Abstract:
An endovenous laser fiber optic member for endovenous laser therapy of peripheral veins of the body including a flexible heat resistant tip shield covering the distal end of the laser fiber optic. The tip shield has an irregular surface to increase ultrasound reflectivity. The tip shield also improves deflectability of the distal end and acts as a heat sink and heat energy dissipater.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to the field of surgical instruments utilizing light application via optical fibers placed within the body. More particularly, the present invention relates to endovenous laser therapy of the peripheral veins, such as greater saphenous veins of the leg, for treatment of varicose veins.  
       BACKGROUND OF THE INVENTION  
       [0002]     Varicose veins are enlarged, tortuous, often blue in color and commonly occur in the legs below the knee. Varicose veins are the most common peripheral vascular abnormality affecting the legs in the United States. Varicose veins often lead to symptomatic venous insufficiency. Greater saphenous vein reflux is the most common form of venous insufficiency in symptomatic patients and is frequently responsible for varicose veins in the lower leg. This occurs in about 25% of women and about 15% of men.  
         [0003]     All veins in the human body have valves that open to allow the flow of blood toward the heart and close to prevent backflow of blood toward the extremities. The backflow of blood is also known as reflux. The venous check valves perform their most important function in the veins of the legs where venous return flow is most affected by gravity. When the venous valves fail to function properly, blood leaks through the valves in a direction away from the heart and flows down the leg in the wrong direction. The blood then pools in the superficial veins under the skin resulting in the bulging appearance typically seen in varicose veins. The pooling of blood in the leg veins tends to stretch the thin elastic walls of the veins, which in turn causes greater disruption in the function of the valves, leading to worsening of the varicosities. When varicose veins become severe, the condition is referred to as chronic venous insufficiency. Chronic venous insufficiency can contribute to the development of pain, swelling, recurring inflammation, leg ulcers, hemorrhage and deep vein thrombosis.  
         [0004]     Traditionally, varicose veins have been treated by a surgical procedure known as stripping. In stripping, varicose veins are ligated and completely removed. More recently, varicose veins have been treated by endovenous laser therapy. Endovenous laser therapy treats varicose veins of the leg by eliminating the highest point at which blood flows back down the veins, thereby cutting off the incompetent venous segment. Endovenous laser therapy has significant advantages over surgical ligation and stripping. In general, endovenous laser therapy has reduced risks related to anesthesia, less likelihood of surgical complications, reduced costs and a shorter recovery period than ligation and stripping.  
         [0005]     Endovenous laser therapy involves the use of a bare tipped laser fiber to deliver laser energy to the venous wall from within the vein lumen that causes thermal vein wall damage at the desired location. The subsequent fibrosis at this location results in occlusion of the vein that prevents blood from flowing back down the vein. Generally, endovenous laser therapy utilizes an 810 to 980 nanometer diode laser as a source of laser energy that is delivered to the venous wall in a continuous mode with a power of about 10 to 15 Watts.  
         [0006]     An exemplary endovenous laser therapy procedure is disclosed in U.S. Pat. No. 4,564,011 issued to Goldman. The Goldman patent discloses the use of an optical fiber to transmit laser energy into or adjacent to a blood vessel to cause clotting of blood within the vessel or to cause scarring and shrinkage of the blood vessel.  
         [0007]     A typical endovenous laser therapy procedure includes the location and mapping of venous segments with duplex ultrasound. An introducer sheath is inserted into the greater saphenous vein over a guide wire, followed by a bare tipped laser fiber about 600 micrometers in diameter. The bare distal end of the laser fiber is advanced to within 1 to 2 cm of the sapheno-femoral junction. Laser energy is then applied at a power level of about 10 to 15 watts along the course of the greater saphenous vein as the laser fiber is slowly withdrawn. Generally, positioning of the laser fiber is done under ultrasound guidance and confirmed by visualization of the red aiming beam of the laser fiber through the skin. The application of laser energy into the vein utilizes the hemoglobin in red blood cells as a chromophore. The absorption of laser energy by hemoglobin heats the blood to boiling, producing steam bubbles which cause full thickness thermal injury to the vein wall. This injury destroys the local venous endothelium and creates a full-length thrombotic occlusion of the greater saphenous vein. An example of current techniques for endovenous laser therapy procedures is described in U.S. Patent Publ. No. 2003/0078569 A1, the disclosure of which is hereby incorporated by reference.  
         [0008]     While current endovenous laser therapy procedures offer a number of advantages over conventional ligation and stripping, challenges remain in successfully implementing an endovenous laser therapy procedure. The accurate localization of the bare distal end of the laser fiber can be difficult even with ultrasound assistance. In addition, the bare distal end of the laser fiber is transparent to fluoroscopy. Because of the relatively small diameter and sharpness of the laser fiber, the distal tip of the laser fiber can sometimes enter or puncture and exit the vein wall while the laser fiber is being advanced up a tortuous greater saphenous vein. Laser fibers used in current endovenous laser therapy procedures are glass optical fibers coaxially surrounded by protective plastic jacket or coating. When this plastic jacket is exposed to heat during the endovenous therapy procedure, the plastic jacket tends to melt or burn back from the distal tip of the fiber as the procedure is performed leaving undesirable foreign matter in the vein. In addition, it is possible for the tip of the laser fiber to come into close contact with the venous wall during the endovenous laser treatment. When this occurs there is an increased possibility of perforation of the venous wall due to the unintended localized application of laser energy and the consequent generation of heat. This can lead to additional complications in the endovenous procedure.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention is an endovenous laser fiber that includes a flexible heat resistant tip shield coaxially surrounding the distal end of the laser fiber and having an irregular surface. The tip shield may take the form of a coil spring, coiled wire or a slotted tube that has a rounded or chamfered distal most end. Preferably, the distal tip shield is formed of a flexible spring formed of stainless steel, platinum-iridium alloy or nitinol that coaxially surrounds the distal portion of the laser fiber transverse to the longitudinal axis of the laser fiber while leaving at least the distal end face exposed.  
         [0010]     The spring coil tip shield substantially increases the visibility of the laser fiber tip to ultrasound because of the increased ultrasound reflectivity. The tip shield also makes the fiber end visible to fluoroscopy when it is made from radio-opaque material. In addition, the tip shield protects the laser fiber from damage and deflects the laser fiber tip from digging into the vein wall during as it is advanced into the vein. The tip shield may be generally cylindrical or tapered in shape. Because the spring coil tip shield tends to deflect the laser fiber tip from the vein wall, the risk of inadvertent application of laser energy directly into the venous wall is also reduced, thereby decreasing the risk of inadvertent venous wall perforation.  
         [0011]     The spring coil tip shield also acts as a heat sink absorbing excess heat generated in the proximity of the distal end of the laser fiber and improving heat dissipation at the distal tip of the laser fiber. Improved heat dissipation and the associated set back provided by the tip shield reduces the potential for burn back of the plastic jacket around the laser fiber and improves heat transfer from the optical fiber to the blood and other surrounding tissue. The improved heat transfer from the spring coil tip shield tends to encourage the clotting of blood in the blood vessel, thus improving results in endovenous laser therapy procedures. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a perspective view of the tip of an embodiment of the laser fiber of the present invention;  
         [0013]      FIG. 2  is an exploded perspective view of the laser fiber of  FIG. 1 ;  
         [0014]      FIG. 3  is a plan view of the laser fiber;  
         [0015]      FIG. 4  is an exploded plan view of the laser fiber;  
         [0016]      FIG. 5  is a graph of deflection comparing the present invention to laser fibers without a tip shield;  
         [0017]      FIG. 6  is a detailed cross-sectional view of an embodiment of laser fiber tip;  
         [0018]      FIG. 7  is a schematic view of the entire length of the laser fiber;  
         [0019]      FIG. 8  is a plan view of another embodiment of the laser fiber;  
         [0020]      FIG. 9  is a cross-sectional view of the laser fiber of  FIG. 8  taken at section line  9 - 9 ; and  
         [0021]      FIG. 10  is a detailed cross-sectional view of the laser fiber depicted in  FIG. 9 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     Referring to  FIGS. 1-7 , the endovenous laser fiber  10  of the present invention generally includes an optic fiber  12  coaxially surrounded by a protective jacket  14  and having at a distal portion  18  a flexible heat resistant tip shield  16  that has an irregular surface.  
         [0023]     Optic fiber  12  is desirably a 400 to 600 micron glass optical fiber with a finely polished distal tip end, although a polymer fiber could be used. Those skilled in the art will understand that the designated dimension of the glass optical fiber refers to the diameter D of the fiber including the core and cladding but exclusive of the protective jacket  14 . The exterior dimensions of the protective jacket are larger. While a single optical fiber is described, it will be recognized that optic fiber  12  could also comprise a stranded arrangement of multiple optical fibers. Desirably the endovenous laser fiber  10  is about three and one half meters long. The optic fiber  12  is preferably provided with a standardized connector  17 , such as an SMA-905 standard connector with an adjustable fiber lock, for connection to a laser source console (not shown). The laser source console is preferably a solid state diode laser console operating at a wavelength of 810 nanometers, 940 nanometers or 980 nanometers and supporting a maximum power output of about 15 Watts.  
         [0024]     Optic fiber  12  is coaxially surrounded by a protective jacket  14 . Protective jacket  14  is generally conventional and is desirably formed of a biocompatible plastic material. Protective jacket  14  preferably covers substantially the entire longitudinal length of optic fiber  12  leaving exposed length L approximately ½ to 2 cm at the distal portion  18  of the optic fiber  12 . At least a portion of this exposed distal end  18  is covered by a rigid or flexible heat resistant tip shield  16 .  
         [0025]     Heat resistant tip shield  16  preferably covers the entire exposed distal portion  18  of optic fiber  12 . Tip shield  16  coaxially surrounds the distal portion  18  of the optic fiber  12  transverse to the longitudinal axis of the optic fiber  12  while leaving the distal tip face  24  exposed. Tip shield  16  is formed of a rigid or flexible, heat resistant, heat conductive material having an irregular ultrasound reflective surface. Tip shield  16  also is desirably, readily deflectable upon encountering an obstruction at an acute angle.  
         [0026]     In a preferred embodiment, tip shield  16  is desirably formed of a stainless steel, platinum/iridium or nitinol coil spring  22  tightly wound about the distal portion  18  of optic fiber  12 . Coil spring  22  is desirably about ½ to 2 cm in length and has an outside diameter of approximately 950 to 1100 μl. Coil spring  22  is desirably formed from heat resistant, thermally conductive wire  24 . Wire  24  is desirably stainless steel having a wire diameter of between 100 and 230 μl. Tip shield  16  can also be formed from stainless steel, platinum/iridium or nitinol in the form of a slotted tube rather than a coil spring. Desirably coil spring  22  is of such a length and position on the distal portion  18  of optic fiber  12  so that tip end  24  of optic fiber  12  is substantially aligned with the distal end  26  of coil spring  22 . Tip shield  16  may be cylindrical or tapering. Tip shield  16  may be secured to glass fiber  12  with a high temperature adhesive.  
         [0027]     Alternately, the tip end  24  of optic fiber  12  may extend slightly beyond distal end  26  of coil spring  22 . For example, tip end  24  may extend beyond the termination of tip shield  16  a distance E of about 0.003 inches. Tip end  24  may be rounded in shape or any other shape but is preferably planar and forms a ninety-degree angle with the long axis of the optic fiber  12 .  
         [0028]     In a preferred embodiment, as shown in the cross-sectional detail of  FIG. 6 , the tip end  24  of optic fiber  12  is surfaced to a substantially flat shape and includes a relatively sharp circumference  30  at the boundary between the substantially flat shape  32  of tip end  24  and the side wall  34  of the optic fiber  12 . It is believed that the circumference  30  of tip end  24  is primarily responsible for the snagging or catching of the tip end  24  along the interior wall of the blood vessel. In order to minimize the potential for snagging or catching of the tip end  24 , the effective transverse thickness  40  of tip shield  16  and the longitudinal offset position  42  of the tip shield  16  relative to the circumference  30  are dimensioned such that a line  44  tangent to tip shield  16  will intersect the circumference  30  assuming that the optic fiber meets the vessel wall at an angle alpha not greater than sixty degrees.  
         [0029]     Tip shield  16  is formed of a heat resistant, heat conductive material. Tip shield  16  is desirably substantially flexible as well. Tip shield  16  desirably preferably should withstand temperatures up to approximately 1000° F. For example, tip shield  16  desirably is formed of a material having a thermal conductivity of at least 12 W/mK at 273 Kelvin.  
         [0030]     Referring to  FIG. 5 , test results demonstrate that the optic fiber  12  with tip shield  16  demonstrates improved deflection qualities as compared to a bare tipped fiber and a finely polished tip fiber. The optic fiber  12  with tip shield  16  requires approximately 0.020 pound less force application to be advanced at a wall contact angle of between 50 and 60 degrees than a polished tip fiber. As compared to a bare tip fiber the tip shielded optic fiber  12  requires about 0.250 pounds less force application at a contact angle of between 50 and 60 degrees.  
         [0031]     Testing was performed in the following fashion. The tested fibers were advanced into a longitudinally halved PTFE tubular sheath representing a model of a blood vessel to contact the sheath wall at the indicated angles and the force required to the advance the fiber against the sheath was measured and recorded. The sheath utilized in the test procedure was of the type typically used in vascular introducers. PTFE material does not closely simulate the qualities of a blood vessel wall but is conventionally utilized for testing purposes because of its ready availability.  
         [0032]     Endovenous laser fiber  10  is utilized with a conventional guide wire and introducer during the endovenous laser therapy process. Insertion and placement of endovenous laser fiber  10  is largely accomplished by conventional techniques.  
         [0033]     In operation, an endovenous laser therapy procedure begins with a physical examination of the limb to be treated. Transverse measurements of the greater saphenous vein are made 2-3 cm below the sapheno-femoral junction and along the course of the greater saphenous vein with ultrasound and Doppler ultrasound. Doppler ultrasound can be utilized to confirm retrograde flow at the sapheno-femoral junction. Utilizing ultrasound, the location of the greater saphenous vein is recorded and an outline of the course of the greater saphenous is made on the leg with a marking pen. A desired insertion site for the catheter is also marked.  
         [0034]     The limb to be treated is then prepped and draped in sterile fashion and the ultrasound transducer is enclosed in a sterile covering. The physician then cannulates the greater saphenous vein, typically using a 19-gauge needle, utilizing the Seldinger technique under ultrasound guidance. The physician should confirm the presence of non-pulsatile venous flow through the needle to confirm that the needle is in the vein. Next, the physician inserts a preferably 0.035 inch guide wire into the vessel and removes the needle over the guide wire. Next, the physician passes an introducer sheath over the guide wire and advances the introducer sheet into the sapheno-femoral junction. Preferably, a 5-French introducer sheath is used. The end of the sheath is desirably positioned at the proximal edge of the treatment area, generally 2-3 cm distal to the sapheno-femoral junction. The distal tip of the introducer sheath should not be positioned closer than 1 cm distal to the sapheno-femoral junction as this will place the fiber tip into the common femoral vein. The physician then removes the internal sheath dilator and guide wire and flushes the sheath with saline using standard technique.  
         [0035]     The physician next prepares the laser console in accordance with its operating instructions and, outside of the sterile field, removes the cover from the laser fiber connector  17  and connects the laser fiber to the laser console and activates a red aiming beam. The physician inserts the endovenous laser fiber  10  into the introducer sheath and advances the laser fiber until a holder (not shown) snaps into the hub of the introducer sheath. The holder is designed so that the laser fiber  10  is exposed by approximately I cm beyond the distal tip of the introducer sheath. Next, utilizing ultrasound the physician confirms the position of the endovenous laser fiber  10  and the introducer sheath. The endovenous laser fiber  10  should be exposed slightly beyond the introducer sheath and located at least 2 cm distal to the sapheno-femoral junction. This is confirmed by visualization of the red aiming beam through the skin with the room lights extinguished.  
         [0036]     The physician then administers a local anesthetic subcutaneously throughout the entire treatment area. While protecting the eyes of all operating room personal with laser safety glasses, the physician places the laser console in the ready mode, usually at 14 watts continuous power. With the lights turned down, the physician holds the introducer sheath by the hub, activates the laser and simultaneously withdraws the introducer sheath, desirably at a rate of about 2 mm per second. The introducer sheath desirably includes markings to aid in measurement during removal. Upon completion of the procedure along the entire treatment length, the laser is turned off, the introducer sheath is removed and the endovenous laser fiber  10  is removed from the vessel. Compression is applied to the wound until bleeding stops and a hemostatic bandage is applied over the percutaneous puncture.  
         [0037]     The present invention may be embodied in other specific form without departing from the spirit of the essential attributes thereof, therefore, the illustrated embodiment should be considered in all respect as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.