Abstract:
A medical system incorporating fluid delivery and lead delivery lumens dispense fluid into a volume of tissue. The fluid comprises or contains a pharmacologic, genetic, or biologic agent. The fluid may be dispensed initially during implantation or later using a minimally invasive medical procedure.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to implantable medical leads and more specifically to an implantable medical lead and fluid delivery system for treating a volume of tissue in which the medical lead may remain implanted. 
   BACKGROUND OF THE INVENTION 
   Electrical stimulation of excitable body tissue is used as a method for treating various pathological conditions. Therapeutic stimulation generally requires making an electrical contact between excitable tissue and an electrical pulse generator through use of one or more stimulation leads. Various lead systems and various techniques for implanting these lead systems in contact with excitable body tissue, and particularly the heart, have been developed. 
   In order to achieve cardiac pacing, sensing, cardioversion and/or defibrillation at different locations in the heart, various types of cardiac leads have been developed including epicardial leads, endocardial leads, and coronary vein leads. A transvenous endocardial lead establishes electrical contact between an electrical pulse generator, such as a pacemaker or implantable cardioverter defibrillator, and the endocardial surface of the heart, typically in a right heart chamber. Endocardial leads, and cardiac leads in general, may be held in place by passive fixation mechanisms, such as tines that interact with the ventricular trabeculae, or active fixation mechanisms, such as a helix. A coronary vein lead may be passed through a venous pathway, into the right atrium, through the coronary sinus ostium and ultimately to a location deep in the cardiac veins. Contact is made with the epicardial surface of the left atrium or left ventricle for delivering stimulation or sensing cardiac signals in the left heart chambers. Epicardial leads are also known in the art and generally require a thoracotomy for placement on the epicardial surface of a heart chamber. 
   The safety, efficacy and longevity of an electrical pulse generator depends, in part, on the performance of the associated cardiac lead(s) used in conjunction with the pulse generator. Various properties of the lead, the electrodes and the tissue interfacing with an electrode will result in a characteristic impedance, stimulation threshold and sensing threshold. 
   Stimulation threshold is the energy required in a stimulation pulse to depolarize, or “capture,” the heart tissue. A relatively high impedance and low threshold is desired to minimize the current drawn from a pulse generator battery in delivering a stimulation pulse. Maximizing the useful life of the pulse generator battery is important since a surgical procedure is required to replace the pulse generator once the battery has reached the end of its useful life. 
   One factor that can affect the stimulation threshold, particularly during the first several weeks after implantation of a lead, is the natural immunological response of the body to the lead as a foreign object. The presence of the lead activates the immunologic response, which ultimately results in fibrotic encapsulation of the lead and its electrodes. Since fibrotic tissue is not excitable tissue, an elevated stimulation threshold can persist due to the degraded electrical properties of the electrode-tissue interface. 
   To reduce the inflammatory response, medical leads that elute an anti-inflammatory steroid have been developed. Steroid eluting leads are described in U.S. Pat. No. 4,506,680 issued to Stokes and related Medtronic U.S. Pat. No. 4,577,642, and 4,606,118, all incorporated herein by reference. Steroid eluting leads may require a monolithic controlled release device (MCRD) to contain the steroid and to thereafter slowly leach out the water soluble steroid into the surrounding tissue. A method for applying a steroid directly to the surface of an electrode is disclosed in U.S. Pat. No. 5,987,746 issued to Williams, incorporated herein by reference in its entirety. Advantages of this method include elimination of additional structures for carrying the steroid and the presentation of the steroid directly at the tissue-electrode interface. 
   One limitation of a steroid eluting electrode or MCRD, however, is that a relatively limited volume of tissue is treated by the eluting drug since the drug is presented only at the endocardial or epicardial surface. Other devices have been proposed which allow the delivery of a drug to a potentially larger volume of tissue by actually penetrating the tissue rather than relying on diffusion of the drug from the tissue surface. Drug delivery catheters may incorporate a drug dispensing needle or helix that penetrates a targeted tissue for delivering a drug or fluid. Catheters that may be used to deliver a fluid or drug into the myocardium are disclosed in U.S. Pat. No. 6,102,887 issued to Altman and U.S. Pat. No. 5,431,649 issued to Mulier et al. 
   Drug delivery catheters may include an electrode to allow sensing or stimulation of the myocardium. An implantable pacing lead having an active fixation electrode with a stylet introduced, anti-inflammatory drug delivery system is disclosed in U.S. Pat. No. 5,447,533 issued to Vachon et al. A delivery system for delivering a therapeutically effective amount of a genetic material to an identified cardiac location adjacent an atrial or ventricular electrode is disclosed in PCT Patent Publication WO 98/02040 issued to Stokes et al, incorporated herein by reference in its entirety. This delivery system may combine a pacing lead and a delivery catheter. Other implantable leads with drug delivery capabilities are disclosed in U.S. Pat. No. 4,360,031 to White, and U.S. Pat. No. 5,496,360 to Hoffman. 
   Advancements in gene therapies and cellular modifications through the delivery of proteins, peptides or even cell delivery, such as stem cell delivery, offer opportunities to alter the properties of tissue to further improve the benefit of a delivered stimulation therapy or improve the ability to sense cardiac signals. Genetic or biologic agents may be used to alter ion channel activity or protein expression at the cellular level. Potential benefits include decreased inflammatory response, increased tissue conductivity for reduction of stimulation thresholds or upregulation of ion channels for increasing membrane potentials to allow better sensing. For example, upregulation of ion channels could enhance cardiac P-waves or R-waves allowing them be more easily sensed by a pacemaker or other cardiac monitor. In particular, cardiac fast sodium channels are responsible for the fast upstroke of the action potential in myocardial cells (Fozzard, et al., Circ. Res. 1995, 56:475–485). A human cardiac voltage-dependent sodium channel, hH1, has been cloned, sequenced, and functionally expressed (Gellens, et al., Proc. Natl. Acad. Sci. USA, 1992, 89:554–558). Alteration of myocardial conductivity may be possible through delivery of proteins that alter cellular electrical coupling. The gap junction protein Connexin43 has been found to play an important role in ventricular conduction (Guerrero PA et al., J. Clin. Invest. 1997, 99:1991–1998). 
   Because locally effective doses of a pharmacologic, genetic, or biologic agent may be toxic when given systemically, it is desirable to provide a method for delivering an agent locally at a targeted tissue site. Drug-eluting electrodes may be limited to treating only a relatively small volume of tissue at an electrode-tissue interface. The pharmacological effect is in part limited by the kinetics of the drug leaving the electrode or lead. Furthermore, because biologic and genetic agents may have a limited shelf life, unique storage requirements such as requiring refrigeration, and may not tolerate sterilization procedures, it is not desirable to package a lead having drug eluting capabilities with the biologic or genetic agent already incorporated therein. Other medical leads having drug dispensing capabilities may require additional components that increase the size, stiffness or complexity of the lead. 
   To take advantage of various genetic or cellular modification therapies, it is desirable to provide an implantable lead and fluid delivery system that allows a pharmaceutical, genetic, or biologic agent to be delivered to a targeted lead implant site at a depth within the myocardium to treat a volume of tissue. Once a fluid agent has been delivered, the fluid delivery components are no longer needed and may be removed from the patient&#39;s body. An acutely implanted fluid delivery system eliminates the need to include dispensing components in the medical lead, reducing its complexity, yet still offers the benefit of treating a volume of tissue at a lead implant site, potentially improving lead performance. There is a need, therefore, for a system that allows an acutely implanted fluid delivery device to treat a volume of tissue during a lead implant procedure, or at any time post-operatively, and further allows a lead to be implanted and remain in the location of the treated tissue. 
   SUMMARY OF THE INVENTION 
   The present invention is directed toward providing a medical lead and fluid delivery system for treating a volume of tissue with a pharmaceutical, genetic, or biologic agent at the time of the medical lead implant and/or at any time post-operatively. 
   In one embodiment of the present invention, a guide catheter is provided with a fluid dispensing, fixation member at its distal end. The fixation member communicates with a lumen extending the length of the guide catheter body through which a fluid may be delivered. The fixation member, which may be provided as a hollow helix, is provided with one or more apertures for dispensing a drug into the surrounding tissue in which the helix is fixed. The fixation member may optionally function as an electrode in addition to being a fixation device. After treating a volume of tissue by dispensing a fluid through the fixation member, a medical lead, advanced through a lead-delivery lumen of the guide catheter, may be implanted in the treated tissue. The guide catheter may then be removed leaving the medical lead implanted at the treated tissue site. 
   In another embodiment, a system is provided including a guide catheter having a fixation member, a fluid delivery device, and an implantable lead. After fixing the guide catheter at a desired implant site, the fluid delivery device, advanced down a lumen of the guide catheter, may be used to treat a volume of tissue at that site. The fluid delivery device may then be removed and an implantable lead may be advanced through the guide catheter to the treated tissue site. The guide catheter may then be removed, leaving the lead implanted at the treated tissue site. 
   In alternative embodiments, a transvenous lead having a distal fixation member is provided with a center lumen through which a fluid delivery device may be advanced to treat a volume of tissue in which the lead is implanted. A seal is preferably provided at the distal end of the lead body to prevent fluid ingress. The distal fixation member may be provided as a passive or active fixation member. In one embodiment, a retractable active fixation member is provided. In another embodiment, the implantable lead may be provided as an epicardial lead. 
   The fluid delivery device may take the form of a hollow needle or stylet that may be advanced through a lumen of the lead body, penetrated through the seal and into the targeted tissue site. The fluid delivery device may be provided with a conductive tip to allow sensing of electrophysiological signals. Fluid delivery may be performed once the delivery device is inserted in the targeted tissue location as verified by sensing electrophysiological signals characteristic of the targeted tissue. After delivery of a fluid, which may be a pharmaceutical, genetic or biologic agent carried in a liquid medium, the fluid delivery device may be removed, leaving the transvenous lead implanted at the treated tissue site. 
   The medical lead may further include a reservoir that may be filled by the fluid delivery device with a pharmaceutical, genetic or biologic agent. The agent will elute from the reservoir into surrounding tissue over time. Treatment of a volume of tissue with a pharmaceutical, genetic or biologic agent may thus be treated by delivering a bolus injection directly into the tissue or slow elution of the agent over time, or both. 
   A fluid may be delivered post-operatively by gaining access to the lumen of an implanted lead through an access port on the implanted device to which the lead is connected. Multiple injections at the lead implant site at various time intervals are possible by inserting a fluid delivery device through the access port and advancing it through the lead lumen. Fluid may be delivered directly to the lead implant site, or a fluid reservoir may be refilled. 
   Thus, the present invention provides a medical lead and fluid delivery system that allows a lead to be implanted in a volume of tissue treated concurrently with the lead implant procedure, or at any time post-operatively, by an acutely delivered fluid delivery device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side, cut-away view of an implantable lead and fluid delivery system including a guide catheter having fluid dispensing capabilities and an implantable medical lead. 
       FIG. 2  is a side, cut-away view of an alternative embodiment of the guide catheter shown in  FIG. 1  in which a fixation member on the guide catheter may also function as an electrode. 
       FIGS. 3A and 3B  are side, cut-away views of the distal end of an implantable medical lead and fluid delivery system that includes a guide catheter, a fluid delivery device and a medical lead. 
       FIG. 4A  is a plan view of an alternative embodiment of an implantable lead and fluid delivery system including a transvenous medical lead and a fluid delivery device that may be deployed through a lumen of the lead. 
       FIG. 4B  is a side cut-away, view of the distal end of the system of  FIG. 4A . 
       FIG. 5  is an exploded, side, cut-away view of the distal end of an implantable lead and fluid delivery system in which the lead is provided with a retractable fixation member. 
       FIG. 6  is an exploded, side, cut-away view of the distal end of an implantable medical lead and fluid delivery system for use on the epicardial surface of the heart. 
       FIG. 7  is a cut-away, side view of the distal end of an implantable medical lead and fluid delivery system wherein the medical lead is provided as a transvenous lead having a passive fixation mechanism. 
       FIG. 8  is side, cut-away view of the distal end of an implantable medical lead and fluid delivery system wherein the medical lead is further provided with a fluid reservoir for holding a pharmaceutical, genetic or biologic agent and allowing the agent to elute into adjacent body tissue over time. 
       FIG. 9  is a side, cut-away view of the distal end of an implantable medical lead and fluid delivery system wherein the medical lead is provided as a transvenous lead having a passive fixation mechanism and a fluid reservoir. 
       FIG. 10  is a plan view of an implantable lead and fluid delivery system that may be used to deliver a fluid agent to a lead implant site post-operatively. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As described above, the present invention is directed at providing an implantable lead and fluid delivery system in which a fluid delivery device may be used to treat a volume of tissue concurrently with a lead implantation procedure, or at any time post-operatively. After delivering a fluid, the fluid delivery device may be removed leaving the lead implanted at the treated tissue site.  FIG. 1  is a side, cut-away view of one embodiment of an implantable lead and fluid delivery system in accordance with the present invention. The system includes a guide catheter  10  having fluid dispensing capabilities. Catheter  10  is provided with a proximal handle  3  and an elongated catheter body  12  having at least two lumens  14  and  16  and is preferably formed from a biocompatible polymer such as polyurethane, silicone, Teflon®, or other acceptable plastic. A fluid-delivery lumen  14  is in communication with an active fixation, fluid dispensing member shown as a hollow fixation helix  18  located at the distal end of guide catheter  10 . An active fixation, fluid dispensing member may alternatively be provided as a hollow “fish hook” type member, stake-like member, or any other type of active fixation member that can be provided as a hollow structure having one or more apertures. Hollow fixation helix  18  is provided with one or more apertures  20  through which fluid injected through lumen  14  may exit into a tissue site. Fixation helix  18  is preferably formed from a biocompatible metal, such as stainless steel, in which apertures  20  may be formed by laser drilling. A hollow fixation helix that may be used for fluid delivery is disclosed in the &#39;649 patent issued to Mulier et al., incorporated herein by reference in its entirety, and the WO 98/02040 patent issued to Stokes et al. A fluid fitting  2 , such as a Luer lock fitting, may be inserted or mounted at the proximal end of fluid delivery lumen  14  to allow connection of a syringe for injecting fluid into lumen  14 . 
   Catheter  10  may be provided as a steerable catheter having a manipulative handle and steering mechanism, such as a pull wire, to aid in maneuvering catheter  10  through body vessels or organs. Steering mechanisms included in catheter  10  may be embodied as generally described in U.S. Pat. No. 5,396,902, issued to Brennen, et al., for example, or U.S. Pat. No. 5,807,249 issued to Qin, et al., both patents incorporated herein by reference in their entirety. 
   A lead-delivery lumen  16  is provided for delivering an implantable lead  22  to a desired implant site. The lead-delivery lumen  16  is sized to allow lead  22  to easily pass through guide catheter  10  without undue friction or resistance. Lead  22  is shown as an exemplary bipolar lead having a helical tip electrode  24  located at the distal lead end and a ring electrode  26  spaced proximally from tip electrode  24 . In other embodiments, lead  22  may be a unipolar, bipolar, or multipolar lead carrying any combination of tip, ring and/or coil electrodes or other sensors. Lead  22  is shown with an active fixation helical electrode  24  but could also be provided with other types of active fixation electrodes or mechanisms, such as a “fish hook” electrode. Lead  22  may alternatively be provided with a generally spherical, hemispherical or ring-shaped tip electrode with passive fixation mechanisms, such as tines as generally known in the art. 
   A connector assembly  8  is provided at the proximal lead end with a pin connector  4  and ring connector  6  which are electrically coupled to respective conductors that extend to tip electrode  24  and ring electrode  26 . Conductors extending the length of lead  22  may be coiled conductors or cabled or stranded conductors as is known in the art. 
   During a lead implantation procedure, guide catheter  10  may be passed through a venous pathway into a desired heart chamber until a desired implantation site is reached. A guide wire or electrophysiological mapping catheter, passed through inner lumen  16 , could be used for passage of the catheter through the venous and cardiac anatomy to allow access to the targeted tissue. This guide wire or electrophysiological catheter could be steerable and would provide the additional benefit of protecting helix  18  to prevent snagging or entanglement with anatomic structures. Fixation helix  18  is advanced into the myocardial wall by rotating catheter  10  at its proximal end. Catheter body  12  is therefore provided with torsional stiffness adequate to translate rotational force to the distal fixation helix  18 . A fluid, which may be a pharmacological, genetic, or biologic agent, may then be injected into drug-delivery lumen  14  such that it is dispersed out of apertures  20  into the tissue surrounding fixation helix  18 . A relatively large volume of tissue may be treated by the relatively large helix  18  on guide catheter  10 . 
   Lead  22  may then be passed through lead delivery lumen  16  and implanted at the treated tissue site by advancing helical tip electrode  24  into the tissue. The position of guide catheter  10  is maintained by helix  18  such that lead  22  may be implanted in the same volume of tissue treated by the injection of fluid through helix  18 . After implanting lead  22 , guide catheter  10  may be removed by rotating catheter  10  in an appropriate direction to remove helix  18  from the tissue site and withdrawing catheter  10  over lead  22 . Catheter  10  may be provided as a splittable or slittable catheter such that it may be removed from lead  22  without passing it over connector assembly  8 . Alternatively, connector assembly  8  may be provided as a low profile connector assembly sized to allow catheter  10  to be readily passed over assembly  8 . 
     FIG. 2  is a side, cut away plan view of an alternative embodiment of the guide catheter  10  shown in  FIG. 1  in which the distal fluid dispensing, fixation member, helix  18 , may function as an electrode. In  FIG. 2 , all identically labeled components correspond to those illustrated in  FIG. 1 . In  FIG. 2 , however, fixation helix  18  is shown coupled to a conductor  15  that extends the length of catheter body  12  to a proximal terminal  17  enabling connection to a monitoring device, such as an electrocardiogram monitor. Helix  18  may thus serve as an electrode allowing electrophysiological signals to be sensed and monitored in order to verify that guide catheter  10  is fixed in a desired location. Monitoring of electrophysiological signals may also aid in verifying a short-term pharmacological effect after delivering a fluid through lumen  14  and helix  18 . 
     FIGS. 3A and 3B  are cut-away plan views of the distal end of an implantable medical lead and fluid delivery system that includes a guide catheter  200 , a fluid delivery device  208 , and a medical lead  212 .  FIG. 3A  shows a guide catheter  200  having an elongated, tubular catheter body  202  with inner lumen  204 . Guide catheter  200  is provided with a fixation member  206 , shown in this embodiment as a helix, that allows catheter  200  to be fixed at a targeted implant site. Fixation member  206  may be a solid helix and may function exclusively as a fixation device. Alternatively, fixation member  206  may also function as an electrode as described above with reference to  FIG. 2 . 
   A separate fluid delivery device  208  may be advanced through catheter lumen  204  until device  208  exits the distal end of catheter  200 . Fluid delivery device  208 , which may generally take the form of a hollow needle or stylet, may be tapered at its distal end and is preferably provided with a sharpened or beveled tip  210  such that it may easily pierce the tissue at the targeted implant site. The tip  210  may also take the form of a helix or other shape that may penetrate the tissue to a desired depth and dispense a fluid through one or more apertures to treat a volume of tissue. Once fluid delivery device  208  is advanced into the tissue, a fluid may be injected in the proximal end of fluid delivery device  208  and dispensed into a volume of tissue through tip  210 . 
   Fluid delivery device  208  may also serve as an electrode, alternatively or in addition to helix  206  of catheter  200 . Fluid delivery device  208 , which may be formed from a conductive metal such as stainless steel, may be provided with an insulating coating, such as a coating of ethylene tetrafluoroethylene (ETFE) or Parylene, except for at distal tip  210 . The proximal end of device  208  may be coupled to a monitor such that electrophysiological signals sensed at uninsulated tip  210  may be monitored. Verification that tip  210  is in a desired tissue site, and not in blood or non-excitable tissue, may be made by monitoring electrophysiological signals sensed at tip  210 . 
   After dispensing a fluid into the targeted implant site, the fluid delivery device  208  may be withdrawn from lumen  204  of guide catheter  200  and replaced with an implantable medical lead  212  as shown in  FIG. 3B . Lead  212  is shown as an exemplary bipolar lead having an active fixation helical tip electrode  214  at its distal end and a ring electrode  216  spaced proximally from tip electrode  214 . Lead  212  may be advanced through lumen  204  and implanted at the treated tissue site by advancing helical tip electrode  214  into the tissue. Guide catheter  200  may then be removed, leaving the electrode  214  implanted in the treated tissue. 
     FIG. 4A  is a plan view of an alternative embodiment of an implantable lead and fluid delivery system. This system includes a transvenous lead  30  and a fluid delivery device  44 . The lead  30  has an elongated, tubular lead body  32 . Lead body  32  may be formed from a resilient, biocompatible polymer, such as silicone or polyurethane. Lead  30  is shown as a unipolar lead having an active fixation tip electrode  34  located at its distal end, shown as a helical electrode. Lead  30  may alternatively be a bipolar or multipolar lead having, in addition to active fixation tip electrode  32 , one or more ring electrodes and/or one or more coil electrodes. 
   A connector assembly  62  is provided at the proximal lead end to allow connection of lead  30  to an implantable pulse generator or monitoring device. Connector assembly  62  includes a pin terminal  64  that is electrically coupled to tip electrode  48  via a conductor extending the length of lead body  32 . Pin terminal  64  is provided as a hollow pin that is in communication with a central lumen of lead body  32 . Sealing rings  63  form a fluid-tight seal with the inner surface of a connector port on an implantable pulse generator or monitoring device. 
   Fluid delivery device  44  is shown inserted into the proximal end of hollow pin terminal  44 . Fluid delivery device  44  may take the form of a hollow needle or stylet as described above in conjunction with  FIG. 3A . Fluid delivery device  44  includes a hollow shaft  46  sized to pass easily through pin terminal  64  and the lumen of lead body  32  such that distal tip  48  of fluid delivery device  44  may exit the distal end of lead  30 . A fluid fitting  60 , which may take the form of a Luer lock fitting, is provided at the proximal end of device  44  to allow connection of a syringe for injecting fluid through shaft  46  to be dispensed from tip  48 . 
     FIG. 4B  is a side cut-away view of the distal end of lead  30  and fluid delivery device  44 . Helical tip electrode  34  is electrically coupled to a conductive sleeve  50 , preferably by laser or resistance welding. Conductive sleeve  50  is electrically coupled to a conductor  36 . Conductor  36  extends to connector assembly  62  at the proximal end of lead  30  and is coupled to pin terminal  64 . Conductive sleeve  50  may be coupled to conductor  36  by crimping conductive sleeve  50  such that it is compressed against conductor  36 , which is supported on its internal diameter by internal sleeve  40 . In this way, electrode  34  is electrically coupled to conductor  36  and pin terminal  64 . 
   Conductor  36  is preferably a coiled conductor provided with insulation  37 . Insulation  37  may be provided as a coating formed from an appropriate insulating material such as polytetrafluoroethylene (PTFE) or ETFE, preferably surrounding each individual filar included in conductor  36 . Insulation  37  may alternatively be provided as heat shrink tubing fabricated from PTFE or ETFE as generally described in U.S. Pat. No. 6,052,625 issued to Marshall, incorporated herein by reference in its entirety. Conductor  36  may alternatively be provided as an insulated cabled or stranded conductor, such as the conductor generally disclosed in U.S. Pat. No. 5,246,014 issued to Williams. Insulation  37  may also be provided as a material having a high Young&#39;s modulus, such as a high durometer polyurethane or polyimide, to impart additional lead body stiffness to the small diameter lead as generally described in U.S. Pat. No. 6,366,819 issued to Stokes, incorporated herein by reference in its entirety. 
   Insulation  37  electrically isolates conductor  36  from tip  48  and shaft  46  of fluid dispensing device  44  allowing distal tip  48  to function as a sensing electrode for detecting electrophysiological signals at a tissue site. When tip  48  is used as a sensing electrode, fluid delivery device  44  may also be insulated along the entire length of shaft  46 , particularly if conductor  36  is not provided with insulation. Distal tip  48  remains uninsulated. Insulation on shaft  46  may be provided by an adhesive coating, such as silicone adhesive, or as a tubular sleeve formed from an insulating material such as PTFE, ETFE or Parylene. A conductive clamp, connected to a monitor such as an ECG monitor, may be coupled to fitting  60  at the proximal end of fluid delivery device  44  for observing electrophysiological signals at the site in which the uninsulated tip  48  is in contact. For example, cardiac P-waves or R-waves could be sensed by tip  48 . 
   Lead  30  is preferably provided with a seal  38  to prevent the ingress of body fluids. Seal  38  is generally cup shaped and may be formed from a resilient, biocompatible polymer, such as molded silicone rubber. Seal  38  is shown in  FIG. 4B  to be molded onto internal sleeve  40 , which is preferably formed from a rigid, insulating material such as Delrin®, available from DuPont. Internal sleeve  40  is provided with an annular, laterally extending flange  52 . Seal  38  is retained by the interaction of flange  52  and conductive sleeve  50 . Seal  38  may be provided as generally described in U.S. Pat. No. 6,192,280 issued to Sommer et al., incorporated herein by reference in its entirety. Alternatively, the seal  38  can be fabricated such that it is entirely contained within a portion of conductor  36  at a point at the distal end of the lead  32  or at a location more proximal. Alternative embodiments of a seal at or near the distal end of a medical lead or medical device that may be adapted for use with the present invention are disclosed in U.S. Pat. Application 20020016622 to Janke et al., and U.S. Pat. Application 20020077685 to Sundquist et al., both of which are incorporated herein by reference in their entirety. Other types of seals for preventing fluid from entering a tubular body may also be used. 
   During an implantation procedure, lead  30  may be deployed to a desired implant site. Lead  30  deployment may be performed with the aid of a guide wire, stylet, or guide catheter. Helical tip electrode  34  may then be fixed in the tissue at the implant site. If a guide wire or stylet is used, it is removed from lumen  42  after lead  30  is positioned so that fluid delivery device  44  may be advanced through lumen  42 . Fluid delivery device tip  48  is preferably sharpened or beveled such that it can easily pierce through seal  38 . The fluid delivery device  46  might also be shapeable, allowing it to be used for positioning of the lead  32 . Seal  38  may be pre-pierced at line  54  to define a path for the fluid delivery device  44  to pass through. Tip  48  is then further advanced into the implant site. Verification that tip  48  is in a desired implant site may be made by monitoring electrophysiological signals sensed by uninsulated tip  48 . If no signal is sensed, tip  48  may not be advanced completely through seal  38  or may not be fully inserted into the tissue site. Once tip  48  is adequately advanced into the implant site, a fluid may be injected through device  44  to treat a volume of tissue in which helical tip electrode  34  is implanted. Fluid delivery device  44  may then be withdrawn and removed, leaving lead  30  implanted with helical tip electrode  34  fixed in the treated tissue. 
     FIG. 5  is an exploded, cut-away plan view of the distal end of an implantable lead and fluid delivery system wherein the lead  70  is provided with a retractable fixation member. A lead  70  is provided with a helical tip electrode  76  that may be retracted into an electrode housing  74 . Electrode housing  74  is preferably formed from a relatively rigid biocompatible polymer, such as polyurethane. Housing  74  is bonded to an elongated, tubular lead body  72 , which may be formed of polyurethane, silicone rubber, or another biocompatible polymer. 
   Helical tip electrode  76  is mounted on a conductive sleeve  78 , which is electrically coupled to a conductor  92 . Conductive sleeve  78 , which is preferably machined from a conductive metal such as stainless steel, includes a retraction mechanism shown as a threaded barrel  86  that is coaxial with sleeve  78  and located on the outer diameter of sleeve  78 . Thread  88 , running along the outer surface of barrel  86 , acts to engage multiple thread guides  90  mounted on the inner diameter of housing  74 . Conductor  92  may be rotated relative to lead body  72  by rotating a connector pin to which conductor  92  is coupled at its proximal end. Rotation of a coiled conductor may be achieved as generally described in U.S. Pat. No. 4,106,512, issued to Bisping, incorporated herein by reference in its entirety. Rotation of conductor  92  causes rotation of sleeve  80  relative to electrode housing  74 . Rotation of sleeve  80  causes advancement of helical electrode  76  as threaded barrel  86  is actuated on thread guides  90 . A stop mechanism  89  may be provided as a ridge or peg near the proximal end of thread  88  that engages a thread guide  90  to prevent over extension of helical electrode  76 . During retraction, threaded barrel  86  will interact with housing  74  at lateral face  96  to prevent over-retraction of helix  76 . Alternatively, a stop mechanism may be provided near the distal end of thread  88  to prevent over-retraction of helix  76 . A retraction stop mechanism that may be adapted for use in the present invention is disclosed in U.S. Pat. No. 5,837,006, issued to Ocel et al., incorporated herein by reference in its entirety. 
   Lead  70  is provided with a seal  82 , preferably formed of a resilient biocompatible polymer such as silicone rubber, molded to the distal end of the conductive sleeve  78  to prevent ingress of body fluids. Seal  82  may be generally cup shaped and may be pre-pierced at line  94  to guide a fluid delivery device  100  as it passes through seal  82 . Seal  82  further includes an annular sealing ring  84 , coaxial with seal  82  and extending laterally from the outer diameter of seal  82 . Sealing ring  84  interacts with the inner surface of housing  74  to complete a fluid-tight seal of the distal end of lead  70 . Sealing ring  84  further acts to center helix  76  within housing  74 . 
   A fluid delivery device  100  is provided which may be generally in the form of a hollow stylet or needle having an elongated shaft  106  extending between a proximal end through which fluid may be injected and a distal tip  102  through which fluid may be dispensed. Distal tip  102  is sharpened or beveled such that it may easily pierce through seal  82  and enter a targeted tissue site. A distal segment  104  of fluid delivery device  100  is provided with a reduced diameter allowing it to extend through conductive sleeve  78  such that distal tip  102  may extend out of housing  74  when helix  76  is extended into a tissue site. Lateral face  108  may act as a mechanical stop by interacting with the distal end of sleeve  78  and thereby control the maximum depth that fluid delivery device  100  is inserted into the targeted tissue site. The outer dimensions of shaft  106  and distal segment  104  and the spacing of lateral face  108  from distal tip  102  may alternatively be dimensioned to provide a stopping interface that interacts with a reduced inner diameter of sleeve  78  or helix  76 . Alternatively, the tip of helix  76  may be bent to cross the center axis of helix  76  to act as a stop for fluid delivery device  100 . Any of these methods for providing a mechanical stop for fluid delivery device  100  allows the tissue depth at which the fluid is injected to be controlled. 
     FIG. 6  is an exploded, cut-away side view of the distal end of an implantable medical lead and fluid delivery system for use on the epicardial surface of the heart. A lead  150  is provided with a lead body  152 , an insulating electrode head  154  and an active fixation electrode  158 . Electrode  158  is shown as a helical electrode but may also take the form of a “fish hook” type electrode, or any other active fixation electrode. Electrode head  154  includes a tapered body  155  and flange  156 , both of which may be formed from silicone rubber and provide a flexible structure for stabilizing the position of lead  150  on the epicardial surface. A tool may be used for implanting lead  150  by attaching to and rotating the electrode head  154  to screw the helical electrode  158  into the epicardium as is generally known in the art. Epicardial leads and tools for implanting epicardial leads are disclosed in U.S. Pat. No. 3,737,539 issued to Bolduc, U.S. Pat. No. 5,143,090 issued to Dutcher, and U.S. Pat. No. 6,010,526 issued to Sandstrom et al., all of which patents are incorporated herein by reference in their entirety. Flange  156  may be reinforced with an embedded netting or mesh material, such as polyester netting. Netting material may optionally be coated with an anti-inflammatory steroid to reduce the inflammatory response at the tissue-lead interface. 
   Helical electrode  158  is electrically coupled to a conductive sleeve  170 , which is further coupled to a conductor  174 , shown as a coiled conductor. Conductive sleeve  170  is provided with an annular flange  172 . A seal  160  is molded to flange  172  to prevent the ingress of bodily fluids into the lead body lumen  164 . Seal  160  may be pre-pierced at line  162  to define a path for fluid delivery device  100  to pass through. Fluid delivery device  100  may correspond to the fluid delivery device shown in  FIG. 5  and is shown in  FIG. 6  with identically labeled components corresponding to those in  FIG. 5 . Lateral face  108  may engage with the proximal end of conductive sleeve to control the depth that fluid delivery device  100  is inserted into the tissue. 
   After implanting lead  150 , fluid delivery device  100  may be extended through lead body lumen  164  and seal  160  to dispense a fluid into the tissue surrounding helical electrode  158 . Fluid delivery device  100  may then be withdrawn from lumen  164  and removed from the patient&#39;s body, leaving lead  150  implanted at the treated tissue site. 
     FIG. 7  is a cut-away, side view of the distal end of an implantable medical lead and fluid delivery system wherein the medical lead is provided as a transvenous lead having a passive fixation mechanism. In this embodiment, all identically labeled components correspond to those illustrated in  FIG. 4B , however, in this case, in place of an active fixation electrode at the tip of the lead  250 , a ring electrode  252  is provided. Ring electrode  252  is electrically coupled to conductive sleeve  50 , which is further coupled to insulated conductor  36  as previously described with reference to  FIG. 4B . To stabilize the implanted position of lead  252 , passive fixation members  254  are provided, which may take the form of tines as is generally known in the art. Seal  38  may be molded onto internal sleeve  40  as described previously and forms a fluid-tight seal with the inner diameter of ring electrode  252 . Ring electrode  252  may be provided with an annular lip  256  which may act to retain seal  38 . 
     FIGS. 8 and 9  are side, cut-away views of the distal end of an implantable medical lead and fluid delivery system wherein the medical lead is further provided with a fluid reservoir for holding a pharmaceutical, genetic or biologic agent and allowing the agent to elute into adjacent body tissue over time. A body implantable lead having a cavity suitable for retaining a drug is disclosed in U.S. Pat. No. 4,506,680 issued to Stokes, incorporated herein by reference in its entirety. A combined catheter and reservoir, useful for applications involving delivery of genetic material, is disclosed in the previously cited PCT Patent Publication WO 98/02040. 
   The lead shown in  FIG. 8  corresponds to the lead of  FIG. 4B  having a helical tip electrode  34  electrically coupled to stem  50  which is further coupled to an insulated conductor  36 . In addition to or in place of a seal at or near the distal end of the lead, a fluid reservoir  300  is located near the distal end of the lead. A fluid delivery device in the form of a hollow stylet or needle, having a shaft  46  and sharpened tip  48 , may be used to fill reservoir  300  with a fluid. Reservoir  300  preferably includes a seal  304  covering a proximal opening to reservoir  300  and a seal  302  covering a distal opening to reservoir  300 . Fluid delivery device tip  48  pierces through the proximal seal  304 , which may be pre-pierced at line  308  and may be provided with a concave proximal surface to guide tip  48  to reservoir  300  and through seal  302 . Fluid may then be injected into reservoir  300 , and the fluid delivery device may be removed. The pharmaceutical, genetic, or biologic agent will elute from reservoir  300 , through distal seal  302 , into the adjacent tissue over time. 
   Fluid reservoir  300  may be formed from silicone rubber or alternatively polyurethane or another elastomer. The seals  302  and  304  are preferably formed from silicone rubber. Seal  304  may be provided as a less permeable material than seal  302  to prevent blood or bodily fluids from entering the lead body lumen  42  while still allowing a pharmaceutical, genetic or biologic material to elute through seal  304 . The reservoir  300  may be provided as a micro-osmotic pump. For example reservoir  300  may optionally contain a salt-loaded silicone material, which would swell over time as salt is replaced by water, or another polymeric material capable of swelling upon exposure to body fluids. Such swelling would aid in “pumping” a fluid agent out of reservoir  300 . 
   Optionally, the fluid delivery device may be further advanced through distal seal  302 , which may be pre-pierced at line  306 . The fluid delivery device may then be inserted into the tissue in which electrode  34  is implanted to deliver a bolus of fluid directly to the tissue site, at a desired depth within the tissue. The fluid delivery device may then be withdrawn into reservoir  300  and used to fill reservoir  300  to allow a pharmaceutical, genetic or biologic agent to elute slowly over time into the adjacent tissue. In this way, local treatment of a volume of tissue may be performed by delivering a bolus of fluid directly into the tissue, or allowing the agent to elute from reservoir  300  over time, or both. Furthermore, one or more fluid agents may be delivered directly into the tissue site, and another fluid agent may be used to fill reservoir  300  and elute over time allowing the volume of tissue in which electrode  34  is implanted to be treated by at least two different pharmaceutical, genetic or biologic agents over different time courses. 
   A fluid reservoir for storing a fluid agent that will elute over time may also be included in other embodiments of medical lead and fluid delivery systems.  FIG. 9  is a cut-away, side view of the distal end of an implantable medical lead and fluid delivery system wherein the medical lead is provided as a transvenous lead having a passive fixation mechanism and a fluid reservoir. The system shown in  FIG. 9  is similar to the system shown in  FIG. 7 , and identically labeled components correspond to those shown in  FIG. 7 . However, in  FIG. 9 , the transvenous lead is shown having a fluid reservoir  300 , similar to the reservoir described above in conjunction with  FIG. 8 . Ring tip electrode  252  is provided with a central bore  310  that may be filled with a porous material through which a pharmaceutical, genetic or biologic agent eluting out of reservoir  300  may pass to reach adjacent body tissue. A porous elution path may be formed from sintered metal structures as disclosed in the above incorporated &#39;680 patent. Alternatively central bore  310  may be left open, as shown previously in  FIG. 7 , to allow a fluid delivery device to be passed through tip electrode  252  to inject fluid directly into the tissue as well as providing an open elution pathway. 
   In some cases, it may be desirable to deliver a therapeutic fluid at a time after the lead implantation procedure. For example, pharmacological, genetic or biological treatments may need to be repeated at certain intervals over time post-operatively in order to achieve a desired therapeutic effect. A situation may also arise requiring a chronically implanted lead to be repositioned due to dislodgment or declining stimulation or sensing performance. It may be desirable to treat the tissue at the new implant site at the time the lead is repositioned. On the other hand, factors that may be causing poor lead function, such as poor tissue conductivity or low membrane potential signals, may be improved by treating the tissue at the chronic lead implant site with a fluid agent, thereby avoiding the need for lead repositioning. 
     FIG. 10  is a plan view of an implantable lead and fluid delivery system that may be used to deliver a fluid agent to a lead implant site post-operatively. In this embodiment, lead  30  corresponds generally to that shown in  FIG. 4A , and all identically labeled components correspond to those illustrated in  FIG. 4A . In  FIG. 10 , connector assembly  62  at the proximal end of lead  30  is inserted into a connector bore  264  of a connector block  262  provided on a medical device  260 , which may be a pacemaker or implantable cardioverter defibrillator, or other type of implantable pulse generator or electrophysiological monitor. Pin terminal  64  is electrically coupled to terminal  266  of connector block  262  to provide electrical connection between lead  30  and device  260 . The lumen  42  (indicated by dashed line) of lead body  32  that is continuous with hollow pin  64  communicates with a lumen  268  within connector block  262 . Lumen  218  may be accessed through access port  272 , which is preferably sealed against body fluids by a grommet  270 . Fluid delivery device  44 , which may generally correspond to the fluid delivery device described in conjunction with  FIG. 4A , may be inserted through access port  272  and grommet  270  such that it may be passed through lumen  268 , hollow pin terminal  64  and lead body lumen  42 . Fluid delivery device  44  may then exit the distal end of lead  30  until it penetrates the tissue at the lead  30  implant site, as described previously. Once penetrated to a desired depth, fluid may be delivered through fluid delivery device  44 . Fluid delivery device  44  may then be removed. Additionally or alternatively, fluid delivery device  44  may be used to refill a fluid reservoir that may be provided near the distal lead end as described in conjunction with  FIGS. 8 and 9 . 
   Access port  272  may be exposed during a minor surgical procedure by making a small skin incision at the site that device  260  is implanted. In this way, a volume of tissue at the lead implant site may advantageously be treated using a fluid delivery device at any time post-operatively without performing major surgery or catheterization procedures. 
   Thus, the present invention provides a system for treating a volume of tissue concurrently with a lead implant procedure such that the lead may remain implanted at the treated tissue site. The present invention further allows tissue at a lead implant site to be treated at any time post-operatively through minimally invasive procedures. The various embodiments described herein include a medical lead and fluid delivery system that allow the fluid delivery components to be removed from the patient&#39;s body after treating a targeted tissue site so that only the lead remains implanted. However, the inventive system may also be used in procedures for treating a volume of tissue in which chronic implantation of a lead is not required. The lead may be used acutely with an associated fluid delivery device to deliver a fluid agent to a targeted tissue site and then removed with the fluid delivery device rather than remaining implanted or implanted at another site. For example, other therapy modalities that may benefit from the inventive system and may or may not require chronic implantation of a lead may include treatment of myocardial infarction via cell delivery or treatment of coronary artery disease via drugs or biologic agents such as angiogenic factors. While the embodiments described herein have been described with regard to cardiac leads and the treatment of cardiac tissue, aspects of the inventive system may also be used in regard to other types of leads and other types of bodily tissue, such as kidney, brain, pancreas, or other organs or tissues. The described embodiments are therefore exemplary and should not be considered limiting with regard to the following claims.