Abstract:
Devices and methods for delivering therapeutic or diagnostic agents to a target tissue of a human body are disclosed. A catheter in accordance with the present invention includes an elongate shaft having a distal end, a proximal end, and a lumen therethrough. The elongate shaft includes a first curved portion proximate the distal end of the elongate shaft. The first curved portion of the elongate shaft defines a first plane. The elongate shaft also includes a second curved portion disposed between the distal end of the elongate shaft and the first curved portion of the elongate shaft. The second curved portion of the elongate shaft defines a second plane. The second plane intersects the first plane at an angle.

Description:
RELATED APPLICATIONS  
       [0001]    The present application is related to U.S. patent application Ser. No. ______, filed by the same assignee on even date herewith and entitled “Controlled Depth Injection Device and Method.” The present application is also related to U.S. patent application Ser. No. ______, filed by the same assignee on even date herewith and entitled “Catheter Shaft Assembly.” 
     
    
     
       FIELD OF THE INVENTION  
         [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 OF THE INVENTION  
         [0003]    Injection catheters may be used to inject therapeutic or diagnostic agents into a variety of organs, such as the heart. 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. A limitation to this method of delivering therapeutic agents to the heart is that the injected fluid tends to leak from the site of the injection after the needle is disengaged from the heart. In fact, fluid may continue to leak over several seconds. In the case of dynamic organs such as the heart, there may be more pronounced leakage with each muscle contraction.  
           [0004]    Many medical procedures involve the delivery of therapeutic and diagnostic agents to a targeted portion of a patient&#39;s body. For example, the delivery of a therapeutic agent is used in the treatment of esophageal varicies, a condition where 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 varice, 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.  
           [0005]    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.  
           [0006]    As mentioned previously, injection catheters may also be used to inject therapeutic or diagnostic agents into the heart. A limitation to this method of delivering therapeutic agents to the heart is that the injected fluid tends to leak from the site of the injection after the needle is disengaged from the heart. In fact, fluid may continue to leak over several seconds. In the case of the heart, there may be more pronounced leakage with each muscle contraction.  
           [0007]    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.  
           [0008]    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.  
           [0009]    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  
           [0010]    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.  
           [0011]    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.  
           [0012]    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  
         [0013]    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.  
           [0014]    A catheter in accordance with the present invention includes a first elongate shaft having a distal end, a proximal end, and a lumen therethrough. The first elongate shaft includes a first curved portion proximate the distal end of the first elongate shaft. In a preferred embodiment, the radius of the first curved portion of the first elongate shaft is selected so that the distal end of the first elongate shaft will be disposed within a wall of an organ (e.g., the heart) during an injection procedure in accordance with a method of the present invention. The first curved portion of the first elongate shaft defines a first plane.  
           [0015]    In one embodiment of the invention, the first elongate shaft also includes a second curved portion disposed between the distal end of the first elongate shaft and the first curved portion of the first elongate shaft. The second curved portion of the first elongate shaft defines a second plane which intersects the first plane at an angle. In a preferred embodiment, the second plane is substantially orthogonal to the first plane. This arrangement reduces the likelihood that the distal end of the first elongate shaft will perforate the wall of an organ (e.g., the heart) during an injection procedure in accordance with a method of the present invention.  
           [0016]    In one embodiment of the present invention, a second elongate shaft is slidingly disposed within the lumen of the first elongate shaft. In this embodiment, the second elongate shaft may include a curve defining a third plane. In a preferred embodiment, the third plane is substantially orthogonal to the first plane. This arrangement reduces the likelihood that the distal end of the second elongate shaft will perforate the wall of an organ (e.g., the heart) during an injection procedure in accordance with a method of the present invention.  
           [0017]    During an injection procedure in accordance with a method of the present invention both the first elongate shaft and the second elongate shaft may be advanced into a target tissue. After the injection of fluid into the target tissue, the first elongate shaft and the second elongate shaft may be withdrawn from the target tissue. In a preferred embodiment, the first elongate shaft and the second elongate shaft each include a plurality of curves. The tortuous path defined by the first elongate shaft and the second elongate shaft reduce the likelihood that injected fluid will escape from the target tissue after the first elongate shaft and the second elongate shaft are disengaged from the target tissue.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a cross sectional view of a catheter in accordance with an exemplary embodiment of the present invention;  
         [0019]    [0019]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;  
         [0020]    [0020]FIG. 3 is a cross sectional view of a catheter in accordance with an exemplary embodiment of the present invention;  
         [0021]    [0021]FIG. 4 is a perspective view of a distal portion of a catheter in accordance with an exemplary embodiment of the present invention;  
         [0022]    [0022]FIG. 5 is a perspective view of a distal portion of a catheter in accordance with an exemplary embodiment of the present invention;  
         [0023]    [0023]FIG. 6 is a cross sectional view of a catheter in accordance with an exemplary embodiment of the present invention;  
         [0024]    [0024]FIG. 7 is a partial cross sectional view of a distal portion of a catheter in accordance with an exemplary embodiment of the present invention;  
         [0025]    [0025]FIG. 8 is a partial cross sectional view of a distal portion of a catheter in accordance with an exemplary embodiment of the present invention;  
         [0026]    [0026]FIG. 9 is a partial cross sectional view of a distal portion of a catheter in accordance with an exemplary embodiment of the present invention;  
         [0027]    [0027]FIG. 10 is a partial cross sectional view of a distal portion of a catheter in accordance with an exemplary embodiment of the present invention; and  
         [0028]    [0028]FIG. 11 is a partial cross sectional view of an additional embodiment of the catheter of FIG. 10.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]    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.  
         [0030]    [0030]FIG. 1 is a cross sectional view of a catheter  100  in accordance with the present invention. Catheter  100  has a distal end  102 , a proximal end  104 , and a sheath  106 . Sheath  106  of catheter  100  includes a distal end  108  and a proximal end  122 . A sheath housing  124  is disposed about sheath  106  proximate proximal end  122  thereof. Sheath  106  defines a sheath lumen  120  extending between distal end  108  and proximal end  122 .  
         [0031]    In the embodiment of FIG. 1, a first elongate shaft  126  is slidingly disposed within sheath lumen  120  of sheath  106 . First elongate shaft  126  has a distal end  128 , a proximal end  132 , and a first shaft lumen  130  extending therebetween. A first hub  134  is disposed about first elongate shaft  126  proximate proximal end  132  thereof. A second elongate shaft  136  is slidingly disposed within first shaft lumen  130  of first elongate shaft  126 . Second elongate shaft  136  has a distal end  138  and a proximal end  142 . In the embodiment of FIG. 1, second elongate shaft  136  forms a point  146  proximate distal end  138  thereof. Second elongate shaft also defines an injection port  148  proximate point  146 . A second hub  144  is disposed about second elongate shaft  136  proximate proximal end  142  thereof. Second hub  144  defines a proximal port  150 . In a preferred embodiment, proximal port  150  is in fluid communication with injection port  148  via an injection lumen  140  defined by second elongate shaft  136 .  
         [0032]    In FIG. 1 it may be appreciated that first elongate shaft  126  includes a first curved portion  152  disposed proximate distal end  128  thereof. In the embodiment of FIG. 1, first curved portion  152  of first elongate shaft  126  defines a first plane  154  which is generally coplanar with the plane of FIG. 1.  
         [0033]    In the embodiment of FIG. 1 a barrel  162  is partially disposed within sheath lumen  120  of sheath  106 . In a preferred embodiment, barrel  162  includes a radial enlargement  164 . In this preferred embodiment, radial enlargement  164  provides a generally enlarged distal contact area  166 . Generally enlarged distal contact area  166  reduces the likelihood that undesired tissue damage will occur when distal end  102  of catheter  100  is urged against bodily tissue. Barrel  162  also defines a barrel lumen  170 . As shown in FIG. 1, first elongate shaft  126  is slidingly disposed within barrel lumen  170 .  
         [0034]    In a preferred embodiment, first elongate shaft  126  and second elongate shaft  136  of catheter  100  comprise hypodermic tubing. First elongate shaft  126  and second elongate shaft  136  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, sheath  106  of catheter  100  comprises an elongate tubular member including a reinforcement member (e.g., braided or coiled wire). Sheath  106  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  20 . Patient  20  has a heart  22  and a vascular system  24  including a blood vessel  26  defining a blood vessel lumen  28 . An access sheath  30  is partially disposed within a leg of patient  20 . A distal end  32  of access sheath  30  is disposed within blood vessel lumen  28  of blood vessel  26 . Access sheath  30  may aid in the introduction of catheter  100  into blood vessel lumen  28 .  
         [0037]    As shown in FIG. 2, a portion of catheter  100  is disposed within blood vessel lumen  28  of blood vessel  26 . Distal end  102  (not visible in FIG. 2) of catheter  100  is disposed within heart  22  of patient  20 . In a preferred embodiment, distal end  102  of catheter  100  is disposed proximate a wall of heart  22 .  
         [0038]    In the embodiment of FIG. 2, a fluid source  34  is coupled to second hub  144  disposed about second elongate shaft  136  of catheter  100 . In the embodiment of FIG. 2, fluid source  34  includes a variable volume chamber  36  defined by a body  38 . In a preferred embodiment, variable volume chamber  36  is in fluid communication with injection lumen  140  of second elongate shaft  136 . A plunger  40  is slidingly disposed within variable volume chamber  36 . Urging the plunger distally has the effect of urging fluid into injection lumen  140  of second elongate shaft  136 . A number of energy sources may be utilized to urge plunger  40  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  34  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  22  of patient  20  may be described with reference to FIG. 2. The distal end of access sheath  30  may be inserted into blood vessel lumen  28  of blood vessel  26 . Distal end  102  of catheter  100  may be inserted into the lumen of access sheath  30 . Distal end  102  of catheter  100  may be advanced through access sheath  30  and into blood vessel lumen  28  of blood vessel  26 . Catheter  100  may be urged forward through vascular system  24  of patient  20  until distal end  102  is proximate the target tissue (e.g., a wall of heart  22 ). In FIG. 2 it may be appreciated that catheter  100  is bent in a plurality of locations to conform with a tortuous path defined by vascular system  24 .  
         [0040]    In a preferred method, distal end  138  of second elongate shaft  136  and distal end  128  of first elongate shaft  126  are disposed within sheath lumen  120  of sheath  106  during the above steps. For example, distal end  128  of first elongate shaft  126  may be pulled into sheath lumen  120  of sheath  106  urging first hub  134  proximally with respect to sheath housing  124 . In a similar fashion, distal end  138  of second elongate shaft  136  may be pulled into first shaft lumen  130  of first elongate shaft  126  by urging second hub  144  proximally with respect to first hub  134 .  
         [0041]    Once distal end  102  of catheter  100  is positioned proximate the target tissue, first elongate shaft  126  may be advanced so that distal end  128  penetrates the bodily tissue at the target site. A physician may, for example, apply a distally directed force to first hub  134  to urge first elongate shaft  126  distally. Second elongate shaft  136  may also be urged distally in concert with first elongate shaft  126 . In a preferred embodiment, first curved portion  152  of first elongate shaft assumes a generally curved shape when it is urged distally out of sheath lumen  120 .  
         [0042]    Second elongate shaft  136  may be advanced so that point  146  penetrates the bodily tissue proximate distal end  128  of first elongate shaft  126 . In a preferred method, second elongate shaft will be advanced until injection port  148  is disposed within the target tissue. With injection port  148  of second elongate shaft  136  disposed within the target tissue, fluid may be urged into the target tissue. For example, force may be applied to plunger  40  urging fluid out of fluid source  34  and into injection lumen  140  of second elongate shaft  136 . The addition of fluid from fluid source  34  results in the injection of fluid into the target tissue.  
         [0043]    After the injection of fluid, first elongate shaft  126  and second elongate shaft  136  may be withdrawn from the target tissue. In a preferred embodiment, the tortuous path taken by first elongate shaft  126  and second elongate shaft  136  reduce the likelihood that injected fluid will escape from the target tissue after first elongate shaft  126  and second elongate shaft  136  are disengaged from the target tissue. Embodiments of catheter  100  have been envisioned in which first elongate shaft  126  and second elongate shaft  136  both include a plurality of curved portions.  
         [0044]    [0044]FIG. 3 is a cross sectional view of an additional embodiment of a catheter  200  in accordance with the present invention. Catheter  200  has a distal end  202 , a proximal end  204 , and a sheath  206 . Sheath  206  of catheter  200  includes a distal end  208 , a proximal end  222 . A sheath housing  224  is disposed about sheath  206  proximate proximal end  222  thereof. Sheath  206  defines a sheath lumen  220  extending between distal end  208  and proximal end  222 .  
         [0045]    In the embodiment of FIG. 3, a first elongate shaft  226  is slidingly disposed within sheath lumen  220  of sheath  206 . First elongate shaft  226  has a distal end  228 , a proximal end  232 , and a first shaft lumen  230  extending therebetween. A first hub  234  is disposed about first elongate shaft  226  proximate proximal end  232  thereof. A second elongate shaft  236  is slidingly disposed within first shaft lumen  230  of first elongate shaft  226 . Second elongate shaft  236  has a distal end  238  and a proximal end  242 . In the embodiment of FIG. 3, second elongate shaft  236  forms a point  246  proximate distal end  238  thereof. Second elongate shaft defines an injection port  248  proximate point  246 . A second hub  244  is disposed about second elongate shaft  236  proximate proximal end  242  thereof. Second hub  244  defines a proximal port  250 . In a preferred embodiment, proximal port  250  is in fluid communication with injection port  248  via an injection lumen  240  defined by second elongate shaft  236 .  
         [0046]    In FIG. 3 it may be appreciated that first elongate shaft  226  includes a first curved portion  252  disposed proximate distal end  228  thereof. In the embodiment of FIG. 3, first curved portion  252  of first elongate shaft  226  defines a first plane  254  which is generally coplanar with the plane of FIG. 3. First elongate shaft  226  also includes a second curved portion  256  defining a second plane  258 . In the embodiment of FIG. 3, second plane  258  is substantially orthogonal to first plane  254 .  
         [0047]    [0047]FIG. 4 is a perspective view of a distal portion  360  of an additional embodiment of a catheter  300  in accordance with the present invention. Catheter  300  includes a sheath  306  defining a sheath lumen  320 . A first elongate shaft  326  is partially disposed within sheath lumen  320  of sheath  306 . First elongate shaft  326  includes a first curved portion  352  defining a first plane  354  and a second curved portion  356  defining a second plane  358  disposed proximate a distal end  328  thereof. In FIG. 4 it may also be appreciated that first elongate shaft  326  forms a point  329  proximate distal end  328  thereof.  
         [0048]    Catheter  300  also includes a second elongate shaft  336  which is partially disposed in a first shaft lumen  330  defined by first elongate shaft  326 . Second elongate shaft  336  defines an injection lumen  340  and an injection port  348 . Second elongate shaft  336  also forms a point  346  proximate a distal end  338  thereof.  
         [0049]    [0049]FIG. 5 is a perspective view of a distal portion  460  of an additional embodiment of a catheter  400  in accordance with the present invention. Catheter  400  includes a second elongate shaft  436  having a curved portion  472 . A portion of second elongate shaft  436  is disposed within a first lumen  430  defined by a first elongate shaft  426 . First elongate shaft  426  includes a first curved portion  452  and a second curved portion  456 . In FIG. 5 it may also be appreciated that first elongate shaft  426  forms a point  429  proximate distal end  428  thereof.  
         [0050]    In the embodiment of FIG. 5, first curved portion  452  of first elongate shaft  426  defines a first plane  454  and second curved portion of first elongate shaft  426  defines a second plane  458 . Also in the embodiment of FIG. 5, curved portion  472  of second elongate shaft  436  defines a third plane  474 . In the embodiment of FIG. 5, second plane  458  is substantially orthogonal to first plane  454 . Also in the embodiment of FIG. 5, third plane  474  is generally co-planar with second plane  458 . In a preferred embodiment, curved portion  472  is biased to return to the shape illustrated in FIG. 5. In this preferred embodiment, curved portion  472  of second elongate shaft  436  may tend to self-align with second curved portion  456  of first elongate shaft  426 . In a particularly preferred embodiment, the radius of curved portion  472  of second elongate shaft  436  is substantially equal to the radius of second curved portion  456  of first elongate shaft  426 .  
         [0051]    In a preferred embodiment, the radius of first curved portion  452  of first elongate shaft  426  is selected so that distal end  428  of first elongate shaft  426  will be disposed within a wall of an organ (e.g., the heart) during an injection procedure in accordance with a method of the present invention. Also in a preferred embodiment, third plane  474  defined by curved portion  472  of second elongate shaft  436  is substantially orthogonal to first plane  454  defined by first curved portion  452  of first elongate shaft  426 . This relationship reduces the likelihood that the distal end of second elongate shaft  436  will perforate the wall of an organ (e.g., the heart) during an injection procedure in accordance with a method of the present invention.  
         [0052]    In a preferred embodiment the radius of first curved portion  452  of first elongate shaft  426  is, for example, between about 1.0 and about 10.0 millimeters. In a particularly preferred embodiment the radius of first curved portion  452  of first elongate shaft  426  is, for example, between about 3.0 and about 7.0 millimeters.  
         [0053]    In a preferred embodiment the radius of second curved portion  456  of first elongate shaft  426  is, for example, between about 1.0 and about 8.0 millimeters. In a particularly preferred embodiment the radius of second curved portion  456  of first elongate shaft  426  is, for example, between about 2.0 and about 5.0 millimeters.  
         [0054]    In a preferred embodiment the radius of curved portion  472  of second elongate shaft  436  is, for example, between about 1.0 and about 8.0 millimeters. In a particularly preferred embodiment the radius of curved portion  472  of second elongate shaft  436  is, for example, between about 2.0 and about 5.0 millimeters.  
         [0055]    Embodiments of catheter  400  have been envisioned in which first elongate shaft  426  and second elongate shaft  436  both include a plurality of curved portions. In a preferred embodiment, the tortuous path taken by first elongate shaft  426  and second elongate shaft  436  reduce the likelihood that fluid will escape from a target tissue after it has been injected therein.  
         [0056]    It is to be appreciated that the radius of curved portion  472  may vary along the length of second elongate shaft  436 . Likewise, it is to be appreciated that the radius of first curved portion  452  and second curved portion  456  may vary along the length of first elongate shaft  426 . To explain further, a curve of constant radius forms a portion of a circle whereas a curve of variable radius may form a portion of a spiral. First elongate shaft  426  and second elongate shaft  436  both may include a plurality of curved portions having various shapes. Embodiments of the present invention have been envisioned in which the injection path includes a plurality of turns. These turns may be any shape. Examples of turn shapes which may be suitable in some applications include circular arcs and spiral arcs. Embodiments of the present invention have also been envisioned in which the injection path is generally in the shape of a helix having an expanding radial pitch.  
         [0057]    [0057]FIG. 6 is a cross sectional view of an additional embodiment of a catheter  500  in accordance with the present invention. Catheter  500  has a distal end  502 , a proximal end  504 , and a sheath  506 . Sheath  506  of catheter  500  includes a distal end  508  and a proximal end  522 . A sheath housing  524  is disposed about sheath  506  proximate proximal end  522  thereof. Sheath  506  defines a sheath lumen  520  extending between distal end  508  and proximal end  522 .  
         [0058]    In the embodiment of FIG. 6, a first elongate shaft  526  is slidingly disposed within sheath lumen  520  of sheath  506 . First elongate shaft  526  has a distal end  528 , a proximal end  532 , and a first shaft lumen  530  extending therebetween. A first hub  534  is disposed about first elongate shaft  526  proximate proximal end  532  thereof.  
         [0059]    A second elongate shaft  536  is slidingly disposed within first shaft lumen  530  of first elongate shaft  526 . A second hub  544  is disposed about second elongate shaft  536  proximate a proximal end  542  thereof. Second hub  544  defines a proximal port  550 . In a preferred embodiment, proximal port  550  is in fluid communication with an injection lumen  540  and an injection port  548  defined by second elongate shaft  536 .  
         [0060]    In the embodiment of FIG. 6 a barrel  562  is partially disposed within sheath lumen  520  of sheath  506 . In a preferred embodiment, barrel  562  includes a radial enlargement  564 . In this preferred embodiment, radial enlargement  564  provides a generally enlarged distal contact area  566 . Generally enlarged distal contact area  566  reduces the likelihood that undesired tissue damage will occur when distal end  502  of catheter  500  is urged against bodily tissue. Barrel  562  also defines a barrel lumen  570 . As shown in FIG. 6, first elongate shaft  526  is slidingly disposed within barrel lumen  570 .  
         [0061]    As shown in FIG. 6, sheath housing  524  defines a first guiding surface  510 . First hub  534  has a first mating surface  512  and a second guiding surface  514 . First mating surface  512  of first hub  534  is disposed in sliding engagement with first guiding surface  510  of sheath housing  524 . In a similar fashion, a second mating surface  516  of second hub  544  is disposed in sliding engagement with second guiding surface  514  of first hub  534 .  
         [0062]    In the embodiment of FIG. 6, first elongate shaft  526  and second elongate shaft  536  are biased to assume curved shapes. In the embodiment of FIG. 6, first elongate shaft  526  and second elongate shaft  536  have been urged proximally so that their respective distal ends are disposed within sheath lumen  520  of sheath  506 . In FIG. 6 it may be appreciated that first elongate shaft  526  and second elongate shaft  536  have been urged into a substantially straight position. In a preferred embodiment, first elongate shaft  526  and second elongate shaft  536  will return to substantially curved shapes when they are urged distally out of sheath lumen  520 .  
         [0063]    When first elongate shaft  526  and second elongate shaft  536  are advanced into a target tissue, injection lumen  540  of second elongate shaft  536  will define a tortuous injection path. The tortuous injection path defined by injection lumen  540  of second elongate shaft  536  may be described utilizing cylindrical coordinates. Cylindrical coordinates are an extension of two dimensional polar coordinates to include a third or longitudinal dimension Z.  
         [0064]    An exemplary tortuous injection path is described in table 1. The first column of table 1 is the linear distance Z which the tortuous injection path extends beyond distal contact area  566  of catheter  500 . The second column in table 1 is the radial distance R in millimeters from the longitudinal axis of barrel lumen  570  of barrel  562  of catheter  500 . The third column of table 1 is an angular dimension φ measured about the longitudinal axis of barrel lumen  570  of barrel  562  of catheter  500 .  
                                     TABLE 1                       Z   R   φ       [mm]   [mm]   [degrees]                                0   0   0       1.0   1.0   0       1.5   1.5   0       2.0   2.0   0       2.5   2.0   0       2.5   2.2   30       2.5   2.5   60       2.5   3.0   90       5.0   4.0   120       5.0   4.0   150       5.0   4.0   180       7.5   6.0   210       7.5   6.0   240       7.5   6.0   270       10.0   8.0   300       10.0   8.0   330       10.0   8.0   360                  
 
         [0065]    [0065]FIG. 7 is a partial cross sectional view of a distal portion  660  of an additional embodiment of a catheter  600  in accordance with the present invention. Catheter  600  includes a first elongate shaft  626  having a distal end  628  and an inside surface  676  defining a first shaft lumen  630 . A barrel  662  is partially disposed within first shaft lumen  630  of first elongate shaft  626  proximate distal end  628 . Barrel  662  includes a first helical member  678  comprising a plurality of turns  680 . In the embodiment of FIG. 7, first helical member  678  comprises a first screw thread  682 .  
         [0066]    A second elongate shaft  636  is partially disposed within first shaft lumen  630  of first elongate shaft  626 . Second elongate shaft  636  forms a second helical member  684 . In the embodiment of FIG. 7, second helical member  684  comprises a coil  686  having a plurality of turns  688 . In FIG. 7, it may be appreciated that a plurality of turns  688  of second helical member  684  are disposed between a plurality of turns  680  of first helical member  678 . Also in FIG. 7, it may be appreciated that second helical member  684  is biased to expand in diameter. A distal end  638  of second elongate shaft  636  may be advanced into a target tissue by rotating second elongate shaft  636 .  
         [0067]    [0067]FIG. 8 is a partial cross sectional view of a distal portion  760  of an additional embodiment of a catheter  700  in accordance with the present invention. In FIG. 8 it may be appreciated that catheter  700  includes a first helical member  778  comprising a plurality of turns  780  disposed within a first shaft lumen  730  defined by an inside surface  776  of a first elongate shaft  726 . In a preferred embodiment, first helical member  778  is fixed to inside surface  776  of first elongate shaft  726 . In the embodiment of FIG. 8, first helical member  778  comprises a first screw thread  782 .  
         [0068]    Also in the embodiment of FIG. 8, a second helical member  784  comprising a plurality of turns  788  is disposed about a second elongate shaft  736 . In the embodiment of FIG. 8, second helical member  784  is preferably fixed to second elongate shaft  736 . In the embodiment of FIG. 8, second helical member  784  comprises a second screw thread  790 . In FIG. 8, it may be appreciated that a plurality of turns  788  of second helical member  784  are disposed between a plurality of turns  780  of first helical member  778 .  
         [0069]    In the embodiment of FIG. 8, a barrel  762  defining a barrel lumen  770  is partially disposed within first shaft lumen  730  of first elongate shaft  726 . A coiled portion  792  of second elongate shaft  736  is disposed within barrel lumen  770  of barrel  762 . In FIG. 8, it may be appreciated that coiled portion  792  is biased to expand in diameter. A distal end  738  of second elongate shaft  736  may be advanced into a target tissue by rotating second elongate shaft  736 .  
         [0070]    [0070]FIG. 9 is a partial cross sectional view of a distal portion  860  of an additional embodiment of a catheter  800  in accordance with the present invention. Catheter  800  includes a first elongate shaft  826  having a distal end  828  and an inside surface  876  defining a first shaft lumen  830 . Catheter  800  also includes a second elongate shaft  836  having a distal end  838  slidingly disposed within first shaft lumen  830  of first elongate shaft  826 .  
         [0071]    In FIG. 9 it may be appreciated that catheter  800  includes a first helical member  878  comprising a plurality of turns  880  disposed within first shaft lumen  830  of first elongate shaft  826 . In a preferred embodiment, first helical member  878  is fixed to an inside surface  876  of first elongate shaft  826 . In the embodiment of FIG. 9, first helical member  878  comprises a first screw thread  882 .  
         [0072]    A second helical member  884  is formed by second elongate shaft  836 . In the embodiment of FIG. 9, second helical member  884  comprises a coil  886  having a plurality of turns  888 . In FIG. 9, it may be appreciated that a plurality of turns  888  of second helical member  884  are disposed between a plurality of turns  880  of first helical member  878 . Embodiments of the present invention have also been envisioned in which first helical member  878  comprises a coil.  
         [0073]    In the embodiment of FIG. 9, a barrel  862  defining a barrel lumen  870  is partially disposed within first shaft lumen  830  of first elongate shaft  826 . A coiled portion  892  of second elongate shaft  836  is disposed within barrel lumen  870  of barrel  862 . In FIG. 9, it may be appreciated that coiled portion  892  is biased to expand in diameter. A distal end  838  of second elongate shaft  836  may be advanced into a target tissue by rotating second elongate shaft  836 .  
         [0074]    [0074]FIG. 10 is a partial cross sectional view of a distal portion  960  of an additional embodiment of a catheter  900  in accordance with the present invention. Catheter  900  includes a first elongate shaft  926  having a distal end  928  and an inside surface  976  defining a first shaft lumen  930 . A tip member  994  is disposed proximate distal end  928  of first elongate shaft  926 . In a presently preferred embodiment, tip member  994  is comprised of an elastomeric material.  
         [0075]    A barrel  962  is partially disposed within first shaft lumen  930  of first elongate shaft  926  proximate tip member  994 . Barrel  962  includes a first helical member  978  comprising a plurality of turns  980 . In the embodiment of FIG. 10, first helical member  978  comprises a first screw thread  982 . A second elongate shaft  936  is partially disposed within first shaft lumen  930  of first elongate shaft  926 . Second elongate shaft  936  forms a second helical member  984 . In the embodiment of FIG. 10, second helical member  984  comprises a coil  986  having a plurality of turns  988 . In FIG. 10, it may be appreciated that a plurality of turns  988  of second helical member  984  are disposed between a plurality of turns  980  of first helical member  978 .  
         [0076]    [0076]FIG. 11 is a partial cross sectional view of distal portion  960  of catheter  900  of FIG. 10. In the embodiment of FIG. 11 second elongate shaft  936  has been advanced distally so that a distal portion of second elongate shaft  936  extends beyond barrel  962 . In FIG. 11, it may be appreciated that second helical member  984  is biased to expand in diameter. Also in FIG. 11, it may be appreciated that the expansion of second helical member  984  has deformed tip member  994 .  
         [0077]    Having thus described the preferred embodiments of the present invention, those of skill in the art will readily appreciate that yet other embodiments may be made and used within the scope of the claims hereto attached. Numerous advantages of the invention covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respects, only illustrative. 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.