Abstract:
The present invention is a lead for use in connection with a myocardial lead attachment system of the type having an anchor for engaging the heart and a tether extending from the anchor. The lead includes a lead body having a proximal end, a distal end and a lumen for accepting the tether. A tapered tip is separate from the lead and positioned adjacent the distal end of the lead. The tip has a longitudinal through-hole for accepting the tether.

Description:
REFERENCES  
       [0001]     The present application claims the benefit of the following U.S. Provisional Applications: Application Ser. No. 60/514,037 filed Oct. 24, 2003, entitled “Absorbable Myocardial Lead Fixation System”, Application Ser. No. 60/514,665 filed Oct. 27, 2003, entitled “Lead Electrode Arrangement for Myocardial Leads”, Application Ser. No. 60/514,042 filed Oct. 24, 2003, entitled “Tapered Tip for Myocardial Lead”, Application Ser. No. 60/514,714 filed Oct. 27, 2003, entitled “Minimally-Invasive Fixation Systems for Over-the-Tether Myocardial Leads”, Application Ser. No. 60/514,039 filed Oct. 24, 2003, entitled “Distal or Proximal Fixation of Over-the-Suture Myocardial Leads”, Application Ser. No. 60/514,146 filed Oct. 24, 2003, entitled “Myocardial Lead with Fixation Mechanism”, Application Ser. No. 60/514,038 filed Oct. 24, 2003 entitled “Delivery Instrument for Myocardial Lead Placement” and Application Ser. No. 60/514,713 filed Oct. 27, 2003, entitled “Drug-Eluting Myocardial Leads”, all of which are incorporated herein by reference.  
         [0002]     Reference is hereby made to the following commonly assigned U.S. patent application Ser. No. 10/821,421, filed Apr. 9, 2004, entitled “Cardiac Electrode Anchoring System” and the following commonly assigned U.S. patent applications filed on an even date herewith, all of which are incorporated herein by reference: application Ser. No. ______, entitled “Myocardial Lead Attachment System”, application Ser. No. ______, entitled “Distal or Proximal Fixation of Over-the-Tether Myocardial Leads”, application Ser. No. ______, entitled “Myocardial Lead with Fixation Mechanism” and application Ser. No. ______, entitled “Absorbable Myocardial Lead Fixation System.” 
     
    
     FIELD OF THE INVENTION  
       [0003]     This invention relates generally to implantable lead assemblies for stimulating and/or sensing electrical signals in muscle tissue. More particularly, it relates to myocardially-implanted leads for cardiac stimulation and systems for anchor the leads.  
       BACKGROUND OF THE INVENTION  
       [0004]     Cardiac rhythm management systems are used to treat heart arrhythmias. Pacemaker systems are commonly implanted in patients to treat bradycardia (i.e., abnormally slow heart rate). A pacemaker system includes an implantable pulse generator and leads, which form the electrical connection between the implantable pulse generator and the heart. An implantable cardioverter defibrillator (“ICD”) is used to treat tachycardia (i.e., abnormally rapid heart rate). An ICD also includes a pulse generator and leads that deliver electrical energy to the heart.  
         [0005]     The leads coupling the pulse generator to the cardiac muscle are commonly used for delivering an electrical pulse to the cardiac muscle, for sensing electrical signals produced in the cardiac muscle, or for both delivering and sensing. The leads are susceptible to categorization according to the type of connection they form with the heart. An endocardial lead includes at least one electrode at or near its distal tip adapted to contact the endocardium (i.e., the tissue lining the inside of the heart). An epicardial lead includes at least one electrode at or near its distal tip adapted to contact the epicardium (i.e., the tissue lining the outside of the heart). Finally, a myocardial lead includes at least one electrode at or near its distal tip inserted into the heart muscle or myocardium (i.e., the muscle sandwiched between the endocardium and epicardium). Some leads have multiple spaced apart distal electrodes at differing polarities and are known as bipolar type leads. The spacing between the electrodes can affect lead performance and the quality of the electrical signal transmitted or sensed through the heart tissue.  
         [0006]     The lead typically consists of a flexible conductor surrounded by an insulating tube or sheath that extends from the electrode at the distal end to a connector pin at the proximal end. Endocardial leads are typically delivered transvenously to the right atrium or ventricle and commonly employ tines at a distal end for engaging the trabeculae.  
         [0007]     The treatment of congestive heart failure (“CHF”), however, often requires left ventricular stimulation either alone or in conjunction with right ventricular stimulation. For example, cardiac resynchronization therapy (“CRT”) (also commonly referred to as biventricular pacing) is an emerging treatment for heart failure, which requires stimulation of both the right and the left ventricle to increase cardiac output. Left ventricular stimulation requires placement of a lead in or on the left ventricle near the apex of the heart. One technique for left ventricular lead placement is to expose the heart by way of a thoracotomy. The lead is then positioned so that the electrodes contact the epicardium or are embedded in the myocardium. Another method is to advance an epicardial lead endovenously into the coronary sinus and then advance the lead through a lateral vein of the left ventricle. The electrodes are positioned to contact the epicardial surface of the left ventricle.  
         [0008]     Unfortunately, insertion through the myocardium can be somewhat traumatic to the muscle tissue. Accordingly, there is a need for a lead that can be implanted with minimal long-term damage to the physiology of the heart.  
       SUMMARY OF THE INVENTION  
       [0009]     According to one embodiment, the present invention is a lead for use in connection with a myocardial lead attachment system of the type having an anchor for engaging the heart and a tether extending from the anchor. The lead includes a lead body having a proximal end, a distal end and a lumen for accepting the tether. A tapered tip is separate from the lead body and is positioned adjacent the distal end of the lead body. The tip has a longitudinal through-hole for accepting the tether.  
         [0010]     According to another embodiment, the present invention is a method of implanting a myocardial lead. An anchor mechanism coupled to a distal end of a tether is advanced through the myocardium to an implant site. An appropriate dilating tip having an internal through-hole is selected. The tip and lead are threaded onto the tether such that the tip is distal to the lead. The tip and lead are advanced over the tether to the implant site.  
         [0011]     According to another embodiment, the present invention is a method of implanting a lead into a myocardium of a heart. A proximal end of an anchor mechanism and tether arrangement is attached to a needle. The needle is advanced through the heart at least until the proximal end of the tether  45  exits the heart. The needle is detached from the tether and the proximal end of the tether is tensioned to cause the anchor mechanism to engage the heart. A lead is advanced over the tether into the heart.  
         [0012]     This summary is not intended to describe each embodiment or every implementation of the present invention. Advantages and a more complete understanding of the invention will become apparent upon review of the detailed description and claims in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a sectional view of a patient&#39;s heart showing a portion of the vasculature and a myocardial lead attachment and pacing system according to one embodiment of the present invention.  
         [0014]      FIG. 2  is a side sectional view of a distal portion of the myocardial lead attachment system of  FIG. 1  in accordance with one embodiment of the present invention.  
         [0015]      FIG. 3  is a side sectional view of a distal portion of the myocardial lead attachment system of  FIG. 1  in accordance with another embodiment of the present invention.  
         [0016]      FIG. 4  is a side sectional view of a distal portion of the myocardial lead attachment system of  FIG. 1  in accordance with yet another embodiment of the present invention.  
         [0017]      FIG. 5  is a side sectional view of a distal portion of the myocardial lead attachment system of  FIG. 1  in accordance with still another embodiment of the present invention.  
         [0018]      FIG. 6A  is a side sectional view of a distal portion of the myocardial lead attachment system of  FIG. 1  in accordance with another embodiment of the present invention.  
         [0019]      FIG. 6B  is a side sectional view of the attachment system of  FIG. 6A  following removal of the tip.  
         [0020]      FIG. 7  is a perspective view of a distal portion of the myocardial lead attachment system of  FIG. 1  in accordance with yet another embodiment of the present invention. 
     
    
       [0021]     While the invention is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the invention to the particular embodiments described. On the contrary, the invention is intended to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.  
       DETAILED DESCRIPTION  
       [0022]      FIG. 1  shows a myocardial lead attachment and pacing system  10  deployed in a human heart  12  according to one embodiment of the present invention. The heart  12  includes a right atrium  14  and a right ventricle  16  separated from a left atrium  18  and a left ventricle  20  by a septum  22 . During normal operation of the heart  12 , deoxygenated blood is fed into the right atrium  14  through the superior vena cava  24  and the inferior vena cava  26 . The deoxygenated blood flows from the right atrium  14  into the right ventricle  16 . The deoxygenated blood is pumped from the right ventricle  16  into the lungs, where the blood is re-oxygenated. From the lungs the oxygenated blood flows into the left atrium  18 , then into the left ventricle  20 . The left ventricle  20  beats forcefully to pump the oxygenated blood throughout the body.  
         [0023]     The outer walls of the heart  12  are lined with a tissue known as the epicardium  28 . The inner walls of the heart are lined with a tissue known as the endocardium  30 . The heart muscle, or myocardium  32 , is sandwiched between the endocardium  30  and the epicardium  28 . A tough outer pericardial sac  33  surrounds the heart  12 .  
         [0024]     The pacing system  10  includes a pulse generator  34  coupled to a myocardial lead  36 . The pulse generator  34  is typically implanted in a pocket formed underneath the skin of the patient&#39;s chest or abdominal region. The lead  36  extends from the pulse generator  34  to the heart  12  and is implanted in the myocardium  32  near an apex  38  of the left ventricle  20 . The lead  36  delivers electrical signals from the pulse generator  34  to at least one electrode located at or near a distal region of the lead  36  to accomplish pacing of the heart  12  (not visible in  FIG. 1 ). Although shown in implanted near the apex  38 , the lead  36  may be implanted anywhere in the heart  12  pacing therapy is needed. An anchor mechanism  44  is coupled to the lead  36  via a tether  45  to secure the lead  36  to the heart  12  and to facilitate delivery of the lead  36  into the heart  12 .  
         [0025]     The pacing lead assembly  36  and anchor mechanism  44  may be implanted in the heart  12  with a delivery instrument and according to methods described in the above-identified application “Myocardial Lead Attachment System”. Briefly, the delivery instrument and anchor mechanism  44  are advanced through the heart  12 , forming a tract through the myocardium  32  (not visible in  FIG. 1 ). The anchor mechanism  44  is deployed on a surface of the heart  12  so that the tether  45  extends longitudinally through the tract. Following implantation of the anchor mechanism  44 , the tether  45  is threaded through the lead  36  and the lead  36  is advanced over the tether  45  into the myocardium  32 . The tether  45  is then tensioned and attached to the lead  36  to secure the lead  36  in place within the myocardium  32 . This structure results in a locally-stable myocardial implant.  
         [0026]     Optionally, the anchor mechanism  44  may be implanted without the aid of a delivery instrument as is described above, but rather with a curved suture needle. The proximal end of the tether  45  is attached to the needle, either directly or to a short length of suture attached to the needle. The needle is used to pierce the epicardium  28 , is pushed through the myocardium  32  and drawn back through the epicardium  28 , pulling the tether  45  through the myocardium  32 . The tether  45  is cut from the needle and tensioned to bring the anchor mechanism  44  in contact with the epicardium  28 . The lead  36  is threaded onto the tether  45  and advanced over the tether  45  as previously described.  
         [0027]      FIG. 2  is a sectional view of a distal portion of the myocardial lead attachment system  10  according to one embodiment of the present invention. The myocardial lead  36  includes two electrodes, a proximal anode  40   a  and a distal cathode  40   b.  An outer insulating sheath  46  is formed around the lead  36  and protects a pair of coiled conductive members  48   a  and  48   b  coupled to the anode  40   a  and cathode  40   b,  respectively. A second inner insulating sheath  50  forms an internal lumen  43  for receiving the tether  45 . A marker band  52  is optionally formed on the outer insulating sheath  46 .  
         [0028]     The lead  36  includes a tapered tip  54  positioned distal to the distal region  42  of the lead  36 . The tapered tip  54  tapers from a first diameter a at a proximal end  54   a  to a second diameter b, smaller than the first diameter a, at a distal end  54   b.  In one embodiment, as shown in  FIG. 2 , the tapered tip  54  is formed in the shape of a cone. In another embodiment, shown in  FIG. 3 , the tip  54  is more rounded and is formed in the shape of a bullet. A bore  56  extends through the tip  54  in communication with the lumen  43  for receiving the tether  45 .  
         [0029]     As the lead  36  is advanced over the tether  45  through the during insertion, the tapered tip  54  does not cut through the myocardial tissue  32 , but rather dissects or dilates the tissue. The tapered tip  54  provides a streamlined leading edge to the lead  36 , reducing trauma to the myocardium  32 . According to one embodiment, the diameter a of the proximal end  54   a  is greater than a diameter of the lead  36 . Such a tip  54  gently dilates or expand the tract to facilitate advancement of the lead  36 . According to other embodiments, the tip  54  has any shape having rounded edges and a streamlined shape chosen to reduce trauma to the myocardium  32  during insertion.  
         [0030]     Prior to lead implantation, the tip  54  may be selected from a plurality of tips having differing shapes based on the physiology of the heart  12 . Where the epicardium  28  and or pericardium  33  are generally undisturbed and in relatively healthy condition, the more bullet shaped tip of the embodiment shown in  FIG. 3  is sufficient to facilitate advancement of the lead  36 . However, sometimes the epicardium  28  and/or pericardium  33  have been damaged, either by disease or previous trauma, resulting in the presence of tough adhesions or scar tissue. The more pointed cone shaped tip  54  of the embodiment shown in  FIG. 2  may be required to effectively traverse such adhesions or scar tissue. Prior to inserting the lead  36 , the surgeon may evaluate the implant site and select an appropriate tip  54 , i.e. pointed or blunt, as deemed necessary to pierce the epicardium  28  and or pericardium  33  and dilate the tract through the heart  12  to facilitate insertion of the lead  36 .  
         [0031]     According to one embodiment, as shown in  FIGS. 2 and 3 , the tapered tip  54  is configured to securely couple with the blunt distal tip  42  of the lead  36 . According to one embodiment, the diameter a of the proximal end  54   a  of the tip  54  is sized to receive the distal tip  42  of the lead  36 . According to other embodiments, the tip  54  and distal tip  42  of the lead  36  are provided with complementary threads for rotational coupling, or are provided with a complementary interlock or other structure for coupling.  
         [0032]      FIG. 4  shows another embodiment, in which the tapered tip  54  is positioned adjacent to the distal tip  42  of the pacing lead  36  without securely coupling to the lead  36 . The tapered tip  54  rides along the tether  45  in front of the lead  36  to facilitate the lead  36  in passing through the myocardium  32 . A tip  54  according to the present embodiment may be used in conjunction with any such commercially available myocardial lead. According to another embodiment, the tapered tip  54  is integrally formed at the distal end  42  of the lead  36 .  
         [0033]      FIG. 5  shows another embodiment in which the system is further provided with a lock  60  and lock housing  61  as is described in the above-identified application “Distal or Proximal Fixation of Over-the-Tether Myocardial Leads”. The tip bore  56  has a diameter c greater than the diameter of the tether  45  such that the tip  54  easily passes over the tether  45 , but smaller than a diameter of the lock  60  formed on the tether  45 . The tip  54  and lead  36  are easily threaded over the tether  45  and advanced along the tether  45 . When the tip  54  contacts the lock  60 , the tip  54  and lead  36  are prevented from advancing further along the tether  45 . The tapered tip  54  is used to prevent the lead  36  from advancing over the lock  60 , and to provide spacing between the lead  36  and the anchor mechanism  44 .  
         [0034]     According to another embodiment, the tip  54  is made from a water-soluble material, such that the tip  54  will dissolve upon placement within the myocardium  32 . The tip  54  may be made from any biocompatible, water-soluble material known in the art, such as a sugar. In one embodiment, the tip  54  is made from mannitol. In another embodiment, the tip  54  is made from polyethylene glycol (“PEG”). The molecular weight of the PEG can be selected to achieve a desired dissolution time of the tapered tip  54 . In yet another embodiment, additives known in the art are used to further control the dissolution time. According to another embodiment, the tip  54  is made of an ablatable material.  
         [0035]     A dissolvable tip  54  reduces the amount of foreign matter located in the heart  12  following dissolution. This may reduce irritation in the heart  12 , as well as the formation of scar tissue. Addition of the tip  54  does not increase the overall size of the lead  36  chronically implanted in the heart  12 . Following dissolution of the tip  54 , the lead  36  may be advanced over the lock  60  to mate the lock  60  with the lock housing  61 . In addition, the dissolved portion of the dissolving tip  54  provides a lubricating coating or film within the tract to further facilitate passage of the lead  36 .  
         [0036]      FIGS. 6A and 6B  show another embodiment of the lead  36 , in which a fixation mechanism  62  is provided at the distal tip  42  of the lead  36 . Such a fixation mechanism  62  facilitates fixation of the lead  36  to myocardial tissue  32 . The above-identified application “Myocardial Lead with Fixation Mechanism” describes various fixation mechanisms suitable for use with a lead  36  according to the present embodiment. The tapered tip  54  is dissolvable as previously described and is configured to mate with the fixation mechanism  62 . According to one embodiment, the fixation mechanism  62  is received in the tip bore  56 .  
         [0037]     Throughout insertion of the lead  36  into the heart  12 , the tapered tip  54  facilitates passage of the lead  36  through the tract and masks the fixation mechanism  62 , which may include sharp edges or points. Upon dissolution of the tip  54 , the fixation mechanism  62  is revealed and operable to retain the lead  36  in a stable position. According to one embodiment, the fixation mechanism  62  is retained in the tip bore  56  in a first collapsed or retracted configuration, as is shown in  FIG. 6A . Following dissolution of the tip  54 , the fixation mechanism  62  deploys to a second expanded configuration, as is shown in  FIG. 6B .  
         [0038]     According to another embodiment, the tip  54  contains a pharmaceutical additive to treat implant trauma. Such an additive may be provided to reduce myocardial irritation or inflammation. This pharmaceutical additive may administer a “bolus” therapeutic agent to treat the implant trauma. In one embodiment, the tip  54  is made of a dissolvable material as described above but which also includes a steroid (or other therapeutic drug) released as the tip  54  dissolves. According to another embodiment, the tip  54  is formed of a material provided with a coating that is drug eluting. The tip  54  may be chosen to have an appropriate amount of steroid (or other therapeutic drug) for a particular situation.  
         [0039]     In one embodiment, pharmaceutical additives as previously described are provided on other portions of the lead  36  in addition to or instead of the tip  54 . In one embodiment, the drug eluting feature is provided as one or more discrete steroid/polymeric rings or collars  64  positioned on the lead  36  to contact the myocardium  32  upon implantation and anchoring (See  FIG. 2 ). In another embodiment, the implanted portion of the lead  20  is coated with a drug (e.g., steroid) eluting coating, such as a paint stripe (not shown). In another embodiment, shown in  FIG. 7 , a polymeric lead body tubing  66  may be fashioned from a steroid-loaded polymer composite. In each of these embodiments, a therapeutic amount of steroid is included on the implanted portion of the lead  36 .  
         [0040]     Various controlled-release techniques known in the art may be incorporated into these embodiments to deliver the therapeutic drug in the right amount and with the right time distribution.  
         [0041]     Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. Accordingly, the scope of the present invention is intended to embrace all such alternative, modifications, and variations as fall within the scope of the claims, together with all equivalents thereof.