Abstract:
A feedthrough assembly for use with implantable medical devices having a shield structure, the feedthrough assembly engaging with the remainder of the associated implantable medical device to form a seal with the medical device to inhibit unwanted gas, liquid, or solid exchange into or from the device. One or more feedthrough wires extend through the feedthrough assembly to facilitate transceiving of the electrical signals with one or more implantable patient leads. The feedthrough assembly is connected to a mechanical support which houses one or more filtering capacitors that are configured to filter and remove undesired frequencies from the electrical signals received via the feedthrough wires before the signals reach the electrical circuitry inside the implantable medical device. The mechanical support may further include an isolation structure that isolates the feedthrough wires.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 12/412,281, filed Mar. 26, 2009, which is a continuation-in-part of U.S. patent application Ser. No. 11/734,146, filed Apr. 11, 2007, now U.S. Pat. No. 7,693,576, which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to implantable medical devices and more particularly to shielded feedthrough structures that connect one or more implantable patient leads to various operational circuitry within the housing of the implantable medical devices while maintaining a hermetic seal of the devices. 
     BACKGROUND OF THE INVENTION 
     A variety of implantable medical devices have been developed and employed for long-term implanted monitoring of one or more patient physiological conditions and/or delivery of indicated therapy. Implantable cardiac stimulation devices are one particular category of implantable devices which are adapted to monitor the patients&#39; physiological conditions, including their cardiac activity, and to generate and deliver indicated therapy to treat one or more arrhythmic conditions. Implantable cardiac stimulation devices typically include either a high voltage circuit for generating high voltage waveforms, a low voltage circuit for generating relatively low voltage pacing stimuli, or both low voltage and high voltage circuits that generate waveforms for delivery to patient tissue. These devices also typically include a microprocessor-based controller which regulates the delivery of the high voltage or pacing pulse waveforms. The high and/or low and/or low voltage circuits and the controller circuitry are generally encased within a biocompatible can or housing along with a battery to power the device. 
     Implantable cardiac stimulation devices typically also include one or more implantable patient leads with associated electrodes. The implantable patient leads are typically connected at one end to a corresponding electrode that delivers therapy to the patient&#39;s heart and at the other end to the high and/or low voltage circuitry and controller in the can or housing. Because of the highly corrosive liquid implanted environment and because the materials and operations of the electrical circuitry are not compatible unless properly isolated from each other, the connection between the leads and the circuitry inside the housing must be such that a hermetic seal is maintained. Thus, typically, connections between the electrical circuits disposed inside the housing of the implantable device and the patient leads outside of the housing are achieved through one or more feedthrough assemblies. 
     The feedthrough assemblies provide for connection between the leads outside of the housing and the circuitry inside the housing while maintaining a hermetic seal. Additionally, the feedthrough assembly of an implantable medical device generally includes circuitry for filtering the electrical signals received through the patient leads so as to attenuate the spectrum of unwanted frequencies before they reach the circuitry inside the housing of the implantable device. Prior art implantable cardiac stimulation devices generally achieve this filtering through multilayer ceramic type capacitors, such as discoidal capacitors. These discoidal type capacitors are typically disposed inside the feedthrough assembly. The capacitors are very specialized, difficult to manufacture, and are therefore expensive. Because of the specialized type capacitors, prior art feedthrough assemblies occupy premium space in the length of the feed-through area. 
     As implantable medical devices are configured to be implanted inside a patient&#39;s body, their overall dimension cannot exceed certain predetermined sizes. An increase in the size of the implantable device may result in added discomfort to the patient while a decrease in size can reduce potential irritation for the patient. Further, due to the limited possible size of these devices, the amount of space inside the device is also limited. Thus, the size of various components used in an implantable medical device is an important design consideration. Smaller components may create space for additional features, while a larger component may limit the size for other features and components. The large size of the feedthrough device due to the inclusion of the filtering capacitors thus reduces the amount of space in that dimension within the housing that can be used for circuitry or therapy delivering components. Hence, there is a need for a feedthrough structure that provides filtering capability but has a reduced footprint within the housing to thereby allow for more space for other components. 
     SUMMARY 
     What is described herein is a shielded feedthrough assembly for coupling implantable patient leads to electrical and other operational circuitry of an implantable medical device. In one implementation, the feedthrough assembly includes one or more feedthrough wires, an insulator, and a feedthrough case. In one embodiment, the feedthrough case is connected to a mechanical support comprised, in one specific embodiment, of multiple ceramic layers. One or more filtering capacitors can be disposed inside a wire bondable ceramic substrate of the mechanical support to filter and inhibit transmission of undesired frequencies from electrical signals received through the implanted patient leads. In one embodiment, the feedthrough wires extend to a second surface of the mechanical support and, in this embodiment, an isolation layer is formed to inhibit the transmission of electrical noise onto the nearby components. In one specific implementation, the isolation layer comprises a first insulating layer that is non-conductive that isolates adjacent wires from each other and a second conductive layer, overlying the first isolation layer, that provides additional shielding The shielded feedthrough assembly, isolation layer, feedthrough wires, the mechanical support, and a housing of the implantable medical device act in combination to provide a shield between the environment and the sensitive circuitry of the device. 
     Thus, one embodiment includes an implantable cardiac stimulation device comprising at least one lead adapted to be implanted adjacent the patient&#39;s heart tissue so as to delivery therapy to the patient&#39;s heart and so as to sense electrical activity indicative of the function of the patient&#39;s heart, a controller that receives signals from the at least one lead indicative of the electrical activity which is indicative of the function of the patient&#39;s heart wherein the controller also induces the delivery of therapeutic electrical stimulation to the patient&#39;s heart via the at least one lead, a casing that defines a cavity that houses the controller wherein the casing is adapted to be implanted within the body of the patient and inhibit the entry of body fluids into the cavity of the casing that contains the controller, wherein the casing defines a feedthrough opening through which the at least one feedthrough wire extends so as to be communicatively coupled to the controller, a feedthrough structure that is positioned within the feedthrough opening wherein the feedthrough structure comprises the at least one feedthrough wire which is coupled to the at least one lead, a mechanical support having a first surface that is coupled to the feedthrough structure via the first surface so as to be positioned within the casing cavity, wherein the mechanical support defines an interior volume and wherein the mechanical support defines an opening through which the at least one feedthrough wire extends so as communicatively couple the controller to the at least one lead, and an isolation structure positioned on a second surface of the mechanical support so as to isolate the feedthrough wire. In one implementation, the isolation structure includes a first isolation layer that is non-conductive and a second layer positioned on the first layer that is conductive. 
     In one embodiment the casing of the implantable cardiac stimulation device is formed of a conductive material and the feedthrough structure defines a structure having a first and a second end that is formed of a conducting material such that when the feedthrough structure is positioned within the opening in the casing, a Faraday cage is established about the controller positioned within the cavity of the casing. In this implementation, the second layer of the isolation structure is conductively coupled to the conducting material so as to enhance the shielding of the Faraday cage. 
     In one embodiment, the mechanical casing is multi-layer and has at least one opening that communicates with the first surface. In this embodiment, the at least one filtering device is electrically coupled to the first surface via the opening. In another embodiment, multiple layers of the mechanical casing have conductive traces. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified diagram illustrating an implantable stimulation device in electrical communication with at least three leads implanted into a patient&#39;s heart for delivering multi-chamber stimulation and shock therapy. 
         FIG. 2  is a functional block diagram of a multi-chamber implantable stimulation device illustrating the basic elements of a stimulation device which can provide cardioversion, defibrillation and pacing stimulation in four chambers of the heart. 
         FIG. 3  illustrates a schematic top view of one embodiment of a shielded feedthrough assembly in an implantable medical device. 
         FIGS. 4A-4B  are top views of one embodiment of a mechanical support in an implantable medical device. 
         FIG. 4C  is a top view of one embodiment of a ceramic layer included in the mechanical support of  FIGS. 4A-4B . 
         FIG. 5  is a circuit diagram of one embodiment of the filtering capacitors disposed in the mechanical support of  FIGS. 4A-4B . 
         FIGS. 6A and 6B  are top and bottom perspective views illustrating a second embodiment of a feedthrough assembly. 
         FIGS. 7A-7C  are side cross-sectional, top cross-sectional and detailed side-cross sectional views of the support member of the second embodiment of the feedthrough assembly of  FIGS. 6A and 6B  illustrating how the capacitors of the support member can be grounded via a surface. 
         FIGS. 8A-8D  are side and top cross sectional views of the support member of  FIGS. 6A and 6B  taken at two different levels illustrating how the capacitors and feedthroughs can be interconnected at different levels. 
         FIGS. 9A-9C  are perspective, bottom and cross-sectional views of a third embodiment of a feedthrough assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made to the drawings wherein like numerals refer to like parts throughout. The following description is of the best mode presently contemplated for practicing the invention. This description is not to be taken in a limiting sense but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be ascertained with reference to the issued claims. In the description of the invention that follows, like numerals or reference designators will be used to refer to like parts or elements throughout. 
     In one embodiment, as shown in  FIG. 1 , a device  10  comprising an implantable cardiac stimulation device  10 , is in electrical communication with a patient&#39;s heart  12  by way of three leads,  20 ,  24  and  30 , suitable for delivering multi-chamber stimulation and shock therapy. To sense atrial cardiac signals and to provide right atrial chamber stimulation therapy, the stimulation device  10  is coupled to an implantable right atrial lead  20  having at least an atrial tip electrode  22 , which typically is implanted in the patient&#39;s right atrial appendage. 
     To sense left atrial and ventricular cardiac signals and to provide left chamber pacing therapy, the stimulation device  10  is coupled to a “coronary sinus” lead  24  designed for placement in the “coronary sinus region” via the coronary sinus ostium (OS) for positioning a distal electrode adjacent to the left ventricle and/or additional electrode(s) adjacent to the left atrium. As used herein, the phrase “coronary sinus region” refers to the vasculature of the left ventricle, including any portion of the coronary sinus, great cardiac vein, left marginal vein, left posterior ventricular vein, middle cardiac vein, and/or small cardiac vein or any other cardiac vein accessible by the coronary sinus. 
     Accordingly, an exemplary coronary sinus lead  24  is designed to receive atrial and ventricular cardiac signals and to deliver left ventricular pacing therapy using at least a left ventricular tip electrode  26 , left atrial pacing therapy using at least a left atrial ring electrode  27 , and shocking therapy using at least a left atrial coil electrode  28 . 
     The stimulation device  10  is also shown in electrical communication with the patient&#39;s heart  12  by way of an implantable right ventricular lead  30  having, in this embodiment, a right ventricular tip electrode  32 , a right ventricular ring electrode  34 , a right ventricular (RV) coil electrode  36 , and a superior vena cava (SVC) coil electrode  38 . Typically, the right ventricular lead  30  is transvenously inserted into the heart  12  so as to place the right ventricular tip electrode  32  in the right ventricular apex so that the RV coil electrode  36  will be positioned in the right ventricle and the SVC coil electrode  38  will be positioned in the superior vena cava. Accordingly, the right ventricular lead  30  is capable of receiving cardiac signals, and delivering stimulation in the form of pacing and shock therapy to the right ventricle. 
     As illustrated in  FIG. 2 , a simplified block diagram is shown of the multi-chamber implantable stimulation device  10 , which is capable of treating both fast and slow arrhythmias with stimulation therapy, including cardioversion, defibrillation, and pacing stimulation. While a particular multi-chamber device is shown, this is for illustration purposes only and one of skill in the art could readily duplicate, eliminate or disable the appropriate circuitry in any desired combination to provide a device capable of treating the appropriate chamber(s) with cardioversion, defibrillation and pacing stimulation. 
     A housing  40  for the stimulation device  10 , shown schematically in  FIG. 2 , is often referred to as the “can”, “case” or “case electrode” and may be programmably selected to act as the return electrode for all “unipolar” modes. The housing  40  may further be used as a return electrode alone or in combination with one or more of the coil electrodes,  28 ,  36  and  38 , for shocking purposes. The housing  40  further includes a connector (not shown) having a plurality of terminals,  42 ,  44 ,  46 ,  48 ,  52 ,  54 ,  56 , and  58  (shown schematically and, for convenience, the names of the electrodes to which they are connected are shown next to the terminals). As such, to achieve right atrial sensing and pacing, the connector includes at least a right atrial tip terminal (A R  TIP)  42  adapted for connection to the atrial tip electrode  22 . 
     To achieve left chamber sensing, pacing and shocking, the connector includes at least a left ventricular tip terminal (V L  TIP)  44 , a left atrial ring terminal (A L  RING)  46 , and a left atrial shocking terminal (A L  COIL)  48 , which are adapted for connection to the left ventricular tip electrode  26 , the left atrial ring electrode  27 , and the left atrial coil electrode  28 , respectively. 
     To support right chamber sensing, pacing and shocking, the connector further includes a right ventricular tip terminal (V R  TIP)  52 , a right ventricular ring terminal (V R  RING)  54 , a right ventricular shocking terminal (R V  COIL)  56 , and an SVC shocking terminal (SVC COIL)  58 , which are adapted for connection to the right ventricular tip electrode  32 , right ventricular ring electrode  34 , the RV coil electrode  36 , and the SVC coil electrode  38 , respectively. 
     At the core of the stimulation device  10  is a programmable microcontroller  60  which controls the various modes of stimulation therapy. As is well known in the art, the microcontroller  60  typically includes a microprocessor, or equivalent control circuitry, designed specifically for controlling the delivery of stimulation therapy and may further include RAM or ROM memory, logic and timing circuitry, state machine circuitry, and I/O circuitry. Typically, the microcontroller  60  includes the ability to process or monitor input signals (data) as controlled by a program code stored in a designated block of memory. The details of the design and operation of the microcontroller  60  are not critical to the invention. Rather, any suitable microcontroller  60  may be used that carries out the functions described herein. The use of microprocessor-based control circuits for performing timing and data analysis functions are well known in the art. 
     As shown in  FIG. 2 , an atrial pulse generator  70  and a ventricular pulse generator  72  generate pacing stimulation pulses for delivery by the right atrial lead  20 , the right ventricular lead  30 , and/or the coronary sinus lead  24  via an electrode configuration switch  74 . It is understood that in order to provide stimulation therapy in each of the four chambers of the heart, the atrial and ventricular pulse generators,  70  and  72 , may include dedicated, independent pulse generators, multiplexed pulse generators, or shared pulse generators. The pulse generators,  70  and  72 , are controlled by the microcontroller  60  via appropriate control signals,  76  and  78 , respectively, to trigger or inhibit the stimulation pulses. 
     The microcontroller  60  further includes timing control circuitry  79  which is used to control the timing of such stimulation pulses (e.g., pacing rate, atrio-ventricular (AV) delay, atrial interconduction (A-A) delay, or ventricular interconduction (V-V) delay, etc.) as well as to keep track of the timing of refractory periods, noise detection windows, evoked response windows, alert intervals, marker channel timing, etc., which is well known in the art. 
     The switch  74  includes a plurality of switches for connecting the desired electrodes to the appropriate I/O circuits, thereby providing complete electrode programmability. Accordingly, the switch  74 , in response to a control signal  80  from the microcontroller  60 , determines the polarity of the stimulation pulses (e.g., unipolar, bipolar, combipolar, etc.) by selectively closing the appropriate combination of switches (not shown) as is known in the art. In this embodiment, the switch  74  also supports simultaneous high resolution impedance measurements, such as between the case or housing  40 , the right atrial electrode  22 , and right ventricular electrodes  32 ,  34  as described in greater detail below. 
     Atrial sensing circuits  82  and ventricular sensing circuits  84  may also be selectively coupled to the right atrial lead  20 , coronary sinus lead  24 , and the right ventricular lead  30 , through the switch  74  for detecting the presence of cardiac activity in each of the four chambers of the heart. Accordingly, the atrial (ATR. SENSE) and ventricular (VTR. SENSE) sensing circuits,  82  and  84 , may include dedicated sense amplifiers, multiplexed amplifiers, or shared amplifiers. The switch  74  determines the “sensing polarity” of the cardiac signal by selectively closing the appropriate switches, as is also known in the art. In this way, the clinician may program the sensing polarity independently of the stimulation polarity. 
     Each sensing circuit,  82  and  84 , preferably employs one or more low power, precision amplifiers with programmable gain and/or automatic gain control, bandpass filtering, and a threshold detection circuit, as known in the art, to selectively sense the cardiac signal of interest. The automatic gain control enables the device  10  to deal effectively with the difficult problem of sensing the low amplitude signal characteristics of atrial or ventricular fibrillation. The outputs of the atrial and ventricular sensing circuits,  82  and  84 , are connected to the microcontroller  60  which, in turn, are able to trigger or inhibit the atrial and ventricular pulse generators,  70  and  72 , respectively, in a demand fashion in response to the absence or presence of cardiac activity in the appropriate chambers of the heart. 
     For arrhythmia detection, the device  10  utilizes the atrial and ventricular sensing circuits,  82  and  84 , to sense cardiac signals to determine whether a rhythm is physiologic or pathologic. As used herein “sensing” is reserved for the noting of an electrical signal, and “detection” is the processing of these sensed signals and noting the presence of an arrhythmia. The timing intervals between sensed events (e.g., P-waves, R-waves, and depolarization signals associated with fibrillation) are then classified by the microcontroller  60  by comparing them to a predefined rate zone limit (i.e., bradycardia, normal, low rate VT, high rate VT, and fibrillation rate zones) and various other characteristics (e.g., sudden onset, stability, physiologic sensors, and morphology, etc.) in order to determine the type of remedial therapy that is needed (e.g., bradycardia pacing, anti-tachycardia pacing, cardioversion shocks or defibrillation shocks, collectively referred to as “tiered therapy”). 
     Cardiac signals are also applied to the inputs of an analog-to-digital (ND) data acquisition system  90 . The data acquisition system  90  is configured to acquire intracardiac electrogram (IEGM) signals, convert the raw analog data into a digital signal, and store the digital signals for later processing and/or telemetric transmission to an external device  102 . The data acquisition system  90  is coupled to the right atrial lead  20 , the coronary sinus lead  24 , and the right ventricular lead  30  through the switch  74  to sample cardiac signals across any pair of desired electrodes. 
     The microcontroller  60  is further coupled to a memory  94  by a suitable data/address bus  96 , wherein the programmable operating parameters used by the microcontroller  60  are stored and modified, as required, in order to customize the operation of the stimulation device  10  to suit the needs of a particular patient. Such operating parameters define, for example, pacing pulse amplitude, pulse duration, electrode polarity, rate, sensitivity, automatic features, arrhythmia detection criteria, and the amplitude, waveshape and vector of each shocking pulse to be delivered to the patient&#39;s heart  12  within each respective tier of therapy. 
     Advantageously, the operating parameters of the implantable device  10  may be non-invasively programmed into the memory  94  through a telemetry circuit  100  in telemetric communication with the external device  102 , such as a programmer, transtelephonic transceiver, or a diagnostic system analyzer. The telemetry circuit  100  is activated by the microcontroller by a control signal  106 . The telemetry circuit  100  advantageously allows IEGMs and status information relating to the operation of the device  10  (as contained in the microcontroller  60  or memory  94 ) to be sent to the external device  102  through an established communication link  104 . 
     In the preferred embodiment, the stimulation device  10  further includes a physiologic sensor  108 , commonly referred to as a “rate-responsive” sensor because it is typically used to adjust pacing stimulation rate according to the exercise state of the patient. However, the physiological sensor  108  may further be used to detect changes in cardiac output, changes in the physiological condition of the heart, or diurnal changes in activity (e.g., detecting sleep and wake states). Accordingly, the microcontroller  60  responds by adjusting the various pacing parameters (such as rate, AV Delay, V-V Delay, etc.) at which the atrial and ventricular pulse generators,  70  and  72 , generate stimulation pulses. 
     The stimulation device additionally includes a battery  110  which provides operating power to all of the circuits shown in  FIG. 2 . For the stimulation device  10 , which employs shocking therapy, the battery  110  is generally capable of operating at low current drains for long periods of time and then be capable of providing high-current pulses (for capacitor charging) when the patient requires a shock pulse. The battery  110  generally also has a predictable discharge characteristic so that elective replacement time can be detected. Accordingly, embodiments of the device  10  including shocking capability preferably employ lithium/silver vanadium oxide batteries. For embodiments of the device  10  not including shocking capability, the battery  110  will preferably be lithium iodide or carbon monoflouride or a hybrid of the two. 
     As further shown in  FIG. 2 , the device  10  is shown as having an impedance measuring circuit  112  which is enabled by the microcontroller  60  via a control signal  114 . 
     In the case where the stimulation device  10  is intended to operate as an implantable cardioverter/defibrillator (ICD) device, it generally should detect the occurrence of an arrhythmia, and automatically apply an appropriate electrical shock therapy to the heart aimed at terminating the detected arrhythmia. To this end, the microcontroller  60  further controls a shocking circuit  116  by way of a control signal  118 . The shocking circuit  116  generates shocking pulses of low (up to 0.5 joules), moderate (0.5-10 joules), or high energy (11 to 40 joules), as controlled by the microcontroller  60 . Such shocking pulses are applied to the patient&#39;s heart  12  through at least two shocking electrodes, and as shown in this embodiment, selected from the left atrial coil electrode  28 , the RV coil electrode  36 , and/or the SVC coil electrode  38 . As noted above, the housing  40  may act as an active electrode in combination with the RV electrode  36 , or as part of a split electrical vector using the SVC coil electrode  38  or the left atrial coil electrode  28  (i.e., using the RV electrode as a common electrode). 
     Cardioversion shocks are generally considered to be of low to moderate energy level (so as to minimize pain felt by the patient), and/or synchronized with an R-wave and/or pertaining to the treatment of tachycardia. Defibrillation shocks are generally of moderate to high energy level (i.e., corresponding to thresholds in the range of 5-40 joules), delivered asynchronously (since R-waves may be too disorganized), and pertaining exclusively to the treatment of fibrillation. Accordingly, the microcontroller  60  is capable of controlling the synchronous or asynchronous delivery of the shocking pulses. 
       FIG. 3  illustrates a partial frontal view of one embodiment of a shielded feedthrough assembly  300  engaged to the housing of an implantable medical device, such as the device  10  of  FIG. 1 . The feedthrough assembly  300  is used in this embodiment to, among other things, connect one or more implantable patient leads to electrical or other operational circuitry inside the housing  40  of the implantable medical device  10 . 
     The feedthrough assembly  300 , in this particular implementation, includes three feedthrough wires  310 , an insulator  320 , and a feedthrough case  330 . As illustrated, the feedthrough assembly  300  extends through a hermetically sealed outer wall of the housing  40  and into the housing  40  to couple one or more implantable patient leads to an electronic hybrid and controller board  360  while maintaining a hermetic seal. 
     The feedthrough wires  310  receive electrical signals from the patient leads and transfer the signals through the feedthrough assembly  300  to the circuitry inside the housing  40 . Thus, the feedthrough wires  310  are lead wires that are each configured for connection, at an upper end, to a patient lead such as the leads  20 ,  24 , or  30  of  FIG. 1 . The feedthrough wires  310  are, in one embodiment, connected to the patient leads through one or more connectors. In one configuration, the connectors are located in one or more headers such as the headers  11  shown in  FIG. 1 . In another embodiment, the connection between the feedthrough wires  310  and the patient leads can be achieved through welding or brazing. In yet another embodiment, the feedthrough wires  310  may form the patient leads by extending out of the feedthrough assembly and into the patient&#39;s body. 
     Each of the feedthrough wires  310  extend through respective openings in the insulator  320  towards the feedthrough case  330  and a mechanical support  340 . Because the feedthrough wires  310  are configured to be placed in an implanted location, the feedthrough wires  310  are preferably comprised of electrically conductive biocompatible materials. In one embodiment, the feedthrough wires  310  are comprised of a platinum-iridium alloy. In other embodiments, other suitable conductive biocompatible materials such as platinum, niobium, titanium, tantalum, or combinations of these alloys can be used. In yet other embodiments, the feedthrough wires  310  may be provided with a biocompatible coating or finish. 
     Although, the feedthrough assembly  300  of  FIG. 3  includes three feedthrough wires, it should be understood that depending on the number of implantable patient leads in a given implantable device, other embodiments may include more or less than three feedthrough wires. For example, in an embodiment where only one patient lead is implanted within the body of the patient, the feedthrough assembly includes only one feedthrough wire. Other implementations are also possible. For example, in some embodiments one feedthrough wire may be used to transfer signals from more than one patient lead. In other embodiments, the number of the feedthrough wires may exceed the number of implantable patient leads. 
     The feedthrough wires extend through the insulator  320 . The insulator  320  is interposed between the outside environment where the device is implanted and the inside of the housing  40  of the implantable device  10 . The insulator  320  has an outer surface  325  and an inner surface  327 . As the outer surface  325  of the insulator  320  is, in this embodiment, exposed to the implanted environment, it is generally formed of biocompatible materials or is provided with a biocompatible coating or finish. The inner surface  327  of the insulator  320  connects the insulator  320  to the feedthrough case  330 . 
     The feedthrough case  330  fits inside an opening  337  (not shown) in the hermetically sealed outer wall of the housing  40  such that there is complete insulation between the outside environment and the inside of the housing  40 . In one embodiment, this insulation is achieved by using a hermetic seal  335 . When the feedthrough case  330  is placed inside the opening  337 , the hermetic seal  335  is wrapped around an upper portion of the feedthrough case  330  and completely seals the inside of the housing  40  from the outside environment. A variety of other methods are also possible. 
     In one embodiment, the feedthrough case  330  includes three openings through which the feedthrough wires  310  extend. The feedthrough case  330  is also connected to the mechanical support  340 . In one embodiment, the mechanical support  340  is acts an interface between the feedthrough wires  310  and the hybrid and controller board  360 . 
     Generally, implantable medical devices such as, for example, the device  10  of  FIG. 1 , need to include a large number of connections between the various electronic circuits inside the housing  40  and one or more feedthrough wires, such as feedthrough wires  310 . Because of the limited space available inside an implantable medical device, routing of the many different wires and directly connecting the different circuits to the wires has become increasingly difficult. The mechanical support  340  provides an interface through which the one or more feedthrough wires  310  can be efficiently connected to the various electronic circuits without requiring too much space. As will be discussed below, the mechanical support  340  includes an interior volume in which a plurality of traces can be formed so as to facilitate routing of electrical conductors in an efficient manner. Hence, the mechanical support  340  provides an intermediate routing component that allows for electrical conductors carrying signals to be re-routed so that the conductors occupy less volume and are better isolated from each other. 
     In addition to being an interface for wire connections, the mechanical support  340  can be used to house one or more circuits used for filtering the electronic signals. Generally, implantable patient leads of an implantable device are formed of materials that provide good conductivity. However, because of their high conductivity properties, these leads sometimes act as an antenna and conduct undesired electromagnetic interference signals (EMI). These undesired signals, if transmitted to the circuitry of the housing  40 , can interfere with and adversely affect the normal operations of the device  10 . Thus, implantable medical devices generally include filtering circuits that attenuate undesired signals before they reach the electronic circuitry of the housing  40 . Previously, these filtering circuits were made of one or more discoidal type capacitors that were disposed inside the feedthrough case  330 . These discoidal type capacitors are generally specialized, need to be custom built, and are thus expensive to manufacture. 
     In order to reduce the overall size of the feedthrough assembly, make more efficient use of the limited space of the housing, and provide a more cost-effective feedthrough assembly, in one or more embodiments of the present invention, instead of being placed inside the feedthrough case  330 , the filtering capacitors are integrated into the mechanical support  340 . Additionally, manufacturing costs are further reduced by using commonly-produced capacitors that are more cost-effective than discoidal type capacitors. 
       FIGS. 4A-4C  illustrate in more detail one embodiment of the mechanical support  340 . The mechanical support  340  is a multilayer structure which includes multiple electrically insulated layers, preferably made of ceramic in one implementation, and includes one or more openings  410  through which one or more feedthrough wires, such as the feedthrough wires  310  of  FIG. 3 , can extend. 
     Additionally, the mechanical support  340  includes multiple wire-bond pads  430  that are attached to a bottom layer  460 . In this embodiment, the bottom layer  460  is used with three feedthrough wires  310 . In some other embodiments, the bottom layer  460  is used with four feedthrough wires in a quad polar feedthrough. In yet other embodiments, the bottom layer  460  is used with six feedthrough wires in a hex polar feedthrough. Generally, whether or not they are used, all pads  430  may be wire bonded to eliminate mistakes. The wire-bond pads  430  are connected at least on one side to a bottom surface of the feedthrough case  330  of  FIG. 3 . In one embodiment, the wire-bond pads  430  are wire-bonded to the internal electronics of the hybrid and controller board  360 . As illustrated in  FIG. 3 , each of the wire-bond pads  430  is connected through at least one connector  355  to the hybrid and controller board  360 . Thus, the wire-bond pads  430  facilitate the transfer of signals from the feedthrough wires  310  to the electronic circuits of the housing  40 . 
     As illustrated in  FIG. 4A , one or more top layers of the mechanical support  340  also include four openings  420  configured for receiving four capacitors. As illustrated, the openings  410  extend through one or more, but not all, layers of the mechanical support  340 . At least one layer of the mechanical support  340 , such as the layer  440  illustrated in  FIG. 4C , includes one or more traces  445  that connect the openings  410  to the wire-bond pads  430 . Thus, when capacitors  450 , illustrated in  FIG. 4B , are placed inside the openings  420 , the traces  445  each connect one side of the capacitors  450  to one of the openings  410  and the other side of the capacitors  450  to one of the wire-bond pads  430 . At least one of the wire bond pads  430  is connected to the outer surface of the feedthrough case  330  and thus acts as the system ground for the mechanical support  340 . Thus in effect, the traces  445  connect the capacitors  450  between the feedthrough wires  310  and the system ground. 
     In one embodiment, the mechanical support  340  also includes a metal shield  350  (shown in  FIG. 3 ) which forms the outside surface of the mechanical support  340 . By encasing the mechanical support  340 , the metal shield  350  creates a Faraday cage effect inside the mechanical support  340 . The Faraday cage effect blocks external electrical fields and thus in effect inhibits external undesired frequencies from entering the mechanical support  340  thus shielding the conductors positioned therein. In other embodiments, the Faraday cage effect is achieved by metallization of the outer surface of the mechanical support  340 . 
     The mechanical support  340  of  FIGS. 4A-4C  is a quad-polar structure. Alternative configurations of the mechanical support  340  are also possible. For example, in one embodiment, the mechanical support  340  can form a hex-polar structure. Other embodiments are also possible. For example, in one embodiment, each of the traces  445  of the mechanical support  340  is placed on a separate layer of the mechanical support  340 . In another embodiment, different layers include two or more, but not all the traces  445 . 
     A mechanical support of a feedthrough assembly is generally manufactured by stacking the various layers that form the mechanical structure on top of one another and laminating the stack with printing to form an assembly. The assembly is then fired into a final state. In implementations where the various layers are formed of ceramic, the firing generally needs to be done at a high temperature to assure proper processing. 
     A mechanical support  340  of an embodiment of the present invention, is manufactured, in one implementation, by stacking the one or more layers on top of one another, placing the one or more capacitors  450  into the openings  420 , and encasing the mechanical support  340  into the metal shield  350  to form an assembly before firing the assembly into a final state. However, in configurations where the various layers are formed of ceramic, the various layers may be stacked on top of another and fired into a final state before connecting the capacitors to the resulting assembly. This may be done in some embodiments, because the high temperature required for firing ceramic layers may in some instances cause damage to some capacitors. Therefore, in one embodiment, the capacitors are connected to the mechanical support  340  through soldering or other similar methods known in the art, after the layers have been fired. 
       FIG. 5  illustrates one exemplary embodiment of a circuit diagram showing the connections between the capacitors  450  of  FIG. 4B  and one or more feedthrough wires  310 . Each of the capacitors  510 - 540  of  FIG. 5  illustrates one of the capacitors  450  of  FIG. 4B . As illustrated, a capacitor  510  is connected between a pin  1  and the ground. Pin  1  is connected to one of the feedthrough wires  310  which is itself connected to the implantable right atrial lead  20  of  FIG. 1 . Because the lead  20  is itself coupled to the right atrial tip electrode  22  of  FIG. 1 , the capacitor  510  is thus connected to and receives signals from the right atrial tip electrode (AT)  22 . 
     Similarly, pins  2  and  3  of  FIG. 5  are connected to feedthrough wires  310  that are themselves connected to the coronary sinus lead  24  of  FIG. 1 . The coronary sinus lead  24  is coupled to the left atrial ring electrode (AR)  27  and the left ventricular tip electrode (VT)  26 . Thus the capacitor  520  which is connected to pin  2  is connected to and receives signals from the left atrial ring electrode (AR)  27  and the capacitor  530  which is connected to pin  3  is connected to and receives signals from the left ventricular tip electrode (VT)  26 . 
     In a similar manner, the capacitor  540  which is connected to pin  4  is connected to a feedthrough wire  310  coupled to the right ventricular lead  30  of  FIG. 1 . Thus, because the right ventricular lead  30  is coupled to the right ventricular ring (VR)  34  of  FIG. 1 , the capacitor  540  is connected to and receives signals from the right ventricular ring (VR)  34 . 
     The capacitors  510 - 540  are chosen such that they can filter and remove undesired frequencies from the electrical signals they receive. Because all four capacitors are connected to the system ground, the undesired frequencies are passed directly to the system ground before they can reach the electrical circuitry of the housing  40  and result in any adverse effects. 
     It will be appreciated that in various embodiments the materials and processes selected can be adapted to the structural and electrical requirements as well as to the expected operating environment of the particular application. For example, as the insulator  320  and the feedthrough wires  310  are in certain embodiments not exposed to the external implanted environment, the insulator  320  and the feedthrough wires  310  can comprise materials and processes which are not generally considered biocompatible, such as solder and/or certain conductive materials. 
       FIGS. 6A and 6B  illustrate an alternative embodiment of a feedthrough assembly  600  similar to the assembly  300  described above. In this implementation, a mechanical support  640  has been modified to provide for a more efficient use of the interior space of the mechanical support  640 . As shown in  FIGS. 6A and 6B , the assembly  600  includes feedthrough wires  610  that can be coupled to the leads  22 ,  24 ,  30  in the same manner as described above. The feedthrough wires enter into a feedthrough case  630  that is substantially similar to the case  330  described above and includes an insulator  620  and a hermetic seal  635  that engages with the housing  40  in the same manner as described above. 
     The case  630  is mounted on an upper surface  641  of a mechanical support  640  of the present embodiment. The upper surface  641  of the mechanical support  640  include openings  651  that receive capacitors  750  in a similar manner as described above. The mechanical support  640  further includes openings  710  that receive the feedthroughs  610  in the same manner as the openings  410  described above in conjunction with  FIGS. 4A-C . In this implementation, the configuration of the interior space of the mechanical support  640  has been re-oriented so as to increase the amount of space that can be used for positioning the capacitors  750  so that the capacitors  750  are positioned more closely to the feedthroughs  610  to thereby reduce impedance and parasitic inductances. 
     The mechanical support further includes wire bonding pads  730  that allow for wire bond connections via connectors  355  to a hybrid and board controller  360  in substantially the same manner as described in conjunction with  FIG. 3  above. As shown in  FIGS. 6A and 6B , however, a conductive ground connection  740  extends from the upper surface  641  of the mechanical support to a lower surface  642 . In this implementation, both the upper surface  641  and the lower surface  642  of the mechanical support  640  are coated with a conductive coating. In one implementation, the upper surface  641  and the lower surface  642  are plated with an electrolytic nickel and gold using a well-known process. The conductive ground connection  740  thereby provides a uniform ground connection between the surfaces  641  and  642 . Further the side surfaces, other than the surface having the wire bonding pads  730  may also be coated for shielding purposes in the manner described above. 
     In the embodiment discussed above in connection with  FIGS. 3 and 4 , the capacitors  420  are connected to ground via traces  445  formed in a layer within the mechanical support  340 . In some implementations, connections to ground via traces formed in a layer of the mechanical support can present spacing issues which can result potential noise related issues that can affect the overall performance of the device. 
     To address this issue, the embodiment of  FIGS. 6-8  connects the capacitors  750  to ground via the conductive upper surface  641  of the mechanical support  640 . More specifically, referring to  FIGS. 7A-7C , the capacitors  750  are positioned within the openings  651 . One end of the capacitors  750  are connected to the feedthroughs  610  via traces  645  in the same manner as discussed above so as to achieve a grounding circuit similar to that shown in  FIG. 5 . As shown in  FIG. 7C , the traces  645  are located proximate the bottom surface  642  of the mechanical support  640  on one or more levels as will be discussed in greater detail hereinbelow. 
     The openings  651  are exposed to the upper surface  641  of the mechanical support  640  and a conductive material  647 , such as conductive polymer, is used to fill the openings up to the level of the surface  641  to thereby electrically interconnect the capacitors  750  to the surface  641 . In this way, all of the capacitors  750  can be coupled to the upper surface  641  of the mechanical support  340  and then subsequently be coupled to ground, in a manner that will be described hereinbelow, without requiring a layer of traces to be formed within the interior of the mechanical support  640 . The electrical connection between the capacitors  750  and the surface  641  can be accomplished in any of a number of ways including the use of conductive epoxy, solder and the like. 
     Referring back to  FIG. 6A , the feedthrough case  630  is preferably made of a conductive material such as titanium and can be electrically coupled to the upper surface  641  of the mechanical support  640  as a result of physical contact. As is also illustrated in  FIG. 6A , a conductive polymer bead  680  or like structure may also be positioned about the outer circumference of the feedthrough case  630  wherein the feedthrough case  630  is positioned proximate the upper surface  641  to thereby enhance the electrical interconnection. As discussed above in connection with the embodiment of  FIGS. 3 and 4 , the feedthrough case  630  is electrically coupled to the housing  40  which serves as ground. 
     Thus, by coating the upper surface  641  with a conductive material and electrically connecting the capacitors  750  to the upper surface  641  via solder or conductive polymer, the capacitors  750  can be coupled to ground via the feedthrough case  630  without requiring the use of a layer of wiring traces within the mechanical support  640 . This increases the amount of available space to form the traces to connect the capacitors  750  to the feedthroughs  610  thereby improving the function of the device as described above. 
     As is also illustrated in  FIGS. 7A-7C  and  8 A- 8 D, the interconnection of the feedthrough  610  to the wire bond pads  730  may be formed on a plurality of different levels within the mechanical support  640 . More specifically, in the exemplary embodiment shown in  FIGS. 8A and 8B , three of the feedthroughs  610   a - 610   c  may be connected to capacitors  750   a - 750   c  and corresponding wire bond pads  730   a - 730   c  via traces  645   a - 645   c  on one vertical level B-B of the mechanical support  640 . Further, a higher level C-C shown in  FIGS. 8C and 8D  may be used to connect a fourth feedthrough  610   d  to a capacitor  750   d  and a wire bond pad  730   d  via a trace  645   d . By offsetting the traces  645  in a vertical direction, the feedthroughs  610  can be positioned more closely to the wire bonds  730  which can further reduce parasitic capacitances and inductances and thereby improve the performance of the device. 
       FIGS. 9A-9C  illustrate another embodiment of a feedthrough assembly  900 . As shown, the assembly  900  includes a case  833  that receives the feedthrough wires  910  in the same manner as described above. The case  833  hermetically seals to the housing and provides passage of the wires  910  into the mechanical support  940  in substantially the same manner as described above. 
     As shown in  FIG. 9A , the bottom surface  942  of the mechanical support  940  includes openings  915  through which the wires  910  pass to be connected to the other circuit components. As is also shown, the region  925  surrounding the openings  915  is generally a non-conductive surface which is then surrounded by the conductive material that is positioned on the surface  942 ,  943  and  941  to provide shielding in the same manner as described above. The non-conductive area  925  provides greater isolation between the adjacent wires  910 . 
     To further enhance the isolation between the wires  910  and the shielding of the feedthrough assembly, additional isolation structures are also positioned on the bottom surface  942  of the mechanical support  940 . As shown in the previous embodiments, the ends of the wires  910  are exposed at the bottom surface  942 . Thus, the wires can pick up electromagnetic radiation which can create noise interior to the housing  40 . 
     To address this issue, this embodiment includes covering the outer surface of the non-conductive region  925  with an isolation structure  950 . In this implementation, the isolation structure  950  includes an insulating layer  945 , such as a non-conductive epoxy, so as to further electrically isolate the wires  910 . Subsequently, a conductive layer  955 , such as a conductive epoxy, is then formed over the non-conductive epoxy comprising the insulating layer  945  so that the conductive epoxy electrically interconnects the entire bottom surface  942  of the support  940 , including the non-conductive region  925 , thereby providing a more complete Faraday cage for shielding. The non-conductive epoxy serves the purpose of maintaining isolation between adjacent conductive wires  910 . 
     It will be appreciated that any of a number of conductive or non-conductive epoxies can be used without departing from the spirit of the present invention. 
     Thus, various embodiments of the present invention provide the capability to incorporate signal filtering into implantable medical device applications. Various embodiments provide and maintain an effective hermetic seal such that possible harmful contaminants are inhibited from entry to or exit from an implantable medical device which might otherwise interfere with intended operation of the device, and/or cause injury to the patient. Various embodiments also shield or inhibit interference between various electronic modules of an implantable medical device. The various embodiments facilitate reducing the size and the cost of a feedthrough assembly used in implantable medical devices. 
     Although the above disclosed embodiments of the present teachings have shown, described and pointed out the fundamental novel features of the invention as applied to the above-disclosed embodiments, it should be understood that various omissions, substitutions, and changes in the form of the detail of the devices, systems and/or methods illustrated may be made by those skilled in the art without departing from the scope of the present teachings. Consequently, the scope of the invention should not be limited to the foregoing description but should be defined by the appended claims.