Abstract:
Structures and methods relating to electrodes for incorporation into a feedthrough with a profile adapted for subcutaneous sensing of physiologic and cardiac signals. Electrode assemblies are adapted for integration with feedthroughs and provide reliable insulation from the implantable medical device housing. Various structures and manufacturing processes are implemented to provide a large sensing surface with a low profile. The subcutaneous sensing electrode assembly can provide a leadless sensing system and further enhances installation and follow-up procedures.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/230,537, filed on Jul. 31, 2009. The disclosure of the above application is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates generally to implantable medical devices; and, more particularly, to securing electrodes to implantable medical devices. 
       BACKGROUND 
       [0003]    Since the implantation of the first cardiac pacemaker, implantable IMD technology has advanced with the development of sophisticated implantable pulse generators (IPGs), implantable cardioverter-defibrillators (ICDs) arrhythmia control devices designed to detect arrhythmias and deliver appropriate therapies. Detection and discrimination between various arrhythmic episodes in order to trigger the delivery of an appropriate therapy is of considerable interest. Prescription for implantation and programming of the implanted device are based on the analysis of the PQRST electrocardiogram (ECG) and the electro gram (EGM). Waveforms are typically separated for such analysis into the P-wave and R-wave in systems that are designed to detect the depolarization of the atrium and ventricle respectively. Such systems employ detection of the occurrence of the P-wave and R-wave, analysis of the rate, regularity, and onset of variations in the rate of recurrence of the P-wave and R-wave, the morphology of the P-wave and R-wave and the direction of propagation of the depolarization represented by the P-wave and R-wave in the heart. Detection, analysis and storage of such EGM data within implanted medical devices are well known in the art. Acquisition and use of ECG tracing(s), on the other hand, has generally been limited to the use of an external ECG recording machine attached to the patient via surface electrodes of one sort or another. 
         [0004]    ECG systems that detect and analyze the PQRST complex depend upon the spatial orientation and number of externally applied electrodes available near or around the heart to detect or sense the cardiac depolarization wave front. Implantable medical device systems increasingly can include communication means between implanted devices and/or an external device, for example, a programming console, monitoring system, and similar systems. For diagnostic purposes, it is desirable that the implanted device communicate information regarding the device&#39;s operational status and the patient&#39;s condition to the physician or clinician. Implantable devices can transmit or telemeter a digitized electrical signal to display electrical cardiac activity (e.g., an ECG, EGM, or the like) for storage, display and/or analysis by an external device. 
         [0005]    To diagnose and measure cardiac events, a cardiologist has several tools from which to choose. Such tools include twelve-lead electrocardiograms, exercise stress electrocardiograms, Holter monitoring, radioisotope imaging, coronary angiography, myocardial biopsy, and blood serum enzyme tests. In spite of these advances in the medical device art, the surface ECG has remained a standard diagnostic tool. A twelve-lead ECG is typically the first procedure used to determine cardiac status prior to implanting a pacing system. An ECG recording device is attached to the patient through ECG leads connected to skin electrodes arrayed on the patient&#39;s body so as to achieve a recording that displays the cardiac waveforms in any one of twelve possible vectors. An example of ECG leads with skin electrodes may be seen with respect to U.S. Pat. No. 6,622,046 to Fraley et al. issued Sep. 16, 2003, and assigned to the assignee of the present invention. Fraley et al. discloses a feed through used in combination with an electrode to sense the human body&#39;s electrical activity. It is desirable to develop new mechanical features related to securing surface ECG electrodes to the housing of an implantable medical device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The following drawings are illustrative of particular embodiments of the present disclosure and therefore do not limit the scope of the disclosure. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description. Embodiments of the present disclosure will hereinafter be described in conjunction with the appended drawings, wherein like numerals denote like elements. 
           [0007]      FIG. 1  is an illustration of a body-implantable device system in accordance with the present disclosure, including a hermetically sealed device implanted in a patient and an external programming unit; 
           [0008]      FIG. 2  is a perspective view of an exemplary external programming unit of  FIG. 1 ; 
           [0009]      FIG. 3  is a schematic view of an implantable medical device; 
           [0010]      FIG. 4  is a schematic view of an exemplary electrode connected to a retention cup; 
           [0011]      FIG. 5  is a schematic view of an electrode connected to a retention cup of  FIG. 4  cutaway along lines  5 - 5 ; 
           [0012]      FIG. 6A  is a side view of electrode connected to a retention cup; 
           [0013]      FIG. 6B  is an angled top view of electrode connected to a retention cup; 
           [0014]      FIG. 7  is a schematic view of an implantable medical device with a dome-shaped electrode; 
           [0015]      FIG. 8  depicts a schematic view of an implantable device with a rectangular hermetic housing; 
           [0016]      FIG. 9  depicts a low profile electrode assembly of the implantable medical device shown in  FIG. 8 ; 
           [0017]      FIG. 10A  is a schematic view of a narrow hermetic housing with a feed through connected thereto; 
           [0018]      FIG. 10B  is a schematic view of a retention bracket connected to the housing; 
           [0019]      FIG. 10C  depicts an insulator cup connected to the retention bracket of  FIG. 10B ; 
           [0020]      FIG. 10D  depicts an electrode placed in the insulator cup of  FIG. 10C ; 
           [0021]      FIG. 10E  depicts a conductive wire that is flush with the surface of the electrode of  FIG. 10D ; 
           [0022]      FIG. 11  depicts a top exterior view of a retention bracket connected to an electrode and housing; 
           [0023]      FIG. 12  depicts a cross-sectional view of a retention bracket connected to an electrode and housing; 
           [0024]      FIG. 13  depicts an enlarged view of the retention bracket connected to an electrode and housing of  FIG. 12 ; and 
           [0025]      FIG. 14  depicts a schematic view of a retention bracket for supporting a surface electrode. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, similar reference numbers are used in the drawings to identify similar elements. The devices described herein include an exemplary number of leads, etc. One will understand that the components, including number and kind, may be varied without altering the scope of the disclosure. Also, devices according to various embodiments may be used in any appropriate diagnostic or treatment procedure, including a cardiac procedure. 
         [0027]      FIG. 1  depicts an implantable medical device system adapted for use in accordance with the present disclosure. The medical device system shown in  FIG. 1  includes an implantable medical device (IMD)  10  that has been implanted in patient  12 . Although the present disclosure will be described herein in an embodiment which includes a pacemaker, the disclosure may be practiced in connection with numerous other types of implantable medical device systems including neurostimulators, implantable defibrillators, and insertable cardiac monitors. 
         [0028]    In accordance with conventional practice in the art, IMD  10  is housed within a hermetically sealed, biologically inert outer housing or casing, which may comprise a metal such as titanium, stainless steel, glass, epoxy, or other suitable material. In other embodiments, the IMD housing is not hermetically sealed. One or more leads, collectively identified with reference numeral  14  in  FIG. 1  are electrically coupled to IMD  10  in a conventional manner and extend into the patient&#39;s heart  16  via a vein  18 . The leads  14  are joined to the IMD  10  by plugging the leads into the connector module  11 . Disposed generally near the distal end of leads  14  are one or more exposed conductive electrodes for receiving electrical cardiac signals and/or for delivering electrical pacing stimuli to heart  16 . Leads  14  may be implanted with their distal end(s) situated in the atrium and/or ventricle of heart  16 . 
         [0029]    Also depicted in  FIG. 1  is an external programming unit  20  for non-invasive communication with IMD  10  via uplink and downlink communication channels, to be hereinafter described in further detail. Associated with programming unit  20  is a programming head  22 , in accordance with conventional medical device programming systems, for facilitating two-way communication between IMD  10  and programmer  20 . In many known implantable device systems, a programming head such as that depicted in  FIG. 1  is positioned on the patient&#39;s body over the implant site of the device, typically within 2- to 3-inches of skin contact, such that one or more antennae within the head can send RF signals to, and receive RF signals from, an antenna disposed within the hermetic enclosure of the implanted device or disposed within the connector block of the device, in accordance with common practice in the art. 
         [0030]      FIG. 2  is a perspective view of an exemplary programming unit  20 . Internally, programmer  20  includes a processing unit (not shown) that in accordance with the present disclosure is a personal computer type motherboard, e.g., a computer motherboard including an Intel Pentium 3, Intel® Core™ microprocessor or other suitable processors and related circuitry such as digital memory. 
         [0031]    Programmer  20  comprises an outer shell  60 , which is preferably made of thermal plastic or another suitably rugged yet relatively lightweight material. A carrying handle, designated generally as  62  in  FIG. 2 , is integrally formed into the front of outer shell  60 . With handle  62 , programmer  20  can be carried like a briefcase. 
         [0032]    An articulating display screen  64  is disposed on the upper surface of outer shell  60 . Display screen  64  folds down into a closed position (not shown) when programmer  20  is not in use, thereby reducing the size of programmer  20  and protecting the display surface of display  64  during transportation and storage thereof. 
         [0033]    A disk drive is disposed within outer shell  60  and is accessible via a disk insertion slot (not shown). A hard disk drive is also disposed within outer shell  60 , and it is contemplated that a hard disk drive activity indicator, (e.g., an LED, not shown) could be provided to give a visible indication of hard disk activation. In the perspective view of  FIG. 2 , programmer  20  is shown with articulating display screen  64 . 
         [0034]    An input device  26  such as a mouse is connected to programmer  20  which serves as an on-screen pointer in a graphical user interface presented via display screen  64 . Input device  26  allows a user to input data. 
         [0035]    To sense signals from tissue of, for example, the heart and/or deliver electrical stimuli to tissue, a low profile surface electrode assembly  110  can be connected to housing  100  of a variety of differently shaped IMDs such as IMD  10 , tubular or pill-shaped IMD  150  and rectangular-shaped IMD  190  depicted in FIGS.  3  and  7 - 9 , respectively. 
         [0036]    Electrode assembly  110  includes an electrode with a feedthrough  150  such that feedthrough  150  secures a electrode  120  to the external surface of the housing  100  of IMD  10 . An example of ECG leads with skin electrodes  120  may be seen with respect to U.S. Pat. No. 6,622,046 to Fraley et al. issued Sep. 16, 2003, and assigned to the assignee of the present invention; the disclosure of which is incorporated by reference in its entirety herein. In other embodiments (such as in  FIGS. 10-14 ) the feedthrough does not secure the electrode to the housing. In one or more embodiments, the electrode  120  can be coated with a high surface area coating to increase the surface area of the electrode  120  without increasing the length and width of the electrode  120 . For example, an electrode  120  can be coated with iridium oxide to increase the surface area. 
         [0037]    Feedthrough  150  can be inserted or placed through the housing  100 . An example of a feedthrough  150  passing through an electrode may be seen with respect to U.S. Pat. No. 6,622,046 to Fraley et al. issued Sep. 16, 2003, and assigned to the assignee of the present invention, the disclosure of which is incorporated by reference in its entirety herein. 
         [0038]    Referring to  FIGS. 4 and 5 , feedthrough  150  serves to connect the electronic components or elements, surrounded by inner wall  104 , to electrode  120  located outside outer wall  102  of housing  100 . Feedthrough  150  typically comprises a feedthrough ferrule  156 , a conductive wire or pin  116 , and a feedthrough insulator  158 . The feedthrough ferrule  156  is placed in a hole or aperture in the housing  100  that is slightly larger than the outer diameter of the main ferrule body. The ferrule  156  is then welded to the housing  100 . A conductive element  116  runs through a hole in about the middle of the ferrule  156  such that an external end  136  (or T-shaped end) is coupled or connected to the electrode  120  while internal end  134  is connected to the electronics. The area between the conductive wire  116  and the ferrule  156  is filled with a hermetic insulator  158  such as glass and/or other suitable material. 
         [0039]    A securing assembly  302  supports and/or connects electrode assembly  110  to housing  100 . In one or more embodiments, securing assembly  302  comprises an insulator cup  130  and a bracket  310  that are configured to conform to the housing of IMD  10 ,  150  and  190 , respectively. For example,  FIG. 7  shows that securing assembly  302  surrounds domed-shaped electrodes  160 , which prevents electrodes  160  from inadvertently electrically shorting to the pill-shaped hermetic housing  180 . Domed-shaped securing assembly  302  also helps push the electrodes  160  away from the housing  180  and into the patient&#39;s  12  tissue. 
         [0040]    Details of the insulator cup  130  and the bracket  310  are depicted in  FIGS. 11-14 . Insulator cup  130  separates or insulates electrode  120  from housing  100 . Insulator cup  130  is configured to surround an outer circumference of feedthrough  150  and extend to an outer diameter. Insulator cup  130  can be circular, dome-shaped, rectangular-shaped or another suitable shape in order to support a surface electrode. In one embodiment, the insulator cup  130  includes at least one planar side  122   a  (also referred to as a first side) possessing a flat or substantially flat surface for connecting with housing  100 . A second side  122   b  such as a nonplanar side, of insulator cup  130  is exposed to body fluids. 
         [0041]    In the embodiment depicted in  FIG. 5 , the insulator cup  130  preferably protrudes less than about 0.1 inches perpendicular from the housing outer wall  102  to reduce any potential discomfort for the patient. In another embodiment, the insulator cup  130  protrudes less than about 0.175 inches from the housing outer wall  102 . In yet another embodiment, the insulator cup is flush with the exterior of the housing  100 . The electrode  120  is aligned with the area of the housing  100  that is covered by the insulator cup  130 . In other embodiments, the electrode  120  is about aligned with the area of the housing  100  that is covered by the insulator cup  130 . About aligned means that the angle is 45 degrees or less between the plane that contains the perimeter of the outer electrode surface  132  and the plane that contains the perimeter of the area of the housing  100  that is covered by the insulator cup  130 . 
         [0042]    A variety of biostable insulative materials can be used to form insulator cup  130 . Exemplary materials that can be used to manufacture insulator cups  130  can include polyetherimide (PEI), polyaryletheretherketone (PEEK), acrylonitrile butadiene styrene (ABS), and/or thermoplastic polyurethane (TPU); however, it should be understood that other suitable polymers can also be used. Insulator cups  130  can be manufactured by employing conventional molding or machining techniques. 
         [0043]    Bracket  310 , shown in greater detail in  FIGS. 11-14 , operates in conjunction with insulator cup  130  to form a securing assembly  310 . Bracket  310 , configured to support and/or connect the load of a surface electrode to the housing, can be Y-shaped, substantially Y-shaped, X-shaped, or other suitable shapes. Each leg  312   a,b,c  of bracket  310  can be integrally formed and spaced apart from each other by an angle θ. Angle θ can range from about 20 degrees to about 90 degrees. In another embodiment, angle θ can range from about 20 degrees to about 180 degrees. Typically, legs  312   a,b,c  are symmetrically spaced apart; however, in other embodiments, legs  312   a,b,c  can be asymmetrically spaced apart. In yet another embodiment, the bracket is disk shaped such that it does not include legs. The disk bracket includes a hole for the pin to pass therethrough. In yet another embodiment, the bracket is integrally formed with the housing. 
         [0044]    In one or more embodiments, retention bracket  310  can include snap protrusions  410  that engage a retention lip  420  on the insulator cup  130 . The vertical extension  430  of the retention bracket  310  is flexible such that pressing the insulator cup  130  onto the retention bracket  310  (causes the retention lip&#39;s lower surface  440  to engage the snap protrusion&#39;s chamfer  446 . The interaction of the retention lip&#39;s lower surface  440  and the snap protrusion&#39;s chamfer  446  causes the vertical extension  430  to flex towards the retention bracket&#39;s center  424 . Flexing towards the retention bracket&#39;s center  424  allows the retention lip  420  to move past the snap protrusion  410 . Once the snap protrusions  410  are located further from the housing outer wall  102  than the retention lip  420 , the snap protrusions  410  securely holds the insulator cup  130  in place because the snap protrusions  410  overhang or protrude over the retention lip  420 . 
         [0045]    The interference between the snap protrusions  410  and the retention lip  420  as the insulator cup  130  is pressed approximately downward onto the bracket  310  forces at least one of the retention bracket  310  and the insulator cup  130  to flex to allow the snap protrusions  410  to move past the retention lip  420 . As mentioned above, the vertical extensions  430  can flex towards the bracket&#39;s center  424 , or in other words, can flex away from the retention lip  420 . When the vertical extensions  430  flex towards the bracket&#39;s center  424 , the vertical extensions  430  flex approximately horizontally. In another embodiment, flexing towards the bracket&#39;s center  424  entails the vertical extension  430  rotating about its intersection with the horizontal portion of the leg  312  that abuts the outer wall  102  of the housing  100 . 
         [0046]    In another embodiment, the vertical extensions  430  do not flex and the snap protrusion&#39;s chamfer  446  forces the retention lip  420  to curl upward or expand in diameter. In yet another embodiment, the retention lip  420  has slots that allow the snap protrusion  410  to move past the retention lip  420  without requiring either the vertical extensions  430  or the retention lip  420  to flex. In this embodiment, the insulator cup  130  is rotated after the snap protrusions  410  have passed through the slots in the retention lip  420  in order to lock the insulator cup  130  in place. 
         [0047]      FIG. 14  shows an embodiment where the retention bracket  310  is insert molded into the insulator cup  130 . Overmolded extensions  450  of the retention bracket  310  are fully encased within the insulator cup  130  to prevent the insulator cup  130  from moving relative to the retention bracket  310 . In particular, overmolded extensions  450  of the retention bracket  310  assist insulator cup  130  to remain stationary relative to the retention bracket  310 . 
         [0048]    In one embodiment, the retention bracket  310  is manufactured by stamping the general sheet metal shape and then bending the ends of the sheet metal to form snap protrusions  410 . In another embodiment, the retention bracket  310  is machined from a metal block using a multi-axis mill. 
         [0049]      FIGS. 10A-E  depict various stages of manufacturing a low-profile electrode with a securing assembly  302 .  FIG. 10A  depicts a feedthrough that has been welded into a narrow hermetic housing  300 .  FIG. 10B  depicts a retention bracket  310  that has been connected to the narrow hermetic housing  300 . For example, the retention bracket  310  can be welded to housing  100 .  FIG. 10C  depicts an insulator cup  130  that has been snapped onto the retention bracket  310 .  FIG. 10D  depicts an electrode  120  that has been placed in on the insulator cup  130 . The conductive wire  116  extends through a small hole  320  in the electrode  120 .  FIG. 10E  depicts a conductive wire  116  that was trimmed to be about flush with the surface of the electrode  120  and then welded to the electrode  120 . Adhesive can be injected under the electrode  120  by placing the tip of the adhesive applicator in the fill hole  144 . Excess adhesive is removed in a variety of ways. For example, excess adhesive can be wiped away from the electrode  120 . 
         [0050]    In the embodiment show in  FIGS. 11-13 , the electrode  120  resides in an indentation  448  in the insulator cup  130 . Indentation  448  can help prevent the electrode  120  from moving relative to the insulator cup  130 . 
         [0051]    In other embodiments, the electrode  120  can be molded into the insulator cup  130 . For example, two weld anchor features can be molded into the insulator cup  130  in addition to the electrode. The two weld anchor features (e.g. one on each side of the electrode), could be simultaneously stamped out with the electrode in a stamped lead frame. The resulting subassembly can then be insert molded. Thereafter, the stamping break-off tab could be removed to electrically isolate the weld anchors from the electrode. This process provides one insert molded part with an electrode in the center of the insulator cup, and two weld anchors, one on each side of the electrode. A hole in the electrode provides access for the feedthrough wire to pass through the electrode for welding. The weld anchors would be welded to the housing to keep the assembly securely in place. 
         [0052]      FIGS. 8-9  depict still yet another securing assembly  302  for IMD  190 . In this embodiment, an elongated, slender implantable device  190  includes a rectangular hermetic housing  200 . Low profile rectangular electrode assemblies  204  can be located on the sides of the long, slender implantable device  190 . Rectangular insulator cups  210  support rectangular electrodes  220 . In this embodiment, securing assembly includes insulator cup  130  adhesively coupled to housing  100 . Adhesive is injected into the fill holes  244  until adhesive  140  begins to exit vents  246  to fill the area underneath the electrode  120  that is between the insulator cup  130  and the housing  100 . 
         [0053]      FIG. 4  depicts yet another embodiment in which electrode can be further adhesively bonded to housing  100 . Adhesive can be injected into the fill hole  144  until adhesive  140  begins to exit the vent  146  from filling the area underneath the electrode  120  that is between the insulator cup  130  and the housing  100 . Exemplary adhesive  140  can include silicone-based medical adhesive, epoxy resin or other suitable material. 
         [0054]    Although the present disclosure has been described in considerable detail with reference to certain disclosed embodiments, the disclosed embodiments are presented for purposes of illustration and not limitation and other embodiments of the disclosure are possible. For example, other embodiments can include ceramic brazed feedthroughs can also be used without departing from the spirit of this disclosure.