgiloy, platinum, iridium, tantalum, titanium, cobalt, chromium, tungsten, or any combinations thereof. In one embodiment, one or more of the guidewires may be made of a polymer, with an electrically conductive core for transmitting electrical energy to the respective electrodes. 
         [0064]    Additional embodiments disclosed here comprise of methods, systems, and devices to recanalize an occluded body vessel by penetrating the distal cap of the occlusion without approaching the distal cap from the retrograde direction through an intercoronary channel; thereafter, RF energy may be delivered in a biopolar arrangement between two longitudinal members as described above. 
         [0065]    Referring now to  FIG. 6 , where one embodiment of the device is shown: The device comprises a first longitudinal member  610  and a second longitudinal member  620 . The first longitudinal member  610  comprises a first distal end  611  and a first proximal end  612 . In one embodiment, the first distal end  611  may be configured to penetrate the proximal cap PC of an occlusion such that the first longitudinal member  610  may advance at least partly into the occlusion body OB from the proximal true lumen PTL in an antegrade fashion. The second longitudinal member  620  comprises a second distal end  621  and a second proximal end  622 . In one embodiment, the second distal end  621  may be configured to penetrate a portion of the occluded body vessel BDL such as the proximal cap PC or a portion of the subintimal space SIS. The second longitudinal member  620  may advance at least partly into the occlusion body OB from the proximal true lumen PTL in an antegrade fashion. Alternatively, the second longitudinal member  620  may advance through the subintimal space SIS without traversing through the occlusion body OB. 
         [0066]    The second distal end  621  may be further configured to be capable of being redirected. In one embodiment, the second distal end  621  may be redirected once the second longitudinal member  620  has at least traversed the length of the occlusion body OB and/or otherwise has entered the distal true lumen DTL. Whereupon redirection, the second distal end  621  may be positioned such that the second distal end  621  may be configured to penetrate the distal cap DC of the occlusion. 
         [0067]    The redirection of the second distal end  621  may be accomplished through various methods. In one embodiment, the device may comprise one or more strings (not shown) attached to the second distal end  621 , wherein a user may manipulate the strings to mechanically redirect the second distal end  621 . In another embodiment, a portion of the second distal end  621  may be constructed of various shape memory alloys and the second distal end  621  may be redirected by exploiting properties of the shape memory alloys. For example, a portion of the second distal end  621  may comprise heat memory alloys, wherein the second distal end  621  is configured to be redirected when it is sufficiently exposed to an elevated temperature environment such as the human body. Alternatively, the second distal end  621  may be pre-shaped or may comprise magnetic shape memory alloy, electric shape memory alloy, etc. 
         [0068]    It is contemplated that the various redirection methods described above may be implemented in combination. For example, the second distal end  621  may comprise one or more shape memory alloy types. Furthermore, the second distal end  621  may comprise one or more shape memory alloy types and may also be subject to mechanical manipulation, such as by strings as described above. 
         [0069]    It is further contemplated that the present embodiments may be combined with the use of various energy modalities. For example, RF energy may be delivered through the first and the second longitudinal members. Specifically, in one embodiment where an energy modality is used to recanalize the occlusion body OB, the first and the second distal ends  611  and  621  may each comprise at least one electrode such that controlled energy deployment is achieved using a bipolar arrangement of the electrodes as described above. 
         [0070]    The method of recanalization using one aspect of the present embodiments is shown schematically as a flow diagram in  FIG. 7  with reference to  FIGS. 8A-8F . At step  710 , the first distal end  611  of the first longitudinal member  610  penetrates the proximal cap PC and at least a portion of the first longitudinal member  610  is advanced into the occlusion body OB in an antegrade fashion as seen in  FIG. 8A . 
         [0071]    At step  720 , the second distal end  621  of the second longitudinal member  620  penetrates a portion of the occluded body vessel BDL. Thereafter, at least a portion of the second longitudinal member  620  is advanced into a body region of, or close to the occlusion. As seen in  FIG. 8B , the second distal end  621  may penetrate the proximal cap PC and the second longitudinal member  620  may advance through a portion of the occlusion body OB. Alternatively, the second distal end  621  may penetrate a site within the proximal true lumen PTL such as the subintimal space SIS near the proximal cap PC. Thereafter, as seen in  FIG. 8B  the second longitudinal member  620  may then enter and advance through the subintimal space SIS. 
         [0072]    At step  730  and as seen in  FIG. 8C , the second longitudinal member  620  may traverse at least the length of the occlusion body OB and it is advanced into the distal true lumen DTL through the subintimal space SIS. Alternatively, the second longitudinal member  620  may be advanced in an antegrade fashion through a portion of the subintimal space SIS without traversing a portion of the occlusion body OB. 
         [0073]    Thereafter, at step  740  and as seen in  FIG. 8C  the second distal end  621  is redirected such that the second distal end  621  is configured to be capable of penetrating the distal cap DC. In one embodiment, a first portion  623  of the second longitudinal member  620  comprising the second distal end  621  is re-configured such that the first portion  623  is at an angle with respect to a second portion  624  of the second longitudinal member  620 . The angle may be configured as any angle wherein the second distal end  621  is positioned such that it is capable of penetrating the distal cap DC. 
         [0074]    At step  750  and as seen in  FIG. 8D , the second distal tip  621  penetrates the distal cap DC and at least a portion of the second longitudinal member  620  is advanced into the occlusion body OB in a retrograde fashion. In one embodiment, the second longitudinal member  620  is advanced into the occlusion body OB until it is positioned at or near the first distal end  611  of the first longitudinal member  610 . In an embodiment where RF energy is used to recanalize the occlusion body OB, the electrodes disposed on the first and the second distal ends  611  and  621  may be positioned substantially towards each other. Furthermore, it is desirable that the electrodes are in contact with the occlusion body OB but are not in contact with the vessel wall to prevent or minimize damage to the vessel wall. Thereafter, at step  760 , RF treatment may be initiated to create a recanalization channel. 
         [0075]    It is noted that in an embodiment where RF energy is delivered through the first and the second longitudinal members, it may not be required for the second distal end  621  of the second longitudinal member  620  to penetrate the distal cap DC and to advance into the occlusion body OB in a retrograde fashion. In fact, it may be sufficient for the second distal end  621  and the first distal end  611  to be positioned within proximity where the radiofrequency spark may cross from the active electrode disposed on one longitudinal member to the return electrode disposed on the other longitudinal member to achieve ablation. For example, the second distal end  621  of the second longitudinal member  620  may be positioned within the distal true lumen DTL, and the first distal end  611  of the first longitudinal member  610  may be positioned within the occlusion body OB, RF energy may then be delivered between the active and return electrodes disposed on the two distal ends to ablate a portion of the occlusion body OB in between the two distal ends. 
         [0076]    Additionally and optionally, as seen in  FIG. 8E , the first and the second longitudinal members may be coupled by using one or more coupling elements (not shown) such that the two longitudinal members may create a recanalization channel between the proximal and distal ends of the occlusion body OB. Furthermore, the controlled antegrade and retrograde tracking (CART) techniques disclosed in the co-pending U.S. patent application Ser. No. 11/706,041 as referenced above may be used to facilitate the coupling. 
         [0077]    The coupling element may be configured to securely lock the first longitudinal element and the second longitudinal element to prevent separation during the guidewire placement procedure. Additionally and optionally, the coupling element may be configured to provide quick and easy detachment of the two longitudinal elements. In one embodiment, the coupling element may comprise a screw mechanism. In another embodiment, the coupling element may comprise a male portion disposed on the distal end of either the first or the second longitudinal member, and a female portion disposed on the distal end of the other longitudinal element, wherein the male portion is configured to be inserted into the female portion. In one embodiment the male portion can be spring loaded to more securely attach inside the female portion. In another embodiment, the coupling element may comprise a flaring rib mechanism in which one longitudinal element is snared by the other longitudinal element as described in the co-pending U.S. patent application Ser. No. 12/150,111 as referenced above. Alternatively, coupling may be achieved by other means of coupling, connecting, or extending longitudinal members such as the use of magnets where the distal ends of the first and the second longitudinal members comprise magnets of opposite polarity. 
         [0078]    Thereafter, the coupled longitudinal members advance in either the antegrade or retrograde direction through the occlusion body OB until one longitudinal member traverses the occlusion body OB and a portion of it is positioned within the true distal lumen DTL. 
         [0079]    As seen in  FIG. 8F , in an embodiment where the coupled longitudinal member is advanced in the antegrade direction, the first longitudinal member  610  is positioned in an antegrade direction through the occlusion body OB. Thereafter, the first longitudinal member  610  and the second longitudinal member  620  may be decoupled, and the second longitudinal member  620  may be removed from the body. 
         [0080]    At step  770 , once a recanalization channel has been created over the wire recanalization techniques that are well known in the art can be performed either in the antegrade fashion or the retrograde fashion to recanalize the occluded body vessel BDL, for example, a balloon catheter for performing an interventional procedure. 
         [0081]    In another embodiment, the second longitudinal member may be delivered into the distal true lumen DTL from an antegrade direction using a delivery element. As seen in  FIG. 9A , the second longitudinal element  820  may be inserted into a delivery lumen of the delivery element  830 . The delivery element  830  may be a delivery catheter, mircocatheter, a dilating catheter, a guiding catheter, or the like. The delivery element  830  then traverses the length of the occlusion body OB as described above. Thereupon reaching the distal true lumen DTL, as seen in  FIG. 9B  the second longitudinal member  820  is advanced through the delivery lumen. In such embodiment, the distal end of the second longitudinal member  820  may be pre-shaped such that the distal end  821  may not need to be redirected in order to penetrate the distal cap DC. Alternatively, the degree of redirection needed to position the distal end  821  of the second longitudinal member  820  may be decreased in comparison to an embodiment where the second longitudinal member  820  is inserted into the body without a delivery element  830 . 
         [0082]    In one embodiment, at least a portion of the pre-shaped distal end  821  may comprise Nitinol or other shape memory alloys such that the second longitudinal member  820  may be compressed when loaded into the delivery element  830 . Upon reaching the distal true lumen DTL, the compression may be relieved when the second longitudinal member  820  is advanced through the delivery element  830  and the distal end  831  may then assume the pre-shaped configuration. 
         [0083]    The delivery element  830  may further comprise an aspiration element (not shown) configured to remove debris products, such as debris produced by the RF treatment. In one such embodiment, the aspiration element comprises an aspiration port disposed on the distal end of the delivery element  830 , and an aspiration lumen connecting the aspiration port and the aspiration source. The debris products may be removed through the aspiration port through pressure differentials generated between the aspiration port and the aspiration source, such that debris products may be transmitted through the aspiration port and are thereby removed. In one embodiment, the delivery lumen may be configured as the aspiration lumen, in another embodiment, the aspiration lumen may be a substantially independent lumen disposed within the delivery element  830 . 
         [0084]    It is contemplated that the distal ends of the first longitudinal member, the second longitudinal member, and/or the delivery element can assume any configurations that enable the first and/or the second distal ends to penetrate the distal cap DC, the subintimal space SIS, and/or any other region of the occluded blood vessel BDL. In one embodiment, one or both distal ends of the longitudinal members and/or the distal end of the delivery element may be configured as deflectable tips. In another embodiment, the distal ends of the longitudinal members or the delivery element may be configured as bevel tips. It is further contemplated that the distal ends of the longitudinal members or the delivery element may be configured as heated tips, whereby the thermal energy radiating from the heated tips may ease the penetration and/or the advancement of the longitudinal members. 
         [0085]    Additionally, a cross-sectional area of the longitudinal members and/or the delivery element may be configured to progressively increase from the distal end towards the proximal end. The tapered configuration may be advantageous in that the narrow distal end may be configured to effectively traverse through the vascular matrix and to penetrate the occlusion and/or the subintimal space SIS, whereas the larger proximal end is configured to allow a user to manipulate the longitudinal members during the operation. Alternatively and optionally, a cross-sectional area of the longitudinal members may be configured to be substantially unchanged throughout the lengths of the longitudinal members. 
         [0086]    It is noted that the flexibility of the longitudinal members may vary over their respective lengths. In one embodiment, the distal ends may be substantially flexible, and the flexibility progressively decreases towards the proximal ends. 
         [0087]    Optionally, the longitudinal members of the present embodiments may comprise at least a layer of structural polymer over the core wire. Additionally and optionally, an outer surface of the longitudinal members may be coated with hydrophilic coating for ease of navigation through tortuous passageways. 
         [0088]    In another embodiment, as seen in  FIG. 10 , both the first and the second longitudinal members  910  and  920  may be advanced in an antegrade fashion into the occlusion body OB. The first and the second distal ends  911  and  921  of the longitudinal members can be configured to be redirected such that the first distal end  911  is directed substantially towards the second distal end  921  and/or the second distal end  921  may be directed substantially towards the first distal end  911 . The redirection may be accomplished through various methods described above. This approach minimizes the potential of the vessel wall becoming perforated or injured, as may otherwise occur in a conventional bipolar RF treatment approach. Because the electrodes are positioned towards each other, the tissue that is ablated by the RF treatment (i.e., the occlusion) is well contained between the electrodes. This also allows the user to localize the treatment to the occlusion while minimizing vessel wall damage. 
         [0089]    The sequence of the recanalization treatment steps where both the first and the second distal ends of two longitudinal members are redirected are illustrated in  FIG. 11  as a flow diagram. At step  1010 , the first and the second longitudinal members  910  and  920  are advanced through the proximal cap PC into the occlusion body OB in an antegrade fashion. 
         [0090]    The longitudinal members may be advanced as deep into the occlusion body as possible to minimize the distance between the electrodes and, consequently, minimize the length of the ablation zone. Confirmation that the electrodes are in an appropriate position can be generated by impedance measurements and/or by using any of the standard imaging techniques employed during interventional procedures, such as fluoroscopy or intravascular ultrasound (IVUS), in which transducers are placed on the distal ends of one or both of the longitudinal member. When using tissue impedance measurements, the calcified occlusion body generally exhibits significantly higher impedance than the vessel wall. If an impedance measurement indicates a low impedance value, it is likely that one or both longitudinal members are in contact with the vessel wall, and appropriate repositioning may be warranted. Alternatively, the first and/or the second longitudinal member may be advanced through the subintimal space SIS and then entered into the occlusion body OB in an antegrade fashion. 
         [0091]    At step  1020 , once the user has confirmed that the first and the second longitudinal members  910  and  920  are positioned at the desired location, one or both of the distal ends  911  and  921  may be redirected such that the electrodes disposed on the first and the second distal ends are positioned towards each other. Furthermore, it is desirable that the electrodes are in contact with the occlusion body OB but are not in contact with the vessel wall to prevent or minimize damage to the vessel wall. At step  1030 , the RF treatment may be initiated. 
         [0092]    Alternatively, the first and/or the second longitudinal members may be delivered into the occlusion body OB wherein the distal ends are pre-shaped such that redirection of one or more of the distal ends is reduced or not required in order for the distal ends to be substantially positioned towards each other. Additionally, the first and/or the second longitudinal members may be delivered into the occlusion body OB using one or more delivery elements as described above and illustrated in  FIGS. 9A-9B . 
         [0093]    At step  1040  once a channel has been created, one of the longitudinal members may be withdrawn and the other longitudinal member may be advanced through the occlusion body OB and standard interventional procedures as described above may be performed. 
         [0094]    The present embodiments further contemplate a centering balloon catheter system configured to position one or more longitudinal members within the body vessel and reduce the likelihood of the longitudinal members slipping away from a portion of the occlusion. In one embodiment as seen in  FIG. 12  the balloon catheter system comprises an inflatable balloon  1120  disposed on a balloon catheter  1110 , wherein the balloon may be inflated with a biocompatible fluid such as a gas (CO 2 ) or a liquid such as saline or contrast agents. The inflation medium may be delivered through a separate inflation lumen (not shown). In one embodiment, upon inflation, the balloon  1120  may be configured to occupy substantially the entire interior of a vessel such that the balloon catheter system may be substantially fixed in place within a body vessel. 
         [0095]    Optionally, the balloon catheter system may comprise a delivery catheter  1130  disposed within the balloon catheter  1110 . The delivery catheter  1130  may be configured to deliver one or more longitudinal members to the occlusion body OB. 
         [0096]    In one embodiment as seen in  FIGS. 13A-13B , the delivery catheter  1230  may comprise helical grooves  1231  and the balloon catheter  1210  comprising an inflatable balloon  1220  may comprise receiving grooves  1211  configured to receive the helical grooves  1231  disposed on the delivery catheter  1230 . The receiving grooves  1211  are configured to allow the helical grooves  1231  to rotate within the balloon catheter  1210  without moving the balloon catheter  1210 . In such configuration, the delivery catheter  1230  may be advanced within the balloon catheter  1210  by twisting or otherwise turning the delivery catheter  1230  while the balloon catheter  1210  maintains a substantially fixed position within the body vessel. 
         [0097]    The delivery catheter may comprise a single lumen as seen or it may comprise multiple lumens (not shown). The multi-lumen configuration may be advantageous by facilitating insertion and/or removal of various apparatus during the operation. Furthermore, the multi-lumen configuration may be advantageous such that one or more of the lumens may be configured as suction lumens, wherein suction force may be applied through the suction lumens to stabilize the delivery catheter upon the occlusion body OB as described in co-pending U.S. application Ser. No. 13/042,411 by the same inventors, which is incorporated herein in its entirety. 
         [0098]    In a multi-lumen configuration, the lumens may assume various positional configurations relative to another lumen within the catheter. For example, the delivery catheter may comprise two or more lumens configured in a non-coaxial manner. In another embodiment, the delivery catheter may comprise two or more lumens configured in a coaxial manner. It is further contemplated that the lumens may assume various shape and position configurations within the catheter. 
         [0099]    Further, in an embodiment where energy may be delivered through the longitudinal members it would be advantageous to have a heat resistant tip on the distal end of the balloon catheter and/or the delivery catheter. 
         [0100]    Various embodiments of the longitudinal member described above may further comprise one or more lumens disposed within the interior of the longitudinal member. In one embodiment, as seen in  FIG. 14  a longitudinal member with a lumen  1300  comprises a distal opening  1320 , a proximal opening (not shown), and an elongated body  1330  disposed in-between. The longitudinal member may be coated with an insulator  1310 , such as Teflon, ceramic, polyimide, parylene, or other suitable materials. Examples of methods which could be employed for coating may include spraying, dipping, vapor deposition, or plasma deposition. The proximal opening may be connected to a fluid source and the distal opening  1320  of the lumen is configured to deliver at least one fluid to the treatment region of the blood vessel, wherein the fluid may be transmitted from the fluid source through the elongated body lumen  1330 . Alternatively, the longitudinal member may comprise an injection port (not shown) that traverses the coating  1310  to connect a fluid source with the elongated body  1330 . The elongated body  1330  may be coated with materials, such as hydrophobic materials that are configured to prevent fluids from exiting the elongated body. It is contemplated that the treatment fluid may be liquids and/or gases such as saline, compressed air, various drugs, or the like. 
         [0101]    In one embodiment, the fluid delivered to the treatment region of the blood vessel may be used as coolants to control the temperature of the treatment region during the ablation procedure. Additionally and optionally, the fluid delivered to the treatment region may be used to weaken and/or break up a portion of the occlusion. For example, it is envisioned that compressed air may be delivered into the occlusion during the advancement of the longitudinal member. The compressed gas may be used to enlarge or expand a space in the occlusion already created by the penetration of the occlusion and/or by the ablation. The expanded space created by the compressed air may aid in further advancement of the longitudinal member. Alternatively, it is contemplated that the fluid delivered to the treatment region may serve other functions such as delivering therapeutic agents to the treatment regions and the like. 
         [0102]    Furthermore, the fluid delivered to the treatment site through the longitudinal member may be a conductive fluid such as isotonic saline. The fluid may immerse a portion of the target site such that the active electrode disposed on another longitudinal member may generate a current density that is sufficiently high to cause sparks crossing over to the fluid immersed target site. In such an embodiment, the fluid may acts as an energy sink, receiving the energy delivered from the active electrode. It is envisioned that the energy as applied from the active electrode may be sufficient to vaporize the fluid such that plasma may be formed to cause disintegration or breakdown of the occlusion in contact with the plasma. 
         [0103]    It is envisioned that various fluids may be delivered in sequence or in tandem. In one embodiment, the guidewire may be advanced at least partly into the occlusion; thereafter, a first fluid, such as compressed air may be delivered into the occlusion to create or expand a space. Thereafter, a second fluid, such as isotonic saline may be delivered into the space created by the first fluid. As described above, the isotonic saline may serve as a conductive fluid that receives radiofrequency energy as delivered by an active electrode. The saline may then be vaporized by the radiofrequency energy to create plasma that causes disintegration of a portion of the occlusion that is in contact with the plasma. 
         [0104]    While the above embodiments refer to the use of RF energy for the purpose of ablation, it should be noted that other energy modalities may be used as well, for example ultrasound energy. In one embodiment, one or more longitudinal members of the recanalization systems of the present invention comprise one or more ultrasound transducers, instead of or in addition to RF electrodes. The ultrasound transducers provide ultrasound energy for ablating an occlusion. In one embodiment, the antegrade and/or the retrograde longitudinal members may comprise ultrasound transducers and ablate the lesion from an antegrade as well as a retrograde direction. Other energy modalities could include microwave and laser. 
         [0105]    It should be noted that the combined antegrade and retrograde energy delivery techniques described above could also be used as an adjunct technique to crossing CTOs in combination with using conventional methods. The technique could be used to sufficiently soften or weaken the occlusion, thereby allowing a guidewire or catheter to cross the occlusion. 
         [0106]    While the above is a complete description of the preferred embodiments of the invention, various alternatives, modifications, and equivalents may be used. Therefore, the above description should not be taken as limiting the scope of the invention which is defined by the appended claims.