Patent Publication Number: US-2013231727-A1

Title: Lead with bioabsorbable metallic fixation structure

Description:
FIELD OF THE INVENTION 
     Aspects of the present invention relate to medical apparatus and methods. More specifically, the present invention relates to implantable medical leads and methods of manufacturing and implanting such leads. 
     BACKGROUND OF THE INVENTION 
     A recent study has analyzed the impact of left ventricular (“LV”) lead stimulation sites on patient outcomes. The study classified lead position around the perimeter of the LV short axis as anterior, posterior or lateral. With respect to the LV long axis view, the lead positioning was described as apical, mid, or basal. 
     It could be determined from the study that bi-ventricular (BiV) pacing from a basal lead position is more effective than apical pacing. The study also suggested that posterior lead positioning and lateral lead positioning are better than anterior lead positioning. Accordingly, for the best outcomes, leads should be implanted in the lateral and posterior basal regions. 
     The lateral and posterial basal locations are regions of last activation. Accordingly, pacing the lateral and posterial basal locations corrects delayed activation and promotes improves resynchronization. 
     There is a need in the art for implantable medical leads and methods of implantation that facilitate pacing the lateral and posterial basal locations. There is also a need in the art for methods of manufacturing such implantable medical leads. 
     BRIEF SUMMARY OF THE INVENTION 
     Disclosed herein is an implantable medical lead for coupling to an implantable pulse generator and targeted stimulation of the lateral and posterior basal left ventricular region of a patient heart. In one embodiment, the lead includes a lead connector end, a tubular body, at least one electrode and at least one fixation structure. The lead connector end is configured to couple to the implantable pulse generator. The tubular body extends distally from the lead connector end and includes a distal portion distally terminating in a distal end. The at least one electrode is located on the distal portion. The at least one fixation structure is located on the distal portion and includes a bioabsorbable metal. Depending on the embodiment, the bioabsorbable metal includes or is iron, an iron alloy with 35% manganese, or a magnesium alloy. The bioabsorbable metal is configured such that the at least one fixation structure will last long enough at an implantation site so as to secure the distal portion of the tubular body in place via fibrotic tissue. 
     In one embodiment, the at least one fixation structure is configured to self-bias into an expanded state. The at least one fixation structure may be a single cantilevered loop or multiple cantilevered loops. The cantilevered loop or loops may be formed of a wire formed of the bioabsorbable metal. The at least one fixation structure may be a single bridged loop or multiple bridged loops. The bridged loop or loops may be formed of a wire formed of the bioabsorbable metal. 
     In one embodiment, the at least one fixation structure may be a stent-like feature. The stent-like feature may be self-expanding or expandable via another mechanism, such as, for example a balloon catheter. 
     In one embodiment, the at least one fixation structure is located on generally an opposite side of the distal portion of the tubular body from the at least one electrode. 
     In one embodiment, the distal portion of the tubular body includes a distal section immediately proximal of the distal end and a proximal section extending towards the lead connector end from the distal section. The distal portion of the tubular body includes a curve in the tubular body between the distal section and the proximal section. The at least one fixation structure extends at least substantially along the distal section and the at least one electrode is located on the distal section. In such an embodiment, the fixation structure may extend at least substantially along the distal section on a portion of the tubular body that transitions into an outside of the curve and the electrodes may be located on the distal section on a portion of the tubular body that transitions into an inside of the curve. 
     While multiple embodiments are disclosed, still other embodiments of the present disclosure will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the disclosure. As will be realized, the invention is capable of modifications in various aspects, all without departing from the spirit and scope of the present disclosure. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic depiction of an electrotherapy system electrically coupled to a patient heart as shown in an anterior view, a distal portion of a LV lead being implanted in the CS. 
         FIGS. 2A and 2B  are, respectively, side and top plan views of the distal portion of a first embodiment of a lead tubular body in a free or non-restricted state, the distal portion having a generally straight distal section, a generally straight proximal section proximal of the distal section, and a bioabsorbable cantilevered fixation loop extending distally from a point on the lead tubular body generally between the distal and proximal sections. 
         FIG. 3  is a side view of the distal portion of a second embodiment of a lead tubular body in a free or non-restricted state, the distal portion having a generally curved distal section, a generally straight proximal section proximal of the distal section, and a bioabsorbable cantilevered fixation loop extending distally from a point on the lead tubular body generally between the distal and proximal sections. 
         FIGS. 4A and 4B  are, respectively, side and top plan views of the distal portion of a third embodiment of a lead tubular body in a free or non-restricted state, the distal portion having a generally straight distal section, a generally straight proximal section proximal of the distal section, and multiple bioabsorbable cantilevered fixation loops positioned on the lead tubular body between the lead tubular body distal end and a point generally between the distal and proximal sections, each cantilevered fixation loop having a single proximal point of contact with the lead tubular body. 
         FIG. 5  is a side view of the distal portion of a fourth embodiment of a lead tubular body in a free or non-restricted state, the distal portion having a generally curved distal section, a generally straight proximal section proximal of the distal section, and multiple bioabsorbable cantilevered fixation loops positioned on the lead tubular body between the lead tubular body distal end and a point generally between the distal and proximal sections, each cantilevered fixation loop having a single proximal point of contact with the lead tubular body. 
         FIGS. 6A and 6B  are, respectively, side and top plan views of the distal portion of a fifth embodiment of a lead tubular body in a free or non-restricted state, the distal portion having a generally straight distal section, a generally straight proximal section proximal of the distal section, and a bioabsorbable bridging fixation loop extending distally from a point on the lead tubular body generally between the distal and proximal sections to a point on the lead tubular body near or at a distal end of the lead tubular body. 
         FIG. 7  is a side views of the distal portion of a sixth embodiment of a lead tubular body in a free or non-restricted state, the distal portion having a generally curved distal section, a generally straight proximal section proximal of the distal section, and a bioabsorbable bridging fixation loop extending distally from a point on the lead tubular body generally between the distal and proximal sections to a point on the lead tubular body near or at a distal end of the lead tubular body. 
         FIGS. 8A and 8B  are, respectively, side and top plan views of the distal portion of a seventh embodiment of a lead tubular body in a free or non-restricted state, the distal portion having a generally straight distal section, a generally straight proximal section proximal of the distal section, and multiple bioabsorbable bridging fixation loops positioned on the lead tubular body between the lead tubular body distal end and a point generally between the distal and proximal sections, each bridging fixation loop having a proximal and distal point of contact with the lead tubular body. 
         FIG. 9  is a side view of the distal portion of a eighth embodiment of a lead tubular body in a free or non-restricted state, the distal portion having a generally curved distal section, a generally straight proximal section proximal of the distal section, and multiple bioabsorbable bridging fixation loops positioned on the lead tubular body between the lead tubular body distal end and a point generally between the distal and proximal sections, each bridging fixation loop having a proximal and distal point of contact with the lead tubular body. 
         FIGS. 10A and 10B  are, respectively, side and top plan views of the distal portion of a ninth embodiment of a lead tubular body in a free or non-restricted state, the distal portion having a generally straight distal section, a generally straight proximal section proximal of the distal section, and an expandable stent positioned on the lead tubular body between the lead tubular body distal end and a point generally between the distal and proximal sections. 
         FIG. 11  is a side view of the distal portion of a tenth embodiment of a lead tubular body in a free or non-restricted state, the distal portion having a generally curved distal section, a generally straight proximal section proximal of the distal section, and at least one expandable stent positioned on the lead tubular body between the lead tubular body distal end and a point generally between the distal and proximal sections. 
         FIG. 12  is a left lateral posterior view of the patient heart, the CS extending along the outer surface of the heart between the LV and LA patient left and generally anterior from the OS, anyone of the lead embodiments of  FIGS. 2A-11  having its distal portion implanted in the CS and LMV. 
         FIG. 13  is the same view and lead embodiment as  FIG. 12 , except the lead distal portion is implanted in the CS and PCV. 
         FIG. 14  is the same view and lead embodiment as  FIG. 12 , except the lead distal portion is implanted in the CS and GCV. 
     
    
    
     DETAILED DESCRIPTION 
     Implementations of the present disclosure involve implantable medical leads  5  and methods of implantation that facilitate the targeted stimulation of the lateral and posterior basal region of the heart. The lateral and posterior cardiac veins are good locations for the electrodes  110   a - d  in order to achieve such targeted stimulation of the lateral and posterior basal region of heart. 
     Fixation of these leads  5  is achieved by using a fixation structure  115  such as, for example, a flexible wire loop or loops or stent like structure to fix the lead distal portion  50  in the basal region of a coronary vein or one of its associated branches. The fixation structures  115  my be a self-biasing loop, loops, stents or other structures that can be compressed inside a delivery catheter or sheath and then allowed to self-bias into an expanded state when freed from the confines of the delivery catheter or sheath by being pushed out of the delivery catheter or sheath to stabilize the lead in a coronary vein in the basal region of the heart. Alternatively, the fixation structure  115  can be a non-self-biasing structure such as, for example, a stent like structure that is expanded inside the vessel with a balloon supported off of a balloon catheter. 
     The fixation structures  115  disclosed herein may be formed of a bioabsorbable metal. The use of such materials results in fixation structures  115  of sufficient strength to secure the lead distal end at the implantation site sufficiently long for fibrotic tissue to secure the lead distal end in the vessel before the bioabsorbable metal is fully absorbed into the body. Such bioabsorbable metals are unlikely to embolize, thrombos, or result in extensive inflammatory response. Further, the permanent fixation via fibrotic tissue and the eventual elimination of the metal fixation structure via bioabsorbtion are unlikely to result in occlusion of the vessel. 
     To begin a general, non-limiting discussion regarding some of the features and deployment characteristics common among the various lead and implantation embodiments disclosed herein, reference is made to  FIG. 1 , which is a diagrammatic depiction of an electrotherapy system  10  electrically coupled to a patient heart  15  as shown in an anterior view. As shown in  FIG. 1 , the system  10  includes an implantable pulse generator (e.g., pacemaker, implantable cardioverter defibrillator (“ICD”), or etc.)  20  and one or more (e.g., three) implantable medical lead  5 ,  6 ,  7  electrically coupling the patient heart  15  to the pulse generator  10 . While the following discussion will focus on the configuration and implantation of the left ventricular (“LV”) lead  5  extending into the coronary sinus (“CS”)  21  via the coronary sinus ostium (“OS”)  22 , it should be remembered that the system  10  may employ only the LV lead  5  or the LV lead  5  in conjunction with other leads, such as, for example, a right ventricular (“RV”) lead  6  and/or right atrial (“RA”) lead  7 . The RV and RA leads  6 ,  7  may employ pacing electrodes  25 , sensing electrodes  30  and shock coils  35  as known in the art to respectively provide electrical stimulation to the right ventricle  40  and right atrium  45  of the heart  15 . 
     Each of the leads  5 ,  7 ,  9  is electrically coupled to the pulse generator  20  via a lead connector end  46  at the lead proximal end  47 . Electrical conductors (e.g., wires, cables, helically coiled filars, etc.) extend through each lead body from electrical contacts on the lead connector end to the various electrodes and shock coil near the distal region of the lead to electrically couple the various electrodes and shock coil to the pulse generator. 
     As can be understood from  FIG. 1 , which shows an anterior view of the patient heart  15 , the CS  21  extends generally patient right to patient left from the OS  22  and, further, posterior to anterior until transitioning into the great cardiac vein  47 , which then extends in a generally inferior direction along the anterior region of the left ventricle (“LV”)  48 . In extending generally posterior to anterior from the OS  22  until transitioning into the great cardiac vein  47 , the CS  22  is inferior to the left atrium (“LA”)  49  and superior to the LV  48 . 
     As indicated in  FIG. 1 , in most embodiments of the LV lead  5  disclosed herein, the distal portion  50  of the LV lead  5  does not extend into the great cardiac vein  47 , but is instead implanted in the CS  21  or vein branches extending off of the CS  21 , as described in detail below. As explained in the discussion below, the distal portion  50  of each embodiment of the LV lead  5  disclosed herein is configured to facilitate the distal portion  50  being implanted in the CS  21  and, more particularly, in the lateral and posterior basal region of the heart. In other words, most of the embodiments of the LV lead  5  disclosed herein are designed specifically for the stimulation of the basal region of the heart. 
     For a discussion of the configuration of the distal portion  50  of a tubular body  55  of a first embodiment of the LV lead  5 , reference is made to  FIGS. 2A and 2B , which are, respectively, side and top plan views of the distal portion  50  of the lead tubular body  55  in a free or non-restricted state. For purposes of discussion, when the distal portion  50  of the tubular body  55  of the LV lead  5  is said to be in a free or non-restricted state, the distal portion  50  exists in a configuration that the distal portion  50  naturally biases to absent the distal portion  50  being acted upon by an outside force such as, for example, a stylet being extended through the distal portion  50 , a sheath or catheter being extended over the distal portion  50 , or the distal portion  50  being confined within a vascular structure such as, for example, the CS  21 . 
     As indicated in  FIGS. 2A and 2B , the distal portion  50  of the tubular body  55  of the first embodiment of the LV lead  5  includes an extreme distal section  100  and a proximal section  105  that proximally extends from the extreme distal section  100  towards the proximal end  47  of the LV lead  5  that connects to the pulse generator  20  via the lead connector end  46 , as can be understood from  FIG. 1 . The distal section  100  distally terminates as the distal end  107  of the lead  5 . The tubular body  55  of the distal section  100  and proximal section  105  are generally linear or straight when in a free or non-restricted state. The tubular body  55  of the distal section  100  and proximal section  105  has a size of between approximately seven French and approximately eight French and is formed of silicone rubber, polyurethane, or silicone rubber polyurethane copolymer (“SPC”). 
     As shown in  FIG. 2A , multiple electrodes  110   a - d  extend distal-proximal in a spaced-apart manner along a bottom surface  112  of the distal section  100  of the tubular body  55  of the first embodiment of the LV lead  5 . These electrodes  110   a - d  may be employed for pacing, sensing and/or defibrillation purposes. Depending on the embodiment, there may be one, two, three, four or more electrodes  110   a - d  so located on the bottom surface  112  of the distal section  100  of the lead tubular body. The electrodes  110   a - d  may extend between approximately two cm and four cm distal to proximal along the lead tubular body. In embodiments of the LV lead  5  where the electrotherapy target for the LV lead  5  is the base of the heart, there is no need for an electrode space that greatly exceeds two cm to four cm. Electrical conductors (e.g., cables, wires, helical coiled filars, etc.) that extend through the tubular body  55  of the LV lead  5  electrically couple the electrodes  100   a - d  to electrical contacts of the lead connector end  46  of the proximal end  47  of the lead  5  that is received in the pulse generator  20  (see  FIG. 1 ). 
     As indicated in  FIG. 2A , a biasing fixation structure  115  extends from a top surface  117  of the distal section  100  of the lead tubular body. Thus, the biasing fixation structure  115  is generally on an opposite side of the lead tubular body  55  from the electrodes  110   a - d.  The biasing fixation structure  115  is configured such that at least a portion  118  of the fixation structure  115  biases away from the outer surface of the lead tubular body when the fixation structure  115  in a free or non-restricted state. In other words, at least a portion  118  of the fixation structure  115  naturally assumes or biases into an arrangement wherein the portion  118  is spaced-apart from the outer surface of the lead tubular body  55  absent the fixation structure  115  being acted upon by an outside force such as, for example, a sheath or catheter being extended over the fixation structure  115  and lead tubular body distal portion  50 , or the fixation structure  115  and lead tubular body distal portion  50  being confined within a vascular structure such as, for example, the CS  21 . 
     In  FIG. 2A , the fixation structure  115  is represented via two different types of lines, namely, a solid line at arrow A and a dashed line at arrow B. The solid line depiction of the fixation structure  115  at arrow A represents the fixation structure  115  when fully biased into its free or non-restricted state. The dashed line depiction of the fixation structure  115  at arrow B represents the fixation structure  115  when confined via, for example, a vascular structure like the CS  21 , and thereby prevented from achieving its fully biased state as indicated at arrow A. When fully deployed into its free or non-restricted state as indicated at arrow A, the lead will have a width or diameter D that extends from the bottom surface  112  of the lead tubular body to a point on the fixation structure  115  that is most extremely spaced-apart from the top surface of the lead tubular body. In one embodiment, such a diameter D will be between approximately 9 mm and approximately 18 mm. 
     As can be understood from  FIG. 2A , when the distal section  100  of the lead tubular body distal portion  50  is located within the confines of a vascular structure, such as, for example the CS  21  or one of its branches as discussed below, the walls of the vascular structure confine the fixation structure such that the fixation structure  115  is not able to fully deploy to the state depicted at arrow A. As a result, the fixation structure  115  in attempting to bias into its fully deployed state as indicated by arrow A exerts a force against the wall of the vascular structure, thereby forcing the electrodes  110   a - d  into excellent electrical contact with cardiac tissue and fixing the distal section  100  of the lead tubular body distal portion  50  in place within the vascular structure. 
     As illustrated in  FIGS. 2A and 2B , the fixation structure  115  has a single point of contact  120  and a free end  125 , thereby forming a cantilevered arrangement with the lead tubular body. As shown in  FIGS. 2A and 2B , the free end  125  may be distal of contact point  120 . In other embodiments, the arrangement may be reversed such that the free end  125  is proximal the contact point  120 . 
     As can be understood from  FIG. 3 , which is a side view of the distal portion  50  of a lead tubular body  55  in a free or non-restricted state for a second embodiment of the LV lead  5 , the lead tubular body  55  may be configured to have a bend or curve as indicated at arrow C. In other words, lead tubular body  55  naturally assumes or biases into a curve at arrow C absent the lead tubular body  55  being acted upon by an outside force such as, for example, a stylet extending through the lead tubular body, a sheath or catheter being extended over the lead tubular body  55 , or the lead tubular body  55  being confined within a vascular structure such as, for example, the CS  21 . Such a curve as indicated by arrow C may be located at or near the junction between the distal section  100  and the proximal section  105  of the lead tubular body distal portion  50  and extend over the most distal part of the proximal section  105  and the most proximal part of the distal section  100 . As can be understood from a comparison of  FIGS. 2A and 3 , all other aspect of the lead distal portion  50  (e.g., the electrodes, fixation structure, etc.) disclosed therein are substantially the same. 
     As can be understood from  FIG. 3 , the fixation structure  115  extends at least substantially along the distal section  100  on a portion of the tubular body  55  that transitions into an outside of the curve indicated by arrow C and the electrodes  115   a - d  are located on the distal section  100  on a portion of the tubular body  55  that transitions into an inside of the curve indicated by arrow C. 
     As shown in  FIGS. 2A and 2B , the contact point  120  is at or near the transition between the distal section  100  and the proximal section  105 . Specifically, the contact point  120  may be just proximal of the most proximal electrode  110   d.  In addition to being a cantilevered arrangement, the fixation structure  115  may be in the form of a wire loop. The wire forming the loop may have a diameter of between approximately 9 mm and approximately 18 mm and be formed of a bioabsorbable metal such as, for example, iron, iron alloy with 35% manganese, or magnesium alloys. 
     Although such metal materials are bioabsorbable and will disappear over time subsequent to implantation, fixation structures  115  formed of such bioabsorbable metals will provide adequate biasing force for a period sufficient for the distal section  100  of the lead body distal portion  50  to become secured in place in the vascular structure via tissue growth about the lead distal section  100 . Further, such bioabsorbable metals are unlikely to result in embolization, thrombosis, or extensive inflammatory response. Iron alloy with 35% manganese has similar mechanical properties to 316 L stainless steel and has higher in vitro corrosion rates than pure iron. Magnesium alloys do no embolize and are electronegatively charged and, as a result, have minimal thrombogenicity. 
     Employing bioabsorbable metals for the fixation structures  115  of the leads  5  disclosed herein is advantageous in that the when such leads are implanted in the coronary vein or associated branches, after only a few months the lead is covered with a thin sheath of fibrotic tissue and the coronary vein or associated branches are unlikely to be occluded with blood flowing parallel to the fibrotic tissue sheath covered lead in the lumen of the blood vessel. Once the fibrotic tissue sheath is formed, the lead will be stabilized inside the vein and the fixation structure  115 , which is formed of bioabsorbable material, will not be needed as disappears due to be absorbed into the body over time. 
     As can be understood from  FIGS. 4A and 4B , which are, respectively, side and top plan views of the distal portion  50  of a lead tubular body  55  in a free or non-restricted state for a third embodiment of the LV lead  5 , the lead tubular body  55  may have multiple cantilevered fixation structures  115   a - c  located along the distal section  100  of the lead tubular body distal portion  50  instead of a single cantilevered fixation structure  115  as discussed above with respect to  FIGS. 2A and 2B . As can be understood from a comparison of the third embodiment of  FIGS. 4A and 4B  to the first embodiment of  FIGS. 2A and 2B , the electrodes  110   a - d  of the third embodiment are the same in number and arrangement to the electrodes  110   a - d  of the first embodiment, and the location of the fixation fixtures  115   a - c  is also on the opposite side of the lead tubular body  55  from the electrodes  110   a - d.  There may be two, three, four or more cantilevered fixation structures  115   a - c  for the third embodiment depicted in  FIGS. 4A and 4B . 
     In  FIG. 4A , the fixation structures  115   a  are represented via two different types of lines, namely, solid lines at arrow A and dashed lines at arrow B. The solid line depiction of the fixation structures  115   a - c  at arrow A represents the fixation structures  115   a - c  when fully biased into the free or non-restricted state. The dashed line depiction of the fixation structures  115   a - c  at arrow B represents the fixation structures  115   a - c  when confined via, for example, a vascular structure like the CS  21 , and thereby prevented from achieving the fully biased state as indicated at arrow A. When fully deployed into the free or non-restricted state as indicated at arrow A, the lead will have a width or diameter D′ that extends from the bottom surface  112  of the lead tubular body to a point  118  on each fixation structure  115   a - c  that is most extremely spaced-apart from the top surface of the lead tubular body. In one embodiment, such a diameter D′ will be between approximately 5 mm and approximately 18 mm. 
     As can be understood from  FIG. 4A , when the distal section  100  of the lead tubular body distal portion  50  is located within the confines of a vascular structure, such as, for example the CS  21  or one of its branches as discussed below, the walls of the vascular structure confine the fixation structures such that the fixation structures  115   a - c  are not able to fully deploy to the state depicted at arrow A. As a result, the fixation structures  115   a - c  in attempting to bias into the fully deployed state as indicated by arrow A exert a force against the wall of the vascular structure, thereby forcing the electrodes  110   a - d  into excellent electrical contact with cardiac tissue and fixing the distal section  100  of the lead tubular body distal portion  50  in place within the vascular structure. 
     As illustrated in  FIGS. 4A and 4B , each fixation structure  115   a - c  has a single point of contact  120   a - c  and a free end  125   a - c,  thereby forming a cantilevered arrangement with the lead tubular body. As shown in  FIGS. 4A and 4B , each free end  125  may be distal of the respective contact point  120   a - c.  In other embodiments, the arrangement may be reversed such that each free end  125   a - c  is proximal the respective contact point  120   a - c.    
     As can be understood from  FIG. 5 , which is a side view of the distal portion  50  of a lead tubular body  55  in a free or non-restricted state for a fourth embodiment of the LV lead  5 , the lead tubular body  55  may be configured to have a bend or curve as indicated at arrow C. In other words, lead tubular body  55  naturally assumes or biases into a curve at arrow C absent the lead tubular body  55  being acted upon by an outside force such as, for example, a stylet extending through the lead tubular body, a sheath or catheter being extended over the lead tubular body  55 , or the lead tubular body  55  being confined within a vascular structure such as, for example, the CS  21 . Such a curve as indicated by arrow C may be located at or near the junction between the distal section  100  and the proximal section  105  of the lead tubular body distal portion  50  and extend over the most distal part of the proximal section  105  and the most proximal part of the distal section  100 . As can be understood from a comparison of  FIGS. 4A and 5 , all other aspect of the lead distal portion  50  (e.g., the electrodes, fixation structures, etc.) disclosed therein are substantially the same. 
     As shown in  FIGS. 4A and 4B , the most proximal fixation structure  115   c  has a contact point  120   c  at or near the transition between the distal section  100  and the proximal section  105 . Specifically, the contact point  120   c  of the most proximal fixation structure  115   c  may be just proximal of the most proximal electrode  110   d.  The rest of the fixation structures  115   a - b  may have respective contact points  120   a - b  that are just distal of the free end  125   b - c  of the respectively immediately proximal fixation structure  115   b - c.  In addition to being a cantilevered arrangement, each fixation structure  115   a - c  may be in the form of a wire loop. The wire forming the loop may have a diameter of between approximately 6 mm and approximately 18 mm and be formed of a bioabsorbable metal such as, for example, iron, iron alloy with 35% manganese, or magnesium alloys. 
     As can be understood from  FIGS. 6A and 6B , which are, respectively, side and top plan views of the distal portion  50  of a lead tubular body  55  in a free or non-restricted state for a fifth embodiment of the LV lead  5 , the lead tubular body  55  may have a single bridging fixation structure  115  located along the distal section  100  of the lead tubular body distal portion  50  instead of a single cantilevered fixation structure  115  as discussed above with respect to  FIGS. 2A and 2B . As can be understood from a comparison of the fifth embodiment of  FIGS. 6A and 6B  to the first embodiment of  FIGS. 2A and 2B , the electrodes  110   a - d  of the fifth embodiment are the same in number and arrangement to the electrodes  110   a - d  of the first embodiment, and the location of the fixation fixture  115  is also on the opposite side of the lead tubular body  55  from the electrodes  110   a - d.    
     In  FIG. 6A , the fixation structure  115  is represented via two different types of lines, namely, a solid line at arrow A and a dashed line at arrow B. The solid line depiction of the fixation structure  115  at arrow A represents the fixation structure  115  when fully biased into the free or non-restricted state. The dashed line depiction of the fixation structure  115  at arrow B represents the fixation structure  115  when confined via, for example, a vascular structure like the CS  21 , and thereby prevented from achieving the fully biased state as indicated at arrow A. When fully deployed into the free or non-restricted state as indicated at arrow A, the lead will have a width or diameter D″ that extends from the bottom surface  112  of the lead tubular body to a point  118  on the fixation structure  115  that is most extremely spaced-apart from the top surface of the lead tubular body. In one embodiment, such a diameter D″ will be between approximately 6 mm and approximately 18 mm. 
     As can be understood from  FIG. 6A , when the distal section  100  of the lead tubular body distal portion  50  is located within the confines of a vascular structure, such as, for example the CS  21  or one of its branches as discussed below, the walls of the vascular structure confine the fixation structure such that the fixation structure  115  is not able to fully deploy to the state depicted at arrow A. As a result, the fixation structure  115  in attempting to bias into the fully deployed state as indicated by arrow A exerts a force against the wall of the vascular structure, thereby forcing the electrodes  110   a - d  into excellent electrical contact with cardiac tissue and fixing the distal section  100  of the lead tubular body distal portion  50  in place within the vascular structure. 
     Unlike the cantilevered fixation structure  115  of the embodiment of  FIGS. 2A and 2B , the bridging fixation structure  115  of the embodiment of  FIGS. 6A and 6B  has a fixation structure  115  with a pair of point contacts  120  and  121  as opposed to a single point contact  120  and a free end  125 . Since the bridging fixation structure  115  of embodiment of  FIGS. 6A and 6B  has a proximal point contact  120  and a distal point contact  121  and a free region between these contacts  120  and  121 , the result is a fixation structure  115  that is supported off of the lead tubular body  55  at the extreme proximal and distal ends of the fixation structure  115 , leaving the extent of the fixation structure  115  to form a bridging type arrangement with the lead tubular body  55 . 
     As can be understood from  FIG. 7 , which is a side view of the distal portion  50  of a lead tubular body  55  in a free or non-restricted state for a sixth embodiment of the LV lead  5 , the lead tubular body  55  may be configured to have a bend or curve as indicated at arrow C. In other words, lead tubular body  55  naturally assumes or biases into a curve at arrow C absent the lead tubular body  55  being acted upon by an outside force such as, for example, a stylet extending through the lead tubular body, a sheath or catheter being extended over the lead tubular body  55 , or the lead tubular body  55  being confined within a vascular structure such as, for example, the CS  21 . Such a curve as indicated by arrow C may be located at or near the junction between the distal section  100  and the proximal section  105  of the lead tubular body distal portion  50  and extend over the most distal part of the proximal section  105  and the most proximal part of the distal section  100 . As can be understood from a comparison of  FIGS. 6A and 7 , all other aspect of the lead distal portion  50  (e.g., the electrodes, fixation structure, etc.) disclosed therein are substantially the same. 
     As shown in  FIGS. 6A and 6B , the bridging fixation structure  115  has a proximal contact point  120  at or near the transition between the distal section  100  and the proximal section  105 . Specifically, the proximal contact point  120  of the fixation structure  115  may be just proximal of the most proximal electrode  110   d.  The bridging fixation structure  115  also has a distal contact point  121  at or near the extreme distal end  107  of the LV lead tubular body  55 . Specifically, the distal contact point  121  of the fixation structure  115  may be just distal of the most distal electrode  110   a.  In addition to being a bridging arrangement, the fixation structure  115  may be in the form of a wire loop. The wire forming the loop may have a diameter of between approximately 6 mm and approximately 19 mm and be formed of a bioabsorbable metal such as, for example, iron, iron alloy with 35% manganese, or magnesium alloys. 
     As can be understood from  FIGS. 8A and 8B , which are, respectively, side and top plan views of the distal portion  50  of a lead tubular body  55  in a free or non-restricted state for a seventh embodiment of the LV lead  5 , the lead tubular body  55  may have multiple bridging fixation structures  115   a - c  located along the distal section  100  of the lead tubular body distal portion  50  instead of a single bridging fixation structure  115  as discussed above with respect to  FIGS. 6A  and  6 B. As can be understood from a comparison of the seventh embodiment of  FIGS. 6A and 6B  to the first embodiment of  FIGS. 2A and 2B , the electrodes  110   a - d  of the seventh embodiment are the same in number and arrangement to the electrodes  110   a - d  of the first embodiment, and the location of the fixation fixtures  115   a - c  is also on the opposite side of the lead tubular body  55  from the electrodes  110   a - d.    
     In  FIG. 8A , the fixation structures  115   a - c  are represented via two different types of lines, namely, solid lines at arrow A and dashed lines at arrow B. The solid line depiction of the fixation structures  115   a - c  at arrow A represents the fixation structures  115   a - c  when fully biased into the free or non-restricted state. The dashed line depiction of the fixation structures  115   a - c  at arrow B represents the fixation structures  115   a - c  when confined via, for example, a vascular structure like the CS  21 , and thereby prevented from achieving the fully biased state as indicated at arrow A. When fully deployed into the free or non-restricted state as indicated at arrow A, the lead will have a width or diameter D′″ that extends from the bottom surface  112  of the lead tubular body to a point  118  on each fixation structure  115   a - c  that is most extremely spaced-apart from the top surface of the lead tubular body. In one embodiment, such a diameter D′″ will be between approximately 7 mm and approximately 19 mm. 
     As can be understood from  FIG. 8A , when the distal section  100  of the lead tubular body distal portion  50  is located within the confines of a vascular structure, such as, for example the CS  21  or one of its branches as discussed below, the walls of the vascular structure confine the fixation structures such that the fixation structures  115   a - c  are not able to fully deploy to the state depicted at arrow A. As a result, the fixation structures  115   a - c  in attempting to bias into the fully deployed state as indicated by arrow A exert a force against the wall of the vascular structure, thereby forcing the electrodes  110   a - d  into excellent electrical contact with cardiac tissue and fixing the distal section  100  of the lead tubular body distal portion  50  in place within the vascular structure. 
     Unlike the multiple cantilevered fixation structures  115  of the embodiment of  FIGS. 4A and 4B , each bridging fixation structure  115   a - c  of the embodiment of  FIGS. 8A and 8B  has a fixation structure  115   a - c  with a pair of point contacts  120   a - c  and  121   a - c  as opposed to a single point contact  120   a - c  and a free end  125   a - c.  Since each bridging fixation fixture  115   a - c  of the embodiment of  FIGS. 8A and 8B  has a proximal point contact  120   a - c  and a distal point contact  121   a - c  and a free region between these contacts  120  and  121 , the result is each bridging fixation structure  115   a - c  is supported off of the lead tubular body  55  at the extreme proximal and distal ends of the fixation structure  115   a - c,  leaving the extent of the fixation structure  115   a - c  to form a bridging type arrangement with the lead tubular body  55 . 
     As can be understood from  FIG. 9 , which is a side view of the distal portion  50  of a lead tubular body  55  in a free or non-restricted state for an eighth embodiment of the LV lead  5 , the lead tubular body  55  may be configured to have a bend or curve as indicated at arrow C. In other words, the lead tubular body  55  naturally assumes or biases into a curve at arrow C absent the lead tubular body  55  being acted upon by an outside force such as, for example, a stylet extending through the lead tubular body, a sheath or catheter being extended over the lead tubular body  55 , or the lead tubular body  55  being confined within a vascular structure such as, for example, the CS  21 . Such a curve as indicated by arrow C may be located at or near the junction between the distal section  100  and the proximal section  105  of the lead tubular body distal portion  50  and extend over the most distal part of the proximal section  105  and the most proximal part of the distal section  100 . As can be understood from a comparison of  FIGS. 8A and 9 , all other aspect of the lead distal portion  50  (e.g., the electrodes, fixation structure, etc.) disclosed therein are substantially the same. 
     As shown in  FIGS. 8A and 8B , the most proximal fixation structure  115   c  has a proximal contact point  120   c  at or near the transition between the distal section  100  and the proximal section  105 . Specifically, the proximal contact point  120   c  of the most proximal fixation structure  115   c  may be just proximal of the most proximal electrode  110   d.  The most proximal fixation structure  115   c  also has a distal contact point  121   c  at or near a proximal contact point  120   b  of the middle fixation structure  115   b.  The middle fixation structure  115   b  also has a distal contact point  121   b  at or near a proximal contact point  120   a  of the most distal fixation structure  115   a.  The most distal fixation structure  115   a  also has a distal contact point  121   a  at or near the most distal end  107  of the LV lead tubular body  55 . In addition to being a bridging arrangement, each fixation structure  115   a - c  may be in the form of a wire loop. The wire forming the loop may have a diameter of between approximately 6 mm and approximately 18 mm and be formed of a bioabsorbable metal such as, for example, iron, iron alloy with 35% manganese, or magnesium alloys. 
     As can be understood from  FIGS. 10A and 10B , which are, respectively, side and top plan views of the distal portion  50  of a lead tubular body  55  in a free or non-restricted state for a ninth embodiment of the LV lead  5 , the lead tubular body  55  may have a stent-like fixation structures  115  located along the distal section  100  of the lead tubular body distal portion  50 . As can be understood from a comparison of the ninth embodiment of  FIGS. 10A and 10B  to the first embodiment of  FIGS. 2A and 2B , the electrodes  110   a - d  of the ninth embodiment are the same in number and arrangement to the electrodes  110   a - d  of the first embodiment, and the location of the stent-like fixation fixture  115  is also on the opposite side of the lead tubular body  55  from the electrodes  110   a - d.    
     In  FIG. 10A , the stent-like fixation structure  115  is represented via two different types of lines, namely, solid lines at arrow A and dashed lines at arrow B. The solid line depiction of the stent-like fixation structure  115  at arrow A represents the stent-like fixation structure  115  when fully biased into the free or non-restricted state. The dashed line depiction of the stent-like fixation structure  115  at arrow B represents the stent-like fixation structure  115  when confined via, for example, a vascular structure like the CS  21 , and thereby prevented from achieving the fully biased state as indicated at arrow A. When fully deployed into the free or non-restricted state as indicated at arrow A, the lead will have a width or diameter D″″ that extends from the bottom surface  112  of the lead tubular body to a point  118  on the sent-like fixation structure  115  that is most extremely spaced-apart from the top surface of the lead tubular body. In one embodiment, such a diameter D″″ will be between approximately 5 mm and approximately 18 mm. 
     As can be understood from  FIG. 10A , when the distal section  100  of the lead tubular body distal portion  50  is located within the confines of a vascular structure, such as, for example the CS  21  or one of its branches as discussed below, the walls of the vascular structure confine the stent-like fixation structure such that the stent-like fixation structure  115  is not able to fully deploy to the state depicted at arrow A. As a result, the stent-like fixation structure  115  in attempting to bias into the fully deployed state as indicated by arrow A exerts a force against the wall of the vascular structure, thereby forcing the electrodes  110   a - d  into excellent electrical contact with cardiac tissue and fixing the distal section  100  of the lead tubular body distal portion  50  in place within the vascular structure. 
     In one embodiment, the stent-like fixation structure  115  is coupled to the distal section  100  of the distal portion  50  of the lead tubular body  55  at two or more locations along the stent-like fixation structure. In one embodiment, the stent-like fixation structure  115  has a generally cylindrical configuration. As can be understood from a comparison between the solid lines and the dashed lines respectively illustrating the stent-like fixation structure  115  in expanded and compressed states in  FIGS. 10A and 10B , the stent-like fixation structure simply increases in diameter when transitioning from the compressed state to the expanded state. In some embodiments, the stent-like fixation structure  115  of  FIGS. 10A-10B  is generally self-biasing such that the stent-like structure  115  will bias on its own into the expanded state once freed from the confines a restricting structure (e.g., stylet, catheter, sheath, vessel wall, etc.). 
     In other embodiments, the stent-like fixation structure  115  of  FIGS. 10A-10B  is expanded by application of an expanding force provided via a separate device such as, for example, the application of an expanding balloon on a balloon catheter used to deliver the lead distal end  107  to the implantation site. Once the stent-like fixation structure  115  is expanded via the balloon, the stent-like balloon structure maintains on its own the expanded diameter, and the balloon and supporting catheter can be withdrawn from the permanently expanded stent-like fixation structure  115 . 
     Regardless of whether the stent-like fixation structure  115  is self-expanding or balloon-expanded, in some embodiments, the stent-like fixation structure  115  is formed of a bioabsorbable metal such as, for example, iron, iron alloy with 35% manganese, or magnesium alloys. 
     As can be understood from  FIG. 11 , which is a side view of the distal portion  50  of a lead tubular body  55  in a free or non-restricted state for an tenth embodiment of the LV lead  5 , the lead tubular body  55  may be configured to have a bend or curve as indicated at arrow C. In other words, the lead tubular body  55  naturally assumes or biases into a curve at arrow C absent the lead tubular body  55  being acted upon by an outside force such as, for example, a stylet extending through the lead tubular body, a sheath or catheter being extended over the lead tubular body  55 , or the lead tubular body  55  being confined within a vascular structure such as, for example, the CS  21 . Such a curve as indicated by arrow C may be located at or near the junction between the distal section  100  and the proximal section  105  of the lead tubular body distal portion  50  and extend over the most distal part of the proximal section  105  and the most proximal part of the distal section  100 . As can be understood from a comparison of  FIGS. 10A and 11 , all other aspect of the lead distal portion  50  (e.g., the electrodes, fixation structure(s), etc.) disclosed therein are substantially the same. 
     As shown in  FIGS. 12-14 , which are each left lateral posterior views of the patient heart  15 , the CS  21  extends along the outer surface of the heart  15  between the LV  48  and LA  49  patient left and generally anterior from the OS  22 . A left marginal cardiac vein (“LMV”)  150 , a posterior cardiac vein (“PCV”)  155  and a middle cardiac vein (“MCV”)  160  extend generally inferior off of the CS  21 . A great cardiac vein (“GCV”)  165  can be seen to extend generally anterior from the CS  21 , and a vein of Marshall (“VM”)  170  can be seen to extend generally anterior from the CS  21  and superior the GCV  165 . A small cardiac vein (“SCV”)  175  can be seen to extend patient right and generally posterior off of the CS  21 . Depending on the individual, the mid-coronary sinus, which extends from the MCV  160  to the PCV  155 , may have a diameter between approximately eight millimeters and approximately ten millimeters. Depending on the individual, the distal-coronary sinus, which extends from the PCV  155  to the GCV  165 , may have a diameter between approximately five millimeters and approximately seven millimeters. 
     As can be understood from  FIGS. 12-14 , in various embodiments, the LV lead  5  can be delivered into the CS  21  and the LMV  150 , the PCV  155  or the GCV  165  via one or more delivery tools (e.g., stylets, guidewires, sheaths, catheters, etc.). When the delivery tools are removed from the distal portion  50  (see  FIGS. 2A-11 ), each fixation structure  115  ( 115   a - c ) of the distal section  100  of the distal portion  50  of the LV lead  5  is free to bias against the inner wall surface of the LMV  150 , PCV  155  or GCV  165 , as the case may be. As a result, each fixation structure  115  (or combination of fixation structures  115   a - c ) exerts a force F of between approximately 8,000 dynes to approximately 36,000 dynes for each centimeter the fixation structure  115  (or combination of fixation structures  115   a - c ) is compressed by the inner wall surface of the vessel (i.e., LMV  150 , PCV  155  or GCV  165 ) from the free or non-restricted state distance D, D′, D″, D′″ or D″″ as the case may be with respect to the fixation structure  115  (or combination of fixation structures  115   a - c ) being any one of the embodiments discussed above with respect to  FIGS. 2A-11 . The distal section  100  extends into the LMV  150 , PCV  155  or GCV  165 , as the case may be, in a generally linear arrangement with the electrodes  110   a - d  oriented so as to generally face the cardiac tissue. 
     While the bioabsorbable fixation structures  115  ( 115   a - c ) will eventually absorb into the patient so as to disappear from the above-discussed implantation sites in the LMV  150 , PCV  155  and GCV  165 , the bioabsorbable fixation structures will last long enough at the implantation sites so as to secure the distal section  100  of the LV lead tubular body  55  in place via fibrotic tissue that will incase the lead distal section  100 . 
     The foregoing merely illustrates the principles of the invention. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous systems, arrangements and methods which, although not explicitly shown or described herein, embody the principles of the invention and are thus within the spirit and scope of the present invention. From the above description and drawings, it will be understood by those of ordinary skill in the art that the particular embodiments shown and described are for purposes of illustrations only and are not intended to limit the scope of the present invention. References to details of particular embodiments are not intended to limit the scope of the invention.