Patent Document

FIELD OF THE INVENTION 
     The invention relates to devices and methods for delivering a therapeutic solution, and more specifically to a steerable needle and a method for delivering an angiogenic substance into a beating heart. 
     BACKGROUND OF THE INVENTION 
     There have been numerous recent advances in therapies such as angioplasty and coronary bypass surgery, which are now commonly used in the treatment of ischemic heart disease. There still exist a significant number of patients for whom these conventional therapies are not feasible options in a number of circumstances. For example, conventional coronary bypass surgery is not a treatment option in patients with diffuse small vessel coronary artery disease due to the small size and large number of diseased vessel segments. Further, re-occlusion of a diseased vessel may occur despite multiple angioplastic procedures or bypass surgeries. 
     One promising alternative treatment for ischemic heart disease is the delivery of angiogenesis-promoting substances to the heart tissue to induce angiogenesis. Angiogenesis is a complex biological process that results in the growth of new blood vessels within tissue. Angiogenesis is an essential process common to several normal and pathologic conditions including embryologic development, wound healing, development of neoplasms, and the like. Angiogenesis involves the disruption of vascular basement membranes, migration and proliferation of endothelial cells, and subsequent blood vessel formation and maturation. 
     Angiogenesis has also been induced in heart tissue for reperfusion of tissue compromised by myocardial ischemia. Several growth factors or mediators are known to elicit angiogenic responses, and administration of these mediators promotes revascularization of ischemic tissues. These growth factors are typically proteins which stimulate endothelial cell reproduction in the target tissue. Vascular endothelial growth factor (VEGF) is one of the most specific of the known angiogenic mediators due to localization of its receptors almost exclusively on endothelial cells. Receptors for VEGF are upregulated under ischemic conditions. Accordingly, the administration of VEGF augments the development of collateral vessels and improves function in peripheral and myocardial ischemic tissue. 
     Delivery of VEGF remains a significant challenge. The half-life of VEGF is very short. Accordingly, the tissue must be exposed to the growth factor for a period of days. The administration of high doses of VEGF, however, is associated with hypotension. 
     The systemic administration of VEGF can induce angiogenesis in tissues other than that which has been targeted, such as occult tumors, or sensitive diseased organs, such as the retina. This promiscuous induction of angiogenesiscan cause blindness, increase the aggressiveness of tumor cells, and lead to a multitude of other negative side-effects. Accordingly, the growth factor should be limited to the target tissue. 
     The growth factor can be delivered to the target tissue through the use of indwelling catheters over a period of time. A preferred method of delivering the growth factor, however, is in the form of gene transfer, for example, by a replication deficient adenoviral vector containing the transgene coding for the growth factor. Under this method, a quantity of the adenoviral vector having the desired genetic component is delivered to the treatment area by injection in solution. 
     In the past, an open-chest procedure has been used to deliver the treatment solution. According to this procedure, the patient&#39;s chest is opened surgically to expose the heart. The solution containing the adenoviral vector is then delivered to the heart tissue by using a syringe to make a number of injections in a grid-like pattern, with the surgeon keeping track of the location of each injection. International Patent Application WO 98/32859 discloses a method of enhancing the level of perfusion of blood to a target tissue during such procedure. 
     Once injected, the adenoviral vector causes the cells in the target tissue to produce the desired growth factor, and this growth factor production of the treated cells will continue for a period of time. Previous studies have shown the feasibility and efficacy of safe, sustained, and localized expression of angiogenesis-promoting growth factors utilizing adenoviral-mediated gene transfer therapy. 
     It is desirable to be able to provide the above described therapy without the necessity of performing open-chest surgery on the patient. U.S. Pat. No. 5,997,509 discloses an injection apparatus and method for providing gene therapy treatment to the heart or other internal organs without necessitating such open heart surgery. A procedure for utilizing a device also is disclosed in International Patent Application WO 99/44656. According to the procedure, the patient&#39;s lung is partially collapsed to enable access to areas of the heart. The therapeutic substance may be injected into the patient&#39;s myocardium by passing the needle directly through the patient&#39;s pericardium. 
     The device disclosed in the &#39;509 patent and International Patent Application WO 99/44656 includes an elongate flexible tubular body having a hollow needle mounted at the distal end for delivery of the therapeutic substance to the tissue. This and other currently available devices have relatively complex designs, and, accordingly, are extremely expensive to manufacture. Further, they may be difficult to manipulate around the contours of the heart or to ensure stability of the needle against the target cardiac tissue. 
     Additionally, access to the target cardiac tissue is often obscured by other organs and tissues. One or more retractors may be used in order to physically move the obscuring organs or tissues in order to gain access to the cardiac tissue. A grasping type of retractor, a mechanically expandable retractor, an inflatable retractor, or another type of retractor known in the art may be utilized as disclosed, for example, in International Patent Application WO 99/44656. In reoperative patients, however, lung tissue frequently adheres directly to the cardiac tissue. Under these conditions, the lung and cardiac tissues cannot typically be separated by conventional methods without damage to either or both of the organs. As a result, retraction devices such as those disclosed in the &#39;509 patent and International Patent Application WO 99/44656 are not readily utilized under such circumstances. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a method and a minimally invasive injection device which is steerable such that it may be maneuvered into a desired position for administering an injection. The device includes a hollow needle which is adapted for connection to a solution supply. The needle has an elongated flexible body with a sharpened tip at its distal end for penetration into tissue. The needle may be steered by means of a steering cable and a moveable steering sleeve. 
     The steering cable is an elongated cable or wire which is coupled to the needle toward its distal end and extends substantially the length of the needle to its proximal end. The user may exert a tensioning force on the steering cable to cause the elongated flexible body of the needle to flex or arch along a flexion radius. The moveable steering sleeve is slideably disposed along the elongated flexible body with the steering cable extending through the steering sleeve. Accordingly, by moving the steering sleeve axially along the needle, the user can adjust the flexion radius of the needle. That is, the needle body will be substantially straight from its proximal end up to and including the section extending through the steering sleeve. As a tension force is exerted on the steering cable, however, the needle body distal the steering sleeve will flex or arch, moving the needle tip toward the proximal end of the needle. The steering sleeve may be slid along the needle by means of a sufficiently rigid steering sleeve adjustment cable, which likewise extends toward and can be operated from the proximal end of the needle. Thus, the device provides a simplified, steerable needle arrangement that may be efficiently and economically produced. 
     A device constructed according to teachings of the invention can be easily controlled and efficiently maneuvered within a body cavity, the flexible needle contouring to cardiac and thoracic geometry to properly position the needle tip and administer the injection. Accordingly, the device may readily be utilized in minimally invasive procedures to deliver angiogenesis-promoting substances from a remote location to an area of ischemic heart tissue without necessitating open-chest surgery. 
     The delivery of the therapeutic substance to the myocardium can be by way of any suitable route, transpericardially, as well as endocardially. While the device may be utilized during open-heart surgery, or advanced into the heart through any artery, including, for example, the femoral artery, the device may also be utilized in the manner disclosed in International Patent Application WO 99/44656. More specifically, the patient&#39;s lung may be partially collapsed by the introduction of gas into the patient&#39;s thoracic cavity. This enlarges the working area for injection of the therapeutic substance and increases access to heart tissue. 
     According to other features of the invention, various methods of delivering a therapeutic substance are disclosed. One such method includes the steps of inserting an elongated device body into a body cavity through an opening, and using the steering cable, and the steering sleeve adjustment cable and steering sleeve to steer the body distal end within the cavity. Another method further includes the steps of inserting the device into the patient&#39;s thoracic cavity through an opening the patient&#39;s chest wall, passing a needle into the heart tissue and delivering the therapeutic substance. Further, the needle may be passed directly into the chest cavity in a true percutaneous technique wherein no incision is made. Under these circumstances, the opening in the chest is limited only the diameter of the device or a small trocar. 
     Inasmuch as access to cardiac tissue is often limited in re-operative patients, however, the invention further includes a methods of administering the therapeutic solution when lung tissue adhering to the heart obscures access. According to the method, the needle is passed directly through the patient&#39;s lung tissue and into the heart tissue. According to another method, the device is stabilized against the tissue by means of a moveable stabilizing platform which is disposed either against the lung tissue or against the pericardium. 
     According to one design, the stabilizing platform is spaced from the distal tip of the needle and can transit the needle tip a sufficient distance to allow the needle tip to penetrate and pass through the lung tissue, and to penetrate the heart tissue to a desired depth. The distal-most position of the movable platform is preferably the optimum cardiac tissue penetration depth. The movable platform may be retained on the needle tip by a stop along the needle tip, or any other appropriate structure or means. According to a preferred embodiment, the platform can transit the needle tip from a position approximately 5-10 mm from the distal tip to approximately 35-50 mm proximal the distal tip. In this way, the needle tip can penetrate and extend through the lung tissue, and then penetrate the cardiac tissue a desired depth to administer the therapeutic solution. 
     According to another feature of the invention, the platform may be stopped, advanced to, or disposed at a desired position to provide the optimum cardiac tissue penetration when cardiac penetration has been confirmed via an ECG signal. An electrode is preferably located on the on the distal tip of the needle, and connected to an ECG. In this way, the surgeon can determine when the needle has penetrated the patient&#39;s myocardium and is properly positioned. Penetration of the myocardium by the needle will show as a current injury on the ECG. 
     By way of further example, the moveable platform may be in the form of an inflatable balloon which may be inflated to a desired volume once cardiac contact has been confirmed. Inflation may be accomplished by means of a gas line extending along the length of the needle body between the platform and an appropriate gas source. The platform of this design is preferably disposed along the needle tip at a given axial position which defines the optimum cardiac penetration depth. The deflated platform may be passed through the lung tissue and then inflated adjacent the heart tissue when proper placement has been confirmed. Other platform designs such as a spring-biased platform may be provided. 
    
    
     These and other features and advantages of the invention will be more readily apparent upon reading the following description of a preferred exemplified embodiment of the invention and upon reference to the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a delivery device constructed in accordance with teachings of the invention in conjunction with a syringe. 
     FIG. 2 is a perspective view of a needle assembly of the delivery device of FIG.  1 . 
     FIG. 3 is a perspective view of the needle of FIG. 2 wherein a tensile force has been applied to the steering cable. 
     FIG. 4 is a plan view if the needle of FIG. 2 similar to FIG. 3 wherein steering sleeve is alternately positioned and a tensile force has been applied to the steering cable. 
     FIG. 5 is a plan view of a patient&#39;s chest showing the organs therein and various instruments positioned for a minimally invasive procedure. 
     FIG. 6 is an enlarged fragmentary view showing the needle constructed according to teachings of the invention penetrating the lung and heart tissue. 
     FIG. 7 is an enlarged plan view of a third embodiment of the invention, a portion of the components being shown in cross-section. 
     FIG. 8 is a fragmentary view of the device of FIG. 7 wherein the platform is inflated. 
     FIG. 9 is an enlarged plan view of an alternate embodiment of the invention, a portion of the components being shown in cross-section. 
     FIG. 10 is a cross-sectional view of the device of FIG. 7 taken along line  10 — 10  in FIG.  9 . 
     FIG. 11 is a fragmentary, partial cross-sectional view of the device of FIG. 9 wherein the platform adjustment sleeve is moved to advance the platform along the needle tip. 
    
    
     While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of the invention as defined by the appended claims. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     There is shown in FIG. 1 a delivery device  12  constructed in accordance with teachings of the invention for use in delivering a therapeutic solution to the tissue of a heart, especially a beating heart. The device  12  includes a needle assembly  14  adapted to be coupled to a syringe or other solution supply device  15 . The distal end of the needle assembly  14  is designated generally as  16  and the proximal end is designated as  18 . The needle assembly  14  includes an elongated body or cannula  20  with a sharpened needle tip  22  at its distal end. In the embodiment illustrated, the needle tip  22  is of a smaller diameter than the needle body  20 . A bore  24  extends through the needle assembly  14  and is in communication with the solution supply device  15 . During use, the device  12  may, for example, be inserted through a thoracoscopic port (not shown), giving thoracoscopic access to the patient&#39;s heart. The therapeutic solution may then be injected from the solution supply device  12  through the bore  24  of the needle assembly  14  directly into the cardiac tissue in a predetermined quantity. 
     In the currently preferred embodiment of the invention, the solution supply device is a conventional syringe  15 . The syringe  15  includes a hollow cylindrical body  30  having a distal necked-in end  32 . A plunger shaft  34  with a plunger  36  mounted on the distal end thereof and a thumb button  38  mounted to the proximal end thereof is slidably disposed within the cylindrical body, the plunger extending outward from the body. During use, the operator may actuate the plunger  36  by depressing the plunger thumb button  38  to deliver the therapeutic solution. The needle assembly  14  may be coupled to the syringe  15  by any appropriate coupling  39 . In the currently preferred design, a metal hub  39  is utilized which has a large bore for receiving the distal necked-in end  32  of the syringe  15 . The hub  39  further includes a smaller bore which communicates with the large bore and the bore  24  of the needle assembly  14  to establish fluid communication between the syringe  15  and the needle tip  22  for delivery of therapeutic fluid. 
     While the solution supply device has been explained with regard to a syringe  15 , it will be appreciated by those of skill in the art that the supply device can be of any appropriate design. Additionally, the supply device may include any appropriate metering device to control the amount of therapeutic substance injected at the injection site. For example, and as explained in International Patent Application WO 99/44656, the syringe  15  may include a shaft having screw threads or include a ratchet mechanism which permits the plunger button to advance within the cylindrical body only a predetermined distance to permit only a predetermined amount of therapeutic solution to be administered at a given injection site. Alternately, the administration of a controlled amount of the therapeutic solution may be facilitated by a computer controlled device. 
     In accordance with the invention, the movement of the distal end  16  of the needle assembly  14  may be controlled by a steering mechanism (designated generally as  40 ). The needle assembly  14  and steering mechanism  40  are enlarged and schematically illustrated in FIGS. 2-4. The steering mechanism includes a steering cable  42  which is coupled to the needle body  20  at a distal attachment  44  toward the distal end  16  of the needle body  20 . The steering cable  42  extends toward the proximal end  18  of the needle assembly  14  and substantially the length of the needle assembly  14 . It will be appreciated by those of skill in the art that the assertion of a tensioning force on the proximal end  46  of the steering cable  42  flexes or arches the distal end  16  of the needle assembly  14  back towards the proximal end  18  of the needle assembly  14  along a dynamic radius of flexure as shown in FIG.  3 . It will be appreciated by those of skill in the art that the needle assembly  14  increasingly arches, that is, the radius of flexure will decrease, as the level of tensioning force on the steering cable  42  is increased. 
     To further control this radius of flexure and the location of the bend, a moveable steering sleeve  50  is provided. The steering sleeve  50  is essentially a hollow tube having an internal bore  52 , which is disposed about the needle body  20  such that the sleeve  50  may slide axially along the needle assembly  14 , the steering cable  42  extending through the bore  52 . As may be seen in FIGS. 3 and 4, during operation, the length of the needle body  20  which remains straight and the length of the needle assembly  14  which arches is determined by the position of the steering sleeve  50  relative to the distal attachment  44  of the steering cable  42 . In this way, the radius of flexure is determined, at least in part, by the position of the steering sleeve  50  as the steering cable  42  is tensioned by the user. 
     In order to move the steering sleeve  50  in the distal and proximal directions along the needle assembly  14 , a steering sleeve adjustment cable  54  is provided. The steering sleeve adjustment cable  54  may be of any appropriate material, so long as it is sufficiently rigid to push the sleeve  50  along needle assembly  14 . The currently preferred embodiment comprises a stainless steel cable on the order of 1-3 mm in diameter. 
     Those of skill in the art will appreciate that the needle body  20  must be sufficiently rigid to support the steering mechanism  40 , while being sufficiently flexible to permit the needle body  20  to arch or flex as a tensioning force is applied to the steering cable  42 . Further, the needle body  40  must be sufficiently resilient such that it remains biased in a substantially straight position to permit its manipulation and use in successive injections if so desired. The needle assembly  14  portion of the device  12  will typically be approximately 300-400 mm long. A needle body  20  on the order of 20-25 Ga. has been found to be adequately flexible, yet sufficiently rigid to permit proper functioning of the steering mechanism  40  and placement of the needle tip  22 . 
     Inasmuch as the steering mechanism  40  does not act directly upon the needle tip  22 , it is not necessary for the needle tip  22  to be as rigid as the needle body  20 . Moreover, it is preferable that the needle tip  22  be of a smaller gauge in order to facilitate penetration of the needle tip  22  into body tissue and to minimize extravasation of injectate. It has been determined that a 25-30 Ga. (e.g., 28 Ga.) cannula is particularly appropriate. While the illustrated needle tip  40  includes a bevel sharp tip  56 , it will be appreciated that an alternate tip geometry or structure may be provided. 
     It will be appreciated that the device  12  can be readily constructed from “off-the-shelf” type components so that it may be economically manufactured. Thus, the manufacture is not cost prohibitive, and the device may be utilized as a single use, disposable device. 
     During use, the elongated needle body  20  is inserted into the patient&#39;s body cavity through an opening. The opening in a true percutaneous technique is the opening formed by the needle assembly  14  itself as it is inserted into the chest wall and through the ribs to the heart. Under these circumstances, the opening is substantially equivalent to the diameter of the device  12 . Alternately, the needle may be inserted through a small trocar. If, for example, the device  12  has a diameter of 3 mm, the trocar might have a diameter of 5 mm. The opening might also be in the form of an airtight port  56  in the chest wall as illustrated in FIG.  5  and disclosed, for example in International Patent Application WO 99/44656. 
     Once inserted, the needle assembly  14  is steered into the desired position using the steering mechanism  40 . That is, the physician exerts a tensile force on the proximal end  46  of the steering cable  42 , the distal end  44  of the steering cable  42  being coupled to the needle body  20  toward the body distal end  16  to steer the body distal end  16  along a flexion radius. The physician may adjust the flexion radius by locating the steering sleeve  50  at a desired position along the needle body  20  using the steering sleeve adjustment cable  52 . Once appropriately positioned, the physician can pass the sharpened needle tip  22  into the heart tissue  62 , and depressing the syringe  15  thumb button  38  to advance the plunger  36  and deliver the therapeutic substance to the patient&#39;s heart. 
     According to another important aspect of the invention, the delivery device  12  is particularly useful when access to heart tissue is obscured by other tissue and cannot be readily separated. For example, in the procedure set forth in International Patent Application WO 99/44656, the patient&#39;s lung is collapsed or partially collapsed in order to provide working space in the thoracic cavity. In reoperative patients, however, the lung tissue  60  frequently adheres to the target heart tissue  62 , as illustrated in FIG.  6 . In accordance with the invention, the needle assembly  14  may be advanced directly through the lung tissue  60  and into the heart tissue  62 . In order to facilitate this passage, the smaller diameter needle tip  22  is sufficiently elongated to allow the needle tip  22  to penetrate and advance through the lung tissue  60  and into the cardiac tissue  62 . In this regard, the needle tip  22  is preferably on the order of 1½ to 2 inches (approximately 35-50 mm) long. It will be appreciated by those of ordinary skill in the art, however, that the needle tip  22  may be shorter or longer, as conditions warrant. 
     In order to determine when the needle tip  22  touches or penetrates the cardiac tissue  62 , an electrode  64  similar to that disclosed in International Patent Application WO 99/44656, may be provided at the needle tip  22 , the remainder of the needle assembly  14  being insulated therefrom. Alternately, the needle tip  22  itself may serve as an electrode if the needle tip  22  is made from a conductive material. Electrical connection of this electrode  64  to an electrocardiograph (“ECG”) (schematically illustrated as  66 ) may be made by running an electrical conductor  68  along the needle assembly  14  to the ECG  66  located outside the patient&#39;s body. Standard surface ECG leads  70  are likewise applied to the patient. When the electrode  64  enters the patient&#39;s myocardium  62  (see FIG.  6 ), the event shows as a current injury. In this way, the cardiologist may ensure that the desired positioning and contact is made with the myocardium  62  prior to actuation of the solution supply device  12 . 
     It will be appreciated that the inclusion of the electrode  64  additionally permits the cardiologist to track or electronically mark the injection sites. Accordingly, the cardiologist may follow the marking to ensure that adequate therapeutic solution is applied to the target cardiac tissue to provide optimum conditions for a desired effect. Additionally, such marking facilitates use of the needle assembly  14  in positions that are typically beyond the line of sight provided by way of a surface incision. 
     It will be further appreciated that alternate marking means and methods may be utilized. For example, markers that may be detected ultrasonographically, radiographically, as, for example, by x-ray or catscan, or electrocardially are appropriate. Virtual marking or mapping may likewise be utilized. Such methods are disclosed, for example, in U.S. application Ser. No. 09/393,873. 
     According to another important feature of the invention, in order to stabilize the needle assembly  14  during injection, a platform  74  is provided which contacts the surface of the lung tissue  60  or the pericardium  72 . To ensure contact of the platform  74  with the tissue and the desired stabilization, the platform  74  is moveable relative to the needle tip  22 . 
     In the embodiment illustrated in FIGS. 5-8, the movable platform  74  is in the form of a collapsible structure. The platform  74  is preferably in the form of an inflatable and deflatable, or collapsible donut-shaped balloon coupled to the periphery of the needle tip  22 . A platform  74  on the order of 4-6 mm in diameter when fully inflated is currently considered adequate to provide desired stabilization against tissue. During insertion into the lung or other tissue  60  obstructing access to the heart  62 , the platform is fully collapsed against the needle tip  22 . In this way, the platform  74  does not interfere with the penetration of the needle tip  22  into and through the lung  60  or other tissue. Rather, the platform  74  passes through the lung  60  or other tissue. The collapsible platform  74  is particularly appropriate when the device  12  is utilized in a true percutaneous technique wherein no incision is made in the chest wall. 
     Air or other inflating gas is supplied to the platform  74  via an air line  76 . The air line  76  extends from a source of gas at its proximal end  78 , such as from a compressed gas source or a simple syringe (not shown), along the needle body  20  and needle tip  22 , to the platform disposed generally toward the distal end  16  of the needle assembly  14 . The deflated, or collapsed, platform  74  is shown in FIG. 7, while the inflated platform is shown in FIG.  8 . 
     The platform  74  is spaced from the distal end  16  of the needle tip  22  to limit the penetration of the needle tip  22  into the cardiac tissue. During use, the collapsed platform  74  is passed through the lung or other obstructing tissue. When the needle tip  22  has penetrated the heart tissue a desired depth, the platform  74  may be inflated to stabilize the needle along the tissue. The platform  74  is preferably inflated, as shown in FIGS. 6 and 8, at a position between the heart tissue  72  or myocardium  62 , and the lung tissue  60 . In this way, the platform  74  limits the depth to which the needle tip  22  penetrates the cardiac tissue  62 . In other words, the platform  74  is preferably spaced from the distal tip  16  of the needle tip  22  a distance equal to the desired needle penetration. 
     It is presently anticipated that the distal surface of the platform  74  will be disposed on the order of 5-10 mm from the distal tip  45 , although alternate spacing may be dictated by factors such as the particular therapeutic solution utilized, or the physical characteristics of the tissue upon which the procedure is to be performed. 
     In an alternate embodiment of the invention, the movable platform  80  is in the form of a disk which is axially slidable relative to the needle tip  22 , as shown in FIGS. 9-11. In this way, the platform  80  may be moved into position against the penetrated tissue at substantially any location along the needle tip  22  in order to stabilize the needle assembly  14  relative to the tissue. In contrast to the movable platform  74  of FIGS. 5-8, which moves by collapsing yet remains stationary relative to the axis of the needle tip  22 , the platform  80  of FIGS. 9-11 is movable relative to the axis of the needle tip  22 . Further, while the collapsible platform  74  is preferably disposed directly against the heart, the platform  80  steadies the needle tip  22  by placement against the first entered tissue, e.g., the lung tissue. 
     The platform  80  may be of any appropriate shape or size and formed of any appropriate material. It has been determined that a platform  80  formed of stainless steel and on the order of 4-6 mm in diameter is particularly suitable. 
     The platform  80  includes a central opening  82  which closely receives the needle tip  22 . In order to prevent the platform  80  from separating from the needle tip  22 , the needle tip  22  preferably includes an enlarged portion  84 . It will be appreciated that the enlarged portion  84  is slightly larger than or presents an interference with the central opening  82  of the platform  80  to prevent the platform  80  from slipping from the end of the needle tip  22 . It will further be appreciated that it is not necessary for the enlarged portion  84  to extend about the circumference of the needle tip  22 , as is shown. Rather, the enlarged portion  84  need only present sufficient interference to prevent passage of the platform central opening over the enlarged portion  84 . 
     To facilitate proper placement of the platform  80  against the penetrated tissue, a platform adjustment mechanism  86  is provided. In the illustrated embodiment, platform adjustment mechanism is in the form of an adjustment sleeve  86 , although an alternate arrangement may be provided. The sleeve  86  is slightly larger than and axially slidably disposed about the needle body  20 . In this way, the adjustment sleeve  86  may be manually advanced toward the distal end  16  of the device  12  to contact and move the platform  80  distally and into contact with the tissue. It will be appreciated that the sleeve  86  may likewise be used to position the platform  80  toward the distal end  16  of the needle tip  22  prior to penetration into the tissue. In this way, sleeve  86  moves in the proximal direction as the needle tip  22  penetrates the tissue and the platform  80  contacts the tissue and slides proximally along the needle tip  22 . Alternately, the platform  80  may remain in a more proximal location along the needle tip  22  until the needle tip  22  has penetrated the tissue. The sleeve  86  may then be used to advance the platform  80  into contact with the tissue to steady the needle in the tissue. 
     In order to permit the surgeon to utilize the steering mechanism  40 , the steering sleeve  50  preferably is disposed about the platform adjustment sleeve  86 , as may best be seen in FIGS. 9 and 10. In this way, the steering sleeve  50  may be advanced along the body  20  to provide the desired bending of the body  20  in conjunction with a tensioning force exerted on the steering cable  42 . Additionally, the adjustment sleeve  86  includes a slot  88  for receiving the steering cable  42 . Thus, as the platform adjustment sleeve  86  moves axially along the needle body  20 , the slot  88  moves along the steering cable  42  such that the sleeve  86  does not interfere with the use of the steering cable  42 . It will be appreciated that the platform adjustment sleeve  86  should be fabricated from a material which is sufficiently rigid that it can be pushed axially along the needle body  20  and engage and move the platform  80 , yet sufficiently flexible that it can be readily flexed as the device  12  is steered into a desired position for injection. It has been determined that a semi-rigid elastomer or rubber is particularly suitable for this application, although it is envisioned that other materials may be utilized. 
     In summary, the invention provides a delivery device  12  that may be easily steered into a desired position and utilized for successive injections. The flexibility of the elongated needle body and the versatility of the control mechanism permit the needle to contour the path of delivery to the cardiac and thoracic geometry, providing the cardiologist great latitude in placement of the needle, and precise delivery of the injectant from a remote distance through a relatively small incision. During use, the needle is advanced into position, and the needle tip penetrates the heart tissue, either directly or through adhering lung tissue or other obscuring tissue. An electrode on the needle indicates when the cardiac tissue has been penetrated, and injection site may be marked to ensure injections occurred to desired relative locations. The platform limits the depth of penetration and allows stabilization of the needle against the epicardial surface of the heart or the surface of the lung or other tissue. The solution then can be injected into the cardiac tissue by actuating the syringe. The device is formed of readily available materials and, accordingly, may be economically constructed. 
     All of the references cited herein, including patents, patent applications, and publications, are hereby incorporated in their entireties by reference. 
     While this invention has been described with an emphasis upon preferred embodiments, it will be obvious to those of ordinary skill in the art that variations of the preferred embodiments may be used and that it is intended that the invention may be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications encompassed within the spirit and scope of the invention as defined by the following claims.

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