Abstract:
A lead for navigating small vessels and a catheter system for implantation of leads into small vessels. Veins that return blood to the heart against the force of gravity often have valves in them to prevent backflow of deoxygenated blood. Leads and catheter systems in accordance with embodiments of the invention allow cannulation and lead implantation in small, tortuous, obstructed, and difficult to access veins enabling a range of stimulation and sensing applications.

Description:
CLAIM OF PRIORITY 
       [0001]    This application claims the benefit and incorporates as relevant by reference U.S. Provisional Application 61/441,559 filed Feb. 10, 2011 entitled “Venous Access Catheter.” 
     
    
     BACKGROUND 
       [0002]    Electrical stimulation of nervous structures has been used to treat pain, breathing disorders, neural disorders, and other conditions. Implantation of electrodes configured as cuffs, paddles, or other structures has typically been a delicate surgical process with potential for nerve damage during the procedure, or as implanted stimulation devices migrate or contact delicate nervous tissue. 
       SUMMARY 
       [0003]    Nerves often course adjacent blood vessels or other lumens in anatomical structures called “complexes.” For example, the vagus complex in the cervical region is comprised of the vagus nerve, the external jugular vein, and the carotid artery. Vagal structures and others are relatively large, but complexes are more often rather small. For example the phrenic complex comprised of the phrenic nerve, the pericardiophrenic vein, and the pericardiophrenic artery is much smaller. 
         [0004]    When such a complex is located below the heart, the Venous system has valves that facilitate return blood flow to the heart and prevent backflow of deoxygenated blood. The placement of a lead in such a small vessel and/or a vessel with valves or other impediments is a challenge. 
         [0005]    In one embodiment in accordance with the invention, a medical electrical lead has an elongate lead body with a lead body diameter defining a lumen therein, the lumen having a lumen diameter. There is a tapered tip at a distal end of the lead, and the tip tapers from about the lumen diameter to the lead body diameter over a length greater than the difference between the lumen diameter and the lead body diameter. In other embodiments, the tip tapers from about the lumen diameter to the lead body diameter over a length greater than twice, three times, and five times the difference between the lumen diameter and the lead body diameter. 
         [0006]    In another embodiment in accordance with the invention, a medical electrical lead has lumen having a constricted section with a constricted lumen diameter extending a length from the tip before transitioning to the nominal lumen diameter. 
         [0007]    In yet another embodiment in accordance with the invention, a catheter system includes a catheter body having a lumen therein. The catheter body has a proximal end and a distal end, and the catheter body has a first catheter body stiffness along the proximal portion and transitions to a less stiff second catheter body stiffness at a transition point proximate the distal end of the catheter. The catheter system of this embodiment has a hook portion of the catheter body at the distal end so that the end of the catheter body is angled relative to a portion of the catheter nearest the hook by at least 80 degrees. 
         [0008]    In yet another embodiment in accordance with the invention, a catheter system includes a catheter body having a lumen therein. The catheter body has a proximal end and a distal end, and the catheter body has a first catheter body stiffness along the proximal portion and transitions to a less stiff second catheter body stiffness at a transition point proximate the distal end of the catheter. The catheter system of this embodiment has a hook portion of the catheter body at the distal end so that the end of the catheter body is angled relative to a portion of the catheter nearest the hook by at least 80 degrees. This embodiment further includes preformed bends in the catheter body configured support a right subclavian vein method of approaching the left pericardiophrenic vein by engaging the venous walls in the subclavian veins in order to provide adequate support for the delivery of a lead. In some embodiments, a preformed curve is configured to nest at the junction of the right and left brachiocephalic veins to stabilize the catheter. 
         [0009]    In yet another embodiment in accordance with the invention, a catheter system includes a catheter body having a lumen therein. The catheter body has a proximal end and a distal. end, and the catheter body has a first catheter body stiffness along the proximal portion and transitions to a less stiff second catheter body stiffness at a transition point proximate the distal end of the catheter. The catheter system of this embodiment has a hook portion of the catheter body at the distal end so that the end of the catheter body is angled relative to a portion of the catheter nearest the hook by at least 80 degrees. This embodiment further includes preformed bends in the catheter body configured support a left subclavian vein method of approaching the left pericardiophrenic vein by engaging the venous walls in the left subclavian vein in order to provide adequate support for the delivery of a lead. 
         [0010]    In yet another embodiment in accordance with the invention, a catheter system includes a catheter body having a lumen therein. The catheter body has a proximal end and a distal end, and the catheter body has a first catheter body stiffness along the proximal portion and transitions to a less stiff second catheter body stiffness at a transition point proximate the distal end of the catheter. The catheter system of this embodiment has a hook portion of the catheter body at the distal end so that the end of the catheter body is angled relative to a portion of the catheter nearest the hook by at least 80 degrees. Iii this embodiment the transition point is within the hook portion of the catheter. Some embodiments include a second stiffness transition point about one-sixth of the length of the catheter from the distal end of the catheter. Some embodiments include a third stiffness transition point about one-third of the length of the catheter from the distal end of the catheter. 
         [0011]    In yet another embodiment in accordance with the invention, a catheter system includes a catheter body having a lumen therein. The catheter body has a proximal end and a distal end, and the catheter body has a first catheter body stiffness along the proximal portion and transitions to a less stiff second catheter body stiffness at a transition point proximate the distal end of the catheter. The catheter system of this embodiment has a hook portion of the catheter body at the distal end so that the end of the catheter body is angled relative to a portion of the catheter nearest the hook by at least 80 degrees. This embodiment further includes a dilator configured to slidably fit within the catheter lumen. 
         [0012]    In yet another embodiment in accordance with the invention, a catheter system includes a catheter body having a lumen therein. The catheter body has a proximal end and a distal end, and the catheter body has a first catheter body stiffness along the proximal portion and transitions to a less stiff second catheter body stiffness at a transition point proximate the distal end of the catheter. The catheter system of this embodiment has a hook portion of the catheter body at the distal end so that the end of the catheter body is angled relative to a portion of the catheter nearest the hook by at least 80 degrees. This embodiment further includes a dilator configured to slidably fit within the catheter lumen. In some embodiments, the dilator body has a first dilator body stiffness along the proximal portion and transitions to a less stiff second dilator body stiffness at a transition point proximate the distal end of the dilator. Some embodiments include a second stiffness transition point about one-sixth of the length of the dilator from the distal end of the dilator. Some embodiments include a third stiffness transition point about one-third of the length of the dilator from the distal end of the dilator. 
         [0013]    In still another embodiment in accordance with the invention, a method of implanting a lead in a small vein includes the steps of advancing a catheter having a hook portion at its distal end through an access vein, advancing the catheter into the ostium of a smaller vein, utilizing a preformed bend in the catheter to stabilize the catheter in the ostium of the smaller vein by engaging the preformed bend with the access vein wall, and advancing a lead through the stabilized catheter and into the smaller vein to a target location. This embodiment may be used, for example, where the access vein is a brachiocephalic vein and the smaller vein is the left pericardiophrenic vein. 
         [0014]    In still another embodiment in accordance with the invention, a method of implanting a lead in a small vein includes the steps of advancing a catheter having a hook portion at its distal end through an access vein, advancing the catheter into the ostium of a smaller vein, utilizing a preformed bend in the catheter to stabilize the catheter in the ostium of the smaller vein by engaging the preformed bend with the access vein wall, advancing a guide wire through the catheter into the smaller vein proximate the target location, advancing a dilator over the guide wire to clear obstructions from the smaller vein, retracting the dilator from the catheter and advancing a lead through the stabilized catheter and into the cleared smaller vein to a target location. 
         [0015]    Embodiments of the present invention include electrode bearing leads configured for transluminal stimulation of tissues, catheters and lead deployment systems capable of implanting such leads in a target lumen, and methods of employing leads and related deployment systems. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a plan view of a lead in accordance with embodiments of the invention. 
           [0017]      FIG. 2  is a plan view of a lead in accordance with embodiments of the invention. 
           [0018]      FIG. 3  is a plan view of a lead in accordance with embodiments of the invention. 
           [0019]      FIG. 4  is a plan view of a catheter in accordance with embodiments of the invention. 
           [0020]      FIG. 5  is a plan view of a dilator in accordance with embodiments of the invention. 
           [0021]      FIG. 6  is a schematic view of catheters in accordance with embodiments of the invention placed in context of a patient&#39;s body. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIG. 1  is a plan view of a lead in accordance with embodiments of the invention. An over the wire open lumen lead is illustrated at  110  that includes a frusto-conical tapered tip  112  that aids in navigating the lead past valves and into small diameter veins. In one exemplary embodiment, the open lumen lead accepts a 0.014 inch diameter lead wire and the interior diameter of the lumen is in a range of between about 0.018 inches and 0.020 inches. An exemplary outer diameter of the lead is about 0.05 inches. A lead and guide wire of these dimensions and configurations may be able to navigate venous valves and also veins having a diameter in the range of about 1 mm to about 3 mm, but it is also contemplated that designs having other dimensions and configurations would occur to those of skill in the art upon reading this disclosure. 
         [0023]    The lead may be constructed of a polyurethane lead body insulating layer that increases the stiffness of the lead as compared to other leads. The increased stiffness of the lead allows for better navigation, for instance, when employed retrograde in veins to get around the valves. The tapered tip  112  allows the lead to more easily navigate the venous valves because the end of the lead has a diameter that is relatively close to the diameter of the lead wire and the tip  112  smoothly transitions to the diameter of the main portion of the lead. 
         [0024]    The distal end of the lead of  FIG. 1  includes spaced apart electrodes  114  and  116 , where the electrodes  114  and  116  are located on the lead proximal the tapered tip  112 . Although two electrodes are illustrated, an alternative configuration of the distal end  112  of the lead includes five electrodes, where three electrodes are stimulation electrodes and two electrodes are sensing electrodes. Providing multiple stimulation electrodes allows the location of the stimulation to be changed to capture the target tissues and reduce the likelihood of spurious or unwanted stimulation of other nerves. Multiple variations of this design are possible, however a lead having a distal end with one or more electrodes is contemplated. 
         [0025]    In one embodiment the tapered distal tip  112  is hot molded on the end of a polyurethane lead out of the underlying polyurethane material. The polyurethane material provides the required rigidity to navigate past the venous valves, if present, and also provides a uni-body or monolithic lead construction that requires no joints or bonding of two materials together. 
         [0026]      FIG. 2  is a plan view of a lead in accordance with embodiments of the invention: Referring to  FIG. 2 , a cross-section of an embodiment of a tapered tip  112  of a lead is illustrated. The central lumen  111  diameter D 2  is only slightly larger than the diameter DI of the guide wire  115 , and is sized to allow passage of the lead  110  over the guide wire  115  with minimal deviation of the lead  110  from the wire  115 . An outer diameter D 4  of the lead  110  at the very distal end is relatively close to the diameter D 1  of the guide wire  115  such that a difference between the diameters D 1  and D 4  is minimized. With the diameter D 4  of the distal end  112  being similar to the diameter DI of the guide wire  115 , the lead  110  is able to closely follow the path of the guide wire  115  around bends in a lumen such as a vein as the lead  110  is advanced over a wire  115 . This is particularly advantageous when navigating tortuous venous structures that include valves. The diameter of the tapered tip  112  smoothly transitions to diameter D 3  from D 4  over a length L of the tip  112  such that the lead  110  is able to smoothly pass through bends, valves, and other challenging pathways. 
         [0027]    In some embodiments in accordance with the invention, length L is greater than the difference between lumen diameter D 2  and lead diameter D 3 . As an example, if the length L were equal to the difference between lumen diameter D 2  and lead diameter D 3 , the taper of the tip would be nominally 45 degrees. 
         [0028]    Referring to  FIG. 2 , another cross-section of an embodiment of a distal tapered tip  112  of a lead  110  is illustrated. The configuration of the lumen  111  results in a lumen diameter that transitions from constricted section  124  having a constricted diameter D 5  to the nominal diameter D 6  of the lumen  111 . The diameter D 5  of the constricted section lumen can extend a length L 1  and then transition to the diameter D 6  at L 2 . Alternatively the diameter can gradually taper from D 5  to D 6  over the length L 1  or the length L 2 . The distal tip  112  with different diameters D 5  and D 6  of the lumen  111  ensures that the lead  110  has adequate clearance between the guide wire  115  and the lumen  111  to easily pass the lead  110  over the guide wire  115  while Minimizing the diameter D 4  of the outer surface of the tip  112  to ensure that the lead  110  can pass through valves and around bends in lumens and closely track the guide wire  115  as it is passed over it. 
         [0029]    The utilization of the lead  110  with the tapered tip configurations in accordance with embodiments of the invention allows for deployment of leads in small vessels with tortuous physiology or obstructions such as valves. Such leads can be employed to stimulate nerves or other tissues from lumens of relatively small diameters that were previously not able to be cannulated or to have leads installed in them. 
         [0030]      FIG. 4  is a plan view of a catheter in accordance with embodiments of the invention. Referring to  FIG. 4 , a catheter  130  is illustrated for implanting a lead into a vein, possibly proximate a nerve, such as a pericardiophrenic vein proximate a phrenic nerve. The catheter  130  includes a splittable hemostasis valve system  132  at a proximal end  134 . Splittable hemostasis valve systems are known in the art and an exemplary description can be found in U.S. Pat. No. 5,125,904 to Lee. The proximal end  134  may optionally include a side port  136  that can be utilized to deliver of contrast medium. The catheter  130  may optionally be configured to have a slittable hub that accepts a hemostatic valve. The hemostatic valve may be of a configured to pass over the electrical terminal pin of a stimulation or sensing lead. 
         [0031]    A distal end  138  of the catheter may include different materials, thicknesses, and transitions along its length. The materials and thicknesses affect the catheter stiffness and provide for a smooth transition that results in a soft and flexible tip while the body of the catheter is stiff enough to be pushed through the venous system and to withstand torque if necessary for positioning or advancing the catheter. Exemplary catheter stiffness transition points are located at  140 ,  142 , and  144  which are at 0.5, 6 and 10 centimeters, respectively, from the distal end  138  of a catheter  136 , where the catheter  130  has a length of 35 cm. However, other transition locations are also contemplated as well as catheters of different lengths. 
         [0032]    The body of the catheter  130  contains a braided material around the circumference thereof to improve the performance of the catheter  130  when subjected to a torque. An inner diameter of an exemplary embodiment of the catheter may be sized to accept a 4 Fr lead. The outer wall of such an embodiment may be about 5 Fr to about 6 Fr such that the wall can contain the braided material and provide the necessary performance when the catheter is subjected to a torque. The distal end  138  of this exemplary catheter  130  may be tapered to less than 5 Fr for cannulation into the venous system. 
         [0033]    The distal end  138  may be configured to have a hook  141  having an angle a ranging from about 90 degrees to about 130 degrees which aids in cannulation of small veins that are generally skew to a larger vein used for catheterization. One example of this anatomical relationship is the junction of the left pericardiophrenic vein with the left brachiocephalic vein. The external and internal surfaces of the catheter  130  may be treated with lubricious coatings that facilitate lead and wire passage (not shown) through the catheter as well as catheter advancement. 
         [0034]      FIG. 5  is a plan view of a dilator in accordance with embodiments of the invention. The tapered guide catheter  130  is introduced into the venous system utilizing a catheter dilator  150  as illustrated in  FIG. 5 . The dilator in one example is about 45 cm which is about 10 centimeters longer than the exemplary catheter  130  described above. However, other lengths of dilators and the catheters are also contemplated. The dilator  150  is utilized to gain entry into the venous system through percutaneous methods. 
         [0035]    The dilator  150  is sized to slide within the catheter  130 . The proximal end  152  of the dilator  150  is fitted with a standard hub  154  that allows the dilator  150  to be flushed. The lumen of the dilator  150  of one embodiment is sized to accept a 0.038″ diameter guide wire (not shown). However, the size of the lumen of the dilator  150  can vary to accept different diameter guide wires. 
         [0036]    The dilator can also have a tapered tip  156  at a distal end  158  with material transition points  160  and  162  that result in a soft and flexible tip  156  while the body of the dilator is stiff enough to manipulate effectively within the catheter and beyond.  FIG. 5  illustrates locations  160  and  162  for transitions of the stiffness, such as 0.75 cm and 5 cm, respectively, from the distal end  158 . However, the locations of the transitions can vary. 
         [0037]    The length of the soft tip  158  of the dilator  150  is proportional to the length of the soft tip  138  of the catheter  130 . The soft tip  158  of the dilator  150  allows the dilator  150  to pass through the catheter tip  138  without substantial deformation of the shape of the catheter  130 . 
         [0038]      FIG. 6  is a schematic view of catheters in accordance with embodiments of the invention placed in context of a patient&#39;s body.  FIG. 6  illustrates one application of a system in accordance with embodiments of the invention that includes a right subclavian vein method of approaching the left pericardiophrenic vein at  160 . Using the right subclavian vein as the entry to the circulatory system, access to the left pericardiophrenic vein is obtained utilizing a shape  162  of the catheter  160 . The catheter  160  enters the right subclavian vein and passes through the right brachiocephalic vein. The shape  162  then transitions into the left brachiocephalic vein in order to gain access to the left pericardiophrenic vein. 
         [0039]    The shape  162  comprises two pre-formed curves  164  and  166  which facilitate access and provide stability of the catheter  160  during deployment of the lead. Curves  164  and  166  engage the venous walls in the subclavian veins in order to provide adequate support for the delivery of the lead. The curved tip of the catheter may work in conjunction with the curves  164  and  166  to provide a stable catheter platform for delivering the lead. For example, a 90 degree hook  141  ( FIG. 4 ) may be used to enter the ostium of the left pericardiophrenic vein. As a lead is advanced through the catheter and into the vein, resistance to the lead is transmitted as force to the catheter at curve  166 , which engages the left brachiocephalic vein and stabilizes the catheter allowing the lead to be pushed into the pericardiophrenic vein. Curve  164  may help facilitate crossover from the right brachiocephalic vein to the left brachiocephalic vein as the catheter is advanced. The curve may then “nest” at the junction of the right and left brachiocephalic veins to further stabilize the catheter as the lead or wire is advanced into the vein. 
         [0040]    Veins that allow blood to return to the heart in an upward flow relative to gravity may have venous valves within them. These valves can restrict access by leads, catheters, and other intravenous devices, especially in smaller bore veins. Methods in accordance with embodiments of the invention allow for cannulation of these veins through the use of a guide wire  115 , catheter  130 , and dilator  150 . In one embodiment, a catheter in accordance with embodiments of the invention is deployed proximate a target location in the venous system. A guide wire is fed through the catheter to a target location. If possible, a lead in accordance with embodiments of the invention is fed over the wire until it is implanted at the desired location. If tortuous vein geometry or valves make implantation of the lead difficult or impossible, a dilator in accordance with embodiments of the invention can be fed over the wire instead of the lead and can push through the valves or tortuosity to create a path through which the lead can be implanted. The dilator is then removed from the catheter and the lead is implanted through the pathway created by the dilator. 
         [0041]    A left subclavian vein method of approaching the left pericardiophrenic vein is also illustrated in  FIG. 6  at  170 . The left subclavian vein method operates similarly to the right subclavian method, except that the shape  172  of the catheter  170  utilizing the left subclavian method comprises two curves  174  and  176  where  176  engages the junction of the left internal jugular vein and the left brachiocephalic vein while the catheter is engaged at the ostium of the pericardiophrenic vein to support the lead&#39;s delivery. The hook  141  of an embodiment configured for a left subclavian approach to the left pericardiophrenic vein through the left brachiocephalic vein may be on the order of 130 degrees, for example. Other hook angles may occur to those of skill in the art upon reading this disclosure. 
         [0042]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.