Abstract:
An intravascular catheter system includes an intravascular catheter that can be easily and safely navigated through severely occluded arteries. The system uniquely includes both an optical fiber for use in providing data for guiding the catheter and a conventional metal guide wire for use in navigating the catheter through the artery passageway. The system further includes optical imaging of the arterial occlusion during guidance of the catheter through the artery passageway. More particularly the system provides a visual indication to the surgeon to determine if the catheter assembly is approaching the arterial wall.

Description:
[0001]     This is a Divisional of co-Pending U.S. Ser. No. 10/759,668 filed Jan. 16, 2004. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to medical devices such as intravascular catheters. More particularly, the invention concerns an intravascular catheter for use in opening partial and total occlusions of an artery passageway.  
         [0004]     2. Discussion of the Prior Art  
         [0005]     A number of procedures have been suggested in the past for treating disease conditions involving the narrowing or obstruction of the lumen of an artery. This condition, generally referred to as an occlusion, is found in patients suffering from atherosclerosis. An occlusion can manifest itself in hypertension and can be partial or total. The occlusions can be found at various locations in the arterial system, including the aorta, the coronary arteries, the carotid arteries and the peripheral arteries.  
         [0006]     In the past, coronary artery occlusions have traditionally been treated by performing coronary bypass surgery, wherein a segment of the patient&#39;s saphenous vein is taken from the patient&#39;s leg and is grafted onto the affected artery at points upstream and downstream of the occluded segment. While bypass surgery can provide dramatic relief, it involves dangerous open chest surgery and typically a long period of convalescence.  
         [0007]     In recent years less invasive procedures have been adopted for the treatment of arterial abnormalities. These procedures typically involve the use a catheter which is introduced into a major artery through a small arterial opening in the patient&#39;s body and is advanced into the area of the stenosis.  
         [0008]     Popular prior art minimally invasive procedures include percutaneous transluminal coronary angioplasty, directional coronary atherectomy and stenting. Percutaneous transluminal coronary angioplasty typically involves the use of a balloon to mechanically dilate the stenosis. In carrying out this procedure, a steerable guide wire is introduced into an arterial opening and advanced under fluoroscopic observation into the stenosed artery and past the stenosis. This done, a balloon catheter is advanced over the guide wire until it is positioned across the stenosed area. The balloon is then inflated to separate the stenosed tissue.  
         [0009]     A somewhat similar prior art procedure, known as stenting, involves the use of a very small wire framework, known as a stent, which is fitted over an inflatable balloon and is then positioned across the stenosed segment of the artery. When the stent is in the proper position, the balloon is inflated, dilating the stent and forcing it against the artery wall.  
         [0010]     It is, of course, apparent that over-the-wire catheters cannot be positioned adjacent the stenosis until the guide wire has been advanced across the stenosed area. In those instances where the artery is occluded, the surgeon may have greater difficulty in guiding the guide wire through the occluded area. For example, the occlusion may contain complex structures which divert the steering end of the guide wire. Thus, without some type of guidance system, the guide wire might undesirably impinge on and possibly perforate or otherwise damage the artery wall.  
         [0011]     In light of the foregoing, there has been a long-felt need to provide a reliable guidance system for guiding a catheter through the occlusion. One prior art guidance system which has been used in conjunction with coronary catheterization involves bi-plane fluoroscopy, wherein the surgeon observes two flat, real-time X-ray images acquired from different angles. However, bi-plane fluoroscopy has been proven to be somewhat costly, unreliable and slow.  
         [0012]     Recently, promising optical systems have been disclosed for imaging an occlusion through a specially designed catheter positioned within the artery. One such system is Optical Coherence Tomography (OCT). In this system, a beam of light carried by an optical fiber illuminates the artery interior and light reflected back into the fiber from features inside the artery is correlated with the emitted light to capture the depth as well as the angular separation of those features. The features are displayed graphically in two or three dimensions through the use of a suitably programmed computer. Examples of such processing are given in U.S. Pat. No. 5,459,570 issued to Swanson, et al. U.S. Pat. No. 5,459,570 is hereby incorporated by reference as though fully set forth herein.  
         [0013]     Another prior art guidance system is disclosed in U.S. Pat. No. 6,010,449 issued to Selmon, et al. This patent discloses an intravascular catheter system that includes a steering apparatus, an imaging member and a therapeutic element within a multi-lumen catheter shaft. In one embodiment of the intravascular catheter system, a rotatable imaging shaft is disposed within the catheter shaft. The imaging shaft contains an optical fiber, which is connected to external optical instruments. At the distal end of the imaging shaft, the optical fiber conducts light from the instruments to illuminate the environment inside the artery and receives optical radiation returned from the environment. The imaging shaft is turned by an external motor encoder, which also measures the rotation of the shaft. As the imaging shaft rotates, the optical beam sweeps circumferentially about the longitudinal axis of the imaging shaft at a fixed angle from the longitudinal axis of the imaging shaft, illuminating different portions of the environment within the artery. The instruments correlate the emitted and received optical data with the rotational data to display an image of the interior of the artery.  
         [0014]     Another promising technology for use in catheter guidance systems is Optical Coherence Reflectometry (OCR). The basic concepts of this technology have been well documented (see for example an article by Mandel L. Wolf entitled “Optical Coherence and Quantum Optics” published in the Cambridge University Press (1995)). In the practice of the OCR technology, a light source is divided into two beams, a reference arm and a sample arm. The light in the reference arm is reflected at a determinable path length. Light in the sample is also reflected or scattered by the material present in the sample. The reflections and back-scattered light are combined at an optic coupler, and if the path lengths of the two arms are within the coherence length of the light, the light will recorrelate or interfere with one another. The detector measures the interference intensity. Since the reference path length is known and adjustable, the intensity profile of scattered light from a sample can be determined as a function of the reference arm path length.  
         [0015]     U.S. Pat. No. 6,451,009 issued to Dasilva, et al, discloses an optical coherence domain reflectometry (OCDR) guided laser ablation device. The Dasilva, et al, device includes a mulitmode laser ablation fiber that is surrounded by one or more single mode optical fibers that are used to image in the vicinity of the laser ablation area to prevent tissue damage. The laser ablation device is combined with an OCDR unit and with a control unit which initializes the OCDR unit and a high power laser of the ablation device. Data from the OCDR unit is analyzed by the control unit and is used to control the high power laser. The OCDR images up to about 3 mm ahead of the ablation surface to enable a user to see sensitive tissue such as a nerve or artery before damaging it by the laser.  
         [0016]     A commercially available, prior art catheter system using the OCR technology is sold by IntraLuminal Therapeutics of Carlsbad, Calif. under the name and style “SAFE-STEER”. The IntraLuminal Therapeutics apparatus comprises an optical guide wire with an optical fiber integrated into it. The apparatus also includes an optical coherence reflectometry system which comprises an optical interferometer, a demodulation computer unit and monitor. In one form of the apparatus a single mode fiber with a polyimide jacket is used for the optics. The proximal portion of the guide wire is made up of commercially available hypodermic tubing that serves as a conduit for the fiber. In operation, the back-scattered light is analyzed through the low coherence interferometer producing a signal that is displayed and periodically updated on an OCR monitor. The signal is periodically monitored to determine if the normal arterial wall interface is within the field of view. If the normal arterial wall is detected, a visual indication of a red bar is displayed on a monitor and the relative distance to the arterial wall is shown. If the normal arterial wall is not in the field of view, a green bar is displayed indicating that the guide wire can be advanced.  
         [0017]     A form of prior art optical fiber guide wire similar to the “SAFE-STEER” guide wire is illustrated and described in an article entitled “Lasers In Surgery: Advanced Characterization Therapeutics, and Systems XI” ( Proceedings of The Society of Photo - Optical Instrumentation Engineers,  Volume 4244).  
         [0018]     A drawback found in certain of the prior art OCR optical fiber guide wire systems resides in the fact that the optical fiber guide wire tends to be substantially more difficult to navigate through the artery passageway than the catheters embodying more conventional metal guide wires such as are used in stent delivery and like procedures. This drawback is uniquely overcome by the apparatus of the present invention which comprises a catheter system that uniquely includes both an optical fiber for use in expeditiously guiding the catheter and a conventional metal guide wire for use in navigating the catheter through the artery passageway.  
         [0019]     Still another commercially available, prior art catheter system using radio frequency technology is sold by IntraLuminal Therapeutics of Carlsbad, Calif. under the name and style “SAFE-CROSS.” The Safe-Cross system was developed to effectively cross and recanalize total occlusions and, according to the manufacturer, comprises a marriage of the OCR technology and controlled Radio Frequency (RF) energy to facilitate guidance through the occlusion.  
         [0020]     The IntraLuminal Therapeutics RF apparatus comprises a 0.14 inch support catheter and a 0.35 inch catheter. The apparatus also includes a console and display, a torquer and an advancing mechanism.  
       SUMMARY OF THE INVENTION  
       [0021]     An object of the present invention is to provide an intravascular catheter system that can be used in the effective treatment of occluded arteries. More particularly, it is an object of the invention to provide such a system which includes an intravascular catheter that can be easily and safely navigated through severely occluded arteries.  
         [0022]     Another object of the invention is to provide a system of the aforementioned character that uniquely includes both an optical fiber for use in providing data for guiding the catheter and a conventional metal guide wire for use in navigating the catheter through the artery passageway.  
         [0023]     Another object of the invention to provide an intravascular catheter system as described in the preceding paragraphs that includes optical imaging of the arterial occlusion during guidance of the catheter through the artery passageway. More particularly, the system provides a visual indication to the surgeon to determine if the catheter assembly is approaching the arterial wall.  
         [0024]     Another object of the invention is to provide an intravascular system that uses a combination of optical imaging and controlled Radio Frequency energy to facilitate guidance through the occlusion.  
         [0025]     Another object of the invention is to provide an intravascular catheter system of the class described which is of a simple construction and is easy to use in a conventional manner. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]      FIG. 1  is a generally perspective view of one form of the intravascular catheter system of the present invention.  
         [0027]      FIG. 2  is a greatly enlarged, cross-sectional view of the portion of the system designated as “ 2 ” in  FIG. 1 .  
         [0028]      FIG. 3  is a cross-sectional view taken along lines  3 - 3  of  FIG. 2 .  
         [0029]      FIG. 4  is a generally perspective view of an alternative form of the intravascular catheter system of the present invention.  
         [0030]      FIG. 5  is a greatly enlarged, cross-sectional view of the portion of the system designated as “ 5 ” in  FIG. 4 .  
         [0031]      FIG. 6  is a cross-sectional view taken along lines  6 - 6  of  FIG. 5 .  
         [0032]      FIG. 7  is a generally perspective view of still another form of the intravascular catheter system of the present invention.  
         [0033]      FIG. 8  is a greatly enlarged, cross-sectional view of the portion of the system designated as “ 8 ” in  FIG. 7 .  
         [0034]      FIG. 9  is a cross-sectional view taken along lines  9 - 9  of  FIG. 8 .  
         [0035]      FIG. 10  is a generally diagrammatic, block diagram view of a prior art optical coherence reflectometry system.  
         [0036]      FIG. 11  is a generally diagrammatic, block diagram view of one form of the optical coherence reflectometry system of the present invention.  
         [0037]      FIG. 12  is a generally perspective view of still another form of the intravascular catheter system of the present invention.  
         [0038]      FIG. 13  is a greatly enlarged, cross-sectional view of the portion of the system designated as “ 13 ” in  FIG. 12 .  
         [0039]      FIG. 14  is a cross sectional view taken along lines  14 - 14  of  FIG. 13 . 
     
    
     DESCRIPTION OF THE INVENTION  
       [0040]     Referring to the drawings and particularly to  FIGS. 1 through 3 , one form of the intravascular catheter system of the invention is there shown and generally designated by the numeral  14 . The catheter system here comprises a catheter  16  having an outer side wall  18 , a proximal end  20  and distal end  22 . As can be seen by referring to  FIGS. 2 and 3 , catheter  16  is provided with a first passageway  24  ( FIG. 2 ) having a diameter of about 0.035 inches, a proximal end  26  and a distal end  28 . Catheter  16  is preferably formed of a biocompatible and hydrophilic compatible material, such as a lubricous polyimide or polyethylene.  
         [0041]     As indicated in  FIG. 2 , a conventional steerable guide wire  30  is slideably receivable within the first passageway  24  and is movable between first and second positions. While various types of steerable guide wires can be used in the catheter assembly of the invention, guide wire  30  is preferably constructed from a flexible, wire-like metal member having a diameter on the order of 0.014 inches.  
         [0042]     Catheter  16  is also provided with a second passageway  32  that is radially spaced-apart from first passageway  24 . Second passageway  32  also has a proximal end  34  and a distal end  36 . An energy transmission means, shown here as an optical fiber  38 , which is carried within second passageway  32  in the manner shown in  FIGS. 2 and 3 , has a first end  40  and a second end  42 , the second end being located adjacent the tip of the catheter and proximate the distal end  36  of second passageway  32 . Optical fiber  38 , which is of a character well known to those skilled in the art, can be of various sizes, but for the present application preferably has a diameter of on the order of 0.0065 inches. As will be discussed hereinafter, the energy transmission means can also comprise a Radio Frequency (RF) transmitter for transmitting RF energy.  
         [0043]     Also comprising a part of the intravascular catheter system of the invention are electronic means which are operably associated with optical fiber  38 . These electronic means, which are generally identified in  FIG. 1  by the numeral  39 , comprise a part of the guidance means of the invention and uniquely provide guidance data to the user of the system to permit the safe navigation of the catheter through the occlusion. The guidance means along with the optical fiber  38  form a part of the optical coherence reflectometry system (OCR) of the invention the character of which will presently be described.  
         [0044]     One form of the method of the invention is carried out using the apparatus shown in  FIGS. 1 through 3 . This method comprises the steps of first advancing the guide wire  30  through a vessel to a location proximate the occlusion. This done, the catheter  16  is interconnected with the guide wire by inserting the guide wire into a guide wire receiving opening  39  formed in the side wall  18  of the catheter-at a location proximate the distal end of the catheter ( FIG. 1 ). Following insertion of the guide wire into the opening  39 , the catheter can be controllably advanced over the guide wire to a location where the distal end of the catheter is located proximate the occlusion. As shown in  FIG. 1  of the drawings, when the catheter is in position within the occluded vessel of the patient, a substantial portion of the guide wire  30  uniquely resides externally of the catheter. With this novel construction, the guide wire passes through only the distal portion of the central passageway of the catheter in the manner shown in  FIG. 1 .  
         [0045]     Turning next to  FIGS. 10 and 11 , it can be seen that the optical coherence reflectometry system of the present form of the invention ( FIG. 11 ) is similar in construction and operation to the prior art optical coherence reflectometry system shown in  FIG. 10  which is used for scanning an article. Referring particularly to  FIG. 10 , the prior art optical coherence reflectometry system there shown can be seen to comprise a low coherence light source  41  that is input into a fiber optic coupler  43  where the light is split and directed into a sample arm  44  and into a reference arm  46 , the latter of which provides a variable optical delay. An optical fiber  48  is connected to the sample arm  44  and extends into a device  50 , which scans the object  52 . Light input into reference arm  46  is reflected back by a reference mirror  54 . As shown in  FIG. 10 , piezoelectric modulator  56  may be included in reference arm  46 . The reflected reference beam from reference arm  46  and a reflected sample beam from sample arm  44  pass back through coupler  43  to detector electronics  58  which processes the signals by techniques well known in the art to produce a backscatter profile (or “image”) that is visually displayed on a suitable display  60 . The prior art system shown in  FIG. 10  is described in greater detail in U.S. Pat. No. 6,175,669 issued to Colsten, et al, which discloses another type of optical fiber guide wire.  
         [0046]     Turning to  FIG. 11 , the optical coherence reflectometry system of the apparatus of the present invention comprises a low coherence light source  62  that is input into a conventional fiber optic coupler  64  where the light is split and directed into a sample arm  66  and a reference arm  68 . The previously identified optical fiber  38  is connected to sample arm  66  and extends into second passageway  32  of the catheter  16  in the manner shown in  FIG. 1 . The light in the reference arm  68  is reflected by reflecting means shown here as a mirror  70  at a determinable variable path length when the catheter system is in an initial position within the artery. Light in the sample arm  66  will be reflected or scattered by the material present in the occlusion within which the distal end of the catheter resides. The reflections and back-scattered light are combined at a coupler  64  in a manner well understood by those skilled in the art. If the path lengths of the two arms are within the coherence length of the light, the light will re-correlate. A detector  72 , which is operably interconnected with the coupler, measures the interference intensity. Detector  72  is also of a character well known in the art. Since the reference path length is known and adjustable, the intensity profile of scattered light from a sample can be determined as a function of the reference arm path length. The scattered light is analyzed by electronic means which here comprises the electronics  74  and a conventional computer system  76 . The cooperative interaction of the electronics and the computer produces a signal tracing that is displayed and periodically updated on a suitable display  78 . In a manner well understood by those skilled in the art, the signal tracing is monitored by the computer through a series of algorithms to determine if the arterial wall is within the field of view. If the arterial wall is detected, a visual indication will appear on the display with the catheter assembly in its initial position within the artery. If visual indication is not shown on the display, the guide wire can be further advanced a small distance into the occlusion. This done, the catheter is inserted over the guide wire to a position proximate the distal end of the guide wire and the monitor is viewed to verify that cautionary visual indication is still not shown on the display. If this is the case, the guide wire can be further inserted a small distance into the occlusion and the catheter then inserted over the guide wire a further distance. This procedure can be repeated until a visual indication appears on the display at which point the surgeon must take steps to reroute the steerable guide wire in a direction away from the arterial wall. Unlike the prior art systems which use the optical fiber and its sheath as a guide wire, the apparatus of the present invention, which uniquely embodies a conventional steerable metal guide wire, such as guide wire  30 , enables the surgeon to safely and expeditiously navigate through the occlusion with a minimum of a lost time and motion.  
         [0047]     Turning next to  FIGS. 4 through 6 , an alternate form of the intravascular catheter system is there shown and generally designated by the numeral  84 . Catheter system  84  is similar in many respects to that shown in  FIGS. 1 through 3  and like numerals are used in  FIGS. 4 through 6  to identify like components. As can be seen in  FIGS. 4 and 5  catheter system  84  comprises a catheter  86  having an outer side wall  88 , a proximal end  90  and distal end  92 . Catheter  86  is provided with a first passageway  94  having a proximal end  96  and a distal end  98 . Catheter  86 , like catheter  14 , is preferably formed of a biocompatible and hydrophilic compatible material, such as a lubricous polyimide or polyethylene. The primary difference between catheter  86  and the previously described catheter  14  is that catheter  86  does not include an opening in its side wall for receiving the guide wire and, additionally, as shown in  FIG. 6 , the passageway which receives the guide wire is axially aligned with the central axis of the catheter.  
         [0048]     As indicated in  FIGS. 5 and 6 , a conventional guide wire  30  is slideably movable within first passageway  94  between first and second positions. Catheter  86  is also provided with a second passageway  102  which is radially spaced-apart from first passageway  94 . Second passageway  102  also has a proximal end  104  and a distal end  105 . An optical fiber  38 , which is carried within second passageway  102  in the manner shown in  FIGS. 5 and 6 , has a first end  107  and a second end  106 , the second end being located proximate the distal end of second passageway  102 . Also comprising a part of the intravascular catheter system of this latest form of the invention are instrument means of the character previously described that are operably associated with optical fiber  38  for providing, in the manner previously described, guidance data to the user of the system to permit the safe navigation of the catheter through the occlusion. The instrument means, along with the optical fiber  38 , forms a part of the optical coherence reflectometry system of the invention the character of which is illustrated in  FIG. 11  of the drawings. The method of the invention using the alternate embodiment of the invention shown in  FIGS. 4 through 6  comprises the steps of first advancing the guide wire  30  through a vessel to a location proximate the occlusion. This done, the catheter  86  is interconnected with the guide wire by inserting the guide wire into the distal end of passageway  94 . Following insertion of the guide wire into passageway  94 , the catheter is controllably advanced over the guide wire to a location wherein the distal end of the catheter is also proximate the occlusion. The guide wire and the catheter are then incrementally inserted into the occlusion in the manner described in connection with the embodiment of the invention shown in  FIGS. 1 through 3  with the surgeon periodically checking the display of the instrument means  39  to make certain that the catheter will not impinge on the artery wall.  
         [0049]     Referring now to  FIGS. 7 through 9 , still another form of the intravascular catheter system is there shown and generally designated by the numeral  114 . Catheter system  114  is similar in many respects to that shown in FIGS.  4  through  6  and like numerals are used in  FIGS. 7 through 9  to identify like components. As has been seen in  FIGS. 7 and 8  catheter system  114  comprises a catheter  116  having an outer side wall  118 , a proximal end  120  and distal end  122 . Catheter  116  is provided with a first passageway  124  having a diameter of approximately 0.035 inches, a proximal end  126  and a distal end  128 . Catheter  116 , like catheter  84 , is preferably formed of a biocompatible and hydrophilic compatible material, such as a lubricous polyimide or polyethylene. The primary difference between catheter  116  and the previously described catheter  84  is that the passageway which receives the guide wire and the passageway that receives the optical fiber are both radially offset from the central axis of the catheter.  
         [0050]     As indicated in  FIGS. 8 and 9 , a conventional guide wire  30 , which has a diameter of about 0.014 inches, is slideably movable within first passageway  124  between first and second positions. Catheter  116  is also provided with a second passageway  132  which is radially spaced-apart from first passageway  124 . Second passageway  132  also has a proximal end  134  and a distal end  135 . An optical fiber  38 , which is carried within second passageway  132  in the manner shown in  FIGS. 8 and 9 , has a first end  136  and a second end  138 , the second end being located proximate the distal end of second passageway  132 . Also comprising a part of the intravascular catheter system of this latest form of the invention are instrument means of the character previously described that are operably associated with optical fiber  38  for providing, in the manner previously described, guidance data to the user of the system to permit to the safe navigation of the catheter through the occlusion. The instrument means, along with the optical fiber  38 , forms a part of the optical coherence reflectometry system of the invention the character of which is illustrated in  FIG. 11  of the drawings. The method of the invention, using the alternate embodiment of the invention shown in  FIGS. 4 through 6 , comprises the steps of first advancing the guide wire  30  through a vessel to a location proximate the occlusion. This done, the catheter  116  is interconnected with the guide wire by inserting the guide wire into the distal end of passageway  124 . Following insertion of the guide wire into passageway  124 , the catheter is controllably advanced over the guide wire to a location wherein the distal end of the catheter is also proximate the occlusion. The guide wire and the catheter are then incrementally inserted into the occlusion in the manner described in connection with the embodiment of the invention shown in  FIGS. 4 through 6  with the surgeon periodically checking the display of the instrument means  39  to make certain that the catheter will not impinge on the artery wall.  
         [0051]     Referring next to  FIGS. 12, 13  and  14  still another form of the intravascular catheter system of the invention is there shown and generally designated by the numeral  134 . This catheter system is similar to that shown in  FIGS. 1 through 3  and like numbers are used in  FIGS. 12 through 14  to identify like components. The primary difference between system  134  and the earlier described embodiments of the invention resides in the fact that the guidance means for guiding the guide wire comprises a marriage of the previously described OCR technology and controlled radio frequency energy.  
         [0052]     As best seen in  FIGS. 12 and 13 , system  134  here comprises a catheter  16  of the character previously described having an outer side wall  18 , and proximal end  20  and a distal end  22 . As before, catheter  16  is provided with a first passageway  24  ( FIG. 13 ) having a diameter of about 0.035 inches, a proximal end  26  and distal end  28 . As indicated in  FIG. 13 , a conventional steerable guide wire  30  is slideably receivable within the first passageway  24  and is movable between first and second positions.  
         [0053]     Catheter  16  is also provided with a second passageway  32  that is radially spaced-apart from first passageway  24 . Second passageway  32  also has a proximal end  34  and a distal end  36 . An energy transmission means, shown here as an energy conduit  136  is carried within second passageway  32 . As indicated in  FIGS. 13 and 14 , conduit  136  has a first end  138  and a second end  140 , the second end being located adjacent the tip of the catheter and proximate the distal end  36  of second passageway  32 . Energy conduit  136 , which is of a character well known to those skilled in the art, can be of various sizes, but for present application preferably has a diameter on the order of 0.0065 inches. Advantageously, energy conduit  136  can be used to penetrate and cross a total occlusion when such an occlusion is encountered.  
         [0054]     Also comprising a part of the intravascular catheter system of the invention are electronic means, which are operably associated with conduit  136 . These electronic means, which are generally identified in  FIG. 12  by the numeral  142 , provide guidance data to the user of the system to permit the safe navigation of the catheter through the occlusion. A system suitable for use in this latest embodiment of the invention is commercially available from IntraLuminal Therapeutics, Inc. of Carlsbad, Calif. under the name and style “SAFE-CROSS.” The details of construction and operation of this RF system are available from this company.  
         [0055]     An alternate form of the method of the invention is carried out using the apparatus shown in  FIGS. 12, 13  and  14 . This method comprises the steps of first advancing the guide wire  30  through a vessel to a location proximate the occlusion. This done, the catheter  16  is interconnected with the guide wire by inserting the guide wire into a guide wire receiving opening  39  formed in the side wall  18  of the catheter at a location proximate the distal end of the catheter ( FIG. 12 ). Following insertion of the guide wire into the opening  39 , the catheter can be controllably advanced over the guide wire to a location where the distal end of the catheter is located proximate the occlusion. As shown in  FIG. 12  of the drawings, when the catheter is in position within the occluded vessel of the patient, a substantial portion of the guide wire  30  uniquely resides externally of the catheter. With this novel construction, the guide wire passes through only the distal portion of the central passageway of the catheter in the manner shown in  FIG. 12 .  
         [0056]     Guidance of the wire is then accomplished using the guidance means of the invention which here comprises the previously identified “SAFE-CROSS” system. The details of the use of this system are available from the previously identified IntraLuminal company.  
         [0057]     Having now described the invention in detail in accordance with the requirements of the patent statutes, those skilled in this art will have no difficulty in making changes and modifications in the individual parts or their relative assembly in order to meet specific requirements or conditions. Such changes and modifications may be made without departing from the scope and spirit of the invention, as set forth in the following claims.