Patent Publication Number: US-11027101-B2

Title: Catheter assembly including ECG sensor and magnetic assemblies

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. patent application Ser. No. 12/545,762, filed Aug. 21, 2009, now U.S. Pat. No. 9,901,714, which claims the benefit of U.S. Provisional Patent Application No. 61/091,233, filed Aug. 22, 2008, and titled “Catheter Including Preloaded Steerable Stylet;” and U.S. Provisional Patent Application No. 61/095,451, filed Sep. 9, 2008, and titled “Catheter Assembly Including ECG and Magnetic-Based Sensor Stylet,” each of which is incorporated herein by reference in its entirety. 
    
    
     BRIEF SUMMARY 
     Briefly summarized, embodiments of the present invention are directed to a stylet for use in guiding a distal tip of a catheter to a predetermined location within the body of a patient. In one embodiment the stylet is configured for use within a lumen of the catheter and comprises a core wire, an ECG sensor, and a magnetic assembly. The ECG sensor senses an ECG signal of a patient when the stylet is disposed within the lumen of the catheter and the catheter is disposed within the body of the patient. The magnetic assembly includes at least one element capable of producing a magnetic or electromagnetic field for detection by a sensor external to the patient. 
     In another embodiment, the stylet includes a pre-shaped distal segment that is deflected with respect to a more proximal portion of the stylet, which in turn causes a distal segment of the catheter to be deflected when the stylet is received within the catheter lumen. 
     These and other features of embodiments of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of embodiments of the invention as set forth hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more particular description of embodiments of the invention will be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1  is a top view of a catheter assembly including a shaped, torqueable stylet according to one example embodiment of the present invention; 
         FIG. 2  is a top view of the stylet of  FIG. 1 ; 
         FIG. 3A  is a top view of a shaped distal portion of the stylet of  FIG. 2 , according to one possible configuration; 
         FIG. 3B  is a top view of the shaped distal portion of the stylet of  FIG. 2 , according to another possible configuration; 
         FIG. 3C  is a top view of the shaped distal portion of the stylet of  FIG. 2 , according to yet another possible configuration; 
         FIG. 3D  is a top view of the shaped distal portion of the stylet of  FIG. 2 , according to still another possible configuration; 
         FIG. 4A  is a top view of a catheter assembly including a stylet loaded therein and configured in accordance with one embodiment of the present invention; 
         FIG. 4B  is a top view of the stylet of  FIG. 4A , according to one embodiment; 
         FIG. 5  is a cross sectional view of a distal segment of the stylet of  FIG. 4B , according to one embodiment; 
         FIGS. 6A-6F  are various views of a stylet in accordance with another embodiment; 
         FIG. 7  is a cross sectional view of a distal segment of the stylet of  FIG. 4B , according to another embodiment; 
         FIG. 8  is a partial cross sectional view of a distal segment of a stylet configured in accordance with one example embodiment; 
         FIG. 9  is a partial cross sectional view of a distal segment of a stylet configured in accordance with another embodiment; 
         FIG. 10  is a partial cross sectional view of a distal segment of a stylet configured in accordance with yet another embodiment; 
         FIG. 11  is a partial cross sectional view of a distal segment of a stylet and catheter configured in accordance with one embodiment; 
         FIG. 12  is a cross sectional view of a distal segment of a stylet configured in accordance with one embodiment; 
         FIG. 13  is a cross sectional view of a distal segment of a stylet configured in accordance with one embodiment; 
         FIG. 14  is a cross sectional view of a distal segment of a stylet configured in accordance with one embodiment; 
         FIG. 15  is a cross sectional view of a distal segment of a stylet configured in accordance with one embodiment; 
         FIG. 16  is a cross sectional view of a distal segment of a stylet configured in accordance with one embodiment; 
         FIG. 17  is a cross sectional view of a distal segment of a stylet configured in accordance with one embodiment; 
         FIG. 18  is a cross sectional view of a distal segment of a stylet configured in accordance with one embodiment; 
         FIG. 19  is a cross sectional view of a distal segment of a stylet configured in accordance with one embodiment; 
         FIG. 20  is a cross sectional view of a distal segment of a stylet configured in accordance with one embodiment; 
         FIG. 21  is a cross sectional view of a distal segment of a stylet configured in accordance with one embodiment; and 
         FIG. 22  is a cross sectional view of a distal segment of a stylet configured in accordance with one embodiment. 
     
    
    
     DETAILED DESCRIPTION OF SELECTED EMBODIMENTS 
     Reference will now be made to figures wherein like structures will be provided with like reference designations. It is understood that the drawings are diagrammatic and schematic representations of exemplary embodiments of the invention, and are not limiting of the present disclosure nor are they necessarily drawn to scale. 
       FIGS. 1-22  depict various features of embodiments of the present invention, which is generally directed, in one embodiment, to a catheter assembly including a pre-loaded stylet therein. In one embodiment, the catheter assembly includes a distal portion shaped in a bent configuration. The bent configuration of the catheter distal portion is caused by the pre-loaded stylet, which includes a pre-shaped distal segment deflected in a bent configuration. Thus, the pre-shaped distal segment of the stylet urges the distal portion of the catheter into a similar bent configuration. 
     Further, the pre-loaded stylet is configured to be torqueable, thus enabling the stylet to be rotatable within the catheter lumen. A hydrophilic coating applied to an outer surface of the stylet facilitates such stylet rotation. Rotation of the shaped stylet enables the pre-shaped distal segment to be changed in orientation. This in turn causes a change in orientation of the distal portion of the catheter to occur. Such “steerability” enables the catheter to be more easily guided through the vasculature of a patient during placement of the catheter. 
     In another embodiment, a stylet for use in guiding a distal tip of a catheter in which the stylet is disposed to a predetermined location within the vasculature of a patient is disclosed. The stylet includes a magnetic assembly proximate its distal tip for use with an external magnetic sensor to provide information relating to general positioning/orientation of the catheter tip during navigation through the patient vasculature. The stylet further includes an ECG sensor proximate its distal tip for use with an external ECG monitoring system to determine proximity of the catheter distal tip relative to an electrical impulse-emitting node of the patient&#39;s heart, such as the SA node in one example. Such electrical impulses are also referred to herein as “ECG signals.” Inclusion of the magnetic and ECG sensors with the stylet enables the catheter to be guided with a relatively high level of precision to a predetermined location proximate the patient&#39;s heart. 
     For clarity it is to be understood that the word “proximal” refers to a direction relatively closer to a clinician using the device to be described herein, while the word “distal” refers to a direction relatively further from the clinician. For example, the end of a catheter placed within the body of a patient is considered a distal end of the catheter, while the catheter end remaining outside the body is a proximal end of the catheter. Further, the words “including,” “has,” and “having,” as used herein, including the claims, shall have the same meaning as the word “comprising.” 
     Reference is first made to  FIG. 1 , which depicts a catheter assembly, generally designated at  10  and configured in accordance with one example embodiment of the present invention. As shown, the catheter assembly  10  includes a catheter  12  having a proximal end  12 A, a distal end  12 B, and defining at least one lumen  14  extending therebetween. In the present embodiment, the catheter is a PICC, though in other embodiments other types of catheters, having a variety of size, lumen, and prescribed use configurations can benefit from the principles described herein. Further, though shown here with an open distal end, the catheter in other embodiments can have a closed distal end. As such, the present discussion is presented by way of example and should therefore not be construed as being limiting of the present invention in any way. Note that the catheter  12  can be formed from one or more of a variety of materials, including polyurethane, polyvinyl chloride, and/or silicone. 
     A bifurcation, or hub  16 , can be included at the catheter proximal end  12 A. The hub  16  permits fluid communication between extension tubing  18  and  20  and the lumen(s)  14  of the catheter  12 . Each extension tubing component  18  and  20  includes on a proximal end a connector  22  for enabling the catheter assembly  10  to be operably connected to one or more of a variety of medical devices, including syringes, pumps, infusion sets, etc. Again note that the particular design and configuration of the afore-described components are exemplary only. 
     The catheter  12  includes a distal portion  24  as part of the catheter that is configured for insertion within the vasculature of a patient. As seen in  FIG. 1 , the distal portion  24  of the catheter  12  includes a deflected, bent configuration with respect to the more proximal portion of the catheter  12 . As will be described further below, this bent configuration is caused by a stylet disposed within the catheter and facilitates relatively easier navigation and placement of the distal tip of the catheter in a preferred location within the patient vasculature. 
     Together with  FIG. 1 , reference is now made to  FIG. 2 .  FIG. 1  further shows a stylet  30  extending from a proximal end of the extension tubing  20  and configured in accordance with one embodiment of the present invention. As shown in  FIG. 2  removed from the catheter  12 , the stylet  30  includes an elongate core wire that defines a proximal end  30 A and a distal end  30 B. The stylet  30  is pre-loaded within the lumen  14  of the catheter  12  such that the distal end  30 B is substantially flush with the opening at the catheter distal end  12 B, and such that the proximal portion of the stylet extends from the proximal end of the catheter or one of the extension tubes  18  and  20 . Note that, though considered here as a stylet, in other embodiments a guidewire or other catheter guiding apparatus could include the principles of embodiments of the present disclosure described herein. 
     As mentioned, the body of the stylet  30  is configured as an elongate core wire and is composed of a memory material such as, in one embodiment, a nickel and titanium-containing alloy commonly known by the acronym “nitinol.” Nitinol possesses characteristics that serve well in the present application, including shape memory and torqueability characteristics, as will be explained. In another embodiment, other suitable materials such as stainless steel could be used for the stylet construction. In yet another embodiment, it is appreciated that the distal segment can be manufactured from a memory material such as nitinol, while the more proximal portion of the stylet core wire is manufactured with stainless steel or other suitable material. 
     The stylet  30  further includes a distal segment  32  that is pre-shaped to have a bent configuration with respect to the more proximal portion of the stylet. In particular, the stylet distal segment  32  is bent off-axis with respect to a substantially linear longitudinal axis  36  of the stylet core wire in the view depicted in  FIG. 2 . Manufacture of the stylet  30  from a shape memory material such as nitinol enables the stylet to be configured such that the core wire retains the curved or other bent distal segment shape shown in  FIG. 2  during use with the catheter assembly  10 . The distal segment  32  is “pre-shaped” in that it is manufactured to possess a bent or offset configuration before its assembly and retains the configuration after insertion within the catheter  12 . 
     The bent configuration of the distal segment  32  in the embodiment illustrated in  FIG. 2  defines an arc or curve having a radius R. In other embodiments, however, the distal segment can be bent or offset from the more proximal portion of the stylet in other ways, such as in  FIG. 3C , for example, where the distal segment is approximately linearly offset to define an angle θ with the longitudinal axis of the proximal portion of the stylet  30 . Combinations of linear and curved bend profiles are also possible. These and other possible bent or offset configurations are therefore contemplated as falling within the claims of the present invention. 
     Reference is now made to  FIG. 3A , which depicts further details of the stylet  30 , according to one embodiment. As shown, the pre-shaped distal segment  32  includes a distal portion of the core wire having a diameter D 2  that is reduced with respect to the diameter D 1  of the more proximal portion of the core wire. The stylet core wire transitions from diameter D 1  to D 2  at a smooth, linear tapered transition region  40 , though in other embodiments a stepped taper, convex or concave taper, or no taper need be present. 
     A tubing sleeve  42  is slid over the reduced diameter stylet core wire along the distal segment  32  and is sized to substantially match the diameter D 1  of the proximal portion of the stylet core wire, though it can be sized differently, if desired. The sleeve  42  is adhered to the core wire near the transition region  40  and at the distal end  30 B of the core wire by an adhesive  46 , such as a UV, 2-part epoxy, or other suitable adhesive. So secured, an air gap  48  is created between an outer surface of the core wire and an inner surface of the sleeve  42 . In other embodiments, the air gap can be enlarged, reduced, or eliminated. 
     In the present embodiment, the sleeve  42  includes reinforcement  44  to maintain the sleeve in a bent configuration similar to the bent configuration of the stylet distal segment core wire. The reinforcement  44  can be a metal coil or braided mesh or substrate that is integrated into the structure of the sleeve  42  and is capable of bending so as to assume and maintain a bent shape similar to that shown in  FIG. 3A . Characteristics of the sleeve  42  that can be adjusted so as to modify its performance include its wall thickness, melt index, and composition. In the present embodiment, the sleeve  42  is composed of polyimide and the reinforcement  44  is coiled stainless steel. Of course, other suitable materials can be employed, either in lieu of or in combination with, these constituents. In other embodiments, the reinforcement can be configured so as to merely strengthen the sleeve and not maintain its bent configuration, or the reinforcement can be removed from all or a portion of the sleeve. In the latter case, a sleeve having no reinforcement can nevertheless be formed so as to have a pre-shaped, bent configuration. In any of the above embodiments, however, the sleeve can be configured to assist the distal segment  32  of the stylet core wire in urging the distal portion of the catheter  12  into a similar bent configuration, as seen in  FIG. 1  and as will be explained in further detail below. 
     As mentioned, the stylet  30  having a pre-shaped distal segment  32 , such as that described in connection with  FIG. 3A , is pre-loaded in one embodiment into the catheter  12  before insertion such that the distal segment resides within the lumen  14  at the distal portion  24  of the catheter, placing the distal tips of both the stylet and the catheter in substantial alignment with one another. Note that in other embodiments the distal tips of the stylet and catheter can be in a non-aligning configuration, if desired, and that the catheter can include multiple lumens. So positioned, the distal segment  32  of the stylet  30  imparts an urging force on the distal portion  24  of the catheter  12  such that the catheter distal portion assumes a bent configuration similar to that of the stylet distal segment. As such, it is appreciated that while the stylet  30  is loaded within the catheter  12 , the distal portion  24  of the catheter takes on the bent configuration of the distal segment  32  of the stylet. Once the stylet  30  is removed, the catheter  12  is free to return to an unbent configuration commensurate with its original shape when manufactured. 
     The stylet  30  in one embodiment further includes on its outer surface a hydrophilic coating  38  to assist in rotating the stylet within the lumen  14  of the catheter  12  during use. The wettable coating  38  can be activated, for instance, by flushing the catheter lumen  14  with saline or other aqueous solution, thereby facilitating rotation of the stylet within the lumen. In other embodiments, no coating is included on the stylet. In yet other embodiments, the coating can be included on an inner surface of the catheter, or the composition of the catheter and stylet can be chosen such that a net low coefficient of friction exists between the two surfaces. 
     A handle  34  can be provided near the proximal end  30 A of the stylet  30  so as to enable a user to rotate the stylet within the catheter lumen  14 . Because the stylet  30  is at least partially composed of nitinol or other suitable material in one embodiment, the stylet is configured to be torqued by user application of a rotational force thereto via the handle  34 . The handle  34  may take one of many shapes and configurations, including that shown in  FIGS. 1 and 2 , for example. Torqueability of the stylet  30 , together with its hydrophilic coating  38 , makes possible selective rotation of the stylet within the catheter lumen  14 , which in turn enables selective rotation and orientation of the bent distal segment  32 . As before mentioned, no coating may be necessary in one embodiment. In addition, the handle  34  is attached to the stylet core wire so as to correspond with the orientation of the bent distal segment  32 . Thus one can determine the orientation of the direction of bend of the distal segment  32  when the distal segment is disposed within the vasculature of a patient by observing the orientation of the handle  34 . The handle  34  in one embodiment may include a visual guide or key thereon to assist the clinician in ascertaining the orientation of the bent distal segment  32 . 
     As mentioned, the stylet distal segment  32 , having a pre-shaped bent configuration, urges the distal portion  24  of the catheter into a similar bent configuration when the stylet  30  is received in the catheter lumen  14  as shown and described. Rotation of the stylet  30  within the catheter lumen  14  in the manner described above therefore causes a corresponding change in the orientation of the bent configuration of the catheter distal portion  24 , shown for example in phantom in  FIG. 1 . Thus, the catheter distal portion  24  and its corresponding distal tip are “steerable” via torqueable rotation of the stylet  30  by a clinician grasping and turning the handle  34 . Such steerability is desirous to enable the catheter distal tip to be navigated through the tortuous vasculature of a patient during placement of the catheter  12 . Note that the distal segment  32  is sufficiently resilient to prevent trauma or damage to the vasculature during navigation therein. 
     In greater detail, with the handle  34  being oriented in a direction corresponding to the direction of bend in the stylet distal segment  32 , the clinician placing the catheter within the patient vasculature can ascertain the orientation of the bent catheter distal portion  24 , which is disposed within the vasculature during placement, by observing the orientation of the handle  34 . The handle  34  therefore acts as a key in determining orientation of the bent configuration of the distal segment  34  of the stylet  30 /distal portion  24  of the catheter  12 . This aspect assists the clinician in placing the catheter  12  in the patient vasculature so as to place the distal tip of the catheter  12  in a predetermined position by advancing the catheter  12  with the pre-loaded stylet  30  therein. Once the catheter  12  has been placed as desired, the stylet  30  can be removed from the catheter lumen  14  and corresponding extension tubing  18 / 20  and the catheter prepared for use. 
     Reference is now made to  3 B and  3 C, which show aspects of other possible stylet distal segment configurations according to embodiments of the present invention. The distal segment  32  shown in  FIG. 3B  includes a reduced diameter core wire as in  FIG. 3A , but includes no sleeve covering the distal core wire segment. The distal segment  32  shown in  FIG. 3C  also includes no sleeve, but includes a core wire segment having a non-reduced diameter with respect to the proximal core wire portion. Thus, it is seen that various core wire diameters and omissions of the sleeve or other components may be intended while still residing within the scope of embodiments of the present invention. 
     Reference is now made to  FIG. 3D , which shows yet another example of a stylet distal segment according to one embodiment. In particular, the stylet distal segment  32  of  FIG. 3D  includes a reduced diameter core wire, sleeve  42  having reinforcement  44 , and air gap  48 , as earlier described in connection with  FIG. 3A . A plurality of magnets  60  is disposed in a portion of the air gap  48 . The magnets  60  are employed in the distal segment to enable the distal segment  32  of the stylet  30  to be observable by an exterior tip location system configured to detect the magnetic field of the magnets as the stylet tip advances, together with the catheter distal tip, through the patient vasculature. In the present embodiment, the magnets  60  are ferromagnetic of a solid cylindrical shape, but in other embodiments they may vary from this design in not only shape, but composition, number, size, magnetic type, and position in the stylet distal segment. For instance, the magnetic assembly may include a single or multiple electromagnets disposed in the distal segment in a uni-polar or bi-polar design, in one embodiment. 
     Note that embodiments of the present disclosure may vary from what is explicitly described herein. For instance, differences in sleeve, air gap, and core wire grind may be present in a stylet distal segment so as to alter bend and resiliency characteristics thereof while still falling under the present claims. 
       FIGS. 4A-11  depict various features of further embodiments of the present disclosure, directed as before to a stylet for use in guiding a distal tip of a catheter in which the stylet is disposed to a predetermined location within the vasculature of a patient. The stylet includes a magnetic assembly proximate its distal tip for use with an external magnetic sensor to provide information regarding general positioning/orientation of the catheter tip during navigation through the patient vasculature. The stylet further includes an ECG sensor proximate its distal tip for use with an external ECG monitoring system to determine proximity of the catheter distal tip relative to an electrical impulse-emitting node of the patient&#39;s heart, such as the SA node in one example. Such electrical impulses are also referred to herein as “ECG signals.” Inclusion of the magnetic assembly and ECG sensor with the stylet enables the catheter to be guided with a relatively high level of precision to a predetermined location proximate the patient&#39;s heart. 
     Reference is first made to  FIG. 4A , which depicts a catheter assembly, generally designated at  110  and configured in accordance with one example embodiment of the present invention. As shown, the catheter assembly  110  includes a catheter  112  having a proximal end  112 A, a distal end  112 B, and defining at least one lumen  114  extending therebetween. In the present embodiment, the catheter is a peripherally-inserted central catheter (“PICC”), though in other embodiments other types of catheters, having a variety of size, lumen, and prescribed use configurations can benefit from the principles described herein. Further, though shown here with an open distal end, the catheter in other embodiments can have a closed distal end. As such, the present discussion is presented by way of example and should therefore not be construed as being limiting of the present invention in any way. 
     A hub  116  is included at the catheter proximal end  112 A. The hub  116  permits fluid communication between extension tubing  118  and  120  and the lumen(s)  114  of the catheter  112 . Each extension tubing component  118  and  120  includes on a proximal end a connector  122  for enabling the catheter assembly  110  to be operably connected to one or more of a variety of medical devices, including syringes, pumps, infusion sets, etc. Again note that the particular design and configuration of the afore-described components are exemplary only. For instance, in one embodiment, the catheter need not include a hub or extension legs. The composition of the catheter in this and other embodiments described herein includes a suitable material, such as polyurethane, silicone, etc. 
     The catheter  112  includes a distal portion  124  configured for insertion within the vasculature of a patient. The catheter  112  is flexible so as to enable it to bend while being advanced through the patient vasculature. 
     Together with  FIG. 4A , reference is now made to  FIG. 4B .  FIG. 4A  further shows a stylet  130  extending from a proximal end of the extension tubing  120  and configured in accordance with one embodiment of the present invention. As shown in  FIG. 4B , the stylet  130  as removed from the catheter  112  defines a proximal end  130 A and a distal end  130 B and generally includes a core wire  131 , a handle  134 , and a tether  135 . The stylet  130  is pre-loaded within the lumen  114  of the catheter  112  in one embodiment such that the distal end  130 B is substantially flush with the opening at the catheter distal end  112 B, and such that the proximal portion of the core wire  131 , the handle  134 , and the tether  135  are located proximal to the proximal end of the catheter or one of the extension tubes  118  and  120 . Note that, though described herein as a stylet, in other embodiments a guidewire or other catheter guiding apparatus could include the principles of the present invention described herein. 
     The core wire  131  defines an elongate configuration and is composed of a suitable stylet material including stainless steel or a memory material such as nitinol in one embodiment. Though not shown here, manufacture of the core wire  131  from nitinol in one embodiment enables the portion of the core wire corresponding to a distal segment  132  of the stylet  130  to have a pre-shaped bent configuration, as has already been described. 
     Further, the nitinol construction lends torqueability to the core wire  131 . Thus, the pre-shaped core wire distal segment  132 , together with core wire torqueability, enables the distal segment of the stylet  130  to be manipulated while disposed within the catheter lumen  114  during catheter insertion, which in turn enables the distal portion  124  of the catheter  112  to be navigated through the vasculature during catheter insertion. In the presently illustrated embodiment, no pre-shaping of the stylet distal segment is shown. 
     Note also that the present stylet can be employed in a catheter placement system that employs one or more of ultrasound, magnetic-based stylet tip tracking, and ECG-based tip navigation/position confirmation technologies to accurately place a catheter in the vasculature of a patient. Details regarding aspects of an example of such a system are given below, and can also be found in U.S. Pat. No. 8,388,541, titled “Integrated System for Intravascular Placement of a Catheter,” filed Nov. 25, 2008; and U.S. Pat. No. 9,649,048, titled “Systems and Methods for Breaching a Sterile Field for Intravascular Placement of a Catheter,” filed Apr. 17, 2009, each which is incorporated herein by reference in its entirety. 
     A handle  134  is provided at a proximal end  131 A of the stylet  130  so as to enable insertion/removal of the stylet from the catheter lumen  114 . In embodiments where the stylet core wire  131  is torqueable, the handle  134  enables the core wire  131  to be rotated within the catheter lumen  114 , such as when rotation of a pre-shaped distal segment  132  of the stylet  130  is desired to assist in navigating the catheter distal portion  124  through the vasculature of the patient. In this case, the handle  134  is attached to the stylet core wire so as to correspond with the orientation of the bent distal segment  132 . Thus one can determine the orientation of the direction of bend of the distal segment  132  when the distal segment is disposed within the vasculature of a patient by observing the orientation of the handle  134 . The handle  134  may include a guide or key thereon to assist the clinician in ascertaining the orientation of the bent distal segment  132 . 
     Rotation, insertion, and/or removal of the stylet  130  via the handle  134  is further facilitated in one embodiment by application of a hydrophilic coating  138  to an outer surface of the core wire  131  and accompanying sleeve to be described further below. The wettable hydrophilic coating  138  can be activated, for instance, by flushing the catheter lumen  114  with saline or other aqueous solution, thereby facilitating rotation of the stylet within the lumen. The handle  134  may take one of many shapes and configurations, including that shown in  FIGS. 2, 4A , and  6 A, for example. Note also that in an unbent configuration, the core wire  31  of the stylet  130  defines a substantially linear longitudinal axis  136 . 
     In the present embodiment, the handle  134  attaches to a distal end of the tether  135 . In the present embodiment, the tether  135  is a flexible, shielded cable housing a plurality of electrically conductive wires. The wires are electrically connected to components, to be discussed below, disposed in the distal segment  132  of the stylet  130 , and as such, they provide a conductive pathway from the distal segment through to the proximal end  130 A of the stylet, where an electrical connector  156  is attached. As will be explained, the electrical connector  156  can take one of many forms and is configured for operable connection to an external magnetic and/or ECG sensor device in assisting navigation of the stylet  130  and catheter  112  to a desired location within the patient vasculature. Note that in another embodiment, the stylet can be un-tethered and electrical connectivity with the stylet distal segment components can be achieved by attaching temporary clips at the handle where the electrical wires from such components exit the stylet, for instance. 
     Reference is now made to  FIG. 5 , which depicts further details of the stylet  130 , according to one embodiment. As shown, the distal segment  132  includes a distal portion of the core wire  131  defining a diameter D 2  that is reduced with respect to the diameter D 1  of the more proximal portion of the core wire. The stylet core wire transitions from diameter D 1  to D 2  at a tapered transition region  140 , though in other embodiments no taper need be present. The reduced diameter portion of the core wire lends desired stiffness and tensile properties thereto, though it is appreciated that in other embodiments no reduction in core wire diameter is necessary. 
     A sleeve  142  is slid over the reduced diameter stylet core wire along the distal segment  132  and is sized to substantially match the diameter D 1  of the proximal portion of the stylet core wire. The sleeve  142  is adhered to the core wire near the transition region  140  and at the distal end  130 B of the core wire by an adhesive  146 , such as a UV, 2-part epoxy, or other suitable adhesive. So secured, an air gap  148  is created between an outer surface of the core wire and an inner surface of the sleeve  142 . In other embodiments, the air gap can be enlarged, reduced, or eliminated. 
     In the present embodiment, the sleeve  142  includes reinforcement  144  to assist the core wire  131  in providing proper stylet distal end stiffness and, in cases where the distal segment of the stylet is pre-shaped in a bent configuration, to assist in maintaining the core wire in the bent configuration. The reinforcement  144  can be a metal coil or braided mesh or substrate that is integrated into the structure of the sleeve  142  and is capable of manipulation so as to assume and maintain a bent shape, if desired. 
     Characteristics of the sleeve  142  that can be adjusted so as to modify its performance include its wall thickness, melt index, and composition. In the present embodiment, the sleeve  142  is composed of materials including polyimide and the reinforcement  144  is coiled stainless steel. Of course, other suitable materials can be employed, either in lieu of or in combination with, these constituents. As mentioned, in embodiments of the present invention the reinforcement can be configured so as to merely strengthen the sleeve and not maintain a bent configuration as in  FIG. 5 , to maintain a bent configuration as in  FIG. 6A , or the reinforcement can be removed from all or a portion of the sleeve. 
     The stylet distal segment  132  further includes an ECG sensor or sensor assembly, generally designated at  150 , according to one embodiment. The ECG sensor assembly  150  enables the stylet, preloaded in the lumen  114  of the catheter  112  during patient insertion, to be employed in detecting an intra-atrial ECG signal produced by an SA or other node of the patient&#39;s heart, thus assisting in navigating the distal end  112 B of the catheter to a predetermined location within the vasculature proximate the patient&#39;s heart. Thus, the ECG sensor assembly  150  serves as an aide in confirming proper placement of the catheter distal end  112 B. 
     In the embodiment illustrated in  FIG. 5 , the ECG sensor assembly  150  includes a distal portion of the core wire  131 , which is electrically conductive, as is the rest of the core wire. A conductive distal coil  152  is disposed about the distal portion of the core wire  131  adjacent the core wire distal tip  131 B. The distal coil  152  is composed of a conductive material, such as stainless steel. A tip weld  154  is included on the core wire distal tip  131 B to bond the distal coil  152  to the core wire distal tip  131 B. The tip weld  154  further provides an atraumatic distal tip configuration for the core wire  131 . In another embodiment, the distal coil  152  is configured so as to define a diameter equal to that of the tubing sleeve  142  and to define a constant diameter along the stylet length. In yet another embodiment, no coil is included. 
     Before catheter placement, the stylet  130  is preloaded into the lumen  114  of the catheter  112 . Note that in one embodiment the stylet  130  is preloaded within the catheter lumen  114  before use such that the distal segment  132  of the stylet resides within the lumen at the distal portion  124  of the catheter, placing the distal tips of both the stylet and the catheter in substantial alignment with one another. Once the catheter has been introduced into the patient vasculature and is advanced toward the patient&#39;s heart, the distal portion of the core wire  131 , being electrically conductive, begins to detect the electrical impulses produced by the SA node or other suitable node of the patient&#39;s heart. The distal coil  152  is included about the core wire distal tip  131 B to increase the relative surface area of the core wire distal portion so as to improve reception of the electrical impulses from the SA node. Note that other structures could be provided to provide the same functionality. As such, the ECG sensor assembly  150  serves as a sensor or electrode for detecting the ECG heart signals. The elongate core wire  131  proximal to the core wire distal segment serves as a conductive pathway to convey the electrical impulses produced by the SA node and received by the ECG sensor assembly  150  away from the distal segment  132  of the stylet  130  to the tether  135 . 
     An electrical wire or other suitable structure in the tether  135  conveys the signals to an ECG sensor module located external to the patient. The tether  135  is operably connected to the ECG sensor module via the electrical connector  156 , or other suitable direct or indirect connective configuration. Monitoring of the ECG signal received by the external sensor module enables a clinician to observe and analyze changes in the signal as the catheter advances toward the SA node. When the received ECG signal matches a desired profile, the clinician can determine that the catheter distal end  112 B has reached a desired position with respect to the SA node. In one implementation, for example, this desired position lies within the lower one-third (⅓ rd ) portion of the superior vena cava (“SVC”). Once it has been positioned as desired, the catheter  112  may be secured in place and the stylet  130  removed from the catheter lumen  114 . 
     In the present embodiment of  FIG. 5 , the distal segment  132  of the stylet  130  further includes a magnetic assembly, generally designated at  160 . The magnetic assembly  160  in the illustrated embodiment includes a plurality of magnets  162  disposed in a portion of the air gap  148 , and as such the magnets are interposed between an outer surface of the core wire  131  and an inner surface of the sleeve  142 . In the present embodiment, the magnets  162  are ferromagnetic of a solid cylindrical shape stacked end-to-end, but in other embodiments they may vary from this design in not only shape, but also composition, number, size, magnetic type, and position in the stylet distal segment. In one particular embodiment, the magnets  162  include neodymium. In other embodiments, other rare-earth or alternative types of magnets or magnetic elements may be employed. In yet other embodiments, an electromagnet or other element capable of producing an electromagnetic field that can be externally detected and monitored may also be used. 
     The magnets  162  are employed in the stylet distal segment  132 , preloaded within the lumen  114  of the catheter  112  during catheter placement within the patient&#39;s vasculature, to enable the position of the distal segment to be observable relative to a magnetic sensor placed in close proximity to the patient&#39;s body as part of an exterior tip location system. The tip location system is configured to detect the magnetic field of the magnets  162  as the stylet distal segment  132  advances, together with the catheter distal portion  124 , through the patient vasculature. In this way, a clinician placing the catheter  112  is able to generally determine the location, orientation, and/or advancement of the catheter distal end  112 B within the patient vasculature and detect when catheter malposition is occurring, such as advancement of the catheter along an undesired vein, for instance. 
     The ECG sensor assembly  150  and magnetic assembly  160  can work in concert in assisting a clinician in placing a catheter within the vasculature. Generally, the magnetic assembly  160  of the stylet  130  assists the clinician in generally navigating the vasculature from initial catheter insertion into the vasculature so as to place the distal end  112 B of the catheter  112  in the general region of the patient&#39;s heart. The ECG sensor assembly  150  can then be employed to guide the catheter distal end  112 B to the desired location within the SVC by enabling the clinician to observe changes in the ECG signals produced by the heart as the stylet distal segment and its ECG sensor assembly approach the SA node. Again, once a suitable ECG signal profile is observed, the clinician can determine that the distal end of both the stylet  130  and catheter  112  have arrived at the desired location with respect to the patient&#39;s heart. 
       FIGS. 6A-6F  depict the stylet  130  for use in a catheter, such as the catheter  110 , according to one embodiment. As shown, the stylet  130  includes the core wire  131  attached to the handle  134 , with the tether  135  extending proximally from the handle to the electrical connector  156  to enable interconnection with an external ECG sensor module or other suitable device for receiving ECG signals detected by the ECG sensor assembly of the stylet. Though not shown here, in one embodiment the stylet  130  can include a shaped distal portion as described in connection with  FIGS. 1-3D  above, such that a distal portion of the catheter is deflected when the stylet is preloaded therein. Note, however, that the discussion to follow applies to stylets including both shaped and non-shaped distal segments. 
     The stylet  130  shown in  FIG. 6B  includes the core wire  131  and the distal segment  132 . As shown in  FIGS. 6C and 6D , the core wire  131  reduces from a diameter D 1  to a diameter D 2  over a relatively longer transition region  140  than in the previous embodiment. The portion of the core wire  131  corresponding to the transition region  140  is disposed within the sleeve  142 , which attaches to the core wire by the adhesive  146  in the manner shown in  FIG. 6C . The air gap  148  is defined between the core wire  131  and the sleeve  142 , as before. The reduced diameter portion of the core wire  131  is deflected from an axially central position in the sleeve to an offset position so as to extend adjacent to a portion of the inner surface of the sleeve  142 , as shown in  FIG. 6D . The core wire  131 , in this deflected state, extends to its distal tip  131 B, which corresponds to the distal end  130 B of the stylet  130 . 
     The deflected position of the core wire  131  provides space for the placement of a plurality of magnetic elements, in this case permanent magnets  162 , along a portion of the length of the distal segment  132 . As illustrated in  FIGS. 6B, 6D, and 6E , 20 cylindrical permanent ferromagnetic magnets are placed end to end. Of course, the type, number, shape, and arrangement of the magnets or other magnetic elements could vary from what is depicted and described herein. So configured, the magnets  162  define the magnetic assembly  160  that enables the distal end  130 B of the stylet  130  to be located via an external magnetic sensor module during a procedure to place the catheter in the patient vasculature. For example, in one embodiment, the magnets  162  are employed in the stylet distal segment  132  to enable the position/orientation of the stylet distal end  130 B to be observable relative to an external sensor placed on the patient&#39;s chest. As has been mentioned, the external sensor is configured to detect the magnetic field of the magnets  162  as the stylet advances with the catheter through the patient vasculature. In this way, a clinician placing the catheter is able to generally determine the location/orientation of the catheter distal end within the patient vasculature and detect when catheter malposition is occurring, such as advancement of the catheter along an undesired vein, for instance. 
     An electrically conductive epoxy  166  fills the hollow distal end of the sleeve proximate the stylet distal end  130 B. The epoxy  166  is in electrical communication with the core wire  131  and serves to increase the relative surface area of the core wire  131  at the distal tip  131 B thereof. So configured, the distal portion of the core wire  131  and conductive epoxy  166  define an ECG sensor, with the rest of the core wire defining a conductive pathway with respect to the sensor, thus enabling the location of the stylet distal end  130 B and corresponding catheter distal end  112 B to be positioned near the SA node of the patient&#39;s heart using an external ECG sensor module, in the manner as described above. Thus, the magnetic assembly and ECG sensor assembly both provide assistance in navigating a catheter or other indwelling device: the magnetic assembly by providing position/orientation data for the catheter, and the ECG sensor assembly providing proximity data for the catheter with reference to an ECG-signal emitting component, such as the SA node of the patient&#39;s heart. These modalities can be used exclusively of one another, successively, or in concert to aid in catheter advancement. Note that in one embodiment the conductive epoxy  166  can be rounded to provide a rounded stylet distal end  130 B. In another embodiment, the conductive epoxy can be replaced by another conductive material such as stainless steel or other suitable metal, etc. 
     As a brief example of the use of the stylet magnetic and ECG sensor assemblies in assisting in the placement of a catheter, in one embodiment an external sensor is employed by a catheter placement system to detect a magnetic field produced by the magnetic elements of the stylet, which is removably predisposed within the lumen of the catheter during catheter insertion and advancement. The external sensor can be placed on the chest of the patient during catheter insertion to enable the magnetic field of the stylet magnetic elements, disposed in the catheter as described above, to be detected during catheter transit through the patient vasculature. As the magnetic elements of the stylet magnetic assembly are co-terminal with the distal end of the catheter, detection by the external sensor of the magnetic field of the magnetic elements provides information to the clinician and enables the clinician to monitor the position/orientation of the catheter distal end during its transit. Such information can be displayed on a display unit of the catheter placement system for instance. In this way, a clinician placing the catheter is able to generally determine the location/orientation of the catheter distal end within the patient vasculature relative to the TLS sensor  50  and detect when catheter malposition, such as advancement of the catheter along an undesired vein, is occurring. 
     As described, the stylet further includes an ECG sensor as a sensing component for sensing ECG signals produced by the SA node. In one embodiment the ECG sensor of the stylet works in concert with reference and ground ECG electrodes placed on the skin surface of the patient. ECG signals detected by the stylet ECG sensor can be received by the external sensor referred to above or other suitable component of a catheter placement system, together with signals received by the reference and ground electrodes on the patient&#39;s skin. These data can be processed and monitored as the stylet-equipped catheter advances through the patient vasculature. In one embodiment, an electrocardiogram waveform is reproduced on the display using the ECG data. The clinician placing the catheter can monitor the ECG data to determine optimum placement of the distal tip of the catheter, such as proximate the SA node in one embodiment. In one implementation, monitoring of the magnetic assembly data are employed during initial advancement of the catheter through the patient vasculature, while the ECG sensor assembly data are monitored as the catheter approaches a desired final location near the heart, though other combinations of these modalities are also contemplated, including simultaneous use of both modalities in one embodiment. 
     Note that, in contrast to what is shown in  FIGS. 6B-6E , the distal segment of the stylet can be configured such that it defines a constant outside diameter with respect to the more proximal portion thereof. 
     As has been previously mentioned, other types of magnetic elements, alternative to the permanent magnets described in connection with  FIGS. 5 and 6A-6E , may be included with the stylet  130  to form a portion of the magnetic assembly  160  for enabling the position/orientation of the catheter distal end  112 B to be generally determined during vasculature navigation.  FIG. 7  depicts an example of one such alternative, wherein an electromagnetic (“EM”) coil  172  is employed in the magnetic assembly  160  of the stylet distal segment  132 . The EM coil  172  is depicted in the present embodiment as a winding of conductive wire, such as insulated copper wire, wound about a portion of the distal core wire  131  in the air gap  148  within the sleeve  142 . Note that the covering of the EM coil  172  by the sleeve  142  provides a secondary level of electrical isolation of electrical energy for the EM coil  172 . The coil wire is electrically insulated in the present embodiment so as to prevent its interfering with the ECG signals carried by the core wire  131 . Lead wires  174  operably connect with the EM coil  172  and extend proximally along the core wire  131 , through the handle  134  and tether  135  to terminate at the connector  156 . The lead wires  174  are disposed along the core wire  131  and the rest of the stylet  130  in a free floating, strain relief configuration in the present embodiment so as to prevent detachment thereof from the EM coil  172 . A suitable power source can be operably coupled to the lead wires  174  to provide electricity to the EM coil  172 . 
     When energized, the EM coil  172  produces an electromagnetic field that is detectable by an external sensor module in a manner similar to that described in connection with  FIG. 5 . Note that the relative strength of the field produced by the EM coil  172  is dependent on various factors including the length of the wire from which the coils are made, number of coil windings, and the thickness of the core wire  131  over which the coil is wound. As such, it is appreciated that the electromagnetic field of the EM coil  172  can be varied by altering these and other aspects of the magnetic assembly  160 . 
     A stylet configured in accordance with yet another embodiment is shown in  FIG. 8 . The stylet  130  of  FIG. 8  includes the ECG sensor assembly  150  and magnetic assembly  160 , as before. In contrast to the previous embodiment, the EM coil  172  is not disposed within the sleeve  142 . Rather, a distal end of the sleeve  142  terminates at and abuts a proximal end of the EM coil  172 . The lead wires  174  for the EM coil  172  are fed through the hollow interior of the sleeve  142  to the handle and tether. 
     The ECG sensor assembly  150  is disposed proximally of the magnetic assembly  160  and has a configuration differing from previous embodiments. As shown, the ECG sensor assembly  150  here includes two ECG leads  182 . Each ECG lead  182 , defining an annular band is disposed about a portion of an outer surface of the sleeve  142  is operably connected to a respective ECG lead wire  174 . Each of the ECG lead wires  174  extends through the hollow interior of the sleeve  142  to the handle and tether, terminating at the electrical connector  156  or other suitable termination. As has been explained, the ECG leads  182  operably connect with an external ECG sensor module, via the lead wires  174  and connector  156 , to enable the catheter distal end  112 B to be navigated through a patient&#39;s vasculature to a predetermined location proximate the heart of the patient. The stylet  130  further includes an atraumatic tip  188  of epoxy, UV adhesive, or other suitable material. 
     Note that the annular band structure of the ECG leads of  FIG. 8  are merely one example of leads that can be included with the stylet/catheter assembly to enable ECG signals produced by the heart to be detected and forwarded to an external ECG sensor module. As such, the depictions and accompanying descriptions herein should not be considered limiting of embodiments of the present invention in any way. Note also that the number and position of the ECG leads on the stylet or catheter can vary from what is shown and described herein. 
       FIGS. 9-11  depict additional possible embodiments of the stylet  130  and catheter assembly  110 . In  FIG. 9 , the stylet distal segment  132  includes the magnetic assembly  160  and ECG sensor assembly  150  as in  FIG. 8 . In contrast to  FIG. 8 , however, the ECG lead wires  184  are encapsulated within the wall of the sleeve  142  to provide strain relief for the lead wires and to facilitate ease of manufacturability. Such a configuration also frees up relatively more space in the central portion of the stylet.  FIG. 10  shows an embodiment similar to that of  FIG. 9 , with the sleeve  142  being extended over the EM coil  172  so as to substantially cover the entirety of the stylet distal segment  132 . 
     In  FIG. 11 , the stylet  130  is shown disposed in the lumen  114  of the catheter  112  and including the sleeve  142  and magnetic assembly  160  in a configuration similar to that shown in  FIG. 8 . In the present embodiment, however, the ECG sensor assembly  150  is not included on the stylet  130 , but rather includes the ECG leads  182  disposed on the catheter itself. Particularly, the ECG leads  182  are integrated into the wall of the catheter such that an outer surface of each lead is exposed at the outer surface of the catheter. This configuration enables the ECG leads  182  of the ECG sensor assembly  150  to serve as electrodes in the manner previously described, but on a catheter having a closed distal end as shown in  FIG. 11 . The ECG lead wires  184  are electrically connected to the ECG leads  182  and disposed within the wall of the catheter itself so as to extend proximally to an external ECG sensor module or other suitable device. 
     Thus, placement of the ECG leads  182  at an outer catheter surface as shown in  FIG. 11  enables the leads to act as electrodes and be in continual contact with the blood present in the vasculature of the patient, which blood serves as a conducting medium for the ECG signal from the heart. Note that in previous embodiments, the ECG leads disposed on the stylet itself are in contact with the blood most often via a catheter having an open proximal end. Again, it should be noted that the embodiments depicted in  FIGS. 8-11  are exemplary of the various possible configurations for the stylet and its magnetic and ECG sensor assemblies, and that the type, size, and number of elements of these components may be varied as one skilled in the art will appreciate. For instance, the ECG sensor can be included on a stylet without the magnetic assembly present in one embodiment. 
     Attention is now directed generally to  FIGS. 12-22 , which depict further examples of the distal segment  132  of the stylet  130  including both magnetic and sensor assemblies, according to present embodiments. In  FIG. 12 , the distal segment  132  includes the tubing  142  inside which is disposed a distal portion of the core wire  131 , terminating at the core wire distal end  131 B. The magnetic assembly  160 , including a plurality of permanent magnets  162  or other suitable magnetic/electromagnetic elements, is disposed distally to the core wire  131 , though other positional configurations for the magnetic assembly are possible. A conductive wire  190  proximally extends within the tubing  142  from the stylet distal end  130 B to the proximal end of the stylet for connection with a suitable ECG sensor module or other suitable monitoring device. A distal end  190 B of the conductive wire  190  is substantially co-terminal with the stylet distal end  130 B, though other more proximal terminating configurations are also possible. A conductive epoxy  166  is included at the distal end of the tubing  142  to secure the conductive wire distal end  190 B and increase the conductive surface area for ECG signal monitoring by the ECG sensor, implemented here as the distal portion of the conductive wire  190 . Of course, other suitable tip configurations can be used, including atraumatic tips, tip welds, non-conductive adhesives, or nothing at all. In another embodiment, the conductive wire can be embedded within the tubing and is exposed only at the distal end of the stylet. 
     The embodiment of  FIG. 13  is similar to that of  FIG. 12 , wherein the conductive wire  190  does not extend the length of the stylet  130  but rather is connected at a proximal end  190 A thereof to the core wire  131 . Thus the conductive pathway from the conductive wire distal end  190 B, which serves as the ECG sensor, is established by the lengths of both the conductive wire  190  and the core wire  131 . The conductive wire proximal end  190 A can be secured to the core wire via a weld, adhesive, etc. This embodiment may be used, for example, where the tubing  142  does not proximally extend the entire length of the stylet  130 , but rather only along the distal segment thereof. Indeed, in the embodiments described herein, the tubing can extend along all or only a portion of the stylet length. 
     In  FIG. 14 , a conductive coil  194  proximally extends within the tubing  142  and about the magnetic assembly  160  from the stylet distal end  130 B to a connection point with the core wire  131  at the proximal end  194 A of the coil. The conductive coil proximal end  194 A can be secured to the core wire  131  via a weld, adhesive, etc. A distal end  194 B of the conductive coil  194  is substantially co-terminal with the stylet distal end  130 B, though other more proximal terminating configurations are also possible. A conductive epoxy  166  is included at the distal end of the tubing  142  to secure the conductive coil distal end  194 B and increase the conductive surface area for ECG signal monitoring by the ECG sensor, implemented here as the distal portion of the conductive coil  194 . In other embodiments, the conductive epoxy or other suitable material can extend a greater or lesser distance into the tubing  142  than what is shown in the accompanying drawings. In another embodiment, the conductive coil can proximally extend the length of the stylet  130  for connection with a suitable ECG sensor module or other suitable monitoring device. In yet another embodiment, a distal portion of the core wire can be shaped, such as via grinding, then coiled to form a conductive coil that is integral to the core wire. 
     In  FIG. 15 , the tubing  142  can be made electrically conductive, such as via impregnation therein of a conductive material, or by coating an inner or outer surface thereof with a conductive material. Thus a distal portion of the tubing  142  at the distal end  130 B of the stylet  130  serves as an ECG sensor and more proximal portions of the tubing define a conductive pathway for carrying the ECG signals therefrom. 
     In  FIG. 16 , internal tubing  198  can be included within the tubing  142  of the stylet distal segment  132  as part of an ECG sensor assembly. In the present embodiment, a proximal end  198 A of the internal tubing  198  is attached to a portion of the core wire  131  via heat-shrinking, adhesive, etc., while a distal end  198 B is substantially co-terminal with the stylet distal end  130 B or is in intimate contact with the conductive epoxy  166  so as to enable the reception of ECG signals for transmission along the internal tubing  198  and core wire  131  to a suitable ECG sensor module external to the patient, as has been described. 
     In  FIG. 17 , the tubing  142  from earlier embodiments is replaced with a conductive tubing structure, such as a metallic hypotube  202 , which attaches to the core wire  131  at a proximal end  202 A and extends to the stylet distal end  130 B of the stylet  130  where its distal end  202 B contacts the conductive epoxy  166 . The hypotube  202  can include perforations  204 , such as horizontal, vertical, round, or helical notches or through-holes completely or partially defined through the hypotube surface so as to increase flexibility of the hypotube. 
     Note that, in this and other embodiments, the conductive epoxy  166  or other tip configuration, such as atraumatic tips, adhesives, tip welds, etc., can be suitable shaped as seen in  FIG. 17  so as to ease advancement of the catheter and stylet through patient vasculature. In one embodiment for example, the conductive epoxy tip can be replaced by a tip including stainless steel, either pre-formed before attachment, e.g., via welding, adhesive, etc., to the stylet distal end or shaped after attachment. Such a tip can be attached directly to the stylet core wire, to another conductive wire in the stylet, or to another ECG sensor configuration. 
       FIG. 18  shows another tubing embodiment, wherein the tubing is defined by a conductive external coil  208 , attached at a proximal end  208 A thereof and extending to a distal end  208 B, which is in contact with the conductive epoxy  166  at the stylet distal end  130 B. A safety wire  210  can be included so as to extend between a distal portion of the core wire  131  and the distal tip epoxy  166  so as to prevent separation of the external coil  208  from the stylet  130 . In another embodiment, the safety wire can be replaced with internal tubing that is disposed about the magnetic assembly  160 . 
     In  FIG. 19 , the conductive epoxy  166  extends proximally from the distal end  130 B of the stylet  130 , contained by the tubing  142 , so as to be in electrical communication with the core wire  131 . Thus, a distal portion of the conductive epoxy  166  serves as an ECG sensor, while more proximal portions thereof provide a conductive pathway, together with the core wire, to enable the transmission of ECG signals through the stylet  130 . Note that in another embodiment, the tubing can extend the length of the stylet. 
     In  FIG. 20 , an annular conductive ring  214  is included as an ECG sensor at the stylet distal end  130 B and is connected to a lead wire  216  that extends proximally along the length of the stylet  130  for connection with a suitable ECG sensor module or other suitable device. The ring  214  can be inset into the tubing  142  and can be in electrical communication with the conductive epoxy  166 . As before, the conductive epoxy can be omitted from the design. In another embodiment, the lead wire  216  can be electrically connected to the core wire instead of extending the entire length of the stylet. 
     In  FIG. 21 , a conductive coil  218  is positioned distal to and attached to the tubing  142 . A tip weld  154  is formed on the stylet distal end  130 B so as to electrically connect with the conductive coil  218 . The conductive wire  190  extends distally from the core wire  131  to the tip weld  154  as shown in  FIG. 21 , or to the conductive coil  218 . In another embodiment, the conductive wire can extend the length of the stylet. In yet another embodiment, the conductive coil can be replaced by a conductive hypotube, if desired, which can act as filler material for the plasma weld that forms the tip weld  154 . 
     In  FIG. 22 , the core wire  130  includes a distal tip  131 B that defines an atraumatic tip configuration, with the conductive epoxy  166  included to secure the distal tip to the tubing  142 . Such a core wire distal tip can be formed by grinding, plasma welding, etc., and provides an ECG sensor with relatively large surface area for reception of ECG signals. 
     It is noted that in example embodiments, distal tips can be formed by a variety of procedures, including grinding or plasma welding as discussed in connection with  FIG. 22 , insertion and adhesion to the stylet of an already formed tip, insertion of a conductive slug into the stylet tubing that is then melted and formed with a die, etc. It should be further noted that the embodiments shown in the previously described drawings are merely examples of possible configurations for providing a magnetic assembly and an ECG sensor with a stylet for guidance of a catheter or other indwelling device within the body of a patient. As such, the claims of the present disclosure should not be construed as being limited to only those embodiments explicitly described herein. 
     Embodiments of the present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative, not restrictive. The scope of the present disclosure is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.