Patent Publication Number: US-2022226636-A1

Title: Lead construction including alignable marker elements

Description:
This application claims the benefit of U.S. Provisional Patent Application 63/139,661 entitled “Lead Construction Including Alignable Marker Elements” and filed on Jan. 20, 2021, and U.S. Provisional Patent Application 63/139,662 entitled “Lead Construction” and filed on Jan. 20, 2021, each of which is incorporated herein by reference in its entirety. 
    
    
     This disclosure generally relates to medical devices and, in particular, additive manufacturing or 3D printing of medical devices, such as catheters and implantable stimulation leads, including alignable marker elements. 
     Medical catheters and leads are commonly used to access vascular and other locations within a body and to perform various functions at those locations, for example, delivery catheters may be used to deliver medical devices, such as implantable medical leads. A number of such medical devices are designed to be navigated through tortuous paths in a human body, such as through a patient&#39;s vasculature. Medical catheters and leads may be designed to be sufficiently flexible to move through turns, or curves, in the vasculature yet sufficiently stiff, or resilient, to be pushed through the vasculature. In many cases, such as those involving cardiovascular vessels, the route to the treatment or deployment site may be tortuous and may present conflicting design considerations that may require compromises between dimensions, flexibilities, material selection, operational controls, and the like. These contrasting properties can present challenges in designing and manufacturing catheters. Existing manufacturing processes, such as conventional extrusion, may also limit options in designing and manufacturing catheters. 
     Alignment of features of a catheter or delivery system in the body can be critical when deploying treatment to specific locations within the anatomy. Three-dimensional spatial orientation when navigating, delivering, and/or implanting an implantable apparatus (e.g., lead, catheter, or other implantable device) can be difficult while looking at imaging. For example, it is known that some implanters may believe that the implantable device (e.g., lead) they are implanting is located proximate the septum of the heart when, in reality, it is located proximate the free wall of the heart. 
     Cardiac resynchronization therapy (CRT) is an effective treatment for heart failure patients. CRT procedure involves simultaneous or different time pacing of the right ventricle (RV) and the left ventricle (LV). Implantation of the LV pacing lead is one of the determinants of CRT response. To obtain effective resynchronization, the final position of the LV pacing lead may target the latest activated areas of the left ventricle by placing the lead in the coronary sinus. However, positioning the LV lead may include several challenging technical issues and depends on the highly variable anatomy of the coronary vessels. Unfortunately, some patients are unable to receive CRT due to their venous anatomy being too small or difficult for the implanter to access with a lead (e.g., a lead may not be able to be navigated through the venous anatomy). 
     SUMMARY 
     The techniques of the present disclosure generally relate to additive manufacturing of medical devices, such as catheters and leads, that allows for further customization of the medical devices by providing an easier way to include components internal to the medical device. For example, the systems and techniques described herein may provide designing and printing an initial layer with internal spaces for components and then printing a finishing layer over, or on top of, the initial layer and components. These systems and techniques may allow for manufacturing more complex medical devices without increasing the complexity of manufacturing. Specifically, in one embodiment, the catheter may include internal grooves within which multiple lumen pull wires may be disposed. In another embodiment, the catheter may define an empty space for fluid travel during balloon inflation and may, e.g., include a bumped surface to help support the outer jacket. 
     The present disclosure further describes various multi-lumen and embedded components on a three-dimensionally (3D) printed or additively manufactured catheter, introducer, or implantable stimulation lead that provide a feature to be activated on the distal/proximal ends of the device while in vivo. The distal/proximal component(s) can aid in navigation, sensing, visualization, electrical stimulation, fixation, or be used to guide a secondary tool to a location. 3D printing with these features may allow such features to have more complexity than traditional manufacturing methods and can easily be combined with complex jacket shaping that cannot be achieved with current manufacturing methods. 
     Illustrative structures that may be manufactured or generated using the present disclosure may include lumens that are used for inflation, articulation, sensing, electrical or secondary tool components. Other processes to create catheters with multiple lumens are commonly shaped by reflowing extruded polymer over the components on a mandrel, which can lead to the catheter taking on the shape of the internal components with little control over the placement of internal components or the final jacket shape. When 3D printing, as described herein, the shaping of the jacket can be designed independently of the internal components and can be designed to focus on mechanical properties and anatomy interactions without impeding the function of the internal components. Further, internal features like those described in this disclosure can be combined with external features. 
     Additionally, it may be described that devices, such as catheters or leads, may be printed with embedded components without extrusion or reflow when using the methods and systems described herein. Because component placement can be done with precision and the 3D printing or additive manufacturing system may be described as being modular, tooling, code, etc. may be freely changed to add or remove a feature. Thus, preparing samples for a patient or in vivo testing can be greatly simplified. Further, it may be described that internal components can be embedded into a 3D printed device without impacting the outer jacket shape. Additionally, 3D printing may be described as “opening up” new cross sections and three-dimensional geometries that may not be able to be achieved with the existing manufacturing methods. Furthermore, these new shapes can be designed to be complementary with various internal embedded components. 
     One or more embodiments that may be formed or manufactured using the illustrative methods and systems described herein include a dual lumen unbraided tube made without an extruder, a dual lumen braided tube, a deflectable catheter with embedded pull-wire made without extrusion or reflow, and a lumen embedded into a raised geometry. 
     One illustrative implantable apparatus may include a body defining a distal end region extending along a distal end region axis and two or more alignable marker elements coupled to the body within the distal end region. Each of two or more alignable marker elements may define a complementary shape that complements the other alignable marker element(s) such that, when the distal end region is viewed axially, the two or more alignable marker elements form a fiducial shape indicative of acceptable alignment of the distal end region for positioning at a target site. 
     One illustrative additive manufacturing system may include one or more heating cartridges. Each heating cartridge may extend from a proximal side to a distal side and comprising a substrate inlet port at the proximal side and a substrate outlet port at the distal side and define an interior volume and a substrate channel extending through the interior volume from the proximal side to the distal side. Further, each heating cartridge defines a first filament port in fluid communication with the interior volume to receive a first filament. The system may further include a heating element thermally coupled to each heating cartridge of the one or more heating cartridges to heat the interior volume and a filament handling system comprising one or more motors to feed at least the first filament through the first filament port into the interior volume. The system may further include a substrate handling system comprising a head stock comprising a distal clamp to secure a distal portion of an elongate substrate, where the substrate is positioned to pass through the substrate channel when secured by the head stock, and one or more motors to translate or rotate one or both of the substrate when secured by the head stock and the heating cartridge relative to one another. The system may further include an intermediate component system positioned proximate the heating cartridge to position two or more alignable marker elements and a controller operably coupled to the heating element, one or more motors of the filament handling system, and one or more motors of the substrate handling system. The controller may be configured to control the one or more motors of the filament handling system to selectively control the feeding of the first filament into the interior volume, activate the heating element to melt any portion of the first filament in the interior volume, control one or more motors of the substrate handling system to move one or both of the substrate and the one or more heating cartridges relative to one another in at least a longitudinal direction to form a first elongate catheter jacket around the substrate, and control the intermediate component system to deposit the two or more alignable marker elements on the first elongate catheter jacket within a distal end region element such that, when the distal end region is viewed axially, the two or more alignable marker elements form a fiducial shape indicative of acceptable alignment of the distal end region for positioning at a target site. 
     One illustrative method for navigating an implantable apparatus in a patient&#39;s heart may include providing an implantable apparatus comprising a body defining a distal end region extending along a distal end region axis and two or more alignable marker elements coupled to the body within the distal end region, wherein each of the two or more alignable marker elements defines a complementary shape that complements the other alignable marker element(s) such that, when the distal end region is viewed axially, two or more alignable marker elements form a fiducial shape. The method may further include navigating the distal end region proximate a target site, generating an image taken perpendicular to the target site of the two or more alignable marker elements, and determining that the two or more alignable marker elements form the fiducial shape in the generated image indicating acceptable alignment of the distal end region. 
     One illustrative method of forming a lead may include providing a lead body extending from a proximal end region to a distal end region defining a lumen, where a conductor is positioned within the lumen, defining an opening through the lead body, extending the conductor outside of the lead body through the lumen, and positioning a C-shaped electrode proximate the conductor outside of the lead body. The method may further include electrically coupling C-shaped electrode to the conductor and mechanically coupling the C-shaped electrode onto the lead body. 
     One illustrative lead may include a lead body extending from a proximal end to a distal end and defining an S-shape region proximate the distal end, a first apex area within the S-shaped region and a second apex area within the S-shaped region. The lead may further include a first electrode positioned at the first apex area and a second electrode positioned at the second apex area. 
     The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the techniques described in this disclosure will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a conceptual diagram of an illustrative additive manufacturing system according to the present disclosure. 
         FIG. 2  is a conceptual diagram of an illustrative additive manufacturing apparatus for use with, for example, the additive manufacturing system of  FIG. 1 . 
         FIG. 3  is a conceptual diagram of an illustrative heating cartridge for use with, for example, the additive manufacturing system of  FIG. 1 . 
         FIG. 4  is a conceptual diagram of an illustrative outlet die that may be used, for example, in the heating cartridge in the additive manufacturing system of  FIG. 1 . 
         FIG. 5  is a conceptual diagram of another illustrative outlet die that may be used, for example, in the heating cartridge in the additive manufacturing system of  FIG. 1 . 
         FIG. 6  is a conceptual diagram of an illustrative catheter jacket having a first jacket and cutouts that may be manufactured using the additive manufacturing system of  FIG. 1 . 
         FIG. 7  is a conceptual diagram of another illustrative additive manufacturing system according to the present disclosure. 
         FIG. 8  is a conceptual diagram of the illustrative catheter jacket of  FIG. 6  including pull wires and a second jacket using the additive manufacturing system described herein. 
         FIG. 9  is cross-sectional conceptual diagram of the illustrative catheter of  FIG. 8 . 
         FIG. 10  is a flow diagram that illustrates one example of a method for use with, for example, the additive manufacturing system of  FIG. 1 . 
         FIG. 11  is a side view of an illustrative quadripolar lead that may be manufactured using the systems and methods described with respect  FIGS. 1-6 . 
         FIG. 12  is an expanded view of an illustrative electrode of the quadripolar lead of  FIG. 11 . 
         FIGS. 13A-13E  are cross-sectional views showing an illustrative method of coupling the electrode of  FIG. 12  to the quadripolar lead of  FIG. 11 . 
         FIGS. 14A-14E  are photographic side views showing an illustrative method of coupling the electrode of  FIG. 12  to the quadripolar lead of  FIG. 11 . 
         FIG. 15  is perspective view of the electrode of  FIGS. 12-14 . 
         FIG. 16  is a side view of an illustrative quadripolar lead that may be manufactured using the systems and methods described with respect  FIGS. 1-6 and 13-14 . 
         FIG. 17  is a side view of another illustrative quadripolar lead that may be manufactured using the systems and methods described with respect  FIGS. 1-6 and 13-14 . 
         FIG. 18  is an illustrative view of a lead including two alignable marker elements implanted in the septal wall of the right ventricle. 
         FIG. 19A  is an illustrative view of the lead of  FIG. 18 . 
         FIG. 19B  is an illustrative view of another lead including two alignable marker elements. 
         FIGS. 20A-20B  are simulated right anterior oblique (RAO) fluoroscopic images taken  20  degrees off perpendicular to the septum depicting a lead including two alignable marker elements where the lead is not in intended alignment for implantation into the septum and where the lead is in intended alignment for implantation into the septum, respectively. 
         FIG. 21A  depicts a side view of an acceptably aligned illustrative lead including two alignable marker elements being positioned proximate a target site. 
         FIG. 21B  depicts an illustrative image of the lead of  FIG. 21A  taken perpendicular to the target site. 
         FIG. 22A  depicts a side view of the illustrative lead of  FIG. 21A  in a less desirable alignment being positioned proximate the target site. 
         FIG. 22B  depicts an illustrative image, taken perpendicular to the target site of  FIG. 21A , where the lead is positioned and oriented as in  FIG. 22A . 
         FIG. 23A  is a simulated RAO fluoroscopic image taken  20  degrees off perpendicular to the septum depicting the lead of  FIG. 21A  including two alignable marker elements where the lead is in intended alignment similar to as shown in  FIGS. 21A-21B . 
         FIG. 23B  is simulated RAO fluoroscopic image taken  20  degrees off perpendicular to the septum depicting the lead of  FIG. 21A  including two alignable marker elements where the lead is not in intended alignment similar to as shown in  FIGS. 22A-22B . 
         FIG. 24A  depicts a side view of a desirably aligned illustrative lead including two alignable marker elements being positioned proximate a target site. 
         FIG. 24B  depicts an illustrative image of the lead of  FIG. 24A  taken perpendicular to the target site. 
         FIG. 25A  depicts a side view of the illustrative lead of  FIG. 24A  in a less desirable alignment being positioned proximate the target site. 
         FIG. 25B  depicts an illustrative image, taken perpendicular to the target site of  FIG. 24A , where the lead is positioned and oriented as in  FIG. 25A . 
         FIG. 26A  is a simulated RAO fluoroscopic image taken  20  degrees off perpendicular to the septum depicting the lead of  FIG. 24A  including two alignable marker elements where the lead is in intended alignment similar to as shown in  FIGS. 24A-24B . 
         FIG. 26B  is a simulated RAO fluoroscopic image taken 20 degrees off perpendicular to the septum depicting the lead of  FIG. 24A  including two alignable marker elements where the lead is not in intended alignment similar to as shown in  FIGS. 25A-25B . 
         FIG. 27  is a cross-sectional view showing an illustrative electrode configuration for the quadripolar leads of  FIGS. 11 and 16-17 . 
         FIG. 28A  depicts a side view of an aligned illustrative lead including two alignable marker elements being positioned proximate a target site. 
         FIGS. 28B and 28C  depict cross-sectional views of the lead of  FIG. 28A . 
         FIG. 28D  depicts an illustrative image, taken perpendicular to the target site of  FIG. 28A , where the lead is positioned and oriented as shown in  FIG. 28A . 
         FIGS. 28E and 28F  depicts illustrative images, taken perpendicular to the target site of  FIG. 28A , where the lead is not positioned and oriented as intended. 
         FIG. 29A  depicts a side view of an aligned illustrative lead including two alignable marker elements being positioned proximate a target site. 
         FIGS. 29B and 29C  depict cross-sectional views of the lead of  FIG. 29A . 
         FIG. 29D  depicts an illustrative image, taken perpendicular to the target site of  FIG. 29A , where the lead is positioned and oriented as shown in  FIG. 29A . 
         FIGS. 29E and 29F  depict illustrative images, taken perpendicular to the target site of  FIG. 29A , where the lead is not positioned and oriented as intended. 
         FIG. 30A  depicts a side view of an aligned illustrative lead including two alignable marker elements being positioned proximate a target site. 
         FIG. 30B  is a simulated left anterior oblique (LAO) fluoroscopic image taken 20 degrees off perpendicular to the septum depicting the lead of  FIG. 30A  including two alignable marker elements. 
         FIG. 31  is a perspective view of an illustrative embodiment of two alignable marker elements coupled using two extension elements. 
         FIG. 32A  depicts a side view of an aligned illustrative lead including two alignable marker elements being positioned proximate a target site. 
         FIGS. 32B and 32C  depict cross-sectional views of the lead of  FIG. 32A . 
         FIG. 32D  depicts an illustrative image, taken perpendicular to the target site of  FIG. 32A , where the lead is positioned and oriented as shown in  FIG. 32A . 
         FIG. 33A  depicts a side view of an aligned illustrative lead including two alignable marker elements being positioned proximate a target site. 
         FIGS. 33B and 33C  depict cross-sectional views of the lead of  FIG. 33A . 
         FIG. 33D  depicts an illustrative image, taken perpendicular to the target site of  FIG. 33A , indicating that the lead is oriented towards the target site. 
         FIG. 33E  depicts an illustrative image, taken perpendicular to the target site of  FIG. 33A , indicating that the lead is oriented away from the target site. 
         FIG. 34A  depicts a side view of an aligned illustrative lead including a plurality of alignable marker elements in a coil being positioned proximate a target site. 
         FIG. 34B  depicts an illustrative image, taken parallel to the target site of  FIG. 34A , indicating that the lead is oriented towards the target site. 
         FIG. 34C  depicts an illustrative image, taken perpendicular to the target site of  FIG. 34A , indicating that the lead is oriented towards the target site. 
         FIG. 34D  depicts an illustrative image, taken parallel to the target site of  FIG. 34A , indicating that the lead is not oriented towards the target site. 
         FIG. 34E  depicts an illustrative image, taken perpendicular to the target site of  FIG. 34A , indicating that the lead is not oriented towards the target site. 
         FIG. 34F  depicts an illustrative image, taken parallel to the target site of  FIG. 34A , indicating that the lead is not oriented towards the target site. 
         FIG. 34G  depicts an illustrative image, taken perpendicular to the target site of  FIG. 34A , indicating that the lead is not oriented towards the target site. 
         FIG. 35A  depicts a side view of an illustrative lead in an unintended and less desirable alignment being positioned proximate the target site. 
         FIG. 35B  depicts an illustrative image, taken perpendicular to the target site of  FIG. 35A , show the lead positioned and oriented as in  FIG. 35A . 
         FIG. 36A  depicts a side view of an aligned illustrative lead including a directionally indicative alignable marker element being positioned proximate a target site. 
         FIG. 36B  depicts an illustrative image, taken perpendicular to the target site of  FIG. 36A , where the lead is positioned and oriented as shown in  FIG. 36A . 
         FIGS. 36C and 36D  depict illustrative images, taken perpendicular to the target site of  FIG. 36A , where the lead is not positioned and oriented as intended. 
         FIG. 37  is a perspective view of an illustrative lead including a plurality of alignable marker elements. 
         FIGS. 38A and 38B  depict side views of an aligned illustrative lead including a plurality of alignable marker elements being positioned proximate a target site. 
         FIG. 38C  depicts an illustrative image, taken perpendicular to the target site of  FIG. 38A , where the lead is positioned and oriented as shown in  FIG. 39A . 
         FIG. 38D  depicts an illustrative image, taken perpendicular to the target site of  FIG. 38A , where the lead is not positioned and oriented as intended. 
         FIG. 39A  depicts a side view of an aligned illustrative lead including a plurality of alignable marker elements being positioned proximate a target site. 
         FIG. 39B  depicts an illustrative image, taken perpendicular to the target site of  FIG. 39A , where the lead is positioned and oriented as shown in  FIG. 39A . 
         FIG. 39C  depicts an illustrative image, taken perpendicular to the target site of  FIG. 39A , where the lead is not positioned and oriented as intended. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure generally provides additive manufacturing systems and methods for medical devices, such as catheters and leads, that allows for providing more than one jacket or layer laid down to form the medical device. For example, one or more layers (e.g., an initial jacket or layer) may define shapes or structures within which internal components may be positioned and subsequent layers or jackets may cover or embed the internal components. The internal shapes and components included may be dictated by desirable functional characteristics or properties of the medical device. Specifically, components or empty space may be included on top of an initial print of filament material (e.g., a first layer or jacket) and a subsequent layer or jacket of filament material may be printed thereon. The printing may be done in multiple stages or as a part of a co-print with multiple printing head and tools, as described herein. Additionally, the present disclosure includes a method of coupling an electrode to a lead, various lead shapes and orientations, and leads including alignable marker elements, each of which may be facilitated using the additive manufacturing systems and methods described herein. 
     As used herein, the term “or” refers to an inclusive definition, for example, to mean “and/or” unless its context of usage clearly dictates otherwise. The term “and/or” refers to one or all of the listed elements or a combination of at least two of the listed elements. 
     As used herein, the phrases “at least one of” and “one or more of” followed by a list of elements refers to one or more of any of the elements listed or any combination of one or more of the elements listed. 
     As used herein, the terms “coupled” or “connected” refer to at least two elements being attached to each other either directly or indirectly. An indirect coupling may include one or more other elements between the at least two elements being attached. Either term may be modified by “operatively” and “operably,” which may be used interchangeably, to describe that the coupling or connection is configured to allow the components to interact to carry out described or otherwise known functionality. For example, a controller may be operably coupled to a resistive heating element to allow the controller to provide an electrical current to the heating element. 
     As used herein, any term related to position or orientation, such as “proximal,” “distal,” “end,” “outer,” “inner,” and the like, refers to a relative position and does not limit the absolute orientation of an embodiment unless its context of usage clearly dictates otherwise. 
     All scientific and technical terms used herein have meanings commonly used in the art unless otherwise specified. The definitions provided herein are to facilitate understanding of certain terms used frequently herein and are not meant to limit the scope of the present disclosure. 
     Reference will now be made to the drawings, which depict one or more aspects described in this disclosure. However, it will be understood that other aspects not depicted in the drawings fall within the scope of this disclosure. Like numbers used in the figures refer to like components, steps, and the like. However, it will be understood that the use of a reference character to refer to an element in a given figure is not intended to limit the element in another figure labeled with the same reference character. In addition, the use of different reference characters to refer to elements in different figures is not intended to indicate that the differently referenced elements cannot be the same or similar. 
       FIG. 1  shows one example of an additive manufacturing system  100  according to the present disclosure. The system  100  may be configured and used to produce a catheter, catheter component, lead, or subassembly. The system  100  may use or include consumable filament materials or pellet form resins having a wide variety of hardness levels. The system  100  may be configured to operate a wide variety of process conditions to produce catheters, catheter components, leads, or subassemblies using filaments or pellet form resins of various hardness levels. In general, the system  100  defines a distal region  128 , or distal end, and a proximal region  130 , or proximal end. The system  100  may include a platform  124  including a rigid frame to support one or more components of the system. 
     Further components of the system  100  and methods of use may be described in U.S. patent application Ser. No. 17/081,815, entitled “Additive Manufacturing for Medical Devices” filed on Oct. 27, 2020, U.S. Prov. Pat. App. Ser. No. 63/001,832 entitled “3D Printed Splines on Medical Devices and Methods to Manufacture the Same” filed on Mar. 30, 2020, U.S. Prov. Pat. App. Ser. No. 63/059,867, entitled “Systems and Methods for Manufacturing 3D Printed Medical Devices” filed on Jul. 31, 2020, U.S. Prov. Pat. App. Ser. No. 63/059,890, entitled “Systems and Methods for Manufacturing 3D Printed Medical Devices” filed on Jul. 31, 2020, U.S. Prov. Pat. App. Ser. No. 63/059,870, entitled “3D Printed Medical Devices Including Internal Shaping” filed on Jul. 31, 2020, and U.S. Prov. Pat. App. Ser. No. 63/130,321, entitled “Medical Devices with Multi-plane Articulation” filed on Dec. 23, 2020, each of which are herein incorporated by reference in their entireties. For example, as shown in the illustrated embodiment, the system  100  may include one or more components, such as a heating cartridge  102 , a heating element  104 , a filament handling system  106 , an optional wire handling system  107 , a substrate handling system  108 , a controller  110 , and a user interface  112 . The filament handling system  106  may be operably coupled to the heating cartridge  102 . The filament handling system  106  may provide one or more filaments  114  to the heating cartridge  102 . The optional wire handling system  107  may be used to provide one or more wires  115  to the heating cartridge  102 . The heating element  104  may be operably coupled, or thermally coupled, to the heating cartridge  102 . The heating element  104  may provide heat to melt filament material in the heating cartridge  102  from the one or more filaments  114  provided by the filament handling system  106 . The optional wires  115  may not be melted by the heating cartridge  102 . The substrate handling system  108  may be operably coupled to the heating cartridge  102 . The substrate handling system  108  may provide a substrate  116  that extends through the heating cartridge. Melted filament material located in the heating cartridge  102  may be applied to the substrate  116 . The substrate  116  or the heating cartridge  102  may be translated or rotated relative to one another by the substrate handling system  108 . The substrate handling system  108  may be used to move the substrate  116  or the heating cartridge  102  relative to one another to cover the substrate  116  with the melted filament material to form a jacket  118 . The optional wires  115  may be incorporated into the jacket  118  (e.g., molded into, bedded within, etc.). 
     The substrate  116  may also be described as a mandrel or rod. The jacket  118  may be formed or deposited around the substrate  116 . In some embodiments, the jacket  118  may be formed concentrically around the substrate  116 . In one example, the jacket  118  is formed concentrically and centered around the substrate  116 . 
     When the system  100  is used to make a catheter or catheter component, the jacket  118  may be described as a catheter jacket. Some or all of the substrate  116  may be removed or separated from the jacket  118  and the remaining structure coupled to the jacket may form the catheter or catheter component, such as a sheath. One example of a catheter that may be formed by the system  100  is shown in  FIG. 6 . 
     The substrate  116  may be formed of any suitable material capable of allowing melted filament material to be formed thereon. In some embodiments, the substrate  116  is formed of a material that melts at a higher temperature than any of the filaments  114 . One example of a material that may be used to form the substrate  116  includes stainless steel. 
     The controller  110  may be operably coupled to one or more of the heating element  104 , the filament handling system  106 , the substrate handling system  108 , and the user interface  112 . The controller  110  may activate, or initiate or otherwise “turn on,” the heating element  104  to provide heat to the heating cartridge  102  to melt the filament material located therein. Further, the controller  110  may control or command one or more motors or actuators of various portions of the system  100 . Furthermore, the controller  110  may control one or more motors or actuators the filament handling system  106  to provide one or more filaments  114 . Further, the controller  110  may control one or more motors or actuators of the substrate handling system  108  to move one or both of the heating cartridge  102  or the substrate  116  relative to one another. Further still, the controller  110  may send or receive data to the user interface  112 , for example, to display information or to receive user commands. Control of the components operably coupled to the controller  110  may be determined based on user commands received by the user interface  112 . In some embodiments, the user commands may be provided in the form of a machine-readable code or coding language. 
     Any suitable implementation may be used to provide the substrate handling system  108 . In some embodiments, the substrate handling system  108  may include one or more of a head stock  120 , an optional tail stock  122 , and one or more motors coupled to or included in the head stock or tail stock. One or both of the head stock  120  and the tail stock  122  may be coupled to the platform  124 . A stock may be defined as a structure that holds or secures the substrate  116  during formation of the jacket  118 . The head stock  120  is defined as the stock closest to the end of the substrate  116  where formation of the jacket  118  begins in the formation process. In the illustrated embodiment, the jacket  118  is shown proximal to the head stock  120  and distal to the heating cartridge  102 . 
     When the substrate  116  is secured by one or both stocks  120 ,  122 , the substrate is generally positioned to pass through a substrate channel defined by the heating cartridge  102 . One or both stocks  120 ,  122  may include a clamp or other securing mechanism to selectively hold the substrate  116 . Such a clamp may be operably coupled to a substrate motor. In some embodiments, the substrate motor may be used to control opening and closing of the clamp. In some embodiments, the substrate motor may be used to rotate the substrate  116  in a clockwise or counterclockwise direction about a longitudinal axis  126 . A translation motor may be operably coupled between a stock  120 ,  122  and the platform  124 . In some embodiments, the translation motor may be used to translate the stock  120 ,  122  in a longitudinal direction along the longitudinal axis  126 . In some embodiments, the translation motor also may be used to translate the stock  120 ,  122  in a lateral direction different than the longitudinal axis  126 . The lateral direction may be oriented substantially orthogonal, or perpendicular, to the longitudinal axis  126 . 
     In some embodiments, the substrate handling system  108  may be configured to move the head stock  120  at least in a longitudinal direction (for example, parallel to the longitudinal axis  126 ) relative to the platform  124 . The substrate  116  may be fed through the substrate channel of the heating cartridge  102  by movement of the head stock  120  relative to the platform  124 . A distal portion of the substrate  116  may be clamped into the head stock  120 . The head stock  120  may be positioned close to the heating cartridge  102  at the beginning of the jacket formation process. The head stock  120  may move distally away from the heating cartridge  102 , for example in a direction parallel to the longitudinal axis  126 . In other words, the head stock  120  may move toward the distal region  128  of the system  100  while pulling the secured substrate  116  through the heating cartridge  102 . As the substrate  116  passes through the heating cartridge  102 , melted filament material from the filament  114  may be formed or deposited onto the substrate  116  to form the jacket  118 . The heating cartridge  102  may be stationary relative to the platform  124 . In some embodiments, the tail stock  122  may be omitted. 
     In some embodiments, the substrate handling system  108  may be configured to move the heating cartridge  102  at least in a longitudinal direction (along the longitudinal axis  126 ) relative to the platform  124 . The substrate  116  may be fed through the substrate channel of the heating cartridge  102 . A distal portion of the substrate  116  may be clamped into the head stock  120 . A proximal portion of the substrate  116  may be clamped into the tail stock  122 . In one example, the heating cartridge  102  may be positioned relatively close to the head stock  120  at the beginning of the jacket formation process. The heating cartridge  102  may move proximally away from the head stock  120 . The heating cartridge  102  may move toward the proximal region  130  of the system  100 . As the heating cartridge  102  passes over the substrate  116 , melted filament material may be deposited onto the substrate  116  to form a jacket. The head stock  120  and the tail stock  122  may be stationary relative to the platform  124 . In another example, the heating cartridge  102  may start near the tail stock  122  and move toward the distal region  128 . 
     One or more motors of the substrate handling system  108  may be used to rotate one or both of the substrate  116  and the heating cartridge  102  relative to one another. In some embodiments, only the substrate  116  may be rotated about the longitudinal axis  126 . In some embodiments, only the heating cartridge  102  may be rotated about the longitudinal axis  126 . In some embodiments, both the substrate  116  and the heating cartridge  102  may be rotated about the longitudinal axis  126 . 
     The heating cartridge  102  may be part of a subassembly  132 . The subassembly  132  may be coupled to the platform  124 . In some embodiments, one or more motors of the substrate handling system  108  may be coupled between subassembly  132  and the platform  124  to translate or rotate the subassembly  132 , including the heating cartridge  102 , relative to the platform  124  or the substrate  116 . In some embodiments, one or more motors of the substrate handling system  108  may be coupled between a frame of the subassembly  132  and the heating cartridge  102  to translate or rotate the heating cartridge relative to the platform  124 . 
     In some embodiments, the substrate  116  may be rotated about the longitudinal axis  126  relative to the heating cartridge  102  to facilitate forming certain structures of the jacket. In one example, the substrate  116  may be rotated by one or both of the head stock  120  and the tail stock  122  of the substrate handling system  108 . In another example, the heating cartridge  102  or subassembly  132  may be rotated by the substrate handling system  108 . 
     The system  100  may include one or more concentricity guides  134 . The concentricity guide  134  may facilitate adjustments to the concentricity of the jacket around the substrate  116  before or after the substrate passes through the heating cartridge  102 . The concentricity guide  134  may be longitudinally spaced from the heating cartridge  102 . In some embodiments, the spacing may be greater than or equal to 1, 2, 3, 4, or 5 cm. The spacing may be sufficient to allow the jacket  118  to cool down and no longer be deformable. In some embodiments, one or more concentricity guides  134  may be positioned distal to the heating cartridge  102  and to engage the jacket  118 . In some embodiments, one or more concentricity guides  134  may be positioned proximal to the heating cartridge  102  to engage the substrate  116 . The concentricity guide  134  may mitigate drooping of the substrate  116  and may mitigate susceptibility to eccentricity in the alignment of the stock  120 ,  122  and the heating cartridge  102 . 
     Any suitable implementation may be used to provide the filament handling system  106 . One or more filaments  114  may be loaded into the filament handling system  106 . For example, filaments  114  may be provided in the form of wound coils. Filaments  114  may be fed to the heating cartridge  102  by the filament handling system  106 . In some embodiments, the filament handling system  106  may include one, two, or more pinch rollers to engage the one or more filaments  114 . In some embodiments, the filament handling system  106  may include one or more motors. The one or more motors may be coupled to the one or more pinch rollers to control rotation of the pinch rollers. The force exerted by the motors onto the pinch rollers and thus onto the one or more filaments  114  may be controlled by the controller  110 . 
     In some embodiments, the filament handling system  106  may be configured to feed the filaments  114  including at least a first filament and a second filament. The jacket  118  may be formed from the material of one or both of the filaments  114 . The filament handling system  106  may be capable of selectively feeding the first filament and the second filament. For example, one motor may feed the first filament and another motor may feed the second filament. Each of the motors may be independently controlled by the controller  110 . Selective, or independent, control of the feeds may allow for the same or different feed forces to be applied to each of the filaments  114 . 
     The filaments  114  may be made of any suitable material, such as polyethylene, PEBAX elastomer (commercially available from Arkema S.A. of Colombes, France), nylon 12, polyurethane, polyester, liquid silicone rubber (LSR), or PTFE. 
     The filaments  114  may have any suitable Shore durometer. In some embodiments, the filaments  114  may have, or define, a Shore durometer suitable for use in a catheter. In some embodiments, the filaments  114  have a Shore durometer of at least 25A and up to 90A. In some embodiments, the filaments  114  have a Shore durometer of at least 25D and up to 80D. 
     In some embodiments, the filament handling system  106  may provide a soft filament as one of the filaments  114 . In some embodiments, a soft filament may have a Shore durometer less than or equal to 90A, 80A, 70A, 80D, 72D, 70D, 60D, 50D, 40D, or 35D. 
     In some embodiments, the filament handling system  106  may provide a hard filament and a soft filament having a Shore durometer less than the soft filament. In some embodiments, the soft filament has a Shore durometer that is 10D, 20D, 30D, 35D, or 40D less than a Shore durometer of the hard filament. 
     The system  100  may be configured to provide a jacket  118  between the Shore durometers of a hard filament and a soft filament. In some embodiments, the filament handling system  106  may provide a hard filament having a Shore durometer equal to 72D and a soft filament having a Shore durometer equal to 35D. The system  100  may be capable of providing a jacket  118  having a Shore durometer that is equal to or greater than 35D and less than or equal to 72D. 
     The system  100  may be configured to provide a jacket  118  having, or defining, segments with different Shore durometers. In some embodiments, the system  100  may be capable of providing a jacket  118  having one or more of a 35D segment, a 40D segment, 55D segment, and a 72D segment. 
     The filaments  114  may have any suitable width or diameter. In some embodiments, the filaments  114  have a width or diameter of 1.75 mm. In some embodiments, the filaments  114  have a width or diameter of less than or equal to 1.75, 1.5, 1.25, 1, 0.75, or 0.5 mm. 
     Segments may have uniform or non-uniform Shore durometers. The system  100  may be configured to provide jacket  118  having one or more segments with non-uniform Shore durometers. In some embodiments, the jacket  118  may include continuous transitions between at least two different Shore durometers, for example, as shown in  FIG. 6 . 
     The controller  110  may be configured to change a feeding force applied to one or more of the filaments  114  to change a ratio of material in the jacket over a longitudinal distance. By varying the feeding force, the system  100  may provide different Shore durometer segments in a jacket  118 , whether uniform or non-uniform. In one example, sharp transitions between uniform segments may be provided by stopping or slowing longitudinal movement while continuously, or discretely with a large step, changing the feeding force of one filament relative to another filament of the substrate  116  relative to the heating cartridge  102 . In another example, gradual transitions between segments may be provided by continuously, or discretely with small steps, changing the feeding force of one filament relative to another filament while longitudinally moving the substrate  116  relative to the heating cartridge  102 . 
     The one or more wires  115  provided by the wire handling system  107  may be introduced in any suitable manner. In some embodiments, the wires  115  may be attached to the substrate  116  and pulled by movement of the substrate. One example of a wire is a pull wire that may be used to steer the catheter produced by the system  100 . In some embodiments, a particularly shaped heating cartridge may be used to accommodate one or more wires  115 . 
     Any suitable type of heating element  104  may be used. In some embodiments, the heating element  104  may be a resistive-type heating element, which may provide heat in response to an electrical current. Other types of heating elements that may be used for the heating element  104  include a radio frequency (RF) or ultrasonic-type heating element. The heating element  104  may be capable of providing heat sufficient to melt the filaments  114 . In some embodiments, the heating element  104  may heat the filaments  114  to greater than or equal to 235, 240, 250, or 260 degrees Celsius. In general, the one or more heating elements  104  may be used to heat the filaments  114  to any suitable melting temperature known to one of ordinary skill in the art having the benefit of this disclosure. 
       FIG. 2  shows one example of an additive manufacturing apparatus  200  of the additive manufacturing system  100  in an end view along the longitudinal axis  126 , which is illustrated as a circle and cross. More detail of some components of the additive manufacturing system  100  are shown, such as the heating cartridge  102  and the filament handling system  106 . 
     The heating cartridge  102  may include a heating block  202  at least partially defining an interior volume  204 . The interior volume  204  may be heated by the heating element  104 . The heating element  104  may be thermally coupled to the heating block  202  to melt filament material in the interior volume  204 . In general, the system  100  may be configured to melt any portion of the filaments  114  in the interior volume  204 . The heating element  104  may be disposed in an exposed or exterior volume defined in the heating block  202 . The heating element  104  may be positioned proximate to or adjacent to the interior volume  204 . In some embodiments, one, two, three, or more heating elements  104  may be thermally coupled to the heating block  202 . 
     The heating block  202  may allow the substrate  116 , which may be an elongate substrate or member, to pass through the heating block. The substrate  116  may be able to extend, or pass, through the interior volume  204 . The substrate channel  206  defined by the heating cartridge  102  may extend through the interior volume  204 . The substrate channel  206  may extend in a same or similar direction as the substrate  116 . The substrate channel  206  may extend along the longitudinal axis  126 . 
     A width or diameter of the interior volume  204  is larger than a width or diameter of the substrate  116 . The width or diameter of the interior volume  204  or the substrate  116  is defined in a lateral direction, which may be orthogonal to the longitudinal axis  126 . In one example, the lateral direction may be defined along a lateral axis  210 . In some embodiments, the clearance between the substrate  116  and interior volume  204  is relatively small to facilitate changes in composition of filament material used to form the jacket  118  ( FIG. 1 ) around the substrate  116 . 
     The portion of the interior volume  204  around the substrate  116  may receive a flow of melted filament material from the filaments  114 . When more than one filament material is provided to the interior volume  204 , the filament materials may flow and blend, or mix, around the substrate  116 . 
     In the illustrated embodiment, the filaments  114  includes a first filament  212  and a second filament  214 . The first filament  212  may be provided into the interior volume  204  through a first filament port  216  at least partially defined by the heating block  202 . The second filament  214  may be provided into the interior volume  204  through a second filament port  218  at least partially defined by the heating block  202 . Each filament port  216 ,  218  may be at least partially defined by the heating block  202 . Each filament port  216 ,  218  may be in fluid communication with the interior volume  204 . 
     The filaments  114  may be delivered to the interior volume  204  in the same or different manners. In the illustrated embodiment, the first filament  212  is delivered to the interior volume  204  in a different manner than the second filament  214 . 
     The filament handling system  106  may include a first handling subassembly  220 . The first handling subassembly  220  may deliver the first filament  212  to the interior volume  204 . The first handling subassembly  220  may include one or more pinch rollers  222 . Each of the one or more pinch rollers  222  may be operably coupled to a motor. Any suitable number of pinch rollers  222  may be used. As illustrated, the first handling subassembly  220  may include two sets of pinch rollers  222 . Pinch rollers  222  may be used to apply a motive force to the first filament  212  to move the first filament, for example, toward the interior volume  204 . 
     The heating cartridge  102  may include a first guide sheath  224 . The first guide sheath  224  may extend between the filament handling system  106  and the interior volume  204 . The first guide sheath  224  may be coupled to the heating block  202 . The first guide sheath  224  may extend into the first filament port  216  from an exterior of the heating block  202 . The first guide sheath  224  may define a lumen in fluid communication with the interior volume  204 . An inner width or diameter of the lumen may be defined to be greater than a width or diameter of the first filament  212 . The first filament  212  may extend through the first guide sheath  224  from the pinch rollers  222  of the first handling subassembly  220  to the first filament port  216  and extend distally past the first guide sheath  224  into the interior volume  204 . 
     As used herein with respect to the filaments  114 , the term “distal” refers to a direction closer to the interior volume  204  and the term “proximal” refers to a direction closer to the filament handling system  106 . 
     In some embodiments, a proximal end of the first guide sheath  224  may terminate proximate to one of the pinch rollers  222 . A distal end of the first guide sheath  224  may terminate at a shoulder  226  defined by the first filament port  216 . A distal portion or distal end of the first guide sheath  224  may be positioned proximate to or adjacent to the interior volume  204 . 
     The inner width or diameter of the lumen of the first guide sheath  224  may be defined to be substantially the same or equal to an inner width or diameter of the first filament port  216 , such as a smallest inner width or diameter of the first filament port. In other words, an inner surface of the first guide sheath  224  may be flush with an inner surface of the first filament port  216 . 
     In some embodiments, the heating cartridge  102  may include a support element  228 . The support element  228  may be coupled to the first guide sheath  224 . The first guide sheath  224  may extend through a lumen defined by the support element  228 . The support element  228  may be proximate to the heating block  202 . In the illustrated embodiment, the support element  228  is coupled to the heating block  202 . The support element  228  may include a coupling protrusion configured to be mechanically coupled to a coupling receptacle  230  defined by the first filament port  216 . In some embodiments, the coupling receptacle  230  may define threads and the coupling protrusion of the support element  228  may define complementary threads. 
     The coupling receptacle  230  may terminate at the shoulder  226  of the first filament port  216 . The coupling protrusion of the support element  228  may be designed to terminate at the shoulder  226 . In some embodiments, a distal end of the support element  228  and the distal end of the first guide sheath  224  may engage the shoulder  226 . In other embodiments, the distal end of the support element  228  may engage the shoulder  226  and the distal end of the first guide sheath  224  may engage a second shoulder (not shown) defined by the first filament port  216  distal to the shoulder  226 . 
     When the first filament port  216  defines one shoulder, the first filament port  216  may define at least two different inner widths or diameters. The larger inner width or diameter may be sized to thread the support element  228  and the smaller inner width or diameter may be sized to match the inner width or diameter of the first guide sheath  224 . 
     When the second filament port  218  defines two shoulders, the first filament port  216  may define at least three different inner widths or diameters. The largest inner width or diameter may be sized to thread the support element  228 . The intermediate inner width or diameter may be sized to receive a distal portion of the first guide sheath  224 . The smallest inner width or diameter may be sized to match the inner width or diameter of the first guide sheath  224 . 
     The filament handling system  106  may include a second handling subassembly  232 . The second handling subassembly  232  may deliver the second filament  214  to the interior volume  204 . The second handling subassembly  232  may include one or more pinch rollers  222 . Each of the one or more pinch rollers  222  may be operably coupled to a motor. Any suitable number of pinch rollers  222  may be used. As illustrated, the second handling subassembly  232  may include one set of pinch rollers  222 . Pinch rollers  222  may be used to apply a motive force to the second filament  214 . 
     The heating cartridge  102  may include one or more of a second guide sheath  234 , a heat sink  236 , and a heat break  238 . The second guide sheath  234  may extend at least between the second handling subassembly  232  and the heat sink  236 . The second guide sheath  234  may be coupled to the heat sink. The second guide sheath  234  may be coupled to the second handling subassembly  232 . The heat sink  236  may be coupled to the heat break  238 . The heat break  238  may be coupled to the heat block  202 . The heat break  238  may extend into the second filament port  218  from an exterior of the heating block  202 . 
     The second guide sheath  234  may define a lumen in fluid communication with the interior volume  204 . The second filament  214  may extend through the second guide sheath  234  from the second handling subassembly  232  to the heat sink  236 , through the heat sink  236 , through the heat break, and through the second filament port  218 . In some embodiments, the second guide sheath  234  may extend to the pinch rollers  222  in the second handling subassembly  232 . In some embodiments, the second guide sheath  234  may extend at least partially into the heat sink  236 . 
     The heat break  238  may be proximate to the heating block  202 . The heat break  238  may be positioned between the heat sink  236  and the heating block  202 . The heat break  238  may include a coupling protrusion configured to mechanically couple to a coupling receptacle  240  defined by the second filament port  218 . In some embodiments, the coupling receptacle  240  may define threads and the coupling protrusion of the heat break  238  may define complementary threads. The second filament port  218  may include one or more shoulders such as those described with respect to the first filament port  216 , except that the second filament port  218  may not be configured to receive the second guide sheath  234 . The inner width or diameter of the support element  228  may be larger than the inner width or diameter of the heat break  238 , for example, to accommodate the outer width or diameter of the first guide sheath  224 . In other embodiments, the second filament port  218  may be configured to receive the second guide sheath  234  in a similar manner to the first filament port  216  receiving the first guide sheath  224 . 
     Any suitable material may be used to make the guide sheaths  224 ,  234 . In some embodiments, one or both guide sheaths  224 ,  234  may include a synthetic fluoropolymer. One or both guide sheaths  224 ,  234  may include polytetrafluoroethylene (PTFE). Another suitable material may include an ultra-high molecular weight polyethylene (UHMWPE). 
     Any suitable material may be used to make the support element  228 . In some embodiments, the support element  228  may be a thermal insulator. The support element  228  may include a thermoplastic. The support element  228  may be made of a polyamide-imide, such as a TORLON polyamide-imide (commercially available from McMaster-Carr Supply Co. of Elmhurst, Ill.). Other suitable materials may include liquid-crystal polymer, polyaryletherketone (PAEK), polyphenylene sulfide, and polysulfone. 
     The support element  228  may provide mechanical support to the first guide sheath  224 . The support element  228  may include a substantially rigid material. In some embodiments, the support element  228  include a material having a higher durometer than material used to make the first guide sheath  224 . 
     Any suitable material may be used to make the heat sink  236 . The heat sink  236  may include a high thermal conductivity material. In some embodiments, the heat sink  236  includes aluminum. 
     Any suitable material may be used to make the heat break  238 . The heat break  238  may include a low thermal conductivity material. In some embodiments, the heat break  238  includes titanium. The heat break  238  may include a necked portion to reduce the amount of material between a proximal portion and a distal portion of the heat break. The necked portion may facilitate a reduced thermal conductivity between the proximal portion and the distal portion of the heat break  238 . 
     In general, use of the apparatus  200  may facilitate using softer filaments at high feed forces and pressures, which tend to compress the soft filament and may result in jamming. Using higher feed forces and pressures may allow for a greater range of process conditions and may provide a consistent jacket around the substrate. In particular, use of the first guide sheath  224  extending at least partially into the first filament port  216  may facilitate the use of softer filament and greater “push-ability.” Additionally, or alternatively, the use of the support element  228  may also facilitate the use of softer filament and greater “push-ability.” In other embodiments, the apparatus  200  may include a screw or static mixer to help push a softer filament. In other words, the screw or static mixer may provide a cavity for softer filament material to be moved forward between the threads of the screw. 
       FIG. 3  shows a partial cross-sectional side view of one example of the heating cartridge  102 . The heating cartridge  102  or the heating block  202  may extend from a proximal side  410  to a distal side  412 . In some embodiments, the heating cartridge  102  may include one or more of the heating block  202 , an inlet die  402  coupled to the proximal side  410  of the heating block, an outlet die  404  coupled to the distal side  412  of the heating block, a proximal retaining plate  406  to facilitate retaining the inlet die adjacent to the heating block, and a distal retaining plate  408  to facilitate retaining the outlet die adjacent to the heating block. 
     The inlet die  402  and the outlet die  404  may be retained in any suitable manner. In the illustrated embodiment, the outlet die  404  may be retained by a distal shoulder of the distal retaining plate  408 . In some embodiments, the inlet die  402  may be retained by the proximal retaining plate  406  between a distal shoulder of the proximal retaining plate  406  and a fastener, such as a nut with a lumen extending through, which may be threaded to the retaining plate to engage a proximal surface of the inlet die. The retaining plates  406 ,  408  may be fastened to the heating block  202  in any suitable manner. 
     The inlet die  402  may at least partially define a substrate inlet port  414 . The outlet die  404  may at least partially define a substrate outlet port  416 . The inlet die  402  may at least partially define the interior volume  204 . The outlet die  404  may at least partially define the interior volume  204 . In some embodiments, an exterior surface of the inlet die  402 , an interior surface of the outlet die  404 , and an interior surface of the heating block  202  may cooperatively define the interior volume  204 . 
     The substrate channel  206  may be described as extending from the proximal side  410  to the distal side  412  of the heating cartridge  102 , or vice versa. The substrate channel  206  may extend through the interior volume  204 . As shown, the substrate channel  206  may extend through one or more of the proximal retaining plate  406 , the inlet die  402 , the heating block  202 , the outlet die  404 , and the distal retaining plate  408 . 
       FIG. 4  shows an end view of one example of an inlet or outlet die  700  that may be used in the heating cartridge  102  ( FIG. 1 ). The die  700  may define a substrate inlet or outlet port  702 . The port  702  may define a main region  704  and one, two, three, four, or more cutouts  706 , or cutout regions. In the illustrated embodiment, the port  702  defines four cutouts  706 . 
     When the interior cross-sectional shape die  700  is used in an outlet die, the jacket formed by the heating cartridge  102  may include a number of protrusions corresponding to the number of cutouts  706  used in the die  700 . For example, the illustrated die  700  would produce four protrusions on the jacket. 
     In some embodiments, one or more of the cutouts  706  may be sized to receive a wire  115  ( FIG. 1 ), such as a pull wire, which may be provided by the wire handling system  107  ( FIG. 1 ). In some embodiments, the interior cross-sectional shape of die  700  may be used in both the input die and the outlet die to accommodate the wires  115  pulled through the cutouts  706 . 
       FIG. 5  shows an end view one example of an inlet or outlet die  720  that may be used in the heating cartridge  102  ( FIG. 1 ). The die  720  may define a substrate inlet or outlet port  722 . The port  722  may define a main region  724  and one, two, three, four, or more protrusions  726 , or cutout regions. In the illustrated embodiment, the port  722  defines two protrusions  726 , or teeth. 
     When the interior cross-sectional shape die  720  is used in an outlet die, the jacket formed by the heating cartridge  102  may include a number of channels corresponding to the number of protrusions  726  used in the die  720 . For example, the illustrated die  720  would produce two channels on the jacket. 
     The shape and feature of the outlet die  720  may control the shape and features of a resultant first jacket  500 . For example, as shown in  FIG. 6 , the first jacket  500  defines cutouts  504  in the outer surface  502  of the first jacket  500 . The first jacket  500  may be similar to the jacket  118  described herein, but may be the initial jacket that is formed and may include geometrical features thereon (e.g., the cutouts  504 ) upon which a second jacket may be subsequently formed. The cutouts  504  may be a result of the corresponding outlet die through which the first jacket  500  was formed. For example, the first jacket  500  of  FIG. 6  defines four symmetrical cutouts having a partially circular shape. Therefore, the outlet die through which the first jacket  500  was formed included four symmetrical protrusions that are semi-circular and extend towards the center of the opening of the outlet die. Further, the cutouts  504  may extend along and parallel to the longitudinal axis  126  or may spiral or corkscrew around the outer surface  502  of the first jacket  500 . While  FIG. 6  illustrates four symmetrical cutouts  504 , the features defined within the first jacket  500  may be any suitable shape and/or size. 
     After forming the first jacket  500  including features as shown in  FIG. 6 , one or more internal components (e.g., a lumen, a pull wire, a liner, marker elements, alignable marker elements, electrodes, electrode couplings, etc.) may be formed or deposited on the first jacket  500  (e.g., within the features defined in the first jacket  500 ). For example, the internal components may be positioned within channels, between protrusions, or within protrusions formed in the first jacket. A pull wire  115  may be provided by the wire handling system  107  (e.g., as shown in  FIG. 1 ) and positioned within the cutout  504 . Specifically, the number of pull wires may correspond to the number of internal components formed on the first jacket  500 . As shown in  FIG. 6 , there may be four pull wires positioned in the first jacket  500  (e.g., one pull wire in each cutout  504 ). By positioning the pull wires within the pre-formed cutouts  504 , the pull wires may be more effectively and consistently spaced apart. 
     Thereafter, a second jacket may be formed around the first jacket  500  and any internal components positioned therein. The second jacket may be formed similar to the first jacket  500  (or, e.g., as described herein as it pertains to the jacket  118 ) such as by feeding a second filament into the interior cavity of the heating cartridge, melting the second filament within the interior cavity, and moving the heating cartridge to form the second jacket. Further, the second jacket may be formed using the same heating cartridge as the first jacket or a different heating cartridge. 
     For example, in one or more embodiments, the heating cartridge  102  of the system  100  (e.g., as shown in  FIG. 1 ) may make multiple passes (e.g., two) along the substrate to form each of the first and second jackets. Once the heating cartridge  102  extends the length of the substrate  116  to form the desired length first jacket  500 , the heating cartridge  102  may return to the starting position and begin forming the second jacket. In other words, a first filament may be fed into and melted within the interior cavity of the heating cartridge  102  to form the first jacket and a second filament may be fed into and melted within the interior cavity of the same heating cartridge  102  to form the second jacket. In such embodiments, the first and second filaments may be the same filament being fed into the heating cartridge  102  (e.g., if the heating cartridge  102  only includes a single filament port). Although in some embodiments, as described herein, the heating cartridge  102  may include at least two filament ports. Therefore, the first jacket may be formed from a first filament and the second jacket may be formed from a second filament different than the first filament. In one or more embodiments, the first and second jackets may be formed from any combination of both the first and second filaments. 
     Also, as shown in  FIG. 7 , the system  101  may include an additional heating cartridge  103  that is distal to or trailing the heating cartridge  102 . Specifically, the additional heating cartridge  103  may be longitudinally spaced (e.g., along the longitudinal axis  126 ) apart from the heating cartridge  102 . The system  101  may include all of the same components as system  100  described in combination with  FIG. 1 , but include the additional heating cartridge  103 . Further, the additional heating cartridge  103  may include all of the same features as the heating cartridge  102 , but may be physically separate from the heating cartridge  102 . In such embodiments, the heating cartridge  102  may form the first jacket and the additional heating cartridge  103  may subsequently form the second jacket around the first jacket. For example, the heating cartridge  102  may define a first filament port in fluid communication with the interior volume to receive the first filament and the additional heating cartridge  103  may define a second filament port in fluid communication with the interior volume of the additional heating cartridge to receive the second filament. 
     Even though the heating cartridges are separate components, the first and second filament may include a same or different filament material. Further, each of the heating cartridge  102  and the additional heating cartridge  103  may include two or more filament ports such that the jacket may be formed from a mixture of materials. As described herein, by combining filament materials into a single jacket, the characteristics (e.g., the flexibility) of the jacket may be customized. The one or more pull wires located within the catheter (e.g., between the first and second jacket) may produce varying types of movement of the catheter depending on the characteristics of the material mixture of the first and second jackets. For example, if the second jacket (e.g., outer jacket) is stiffer than the first jacket (e.g., inner jacket), the pull wires may provide greater range of motion. 
     As shown in each of  FIGS. 1 and 7 , the wire handling system  107  (which may include the one or more pull wires) may feed the pull wires  115  through the heating cartridge  102  to be positioned along the catheter. When the system  100  (e.g., as shown in  FIG. 1 ) includes a single heating cartridge  102  making multiple passes, the pull wire  115  may be positioned after the first jacket is formed and prior to the second jacket being formed. When the system  101  (e.g., as shown in  FIG. 7 ) includes a heating cartridge  102  and an additional heating cartridge  103 , the pull wire  115  may be configured to be positioned between the heating cartridge  102  and the additional heating cartridge  103  (e.g., between the formation of the first and second jackets). 
       FIG. 8  shows one example of a catheter  600  that may be manufactured using the system  100  before the substrate  116  is removed. The substrate  116  may include a lubricious coating on its exterior surface to facilitate removal. The lubricious coating may extend around the circumference of the substrate  116 . One example of a lubricious coating is a PTFE coating. 
     The substrate  116  may be covered with a liner  602 , such as a PTFE layer. The liner  602  may be placed over the lubricious coating. The liner  602  may extend around the circumference of the substrate  116 . The liner  602  may be covered with a braid  604 , such as a stainless-steel braid layer. The braid  604  may be placed over the liner  602 . The braid  604  may extend around the circumference of the liner  602 . The braid  604  may be porous. The first jacket  500  may be applied to the braid  604 . When the first jacket  500  is formed, the liner  602  may adhere to the first jacket  500  through pores in the braid  604 . 
     As described herein the first jacket  500  may be formed with one or more cutouts (e.g., see  FIG. 6 ). As shown in  FIG. 8 , the cutouts are filled with pull wires  115  extending along the length of the catheter  600 . Thereafter, the second jacket  510  may be formed around the first jacket  500  and the pull wires  115 . 
     In the illustrated embodiments, the catheter  600  includes a first segment  606 , a second segment  608 , and a third segment  610 . Each segment  606 ,  608 ,  610  may have different durometers. In some embodiments, the first segment  606  may have a high durometer, the third segment  610  may have a low durometer, and the second segment  608  may have a continuously varying durometer in a longitudinal direction between the durometers of the first and third segments. For example, the first segment  606  may have a Shore durometer equal to 72D, the third segment  610  may have a Shore durometer equal to 35D, and the second segment  608  may have a Shore durometer that gradually changes from 72D to 35D over its length. Further, the first and second jackets  500 ,  510  may have the same or differing profiles extending along the longitudinal direction. 
       FIG. 9  illustrates the catheter  600  of  FIG. 8  from the conceptual cross-sectional view and without the substrate  116  positioned therein. As described herein, the first jacket  500  is formed around the braid  604  and the liner  602 . The pull wires  115  are positioned within a portion of the first jacket  500  and surrounded by a liner  512  (e.g., a PTFE pull wire liner). The second jacket  510  may be formed around the first jacket  500  and the pull wire liners  512 . The pull wires  115  may be symmetrically positioned around and embedded in the catheter  600 . The process of embedding internal components as described herein may assist in easily spacing those internal components in a concentric way that may benefit mechanical properties and physician handling (e.g., moving the pull wires). 
       FIG. 10  shows one example of a method  800  of using the systems  100 ,  101  ( FIGS. 1 and 7 ) for additive manufacturing. The method  800  may be used to manufacture an implantable medical device. The method  800  may include feeding the substrate  802 , for example, through a substrate channel in one or more heating cartridges. The substrate channel may be in fluid communication with an interior cavity of the heating cartridge. The method  800  may include feeding at least a first filament  804  through a filament port of the heating cartridge into the interior cavity. The method  800  may include melting the first filament  806 , for example, in the interior cavity. Any portion of the filaments contained in the interior cavity may be melted. 
     The method  800  may include moving the heating cartridge relative to the substrate  808 , for example, at least in a longitudinal direction to form a first jacket comprising material from at least the first filament. The heating cartridge or substrate may also be rotated relative to one another. The jacket may be formed from material of at least the first filament. In some embodiments, the jacket may be formed from material of at least the first filament and the second filament. In one or more embodiments, the outlet die may form various surface features within the outer surface of the first jacket. 
     For example, in one or more embodiments, forming the first jacket may include defining one or more protrusions extending from an outer surface of the first jacket. In one or more embodiments, forming the first jacket may include defining one or more channels or cutouts extending inward from an outer surface of the first jacket. 
     The method  800  may also include depositing one or more internal components  810  on the first jacket (e.g., relative to the features formed on the surface of the first jacket). For example, the one or more components may be deposited between the one or more protrusions or within the one or more channels. The method  800  may further include feeding at least a second filament  812  through a filament port of the heating cartridge into the interior cavity and melting the second filament  814  in the interior cavity of the one or more heating cartridges. 
     The method  800  may include moving the heating cartridge relative to the substrate  816 , for example, at least in a longitudinal direction to form a second jacket comprising material from at least the second filament. The heating cartridge or substrate may also be rotated relative to one another. The jacket may be formed from material of at least the second filament. In some embodiments, the jacket may be formed from material of at least the first filament and the second filament. Further, the first and second jackets may be formed by a single heating cartridge making multiple passes along the substrate or by two separate heating cartridges that are spaced apart from one another. 
     An illustrative lead described herein may include an innovative electrode design and connection between such electrode and a conductor wire to reduce the outer diameter. Furthermore, the illustrative lead may not utilize insulation core tubing that is often used between an electrode and a coil and/or jacket of existing leads. In one embodiment, the illustrative lead utilizes a platinum-lawrencium electrode, 004 Ag/MP 35 nw/Si conductor coil, a polyurethane lead body, and a monolithic controlled release device (MCRD) silicon ring. 
     The illustrative leads described herein may be thinner than current leads so as to track better into small vessels (e.g., better trackability). Further, the illustrative leads may have better “pushability” and utilize less than around 80% force utilized with prior leads when placed into curved paths. Additionally, although the outer diameter of the illustrative leads may be reduced (e.g., 3 Fr, less than 3 Fr, etc.), the leads may still be compatible with current delivery systems (e.g., 0.014 inch guidewires), which means that the physicians may not have to change their clinical practice to implant these illustrative leads. Furthermore, the illustrative leads can improve CRT response by targeting optimal pacing options that are not reachable by other leads. Still further, the illustrative leads could be potentially used for other pacing therapy like hypoglossal nerve stimulation for sleep apnea. 
     Additionally, the leads become thinner (e.g., smaller outer diameter such as less than 4 Fr or less than 4 Fr), contact between the electrodes and the coronary vessel wall may be decreased than thicker leads. Consequently, a pacing capture threshold (PCT) for the thinner leads may tend to be higher, which can lead to a quicker depletion of the battery. 
     The illustrative leads described herein are designed to overcome such challenges of thinner leads (e.g., less than 4 Fr, less than 3 Fr, etc.) to lower the PCT and be sure the lead can deliver acceptable electrical signals without hampering the battery longevity. Generally, such leads utilize platinum-lawrencium electrodes, polyurethane tubing shaped with a specific design, and a conductive inner coil. 
     As described herein, the illustrative lead may include a lead body is used directly as insulating core tubing. An electrode may be a one-part platinum-lawrencium tube with a slit. In one or more embodiments, the illustrative leads may be manufactured, made, or formed by cutting a slit into the lead body and extending a conducting wire out of the lead body. Then, the lead body may be thermo-bonded over 2 millimeters to reduce the outer diameter on the section where the electrode will be positioned. The thermo-bonded process may also close the previous slit that was made to extend the conducting wire. The electrode may be opened a bit (e.g., using the slit) and slid over the lead body until it reaches the reduced diameter section. Then, the conducting wire may be optionally welded from the exterior on the electrode. Lastly, the electrode may be closed by deformation (e.g., crimping) and then welding the slit. 
     In view thereof, various illustrative leads and constructions thereof are depicted in  FIGS. 11-17  that may provide thinner leaders that may better navigate small, tortious paths such as some coronary vessels than previous leads. For example, an illustrative quadripolar lead  900  that may be manufactured using the systems and methods described with respect  FIGS. 1-6  is depicted in  FIG. 11 . The lead  900  may extend from a proximal end to a distal end  904 . The distal end region, which extends from the distal end  904  for a selected length towards to the proximal end, is depicted in  FIG. 11 . 
     In this embodiment, the lead  900  may include four electrodes  906  coupled to a lead body  901 . It is to be understood that other embodiments similar to lead  900  may include less than four electrode or more than four electrodes. In particular, this lead  900  includes a tip electrode  906 A and three ring, or body, electrodes  906 B,  906 C,  906 D. The tip electrode  906 A is located at the distal end  904  of the lead  900  so as to be positioned furthest along a vessel while the remaining ring electrodes  906 B,  906 C,  906 D may be distributed along vessel. The electrodes  906  may include one or more conductive materials so as to be able to sense electrical cardiac activity and deliver electrical cardiac therapy to cardiac tissue. For example, the electrodes  906  may include one or more of platinum, platinum alloy, and/or other materials known to be usable in implantable electrodes. 
     The ring electrodes  906 B,  906 C,  906 D may be spaced apart along the lead body  901  to, e.g., provide various sensing and pacing locations when the lead  900  is implanted. Additionally, as shown the lead  900  may include a coil-style fixation element  909  located proximal to the ring electrode  906 D. The fixation element  909  may be configured to fixate, or couple, the lead  900  to cardiac tissue so as to secure the lead  900  from moving after positioning the lead  900  in the desired location (e.g., to position the electrodes  906  in acceptable locations to provide the desired sensing and pacing capabilities for a selected therapy). 
     The lead  900  may be thinner or have smaller diameter  911  than typical leads. For example, the lead  900  may be less than 4 French (4 Fr), which is less than 1.333 millimeters (mm) in diameter. Further, for example, the lead  900  may be 3 Fr, which is a 1 mm diameter. Further, for example, the lead  900  may be 3.5 Fr, which is a 1.166666 mm diameter. Further, for example, the lead  900  may be less than 3 Fr. To facilitate the small size, or diameter, of the lead  900 , the present disclosure describes an electrode coupling construction (or arrangement) and method of manufacturing such lead that will be described with respect to the  FIGS. 12-15 . 
     An expanded, cross-sectional view of an illustrative ring electrode  906 C of the quadripolar lead  900  of  FIG. 11  is depicted in  FIG. 12 . As shown, the ring electrode  906 C is positioned around the lead body  901 , and additionally, a coil conductor  910  is located inside a lumen  907  of the lead body  901 . The coil conductor  910  is electrically and mechanically coupled to the ring electrode  906 C as will be described further herein. 
     Additionally, the lead  900  shown in  FIGS. 11-12  also includes monolithic controlled release devices (MCRD)  905 , each located proximate one of the electrodes  906 . The MCRDs  905  may be integrated with or separate from the electrodes  906  and may be coupled to the lead body  901  in the same or similar way as the electrodes  906 . 
     Cross-sectional views showing an illustrative method of coupling the electrode  906 C to the lead body  901  are depicted in  FIGS. 13A-E . First, a lead body  901  is provided. The lead body  901  may be manufactured or formed using the additive manufacturing systems and processes described herein with respect to  FIGS. 1-10 . Generally, similar to as described with respect to  FIGS. 11 , the lead body  901  may extend from a proximal end to a distal end  904  and defining a lumen  907 . Further, a conductor  910  may be positioned within the lumen  907 . 
     It to be understood that only a small portion or region of the lead  900  is depicted in  FIGS. 13A-E  to show or illustrate the coupling of the electrode  906 C thereto. In one embodiment, the small portion or region of the lead  900  depicted in  FIGS. 13A-E  includes two different diameters for two different regions of the lead body  901 . In particular, the lead body  901  includes an extension region  912  and an electrode coupling region  914 . The electrode coupling region  914  is where the electrode  906 C is coupled to the lead body  901 . The extension region  912  defines a first outer diameter  913  and the electrode coupling region  914  defines a second outer diameter  915  that is less than the first outer diameter  913 . For example, the first outer diameter may be between about 0.75 mm and about 1.25 mm and the second outer diameter may be between about 0.5 mm and about 1 mm. In at least one embodiment, the first outer diameter may be about 3 Fr or 1 mm, and the second outer diameter may be about 0.7 mm. 
     The electrode coupling region  914  may provide an indentation, or space,  919  to receive the ring electrode  906 C such that, e.g., an outer surface  920  of the lead body  901  may be substantially flush with an outer surface  928  of the ring electrode  906 C when the ring electrode  906 C is attached thereto. The indentation  919  may define a depth that is the difference between the first outer diameter  913  and the second outer diameter  915 . Further, as shown in this embodiment, the indentation  919  may also define beveled sides transitioning the electrode coupling region  914  to the extension region  912  that correspond to beveled sides of the electrode  906 C, which shown be shown in  FIGS. 13C-13D . In other embodiments, the indentation  919  may have straight side walls. 
     As described herein, the lead body  901  including the extension regions  912  and electrode coupling regions  914  may be formed, or manufactured, using the additive manufacturing systems and processes described herein with respect to  FIGS. 1-10 . For example, when the electrode coupling regions  914  are formed, or created, less material may be applied to the substrate (e.g., rod, mandrel, core, conducting coil wrapped over the substrate, etc.) than when forming the extension regions  912  to define the second outer diameter  915  that is smaller than the first outer diameter  913 . 
     Next, an opening  952  may be defined through the lead body  901  and a coupling portion, or segment,  950  of the coil conductor  910  may be extended outside of the lead body  901 . In this example, the opening  952  is made in the electrode coupling region  914  of the lead body  901 . More specifically, the opening  952  may be made through the wall of the lead body  901  from the exterior to the lumen  907  of the lead body  901 . 
     In one or more embodiments, the opening  952  through which the coupling portion  950  of the coil conductor  910  is extended may be closed or “filled-in.” For example, the electrode coupling region  914  may be thermo-bonded, which may reflow the polymer of the lead body  901  thereby closing or filling in any remaining gaps of the opening  952  around the conductor  910  extending therethrough. 
     Then, the ring electrode  906 C may be positioned proximate the conductor outside of the lead body  901  in the electrode coupling region  914 . An illustrative ring electrode  906  prior to fixation, or prior-fixation electrode  906 , to the lead body  901  is depicted in  FIG. 15 . As shown, the prior-fixation electrode  906  may define a C-shape. More specifically, the prior-fixation electrode  906  may extend around a circumference from a first end  930  to a second end  932  and defines a gap  931  between the first end  930  and the second end  932 . Further, the ring electrode  906 C prior to fixation to the lead body  901  may be described as defining an inner surface  926 , an outer surface  928 , and a thickness  927  between the inner surface  926  and the outer surface  928 . The thickness  927  of the ring electrode  906 C prior to fixation to the lead body  901  is less than or equal to half of the difference between the first outer diameter  913  and the second outer diameter  915  of the lead body  901 . 
     The ring electrode  906 C may define a C-shape. More specifically, the ring electrode  906 C may define an inner diameter that is slightly greater than the first outer diameter  913  of the extension region  914  the lead body  901 , e.g., so as to be able to be moved thereabout. This, the C-shaped ring electrode  906 C may be slide down, or over, the lead body  901  to the electrode coupling region  914  as shown in  FIGS. 13C-13D . 
     Then, the ring electrode  906 C may be mechanically coupled to the lead body  901  and electrically coupled to the coil conductor  910  (in particular, the segment or portion of the coil conductor  910  that extends outside of the lumen  907  of lead body  901 ). The electrode  906 C may be mechanically coupled to the lead body  901  in a variety of ways. In at least one example, the electrode  906 C may be deformed, or inwardly radially crushed, as indicated by arrows  939  to decrease the inside diameter of the ring electrode  906 C to contact and fixate the inner surface  926  to the outer surface  920  of the lead body  901 . In one or more embodiments, in doing so, the gap  931  defined between the first end  930  and the second end  932  may be closed. In other words, mechanically coupling the C-shaped electrode  906 C onto the lead body  901  may include applying a force as indicated by arrows  939  to the C-shaped electrode  906 C to deform the C-shaped electrode  906 C to close the gap  931  such that the first end  930  contacts the second end  932 . 
     Likewise, the electrode  906 C may be electrically coupled to the coil conductor  910  in a variety of ways. For example, the mechanical coupling described herein may be sufficient to press the coil conductor  910  and the inner surface of the  926  of the ring electrode  906 C into contact so as to provide a durable, acceptable electrical coupling therebetween. Further, for example, the electrode  906 C and the coil conductor  910  may be laser welded together thereby electrically coupling to each other. In at least one embodiment, laser welding is applied to the outer surface of the C-shaped electrode to electrically couple the inner surface  926  to the coil conductor  910 . 
     As a result, the outer surface  928  of the electrode  906 C may be flush or substantially flush with the outer surface  920  of the extension region  914  of the lead body  901  as shown in  FIG. 13E . Thus, the electrode coupling region  914  of the lead body  901 , after the electrode  906 C has been coupled thereto, may define a diameter that is less than or equal to about 1.33333 mm such as, e.g., 1.0 mm. 
     Additionally, although embodiment depicted in  FIGS. 11-13  utilizes a ring electrode  906 , it is be understood that the lead  900  may also utilize a coil electrode  916  and a C-shaped electrode  917  as depicted in  FIG. 27 . More specifically, for example, the coil electrode  916  may be electrically coupled (e.g., welded) to C-shaped electrode  917 , which may be electrically coupled to the coil conductor  910  through the body  901  and mechanically coupled to the body  901 , e.g., in a similar way as described herein with respect to  FIGS. 13A-E . For instance, as shown, the coil electrode  916  and ring electrode  917  is positioned in the indentation such that an outside of the coil electrode  916  is flush with the outer surface  920  of the body  901 . The coil electrode  916  may be described as being beneficial to bring support to a thinner (e.g., 3Fr) lead to maintain a S-shape as shown in  FIGS. 16-17 . 
     Photographic side views showing an illustrative method of coupling an electrode to a quadripolar lead are depicted in  FIGS. 14A-E . As shown in  FIG. 14A , a lead body including an electrode coupling region (e.g., an indentation) may be provided. An opening may be made (e.g., formed) through the lead body and a coil conductor may be extended through the opening as shown in  FIG. 14B . After the coil conductor is extended therethrough, the lead body may be thermo-bonded to reflow the polymer to seal the opening. A C-shaped electrode may be slide, or moved, along the lead body as shown in  FIG. 14C , and then electrically coupled to the coil conductor (e.g., through las welding) as shown in  FIG. 14D . Lastly, the C-shaped electrode may be deformed through crimping as shown in  FIG. 14E  to mechanically coupled the electrode to the lead body. 
     The illustrative thinner leads (e.g., defining an outer diameter less than 1.333 mm) described herein may have various shapes and configurations. A few illustrative shapes and configurations are depicted in  FIGS. 16-17 . The lead  1000  of  FIG. 16  may be described as having a lead body  1001  extending from a proximal end  1002  to a distal end  1004  and defining an S-shape region  1005  proximate the distal end  1004 , a first apex area  1007  within the S-shaped region and a second apex area  1009  within the S-shaped region. 
     Each apex area  1007 ,  1009  may be described as the areas of the lead body  1001  that deviate a maximum distance away from a central axis  1010 . More specifically, the lead body  1001  may be described as further defining a straight portion  1011  positioned proximal to the S-shaped region  1005 . The straight portion  1011  may extend along and define the central axis  1010  when undeflected. The one or both of the first and second apex areas  1007 ,  1009 , when undeflected, may be located away from the axis  1010  at a perpendicular radial distance that is greater than any other the remainder of the lead body  1001 . Additionally, it may be described that the first apex area  1007  is located on the opposite side of the axis  1010  than the second apex area  1009 . 
     Furthermore, each of the apex areas  1007 ,  1009  may be centered within one of the curve portions  1006 ,  1008  of the S-shaped region  1005 . In this example, the first curve portion  1006  defines a first radius  1012  and the second curve portion  1008  defines a second radius  1014 , and, when the lead  1000  is undeflected, the second radius  1014  is same the first radius  1012 . 
     The lead  1000  may be described as being a quadripolar lead as the lead  1000  includes four electrodes. It is be understood that the lead  1000  may include more or less than four electrodes. In particular, as shown, the lead  1000  includes a tip electrode  1020 , a first coil electrode  1022 , a second coil electrode  1024 , and a ring electrode  1026 . The tip electrode  1020  is located and coupled to the distal end  1004  of the lead body  1001 . The first coil electrode  1022  is coupled to the lead body  1001  and positioned at the first apex area  1007 , and the second coil electrode  1024  is coupled to the lead body  1001  and positioned at the second apex area  1009 . The positioning of the coil electrodes  1022 ,  1024  at the apex areas  1007 ,  1009  may facilitate consistent contact with a vessel wall to, e.g., to sense signals therefrom, to delivery pacing therapy thereto, etc. 
     In other words, the illustrative lead  1000  depicted in  FIG. 16 . may be described as a combination of a S-shaped 3 Fr lead with coil electrodes  1022 ,  1024 . The coil electrodes  1022 ,  1024  may allow for a better conformability to the curved lead body and to the vessel wall. In other words, the coil electrodes  1022 ,  1024  may keep, or maintain, flexibility, and therefore, the electrodes  1022 ,  1024  can be designed longer than the usual tubular ring electrodes. In addition, the coil electrodes  1022 ,  1024  may be placed on, or positioned at, the apex areas  1007 ,  1009  of the S-shape  1005  to ensure contact between the coil electrodes  1022 ,  1024  and the vessel. In particular, the S-shape  1005  will press the coil electrodes  1022 ,  1024  onto the coronary vessel wall. 
     The lead  1000  of  FIG. 17  may be described as having a lead body  1101  extending from a proximal end  1102  to a distal end  1104  and defining a S-shape region  1105  proximate the distal end  1104 , a first apex area  1107  within the S-shaped region  1105 , and a second apex area  1009  within the S-shaped region  1105 . 
     Each apex area  1107 ,  1109  may be described as the areas of the lead body  1101  that deviate a maximum distance away from a central axis  1110 . More specifically, the lead body  1001  may be described as further defining a straight portion  1111  positioned proximal to the S-shaped region  1005 . The straight portion  1111  may extend along and define the central axis  1010  when undeflected. The one or both of the first and second apex areas  1107 ,  1109 , when undeflected, may be located away from the axis  1110  at a perpendicular radial distance that is greater than any other the remainder of the lead body  1101 . Additionally, it may be described that the first apex area  1107  is located on the opposite side of the axis  1110  than the second apex area  1109 . 
     Furthermore, each of the apex areas  1107 ,  1109  may be centered within one of three curve portions  1106 ,  1108 ,  1103  of the S-shaped region  1105 . In this example, the first curve portion  1106  defines a first radius  1112  and the second curve portion  1008  defines a second radius  1114 , and, when the lead  1000  is undeflected, the second radius  1114  is greater than the first radius  1112 . Additionally, the end curve portion  1103 , that is distal from the, the first curve portion  1106 , may define a third radius  1115  that is less than the first radius  1112 . 
     The lead  1100  may be described as being a quadripolar lead as the lead  1100  includes four electrodes. It is be understood that the lead  1100  may include more or less than four electrodes. In particular, as shown, the lead  1100  includes a tip electrode  1120 , a first coil electrode  1122 , a second coil electrode  1124 , and a ring electrode  1126 . The tip electrode  1120  is located and coupled to the distal end  1104  of the lead body  1101 . The first coil electrode  1122  is coupled to the lead body  1101  and positioned at the first apex area  1107 , and the second coil electrode  1124  is coupled to the lead body  1101  and positioned at the second apex area  1109 . The positioning of the coil electrodes  1122 ,  1124  at the apex areas  1107 ,  1109  may facilitate consistent contact with a vessel wall to, e.g., to sense signals therefrom, to delivery pacing therapy thereto, etc. 
     The illustrative lead  1100  depicted in  FIG. 17 . may be described as being similar to the lead  1000  of  FIG. 16 , except that the radius of the curved portions  1108 ,  1106 ,  1103  of the S-shape  1105  decreases over the length of the lead towards the distal end  1104 . The two most distal electrodes  1120 ,  1122  may be placed into smaller vessels compared to the remaining electrodes  1124 ,  1126  which may be located into larger, more proximal sections of the coronary vessels. The curve radius decreasing along the illustrative lead  1100  of  FIG. 17  may provide an ability of the lead  1100  to adapt to different vessel diameters. 
     Generally, the illustrative leads of  FIGS. 16-17  may lower the pacing capture threshold, provide better contact between the electrodes and the vessel walls, provide flexible electrodes that conform to the curved lead body and to the vessel wall, adapt to the variability of the diameters over the coronaries, and, due to the flexibility of the coil electrodes, provide better trackability in tortuous vessels. 
     The present disclosure provides various design-based methods to create an alignment or targeting feature within a delivery system, catheter, sheath, lead, or similar device. Additionally, the present disclosure could also be applied to valve delivery, stent, or any other implant delivery system. In one or more embodiments, it may be described that the present disclosure utilizes one or more markers (e.g., radiopaque markers, echogenic markers, etc.) of a specific geometric design (e.g., hemispherical annulus, annular ring/marker band, or other shape) that can be used to create a target fiducial shape when aligned. The markers may be spaced and aligned to provide a different target fiducial shape or image when in different imaging planes (e.g., fluoroscopic imaging, ultrasound imaging, etc.). When the alignment of the markers is correct, the catheter, lead, or other implantable device may be positioned in 90-degree opposition to a target site (e.g., the target site may be a substantially planar wall such as the septal wall). Thus, the alignment of the marks in 90-degree opposition may be described as giving a visual signal (e.g., a fiducial shape) to the implanting physician within the image thereby indicating that the catheter, lead, or other implantable device is aligned correctly prior to, e.g., fixating or deploying the device screw the lead or catheter or deploy the device in the preferred, target location with the appropriate, desired angle. 
     An additional approach would be to use one marker on a delivery catheter shaft and another marker on a lead being delivered by the delivery catheter. The proximal marker can be located on the delivery catheter shaft and the distal marker can be located on the lead body. Alternately, the proximal marker could also be located on the lead body and the distal marker could be located on the delivery catheter shaft. Both options would result in the markers forming a “target” fiducial shape when the delivery catheter and the lead are properly aligned. 
     The present disclosure may be described as making a difficult implanting procedure significantly easier as it provides a visual signal (e.g., fiducial shape) to the implanter that they are in the proper alignment to deploy therapy. This can translate into significant reductions in complications, procedure time, and procedure/implanter efficacy that would result in less devices used and better outcomes for the patient. Simplification of the delivery process of implantable cardiac devices, specifically the utilization of existing technologies with new modalities to create a repeatable, predictable implant are valuable, can lead to more efficient procedures, better patient outcomes, and reduced implant times. 
     Furthermore, the present disclosure may be described as providing marker bands that when aligned in a prescribed fluoroscopic or ultrasound projection will help the implanter navigate toward a desired target site or structure. In one or more embodiments, the described technology incorporates the use of radiopaque or echogenic materials incorporated in the design of delivery systems or implantable devices in conjunction with methods that guide an implanting physician to use and align the delivery tools for ideal fixation or implantation of devices. When used in a prescribed orientation, these markers may guide and help the implanter navigate three-dimensionally while the implanter is viewing a two-dimensional image (e.g., a fluoroscopic or echogenic image). 
     In at least one embodiment, the present disclosure provides methods that includes pre-procedure or intraprocedural imaging (e.g., computing tomography (CT), ultrasound, etc.) to identify general structures or points within the anatomy that are relevant to the implant procedure. This may include, among other things, septal wall thickness, septal wall angle with relation to the tricuspid valve plane, right ventricle orientation and size, etc. Further, the method may include selection of proper device for implantation having proper specifications, which may include lead length, catheter length, catheter shape, etc. The method may further include using simple tools, algorithms, and tip cards for pre-procedure planning of imaging views based on the previous steps or processes. 
     In embodiments where implantable electrodes are to be implanted in the septum to, e.g., deliver cardiac conduction system pacing therapy, the method may include typical access procedures to navigate and deliver the device (e.g., delivery catheter, lead, etc.) to the right ventricle. Additionally, in one or more embodiments, the bundle of His may be mapped to, e.g., confirm a generalized implant location and establish iso-centered orientation of right anterior and left anterior oblique fluoroscopic planes, which may have been determined during pre-procedure or intraprocedural imaging. The imaging plane developed pre-procedure may be confirmed and adjustments may be made during the implant operation. Then, the method may include moving the device to the target location and aligning the markers (e.g., radiopaque markers, echogenic markers, etc.) as viewed “live” using imaging. Once the markers are aligned as shown in the imaging plane, the device may be deployed and fixated at the target site or location. 
     In one or more embodiments utilizing echogenic catheters, a trans-thoracic echo (TTE) may be utilized to obtain optimal four chamber, short axis, and other relevant views that show the interventricular septum (IVS). Alternatively, TEE or intracardiac echocardiography (ICE) could be used to achieve similar relevant views to guide this procedure. Further, the device may be tracked with distal region or features coated with echogenic material to the target location and the position and orientation of the distal tip of the device may be evaluated using the imaging views. Based on the imaging, the device location and orientation may be adjusted to obtain perpendicular orientation of the device to the septum, and then the device may be deployed and fixated at the target site or location. 
     In other words, in one embodiment, when a distal end region of an implantable device, such as a delivery catheter or lead, that includes two or more alignable marker elements is a perpendicularly aligned to a target location such as the septum, the marker elements may create a fiducial shape (e.g., a circle, an aperture, a sight ring, etc.) known to the implanter. Thus, the implanter, upon viewing the imaging during implant, will know whether the implantable device is appropriately aligned for implantation or delivery. The present disclosure may be described as being able to reduce complexity for implanters and provide greater procedural efficiency and predictability, which will decrease complications and save valuable resources for hospital systems. Additionally, in one or more embodiments, when the two or more alignable marker elements are not perpendicularly aligned to a target location such as the septum, the marker elements may create a non-alignment fiducial shape (e.g., overlapping circles or portions of a circle, staggered rings, arrows, etc.) to indicate to the implanter that the implantable device is not aligned or imperfectly aligned. Furthermore, non-alignment fiducial shape may include features that allow the implanter to understand the direction the implantable device may be moved, flexed, or other manipulated to position the implantable device in proper alignment. 
     In view thereof, an illustrative lead  1200  implanted in a patient&#39;s heart  12  in  FIG. 18 . More specifically, the lead  1200  may extend into the heart  12  of the patient to sense electrical activity of the heart  12  and/or to deliver electrical stimulation to the heart  12 , and in particular, to sense electrical activity and/or to deliver electrical stimulation to the interventricular septum  10  of the heart  12 . For example, the lead  1200  may be configured to delivery cardiac conduction system pacing therapy to the left and/or right bundle branches, the bundle of His, etc. from a location in the septum  10 . Further, for example, the lead  1200  may be configured to delivery traditional myocardial pacing therapy to left and/or right ventricular myocardial tissue from a location in the septum  10 . In the example shown in  FIG. 18 , the lead  1200  extends through one or more veins (not shown), the superior vena cava (not shown), the right atrium  26 , and into the right ventricle  28 . Then, the lead  1200  is positioned adjacent to the septum  10  in the right ventricle  28 . Additionally, although a single lead is depicted in  FIG. 18 , it is to be understood that the lead  1200  may be used with one or more additional leads or leadless devices configured to sense electrical activity and/or deliver pacing therapy to the left ventricle, right ventricle, right atrium, etc. For example, the lead  1200  may be used in conjunction with a traditional left ventricular coronary sinus lead extending through one or more veins, the vena cava, the right atrium  26 , and into the coronary sinus  30  to a region adjacent to the free wall of the left ventricle  32  of the heart  12  and/or a right atrial lead extending through one or more veins and the vena cava, and into the right atrium  26  of the heart  12 . 
     Additionally, as diagrammatically shown, the lead  1200  may be operably coupled to an implantable medical device (IMD)  16 . The IMD  16  may sense, among other things, electrical signals attendant to the depolarization and repolarization of the heart  12  via electrodes coupled to the lead  1200  or another lead such as a left ventricular lead, right atrial lead, etc. In some examples, the IMD  16  provides pacing therapy (e.g., pacing pulses) to the heart  12  based on the electrical signals sensed within the heart  12 . The IMD  16  may be operable to adjust one or more parameters associated with the pacing therapy such as, e.g., A-V delay and other various timings, pulse wide, amplitude, voltage, burst length, etc. Further, the IMD  16  may be operable to use various electrode configurations to deliver pacing therapy, which may be unipolar, bipolar, quadripolar, or further multipolar. For example, a multipolar lead may include several electrodes that can be used for delivering pacing therapy. Hence, a multipolar lead system may provide, or offer, multiple electrical vectors to pace from. A pacing vector may include at least one cathode, which may be at least one electrode located on at least one lead, and at least one anode, which may be at least one electrode located on at least one lead (e.g., the same lead, or a different lead) and/or on the casing, or can, of the IMB. While improvement in cardiac function as a result of the pacing therapy may primarily depend on the cathode, the electrical parameters like impedance, pacing threshold voltage, current drain, longevity, etc. may be more dependent on the pacing vector, which includes both the cathode and the anode. 
     The septal pacing lead  1200  may be described as including a body  1201  extending from a proximal end region  1202  to a distal end region  1204 . The proximal end region or portion  1202  may be located proximate the IMD  16  for operably coupling thereto and the distal end region or portion  1204  may be locatable, or positioned, at a target site, which in the example depicted in  FIG. 18  is the intraventricular septum  10 . 
     In the embodiment depicted, the distal end region  1204  may extend along a distal end region axis  1205 . More specifically, the distal end region axis  1205  may be a straight, uncurving line, which the distal end region  1204  may extend along, and thus, the distal end region  1204  may also define a straight, uncurving line. In other embodiments, the distal end region  1204  may not extend along an axis, and may, for example, define a variety of different shapes or curves, and the alignable marker elements described further herein, may be configured to take into account the shape and curvature of the distal end region  1204 . 
     The distal end region  1204  of the lead  1200  is depicted in  FIG. 19A . As shown in this embodiment, the lead  1200  further includes two alignable marker elements  1210 A,  1210 B coupled to the body  1201 . Each of the alignable marker elements  1210  defines a complementary shape that complements the other alignable marker element such that, when the distal end region  1204  is viewed axially, the two alignable marker elements  1210  form a fiducial shape indicative of acceptable alignment of the distal end region  1204  for positioning at a target site (e.g., in alignment with the target site). 
     The alignable marker elements  1210  may include one or more materials capable of being imaged when located inside a patient (e.g., capable of being imaged through tissue) such as, e.g., when located inside the heart of a patient. For example, the alignable marker elements  1210  may include one or more of radiopaque materials viewable through fluoroscopy, echogenic materials viewable with ultrasound, etc. The radiopaque materials may include one or more of gold, platinum, platinum/iridium, titanium, tantalum, barium silicate, barium tungsten, barium sulfate, bismuth trioxide, bismuth oxychloride, bismuth subcarbonate, and/or combinations or compounds thereof. The echogenic materials may include one or more of perfluorocarbon, coated tungsten, tungsten carbide particles distributed within a base polymeric material, etc. 
     The alignable marker elements  1210  may be partially or fully embedded within the body  1201  of the lead  1200  such that some or no portions of the alignable marker elements  1210  may be exposed to, e.g., body fluid, tissue, etc. In one embodiment, the alignable marker elements  1210  may also provide other functionality such as pacing and/or sensing electrodes, and thus, may be electrically coupled to circuity including conductors and the IMD  16 . 
     The distal end region  1204  may define a distal end region length  1207  that may vary depending on application. The distal end region  1204  may be defined by the portion of the lead body  1201  that extends in a straight line along the distal end region axis  1205 . In the present application of pacing the septum  10  from the right ventricle  28 , the distal end region length  1207  may be between about 5 millimeters (mm) and about 20 mm. Additionally, the alignable marker elements  1210  may be spaced apart from each other at a spacing distance  1209 . In other words, the most distal alignable marker element  1210 A, which may be referred to as the distal alignable marker element  1210 A, may be located the spacing distance  1209  away from the most proximal alignable marker element  1210 B, which may be referred to as the proximal alignable marker element  1210 B. Similar to the distal end region length  1207 , the spacing distance  1209  may vary depending on application. In the present application of pacing the septum  10  from the right ventricle  28 , the spacing distance  1209  may be between about 3 mm and about 30 mm. In at least one embodiment, the spacing distance  1209  is 10 mm. Additionally, the spacing distance  1209  may be selected and/or the shape and size of the alignable marker elements may be adjusted depending on the target site and tolerance of implantation thereto. For example, when implanting a lead into the intraventricular septum, acceptable alignment may be within 20% to being substantially perpendicular to the septum. Thus, the spacing distance  1209  may be selected and/or the size and shape of the alignable marker elements  1210  may be adjusted to achieve the with 20% of perpendicular for this implant location. 
     Furthermore, the distal alignable marker element  1210 A may be located proximate the distal end  1203  of the lead  1200 , which may be configured to be adjacent, or in contact, with the target site or location when the lead  1200  is properly implanted. Additionally, although not shown in  FIG. 19A  but shown in  FIG. 18 , the lead  1200  may further include a fixation element  1215  extending from the distal end  1203  configured to fixate or attached the distal end  1203  of the lead  1200  to the target site. In one embodiment, the fixation element  1215  may be a helical fixation element that may be “screwed” into tissue such as the septum  10 . 
     As described herein, each of the alignable marker elements  1210  defines a complementary shape that complements the other alignable marker element such that, when the distal end region  1204  is viewed axially, the two alignable marker elements  1210  form a fiducial shape indicative of acceptable alignment of the distal end region  1204  for positioning at a target site. The complementary shapes of the alignable marker elements  1210  can be virtually any shape or size so as to provide the functionality of being able to determine whether the distal end region  1204  is properly aligned at the target site when viewed axially (e.g., looking along the distal end region axis  1205 , in imaging plane perpendicular to the distal end region axis  1205 , etc.). Additionally, as will be described further herein, the complementary shapes of the alignable marker elements  1210  can be virtually any shape or size so as to provide the functionality of being able to determine in what direction the distal end region  1204  is not aligned to the target site when viewed axially (e.g., looking along the distal end region axis  1205 , in imaging plane perpendicular to the distal end region axis  1205 , etc.). 
     For example, the complementary shape of each of the two alignable marker elements  1210  in  FIG. 19A  is a semicircle. The semicircular shape of the proximal alignable marker element  1210 B opens in an opposite direction to the semicircular shape of the distal alignable marker element  1210 A. Thus, when the distal end region  1204  of  FIG. 19A  is imaged axially, the fiducial shape would be the combination of the two opposite semicircles, which is a single circle. Additionally, when the distal end region  1204  of  FIG. 19A  is imaged off axis, the two opposite semicircles would not combine to form, or define a single circle, and thus, not providing a fiducial shape. 
     Another example is depicted in  FIG. 19B  where each of the two alignable marker elements  1210  has the same complementary shape, which is a circle. Thus, when the distal end region  1204  of  FIG. 19B  is imaged axially, the fiducial shape would be the combination of the two circles, which is a single circle. Additionally, when the distal end region  1204  of  FIG. 19B  is imaged off axis, the two circles of the two alignable marker elements  1210  would not combine to form, or define a single circle, and instead, would depict two separate circles or two circles only partially overlapping, and thus, not provide a fiducial shape. 
     Other examples of complementary shapes for the alignable marker elements may include complete or partial triangles, pentagons, squares, rectangles, alphanumeric symbols, “puzzle” shapes, a zig-zag, etc. 
     Simulated right anterior oblique (RAO) fluoroscopic images taken 20 degrees off perpendicular to the septum depicting the lead  1200  including two alignable marker elements  1210  of  FIG. 19B  are shown in  FIGS. 20A and 20B . As shown, the distal end region  1204  is not in alignment in  FIG. 20A  as the two alignable marker elements  1210 , which are both circles, do not even partially overlap to create the fiducial shape of a single circle. Instead, the simulated RAO fluoroscopic image clearly shows two separate circles, each from a different alignable marker element  1210 , thereby indicating that the distal end region  1204  is not aligned perpendicularly to the RAO imaging plane. 
     Conversely, the distal end region  1204  is in alignment in  FIG. 20B  as the two alignable marker elements  1210 , which are both circles, overlap to create the fiducial shape of a single circle. More specifically, the simulated RAO fluoroscopic image clearly shows a single circle as opposed to two separate circles or a shape formed by partially overlapping circles, thereby indicating that the distal end region  1204  is aligned perpendicularly to the RAO imaging plane. 
     Another illustrative lead  1200  is depicted in  FIGS. 21-23  that includes two alignable marker elements  1210  that each have complementary shapes that are complete circles. More specifically, diagrammatic side views of the distal lead region  1204  with respect to a target site and illustrative images taken perpendicular to the target site are shown with the distal lead region  1204  in alignment in  FIGS. 21A and 21B  and out of alignment in  FIGS. 22A   22 B. More specifically, as shown in  FIG. 21A , the distal end region axis  1205  of the distal end region  1204  is substantially perpendicular to the target site  1250 , e.g., the intraventricular septum, and thus, the image taken perpendicular to the target site depicted in  FIG. 21B  depicts the fiducial shape of a single circle. Further, as shown in  FIG. 22B , the distal end region axis  1205  of the distal end region  1204  is substantially not perpendicular to the target site  1250 , e.g., the intraventricular septum, (e.g., instead, the distal end region axis  1205  is about 30 degrees away from perpendicular), and thus, the image taken perpendicular to the target site depicted in  FIG. 22B  does not depict the fiducial shape of a single circle, and instead, depicts two separate circles. 
     A simulated right anterior oblique (RAO) fluoroscopic image taken 20 degrees off perpendicular to the septum depicting the distal lead region  1204  as aligned in  FIGS. 21A  is shown in  FIG. 23A . As can been seen in the image of  FIG. 23A , a fiducial shape of a single circle is present indicating alignment. Conversely, a simulated RAO fluoroscopic image taken 20 degrees off perpendicular to the septum depicting the distal lead region  1204  as unaligned in  FIGS. 22A  is shown in  FIG. 23B . As can been seen in the image of  FIG. 23B , no fiducial shape of a single circle is present, and instead, two separate circles are present indicating non-acceptable alignment. 
     Another illustrative lead  1200  is depicted in  FIGS. 24-26  that includes two alignable marker elements  1210  that each have complementary shapes that are opposing semicircles (e.g., half circles facing with the open sides facing each other). More specifically, diagrammatic side views of the distal lead region  1204  with respect to a target site and illustrative images taken perpendicular to the target site are shown with the distal lead region  1204  in alignment in  FIGS. 24A and 24B  and out of alignment in  FIGS. 25A and 25B . More specifically, as shown in  FIG. 24A , the distal end region axis  1205  of the distal end region  1204  is substantially perpendicular to the target site  1250 , e.g., the intraventricular septum, and thus, the image taken perpendicular to the target site depicted in  FIG. 24B  depicts the fiducial shape of a single circle. Further, as shown in  FIG. 24B , the distal end region axis  1205  of the distal end region  1204  is substantially not perpendicular to the target site  1250 , e.g., the intraventricular septum, (e.g., instead, the distal end region axis  1205  about 30 degrees away from perpendicular), and thus, the image taken perpendicular to the target site depicted in  FIG. 25B  does not depict the fiducial shape of a single circle, and instead, depicts two separate semicircles spaced apart from one another. 
     A simulated right anterior oblique (RAO) fluoroscopic image taken 20 degrees off perpendicular to the septum depicting the distal lead region  1204  as aligned in  FIGS. 24A  is shown in  FIG. 26A . As can been seen in the image of  FIG. 26A , a fiducial shape of a single circle is present indicating alignment. Conversely, a simulated RAO fluoroscopic image taken 20 degrees off perpendicular to the septum depicting the distal lead region  1204  as unaligned in  FIGS. 25A  is shown in  FIG. 26B . As can been seen in the image of  FIG. 26B , no fiducial shape of a single circle is present, and instead, two separate semicircles spaced apart from one another are present indicating non-acceptable alignment. 
     Another illustrative lead  1300  aligned with respect to the target site  1250  and including two alignable marker elements  1310  that each have complementary shapes is depicted in  FIGS. 28A-28C . The first alignable marker element  1310 A includes two arcuate portions of a circle and the second alignable marker element  1310 B includes a single arcuate portion of a circle or a semicircle. A cross sectional view of the lead body  1301  including the first alignable marker element  1310 A taken across line  1399  is shown in  FIG. 28C , and a cross sectional view of the lead body  1301  including the second alignable marker element  1310 B taken across line  1398  is shown in  FIG. 28B . As shown in  FIG. 28A , the distal end region axis  1305  of the distal end region  1304  is substantially perpendicular to the target site  1250 , e.g., the intraventricular septum, and thus, an image taken perpendicular to the target site depicted in  FIG. 28D  shows the fiducial shape of a single U-shape. Images taken perpendicular to the target site where the distal end region axis  1305  of the distal end region  1304  is not substantially perpendicular to the target site  1250  are shown in  FIGS. 28E and 28F , where the first and second alignable marker elements  1310 A,  1310 B do not form the fiducial (such as the shape of a single U), thereby indicating misalignment. 
     Another illustrative lead  1400  aligned with respect to the target site  1250  and including two alignable marker elements  1410  that each have complementary shapes is depicted in  FIGS. 29A-29C . The first alignable marker element  1410 A includes a single arcuate portion of a circle (in particular, a semicircle extending approximately 90 degrees) and the second alignable marker element  1410 B also includes a single arcuate portion of a circle (in particular, a semicircle extending 180 degrees). A cross sectional view of the lead body  1401  including the first alignable marker element  1410 A taken across line  1499  is shown in  FIG. 29C , and a cross sectional view of the lead body  1401  including the second alignable marker element  1410 B taken across line  1498  is shown in  FIG. 29B . As shown in  FIG. 29A , the distal end region axis  1405  of the distal end region  1404  is substantially perpendicular to the target site  1250 , e.g., the intraventricular septum, and thus, an image taken perpendicular to the target site depicted in  FIG. 29D  shows the fiducial shape of a single U-shape opened to the upper left. Images taken perpendicular to the target site where the distal end region axis  1405  of the distal end region  1404  is not substantially perpendicular to the target site  1250  are shown in  FIGS. 29E and 29F , where the first and second alignable marker elements  1410 A,  1410 B do not form the fiducial shape (such as the shape of a single U), thereby indicating misalignment. 
     Another illustrative lead  1500  aligned with respect to the target site  1250  and including two alignable marker elements  1510  that each have complementary shapes is depicted in  FIGS. 30A-30B . The first alignable marker element  1510 A may be a circular, or ring shaped, element and the second alignable marker element  1510 B may be a portion of a circle (e.g., semicircle). In this embodiment, the first alignable marker element  1510 A and the second alignable mark element  1510 B define, or are, different sizes. In particular, the first alignable marker element  1510 A defines a first length  1519  and the second marker element  1510 B defines a second length  1512  that is shorter, or less, than the first length  1519 . In one embodiment, the first length  1519  may be about  3  mm and the second length  1512  may be about  1  mm. It is be understood that, in other embodiments, the first marker element  1510 A may have, or define, a length  1519  that is smaller, or less, than a length  1512  of the second marker element  1510 B. The alignable marker elements having different lengths may help physicians to identify at-tip or behind-tip during advancing or rotating of the lead body  1501 . Further, physicians may use a left anterior oblique (LAO) image or view, as shown in  FIG. 30B , to check direction of catheter tip against septum, and depth pacing lead penetration. An LAO image may be taken from direction  1509  as shown in  FIG. 30A . 
     A perspective view of two alignable marker elements  1550 A,  1550 B coupled using two extension elements  1511  is shown in  FIG. 31 . Although two extension elements  1511  are depicted herein, it is to be understood that one extension element or more than two extensions elements may be utilized. The extensions elements  1511  may provide fixed spacing between two alignable marker elements  1550 A,  1550 B such that, e.g., a physician may be able to use the distance between the two alignable marker elements  1550 A,  1550 B to determine penetration depth into the target region such as e.g., the ventricular septum. The extensions elements  1511  may comprise, or be formed of, the same material as the alignable marker elements  1550 A,  1550 B. In at least one embodiment, the two alignable marker elements  1550 A,  1550 B and two extension elements  1511  may be machined from tubing, which would aid in manufacturing and provide a given distance between the alignable marker elements  1550 A,  1550 B. The fixed spacing, or given distance, may allow a physician to make a small calculation to determine the angle of approach to the septal wall. Additionally, the extensions elements  1511  may assist in stiffening a distal end region of a lead (in other words, the distal end of the region may be more resilient as a result of the extension elements  1511  coupling the alignable marker elements  1550 A,  1550 B), which can negate effects of bending that may lead to misalignment during implantation. In at least one embodiment, the two alignable marker elements  1550 A,  1550 B and extension elements  1511  may be provided to the additive manufacturing systems described herein with respect to  FIGS. 1-6 . 
     Another illustrative lead  1600  aligned with respect to the target site  1250  and including two alignable marker elements  1610  that each have complementary shapes is depicted in  FIGS. 32A-32C . The first alignable marker element  1610 A includes four arcuate portions of a circle and the second alignable marker element  1610 B includes three arcuate portions of a circle. Thus, the alignable marker elements  1610  of the lead  1600  are asymmetric, which may be used by a physician to determine where the distal end  1603  of the lead  1600  is located when viewed on imaging. Additionally, a physician may utilize the asymmetric alignable marker elements  1610  to count turns of the distal end region  1604  of the lead body  1601  about the axis  1605 , for example, when implanting a fixation element such as a helix in the target site  1250 . A cross sectional view of the lead body  1601  including the first alignable marker element  1610 A taken across line  1699  is shown in  FIG. 32C , and a cross sectional view of the lead body  1601  including the second alignable marker element  1610 B taken across line  1698  is shown in  FIG. 32B . As shown in  FIG. 32A , the distal end region axis  1605  of the distal end region  1604  is substantially perpendicular to the target site  1250 , e.g., the intraventricular septum, and thus, an image taken perpendicular to the target site depicted in  FIG. 32D  depicts the fiducial shape of nearly complete circle defining a gap  1615 . In one or more embodiments, the alignable marker elements  1610  may be configured such that the gap  1615  indicates the direction of deflection  1650 , e.g., via a pull-wire or the like, of the lead body  1601 . Thus, it may be described that, when the alignable marker elements  1610  were aligned, the deflection direction  1650  may be shown in the imaging to aid a physician in alignment of the distal end region  1604  with the target site  1250 . 
     Another illustrative lead  1700  aligned with respect to the target site  1250  and including two alignable marker elements  1710  that each have complementary shapes is depicted in  FIGS. 33A-33C . Each of the first alignable marker element  1710 A and the second alignable marker element  1710 B are circles or rings, each having a different diameter. In this example, the first alignable marker element  1710 A defines a smaller diameter than, the second alignable marker element  1710 B. Thus, the alignable marker elements  1710  of the lead  1700  are asymmetric, which may be used by a physician to determine the distal end  1703  of the lead  1700  when viewed on imaging. A cross sectional view of the lead body  1701  including the first alignable marker element  1710 A taken across line  1799  is shown in  FIG. 33C , and a cross sectional view of the lead body  1701  including the second alignable marker element  1710 B taken across line  1798  is line shown in  FIG. 33B . As shown in  FIG. 33A , the distal end region axis  1705  of the distal end region  1604  is substantially perpendicular to the target site  1250 , e.g., the intraventricular septum, and thus, a RAO image taken perpendicular to the target site  1250  depicted in  FIG. 33E  depicts the fiducial shape of two concentric circles. A RAO image taken perpendicular to the target site where the distal end region axis  1705  of the distal end region  1704  is not substantially perpendicular to the target site  1250  is shown in  FIG. 33D , where the first and second alignable marker elements  1710 A,  1710 B do not form the fiducial shape and instead form a single circle thereby indicating misalignment. In other words, the alignable marker elements  1710 A,  1710 B may be used to align and also to differentiate which direction the distal end region  1704  is pointing. If the smaller diameter, first alignable marker element  1710 A is closer to the viewer (e.g., from where the imaging is being captured or taken), then the alignable marker elements  1710 A,  1710 A appear concentric. Conversely, if the larger diameter, second alignable marker element  1710 B is closer to the viewer (e.g., from where the imaging is being captured or taken), then the alignable marker elements  1710 A,  1710 A will overlap and appear as a single circle. 
     Illustrative alignable marker elements  1810  may be included as part of a coil or helix as shown in the illustrative lead  1800  aligned with respect to the target site  1250  in  FIG. 34A . In this embodiment, the lead  1800  includes an imageable coil  1811 , e.g., comprising imageable material, positioned in a distal end region  1804  that may be described as including a plurality of alignable marker elements, each alignable marker element being a single  360  turn of the coil  1811 . Two alignable marker elements are labeled in the embodiment of  FIG. 34 : a first alignable marker element  1810 A; and a second alignable marker element  1810 B. Perpendicular and parallel views of this embodiment may be used to determine alignment of distal end region  1804  of the lead body  1801  with the target site  1250  as shown in with respect to  FIGS. 34B-34G . 
     For instance, the lead  1800  is aligned in  FIGS. 34B and 34C , which are illustrative images, the former taken parallel to the target site  1250  (e.g., radially to the axis  1805 ) and the later taken perpendicular to the target site  1250  (e.g., axially to the axis  1805 ). The coil  1811  includes uniform spacing between coils in  FIG. 34B  and forms a fiducial shape of a circle in  FIG. 34C  thereby indicating that the lead  1800  is oriented towards the target site. Further, the lead  1800  is not aligned to the target site  1250  in  FIGS. 34D-34G , which are also illustrative images where  FIGS. 34D and 34F  are taken parallel to the target site  1250  and  FIGS. 34E and 34G  are taken perpendicular (e.g., RAO) to the target site  1250 . The coil  1811  does not have uniform spacing or uniform shape between coils in  FIG. 34D  and does not form a fiducial shape of a circle in  FIG. 34E  (e.g., horizontally overlapping circles are shown) thereby indicating that the lead  1800  is misaligned with respect to the target site  1250 . Likewise, the coil  1811  appears tilted or angled in  FIG. 34F  and does not form a fiducial shape of a circle in  FIG. 34G  (e.g., vertically overlapping circles are shown) thereby indicating that the lead  1800  is misaligned with respect to the target site  1250 . In one or more embodiments, a decoder (e.g., a set of examples of the shape of the coil  1811  when in parallel to the target site  1250  at various angles) may be used to determine the offset angle or angle not perpendicular to the target site  1250 . Further, in at least one embodiment, the coil  1811  could be variable pitch to aid in diagnosis of offset. 
     Optionally, this embodiment also includes a tip alignable marker element  1810 C, which is not part of the coil  1811 . The orientation of a distal end  1803  of the distal end region  1804  would be able to be determined using the tip alignable marker element  1810 C with respect to the coil  1811 . Additionally, the tip alignable marker element  1810 C would “stack” with the coil  1811  creating a fiducial shape of a concentric bright ring when viewed axially along the axis  1805  as shown in  FIG. 34C . 
     As described herein, the illustrative implantable medical devices, e.g., leads, catheters, etc. may include more than two alignable marker elements. An illustrative lead  1900  positioned in an unintended and less desirable alignment with respect to the target site  1250  is depicted in  FIG. 35A . The lead  1900  includes four alignable marker elements  1910 A,  1910 B,  1910 C,  1910 D. Alignable marker elements  1910 A,  1910 C are circular and alignable marker elements  1910 B,  1910 D are semicircular such that when the distal end region  1904  is of the lead  1900  is misaligned, an image, taken perpendicular to the target site of  FIG. 35A  will show two circles, one of which is darker or thicker than the other, as shown in  FIG. 35B . The darker circle being above the lighter circle, in this example, shows that the distal end or tip  1903  is pointing up. In other words, the distal region  1904  of the lead  1900  is misaligned vertically in the upward direction. 
     One or more alignable marker elements may define a directionally indicative shape that, when viewed using imaging, may indicate the direction of the distal end region with respect to the target site. An aligned illustrative lead  2000  including a directionally indicative alignable marker element  2010  being positioned proximate a target site  1250  is depicted in  FIG. 36A . As shown, the distal end region  2004  is positioned substantially perpendicular to the target site  1250  (e.g., the distal axis  2005  extending along the distal end region  2004  is perpendicular to a plane of the target site  1250 ). In this embodiment, the directionally indicative alignable marker element  2010  includes, or defines, an arrow shape that points towards the distal end, or tip,  2003  of the lead body  2001 . An illustrative image, taken perpendicular to the target site  1250 , where the lead is positioned and oriented as shown in  FIG. 36A , is shown in  FIG. 36B . As shown in  FIG. 36B , the arrow is not visible since the distal end region  2004  is substantially aligned with (e.g., perpendicular to) the target site  1250 . Illustrative images, taken perpendicular to the target site of  FIG. 36A , where the lead is not positioned and oriented as intended are shown in  FIGS. 36C and 36D . As shown in  FIG. 36C , the “arrow” image appears to point upward, which may indicate that the distal end region  2004  is vertically misaligned upwardly. As shown in  FIG. 36C , the “arrow” image appears to point down and to the left, which may indicate that the distal end region  2004  is vertically misaligned downwardly and horizontally misaligned to the left. 
     As described herein, multiple alignable marker elements may be utilized that define different shapes and sizes. A perspective view of an illustrative lead  2100  including a plurality of alignable marker elements  2110  having trapezoidal shapes in depicted in  FIG. 37 . In other words, the “wedge”-shaped alignable marker elements  2110  may define, or form, the fiducial shape of an annular ring when aligned. When the distal end region  2104  is not aligned, the long trapezoid shape of the alignable marker elements  2110  may create, or generate, a shadow type projection indicating that the distal end region  2104  is offset. Additionally, in other views, orientation can be determined based on nonuniform geometry of the alignable marker elements  2110 . 
     A few more embodiments including a plurality of alignable marker elements are depicted in  FIGS. 38-39 . An aligned illustrative lead  2200  including a plurality of alignable marker elements  2210 A,  2210 B being positioned proximate a target site  1250  is depicted in  FIG. 38A . In this embodiment, each of the first alignable marker element  2210 A and the second alignable marker element  2210 B include, or comprise, a plurality of marker portions arranged in a circular fashion and spaced about circumferentially and axially. An additional side view of the distal region  2204  of the lead  2200  rotated about the axis  2205  90 degrees from the view of  FIG. 38A  is depicted in  FIG. 38B . As shown in  FIG. 38A , the distal end region axis  2205  of the distal end region  2204  is substantially perpendicular to the target site  1250 , e.g., the intraventricular septum, and thus, an image taken perpendicular to the target site  1250  depicted in  FIG. 38C  shows the fiducial shape of a broken circle. Additionally, it may be described that “clear” slots indicate perfect alignment. Another image taken perpendicular to the target site where the distal end region axis  2205  of the distal end region  2204  is not substantially perpendicular to the target site  1250  is shown in  FIG. 38D , where the first and second alignable marker elements  2210 A,  2210 B do not form the fiducial shape and instead overlap thereby indicating misalignment. Additionally, the longer span, or distance, between the first alignable marker element  2210 A and the second alignable marker element  2210 B may allow better resolution in axial view alignment. 
     An aligned illustrative lead  2300  including a plurality of alignable marker elements  2310 A,  2310 B,  2310 C,  2310 D being positioned proximate a target site  1250  is depicted in  FIG. 39A . In this embodiment, each of the alignable marker elements  2310 A,  2310 B,  2310 C,  2310 D include, or comprise, two semi circles or arcs opposite each other about the leady body  2301 . Further, the alignable marker elements  2310 A,  2310 B,  2310 C,  2310 D are uniformly spaced from each other along the distal end axis  2305 . As shown in  FIG. 39A , the distal end region axis  2305  of the distal end region  2304  is substantially perpendicular to the target site  1250 , e.g., the intraventricular septum, and thus, an image taken perpendicular to the target site  1250  depicted in  FIG. 39B  shows the fiducial shape of a two partial circles or arcs opposite each other. An image taken perpendicular to the target site where the distal end region axis  2305  of the distal end region  2304  is not substantially perpendicular to the target site  1250  is shown in  FIG. 39C , where the plurality of alignable marker elements  2310 A,  2310 B,  2310 C,  2310 D do not form the fiducial shape and instead overlap thereby indicating misalignment. Additionally, a blurry or out of focus image may also indicate unintended alignment. When imaged or view laterally (e.g., from the side), clear slots between alignable marker elements  2310 A,  2310 B,  2310 C,  2310 D indicate between acceptable alignment. In one or more embodiments, one or more of the alignable marker elements  2310 A,  2310 B,  2310 C,  2310 D may only include a single arc, which may be used to indicate a deflection plane. Additionally, a longer span, or distance, between the alignable marker elements  2310 A,  2310 B,  2310 C,  2310 D may provide, or allow, better resolution in axial view alignment. When imaged or view laterally (e.g., from the side), too many bars or stripes may indicate misalignment because both of the two arcs of each of the alignable marker elements  2310 A,  2310 B,  2310 C,  2310 D may be visible as opposed to overlapping. 
     It is to be understood that the alignable marker element concepts described herein may be utilized with any implantable medical device such as, e.g., leads, catheters, leadless devices, etc. Further, in one or more embodiments, one alignable marker element may be located on a delivery catheter and another alignable element may be located on the device being delivered by the delivery catheter (such as, e.g., a lead). 
     While the present disclosure is not so limited, an appreciation of various aspects of the disclosure will be gained through a discussion of the specific examples and illustrative embodiments provided below. Various modifications of the examples and illustrative embodiments, as well as additional embodiments of the disclosure, will become apparent herein. 
     ILLUSTRATIVE EXAMPLES 
     Example 1: An implantable apparatus comprising: 
     a body defining a distal end region extending along a distal end region axis; and 
     two alignable marker elements coupled to the body within the distal end region, wherein each of two alignable marker elements defines a complementary shape that complements the other alignable marker element such that, when the distal end region is viewed axially, the two alignable marker elements form a fiducial shape indicative of acceptable alignment of the distal end region for positioning at a target site. 
     Example 2: The apparatus of example 1, wherein the two alignable marker elements are radiopaque and viewable when located within a patient&#39;s heart using fluoroscopy. 
     Example 3: The apparatus of example 1, wherein the two alignable marker elements are echogenic and viewable when located within a patient&#39;s heart using ultrasound. 
     Example 4: The apparatus as in any one of examples 1-3, wherein the complementary shape of each of the two alignable marker elements is a circle and the fiducial shape is a single circle. 
     Example 5: The apparatus as in any one of examples 1-3, wherein the complementary shape of each of the two alignable marker elements is a semicircle and the fiducial shape is a single circle. 
     Example 6: The apparatus as in any one of examples 1-3, wherein the complementary shape of each of the two alignable marker elements is at least a portion of a circle and the fiducial shape is at least a portion of a single circle. 
     Example 7: The apparatus as in any of examples 1-6, wherein each of the two alignable marker elements defines a different size than each other. 
     Example 8: The apparatus as in example 7, wherein a first alignable marker element of the two alignable marker elements defines a first length along the distal end region axis and a second alignable marker element of the two alignable marker elements defines a second length along the distal end region axis, wherein the first length is greater than the second length. 
     Example 9: The apparatus as any one of examples 7-8, wherein each of the two alignable marker elements defines a different diameter than each other. 
     Example 10: The apparatus as in any one of examples 1-3, wherein the complementary shape of each of the two alignable marker elements comprises a plurality of portions of circle and the fiducial shape is a near-complete portion of a single circle defining a gap, wherein the gap is indicative of deflection direction of the body. 
     Example 11: The apparatus as in example 10, wherein a first alignable marker element of the two alignable marker elements comprises a first number of portions of the circle and a second alignable marker elements of the two alignable marker elements a second number of portions of the circle, wherein the first number is greater than the second number. 
     Example 12: The apparatus as in any one of examples 1-11, further comprising at least one additional alignable marker element that defines another complementary shape that complements the two alignable marker elements such that, when the distal end region is viewed axially, the two alignable marker elements and the at least one additional alignable marker element form the fiducial shape indicative of acceptable alignment of the distal end region for positioning at the target site. 
     Example 13: The apparatus as in example 12, wherein the at least one additional alignable marker element defines a different size than at least one of the two alignable marker elements, wherein, when the distal end region is viewed axially, the two alignable marker elements and the at least one additional alignable marker element form a non-alignment fiducial shape indicative of unacceptable alignment of the distal end region. 
     Example 14: The apparatus as in any one of examples 1-13, wherein the two alignable marker elements define a coil extending along the distal axis, wherein, when the distal end region is viewed radially, a minimum length between the two alignable marker elements is indicative of acceptable alignment of the distal end region for positioning at the target site. 
     Example 15: The apparatus as in any one of examples 1-13, further comprising at least one extension member coupled to and extending between the two alignable marker elements. 
     Example 16: The apparatus as in any of examples 1-15, wherein the body is a delivery catheter or a lead. 
     Example 17: The apparatus as in any of examples 1-15, wherein the body comprises: 
     a delivery catheter defining a lumen, wherein a first alignable marker element of the two alignable marker elements is coupled to the delivery catheter; and 
     a lead located within the delivery catheter, wherein a second alignable marker element of the two alignable marker elements is coupled to the lead. 
     Example 18: The apparatus as in any of examples 1-17, further comprising a fixation element coupled to the distal end region of the body to couple the body to the target site. 
     Example 19: An implantable apparatus comprising: 
     a body defining a distal end region extending along a distal end region axis; and 
     an alignable marker element coupled to the body within the distal end region defining a directionally indicative shape that, when the distal end region is viewed axially, is indicative of the direction of the distal end region away a target site. 
     Example 20: An additive manufacturing system comprising: 
     one or more heating cartridges, each extending from a proximal side to a distal side and comprising a substrate inlet port at the proximal side and a substrate outlet port at the distal side, each heating cartridge defining an interior volume and a substrate channel extending through the interior volume from the proximal side to the distal side, each heating cartridge defining a first filament port in fluid communication with the interior volume to receive a first filament; 
     a heating element thermally coupled to each heating cartridge of the one or more heating cartridges to heat the interior volume; 
     a filament handling system comprising one or more motors to feed at least the first filament through the first filament port into the interior volume; 
     a substrate handling system comprising: 
     a head stock comprising a distal clamp to secure a distal portion of an elongate substrate, wherein the substrate is positioned to pass through the substrate channel when secured by the head stock; and 
     one or more motors to translate or rotate one or both of the substrate when secured by the head stock and the heating cartridge relative to one another; 
     an intermediate component system positioned proximate the heating cartridge to position two alignable marker elements, wherein each of two alignable marker elements defines a complementary shape that complements the other alignable marker element; and 
     a controller operably coupled to the heating element, one or more motors of the filament handling system, and one or more motors of the substrate handling system, the controller configured to:
         control the one or more motors of the filament handling system to selectively control the feeding of the first filament into the interior volume;   activate the heating element to melt any portion of the first filament in the interior volume;   control one or more motors of the substrate handling system to move one or both of the substrate and the one or more heating cartridges relative to one another in at least a longitudinal direction to form a first elongate catheter jacket around the substrate; and   control the intermediate component system to deposit the two alignable marker elements on the first elongate catheter jacket within a distal end region element extending along a distal end region axis such that, when the distal end region is viewed axially, the two alignable marker elements form a fiducial shape indicative of acceptable alignment of the distal end region for positioning at a target site.       

     Example 21: The system as in example 20, wherein the controller is further configured to: 
     control the one or more motors of the filament handling system to selectively control the feeding of a second filament into the interior volume; 
     activate the heating element to melt any portion of the second filament in the interior volume; and 
     control one or more motors of the substrate handling system to move one or both of the substrate and the one or more heating cartridges relative to one another in at least a longitudinal direction to form a second elongate catheter jacket around the first elongate catheter jacket and the two alignable marker elements. 
     Example 22: The system as in any one of examples 20-21, wherein the two alignable marker elements are radiopaque and viewable when located within a patient&#39;s heart using fluoroscopy. 
     Example 23: The system as in any one of examples 20-21, wherein the two alignable marker elements are echogenic and viewable when located within a patient&#39;s heart using ultrasound. 
     Example 24: The system as in any one of examples 20-23, wherein the complementary shape of each of the two alignable marker elements is at least one portion of a circle and the fiducial shape is a single circle. 
     Example 25: A method for navigating an implantable apparatus in a patient&#39;s heart comprising: 
     providing an implantable apparatus comprising:
         a body defining a distal end region extending along a distal end region axis; and   two alignable marker elements coupled to the body within the distal end region, wherein each of two alignable marker elements defines a complementary shape that complements the other alignable marker element such that, when the distal end region is viewed axially, the two alignable marker elements form a fiducial shape;       

     navigating the distal end region proximate a target site; 
     generating an image taken perpendicular to the target site of the alignable marker elements; and 
     determining that the alignable marker elements form the fiducial shape in the generated image indicating acceptable alignment of the distal end region. 
     Example 26: The method as in example 25, further comprising: 
     adjusting one or both of orientation and location of the distal end region proximate the target site if the alignable marker elements do not form the fiducial shape in the generated image; 
     generating another image taken perpendicular to the target site of the alignable marker elements; and 
     determining that the alignable marker elements form the fiducial shape in the generated another image indicating acceptable alignment of the distal end region. 
     Example 27: The method as in any one of examples 25-26, wherein the image taken perpendicular to the target site of the alignable marker elements is a left anterior oblique image of the patient&#39;s heart. 
     Example 28: The method as in any one of examples 25-27, wherein the two alignable marker elements are radiopaque and viewable when located within a patient&#39;s heart using fluoroscopy, wherein the image taken perpendicular to the target site of the alignable marker elements is a fluoroscopic image. 
     Example 29: The method as in any one of examples 25-27, wherein the two alignable marker elements are echogenic and viewable when located within a patient&#39;s heart using ultrasound, wherein the image taken perpendicular to the target site of the alignable marker elements is an ultrasound image. 
     Example 30: The method as in any one of examples 25-29, wherein the complementary shape of each of the two alignable marker elements is at least one portion of a circle and the fiducial shape is a single circle. 
     Example 31: The method as in any one of examples 25-30, wherein the target site is the intraventricular septum, wherein navigating the distal end region proximate the target site comprising navigating the distal end region into the right ventricular proximate the intraventricular septum. 
     Example 32: A method of forming a lead comprising: 
     providing a lead body extending from a proximal end region to a distal end region defining a lumen, wherein a conductor is positioned within the lumen; 
     defining an opening through the lead body; 
     extending the conductor outside of the lead body through the lumen; 
     positioning a C-shaped electrode proximate the conductor outside of the lead body; 
     electrically coupling C-shaped electrode to the conductor; and 
     mechanically coupling the C-shaped electrode onto the lead body. 
     Example 33: The method as in example 32, wherein the lead body comprises an extension region and an electrode coupling region, wherein the electrode coupling region is where the C-shaped electrode is coupled to the lead body, wherein the extension region defines a first outer diameter and the electrode coupling region defines a second outer diameter that is less than the first outer diameter. 
     Example 34: The method as in example 33, wherein the C-shaped electrode defines an inner surface, an outer surface, and a thickness between the inner surface and the outer surface, wherein the thickness of the C-shaped electrode is less than or equal to a difference between the first outer diameter and the second outer diameter. 
     Example 35: The method as in any of examples 32-34, wherein providing the lead body comprises utilizing additive manufacturing to form the lead body about the conductor. 
     Example 36: The method as in any of examples 32-35, wherein electrically coupling C-shaped electrode to the conductor comprises laser welding the C-shaped electrode to the conductor. 
     Example 37: The method as in example 36, wherein the C-shaped electrode defines an inner surface and an outer surface, wherein the laser welding is applied to the outer surface of the C-shaped electrode to electrically couple the inner surface to the conductor. 
     Example 38: The method as in any of examples 32-37, wherein the C-shaped electrode extends along a circumference from a first end to a second end and defines a gap between the first end and the second end, wherein mechanically coupling the C-shaped electrode onto the lead body comprises deforming the C-shaped electrode to the conductor to close the gap such that the first end contacts the second end. 
     Example 39: The method as in any of examples 32-38, wherein the method further comprises closing the opening in the lead body after extending the conductor outside of the lead body through the lumen. 
     Example 40: The method of example 39, wherein closing the opening in the lead body comprises thermo-bonding the lead body. 
     Example 41: The method as in any of examples 32-40, wherein the lead body is less than or equal to 3 Fr. 
     Example 42: The method as in any of examples 32-41, wherein the lead body is less than or equal to 4 Fr. 
     Example 43: A lead comprising: 
     a lead body extending from a proximal end to a distal end and defining an S-shape region proximate the distal end, a first apex area within the S-shaped region and a second apex area within the S-shaped region; 
     a first electrode positioned at the first apex area; and 
     a second electrode positioned at the second apex area. 
     Example 44: The lead of example 43, wherein each of the first and second electrodes is a coil electrode. 
     Example 45: The lead as in any of examples 43-44, wherein the lead body is less than or equal to 3 Fr. 
     Example 46: The lead as in any of examples 43-44, wherein the lead body is less than or equal to 4 Fr. 
     Example 47: The lead as in any of examples 43-46, wherein the lead body further defines a straight portion positioned proximal to the S-shaped region, wherein the straight portion extends along and defines an axis when undeflected, wherein at least one of the first and second apex areas, when undeflected, are located away from the axis at a perpendicular radial distance that is greater than the remainder of the lead body. 
     Example 48: The lead as in example 47, wherein both of the first and second apex areas, when undeflected, are located away from the axis at a radial distance that is greater than the remainder of the lead body. 
     Example 49: The lead as in any of examples 43-48, wherein the first apex area is located on the opposite side of the axis than the second apex area. 
     Example 50: The lead as in any of examples 43-49, wherein the S-shaped region defines a first curve portion and a second curve portion distal from the first curve portion, wherein the first curve portion defines a first radius and the second curve portion defines a second radius, wherein, when the lead is undeflected, the second radius is less than the first radius. 
     Example 51: The lead as in example 50, wherein the lead body defines an end curve portion distal to the S-shaped region. 
     Example 52: The lead as in example 51, wherein the end curve portion defines a third radius that, when the lead is undeflected, is less than the second radius. 
     Thus, various embodiments described herein are disclosed. It should be understood that various aspects disclosed herein may be combined in different combinations than the combinations specifically presented in the description and accompanying drawings. It should also be understood that, depending on the example, certain acts or events of any of the processes or methods described herein may be performed in a different sequence, may be added, merged, or left out altogether (e.g., all described acts or events may not be necessary to carry out the techniques). In addition, while certain aspects of this disclosure are described as being performed by a single module or unit for purposes of clarity, it should be understood that the techniques of this disclosure may be performed by a combination of units or modules associated with, for example, a medical device. 
     In one or more examples, the described techniques may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include non-transitory computer-readable media, which corresponds to a tangible medium such as data storage media (e.g., RAM, ROM, EEPROM, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer). 
     Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor” as used herein may refer to any of the foregoing structure or any other physical structure suitable for implementation of the described techniques. Also, the techniques could be fully implemented in one or more circuits or logic elements. 
     All references and publications cited herein are expressly incorporated herein by reference in their entirety for all purposes, except to the extent any aspect directly contradicts this disclosure. 
     Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims may be understood as being modified either by the term “exactly” or “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein or, for example, within typical ranges of experimental error. 
     As used herein, the term “configured to” may be used interchangeably with the terms “adapted to” or “structured to” unless the content of this disclosure clearly dictates otherwise. 
     The singular forms “a,” “an,” and “the” encompass embodiments having plural referents unless its context clearly dictates otherwise. 
     As used herein, “have,” “having,” “include,” “including,” “comprise,” “comprising” or the like are used in their open-ended sense, and generally mean “including, but not limited to.” It will be understood that “consisting essentially of” “consisting of,” and the like are subsumed in “comprising,” and the like. 
     Reference to “one embodiment,” “an embodiment,” “certain embodiments,” or “some embodiments,” etc., means that a particular feature, configuration, composition, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. Thus, the appearances of such phrases in various places throughout are not necessarily referring to the same embodiment of the disclosure. Furthermore, the particular features, configurations, compositions, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The words “preferred” and “preferably” refer to embodiments of the disclosure that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the disclosure.