Patent Publication Number: US-9853743-B2

Title: Systems and methods for communication between medical devices

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/207,686 filed on Aug. 20, 2015, the disclosure of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure generally relates to systems, devices, and methods for communicating between medical devices, and more particularly, to systems, devices, and methods for communicating between medical devices using conducted communication. 
     BACKGROUND 
     Active implantable medical devices are routinely implanted with a patient&#39;s body. Such implantable medical devices are often used to provide therapy, diagnostics or both. In some cases, it can be desirable to communicate with such implantable medical devices via the skin, such as via a programmer or the like located outside of the body. Such communication can be though conducted communication, which conducts electrical current through the patient&#39;s body tissue from one device to the other. In the programmer example, the programmer may be electrically connected to the patient&#39;s body through electrode skin patches or the like. Such communication may facilitate the programmer in programming and/or re-programming the implantable medical device, reading data collected by the implantable medical device, and/or collecting or exchanging any other suitable information. In some instances, two or more implantable medical devices may be implanted with a patient. In such cases, it can be desirable to establish communication between the two or more implanted medical devices using conducted communication. Such communication may facility the implanted medical devices in sharing data, distribution of control and/or delivery of therapy, and/or in performing other desired functions. These are just some example uses of conducted communication in the body. 
     SUMMARY 
     The present disclosure generally relates to systems, devices, and methods for communicating between medical devices, and more particularly, to systems, devices, and methods for communicating between medical devices using conducted communication. 
     In one embodiment, a method of communicating with a medical device implanted within a patient may comprise receiving, at a medical device via electrodes connected to the patient, a conducted communication signal, wherein the conducted communication signal comprises a signal component and a noise component. In some additional embodiments, the method may further include adjusting, by the medical device, a receive threshold based at least in part on an amplitude of the received conducted communication signal, and wherein adjusting the receive threshold at least partially reduce an amplitude of the noise component of the conducted communication signal. 
     Additionally, or alternatively, in any of the above described embodiments, adjusting the receive threshold based at least in part on the amplitude of the received conducted communication signal may comprise: counting, by the medical device, a number of pulses in the conducted communication signal having an amplitude greater than the receive threshold the during a communication window, determining, by the medical device, whether the counted number of pulses exceeds a pulse count threshold, and after determining the counted number of pulses exceeds the pulse count threshold, increasing, by the medical device, the receive threshold. 
     Additionally, or alternatively, any of the above described embodiments may further comprise increasing the receive threshold by a predetermined amount. 
     Additionally, or alternatively, in any of the above described embodiments, the pulse count threshold may represent a maximum number of pulses that may form a message. 
     Additionally, or alternatively, any of the above described embodiments may further comprise, after determining the counted number of pulses exceeds the pulse count threshold, beginning, by the medical device, a new communication window. 
     Additionally, or alternatively, any of the above described embodiments may further comprise, by the medical device: tracking a communication session timer, and after determining the communication session timer has reached a threshold value, setting, by the medical device, the receive threshold to a lower predetermined value. 
     Additionally, or alternatively, any of the above described embodiments may further comprise resetting, by the medical device, the communication session timer after successfully receiving a message. 
     Additionally, or alternatively, in any of the above described embodiments, adjusting the receive threshold based at least in part on an amplitude of the received conducted communication signal may comprise: after a communication window timer reaches a threshold value, determining, by the medical device, whether a message was received before the communication window timer reached the threshold value, wherein the message represents a predefined sequence of pulses in the communication signal having an amplitude above the receive threshold, and, after determining that no message was received before the communication window timer reached the threshold value, increasing, by the medical device, the receive threshold. 
     Additionally, or alternatively, in any of the above described embodiments, increasing the receive threshold may comprise increasing the receive threshold by a predetermined amount. 
     Additionally, or alternatively, any of the above described embodiments may further comprise: before the communication window timer has reached the threshold value, determining, by the medical device, whether a message has been received, and, after determining that a message has been received before the communication window timer has reached the threshold value, resetting, by the medical device, the communication window timer value. 
     Additionally, or alternatively, any of the above described embodiments, may further comprise: tracking, by the medical device, a communication session timer, and after determining that the communication session timer has reached a threshold value, setting, by the medical device, the receive threshold to a lower predetermined value. 
     Additionally, or alternatively, any of the above described embodiments may further comprise resetting, by the medical device, the communication session timer after determining that a message has been received. 
     Additionally, or alternatively, in any of the above described embodiments, adjusting the receive threshold based at least in part on an amplitude of the received conducted communication signal may comprise setting, by the medical device, the receive threshold to a value proportional to a maximum amplitude of a pulse of the communication signal having an amplitude above the receive threshold. 
     Additionally, or alternatively, in any of the above described embodiments, setting the receive threshold to a value proportional to the maximum amplitude of a pulse of the communication signal having an amplitude above the receive threshold may comprise setting the receive threshold to the maximum value of the amplitude of the pulse of the communication signal having an amplitude above the receive threshold. 
     Additionally, or alternatively, any of the above described embodiments may further comprising setting, by the medical device, the receive threshold to a value proportional to a maximum amplitude of each pulse of the communication signal having an amplitude above the receive threshold. 
     Additionally, or alternatively, in any of the above described embodiments, the receive threshold may decay according to a predetermined function. 
     In other embodiment, a medical device may comprise one or more electrode, and a controller connected to the one or more electrodes. In some of these embodiments, the controller may be configured to receive a signal comprising a conducted communication signal communicated from an external medical device and noise signals via the one or more electrodes and adjust the receive threshold based at least in part on an amplitude of the conducted communication signal and the noise signals to filter out noise signals from the received signal. 
     Additionally, or alternatively, in any of the above described embodiments, the controller may be further configured to adjust the receive threshold by setting the receive threshold to a value proportional to a maximum amplitude of each pulse of the received signal that exceeds the receive threshold. 
     Additionally, or alternatively, in any of the above described embodiments, the receive threshold may be configured to decay according to a predetermined decay function. 
     In still another embodiment, a medical device may comprise one or more electrodes, and a controller connected to the one or more electrodes. In some of these embodiments, the controller may be configured to receive a conducted communication signal via the one or more electrodes during a communication window and count a number of pulses of the conducted communication signal within the communication window and having an amplitude greater than a receive threshold. Additionally, the controller may be further configured to, if the pulse count reaches a pulse count threshold, increase the receive threshold and begin a new communication window. 
     The above summary is not intended to describe each embodiment or every implementation of the present disclosure. Advantages and attainments, together with a more complete understanding of the disclosure, will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure may be more completely understood in consideration of the following description of various illustrative embodiments in connection with the accompanying drawings, in which: 
         FIG. 1  is a schematic block diagram of an illustrative leadless cardiac pacemaker (LCP) according to one embodiment of the present disclosure; 
         FIG. 2  is a schematic block diagram of another illustrative medical device that may be used in conjunction with the LCP of  FIG. 1 ; 
         FIG. 3  is a schematic diagram of an exemplary medical system that includes multiple LCPs and/or other devices in communication with one another; 
         FIG. 4  is a schematic diagram of a medical device system including devices that are configured for conducted communication through the body; 
         FIG. 5  depicts an example conducted communication signal sensed by a medical device including a noise component and a signal component; 
         FIG. 6  depicts an example conducted communication signal after having been relayed through a comparator circuit having a first receive threshold, in accordance with techniques of the present disclosure; 
         FIG. 7  is a flow diagram of an illustrative method that may be implemented by a medical device or medical device system, such as the illustrative medical devices and medical device systems described with respect to  FIGS. 1-4 ; 
         FIG. 8  depicts another example conducted communication signal after having been relayed through a comparator circuit with a second receive threshold, in accordance with techniques of the present disclosure; 
         FIG. 9  is a flow diagram of an illustrative method that may be implemented by a medical device or medical device system, such as the illustrative medical devices and medical device systems described with respect to  FIGS. 1-4 ; 
         FIG. 10  depicts another example conducted communication signal along with a decaying receive threshold, in accordance with techniques of the present disclosure; 
         FIG. 11A  depicts an example patch-integrity signal; 
         FIG. 11B  depicts an example cancelling or inverse signal which may be generated by a medical device such as the illustrative medical devices and medical device systems described with respect to  FIGS. 1-4 , in accordance with the techniques disclosed herein; 
         FIG. 12  depicts an example patch-integrity signal that may be sensed by a first medical device while a second medical device is delivering a cancelling or inverse signal, in accordance with techniques disclosed herein; 
         FIG. 13  is a schematic diagram of an example user interface that may be included on an external support device; and 
         FIG. 14  is a schematic diagram of a medical device system for alternately connecting a first medical device and a second medical device to a pair of electrodes connected to a patient to enhance conducted communication through the patient, in accordance with techniques disclosed herein. 
     
    
    
     While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit aspects of the disclosure to the particular illustrative embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure. 
     DESCRIPTION 
     The following description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The description and the drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the disclosure. 
     This disclosure describes systems, devices, and methods for communicating between medical devices. Some medical device systems of the present disclosure may communicate using conducted communication techniques, which may include delivering electrical communication signals into a body of a patient for conduction through the patient&#39;s body. This signal may be received by another medical device, thereby establishing a communication link between the devices. 
       FIG. 1  is a conceptual schematic block diagram of an exemplary leadless cardiac pacemaker (LCP) that may be implanted on the heart or within a chamber of the heart and may operate to sense physiological signals and parameters and deliver one or more types of electrical stimulation therapy to the heart of the patient. Example electrical stimulation therapy may include bradycardia pacing, rate responsive pacing therapy, cardiac resynchronization therapy (CRT), anti-tachycardia pacing (ATP) therapy and/or the like. As can be seen in  FIG. 1 , LCP  100  may be a compact device with all components housed within LCP  100  or directly on housing  120 . In some instances, LCP  100  may include communication module  102 , pulse generator module  104 , electrical sensing module  106 , mechanical sensing module  108 , processing module  110 , energy storage module  112 , and electrodes  114 . While a leadless cardiac pacemaker (LCP) is used as an example implantable medical device, it is contemplated that any suitable implantable medical device may be used, including implantable medical devices that provide therapy (e.g. pacing, neuro-stimulation, etc.), diagnostics (sensing), or both. 
     As depicted in  FIG. 1 , LCP  100  may include electrodes  114 , which can be secured relative to housing  120  and electrically exposed to tissue and/or blood surrounding LCP  100 . Electrodes  114  may generally conduct electrical signals to and from LCP  100  and the surrounding tissue and/or blood. Such electrical signals can include communication signals, electrical stimulation pulses, and intrinsic cardiac electrical signals, to name a few. Intrinsic cardiac electrical signals may include electrical signals generated by the heart and may be represented by an electrocardiogram (ECG). 
     Electrodes  114  may include one or more biocompatible conductive materials such as various metals or alloys that are known to be safe for implantation within a human body. In some instances, electrodes  114  may be generally disposed on either end of LCP  100  and may be in electrical communication with one or more of modules  102 ,  104 ,  106 ,  108 , and  110 . In embodiments where electrodes  114  are secured directly to housing  120 , an insulative material may electrically isolate the electrodes  114  from adjacent electrodes, housing  120 , and/or other parts of LCP  100 . In some instances, some or all of electrodes  114  may be spaced from housing  120  and connected to housing  120  and/or other components of LCP  100  through connecting wires. In such instances, the electrodes  114  may be placed on a tail (not shown) that extends out away from the housing  120 . As shown in  FIG. 1 , in some embodiments, LCP  100  may include electrodes  114 ′. Electrodes  114 ′ may be in addition to electrodes  114 , or may replace one or more of electrodes  114 . Electrodes  114 ′ may be similar to electrodes  114  except that electrodes  114 ′ are disposed on the sides of LCP  100 . In some cases, electrodes  114 ′ may increase the number of electrodes by which LCP  100  may deliver communication signals and/or electrical stimulation pulses, and/or may sense intrinsic cardiac electrical signals, communication signals, and/or electrical stimulation pulses. 
     Electrodes  114  and/or  114 ′ may assume any of a variety of sizes and/or shapes, and may be spaced at any of a variety of spacings. For example, electrodes  114  may have an outer diameter of two to twenty millimeters (mm). In other embodiments, electrodes  114  and/or  114 ′ may have a diameter of two, three, five, seven millimeters (mm), or any other suitable diameter, dimension and/or shape. Example lengths for electrodes  114  and/or  114 ′ may include, for example, one, three, five, ten millimeters (mm), or any other suitable length. As used herein, the length is a dimension of electrodes  114  and/or  114 ′ that extends away from the outer surface of the housing  120 . In some instances, at least some of electrodes  114  and/or  114 ′ may be spaced from one another by a distance of twenty, thirty, forty, fifty millimeters (mm), or any other suitable spacing. The electrodes  114  and/or  114 ′ of a single device may have different sizes with respect to each other, and the spacing and/or lengths of the electrodes on the device may or may not be uniform. 
     In the embodiment shown, communication module  102  may be electrically coupled to electrodes  114  and/or  114 ′ and may be configured to deliver communication pulses to tissues of the patient for communicating with other devices such as sensors, programmers, other medical devices, and/or the like. Communication signals, as used herein, may be any modulated signal that conveys information to another device, either by itself or in conjunction with one or more other modulated signals. In some embodiments, communication signals may be limited to sub-threshold signals that do not result in capture of the heart yet still convey information. The communication signals may be delivered to another device that is located either external or internal to the patient&#39;s body. In some instances, the communication may take the form of distinct communication pulses separated by various amounts of time. In some of these cases, the timing between successive pulses may convey information. Communication module  102  may additionally be configured to sense for communication signals delivered by other devices, which may be located external or internal to the patient&#39;s body. 
     Communication module  102  may communicate to help accomplish one or more desired functions. Some example functions include delivering sensed data, using communicated data for determining occurrences of events such as arrhythmias, coordinating delivery of electrical stimulation therapy, and/or other functions. In some cases, LCP  100  may use communication signals to communicate raw information, processed information, messages and/or commands, and/or other data. Raw information may include information such as sensed electrical signals (e.g. a sensed ECG), signals gathered from coupled sensors, and the like. In some embodiments, the processed information may include signals that have been filtered using one or more signal processing techniques. Processed information may also include parameters and/or events that are determined by the LCP  100  and/or another device, such as a determined heart rate, timing of determined heartbeats, timing of other determined events, determinations of threshold crossings, expirations of monitored time periods, activity level parameters, blood-oxygen parameters, blood pressure parameters, heart sound parameters, and the like. Messages and/or commands may include instructions or the like directing another device to take action, notifications of imminent actions of the sending device, requests for reading from the receiving device, requests for writing data to the receiving device, information messages, and/or other messages commands. 
     In at least some embodiments, communication module  102  (or LCP  100 ) may further include switching circuitry to selectively connect one or more of electrodes  114  and/or  114 ′ to communication module  102  in order to select which electrodes  114  and/or  114 ′ that communication module  102  delivers communication pulses. It is contemplated that communication module  102  may be communicating with other devices via conducted signals, radio frequency (RF) signals, optical signals, acoustic signals, inductive coupling, and/or any other suitable communication methodology. Where communication module  102  generates electrical communication signals, communication module  102  may include one or more capacitor elements and/or other charge storage devices to aid in generating and delivering communication signals. In the embodiment shown, communication module  102  may use energy stored in energy storage module  112  to generate the communication signals. In at least some examples, communication module  102  may include a switching circuit that is connected to energy storage module  112  and, with the switching circuitry, may connect energy storage module  112  to one or more of electrodes  114 / 114 ′ to generate the communication signals. 
     As shown in  FIG. 1 , a pulse generator module  104  may be electrically connected to one or more of electrodes  114  and/or  114 ′. Pulse generator module  104  may be configured to generate electrical stimulation pulses and deliver the electrical stimulation pulses to tissues of a patient via one or more of the electrodes  114  and/or  114 ′ in order to effectuate one or more electrical stimulation therapies. Electrical stimulation pulses as used herein are meant to encompass any electrical signals that may be delivered to tissue of a patient for purposes of treatment of any type of disease or abnormality. For example, when used to treat heart disease, the pulse generator module  104  may generate electrical stimulation pacing pulses for capturing the heart of the patient, i.e. causing the heart to contract in response to the delivered electrical stimulation pulse. In some of these cases, LCP  100  may vary the rate at which pulse generator  104  generates the electrical stimulation pulses, for example in rate adaptive pacing. In other embodiments, the electrical stimulation pulses may include defibrillation/cardioversion pulses for shocking the heart out of fibrillation or into a normal heart rhythm. In yet other embodiments, the electrical stimulation pulses may include anti-tachycardia pacing (ATP) pulses. It should be understood that these are just some examples. When used to treat other ailments, the pulse generator module  104  may generate electrical stimulation pulses suitable for neuro-stimulation therapy or the like. Pulse generator module  104  may include one or more capacitor elements and/or other charge storage devices to aid in generating and delivering appropriate electrical stimulation pulses. In at least some embodiments, pulse generator module  104  may use energy stored in energy storage module  112  to generate the electrical stimulation pulses. In some particular embodiments, pulse generator module  104  may include a switching circuit that is connected to energy storage module  112  and may connect energy storage module  112  to one or more of electrodes  114 / 114 ′ to generate electrical stimulation pulses. 
     LCP  100  may further include an electrical sensing module  106  and mechanical sensing module  108 . Electrical sensing module  106  may be configured to sense intrinsic cardiac electrical signals conducted from electrodes  114  and/or  114 ′ to electrical sensing module  106 . For example, electrical sensing module  106  may be electrically connected to one or more electrodes  114  and/or  114 ′ and electrical sensing module  106  may be configured to receive cardiac electrical signals conducted through electrodes  114  and/or  114 ′ via a sensor amplifier or the like. In some embodiments, the cardiac electrical signals may represent local information from the chamber in which LCP  100  is implanted. For instance, if LCP  100  is implanted within a ventricle of the heart, cardiac electrical signals sensed by LCP  100  through electrodes  114  and/or  114 ′ may represent ventricular cardiac electrical signals. Mechanical sensing module  108  may include, or be electrically connected to, various sensors, such as accelerometers, blood pressure sensors, heart sound sensors, piezoelectric sensors, blood-oxygen sensors, and/or other sensors which measure one or more physiological parameters of the heart and/or patient. Mechanical sensing module  108 , when present, may gather signals from the sensors indicative of the various physiological parameters. Both electrical sensing module  106  and mechanical sensing module  108  may be connected to processing module  110  and may provide signals representative of the sensed cardiac electrical signals and/or physiological signals to processing module  110 . Although described with respect to  FIG. 1  as separate sensing modules, in some embodiments, electrical sensing module  106  and mechanical sensing module  108  may be combined into a single module. In at least some examples, LCP  100  may only include one of electrical sensing module  106  and mechanical sensing module  108 . In some cases, any combination of the processing module  110 , electrical sensing module  106 , mechanical sensing module  108 , communication module  102 , pulse generator module  104  and/or energy storage module may be considered a controller of the LCP  100 . 
     Processing module  110  may be configured to direct the operation of LCP  100 . For example, processing module  110  may be configured to receive cardiac electrical signals from electrical sensing module  106  and/or physiological signals from mechanical sensing module  108 . Based on the received signals, processing module  110  may determine, for example, occurrences and types of arrhythmias. Processing module  110  may further receive information from communication module  102 . In some embodiments, processing module  110  may additionally use such received information to determine occurrences and types of arrhythmias. In still some additional embodiments, LCP  100  may use the received information instead of the signals received from electrical sensing module  106  and/or mechanical sensing module  108 —for instance if the received information is deemed to be more accurate than the signals received from electrical sensing module  106  and/or mechanical sensing module  108  or if electrical sensing module  106  and/or mechanical sensing module  108  have been disabled or omitted from LCP  100 . 
     After determining an occurrence of an arrhythmia, processing module  110  may control pulse generator module  104  to generate electrical stimulation pulses in accordance with one or more electrical stimulation therapies to treat the determined arrhythmia. For example, processing module  110  may control pulse generator module  104  to generate pacing pulses with varying parameters and in different sequences to effectuate one or more electrical stimulation therapies. As one example, in controlling pulse generator module  104  to deliver bradycardia pacing therapy, processing module  110  may control pulse generator module  104  to deliver pacing pulses designed to capture the heart of the patient at a regular interval to help prevent the heart of a patient from falling below a predetermined threshold. In some cases, the rate of pacing may be increased with an increased activity level of the patient (e.g. rate adaptive pacing). For instance, processing module  110  may monitor one or more physiological parameters of the patient which may indicate a need for an increased heart rate (e.g. due to increased metabolic demand). Processing module  110  may then increase the rate at which pulse generator  104  generates electrical stimulation pulses. 
     For ATP therapy, processing module  110  may control pulse generator module  104  to deliver pacing pulses at a rate faster than an intrinsic heart rate of a patient in attempt to force the heart to beat in response to the delivered pacing pulses rather than in response to intrinsic cardiac electrical signals. Once the heart is following the pacing pulses, processing module  110  may control pulse generator module  104  to reduce the rate of delivered pacing pulses down to a safer level. In CRT, processing module  110  may control pulse generator module  104  to deliver pacing pulses in coordination with another device to cause the heart to contract more efficiently. In cases where pulse generator module  104  is capable of generating defibrillation and/or cardioversion pulses for defibrillation/cardioversion therapy, processing module  110  may control pulse generator module  104  to generate such defibrillation and/or cardioversion pulses. In some cases, processing module  110  may control pulse generator module  104  to generate electrical stimulation pulses to provide electrical stimulation therapies different than those examples described above. 
     Aside from controlling pulse generator module  104  to generate different types of electrical stimulation pulses and in different sequences, in some embodiments, processing module  110  may also control pulse generator module  104  to generate the various electrical stimulation pulses with varying pulse parameters. For example, each electrical stimulation pulse may have a pulse width and a pulse amplitude. Processing module  110  may control pulse generator module  104  to generate the various electrical stimulation pulses with specific pulse widths and pulse amplitudes. For example, processing module  110  may cause pulse generator module  104  to adjust the pulse width and/or the pulse amplitude of electrical stimulation pulses if the electrical stimulation pulses are not effectively capturing the heart. Such control of the specific parameters of the various electrical stimulation pulses may help LCP  100  provide more effective delivery of electrical stimulation therapy. 
     In some embodiments, processing module  110  may further control communication module  102  to send information to other devices. For example, processing module  110  may control communication module  102  to generate one or more communication signals for communicating with other devices of a system of devices. For instance, processing module  110  may control communication module  102  to generate communication signals in particular pulse sequences, where the specific sequences convey different information. Communication module  102  may also receive communication signals for potential action by processing module  110 . 
     In further embodiments, processing module  110  may control switching circuitry by which communication module  102  and pulse generator module  104  deliver communication signals and/or electrical stimulation pulses to tissue of the patient. As described above, both communication module  102  and pulse generator module  104  may include circuitry for connecting one or more electrodes  114  and/ 114 ′ to communication module  102  and/or pulse generator module  104  so those modules may deliver the communication signals and electrical stimulation pulses to tissue of the patient. The specific combination of one or more electrodes by which communication module  102  and/or pulse generator module  104  deliver communication signals and electrical stimulation pulses may influence the reception of communication signals and/or the effectiveness of electrical stimulation pulses. Although it was described that each of communication module  102  and pulse generator module  104  may include switching circuitry, in some embodiments, LCP  100  may have a single switching module connected to the communication module  102 , the pulse generator module  104 , and electrodes  114  and/or  114 ′. In such embodiments, processing module  110  may control the switching module to connect modules  102 / 104  and electrodes  114 / 114 ′ as appropriate. 
     In some embodiments, processing module  110  may include a pre-programmed chip, such as a very-large-scale integration (VLSI) chip or an application specific integrated circuit (ASIC). In such embodiments, the chip may be pre-programmed with control logic in order to control the operation of LCP  100 . By using a pre-programmed chip, processing module  110  may use less power than other programmable circuits while able to maintain basic functionality, thereby potentially increasing the battery life of LCP  100 . In other instances, processing module  110  may include a programmable microprocessor or the like. Such a programmable microprocessor may allow a user to adjust the control logic of LCP  100  after manufacture, thereby allowing for greater flexibility of LCP  100  than when using a pre-programmed chip. 
     Processing module  110 , in additional embodiments, may include a memory circuit and processing module  110  may store information on and read information from the memory circuit. In other embodiments, LCP  100  may include a separate memory circuit (not shown) that is in communication with processing module  110 , such that processing module  110  may read and write information to and from the separate memory circuit. The memory circuit, whether part of processing module  110  or separate from processing module  110 , may be volatile memory, non-volatile memory, or a combination of volatile memory and non-volatile memory. 
     Energy storage module  112  may provide a power source to LCP  100  for its operations. In some embodiments, energy storage module  112  may be a non-rechargeable lithium-based battery. In other embodiments, the non-rechargeable battery may be made from other suitable materials. In some embodiments, energy storage module  112  may include a rechargeable battery. In still other embodiments, energy storage module  112  may include other types of energy storage devices such as capacitors or super capacitors. 
     To implant LCP  100  inside a patient&#39;s body, an operator (e.g., a physician, clinician, etc.), may fix LCP  100  to the cardiac tissue of the patient&#39;s heart. To facilitate fixation, LCP  100  may include one or more anchors  116 . The one or more anchors  116  are shown schematically in  FIG. 1 . The one or more anchors  116  may include any number of fixation or anchoring mechanisms. For example, one or more anchors  116  may include one or more pins, staples, threads, screws, helix, tines, and/or the like. In some embodiments, although not shown, one or more anchors  116  may include threads on its external surface that may run along at least a partial length of an anchor member. The threads may provide friction between the cardiac tissue and the anchor to help fix the anchor member within the cardiac tissue. In some cases, the one or more anchors  116  may include an anchor member that has a cork-screw shape that can be screwed into the cardiac tissue. In other embodiments, anchor  116  may include other structures such as barbs, spikes, or the like to facilitate engagement with the surrounding cardiac tissue. 
     In some examples, LCP  100  may be configured to be implanted on a patient&#39;s heart or within a chamber of the patient&#39;s heart. For instance, LCP  100  may be implanted within any of a left atrium, right atrium, left ventricle, or right ventricle of a patient&#39;s heart. By being implanted within a specific chamber, LCP  100  may be able to sense cardiac electrical signals originating or emanating from the specific chamber that other devices may not be able to sense with such resolution. Where LCP  100  is configured to be implanted on a patient&#39;s heart, LCP  100  may be configured to be implanted on or adjacent to one of the chambers of the heart, or on or adjacent to a path along which intrinsically generated cardiac electrical signals generally follow. In these examples, LCP  100  may also have an enhanced ability to sense localized intrinsic cardiac electrical signals and deliver localized electrical stimulation therapy. 
       FIG. 2  depicts an embodiment of another device, medical device (MD)  200 , which may operate to sense physiological signals and parameters and/or deliver one or more types of electrical stimulation therapy to tissues of the patient. In the embodiment shown, MD  200  may include a communication module  202 , a pulse generator module  204 , an electrical sensing module  206 , a mechanical sensing module  208 , a processing module  210 , and an energy storage module  218 . Each of modules  202 ,  204 ,  206 ,  208 , and  210  may be similar to modules  102 ,  104 ,  106 ,  108 , and  110  of LCP  100 . Additionally, energy storage module  218  may be similar to energy storage module  112  of LCP  100 . However, in some embodiments, MD  200  may have a larger volume within housing  220 . In such embodiments, MD  200  may include a larger energy storage module  218  and/or a larger processing module  210  capable of handling more complex operations than processing module  110  of LCP  100 . 
     While MD  200  may be another leadless device such as shown in  FIG. 1 , in some instances MD  200  may include leads, such as leads  212 . Leads  212  may include electrical wires that conduct electrical signals between electrodes  214  and one or more modules located within housing  220 . In some cases, leads  212  may be connected to and extend away from housing  220  of MD  200 . In some embodiments, leads  212  are implanted on, within, or adjacent to a heart of a patient. Leads  212  may contain one or more electrodes  214  positioned at various locations on leads  212  and various distances from housing  220 . Some leads  212  may only include a single electrode  214 , while other leads  212  may include multiple electrodes  214 . Generally, electrodes  214  are positioned on leads  212  such that when leads  212  are implanted within the patient, one or more of the electrodes  214  are positioned to perform a desired function. In some cases, the one or more of the electrodes  214  may be in contact with the patient&#39;s cardiac tissue. In other cases, the one or more of the electrodes  214  may be positioned subcutaneously but adjacent the patient&#39;s heart. The electrodes  214  may conduct intrinsically generated electrical cardiac signals to leads  212 . Leads  212  may, in turn, conduct the received electrical cardiac signals to one or more of the modules  202 ,  204 ,  206 , and  208  of MD  200 . In some cases, MD  200  may generate electrical stimulation signals, and leads  212  may conduct the generated electrical stimulation signals to electrodes  214 . Electrodes  214  may then conduct the electrical stimulation signals to the cardiac tissue of the patient (either directly or indirectly). MD  200  may also include one or more electrodes  214  not disposed on a lead  212 . For example, one or more electrodes  214  may be connected directly to housing  220 . 
     Leads  212 , in some embodiments, may additionally contain one or more sensors, such as accelerometers, blood pressure sensors, heart sound sensors, blood-oxygen sensors, and/or other sensors which are configured to measure one or more physiological parameters of the heart and/or patient. In such embodiments, mechanical sensing module  208  may be in electrical communication with leads  212  and may receive signals generated from such sensors. 
     While not required, in some embodiments MD  200  may be an implantable medical device. In such embodiments, housing  220  of MD  200  may be implanted in, for example, a transthoracic region of the patient. Housing  220  may generally include any of a number of known materials that are safe for implantation in a human body and may, when implanted, hermetically seal the various components of MD  200  from fluids and tissues of the patient&#39;s body. In such embodiments, leads  212  may be implanted at one or more various locations within the patient, such as within the heart of the patient, adjacent to the heart of the patient, adjacent to the spine of the patient, or any other desired location. 
     In some embodiments, MD  200  may be an implantable cardiac pacemaker (ICP). In these embodiments, MD  200  may have one or more leads, for example leads  212 , which are implanted on or within the patient&#39;s heart. The one or more leads  212  may include one or more electrodes  214  that are in contact with cardiac tissue and/or blood of the patient&#39;s heart. MD  200  may be configured to sense intrinsically generated cardiac electrical signals and determine, for example, one or more cardiac arrhythmias based on analysis of the sensed signals. MD  200  may be configured to deliver CRT, ATP therapy, bradycardia therapy, and/or other therapy types via leads  212  implanted within the heart. In some embodiments, MD  200  may additionally be configured to provide defibrillation/cardioversion therapy. 
     In some instances, MD  200  may be an implantable cardioverter-defibrillator (ICD). In such embodiments, MD  200  may include one or more leads implanted within a patient&#39;s heart. MD  200  may also be configured to sense electrical cardiac signals, determine occurrences of tachyarrhythmias based on the sensed electrical cardiac signals, and deliver defibrillation and/or cardioversion therapy in response to determining an occurrence of a tachyarrhythmia (for example by delivering defibrillation and/or cardioversion pulses to the heart of the patient). In other embodiments, MD  200  may be a subcutaneous implantable cardioverter-defibrillator (SICD). In embodiments where MD  200  is an SICD, one of leads  212  may be a subcutaneously implanted lead. In at least some embodiments where MD  200  is an SICD, MD  200  may include only a single lead which is implanted subcutaneously but outside of the chest cavity, however this is not required. 
     In some embodiments, MD  200  may not be an implantable medical device. Rather, MD  200  may be a device external to the patient&#39;s body, and electrodes  214  may be skin-electrodes that are placed on a patient&#39;s body. In such embodiments, MD  200  may be able to sense surface electrical signals (e.g. electrical cardiac signals that are generated by the heart or electrical signals generated by a device implanted within a patient&#39;s body and conducted through the body to the skin). MD  200  may further be configured to deliver various types of electrical stimulation therapy, including, for example, defibrillation therapy via skin-electrodes  214 . 
       FIG. 3  illustrates an embodiment of a medical device system and a communication pathway through which multiple medical devices  302 ,  304 ,  306 , and/or  310  of the medical device system may communicate. In the embodiment shown, medical device system  300  may include LCPs  302  and  304 , external medical device  306 , and other sensors/devices  310 . External device  306  may be a device disposed external to a patient&#39;s body, as described previously with respect to MD  200 . In at least some examples, external device  306  may represent an external support device such as a device programmer, as will be described in more detail below. Other sensors/devices  310  may be any of the devices described previously with respect to MD  200 , such as ICPs, ICDs, and SICDs. Other sensors/devices  310  may also include various diagnostic sensors that gather information about the patient, such as accelerometers, blood pressure sensors, or the like. In some cases, other sensors/devices  310  may include an external programmer device that may be used to program one or more devices of system  300 . 
     Various devices of system  300  may communicate via communication pathway  308 . For example, LCPs  302  and/or  304  may sense intrinsic cardiac electrical signals and may communicate such signals to one or more other devices  302 / 304 ,  306 , and  310  of system  300  via communication pathway  308 . In one embodiment, one or more of devices  302 / 304  may receive such signals and, based on the received signals, determine an occurrence of an arrhythmia. In some cases, device or devices  302 / 304  may communicate such determinations to one or more other devices  306  and  310  of system  300 . In some cases, one or more of devices  302 / 304 ,  306 , and  310  of system  300  may take action based on the communicated determination of an arrhythmia, such as by delivering a suitable electrical stimulation to the heart of the patient. One or more of devices  302 / 304 ,  306 , and  310  of system  300  may additionally communicate command or response messages via communication pathway  308 . The command messages may cause a receiving device to take a particular action whereas response messages may include requested information or a confirmation that a receiving device did, in fact, receive a communicated message or data. 
     It is contemplated that the various devices of system  300  may communicate via pathway  308  using RF signals, inductive coupling, optical signals, acoustic signals, or any other signals suitable for communication. Additionally, in at least some embodiments, the various devices of system  300  may communicate via pathway  308  using multiple signal types. For instance, other sensors/device  310  may communicate with external device  306  using a first signal type (e.g. RF communication) but communicate with LCPs  302 / 304  using a second signal type (e.g. conducted communication). Further, in some embodiments, communication between devices may be limited. For instance, as described above, in some embodiments, LCPs  302 / 304  may communicate with external device  306  only through other sensors/devices  310 , where LCPs  302 / 304  send signals to other sensors/devices  310 , and other sensors/devices  310  relay the received signals to external device  306 . 
     In some cases, the various devices of system  300  may communicate via pathway  308  using conducted communication signals. Accordingly, devices of system  300  may have components that allow for such conducted communication. For instance, the devices of system  300  may be configured to transmit conducted communication signals (e.g. current and/or voltage pulses, referred herein as electrical communication pulses) into the patient&#39;s body via one or more electrodes of a transmitting device, and may receive the conducted communication signals via one or more electrodes of a receiving device. The patient&#39;s body may “conduct” the conducted communication signals from the one or more electrodes of the transmitting device to the electrodes of the receiving device in the system  300 . In such embodiments, the delivered conducted communication signals may differ from pacing pulses, defibrillation and/or cardioversion pulses, or other electrical stimulation therapy signals. For example, the devices of system  300  may deliver electrical communication pulses at an amplitude/pulse width that is sub-threshold. That is, the communication pulses may have an amplitude/pulse width designed to not capture the heart. In some cases, the amplitude/pulse width of the delivered electrical communication pulses may be above the capture threshold of the heart, but may be delivered during a refractory period of the heart and/or may be incorporated in or modulated onto a pacing pulse, if desired. In some cases, the delivered electrical communication pulses may be notches or other disturbances in a pacing pulse. 
     Unlike normal electrical stimulation therapy pulses, the electrical communication pulses may be delivered in specific sequences which convey information to receiving devices. For instance, delivered electrical communication pulses may be modulated in any suitable manner to encode communicated information. In some cases, the communication pulses may be pulse width modulated and/or amplitude modulated. Alternatively, or in addition, the time between pulses may be modulated to encode desired information. In some cases, a predefined sequence of communication pulses may represent a corresponding symbol (e.g. a logic “1” symbol, a logic “0” symbol, an ATP therapy trigger symbol, etc.). In some cases, conducted communication pulses may be voltage pulses, current pulses, biphasic voltage pulses, biphasic current pulses, or any other suitable electrical pulse as desired. 
       FIG. 4  shows an illustrative medical device system  400  that may be configured to operate according to techniques disclosed herein. For example, the system may include multiple devices connected to a patient represented by heart  410  and skin  415 , where at least some of the devices are configured for communication with other devices. In the exemplary system  400 , an LCP  402  is shown fixed to the interior of the right ventricle of the heart  410 , and external support device  420  and external defibrillator  406  are shown connected to skin  415  through skin electrodes  404  and  408 , respectively. External support device  420  can be used to perform functions such as device identification, device programming and/or transfer of real-time and/or stored data between devices using one or more of the communication techniques described herein. In at least some embodiments, LCP  402  and external support device  420  are configured to communicate through conducted communication. 
     In some embodiments, external defibrillator  406  may be configured to deliver a voltage and/or current signal into the patient through skin  415  as a patch-integrity signal, and may further sense the patch-integrity signal in order to determine information about the contact between electrodes  408  and skin  415 . External defibrillator  406  may be configured to display or emit an alarm if the received patch-integrity signal indicates insufficient contact between electrodes  408  and skin  415  to achieve sufficient sensing by the patch electrodes  408  of cardiac electrical signals of heart  410  and/or for safe delivery of defibrillation and/or cardioversion pulses. In some embodiments, the patch-integrity signal may represent a continuous signal, such as a sine-wave, square-wave, saw-tooth wave, or the like. Additionally, and in some cases, the patch-integrity signal may have a frequency of between about 50 kHz and about 150 kHz, but this is not required. In some instances, this patch-integrity signal may interfere with the conducted communication signals delivered and received by LCP  402  and external support device  420 . Accordingly, the LCP  402  and/or external support device  420  may employ one or more techniques for enhancing the effectiveness of their conducted communication scheme, as described in more detail below. 
     It should be understood that the system of  FIG. 4  is just one example system that may benefit from the techniques disclosed herein. Other system may include additional and/or different devices, but may still include a device delivering a conducted signal into the body of a patient that may interfere with conducted communication signals delivered into the patient&#39;s body for inter-device communication. Additionally, other systems may have different communication schemes that use additional communication modalities and/or include intermediary devices that receive conducted communication signals from a first device and relay received messages to a second device. 
       FIG. 5  depicts an example conducted communication signal  500  that may be received by LCP  402 . Although the description of the following examples uses external support device  420  as a transmitter and LCP  402  as a receiver, it should be understood that this is only for ease of description. The below described techniques may be implemented by any device of a system, such as system  400 , with any of the devices of the system acting as the transmitter and any of the devices of the system acting as the receiver. This may include inter-device communication between, for example, two or more implanted medical devices, such as LCP  402  and another LCP (not shown in  FIG. 4 .) and/or other implanted device. 
     In the example shown in  FIG. 5 , conducted communication signal  500  includes signal component  502  and noise component  504 . In the example shown, signal component  502  represents a series of communication pulses  503  delivered by external support device  420  (or other internal or external device). In the example shown, noise component  504  represents a patch-integrity signal delivered by external defibrillator  406 . Once LCP  402  receives the conducted communication signal, LCP  402  may perform initial amplification and/or filtering. Conducted communication signal  500  of  FIG. 5  may represent the output of the initial amplification and/or filtering. LCP  402  may provide the conducted communication signal  500  to a comparator circuit, which may be part of a communication module of LCP  402 . The comparator circuit may compare the conducted communication signal  500  to a receive threshold, such as a programmable receive threshold  505 . In some cases, the comparator circuit may produce a pulse each time the conducted communication signal  500  is above the programmable receive threshold  505 , resulting in a conducted communication signal  550  such as shown in  FIG. 6 . That is, in the example shown, the comparator circuit may generate a high signal (e.g. one of pulses  552 ) whenever the amplitude of conducted communication signal  500  is higher than the receive threshold  505 . 
     As described, in some conducted communication schemes, the specific characteristics or spacing of received pulses, such as pulses  552  of conducted communication signal  550 , may convey information. In some embodiments, LCP  402  and external support device  420  may be configured according to a specific communication protocol, whereby specific patterns of pulse characteristics and/or pulse spacing may represent predefined messages. Some example messages may include identification messages, commands, requests for data, and the like. If a received set of pulses do not have the characteristics that correspond to a recognized message format, the device may determine that a valid message has not been received, and conversely if a received set of pulses do have the characteristics that correspond to a recognized message formats, the device may determine that a valid message has been received. 
     In at least some instances, LCP  402  and/or external support device  420  may also determine whether a received message is valid by checking a received message for errors. For instance, the receiving device, even after receiving a series of pulses that correspond to a recognized message format, may employ one or more error checking schemes, such as repetition codes, parity bits, checksums, cyclic redundancy checks (CRC), or the like. When so provided, the device may only determine that a received message is valid if the error checking algorithm determines that there are no errors, or no significant errors, in the received message. 
     As can be seen in  FIG. 6 , conducted communication signal  550  includes pulses  552  generated from both signal component  502  and noise component  504  of conducted communication signal  500 . Accordingly, and in some instances, LCP  402  may determine that conducted communication signal  550  is not a valid message as the pulse pattern will not match a recognized message format. In this example, receive threshold  505  is set too low such that portions of noise component  504  have an amplitude high enough to pass through the comparator circuit and generate pulses  552  in conducted communication signal  550 . 
       FIG. 7  is a flow diagram of an illustrative method  700  that LCP  402  (or another device) may implement in order to adjust receive threshold  505  based, at least in part, on the amplitude of conducted communication signal  500 . Adjusting receive threshold  505  to be above the amplitude of noise component  504  of conducted communication signal  500  may allow only signal component  502  to pass through the comparator circuit resulting in a conducted communication signal that only includes pulses due to signal component  502 . This may produce a valid message received at LCP  402 . 
     In the example method  700 , LCP  402  may begin by setting receive threshold  505  to an initial value, as shown at  702 . The initial value may be set such that, under most conditions, receive threshold  505  is below the amplitude of signal component  502  of conducted communication signal  500 . Next, LCP  402  may reset and begin a communication window timer, as shown at  704 , and reset and begin a communication session timer, as shown at  706 . In some embodiments, LCP  402  may begin the communication window timer only at predefined times. For instance, the communication window timer may be synchronized to line up with one or more features of a sensed cardiac electrical signal, such as an R-wave. In such an example, once LCP  402  resets the communication window timer, LCP  402  may wait to start the communication window timer until sensing a particular feature in the cardiac electrical signal. In at least some instances, LCP  402  may start the communication window timer after a predefined time after sensing the particular feature. As one example, LCP  402  may wait between about 50 ms and about 150 ms after sensing an R-wave to begin the communication window timer. 
     In some cases, LCP  402  may count the number of received pulses in a received conducted communication signal, as shown at  708 . For instance, received conducted communication signal  500  may be passed through the comparator circuit using receive threshold  505 , resulting in conducted communication signal  550 . As one example implementation, LCP  402  may increment a pulse count value every time LCP  402  detects a pulse in conducted communication signal  550 . 
     Next, LCP  402  may determine whether the communication session timer has exceeded the communication session timer threshold, as shown at  710 . If the communication session timer has exceeded the communication session timer threshold, LCP  402  may begin method  700  again back at  702 . The communication session timer may help ensure that if receive threshold  505  ever gets set above the maximum amplitude of signal component  502  of conducted communication signal  500 , receive threshold  505  is reset to a lower value. Although step  702  includes setting receive threshold  505  back to its initial value, in some instances, if LCP  402  arrives at step  702  through block  712 , LCP  402  may set receive threshold  505  to a lower value that is different than the initial value. For instance, LCP  402  may simply reduce the value of receive threshold  505  instead of setting it back to its initial value. 
     If LCP  402  determines that the communication session timer has not exceeded the communication session timer threshold, LCP  402  may determine whether the communication window timer has exceeded the communication window timer threshold, as shown at  712 . If LCP  402  determines that the communication window timer exceeded the communication window timer threshold, LCP  402  may reset the pulse count and reset and begin the communication window timer, as shown at  720 , and then begin again with counting received pulses at  708 . 
     If LCP  402  determines that the communication window timer does not exceed the communication window timer threshold, LCP  402  may determine whether a valid message was received, as shown at  714 . For example, LCP  402  may compare the pattern of received pulses to predefined pulse patterns that represent messages. In some instances, LCP  402  may run one or more error checking schemes before or after determining whether the pattern of received pulses corresponds to one of the predefined pulse patterns. LCP  402  may determine that a valid message has been received after determining that the pattern of received pulses corresponds to one of the predefined pulse patterns, and if so provided, after determining that t there are no errors, or significant errors, in the received pulse pattern. If LCP  402  determines that a valid message has been received, LCP  402  may begin the method again at block  706 , such as by following the ‘YES’ branch of block  714 . 
     If no valid message has yet been received, LCP  402  may determine whether the pulse count is greater than the pulse count threshold, as shown at  716 . The pulse count threshold may be set to above a maximum number of pulses that LCP  402  could possibly receive in a valid message. For instance, if each message may correspond to a predefined pulse pattern or sequence, there may be a maximum number of pulses that may be sent in a given message. Accordingly, if LCP  402  receives a number of pulses that is above the pulse count threshold within a communication window, LCP  402  may conclude that the conducted communication signal  550  has been corrupted by noise. Therefore, if LCP  402  determines that the pulse count has exceeded the pulse count threshold, LCP  402  may increase the value of receive threshold  505  and reset the pulse count, as shown at  718 , and begin method  700  again at step  704 . LCP  402  may increase the value of receive threshold  505  by a predetermined amount, based on how long it took for the number of received pulses to exceed the pulse count threshold, based on how much the number of received pulses exceeded the pulse count threshold, and/or based on any other suitable criteria. If the pulse count has not exceed the pulse count threshold, LCP  402  may loop back to step  708  and continue counting received pulses. 
     In some instances, LCP  402  may wait until the end of a communication window to determine whether a valid message was received and whether the pulse count exceeded the pulse count threshold. For instance, blocks  714  and  716  may be connected to the ‘YES’ branch block  712 , such that LCP  402  only determines whether a valid message was received and whether the pulse count exceeded the pulse count threshold after the communication window timer exceeds the communication window timer threshold. Block  720  may then be connected to the ‘NO’ branch of block  716 . 
     The LCP  402  may be configured to adjust receive threshold  505  based at least in part on the amplitude of conducted communication signal  500 . Setting receive threshold  505  at an appropriate level effectively filters out noise component  504  in conducted communication signal  550 . In operation, method  700  may work to increase receive threshold  505  above the peak amplitude of noise component  504  such that the peaks of noise component  504  are below receive threshold  505  such that the comparator circuit does not produce corresponding pulses in conducted communication signal  550 . However, receive threshold  505  may remain below the peak amplitude of signal component  502 , such that the comparator circuit does produce pulses in conducted communication signal  550  that correspond to the pulses in signal component  502 . 
       FIG. 8  depicts conducted a communication signal  550   a , which represents the output of the comparator circuit when the receive threshold  505  had been set higher than the maximum amplitude of noise component  504  but lower than the maximum amplitude of signal component  502 . As can be seen, conducted communication signal  550  only includes pulses due to signal component  502  of conducted communication signal  500 . When so provided, LCP  402  may interpret conducted communication signal  550   a  as a valid message. 
       FIG. 9  depicts a flowchart of another illustrative method  750  that LCP  402  (or another device) may use to adjust the receive threshold  505 . In this case, the receive threshold  505  may be adjusted based, at least in part, on the amplitude of conducted communication signal  500 . In the illustrative method  750 , LCP  402  may receive regular messages from another device, such as external support device  420 . In one example, at least one message may be received during each communication window. 
     LCP  402  may begin, as shown in method  700 , by setting receive threshold  505  to an initial value, resetting and beginning a communication window timer, and resetting and beginning a communication session timer, as shown at  752 ,  754 , and  756 , respectively. Next, LCP  452  may determine whether the communication session timer has exceeded the communication session timer threshold, as shown at  758 . 
     If LCP  402  determines that the communication window session timer has not exceeded the communication window session threshold, LCP  402  may determine whether the communication window timer has exceeded the communication window timer threshold, as shown at  760 . If LCP  402  determines that the communication window timer has not exceeded the communication window timer threshold, LCP  402  may determine whether a valid message has been received, as a shown t  764 . If no valid messaged has been received, LCP  402  may loop back to block  758 . In this manner, LCP  402  may continue to check whether a valid message has been received during a communication window. 
     If LCP  402  determines that the communication window timer has exceeded the communication window timer threshold, LCP  402  may determine whether at least one valid messaged was received during the communication window. If no valid message was received, LCP  402  may increase receive threshold  505  and reset and begin the communication window timer, as shown at  766 , and begin method  750  again at  758 . LCP  402  may increase the value of receive threshold  505  by a predetermined amount, based on how long it took for the number of received pulses to exceed the pulse count threshold, or based on other criteria. If LCP  402  determines that at least one valid message has been received, LCP  402  may begin method  750  again at block  754 . 
     In this manner, if receive threshold  505  is set too low, e.g. below the maximum amplitude of noise component  504 , LCP  402  will not readily receive valid messages and will then increase the receive threshold  505 . This will continue until receive threshold  505  is set above the amplitude of noise component  504  and LCP  402  may begin to receive valid messages based on only the signal component  502 . 
     In some instances, LCP  402  may wait until after the communication window timer has exceeded the communication window timer threshold before determining whether a valid message has been received. For example, method  750  may not include block  764  at all. Instead, the ‘NO’ branch of block  760  may connect directly to block  756 . 
     In some instances, LCP  402  may wait longer than a single communication window period before determining whether a pulse count exceeds a pulse count threshold or whether a valid message was received. For example, LCP  402  may wait until two, three, or even four communication windows have elapsed before making any determinations. These are just some example alternatives to the method shown in  FIG. 9 . 
       FIG. 10  depicts another method for adjusting the receive threshold  505 .  FIG. 10  depicts conducted communication signal  500  along with a dynamic receive threshold  505 A, where the dynamic receive threshold  505 A is reset to a new value on each of the peaks of conducted communication signal  500  that exceed the then present dynamic receive threshold  505 A. 
     In the example of  FIG. 10 , dynamic receive threshold  505 A may be set to an initial value and may be configured to decay over time to lower values. It should be understood that the decay shape of dynamic receive threshold  505 A depicted in  FIG. 10  is an example only. In one non-limiting example, dynamic receive threshold  505 A may decay to about half of its initial value after 100 ms, and then decay to about one-quarter of its initial value over the subsequent 100 ms. The specific decay values and time periods may differ. It is contemplated that dynamic receive threshold  505 A may decay in a logarithmic or natural logarithmic fashion, in an exponential fashion, in a step wise fashion, or any other desirable way. 
     As can be seen, dynamic receive threshold  505 A is configured to decay after the conducted communication signal  500  reaches a peak amplitude that is above the then existing dynamic receive threshold  505 A. For example, in  FIG. 10 , the dynamic receive threshold  505 A begins to decay at peak  800  and at the end of peak  801 . LCP  402  may reset the dynamic receive threshold  505 A to a new higher value when conducted communication signal  500  reaches a new peak amplitude that is above the then existing dynamic receive threshold  505 A. In some embodiments, LCP  402  may continually reset dynamic receive threshold  505 A to a new, higher value as conducted communication signal  500  keeps providing peaks that exceed the decaying dynamic receive threshold  505 A. As can be seen, once conducted communication signal  500  begins to drop in amplitude, dynamic receive threshold  505 A will begin to decay. In some embodiments, dynamic receive threshold  505 A may be configured to wait to decay for a short predefined time period after being set to a new value. In some cases, instead of continually resetting dynamic receive threshold  505 A to a new, higher value, LCP  402  may wait to determine a peak of conducted communication signal  500 . In some cases, resetting a new, higher value for dynamic receive threshold  505 A may lag conducted communication signal  500  by a short period of time. 
     In some instances, instead of setting dynamic receive threshold  505 A to the value of the most recent peak of conducted communication signal  500 , LCP  402  may set dynamic receive threshold  505 A to a value that is proportional to the most recent peak of conducted communication signal  500 . For instance, LCP  402  may set dynamic receive threshold  505 A to a value that is between 60%-99% of the maximum value of the most recent peak. This is just one example. Other examples include between 70%-99%, 80%-99%, or 90%-99% of the maximum value of the most recent peak of conducted communication signal  500 . 
     In some cases, the decay characteristics of the dynamic receive threshold  505 A may be based, at least partially, on the characteristics of the conducted communication signal  500 . For example, dynamic receive threshold  505 A may be configured to decay more quickly for higher values of the dynamic receive threshold  505 A. In another example, dynamic receive threshold  505 A may be configured to decay more quickly the longer it has been since the dynamic receive threshold  505 A has been reset, which would correspond to a longer period of low amplitude activity of conducted communication signal  500 . These are just examples. 
     In some alternative embodiments, LCP  402  may adjust the receive threshold to a value where LCP  402  detects that it successfully receives communication signals but does not receive noise signals. For instance, LCP  402  may initiate a search algorithm in order to adjust a receive threshold, such as threshold  505  or  505   a . In some embodiments, the algorithm may have the receive threshold decay in a step-wise manner, and the time between decay steps may range from between about 4 ms to about 10,000 ms. The 4 ms value may represent the shortest length communication. The 10,000 ms value may represent a slow respiratory cycle which could impact a signal to noise ratio. However, in other embodiments, the time between decay steps may have any value between 4 ms and 10,000 ms. In some embodiments, the decay at each step may occur in binary ratios, such as 1/16, 1/32, 1/64, 1/128, or 1/256 or the like. For instance, at each decay step, receive threshold  505   a  may decay by the chosen 1/16 (or other chosen binary ratio) of the current value of receive threshold  505   a . In further embodiments, the decay value may change at successive steps. For instance, the first decay amount may be 1/256 of receive threshold  505   a , the second decay amount may be 1/128 of receive threshold  505   a , the third decay amount may be 1/64 of receive threshold  505   a , and the like. Once LCP  100  sets the receive threshold to a value where LCP  100  determines that it is receiving both a signal component and a noise component in received communication signals, LCP  100  may set the receive threshold to the previous value where LCP  100  did not detect both signal components and noise components in received communication signals. One particularly useful embodiments may include setting the time between decay steps at 25 ms and the decay value to 1/64. However, this is just one example. 
     In some cases, LCP  402  may employ an adaptive filter to help filter out noise component  504 . As described, the patch-integrity signal of an external defibrillator  406  may be a continuous signal having generally static characteristics, such as frequency and/or amplitude. In such cases, LCP  402  may sense, outside of a communication period, the patch-integrity signal. LCP  402  may then process the patch-integrity signal to determine at least the frequency of the signal and may configure an adaptive filter into a notch filter centered at the frequency of the patch-integrity signal. In cases where patch-integrity signal has a single frequency, or a narrow frequency spectrum, the notch filter may be particularly effective in filtering out, or at least reducing in amplitude, the noise component  504 . 
     Although the techniques were generally described separately, in instances, LCP  402  may employ multiple of the disclosed techniques simultaneously. For example, LCP  402  may implement the pulse-counting method described above in addition to a dynamic receive threshold. In another example, LCP  402  may implement the pulse counting method along with an adaptive filter. In general, in different embodiments, LCP  402  may include all combinations of the above described techniques. 
     It should be understood that although the above methods were described with LCP  402  as a receiver and external support device  420  as a transmitter, this was just for illustrative purposes. In some cases, external support device  420  may act as a receiver and may implement any techniques described with respect to LCP  402 . Additionally, it should be understood that the described techniques are not limited to system  400 . Indeed, the described techniques may be implemented by any device and/or system that uses conducted communication. 
     In some cases, one or more of the devices of system  400  (or other system) may be configured to actively cancel the patch-integrity signal. For instance, in the example of  FIG. 4 , instead of (or in addition to) devices of system  400  adjusting receive thresholds or adaptive filters, one or more of the devices of system  400  may inject a cancelling or inverse signal into the patient body in order to cancel out, or at least reduce the amplitude of, the patch-integrity signal delivered by external defibrillator  406 . The below description uses external support device  420  only as an example of a device that may perform the described techniques. It should be understood, however, that the techniques described herein may be applied by any of the devices of system  400 , or by other devices in other systems as desired. 
       FIG. 11A  depicts an example patch-integrity signal  810  signal that may be delivered by an external defibrillator  406 . External support device  420  may sense signals propagating through a patient&#39;s body, including patch-integrity signal  810 , during a period of relative electrical quietness within the patient&#39;s body. For instance, external support device  420  may sense propagating electrical signals in the patient via electrodes  404  between heartbeats of the patient and while no conducted communication signals are propagating through the patient&#39;s body. Where patch-integrity signal  810  is sufficiently different from other signals propagating through the patient&#39;s body, external support device  420  may employ one or more filters to filter out signals other than patch-integrity signal  810 , leaving only patch-integrity signal  810 . For instance, external support device  420  may employ one or more low-pass, high-pass, bandpass, notch, and/or any other suitable filter. External support device  420  may determine various characteristics of patch-integrity signal  810 . For instance, external support device  420  may determine the frequency components, the amplitude, and/or the phase of patch-integrity signal  810 . 
     In some instances, external support device  420  may include a pulse generator module whereby external support device  420  may generate varied waveforms. After external support device  420  senses patch-integrity signal  810 , external support device  420  may generate a cancelling or inverse signal  812  (see  FIG. 11B ) using the determined characteristics. For instance, external support device  420  may generate inverse signal  812  to have a similar amplitude and frequency as patch-integrity signal  810 . However, external support device  420  may generate inverse signal  812  at a phase that is shifted relative to inverse signal  812  by one-hundred eighty degrees. An example of inverse signal  812  is depicted in  FIG. 11B . If the patch-integrity signal  810  is not a regular signal as shown in  FIG. 11A , the external support device  420  may simply generate an inverse signal  812  that will cancel out, or at least reduce the amplitude of, the patch-integrity signal  810 . Other example inverse signals may include signals that are not true inverses of the patch-integrity signal. For instance, the inverse signal, when added to the patch-integrity signal, may reduce the amplitude of the patch-integrity signal received at a device of the system which includes external support device  420 . Alternatively, the inverse signal, when added to the patch-integrity signal, may produce a signal that is received by a device of the system that include external support device  420  having an increased frequency than the original patch-integrity signal. This increased frequency of the patch-integrity signal may allow the signal to be more easily filtered out by the receiving device. Accordingly, although the description throughout this disclosure may focus on or discus an inverse signal that is a true inverse signal of the patch-integrity signal, or a close analog to a true inverse signal, it should be understood that this is merely for ease of description. In general, external support device  420  may generate an inverse signal that is not a true inverse signal, but interferes or changes the patch-integrity signal sufficiently to allow a receiving device to distinguish between the patch-integrity signal and communication signals or to filter the patch-integrity signal without filtering communication signals. 
     External support device  420  may deliver the generated inverse signal  812  into the body of the patient, for example through electrodes  404 . Since inverse signal  812  has similar but opposite characteristics of patch-integrity signal  810 , inverse signal  812  may destructively interfere with patch-integrity signal  810 , thereby canceling out and/or at least reducing the amplitude of patch-integrity signal  810  sensed by other devices connected to the patient, such as LCP  402 . In some examples, inverse signal  812  may be the exact opposite of patch-integrity signal  810  and may fully cancel inverse signal  812  such that LCP  402  does not sense patch-integrity signal  810 . In other examples, inverse signal  812  may only be similar to patch-integrity signal  810  and may only reduce the amplitude of patch-integrity signal  810  sensed by LCP  402 . In any case, the delivered inverse signal  812  may reduce the amplitude of patch-integrity signal  810  sensed by LCP  402 , which can enhance the signal-to-noise ratio (SNR) of conducted communication between external support device  420  and LCP  402  (and/or between LCP  402  and another implanted devices). An example of a signal sensed by LCP  402  while external support device  420  is delivering inverse signal  812  is shown in  FIG. 12  as signal  814 . 
     In at least some embodiments, instead of attempting to match the amplitude of patch-integrity signal  810 , external support device  420  may generate inverse signal  812  having a different amplitude than patch-integrity signal  810 . The amplitude of patch-integrity signal  810  sensed by devices connected to the patient other than external support device  420 , such as LCP  402 , may differ than the amplitude of patch-integrity signal  810  sensed by external support device  420 . Accordingly, delivering inverse signal  812  into the patient with an amplitude similar to patch-integrity signal  810  sensed by external support device  420  may cancel out patch-integrity signal  810  sensed by LCP  402 , but may additionally introduce noise in the form of inverse signal  812 , which was not fully cancelled out by patch-integrity signal  810 . Accordingly, in some instances, external support device  420  may generate inverse signal  812  having an amplitude higher, or lower, than the amplitude of patch-integrity signal  810  sensed by external support device  420 . External support device  420  may attempt to match the amplitude of inverse signal  812  sensed by LCP  402  to the amplitude of patch-integrity signal  810  sensed by LCP  402 . For example, external support device  420  may adjust the amplitude of inverse signal  812  based on feedback received from LCP  402 , or based on a presence or absence of received messages from LCP  402 . In other embodiments, external support device  420  may include a physical dial or gain adjuster  424  that a user may adjust to increase or decrease the amplitude of generated inverse signal  812  (see  FIG. 13 ). 
     Delivering inverse signal  812  into the patient&#39;s body may enhance the signal-to-noise ratio (SNR) of conducted communication with the body by removing or reducing the patch-integrity signal  810  in the body. In some embodiments, external support device  420  may deliver inverse signal  812  into the patient&#39;s body continuously. In other cases, the delivered inverse signal  812  may cause external defibrillator  406  to generate or emit an alarm as patch-integrity signal  810  sensed by external defibrillator  406  may be fully cancelled or reduced in amplitude below a certain alarm threshold. Accordingly, in some cases, external support device  420  may only selectively deliver inverse signal  812  into the patient&#39;s body. For example, external support device  420  may only deliver inverse signal  812  into the patient&#39;s body while external support device  420  or LCP  402  are delivering conducted communication signals into the patient&#39;s body. In some cases, LCP  402  may have an easier time discriminating between the delivered conducted communication signals from patch-integrity signal  810 . In some cases, the conducted communication scheme of external support device  420  and LCP  402  may include only delivering conducted communication signals during predefined time periods. For instance, external support device  420  and LCP  402  may be configured to only deliver conducted communication signals during communication windows lasting about 100 ms, with each communication window separated by 800 ms. These numbers are just examples. The communication window lengths and spacing may be any suitable values. 
     In some cases, the communication windows may be synchronized to one or more features of the cardiac electrical signals. For instance, external support device  420  and LCP  402  may be configured to communication during communication windows that occur about 100-250 ms after each detected R-wave. External support device  420  may be configured to only deliver inverse signal  812  into the patient&#39;s body during these communication windows. Both external support device  420  and LCP  402  may benefit from enhanced discrimination between sensed conducted communication signals and patch-integrity signal  810 . 
     The patch-integrity signal  810  depicted in  FIG. 11A  is only one example. Different external defibrillators currently on the market may use differently shaped patch-integrity signals. Accordingly, in some embodiments, instead of having a general waveform generator capable of generating any, or a large number of different types of waveforms, external support device  420  may include hardware or circuitry that may generate inverse signals of various different known patch-integrity signals used in available external defibrillators. 
       FIG. 13  depicts an example interface of an external support device  420 . External support device  420  may include a dial, switch, or other mechanical selector, such as dial  424 , or a menu option in graphical user interface  422 , that allows a user to select a particular inverse waveform from a set of preprogrammed inverse waveforms that correspond to the different available external defibrillators. The preprogrammed inverse waveforms may be stored in a memory of external support device  420 . Each selectable waveform may have an identifier correlating the waveform to a particular brand or product to easily identify the appropriate inverse waveform. These features may allow external support device  420  to be less complex and less costly to manufacture than when the external support device  420  is required to sense the patch-integrity signal and then generate an inverse signal using a general waveform generator. 
       FIG. 14  depicts system  900  which may help enhance discrimination between conducted communication signals and noise signals such as patch-integrity signals. System  900  may include external support device  920 , external defibrillator  906 , and switching unit  910 . External defibrillator  906  may be connected to switching unit  910  through wires  908 , and external support device  920  may be connected to switching unit  910  by wires  922 . Switching unit  910  may be connected to electrodes  904  attached to patient skin  915  through wires  912 . 
     In system  900 , a switching unit  910  may be configured to switch between wires  922  from external support device  920  and wires  908  from external defibrillator  906  to connect/disconnect each device to electrodes  904 . Switching unit  910  may initially connect wires  908  to electrodes  904 , allowing external defibrillator  906  to deliver a patch-integrity signal through electrode  904  and into the patient through skin  915 . In some cases, when external support device  920  is to deliver conducted communication signals into the patient, switching unit  910  may disconnect wires  908  of external defibrillator  906  from the electrodes  904  and connect wires  922  from external support device  920  to the electrodes  904 . In this configuration, external support device  920  may deliver conducted communication signals into the patient through electrodes  904 . With the external defibrillator  906  disconnected from the electrodes  904 , the patch-integrity signal is effectively blocked from entering the patient, and devices may communicate through conducted communication signals without interference from the patch-integrity signal. Once the conducted communication signals have been sent and received, switching unit  910  may disconnect wires  922  of the external support device  920  from the electrodes  904  and connect wires  908  of the external defibrillator  906  to the electrodes  904 . The patch-integrity signal of the external defibrillator  906  may then be delivered to the patient, verifying to the external defibrillator  906  that the patch electrodes  904  are sufficiently in electrical communication with the skin. If the communication period is kept short enough, a patch verification alarm of the external defibrillator  906  may not be triggered. 
     In some instances, external support device  920  may control switching unit  910  to connect/disconnect wires  908 ,  922  from wires  912 . In other instances, external defibrillator  906  may control switching unit  910 , a different device may control switching unit  910 , or both of external defibrillator  906  and external support device  920  may control switching unit  910 . For ease of description, the techniques are described below from the perspective of external support device  920  controlling switching unit  910 . 
     In operation, external defibrillator  906  may normally be connected to electrode  904  to deliver a patch-integrity signal and/or sense cardiac electrical signals. Before external support device  920  delivers conducted communication signals into the patient, external support device  920  may command switching unit  910  to disconnect wires  908  of the external defibrillator  906  from the electrodes  904  and connect wires  922  of the external support device  920  to the electrodes  904 , thereby blocking the patch-integrity signal from external defibrillator  906  from being delivered to the patient. Once external support device  920  is finished delivering the conducted communication signals, external support device  920  may command switching unit  910  to reconnect wires  908  of the external defibrillator  906  to the electrodes  904 . 
     In some instances, instead of only commanding switching unit  910  to connect wires  922  of the of the external support device  920  to the electrodes  904  before external support device  920  delivers conducted communication signals into the patient, external support device  920  may cause switching unit  910  to switch at regular intervals. For instance, in some cases where external support device  920  and another device, such as an LCP device, are connected to the patient and are configured to communicate using conducted communication only during predefined communication windows, external support device  920  may command switching unit  910  to connect wires  922  of the external support device  920  to the electrodes  904  during each of the communication windows. 
     When wires  908  of the external defibrillator  906  are disconnected from the electrodes  904 , wires  908  may form an open circuit which may cause external defibrillator  906  to generate or emit an alarm, as external defibrillator  906  may no longer sense the patch-integrity signal. In some embodiments, in order help prevent external defibrillator  906  from generating an alarm, when switching unit  910  disconnects wires  908  of the external defibrillator  906  from the electrodes  904 , switching unit  910  may connect wires  908  directly together, or may connect wires  908  together through a resistive or other network contained within switching unit  910 . In these embodiments, switching unit  910  may maintain a closed loop for the patch-integrity signal, which may help prevent external defibrillator  906  from generating or emitting an alarm. 
     Although system  900  is depicted as including external defibrillator  906 , switching unit  910 , and external support device  920 , it is contemplated that system  900  may include fewer or more devices. For instance, the support functions of external support device  920  and the switching functions of switching unit  910  may be built into external defibrillator  906 . When so provided, external defibrillator  906  may have an internal switching mechanism and can control the switching mechanism to help support conducted communication via other devices within the patient. 
     In general, those skilled in the art will recognize that the present disclosure may be manifested in a variety of forms other than the specific embodiments described and contemplated herein. For instance, as described herein, various embodiments include one or more modules described as performing various functions. However, other embodiments may include additional modules that split the described functions up over more modules than that described herein. Additionally, other embodiments may consolidate the described functions into fewer modules. Accordingly, departure in form and detail may be made without departing from the scope and spirit of the present disclosure as described in the appended claims.