Abstract:
An injection catheter assembly is provided. This assembly can include an outer elongated member having a proximal end, a distal end, and an external diameter and an inner elongated member having a proximal region and a distal region. The inner elongated member may be positioned at least partially within the outer elongated member, may have a piercing tip at the end of the proximal region and may be rotatable within the outer elongated member with the degree of rotation of the inner elongated member adjusting the distance that the piercing tip can extend from the distal end of the outer elongated member.

Description:
RELATED APPLICATIONS  
       [0001]    The present application is related to U.S. patent application Ser. No. 09/634,117, entitled “Tortuose Path Injection Device And Method” now U.S. Pat. No. ______, U.S. patent application Ser. No. 09/635,083, entitled “Cather Shaft Assembly,” and is a continuation of U.S. patent application Ser. No. 09/633,924, now U.S. Pat. No. ______. 
     
    
     
       RELATED FIELD  
         [0002]    The present invention relates generally to devices and methods for delivering therapeutic or diagnostic agents to a portion of the human body. More particularly, the present invention relates generally to devices and methods for delivering and injecting fluid into heart tissue.  
         BACKGROUND  
         [0003]    Intravascular catheters are currently utilized in a wide variety of minimally invasive or percutaneous medical procedures. Generally, an intravascular catheter enables a physician to remotely perform a medical procedure by inserting the catheter into the vascular system of the patient at an easily accessible location and navigating the tip of the catheter to a desirable target site. By this method, virtually any target site in the patient&#39;s vascular system may be remotely accessed.  
           [0004]    Typically, a percutaneous procedure begins with the step of inserting a distal portion of the catheter into the patient&#39;s vasculature at a convenient location. Once the distal portion of the catheter has entered the patient&#39;s vascular system the physician may urge the distal tip forward by applying longitudinal forces to the proximal portion of the catheter. Frequently the path taken by a catheter through the vascular system is tortuous, requiring the catheter to change direction frequently. While advancing the catheter through the tortuous path of the patient&#39;s vasculature, the physician must steer the distal end of the catheter. During a percutaneous procedure, the physician typically is not able to manipulate the distal portion of the catheter directly. For this reason, physicians typically must steer the distal end of the catheter by applying torsional forces to the proximal portion of the catheter.  
           [0005]    Injection catheters are a type of catheter which may be used to inject therapeutic or diagnostic agents into various target tissues within the human body. An advantage of injection catheters is that the target tissue may be accessed utilizing minimally invasive surgical techniques. As with other types of catheters, the physician typically is not able to manipulate the distal portion of an injection catheter directly.  
           [0006]    In many applications the target tissue is within a wall of an organ such as the stomach or the heart. When the target tissue is within the wall of an organ it is often desirable to inject the therapeutic or diagnostic agent into the tissue proximate the center of the organ wall. If the needle of the injection catheter inadvertently passes through the wall, the therapeutic or diagnostic agents dispensed from the distal end of the needle will not be effectively delivered to the target tissue. Wall thickness may vary from organ to organ. Additionally, wall thickness may vary within one organ.  
           [0007]    One example of a medical procedure involving the delivery of a therapeutic and/or diagnostic agent to a targeted portion of a patient&#39;s body is the treatment of esophageal varicies. This is a condition in which blood vessels of the esophagus are enlarged and may potentially burst. For such a procedure, a therapeutic agent is injected into the varix. When treating an esophageal varix, the agent may be a coagulant such as sodium morrhuate. When a coagulant is injected into a varix, it causes it to occlude. An injection catheter may be used to deliver the therapeutic agent in order to minimize the invasive nature of the procedure.  
           [0008]    In a similar procedure, an injection catheter may be utilized in the treatment of ulcers in the stomach lining. With such treatment, an injection catheter may be used to deliver drugs such as sclerosing or vasoconstrictive agents. These drugs typically clot or occlude the bleeding tissue to stop bleeding or to reduce the possibility of a blood vessel bursting.  
           [0009]    Injection catheters may also be used to inject therapeutic or diagnostic agents into the heart. Examples of agents delivered to the heart include genes, proteins, or drugs. In the case of injecting a therapeutic agent into the heart, 27 or 28 gauge needles are generally used to inject solutions carrying genes, proteins, or drugs directly into the myocardium. A typical volume of an agent delivered to an injection site is about 100 microliters.  
           [0010]    Therapeutic and diagnostic agents may be delivered to a portion of the heart as part of a percutaneous myocardial revascularization (PMR) procedure. PMR is a procedure which is aimed at assuring that the heart is properly oxygenated. Assuring that the heart muscle is adequately supplied with oxygen is critical to sustaining the life of a patient. To receive an adequate supply of oxygen, the heart muscle must be well perfused with blood. In a healthy heart, blood perfusion is accomplished with a system of blood vessels and capillaries. However, it is common for the blood vessels to become occluded (blocked) or stenotic (narrowed). A stenosis may be formed by an atheroma which is typically a harder, calcified substance which forms on the walls of a blood vessel.  
           [0011]    Historically, individual stenotic lesions have been treated with a number of medical procedures including coronary bypass surgery, angioplasty, and atherectomy. Coronary bypass surgery typically involves utilizing vascular tissue from another part of the patient&#39;s body to construct a shunt around the obstructed vessel. Angioplasty techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA) are relatively non-invasive methods of treating a stenotic lesion. These angioplasty techniques typically involve the use of a guidewire and a balloon catheter. In these procedures, a balloon catheter is advanced over a guidewire such that the balloon is positioned proximate a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened. A third technique which may be used to treat a stenotic lesion is atherectomy. During an atherectomy procedure, the stenotic lesion is mechanically cut or abraded away from the blood vessel wall.  
           [0012]    Coronary by-pass, angioplasty, and atherectomy procedures have all been found effective in treating individual stenotic lesions in relatively large blood vessels. However, the heart muscle is perfused with blood through a network of small vessels and capillaries. In some cases, a large number of stenotic lesions may occur in a large number of locations throughout this network of small blood vessels and capillaries. The torturous path and small diameter of these blood vessels limit access to the stenotic lesions. The sheer number and small size of these stenotic lesions make techniques such as cardiovascular by-pass surgery, angioplasty, and atherectomy impractical  
           [0013]    When techniques which treat individual lesion are not practical percutaneous myocardial revascularization (PMR) may be used to improve the oxygenation of the myocardial tissue. A PMR procedure generally involves the creation of holes, craters or channels directly into the myocardium of the heart. In a typical PMR procedure, these holes are created using radio frequency energy delivered by a catheter having one or more electrodes near its distal end. After the wound has been created, therapeutic agents are sometimes ejected into the heart chamber from the distal end of a catheter.  
           [0014]    Positive clinical results have been demonstrated in human patients receiving PMR treatments. These results are believed to be caused in part by blood flowing within a heart chamber through channels in myocardial tissue formed by PMR. Increased blood flow to the myocardium is also believed to be caused in part by the healing response to wound formation. Specifically, the formation of new blood vessels is believed to occur in response to the newly created wound. This response is sometimes referred to as angiogenisis. After the wound has been created, therapeutic agents which are intended to promote angiogenisis are sometimes ejected into the heart chamber. A limitation of this procedure is that the therapeutic agent may be quickly carried away by the flow of blood through the heart.  
           [0015]    In addition to promoting increased blood flow, it is also believed that PMR improves a patient&#39;s condition through denervation. Denervation is the elimination of nerves. The creation of wounds during a PMR procedure results in the elimination of nerve endings which were previously sending pain signals to the brain as a result of hibernating tissue.  
         SUMMARY OF THE INVENTION  
         [0016]    The present invention relates generally to devices and methods for delivering therapeutic or diagnostic agents to a portion of the human body. More particularly, the present invention relates generally to devices and methods for delivering and injecting fluid into heart tissue.  
           [0017]    An injection catheter in accordance an exemplary embodiment of the present invention includes a first elongate shaft having a lumen and a second elongate shaft disposed within the lumen of the first elongate shaft. In this exemplary embodiment, the second elongate shaft includes a point and an injection orifice proximate it&#39;s distal end. In many applications it is desirable to advance the distal end of the second elongate shaft by a known distance relative to the distal end of the first elongate shaft. For example, this know displacement may be desireable when a physician wishes to inject a fluid into the wall of an organ.  
           [0018]    In one embodiment, a knob is fixed to the second elongate shaft of the exemplary injection catheter proximate a proximal end thereof. Also in this embodiment, a housing is disposed about the first elongate shaft of the exemplary injection catheter proximate the proximal end thereof. A physician utilizing the catheter in a surgical procedure may advance the distal end of the second elongate shaft by rotating the second elongate shaft relative to the first elongate shaft. To facilitate this relative rotation, the physician may grasp the housing and apply a torque to the knob.  
           [0019]    In a particularly preferred embodiment, there is a known relationship between the rotary motion of the second elongate shaft relative to the first elongate shaft and the linear motion of the second elongate shaft relative to the first elongate shaft. For example, the physician may advance the second elongate shaft by a desired distance by rotating the second elongate shaft by a corresponding number of turns. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 is a plan view of a catheter in accordance with an exemplary embodiment of the present invention;  
         [0021]    [0021]FIG. 2 is a diagrammatic view including the catheter of FIG. 1 and a patient having a heart and a vascular system including a blood vessel defining a blood vessel lumen;  
         [0022]    [0022]FIG. 3 is a cross sectional view of a distal portion of the catheter of FIG. 1 and FIG. 2;  
         [0023]    [0023]FIG. 4 is a partial cross sectional view of a distal portion of an additional exemplary embodiment of a catheter in accordance with the present invention;  
         [0024]    [0024]FIG. 5 is a partial cross sectional view of a distal portion of an additional exemplary embodiment of a catheter in accordance with the present invention;  
         [0025]    [0025]FIG. 6 is a partial cross sectional view of a distal portion of an additional exemplary embodiment of a catheter in accordance with the present invention;  
         [0026]    [0026]FIG. 7 is a partial cross sectional view of a catheter having an inner assembly in accordance with an exemplary embodiment of the present invention; and  
         [0027]    [0027]FIG. 8 is a partial cross sectional view of the inner assembly of FIG. 7. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]    The following detailed description should be read with reference to the drawings, in which like elements in different drawings are numbered in like fashion. The drawings which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. In some cases., the drawings may be highly diagrammatic in nature. Examples of constructions, materials, dimensions, and manufacturing processes are provided for various elements. Those skilled in the art will recognize that many of the examples provided have suitable alternatives which may be utilized.  
         [0029]    [0029]FIG. 1 is a plan view of a catheter  100  in accordance with the present invention. Catheter  100  has a distal end  102 , a proximal end  104 , and a shaft assembly  106 . Shaft assembly  106  comprises a first elongate shaft  120  having a distal end  122 , a proximal end  124 , and an inside surface  126  defining a lumen  128 . Shaft assembly  106  also includes a second elongate shaft  130  disposed within lumen  128  of first elongate shaft  120 .  
         [0030]    Second elongate shaft  130  has a distal end  132  and a proximal end  134 . In many applications it is desirable to advance distal end  132  of second elongate shaft  130  by a known distance relative to distal end  122  of first elongate shaft  120 . In the embodiment of FIG. 1, a knob  138  is fixed to second elongate shaft  130 . Also in the embodiment of FIG. 1, a housing  140  is disposed about first elongate shaft  120  proximate proximal end  124  thereof. In a preferred embodiment, a physician utilizing catheter  100  in a surgical procedure may advance distal end  132  of second elongate shaft  130  by rotating second elongate shaft  130  relative to first elongate shaft  120 . To facilitate this relative rotation, the physician may grasp housing  140  and apply a torque to knob  138 .  
         [0031]    In a particularly preferred embodiment, there is a known relationship between the rotary motion of second elongate shaft  130  relative to first elongate shaft  120  and the linear motion of second elongate shaft  130  relative to first elongate shaft  120 . For example, the physician may advance second elongate shaft  130  by a desired distance by rotating second elongate shaft  130  by a corresponding number of turns.  
         [0032]    In the embodiment of FIG. 1, second elongate shaft  130  forms a point  142  proximate distal end  132  thereof. Second elongate shaft  130  also defines an injection port  144  proximate point  142 . A hub  146  is disposed about second elongate shaft  130 . Hub  146  defines a proximal port  148 . In a preferred embodiment, proximal port  148  is in fluid communication with injection port  144  via an injection lumen  150  defined by second elongate shaft  130 .  
         [0033]    Catheter  100  of FIG. 1 may be generally referred to as an injection catheter. It is to be appreciated that a catheter in accordance with the present invention may comprise various types of catheters without deviating from the spirit and scope of the present invention.  
         [0034]    In a preferred embodiment, second elongate shaft  130  of catheter  100  comprises hypodermic tubing. Second elongate shaft  130  may comprise various metallic and non-metallic materials without deviating from the spirit and scope of the present invention. Examples of metallic materials which may be suitable in some applications include stainless steel, and nickel-titanium alloy. Examples of non-metallic materials which may be suitable in some applications are included in the list below which is not exhaustive: polycarbonate, poly(L-lactide) (PLLA), poly(D,L-lactide) (PLA), polyglycolide (PGA), poly(L-lactide-co-D,L-lactide) (PLLA/PLA), poly(L-lactide-co-glycolide) (PLLA/PGA), poly(D, L-lactide-co-glycolide) (PLA/PGA), poly(glycolide-co-trimethylene carbonate) (PGA/PTMC), polyethylene oxide (PEO), polydioxanone (PDS), polycaprolactone (PCL), polyhydroxylbutyrate (PHBT), poly(phosphazene), polyD,L-lactide-co-caprolactone) (PLA/PCL), poly(glycolide-co-caprolactone) (PGA/PCL), polyanhydrides (PAN), poly(ortho esters), poly(phoshate ester), poly(amino acid), poly(hydroxy butyrate), polyacrylate, polyacrylamid, poly(hydroxyethyl methacrylate), polyurethane, polysiloxane and their copolymers.  
         [0035]    In a preferred embodiment, first elongate shaft  120  of catheter  100  comprises an elongate tubular member including a reinforcement member (e.g., braided or coiled wire). Second elongate shaft  130  may comprise various metallic and non-metallic materials without deviating from the spirit and scope of the present invention. Examples of metallic materials which may be suitable in some applications include stainless steel, and nickel-titanium alloy. Examples of non-metallic materials which may be suitable in some applications include: polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC), polyurethane, polytetrafluoroethylene (PTFE), polyether block amide (PEBA), polyamide, and polyimide.  
         [0036]    [0036]FIG. 2 is a diagrammatic view including catheter  100  of FIG. 1 and a patient  110 . Patient  110  has a heart  111  and a vascular system  112  including a blood vessel  113  defining a blood vessel lumen  114 . An access sheath  115  is partially disposed within a leg of patient  110 . A distal end of access sheath  115  is disposed within blood vessel lumen  114  of blood vessel  113 . Access sheath  115  may aid in the introduction of catheter  100  into blood vessel lumen  114 .  
         [0037]    As shown in FIG. 2, a portion of catheter  100  is disposed within blood vessel lumen  114  of blood vessel  113 . Distal end  102  (not visible in FIG. 2) of catheter  100  is disposed within heart  111  of patient  110 . In a preferred embodiment, distal end  102  of catheter  100  is disposed proximate a wall of heart  111 .  
         [0038]    In the embodiment of FIG. 2, a fluid source  116  is coupled to hub  146  disposed about second elongate shaft  130  of catheter  100 . In the embodiment of FIG. 2, fluid source  116  includes a variable volume chamber  117  defined by a body  118 . In a preferred embodiment, variable volume chamber  117  is in fluid communication with injection lumen  150  of second elongate shaft  130 . A plunger  119  is slidingly disposed within variable volume chamber  117 . Urging the plunger distally has the effect of urging fluid into injection lumen  150  of second elongate shaft  130 . A number of energy sources may be utilized to urge plunger  119  distally. Energy sources which may be suitable in some applications include springs, compressed gas, a human being, and electricity. Various additional embodiments of fluid source  116  are possible without deviating from the spirit and scope of the present invention. Examples of fluid sources which may be suitable in some applications include syringes, peristaltic pumps, and an I.V. bag with pressure applied to its outer surface.  
         [0039]    A method of injecting a fluid into heart  111  of patient  110  may be described with reference to FIG. 2. The distal end of access sheath  115  may be inserted into blood vessel lumen  114  of blood vessel  113 . Distal end  102  of catheter  100  may be inserted into the lumen of access sheath  115 . Distal end  102  of catheter  100  may be advanced through access sheath  115  and into blood vessel lumen  114  of blood vessel  113 . Catheter  100  may be urged forward through vascular system  112  of patient  110  until distal end  102  is proximate the target tissue (e.g., a wall of heart  111 ). In FIG. 2 it may be appreciated that shaft assembly  106  of catheter  100  is bent in a plurality of locations to conform with a tortuous path defined by vascular system  112 .  
         [0040]    In a preferred method, distal end  132  of second elongate shaft  130  is disposed within lumen  128  of first elongate shaft  120  during the above steps. Once distal end  102  of catheter  100  is positioned proximate the target tissue, second elongate shaft  130  may be advanced so that point  142  penetrates the bodily tissue at the target site. With injection port  144  of second elongate shaft  130  disposed within the target tissue, fluid may be urged into the target tissue. For example, force may be applied to plunger  119  urging fluid out of fluid source  116  and into injection lumen  150  of second elongate shaft  130 . The addition of fluid from fluid source  116  results in the injection of fluid into the target tissue.  
         [0041]    In many applications it is desirable to advance point  142  and injection port  144  into the target tissue by a known distance. A physician may advance point  142  and injection port  144  into the target tissue by rotating knob  138 . The physician may determine the depth of penetration, for example, by observing the angle of rotation of knob  138  relative to housing  140  disposed about second elongate shaft  130 . Embodiments have been envisioned in which knob  138  and/or housing  140  include indicia to aid the physician.  
         [0042]    The fluid injected into the target area may include various therapeutic or diagnostic agents adapted to treat the medical condition which the physician is treating. It is to be appreciated that methods in accordance with the present invention may be used in the treatment of a number of medical conditions. For example, methods and devices of performing percutaneous myocardial revascularization (PMR) in accordance with the present invention have been envisioned. For example, a plurality of wounds may be created in hibernating tissue of the heart. These wounds may be created by injecting a fluid into the tissue of the heart. As a result of these wounds, there will be increased blood flow to the myocardium caused in part by the body&#39;s healing response to the wound. One healing response of the body is sometimes referred to as angiogenisis. In addition to promoting increased blood flow, it is also believed that PMR improves a patient&#39;s condition through denervation. Denervation is the elimination of nerves. The creation of wounds during this procedure results in the elimination of nerve endings which were previously sending pain signals to the brain as a result of hibernating tissue.  
         [0043]    Suitable wounds may be created by injecting a fluid such as water, saline, or ringers solution into the heart tissue. Wound formation and revascularization of myocardial tissue may enhanced by injecting a fluid including a therapeutic agent into the tissue of the heart. Examples, of therapeutic agents which may be suitable include growth factors, drugs and caustic agents. The fluid injected into the heart tissue may also include a radiopaque material. Injecting a radiopaque material into the wound effectively marks the locations which have been treated. This will aid the physician in procedures which are being performed percutaneously using fluoroscopic equipment.  
         [0044]    In the exemplary embodiment of FIG. 2, catheter  100  may be utilized to inject fluid into heart  111  of patient  110 . It is to be appreciated that catheter  100  may by utilized in the treatment various medical conditions occurring in various locations in the body. For example, catheter  100  may be used in the treatment of esophageal varicies, a condition in which blood vessels of the esophagus are enlarged and may potentially burst. For such a procedure, injection port  144  would be disposed proximate the enlarged varix and an appropriate agent would be injected into the varix. When treating an esophageal varice, the agent may be a coagulant such as sodium morrhuate. When a coagulant is injected into a varix, it causes the occlusion thereof.  
         [0045]    [0045]FIG. 3 is a cross sectional view of a distal portion  152  of catheter  100  of FIG. 1 and FIG. 2. In FIG. 3 it may be appreciated that catheter  100  includes a first helical member  154  comprising a plurality of turns  156  disposed within lumen  128  of first elongate shaft  120 . In a preferred embodiment, first helical member  154  is fixed to inside surface  126  of first elongate shaft  120 . In the embodiment of FIG. 3, first helical member  154  comprises a first screw thread  158 .  
         [0046]    Also in the embodiment of FIG. 3, a second helical member  160  comprising a plurality of Turns  162  is disposed about second elongate shaft  130 . In the embodiment of FIG. 3, second helical member  160  is preferably fixed to second elongate shaft  130 . In the embodiment of FIG. 3, second helical member  160  comprises a second screw thread  164 . In FIG. 3, it may be appreciated that a plurality of Turns  162  of second helical member  160  are disposed between a plurality of turns  156  of first helical member  154 .  
         [0047]    In the embodiment of FIG. 3, a header  166  is partially disposed within lumen  128  of first elongate shaft  120 . In a preferred embodiment, header  166  includes a radial enlargement  161 . In this preferred embodiment, radial enlargement  161  provides a generally enlarged distal contact surface  170 . Generally enlarged distal contact surface  170  reduces the likelihood that undesired tissue damage will occur when distal end  102  of catheter  100  is urged against bodily tissue. Header  166  also defines a header lumen  168 . As shown in FIG. 3, second elongate shaft  130  is slidingly disposed within header lumen  168 .  
         [0048]    [0048]FIG. 4 is a partial cross sectional view of a distal portion  252  of an additional embodiment of a catheter  200  in accordance with the present invention. Catheter  200  includes a shaft assembly  206  comprising a first elongate shaft  220  having a distal end  222  and an inside surface  226  defining a lumen  228 . Shaft assembly  206  also includes a second elongate shaft  230  having a distal end  232  slidingly disposed within lumen  228  of first elongate shaft  220 .  
         [0049]    In many applications it is desirable to advance distal end  232  of second elongate shaft  230  by a known distance relative to distal end  222  of first elongate shaft  220 . In the embodiment of FIG. 4, second elongate shaft  230  may be selectively advanced and retracted.  
         [0050]    In FIG. 4 it may be appreciated that catheter  200  includes a first helical member  254  comprising a plurality of turns  256  disposed within lumen  228  of first elongate shaft  220 . In the embodiment of FIG. 4, first helical member  254  is preferably fixed to inside surface  226  of first elongate shaft  220 . In the embodiment of FIG. 4, first helical member  254  comprises a first screw thread  258 . Embodiments of the present invention have been envisioned in which first helical member  254  comprises a rib formed by first elongate shaft. Embodiments of the present invention have also been envisioned in which first helical member  254  comprises a coil.  
         [0051]    A second helical member  260  is formed by second elongate shaft  230 . In the embodiment of FIG. 4, second helical member  260  comprises a coil  272  having a plurality of Turns  262 . In FIG. 4, it may be appreciated that a plurality of Turns  262  of second helical member  260  are disposed between a plurality of turns  256  of first helical member  254 .  
         [0052]    In the embodiment of FIG. 4, a header  266  is partially disposed within lumen  228  of first elongate shaft  220 . In a preferred embodiment, header  266  includes a radial enlargement  261 . In this preferred embodiment, radial enlargement  261  provides a generally enlarged distal contact surface  270 . Generally enlarged distal contact surface  270  reduces the likelihood that undesired tissue damage will occur when distal end  202  of catheter  200  is urged against bodily tissue. Header  266  also defines a header lumen  268 . As shown in FIG. 4, second elongate shaft  230  is slidingly disposed within header lumen  268 .  
         [0053]    In the embodiment of FIG. 4, second elongate shaft  230  forms a point  242  proximate distal end  232  thereof. Second elongate shaft  230  also defines an injection port  244  proximate point  242 . A physician may advance point  242  and injection port  244  of second elongate shaft  230  into a target tissue by rotating second elongate shaft  230 . In a particularly preferred embodiment, there is a known relationship between the rotary motion of second elongate shaft  230  relative to first elongate shaft  220  and the linear motion of second elongate shaft  230  relative to first elongate shaft  220 . For example, the physician may advance point  242  and injection port  244  of second elongate shaft  230  by a desired distance by rotating second elongate shaft  230  by a corresponding number of turns.  
         [0054]    [0054]FIG. 5 is a partial cross sectional view of a distal portion  352  of an additional embodiment of a catheter  300  in accordance with the present invention. Catheter  300  includes a shaft assembly  306  comprising a first elongate shaft  320  having a distal end  322  and an inside surface  326  defining a lumen  328 . A header  366  is partially disposed within lumen  328  of first elongate shaft  320  proximate distal end  322 . Header  366  includes a first helical member  354  comprising a plurality of turns  356 . In the embodiment of FIG. 5, first helical member  354  comprises a first screw thread  358 .  
         [0055]    A second elongate shaft  330  is partially disposed within lumen  328  of first elongate shaft  320 . Second elongate shaft  330  forms a second helical member  360 . In the embodiment of FIG. 5, second helical member  360  comprises a coil  372  having a plurality of Turns  362 . In FIG. 5, it may be appreciated that a plurality of Turns  362  of second helical member  360  are disposed between a plurality of turns  356  of first helical member  354 . A distal end  332  of second elongate shaft  330  may be advanced into a target tissue by rotating second elongate shaft  330 . In a particularly preferred embodiment, there is a known relationship between the rotary motion of second elongate shaft  330  relative to first elongate shaft  320  and the linear motion of second elongate shaft  330  relative to first elongate shaft  320 . For example, the physician may advance point  342  and injection port  344  of second elongate shaft  330  by a desired distance by rotating second elongate shaft  330  by a corresponding angle.  
         [0056]    [0056]FIG. 6 is a partial cross sectional view of a distal portion  452  of an additional embodiment of a catheter  400  in accordance with the present invention. Catheter  400  includes a shaft assembly  406  comprising a first elongate shaft  420 , a second elongate shaft  430 , and a third elongate shaft  474 . First elongate shaft  420  has a distal end  422  and an inside surface  426  defining a lumen  428 . Third elongate shaft  474  is disposed within lumen  428  of first elongate shaft  420 . Second elongate shaft  430  is disposed within a third lumen  429  defined by third elongate shaft  474 .  
         [0057]    In the embodiment of FIG. 6, a header  466  is partially disposed within lumen  428  of first elongate shaft  420 . In a preferred embodiment, header  466  includes a radial enlargement  461 . In this preferred embodiment, radial enlargement  461  provides a generally enlarged distal contact surface  470 . Generally enlarged distal contact surface  470  reduces the likelihood that undesired tissue damage will occur when distal end  402  of catheter  400  is urged against bodily tissue. Header  466  also defines a header lumen  427 . As shown in FIG. 6, second elongate shaft  430  is slidingly disposed within header lumen  427 .  
         [0058]    A first helical member  454  comprising a plurality of turns  456  is disposed within third lumen  429  of third elongate shaft  474 . In the embodiment of FIG. 6, first helical member  454  comprises a first screw thread  458 . First helical member  454  is adapted to threadingly engage a second helical member  460  having a plurality of Turns  462 . As shown in FIG. 6, second helical member  460  is formed by a portion of header  466 . Header  466  is partially disposed within lumen  428  of first elongate shaft  420 . In the embodiment of FIG. 6, second helical member  460  comprises a second screw thread  464 . Header  466  also defines a header lumen  427 . As shown in FIG. 6, second elongate shaft  430  is disposed within header lumen  427 .  
         [0059]    In the embodiment of FIG. 6, a flange  476  is disposed about second elongate shaft  430 . Third elongate shaft  474  includes a stop  478 . In a presently preferred embodiment, stop  478  and flange  476  are adapted to limit the longitudinal travel of second elongate shaft  430  relative to first elongate shaft  420 .  
         [0060]    Third elongate shaft  474  may be utilized to adjust the depth of injection during a surgical procedure. A physician may apply a rotational force to a proximal end of third elongate shaft  474  causing it to rotate relative to header  466 . In a preferred embodiment, rotation of third elongate shaft  474  will alter the distance between a proximal surface  480  of stop  478  and distal contact surface  470  of header  466 . It may be appreciated that a change in the distance between a proximal surface  480  of stop  478  and distal contact surface  470  of header  466  will result in a change in the depth of injections made with catheter  400 . In the embodiment of FIG. 6, the travel of second elongate shaft  430  preferably stops when flange  476  contacts stop  478 .  
         [0061]    [0061]FIG. 7 is a partial cross sectional view of a distal portion  552  of an additional embodiment of a catheter  500  in accordance with the present invention. Catheter  500  includes a first elongate shaft  520  having a distal end  522  and an inside surface  526  defining a lumen  528 . A header  566  is partially disposed within lumen  528  of first elongate shaft  520  proximate the distal end thereof. An inner assembly  582  is slidingly disposed within lumen  528  of first elongate shaft  520 .  
         [0062]    [0062]FIG. 8 is a partial cross sectional view of inner assembly  582  of FIG. 7. In the embodiment of FIG. 8, inner assembly  582  has been withdrawn from lumen  528  of first elongate shaft  520 . Inner assembly  582  includes a third elongate shaft  574 , a second elongate shaft  530 , and a ferrule  584 . Second elongate shaft  530  is partially disposed within a third lumen  529  defined by third elongate shaft  574 .  
         [0063]    Third elongate shaft  574  of inner assembly  582  includes a first helical member  554 . Ferrule  584  of inner assembly  582  includes a second helical member  560 . In the embodiment of FIG. 8, first helical member  554  and second helical member  560  comprise a first screw thread  558  and a second screw thread  564  respectively. A plurality of turns  556  of first helical member  554  are disposed in threaded engagement with a plurality of Turns  562  of second helical member  560 .  
         [0064]    Ferrule  584  includes a distal end  586  and a ferrule lumen  588 . Ferrule lumen  588  allows second elongate shaft  530  to extend through ferrule  584 . In the embodiment of FIG. 8, a flange  576  is disposed about second elongate shaft  530 . Third elongate shaft  574  includes a stop  578 . In a preferred embodiment, stop  578  and flange  576  are adapted to limit the longitudinal travel of distal end  532  of second elongate shaft  530  relative to distal end  586  of ferrule  584 .  
         [0065]    Inner assembly  582  may be utilized to adjust the depth of injection during a surgical procedure. For example, a physician may withdraw inner assembly  582  from catheter  500  and rotate ferrule  584  relative to third elongate shaft  574 . In a preferred embodiment, relative rotation between third elongate shaft  574  and ferrule  584  will alter the distance between a proximal surface  580  of stop  578  and distal end  586  of ferrule  584 . It may be appreciated that a change in the distance between proximal surface  580  of stop  578  and distal end  586  of ferrule  584  will result in a change to the depth of injections made with catheter  500 . In the embodiment of FIG. 7 and FIG. 8, the travel of second elongate shaft  530  preferably stops when flange  576  contacts stop  578 . Changes may be made in details, particularly in matters of shape, size, and arrangement of parts without exceeding the scope of the invention. The invention&#39;s scope is, of course, defined in the language in which the appended claims are expressed.