Patent Publication Number: US-11653880-B2

Title: System for cardiac monitoring with energy-harvesting-enhanced data transfer capabilities

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This non-provisional patent application is a continuation of U.S. Pat. No. 11,116,451, issued Sep. 14, 2021; which claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent application, Ser. No. 62/870,506, filed Jul. 3, 2019, the disclosure of which is incorporated by reference. 
    
    
     FIELD 
     This application relates in general to electrocardiographic monitoring and, in particular, to a system for cardiac monitoring with energy-harvesting-enhanced data transfer capabilities. 
     BACKGROUND 
     The electrocardiogram (ECG) was invented by a Dutch physiologist, Willem Einthoven, in 1903. Physicians have since used ECGs to diagnose heart problems and other medical concerns. The medical and engineering principles underlying Einthoven&#39;s work are still applicable today, and although ECG machines have evolved to a broad array of different systems, over the past century, the fundamental role of an ECG machine remains the same: to record from the skin surface transmembrane ionic currents that are generated within the heart during cardiac activation and recovery. 
     Cardiac depolarization, which is the spread of electrical current throughout the heart, originates in the sinoatrial (SA) node in the right atrium and spreads leftward towards the left atrium and inferiorly towards the atrioventricular (AV) node. Thereafter a delay, occasioned by the AV node, allows atrial blood to enter the ventricles, prior to the continuation of the depolarization current proceeding down the Bundle of His and into the right and left bundle branches, then advancing to the Purkinje fibers, and finally spreading to activate the right and left ventricular muscle fibers themselves that lead to the heart muscle squeezing the blood supply forward. 
     During each cardiac cycle, the transmembrane ionic currents create an electrical field in and around the heart that can be detected by ECG electrodes either placed on the skin or implanted under the skin of the thorax to record far field electrical signals from the heart. These far field electrical signals are the captured ECG signals that can be visually depicted in an ECG trace as the PQRSTU waveforms, each letter of which represents a specific electrical activity in the heart well known to cardiologists. Within each cardiac cycle, these waveforms indicate key aspects of cardiac electrical activity. The critical P-wave component of each heartbeat represents atrial electrical activity, the electrical signal that is essential if one is to understand heart rhythm disorders. The QRS components represent ventricular electrical activity, equally critical to understanding heart rhythm disorders. The TU components represent ventricular cell voltages that are the result of resetting cellular currents in preparation for the next cardiac cycle. The TU components are generally of limited value for the purposes of understanding heart rhythm disorders and are rarely addressed in the analysis of heart rhythm disorders per se. (Note that the signals involved in the resetting of the atria are so minuscule as to not be visible in an ECG trace or, even in a standard intra-cardiac recording.) 
     Practically, the QRS components of the ventricle electrical activity are often termed the “R-wave,” in brief, as a shorthand way of identifying ventricular electrical activity in its entirety. (Henceforth, the shorthand version of “R-wave” will be used to indicate ventricular activity and “P-wave” will be used to indicate atrial activity.) These “waves” represent the two critical components of arrhythmia monitoring and diagnosis performed every day hundreds of thousands of times across the United States. Without a knowledge of the relationship of these two basic symbols, heart rhythm disorders cannot be reliably diagnosed. Visualizing both the P-wave and the R-wave allow for the specific identification of a variety of atrial tachyarrhythmias (also known as supraventricular tachyarrhythmias, or SVTs), ventricular tachyarrhythmias (VTs), and bradycardias related to sinus node and atrioventricular (AV) node dysfunction. These categories are well understood by cardiologists but only accurately diagnosable if the P-wave and the R-wave are visualized and their relationship and behavior are clear. Visualization of the R-wave is usually readily achievable, as the R-wave is a high voltage, high frequency signal easily recorded from the skin&#39;s surface. However, as the ECG bipole spacing and electrode surface area decreases, even the R-wave can be a challenge to visualize. To make matters of rhythm identification more complicated, surface P-waves can be much more difficult to visualize from the surface because of their much lower voltage and signal frequency content. P-wave visualization becomes exacerbated further when the recording bipole inter-electrode spacing decreases. 
     Subcutaneous ECG monitors, because of their small size, have greater problems of demonstrating a clear and dependable P-wave. The issues related to a tiny atrial voltage are exacerbated by the small size of insertable cardiac monitors (ICMs), the signal processing limits imposed upon them by virtue of their reduced electrode size, and restricted inter-electrode spacing. Conventional subcutaneous ICMs, as well as most conventional surface ECG monitors, are notorious for poor visualization of the P-wave, which remains the primary reason that heart rhythm disorders cannot precisely be identified today from ICMs. Furthermore, even when physiologically present, the P-wave may not actually appear on an ECG because the P-wave&#39;s visibility is strongly dependent upon the signal capturing ability of the ECG recording device&#39;s sensing circuitry. This situation is further influenced by several factors, including electrode configuration, electrode surface areas and shapes, inter-electrode spacing; where the electrodes are placed on or within the body relative to the heart&#39;s atria. Further, the presence or absence of ambient noise and the means to limit the ambient noise is a key aspect of whether the low amplitude atrial signal can be seen. 
     Conventional ICMs are generally capable of monitoring a patient&#39;s heart rhythm for up to three years and are often used after diagnostic measures when dermal ECG monitors fail to identify a suspected arrhythmia. Consequently, when a physician is strongly suspicious of a serious cardiac rhythm disorder that may have caused loss of consciousness or stroke, for example, the physician will often proceed to the insertion of an ICM under the skin of the thorax. Although traditionally, the quality of the signal is limited with ICMs with respect to identifying the P-wave, the duration of monitoring is hoped to compensate for poor P-wave recording. This situation has led to a dependence on scrutiny of R-wave behavior, such as RR interval (R-wave-to-R-wave interval) behavior, often used as a surrogate for diagnosing atrial fibrillation, a potential cause of stroke. To a limited extent, this approach has some degree of value. Nevertheless, better recording of the P-wave would result in a significant diagnostic improvement, not only in the case of atrial fibrillation, but in a host of other rhythm disorders that can result in syncope or loss of consciousness, like VT or heart block. 
     The P-wave is the most difficult ECG signal to capture by virtue of originating in the low tissue mass atria and having both low voltage amplitude and relatively low frequency content. Notwithstanding these physiological constraints, ICMs are popular, albeit limited in their diagnostic yield. The few ICMs that are commercially available today, including the Reveal LINQ ICM, manufactured by Medtronic, Inc., Minneapolis, Minn., the BioMonitor 2 (AF and S versions), manufactured by Biotronik SE &amp; Co. KG, Berlin, Germany, and the Abbott Confirm Rx ICM, manufactured by Abbott Laboratories, Chicago, Ill., all are uniformly limited in their abilities to clearly and consistently sense, record, and deliver the P-wave. 
     Typically, the current realm of ICM devices use a loop recorder where cumulative ECG data lasting for around an hour is continually overwritten unless an episode of pre-programmed interest occurs or a patient marker is manually triggered. The limited temporal window afforded by the recordation loop is yet another restriction on the evaluation of the P-wave, and related cardiac morphologies, and further compromises diagnostic opportunities. 
     For instance, Medtronic&#39;s Reveal LINQ ICM delivers long-term subcutaneous ECG monitoring for up to three years, depending on programming. The monitor is able to store up to 59 minutes of ECG data, include up to 30 minutes of patient-activated episodes, 27 minutes of automatically detected episodes, and two minutes of the longest atrial fibrillation (AF) episode stored since the last interrogation of the device. The focus of the device is more directed to recording duration and programming options for recording time and patient interactions rather than signal fidelity. The Reveal LINQ ICM is intended for general purpose ECG monitoring and lacks an engineering focus on P-wave visualization. Moreover, the device&#39;s recording circuitry is intended to secure the ventricular signal by capturing the R-wave, and is designed to accommodate placement over a broad range of subcutaneous implantation sites, which is usually sufficient if one is focused on the R-wave given its amplitude and frequency content, but of limited value in capturing the low-amplitude, low-frequency content P-wave. Finally, electrode spacing, surface areas, and shapes are dictated (and limited) by the physical size of the monitor&#39;s housing which is quite small, an aesthetic choice, but unrealistic with respect to capturing the P-wave. 
     Similar in design is the titanium housing of Biotronik&#39;s BioMonitor 2 but with a flexible silicone antenna to mount a distal electrode lead, albeit of a standardized length. This standardized length mollifies, in one parameter only, the concerns of limited inter-electrode spacing and its curbing effect on securing the P-wave. None of the other factors related to P-wave signal revelation are addressed. Therefore the quality of sensed P-waves reflects a compromise caused by closely-spaced poles that fail to consistently preserve P-wave fidelity, with the reality of the physics imposed problems of signal-to-noise ratio limitations remaining mostly unaddressed. 
     Further, the physical size of existing implantable monitors limits the size of a power source present in those monitors, which in turn limits a duration of a monitoring possible without a surgical intervention to replace the power source in the monitoring. For a patient whose condition requires extended, potentially periodic life-long monitoring, the existing implantable monitors are of a limited usefulness, subjecting them to surgical intervention and possible associated complications when the power supply of such an implantable monitor runs out. Further, the limitations of the power supply impact how often and how much the implantable monitor offloads collected data due to a large power consumption associated with the wireless transmission. 
     Therefore, a need remains for a continuously recording long-term ICM particularly attuned to capturing low amplitude cardiac action potential propagation from the atria, that is, the P-wave, for accurate arrhythmia event capture and subsequent diagnosis, as well as capable of a prolonged monitoring and frequent data offload without needing a surgical intervention to replace the power source within the ICM. 
     SUMMARY 
     Long-term electrocardiographic and physiological monitoring over a period lasting up to several years in duration can be provided through a continuously-recording subcutaneous insertable cardiac monitor (ICM). The sensing circuitry and the physical layout of the electrodes are specifically optimized to capture electrical signals from the propagation of low amplitude, relatively low frequency content cardiac action potentials, particularly the P-waves that are generated during atrial activation. In general, the ICM is intended to be implanted centrally and positioned axially and slightly to either the left or right of the sternal midline in the parasternal region of the chest. 
     The length of the monitoring is extended, potentially for a life time of the patient, by including an internal energy harvesting module in the ICM. The energy harvesting module harvests energy from outside the ICM, and provides the harvested energy for powering the circuitry of the ICM, either directly or by recharging a power cell within the ICM. As the circuitry of the ICM requires a low amount of electrical power, the harvested energy can be sufficient to support the functioning of the ICM  12  even when the electrical power stored on the ICM at the time of implantation runs out. The presence of the energy harvesting module further allows for a frequent wireless transmission of a large amount of collected data. 
     In one embodiment, a system for cardiac monitoring with radio-wave-based recharging capabilities is provided. The system includes an implantable cardiac monitor and an external device. The implantable cardiac monitor includes an implantable housing implantable into a living body for at least a duration of a cardiac monitoring, at least a portion of the housing composed of a radio transparent material; at least one pair of ECG sensing electrodes provided with the implantable housing operatively placed to facilitate the monitoring of cardiac action potentials from the subcutaneous thoracic space that are generated during atrial activation; electronic circuitry configured to use electrical energy and provided within the housing assembly including a low power microcontroller, an ECG front end circuit interfaced to the microcontroller and configured to capture the cardiac action potentials sensed by the pair of ECG sensing electrodes which are output as ECG signals, a memory electrically interfaced with the microcontroller and operable to store data from the ECG signals sensed with substantially every heartbeat, and a wireless transceiver interfaced to the microcontroller; and an energy harvesting module electrically interfaced to the electronic circuitry and configured to generate at least some of the electrical energy based on input from an environment outside of the implantable housing when the implantable housing is implanted into the living body, the energy harvesting module further including: an antenna within the implantable housing configured to generate alternating current upon receiving radio waves from outside the housing when the implantable housing is implanted within the living body; and a diode interfaced to the antenna and configured to convert the alternating current to direct current, wherein the direct current is provided to the electrical circuitry as the electrical energy. The external device includes: an energy transmission module configured to provide the radio waves to the antenna when the implantable cardiac monitor is implanted within the living body and the external device is outside the living body; and a data transfer module configured to receive the ECG signal data from the wireless transceiver at the same time as the energy transmission module provides at least a portion of the radio waves to the antenna, wherein a data transfer rate for the ECG signal data to the data transfer module is dependent on amount of the electrical energy used by the wireless transceiver. 
     In a further embodiment, a system for cardiac monitoring with energy-harvesting-enhanced data transfer capabilities is provided. The system includes an implantable cardiac monitor and an external device. The implantable cardiac monitor includes an implantable housing implantable into a living body at least for a duration of a cardiac monitoring; at least one pair of ECG sensing electrodes provided with the implantable housing operatively placed to facilitate the monitoring of cardiac action potentials from the subcutaneous thoracic space that are generated during atrial activation; electronic circuitry provided within the housing assembly including a low power microcontroller, an ECG front end circuit interfaced to the microcontroller and configured to capture the cardiac action potentials sensed by the pair of ECG sensing electrodes which are output as ECG signals, a memory electrically interfaced with the microcontroller and operable to store data from the ECG signals sensed with substantially every heartbeat, and a wireless transceiver interfaced to the microcontroller; and an energy harvesting module electrically interfaced to the electronic circuitry and configured to generate electrical energy based on input from an environment outside of the implantable housing when the implantable housing is implanted into the living body, wherein at least a portion of generated electrical energy is used by the electronic circuitry. The external device includes an energy transmission module configured to wirelessly provide the input to the energy harvesting module when the implantable cardiac monitor is implanted within the living body and the external device is outside the living body; and a data transfer module configured to receive the ECG signal data from the wireless transceiver at the same time as the energy transmission module provides the input to the energy harvesting module, wherein a data transfer rate for the ECG signal data to the data transfer module is dependent on amount of the electrical energy used by the wireless transceiver and wherein the microcontroller of the implantable cardiac monitor is configured to monitor the data transfer rate, to compare the data transfer rate to a threshold, and to increase the amount of the electrical energy used by the wireless transceiver upon the data transfer rate being the below threshold to a level possible for the duration of the cardiac monitoring due to the electrical energy generated by the energy harvesting module. 
     In a still further embodiment, a system for cardiac monitoring with energy-harvesting-enhanced programmable data transfer capabilities is provided. The system includes an implantable cardiac monitor and an external device. The implantable cardiac monitor includes an implantable housing implantable into a living body at least for a duration of a cardiac monitoring; at least one pair of ECG sensing electrodes provided with the implantable housing operatively placed to facilitate the monitoring of cardiac action potentials from the subcutaneous thoracic space that are generated during atrial activation; electronic circuitry provided within the housing assembly including a low power microcontroller, an ECG front end circuit interfaced to the microcontroller and configured to capture the cardiac action potentials sensed by the pair of ECG sensing electrodes which are output as ECG signals, a memory electrically interfaced with the microcontroller and operable to store data from the ECG signals sensed with substantially every heartbeat, and a wireless transceiver interfaced to the microcontroller; and an energy harvesting module electrically interfaced to the electronic circuitry and configured to generate electrical energy based on input from an environment outside of the implantable housing when the implantable housing is implanted into the living body, wherein at least a portion of generated electrical energy is used by the electronic circuitry. The external device includes an energy transmission module configured to wirelessly provide the input to the energy harvesting module when the implantable cardiac monitor is implanted within the living body and the external device is outside the living body; and a data transfer module configured to receive the ECG signal data from the wireless transceiver at the same time as the energy transmission module provides the input to the energy harvesting module, wherein a data transfer rate for the ECG signal data to the data transfer module is dependent on amount of the electrical energy used by the wireless transceiver and wherein the microcontroller of the implantable cardiac monitor is configured to, upon receiving a signal from an external programmer triggered by an analysis of the data transfer rate, increase the amount of the electrical energy used by the wireless transceiver to a level sustainable for the duration of the cardiac monitoring due to the electrical energy generated by the energy harvesting module. 
     Still other embodiments will become readily apparent to those skilled in the art from the following detailed description, wherein are described embodiments by way of illustrating the best mode contemplated. As will be realized, other and different embodiments are possible and the embodiments&#39; several details are capable of modifications in various obvious respects, all without departing from their spirit and the scope. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive. 
    
    
     
       BRIEF DESCRIPTIONS OF DRAWINGS 
         FIG.  1    is a diagram showing, by way of example, a subcutaneous P-wave centric insertable cardiac monitor (ICM) for long term electrocardiographic monitoring in accordance with one embodiment. 
         FIGS.  2  and  3    are respectively top and bottom perspective views showing the ICM of  FIG.  1   . 
         FIG.  4    is a bottom perspective view showing the ICM of  FIG.  1    in accordance with a further embodiment. 
         FIGS.  5  and  6    are respectively top and bottom perspective views showing an ICM in accordance with a still further embodiment. 
         FIG.  7    is a plan view showing further electrode configurations. 
         FIG.  8    is a functional block diagram showing the P-wave focused component architecture of the circuitry of the ICM of  FIG.  1   . 
         FIG.  9    is a functional block diagram showing a system for wirelessly interfacing with an ICM in accordance with one embodiment. 
         FIG.  10    is a flow diagram showing an ICM-implemented method for monitoring ECG data. 
         FIG.  11    is a functional block diagram showing the signal processing functionality of the microcontroller. 
         FIG.  12    is a functional block diagram showing the operations performed by the download station. 
         FIG.  13    is a diagram showing a power source of the ICM of  FIG.  8    in accordance with one embodiment. 
         FIG.  14    is a diagram showing the energy harvesting module of  FIG.  13    with a configuration to harvest kinetic energy in accordance with one embodiment. 
         FIG.  15    is a diagram showing the energy harvesting module of  FIG.  13    with a configuration to receive energy from an external inductive coil via inductive coupling in accordance with one embodiment. 
         FIG.  16    is a diagram showing the energy harvesting module of  FIG.  13    with a configuration that includes a piezoelectric energy generator in accordance with one embodiment. 
         FIG.  17    is a diagram showing the energy harvesting module of  FIG.  13    with a configuration to generate electrical energy upon a change in the patient&#39;s bodily temperature in accordance with one embodiment. 
         FIG.  18    is a diagram showing the energy harvesting module of  FIG.  13    with a configuration to harvest energy of radio waves in accordance with one embodiment. 
         FIG.  19    is a diagram showing an external device combining energy transmission and data download capabilities for use with the ICM in accordance with one embodiment. 
     
    
    
     DETAIL DESCRIPTION 
     Long-term electrocardiographic and physiological monitoring over a period lasting up to several years in duration can be provided through a continuously-recording subcutaneous insertable cardiac monitor (ICM).  FIG.  1    is a diagram showing, by way of example, a subcutaneous P-wave centric ICM  12  for long term electrocardiographic monitoring in accordance with one embodiment. The ICM  12  is implanted in the parasternal region  11  of a patient  10 . The sensing circuitry and components, compression algorithms, and the physical layout of the electrodes are specifically optimized to capture electrical signals from the propagation of low amplitude, relatively low frequency content cardiac action potentials, particularly the P-waves generated during atrial activation. The position and placement of the ICM  12  coupled to engineering considerations that optimize the ICM&#39;s sensing circuitry, discussed infra, aid in demonstrating the P-wave clearly. 
     Implantation of a P-wave centric ICM  12  in the proper subcutaneous site facilitates the recording of high quality ECG data with a good delineation of the P-wave. In general, the ICM  12  is intended to be implanted anteriorly and be positioned axially and slightly to either the right or left of the sternal midline in the parasternal region  11  of the chest, or if sufficient subcutaneous fat exists, directly over the sternum. Optimally, the ICM  12  is implanted in a location left parasternally to bridge the left atrial appendage. However, either location to the right or left of the sternal midline is acceptable; placement of the device, if possible, should bridge the vertical height of the heart, which lies underneath the sternum  7 , thereby placing the ICM  12  in close proximity to the anterior right atrium and the left atrial appendage that lie immediately beneath. 
     The ICM  12  is shaped to fit comfortably within the body under the skin and to conform to the contours of the patient&#39;s parasternal region  11  when implanted immediately to either side of the sternum  7 , but could be implanted in other locations of the body. In most adults, the proximal end  13  of the ICM  12  is generally positioned below the manubrium  8  but, depending upon patient&#39;s vertical build, the ICM  12  may actually straddle the region over the manubrium  8 . The distal end  14  of the ICM  12  generally extends towards the xiphoid process  9  and lower sternum but, depending upon the patient&#39;s build, may actually straddle the region over or under the xiphoid process  9 , lower sternum and upper abdomen. 
     Although internal tissues, body structures, and tissue boundaries can adversely affect the current strength and signal fidelity of all body surface potentials, subsurface low amplitude cardiac action potentials, particularly P-wave signals with a normative amplitude of less than 0.25 millivolts (mV) and a normative duration of less than 120 milliseconds (ms), are most apt to be negatively impacted by these factors. The atria, which generate the P wave, are mostly located posteriorly within the thoracic cavity (with the exception of the anterior right atrium, right atrial appendage and left atrial appendage). The majority of the left atrium constitutes the portion of the heart furthest away from the surface of the skin on the chest and harbors the atrial tissue most likely to be the source of serious arrhythmias, like atrial fibrillation. Conversely, the ventricles, which generate larger amplitude signals, are located anteriorly as in the case of the anterior right ventricle and most of the anterior left ventricle situated relatively close to the skin surface of the central and left anterior chest. These factors, together with larger size and more powerful impulse generation from the ventricles, contribute to the relatively larger amplitudes of ventricular waveforms. 
     Nevertheless, as explained supra, both the P-wave and the R-wave are required for the physician to make a proper rhythm diagnosis from the dozens of arrhythmias that can occur. Yet, the quality of P-waves is more susceptible to weakening from distance and the intervening tissues and structures and from signal attenuation and signal processing than the high voltage waveforms associated with ventricular activation. The added value of avoiding further signal attenuation resulting from dermal impedance makes a subcutaneous P-wave centric ICM even more likely to match, or even outperform dermal ambulatory monitors designed to analogous engineering considerations and using similar sensing circuitry and components, compression algorithms, and physical layout of electrodes, such as described in U.S. Pat. No. 9,545,204, issued Jan. 17, 2017 to Bishay et al.; U.S. Pat. No. 9,730,593, issued Aug. 15, 2017 to Felix et al.; U.S. Pat. No. 9,700,227, issued Jul. 11, 2017 to Bishay et al.; U.S. Pat. No. 9,717,433, issued Aug. 1, 2017 to Felix et al.; and U.S. Pat. No. 9,615,763, issued Apr. 11, 2017 to Felix et al., the disclosures of which are incorporated by reference. 
     The ICM  12  can be implanted in the patient&#39;s chest using, for instance, a minimally invasive subcutaneous implantation instrument or other suitable surgical implement. The ICM  12  is positioned slightly to the right or left of midline, covering the center third of the chest, roughly between the second and sixth ribs, approximately spanning between the level of the manubrium  8  and the level of the xiphoid process  9  on the inferior border of the sternum  7 , depending upon the vertical build of the patient  10 . 
     During monitoring, the amplitude and strength of action potentials sensed by an ECG devices, including dermal ECG monitors and ICMs, can be affected to varying degrees by cardiac, cellular, extracellular, vector of current flow, and physical factors, like obesity, dermatitis, lung disease, large breasts, and high impedance skin, as can occur in dark-skinned individuals. Performing ECG sensing subcutaneously in the parasternal region  11  significantly improves the ability of the ICM  12  to counter some of the effects of these factors, particularly high skin impedance and impedance from subcutaneous fat. Thus, the ICM  12  exhibits superior performance when compared to conventional dermal ECG monitors to existing implantable loop recorders, ICMs, and other forms of implantable monitoring devices by virtue of its engineering and proven P-wave documentation above the skin, as discussed in W. M. Smith et al., “Comparison of diagnostic value using a small, single channel, P-wave centric sternal ECG monitoring patch with a standard 3-lead Holter system over 24 hours,” Am. Heart J., March 2017; 185:67-73, the disclosure of which is incorporated by reference. 
     Moreover, the sternal midline implantation location in the parasternal region  11  allows the ICM&#39;s electrodes to record an ECG of optimal signal quality from a location immediately above the strongest signal-generating aspects of the atrial. Signal quality is improved further in part because cardiac action potential propagation travels simultaneously along a north-to-south and right-to-left vector, beginning high in the right atrium and ultimately ending in the posterior and lateral region of the left ventricle. Cardiac depolarization originates high in the right atrium in the SA node before concurrently spreading leftward towards the left atrium and inferiorly towards the atrioventricular (AV) node. On the proximal end  13 , the ECG electrodes of the ICM  12  are subcutaneously positioned with the upper or superior pole (ECG electrode) slightly to the right or left of the sternal midline in the region of the manubrium  8  and, on the distal end  14 , the lower or inferior pole (ECG electrode) is similarly situated slightly to the right or left of the sternal midline in the region of the xiphoid process  9  and lower sternum  7 . The ECG electrodes of the ICM  12  are placed primarily in a north-to-south orientation along the sternum  7  that corresponds to the north-to-south waveform vector exhibited during atrial activation. This orientation corresponds to the aVF lead used in a conventional 12-lead ECG that is used to sense positive or upright P-waves. In addition, the electrode spacing and the electrodes&#39; shapes and surface areas mimic the electrodes used in the ICM&#39;s dermal cousin, designed as part of the optimal P-wave sensing electrode configuration, such as provided with the dermal ambulatory monitors cited supra. 
     Despite the challenges faced in capturing low amplitude cardiac action potentials, the ICM  12  is able to operate effectively using only two electrodes that are strategically sized and placed in locations ideally suited to high fidelity P-wave signal acquisition. This approach has been shown to clinically outperform more typical multi-lead monitors because of the improved P-wave clarity, as discussed in W. M. Smith et al., cited supra.  FIGS.  2  and  3    are respectively top and bottom perspective views showing the ICM  12  of  FIG.  1   . Physically, the ICM  12  is constructed with a hermetically sealed implantable housing  15  with at least one ECG electrode forming a superior pole on the proximal end  13  and at least one ECG electrode forming an inferior pole on the distal end  14 . 
     When implanted, the housing  15  is oriented most cephalad. The housing  15  is constructed of titanium, stainless steel or other biocompatible material. The housing  15  contains the sensing, recordation and interfacing circuitry of the ICM  12 , plus a long life battery. A wireless antenna is integrated into or within the housing  15  and can be positioned to wrap around the housing&#39;s internal periphery or location suited to signal reception. Other wireless antenna placement or integrations are possible, as further described below with reference to  FIG.  18   . 
     Physically, the ICM  12  has four ECG electrodes  16 ,  17 ,  18 ,  19 . There could also be additional ECG electrodes, as discussed infra. The ECG electrodes include two ventral (or dorsal) ECG electrodes  18 ,  19  and two wraparound ECG electrodes  16 ,  17 . One ventral ECG electrode  18  is formed on the proximal end  13  and one ventral ECG electrode  19  is formed on the distal end  14 . One wraparound ECG electrode  16  is formed circumferentially about the proximal end  13  and one wraparound ECG electrode  17  is formed circumferentially about the distal end  14 . Each wraparound ECG electrode  16 ,  17  is electrically insulated from its respective ventral ECG electrode  18 ,  19  by a periphery  20 ,  21 . 
     The four ECG electrodes  16 ,  17 ,  18 ,  19  are programmatically controlled by a microcontroller through onboard firmware programming to enable a physician to choose from several different electrode configurations that vary the electrode surface areas, shapes, and inter-electrode spacing. The sensing circuitry can be programmed, either pre-implant or in situ, to use different combinations of the available ECG electrodes (and thereby changing electrode surface areas, shapes, and inter-electrode spacing), including pairing the two ventral ECG electrodes  16 ,  17 , the two wraparound ECG electrodes  18 ,  19 , or one ventral ECG electrode  16 ,  17  with one wraparound ECG electrode  18 ,  19  located on the opposite end of the housing  15 . In addition, the periphery  20 ,  21  can be programmatically controlled to logically combine the wraparound ECG electrode  16 ,  17  on one end of the ICM  12  with its corresponding ventral ECG electrode  18 ,  19  to form a single virtual ECG electrode with larger surface area and shape. (Although electronically possible, the two ECG electrodes that are only on one end of the ICM  12 , for instance, wraparound ECG electrode  16  and ventral ECG electrode  18 , could be paired; however, the minimal inter-electrode spacing would likely yield a signal of poor fidelity in most situations.) 
     In a further embodiment, the housing  15  and contained circuitry can be provided as a standalone ICM core assembly to which a pair of compatible ECG electrodes can be operatively coupled to form a full implantable ICM device. 
     Other ECG electrode configurations are possible. For instance, additional ECG electrodes can be provided to increase the number of possible electrode configurations, all of which are to ensure better P-wave resolution.  FIG.  4    is a bottom perspective view showing the ICM  12  of  FIG.  1    in accordance with a further embodiment. An additional pair of ventral ECG electrodes  22 ,  23  are included on the housing&#39;s ventral surface. These ventral ECG electrodes  22 ,  23  are spaced closer together than the ventral ECG electrodes  18 ,  19  on the ends of the housing  15  and a physician can thus choose to pair the two inner ventral ECG electrodes  22 ,  23  by themselves to allow for minimal electrode-to-electrode spacing, or with the other ECG electrodes  16 ,  17 ,  18 ,  19  to vary electrode surface areas, shapes, and inter-electrode spacing even further to explore optimal configurations to acquire the P-wave. 
     Other housing configurations of the ICM are possible. For instance, the housing of the ICM can be structured to enhance long term comfort and fitment, and to accommodate a larger long life battery or more circuitry or features, including physiologic sensors, to provide additional functionality.  FIGS.  5  and  6    are respectively top and bottom perspective views showing an ICM  30  in accordance with a still further embodiment. The ICM  30  has a housing  31  with a tapered extension  32  that is terminated on the distal end with an electrode  34 . On a proximal end, the housing  31  includes a pair of ECG electrodes electrically insulated by a periphery  37  that include a ventral ECG electrode  33  and a wraparound ECG electrode  34 . In addition, a ventral ECG electrode  36  is oriented on the housing&#39;s distal end before the tapered extension  32 . Still other housing structures and electrode configurations are possible. 
     In general, the basic electrode layout is sufficient to sense cardiac action potentials in a wide range of patients. Differences in thoracic tissue density and skeletal structure from patient to patient, though, can affect the ability of the sensing electrodes to efficaciously capture action potential signals, yet the degree to which signal acquisition is affected may not be apparent until after an ICM has been implanted and deployed, when the impacts of the patient&#39;s physical constitution and his patterns of mobility and physical movement on ICM monitoring can be fully assessed. 
     In further embodiments, the electrodes can be configured post-implant to allow the ICM to better adapt to a particular patient&#39;s physiology. For instance, electrode configurations having more than two sensing electrodes are possible.  FIG.  7    is a plan view showing further electrode configurations. Referring first to  FIG.  7 ( a ) , a single disc ECG electrode  40  could be bifurcated to form a pair of half-circle ECG electrodes  41 ,  42  that could be programmatically selected or combined to accommodate a particular patients ECG signal characteristics post-ICM implant. Referring next to  FIG.  7 ( b ) , a single disc ECG electrode  45  could be divided into three sections, a pair of crescent-shaped ECG electrodes  46 ,  47  surrounding a central semicircular ECG electrode  48  that could similarly be programmatically selected or combined. Still other ECG electrode configurations are possible. 
     ECG monitoring and other functions performed by the ICM  12  are provided through a micro controlled architecture.  FIG.  8    is a functional block diagram showing the P-wave focused component architecture of the circuitry  80  of the ICM  12  of  FIG.  1   . The circuitry  80  is powered through the long life battery  21  provided in the housing  15 . Operation of the circuitry  80  of the ICM  12  is managed by a microcontroller  81 , such as the EFM32 Tiny Gecko 32-bit microcontroller, manufactured by Silicon Laboratories Inc., Austin, Tex. The microcontroller  81  has flexible energy management modes and includes a direct memory access controller and built-in analog-to-digital and digital-to-analog converters (ADC and DAC, respectively). The microcontroller  81  also includes a program memory unit containing internal flash memory (not shown) that is readable, writeable, and externally programmable. 
     The microcontroller  81  operates under modular micro program control as specified in firmware stored in the internal flash memory. The functionality and firmware modules relating to signal processing by the microcontroller  81  are further described infra with reference to  FIG.  11   . The microcontroller  81  draws power from the battery provided in the housing  15  and connects to the ECG front end circuit  83 . In a further embodiment, the front end circuit  83  measures raw dermal electrical signals using a driven reference signal that eliminates common mode noise, as further described infra. 
     The circuitry  80  of the ICM  12  also includes a flash memory  82  external to the microcontroller  81 , which the microcontroller  81  uses for continuously storing samples of ECG monitoring signal data and other physiology, such as respiratory rate, blood oxygen saturation level (SpO 2 ), blood pressure, temperature sensor, and physical activity, and device and related information. The flash memory  82  also draws power from the battery provided in the housing  15 . Data is stored in a serial flash memory circuit, which supports read, erase and program operations over a communications bus. The flash memory  82  enables the microcontroller  81  to store digitized ECG data. The communications bus further enables the flash memory  82  to be directly accessed wirelessly through a transceiver  85  coupled to an antenna  17  built into (or provided with) the housing  15 , as further described infra with reference to  FIG.  9   . The transceiver  85  can be used for wirelessly interfacing over Bluetooth or other types of wireless technologies for exchanging data over a short distance with a paired mobile device, including smartphones and smart watches, that are designed to communicate over a public communications infrastructure, such as a cellular communications network, and, in a further embodiment, other wearable (or implantable) physiology monitors, such as activity trackers worn on the wrist or body. Other types of device pairings are possible, including with a desktop computer or purpose-built bedside monitor. The transceiver  85  can be used to offload stored ECG monitoring data and other physiology data and information and for device firmware reprogramming. In a further embodiment, the flash memory  82  can be accessed through an inductive coupling (not shown). 
     The microcontroller  81  includes functionality that enables the acquisition of samples of analog ECG signals, which are converted into a digital representation, as further described infra with reference to  FIG.  11   . In one mode, the microcontroller  81  implements a loop recorder feature that will acquire, sample, digitize, signal process, and store digitized ECG data into available storage locations in the flash memory  82  until all memory storage locations are filled, after which existing stored digitized ECG data will either be overwritten through a sliding window protocol, albeit at the cost of potentially losing the stored data that was overwritten, if not previously downloaded, or transmitted wirelessly to an external receiver to unburden the flash memory. In another mode, the stored digitized ECG data can be maintained permanently until downloaded or erased to restore memory capacity. Data download or erasure can also occur before all storage locations are filled, which would free up memory space sooner, albeit at the cost of possibly interrupting monitoring while downloading or erasure is performed. Still other modes of data storage and capacity recovery are possible. 
     The circuitry  80  of the ICM  12  can include functionality to programmatically select pairings of sensing electrodes when the ICM  12  is furnished with three or more electrodes. In a further embodiment, multiple sensing electrodes could be provided on the ICM  12  to provide a physician the option of fine-tuning the sensing dipole (or tripole or multipole) in situ by parking active electrodes and designating any remaining electrodes inert. The pairing selection can be made remotely through an inductive coupling or by the transceiver  85  via, for instance, a paired mobile device, as further described infra. Thus, the sensing electrode configuration, including number of electrodes, electrode-to-electrode spacing, and electrode size, shape, surface area, and placement, can be modified at any time during the implantation of the ICM  12 . 
     In a further embodiment, the circuitry  80  of the ICM  12  can include an actigraphy sensor  84  implemented as a 3-axis accelerometer. The accelerometer may be configured to generate interrupt signals to the microcontroller  81  by independent initial wake up and free fall events, as well as by device position. In addition, the actigraphy provided by the accelerometer can be used during post-monitoring analysis to correct the orientation of the ICM  12  if, for instance, the ICM  12  has been inadvertently implanted upside down, that is, with the ICM&#39;s housing oriented caudally, as well as for other event occurrence analyses. 
     In a still further embodiment, the circuitry  80  of the ICM  12  can include one or more physiology sensors. For instance, a physiology sensor can be provided as part of the circuitry  80  of the ICM  12 , or can be provided on the electrode assembly  14  with communication with the microcontroller  81  provided through a circuit trace. The physiology sensor can include an SpO 2  sensor, blood pressure sensor, temperature sensor, respiratory rate sensor, glucose sensor, airflow sensor, volumetric pressure sensing, or other types of sensor or telemetric input sources. 
     In a yet further embodiment, firmware with programming instructions, including machine learning and other forms of artificial intelligence-originated instructions, can be downloaded into the microcontroller&#39;s internal flash memory. The firmware can include heuristics to signal patient and physician with alerts over health conditions or arrhythmias of selected medical concern, such as where a heart pattern particular to the patient is identified and the ICM  12  is thereby reprogrammed to watch for a reoccurrence of that pattern, after which an alert will be generated and sent to the physician (or other caregiver) through the transceiver  85  via, for instance, a paired mobile device. Similarly, the firmware can include heuristics that can be downloaded to the ICM  12  to actively identify or narrow down a pattern (or even the underlying cause) of sporadic cardiac conditions, for instance, atrial tachycardia (AT), atrial fibrillation (AF), atrial flutter (AFL), AV node reciprocating tachycardia, ventricular tachycardia (VT), sinus bradycardia, asystole, complete heart block, and other cardiac arrhythmias, again, after which an alert will be generated and sent to the physician (or other caregiver) through the transceiver  85 . For instance, an alert that includes a compressed ECG digitized sample can also be wirelessly transmitted by the ICM  12  upon the triggering of a preset condition, such as an abnormally low heart rate in excess of 170 beats per minute (bpm), an abnormally low heart rate falling below 30 bpm, or AF detected by onboard analysis of RR interval variability by the microcontroller  61 . Finally, a similar methodology of creating firmware programming tailored to the monitoring and medical diagnostic needs of a specific patient (or patient group or general population) can be used for other conditions or symptoms, such as syncope, palpitations, dizziness and giddiness, unspecified convulsions, abnormal ECG, transient cerebral ischemic attacks and related syndromes, cerebral infarction, occlusion and stenosis of pre-cerebral and cerebral arteries not resulting in cerebral infarction personal history of transient ischemic attack, and cerebral infarction without residual deficits, to trigger an alert and involve the physician or initiate automated analysis and follow up back at the patient&#39;s clinic. Finally, in a still further embodiment, the circuitry  80  of the ICM  12  can accommodate patient-interfaceable components, including an external tactile feedback device (not shown) that wirelessly interfaces to the ICM  12  through the transceiver  85 . A patient  10  can press the external tactile feedback device to mark events, such as a syncope episode, or to perform other functions. The circuitry  80  can also accommodate triggering an external buzzer  67 , such as a speaker, magnetic resonator or piezoelectric buzzer, implemented as part of the external tactile feedback device or as a separate wirelessly-interfaceable component. The buzzer  67  can be used by the microcontroller  81  to indirectly output feedback to a patient  10 , such as a low battery or other error condition or warning. Still other components, provided as either part of the circuitry  80  of the ICM  12  or as external wirelessly-interfaceable devices, are possible. 
     In a further embodiment, the ECG front end circuit  83  of the ICM  12  measures raw dermal electrical signals using a driven reference signal, such as described in U.S. Pat. Nos. 9,700,227, 9,717,433, and 9,615,763, cited supra. The driven reference signal effectively reduces common mode noise, power supply noise and system noise, which is critical to preserving the characteristics of low amplitude cardiac action potentials, especially the P wave signals originating from the atria. 
     The ECG front end circuit  83  is organized into a passive input filter stage, a unity gain voltage follower stage, a passive high pass filtering stage, a voltage amplification and active filtering stage, and an anti-aliasing passive filter stage, plus a reference generator. The passive input filter stage passively shifts the frequency response poles downward to counter the high electrode impedance from the patient on the signal lead and reference lead, which reduces high frequency noise. The unity gain voltage follower stage allows the circuit to accommodate a very high input impedance, so as not to disrupt the subcutaneous potentials or the filtering effect of the previous stage. The passive high pass filtering stage includes a high pass filter that removes baseline wander and any offset generated from the previous stage. As necessary, the voltage amplification and active filtering stage amplifies or de-amplifies (or allows to pass-through) the voltage of the input signal, while applying a low pass filter. The anti-aliasing passive filter stage  75  provides an anti-aliasing low pass filter. The reference generator drives a driven reference signal containing power supply noise and system noise to the reference lead and is connected directly to the patient, thereby avoiding the thermal noise of the protection resistor that is included as part of the protection circuit  72 . 
     The ICM circuitry  80  further includes a power source  86  that is interfaced to other components of the circuitry  80  and powers those components.  FIG.  13    is a diagram showing a power source  86  of the ICM  12  in accordance with one embodiment. The power source  86  includes a rechargeable power cell  87  and an energy harvesting module  88 , which generates electrical energy based on input from an environment outside of the implantable housing, including when the implantable housing has been implanted within the patient  10 . In one embodiment, the rechargeable power cell  87  can be a lithium-titanate battery, which recharges at a significantly faster rate due to an increased surface area at the anode (when compared to many other types of batteries). Other kinds of the rechargeable power cells  87  are also possible. 
     While in the description below beginning with reference to  FIG.  14    the energy harvesting module  88  is described as having a single energy-generating mechanism, in a further embodiment, a single energy harvesting module could combine multiple energy harvesting mechanisms (such as those described with reference to  FIGS.  14 - 18   ). Further while particular embodiments of the energy harvesting module  88  are described with reference to  FIGS.  14 - 18   , other embodiments of the energy harvesting module  88  are also possible. 
     The energy harvesting module  88  can provide the harvested energy to the rechargeable power cell  87 , recharging the power cell  87  and allowing the power cell  87  to power other components of the circuitry  80 . In a further embodiment, the power cell  87  can be absent from the power source  86 , and the electrical energy generated by the energy harvesting module  88  is the only electrical energy powering other components of the circuitry  87 . Thus, the energy harvesting is either indirectly, via the power cell  87 , or directly, interfaced to other components of the circuitry  80 , providing power for those components of the circuitry  80 . 
     When operated standalone, the recording circuitry of the ICM  12  senses and records the patient&#39;s ECG data into an onboard memory. The ICM  12  can interoperate with other devices wirelessly through the transceiver  85 .  FIG.  9    is a functional block diagram showing a system  90  for wirelessly interfacing with an ICM  12  in accordance with one embodiment. The ICM  12  is designed for long-term electrocardiographic and physiological monitoring lasting up to several years in duration. During that time, stored data ECG monitoring data and other physiology and information will need to be offloaded and the ICM&#39;s firmware may need to be reprogrammed, and the transceiver  85  enables the ICM  12  to communicate with external devices to facilitate these functions. 
     In one embodiment, the ICM  12  can be wirelessly connected to a download station  92  executing data link software (“DL”)  93  that permits the secure remote retrieval of stored ECG monitoring data, execution of diagnostics on or programming of the ICM  12 , or performance of other functions. The ICM  12  connects to the download station  92  over a wireless network  91  via the transceiver  85 . In turn, the download station  92  executes the data link software  93  or similar program that wirelessly interacts with the ICM  12  to retrieve the stored ECG monitoring data or perform other function. The download station  92  could be a server, personal computer, tablet or handheld computer, smart mobile device, or purpose-built programmer designed specific to the task of interfacing with a ICM  12 , such as described below with reference to  FIG.  19   . Still other forms of download station  92  are possible. 
     Upon retrieving stored ECG monitoring data from a ICM  12 , middleware (not shown) executing on the download station  92  first operates on the retrieved data to adjust the ECG capture quality, as necessary, and to convert the retrieved data into a format suitable for use by third party post-monitoring analysis software, as further described infra with reference to  FIG.  12   . The formatted data can then be retrieved from the download station  92 . The middleware could alternatively be executed by a separate device other than the download station  92 . 
     A client-server model could be used to employ a server  94  to remotely interface with the download station  92  over the network  91  and retrieve the formatted data or other information. The server  94  executes a patient management program  95  (“Mgt”) or similar application that stores the retrieved formatted data, recorded physiology, and other information in a secure database  96  cataloged in that patient&#39;s electronic medical records (EMRs)  97 , along with tracking and correlating patient symptoms. In addition, the patient management program  95  could manage a subscription service that authorizes an ICM  12  to operate for a set period of time or under pre-defined operational parameters. 
     The patient management program  95 , or other trusted application, also maintains and safeguards the secure database  96  to limit access to patient EMRs  97  to only authorized parties for appropriate medical or other uses, such as mandated by state or federal law, such as under the Health Insurance Portability and Accountability Act (HIPAA) or per the European Union&#39;s Data Protection Directive. For example, a physician may seek to review and evaluate his patient&#39;s ECG monitoring data, as securely stored in the secure database  96 . 
     Physician and other authorized healthcare personnel are able to securely access the retrieved formatted data and other information stored in the EMRs  97  in the secure database  96  by executing an application program (“MD”)  98 , such as a post-monitoring ECG analysis program, on a personal computer  99  or other connectable computing device, and, through the application program  98 , coordinate access to his patient&#39;s EMRs  97  with the patient management program  95  and perform other functions. The application program  98  can include the capability to actively or interactively diagnose or narrow down the underlying cause of sporadic cardiac conditions, for instance, atrial tachycardia (AT), AF, atrial flutter, AV node reciprocating tachycardia, ventricular tachycardia (VT), sinus bradycardia, asystole, complete heart block, and other cardiac arrhythmias. Other diagnoses are possible. 
     In a further embodiment, RR interval data can be extracted from the retrieved formatted data and be presented to physicians in a format that includes views of relevant near field and far field ECG data, which together provide contextual information that improves diagnostic accuracy, such as described in U.S. Pat. No. 9,408,551, issued Aug. 9, 2016 to Bardy et al., the disclosure of which is incorporated by reference. Both near field and far field ECG data views are temporally keyed to an extended duration RR interval data view. The durations of the classical “pinpoint” view, the pre- and post-event “intermediate” view, and the RR interval plot are flexible and adjustable. Thus, the pinpoint “snapshot” and intermediate views of ECG data with the extended term RR interval data allow a physician to comparatively view heart rate context and patterns of behavior prior to and after a clinically meaningful arrhythmia, patient concern or other indicia, thereby enhancing diagnostic specificity of cardiac rhythm disorders and providing physiological context to improve diagnostic ability. Similarly, the data wirelessly offloaded by the ICM can also be used to create a diagnostic composite plot of cardiac data, as further described in U.S. Pat. No. 9,408,551, issued Aug. 9, 2016, the disclosure of which is incorporated by reference. As the amount of data necessary to construct an RR interval plot can be as large as 0.25 megabyte, the energy provided by the energy harvesting module  88  becomes critical for continuous offloading of the collected data at rates high enough to enable such processing. 
     As a result, with the assistance of the server  94 , a complete end-to-end closed loop of patient care can be provided, with the ICM  12  providing long-term ECG and physiology monitoring and data reporting, the patient management program  95  managing ECG and physiology data retrieval and patient symptom tracking and correlation, the application program  98  empowering physicians with the ability to effectively identify the underlying cause of sporadic cardiac conditions, particularly cardiac rhythm disorders, and the ICM  12  again facilitating patient following upon diagnosis and throughout treatment. 
     In a further embodiment, the ICM  12  can interoperate wirelessly with other physiology monitors and activity sensors  104 , whether implanted or dermal, such as activity trackers worn on the wrist or body, and with mobile devices  102 , including smartphones and smart watches, that are designed to communicate over a public communications infrastructure, such as a cellular communications network. Wearable physiology monitors and activity sensors  104  encompass a wide range of wirelessly interconnectable devices that measure or monitor a patient&#39;s physiological data, such as heart rate, temperature, blood pressure, respiratory rate, blood pressure, blood sugar (with appropriate subcutaneous probe), oxygen saturation, minute ventilation, and so on; physical states, such as movement, sleep, footsteps, and the like; and performance, including calories burned or estimated blood glucose level. 
     The physiology sensors in non-wearable mobile devices  102 , particularly smartphones, are generally not meant for continuous tracking and do not provide medically precise and actionable data sufficient for a physician to prescribe a surgical, catheter or serious drug intervention; such data can be considered screening information that something may be wrong, but not data that provides the highly precise information that may allow for a surgery, such as implantation of a pacemaker for heart block or a defibrillator for ventricular tachycardia, or the application of serious medications, like blood thinners for atrial fibrillation or a cardiac ablation procedure. Such devices, like smartphones, are better suited to pre- and post-exercise monitoring or as devices that can provide a signal that something is wrong, but not in the sufficient detail and FDA approved, legally meaningful validation to allow for medical action. Conversely, medically actionable wearable sensors and devices sometimes provide continuous recording for relatively short time periods, up to 80 days, but do not span years and, further, must be paired with a smartphone or computer to offload and evaluate the recorded data, especially if the data is of urgent concern. 
     Wearable physiology monitors and activity sensors  104 , also known as “activity monitors,” and to a lesser extent, “fitness” sensor-equipped mobile devices  102 , can trace their life-tracking origins to ambulatory devices used within the medical community to sense and record traditional medical physiology that could be useful to a physician in arriving at a patient diagnosis or clinical trajectory, as well as from outside the medical community, from, for instance, sports or lifestyle product companies who seek to educate and assist individuals with self-quantifying interests. Data is typically tracked by the wearable physiology monitors or activity sensors  104  and mobile device  102  for only the personal use of the wearer. The physiological monitoring is strictly informational, even where a device originated within the medical community, and the data is generally not time-correlated to physician-supervised monitoring. Importantly, medically-significant events, such as cardiac rhythm disorders, including tachyarrhythmias, like ventricular tachycardia or atrial fibrillation, and bradyarrhythmias, like heart block, while potentially detectable with the appropriate diagnostic heuristics, are neither identified nor acted upon by the wearable physiology monitors and activity sensors  104  and the mobile device  102 . 
     Frequently, wearable physiology monitors and activity sensors  104  are capable of wirelessly interfacing with mobile devices  102 , particularly smart mobile devices, including so-called “smartphones” and “smart watches,” as well as with personal computers and tablet or handheld computers, to download monitoring data either in real-time or in batches. The wireless interfacing of such activity monitors is generally achieved using transceivers that provide low-power, short-range wireless communications, such as Bluetooth, although some wearable physiology monitors and activity sensors  104 , like their mobile device cohorts, have transceivers that provide true wireless communications services, including 4G or better mobile telecommunications, over a telecommunications network. Other types of wireless and wired interfacing are possible. 
     In a further embodiment, where the wearable physiology monitors and activity sensors  104  are paired with a mobile device  102 , the mobile device  102  executes an application (“App”)  103  that can retrieve the data collected by the wearable physiology monitor and activity sensor  104  and evaluate the data to generate information of interest to the wearer, such as an estimation of the effectiveness of the wearer&#39;s exercise efforts. Where the wearable physiology monitors and activity sensors  104  has sufficient onboard computational resources, the activity monitor itself executes an app without the need to relay data to a mobile device  102 . The app can include or be supplemented by downloadable programming instructions, including machine learning and other forms of artificial intelligence-originated instructions. The app can include heuristics to signal patient and physician with alerts over health conditions or arrhythmias of selected medical concern, such as where a heart pattern particular to the patient is identified and the mobile device  102 , in collaboration with the ICM  12 , is thereby reprogrammed to watch for a reoccurrence of that pattern, after which an alert will be generated and sent to the physician (or other caregiver). Similarly, the app can include heuristics that can actively identify or narrow down a pattern (or even the underlying cause) of sporadic cardiac conditions, for instance, atrial tachycardia (AT), atrial fibrillation (AF), atrial flutter (AFL), AV node reciprocating tachycardia, ventricular tachycardia (VT), sinus bradycardia, asystole, complete heart block, and other cardiac arrhythmias, again, after which an alert will be generated and sent to the physician (or other caregiver). For instance, an alert that includes a compressed ECG digitized sample can also be wirelessly transmitted by the app upon the triggering of a preset condition, such as an abnormally low heart rate in excess of 170 beats per minute (bpm), an abnormally low heart rate falling below 30 bpm, or AF detected by onboard analysis of RR interval variability by the app. Finally, a similar methodology of creating app programming tailored to the monitoring and medical diagnostic needs of a specific patient (or patient group or general population) can be used for other conditions or symptoms, such as syncope, palpitations, dizziness and giddiness, unspecified convulsions, abnormal ECG, transient cerebral ischemic attacks and related syndromes, cerebral infarction, occlusion and stenosis of pre-cerebral and cerebral arteries not resulting in cerebral infarction personal history of transient ischemic attack, and cerebral infarction without residual deficits, to trigger an alert and involve the physician or initiate automated analysis and follow up back at the patient&#39;s clinic. Still other activity monitor and mobile device functions on the collected data are possible. 
     In a yet further embodiment, a wearable physiology monitor, activity sensor  104 , or mobile device  102  worn or held by the patient  10 , or otherwise be used proximal to the patient&#39;s body, can be used to first obtain and then work collaboratively with the more definitive and capable ICM  12  to enable the collection of physiology by the ICM  12  before, during, and after potentially medically-significant events. The wearable physiology monitor, activity sensor  104 , or mobile device  102  must be capable of sensing cardiac activity, particularly heart rate or rhythm, or other types of physiology or measures, either directly or upon review of relayed data. Where the wearable physiology monitor or activity sensor  104  is paired with a mobile device  102 , the mobile device  102  serves as a relay device to trigger a medical alert upon detecting potentially medically-significant events in the data provided by the paired activity monitor, such as cardiac rhythm disorders, including tachyarrhythmias and bradyarrhythmias. Finally, if the wearable physiology monitor or activity sensor  104  has sufficient onboard computational resources and also is equipped with a wireless communications services transceiver, the wearable physiology monitor or activity sensor  104  effectively becomes the mobile device and executes an application (not shown) that will trigger the medical alert directly. Still other configurations of the detection app are possible. 
     In a still further embodiment, the monitoring data recorded by the ICM  12  can be uploaded directly into the patient&#39;s EMRs  97 , either by using a mobile device  102  as a conduit for communications with the secure database  96  via the server  94 , or directly to the server  94 , if the ICM  12  is appropriately equipped with a wireless transceiver  85  (shown with reference to  FIG.  8   ) or similar external data communications interface. As described below, the wireless data offloaded from the ICM  12  can be used in a variety of ways, with the use requiring a frequent wireless transmission of large collected data sets, including full disclosure HRV. Such frequent transmission of large data sets is made possible by the presence of the energy harvesting module  88  described below. Further, the availability of the energy harvesting module  88  allows to increase the amount of power used by the wireless transceiver  85  to allow fast and efficient data transfer rates through subcutaneous fat of the patient  10 . The increased amount of power used by the wireless transceiver  85  can be pre-set prior to the implantation of the ICM  12 , or done following the implantation. For example, the amount of power used by the wireless transceiver  85  can be wirelessly adjusted by an external programmer (such as upon the rates of data transfer from the ICM  12  being unsatisfactory), or done by the microcontroller  81  upon detection that the rates of data transfer are below a threshold level. 
     Thus, the data recorded by the ICM  12  would directly feed into the patient&#39;s EMRs  97 , thereby allowing the data to be made certifiable for immediate use by a physician or authorized healthcare provider. No intermediate steps would be necessary when going from subcutaneously sensing cardiac electric signals and collecting the patient&#39;s physiology using a ICM  12  to presenting that recorded data to a physician or healthcare provider for medical diagnosis and care. The direct feeding of data from the ICM  12  to the EMRs  97  clearly establishes the relationship of the data, as recorded by the ICM  12 , to the patient  10  that the physician is seeing and appropriately identifies any potentially medically-significant event recorded in the data as originating in the patient  10  and nobody else. Based on the monitoring data, physicians and healthcare providers can rely on the data as certifiable and can directly proceed with determining the appropriate course of treatment for the patient  10 , including undertaking further medical interventions as appropriate. 
     In a yet further embodiment, the server  94  can evaluate the recorded data, as fed into the patient&#39;s EMRs  97 , to refer the patient  10  for medical care to a general practice physician or medical specialist, for instance, a cardiac electrophysiologist referral from a cardiologist when the recorded data indicates an event of sufficient potential severity to warrant the possible implantation of a pacemaker for heart block or a defibrillator for ventricular tachycardia. Other uses of the data recorded by the ICM  12  are possible. For instance, a patient  10  who has previously suffered heart failure is particularly susceptible to ventricular tachycardia following a period of exercise or strenuous physical activity. A wearable sensor  104  or device  102  that includes a heart rate monitor would be able to timely detect an irregularity in heart rhythm. The application executed by the sensor  104  or device  102  allows those devices to take action by triggering the dispatch of a ICM  12  to the patient  10 , even though the data recorded by the sensor  104  or device  102  is itself generally medically-insufficient for purposes of diagnosis and care. Thus, rather than passively recording patient data, the sensor  104  or device  102  takes on an active role in initiating the provisioning of medical care to the patient  10  and starts a cascade of appropriate medical interventions under the tutelage of and followed by physicians and trained healthcare professionals. 
     In a still further embodiment, based upon machine learning instructions executed by the ICM  12  that generates alerts over health conditions or arrhythmias of selected medical concern, the ICM  12  could upload an event detection application to the sensor  104  or device  102  to enable those devices to detect those types of potentially medically-significant events. Alternatively, the event detection application could be downloaded to the sensor  104  or device  102  from an online application store or similar online application repository. Finally, the ICM  12  could use the sensor  104  or device  102  to generate an appropriate alert, including contacting the patient&#39;s physician or healthcare services, via wireless (or wired) communications, upon detecting a potentially medically-significant event or in response to a patient prompting. 
     The mobile device  102  could also serve as a conduit for providing the data collected by the wearable physiology monitor or activity sensor  104  to a server  122 , or, similarly, the wearable physiology monitor or activity sensor  104  could itself directly provide the collected data to the server  122 . The server  122  could then merge the collected data into the wearer&#39;s EMRs  134  in the secure database  124 , if appropriate (and permissible), or the server  122  could perform an analysis of the collected data, perhaps based by comparison to a population of like wearers of the wearable physiology monitor or activity sensor  104 . Still other server  122  functions on the collected data are possible. 
     Finally, in a yet further embodiment, the ICM  12  can be interrogated using a conventional inductive programmer  100 , which could be interfaced to the application program  98  executing on a physician&#39;s device, or in a standalone fashion. Inductive interfacing may be necessary where the transceiver  85  has suffered an error condition or is otherwise unable to communicate externally. 
     The ICM  12  continuously monitors the patient&#39;s ECG, heart rate and physiology over a long period of time lasting up to several years in duration.  FIG.  10    is a flow diagram showing an ICM-implemented method  110  for monitoring ECG data. Initially, upon successful implantation, the microcontroller  61  executes a power up sequence (step  111 ). During the power up sequence, the voltage of the battery is checked, the state of the flash memory  62  is confirmed, both in terms of operability check and available capacity, and microcontroller operation is diagnostically confirmed. 
     Following satisfactory completion of the power up sequence, an iterative processing loop (steps  112 - 121 ) is continually executed by the microcontroller  61 . During each iteration (step  112 ) of the processing loop, the ECG frontend  63  (shown in  FIG.  11   ) continually senses the dermal ECG electrical signals (step  113 ,  FIG.  10   ) via the ECG electrodes  16  and  17  and is optimized to maintain the integrity of the P-wave. A sample of the ECG signal is read (step  114 ) by the microcontroller  61  by sampling the analog ECG signal that is output by the ECG front end circuit  63 . Each sampled ECG signal, in quantized and digitized form, is processed by signal processing modules as specified in firmware (step  115 ), as described infra, and temporarily staged in a buffer (step  116 ), pending compression preparatory to storage in the flash memory  62  (step  117 ). Following compression, the compressed ECG digitized sample is again buffered (step  118 ), then written to the flash memory  62  (step  119 ) using the communications bus. In a further embodiment, an alert that includes the compressed ECG digitized sample can also be wirelessly transmitted upon the triggering of a preset condition (step  120 ), such as an abnormally low heart rate in excess of 170 beats per minute (bpm), an abnormally low heart rate falling below 30 bpm, or AF detected by onboard analysis of RR interval variability by the microcontroller  61 . Processing continues for an indefinite duration (step  121 ). Still other operations and steps are possible. 
     The microcontroller  61  operates under modular micro program control that includes processing of raw analog ECG signals.  FIG.  11    is a functional block diagram showing the signal processing functionality  130  of the microcontroller  61 . The microcontroller  61  operates under modular micro program control as specified in firmware  132 . The firmware modules  132  include high and low pass filtering  133 , and compression  134 . Other modules are possible. The microcontroller  61  has a built-in ADC, although ADC functionality could also be provided in the firmware  132 . 
     The ECG front end circuit  63  first outputs an analog ECG signal, which the ADC  131  acquires, samples and converts into an uncompressed digital representation. The microcontroller  61  includes one or more firmware modules  133  that perform filtering. In one embodiment, three low pass filters and two high pass filters are used. Following filtering, the digital representation of the cardiac activation wave front amplitudes are compressed by a compression module  134  before being written out to storage  135 . 
     The download station  92  (shown in  FIG.  9   ) executes a data link program (“DL”)  93  or similar program that wirelessly interfaces with the ILR  12  to retrieve the stored ECG monitoring data and perform other functions.  FIG.  12    is a functional block diagram showing the operations  140  performed by the download station  141 . The download station  141  could be a server, personal computer (as shown), tablet or handheld computer, smart mobile device, or purpose-built programmer designed specific to the task of wirelessly interfacing with a ICM  12 . Still other forms of download station are possible, including download stations connected through indirect wireless interfacing using, for instance, a smart phone connected to the ICM  12  through Bluetooth or Wi-Fi, or over an inductive coupling. 
     The download station  141  is responsible for offloading stored ECG monitoring data from a ICM  12 . The download station  141  operates under programmable control as specified in software. The stored ECG monitoring data remotely retrieved from storage  142  on a ICM  12  is first decompressed by a decompression module  143 , which converts the stored ECG monitoring data back into an uncompressed digital representation more suited to signal processing than a compressed signal. The retrieved ECG monitoring data may be stored into local storage (not shown) for archival purposes, either in original compressed form, or as uncompressed. 
     The download station  141  can include an array of filtering modules. For instance, a set of phase distortion filtering tools  144  may be provided, where corresponding software filters can be provided for each filter implemented in the firmware executed by the microcontroller  61 . The digital signals are run through the software filters in a reverse direction to remove phase distortion. For instance, a 45 Hertz high pass filter in firmware may have a matching reverse 45 Hertz high pass filter in software. Most of the phase distortion is corrected, that is, canceled to eliminate noise at the set frequency, but data at other frequencies in the waveform remain unaltered. As well, bidirectional impulse infinite response (IIR) high pass filters and reverse direction (symmetric) IIR low pass filters can be provided. Data is run through these filters first in a forward direction, then in a reverse direction, which generates a square of the response and cancels out any phase distortion. This type of signal processing is particularly helpful with improving the display of the ST-segment by removing low frequency noise. 
     An automatic gain control (AGC) module  145  can also be provided to adjust the digital signals to a usable level based on peak or average signal level or other metric. AGC is particularly critical to single-lead ECG monitors, where physical factors, such as the tilt of the heart, can affect the electrical field generated. On three-lead Holter monitors, the leads are oriented in vertical, horizontal and diagonal directions. As a result, the horizontal and diagonal leads may be higher amplitude and ECG interpretation will be based on one or both of the higher amplitude leads. In contrast, the ICM  12  has only a single lead that is oriented in the vertical direction, so variations in amplitude will be wider than available with multi-lead monitors, which have alternate leads to fall back upon. 
     In addition, AGC may be necessary to maintain compatibility with existing ECG interpretation software, which is typically calibrated for multi-lead ECG monitors for viewing signals over a narrow range of amplitudes. Through the AGC module  145 , the gain of signals recorded by the ICM  12  of the electrocardiography monitor  12  can be attenuated up (or down) to work with FDA-approved commercially available ECG interpretation. 
     AGC can be implemented in a fixed fashion that is uniformly applied to all signals in an ECG recording, adjusted as appropriate on a recording-by-recording basis. Typically, a fixed AGC value is calculated based on how an ECG recording is received to preserve the amplitude relationship between the signals. Alternatively, AGC can be varied dynamically throughout an ECG recording, where signals in different segments of an ECG recording are amplified up (or down) by differing amounts of gain. 
     Typically, the ICM  12  will record a high resolution, low frequency signal for the P-wave segment similar to the ICM&#39;s dermal cousin, such as provided with the dermal ambulatory monitors cited supra. However, for some patients, the result may still be a visually small signal. Although high resolution is present, the unaided eye will normally be unable to discern the P-wave segment. Therefore, gaining the signal is critical to visually depicting P-wave detail. This technique works most efficaciously with a raw signal with low noise and high resolution, as typically generated by the ICM  12 . Automatic gain control applied to a high noise signal will only exacerbate noise content and be self-defeating. 
     Finally, the download station can include filtering modules specifically intended to enhance P-wave content. For instance, a P-wave based boost filter  146 , which is a form of a pre-emphasis filter, can be applied to the signal to restore missing frequency content or to correct phase distortion. Still other filters and types of signal processing are possible. 
     In one embodiment, the ICM  12  can simply be inserted with a small surgical incision that is the width of the widest part of the ICM, typically the transverse cross section of the thickest aspect of the housing  15 . Blunt dissection thereafter under local anesthesia can be used to create the subcutaneous space to receive the ICM  12 , which would generally be inserted into the implantation site, proximal (housing) end first, followed by the distal (electrode assembly) end. In a further embodiment, the ICM  12  can be implanted in the patient&#39;s chest using, for instance, a minimally invasive subcutaneous implantation instrument, such as described in U.S. Pat. No. 6,436,068, issued Aug. 20, 2002 to Bardy, the disclosure of which is incorporated by reference. 
     The energy harvesting module  88  provides a way to continually obtain additional energy for powering the ICM  12  while implanted within the patient  10 , potentially extending the term of use of the ICM  12  to the lifetime of the patient. One source of the energy being harvested can be the kinetic energy generated by the patient  10 .  FIG.  14    is a diagram showing the energy harvesting module  88  of  FIG.  13    with a configuration to harvest kinetic energy in accordance with one embodiment. In this embodiment, the energy harvesting module  88  includes an electrical motor  250  that is composed of a rotor  251  that is integrated into a stator  253 , with the stator  253  producing electrical energy upon the rotation of the rotor  251 . An oscillating weight  252  is fixedly attached to the rotor  251 . The weight  252  pivots during normal movements of the patient due to the changes in the position of the patient&#39;s body (such as getting up, lying or sitting down, walking, and exercising). The pivoting of the weight  252  causes the rotation of the rotor  251 , which causes the stator  253  to produce electrical energy. While the weight is shown to be of a particular shape with reference to  FIG.  14   , other shapes of the weight  253  are also possible. The generated electrical energy is provided either to the power cell  87  or directly to other components of the circuitry  80  of the ICM  12 . In one embodiment, the production of electrical energy by the energy harvesting module can be detected by the microcontroller  81  and recorded into the flash memory  82  as an indication of the patient moving during the time the energy harvesting module  88  produces the energy. Such movement data can subsequently be unloaded and processed along with the electrophysiological data collected by the ICM  12  and provide additional context for any cardiac events. 
     The energy harvesting module  88  can also harvest energy that is deliberately directed at the ICM  12 .  FIG.  15    is a diagram showing the energy harvesting module  88  of  FIG.  13    with a configuration to receive energy from an external inductive coil via inductive coupling in accordance with one embodiment. In this embodiment, the energy harvesting module  88  includes an inductive coil  261  that generates alternating current upon being exposed to a magnetic field generated by a further coil  263  located outside the patient  10 . Thus, when the ICM  12  is implanted into the patient  10 , the external coil  263  (which can be included in a wand operated by qualified medical personnel) can be positioned in proximity to the patient&#39;s chest, with the external coil  263  generating a magnetic field upon electricity being ran through the external coil  263 . The magnetic field induces the generation of the alternating current within the inductive coil  261  within the energy harvesting module  88  in accordance with Faraday&#39;s law of induction. The generated alternated current is provided to a rectifier  262 , which converts the alternating current to direct current is provided either to the power cell  87  or directly to other components of the circuitry  80  of the ICM (such as via wires  271 ). The transfer of energy to the inductive coil  261  can be performed at the same time as offloading of data collected by the ICM  12 , as further described below with reference to  FIG.  19   . 
     Vibrations that the ICM  12  is exposed while being inside the patient&#39;s body, which can be caused either by the patient&#39;s movements or caused by external factors, can also be harvested and used for energy generation.  FIG.  16    is a diagram showing the energy harvesting module  88  of  FIG.  13    with a configuration that includes a piezoelectric energy generator  223  in accordance with one embodiment. The generator  223  includes a piece of piezoelectric material, such as piezoelectric rubber, that is stretched (under tension) on a partition  267  within the energy harvesting module  88 . Upon vibrations reaching the energy harvesting module  88 , the vibrations cause a deformation of the stretched piezoelectric material, which produces alternating current. The piezoelectric generator  88  is interfaced via wires  224 ,  225  to a rectifier  226 , which converts the alternating current to direct current, which in turn is provided either to the power cell  87  or directly to other components of the circuitry  80  of the ICM  12  (such via wires  172 ). In one embodiment, the vibrations that the energy harvesting module  88  harvests to produce electrical energy can be vibrations of caused by the patient&#39;s heartbeat, though other sources of vibrations are possible. 
     The patient&#39;s bodily temperature fluctuates depending on time of day, activity level, dietary intake, and other factors. This fluctuation in temperature can be taken advantage of to generate electrical energy for the ICM  12 .  FIG.  17    is a diagram showing the energy harvesting module  88  of  FIG.  13    with a configuration to generate electrical energy upon a change in the patient&#39;s bodily temperature in accordance with one embodiment. In this embodiment, the energy harvesting module  88  includes a pyroelectric material  227 , such as a pyroelectric crystal (though other pyroelectric materials are also possible) that generates alternating current upon the change in the temperature of the patient&#39;s body (and consequently, the change in the temperature of the pyroelectric material). The pyroelectric material  227  is interfaced via wires  228 ,  229  to a rectifier  240 , which converts the alternating current to direct current, which in turn is provided either to the power cell  87  or directly to other components of the circuitry  80  of the ICM  12  (such as via wires  173 ). 
     A further source of energy that the energy harvesting module  88  can take advantage of are radio waves, which are plentiful in most populated areas.  FIG.  18    is a diagram showing the energy harvesting module  88  of  FIG.  13    with a configuration to harvest energy of radio waves in accordance with one embodiment. In this embodiment, at least a portion (such as one side) of the housing  15  of the ICM  12  is made of a material that is transparent to radio waves, such as plastic, though other radio transparent materials are possible. The energy harvesting module  88  includes an antenna  330  that generates alternating current upon capturing radio waves originating from outside the patient&#39;s body. The antenna  330  is interfaced by wires  331 ,  332  to a rectifier  337 , such as a diode (though other rectifiers are possible) that converts the alternating current to direct current, and which supplies the direct current either to the power cell  87  or directly to other components of the circuitry  80  of the ICM  12  (such as via wires  374 ). In one embodiment, the antenna  330  could be a folded unipole antenna. In a further embodiment, the antenna  330  could be a dipole antenna. Still other kinds of antennas  330  are possible. While the antenna  330  is shown to be compartmentalized to the energy harvesting module  88  of the ICM  12 , in a further embodiment, at least a portion of the antenna  330  can be located in other portions of the housing  15 , such as being wrapped around the internal periphery of the housing  15 . In a still further embodiment, at least a portion of the antenna  330  could be located on the outside of the housing  15 . Further, while the antenna  330  could be a stand-alone antenna that only has the function of harvesting power (with a different antenna being used by the wireless transceiver  85  for communication and data offloading), in a further embodiment, the antenna  330  could also be used by the wireless transceiver  85  to offload collected data and other wireless communication, with no additional antenna used exclusively by the wireless transceiver  85  being included in the ICM  12 . 
     While the energy harvesting module  88  can produce electrical energy using radio waves originating from many sources outside of the patient&#39;s body, the radio waves can also be specifically directed at the energy harvesting module. Thus, a properly-trained patient or a qualified medical professional can use an external source of the radio waves to specifically provide the power to the energy harvesting module  88 . The source of radio waves can also include the capability to wirelessly receive data collected by the ICM  12 , which the ICM  12  can offload at the same time as the energy harvesting module  88  is receiving energy.  FIG.  19    is a diagram showing an external device  380  combining energy transmission and data download capabilities for use with the ICM  12  in accordance with one embodiment. The external device  380  can be shaped as a puck that can be pressed against (or held close to) the patient&#39;s chest in the parasternal region at the level at which the ICM  12  is implanted. The external device  380  includes an energy transmission module  381  that is capable of interfacing with the energy harvesting module  88  to provide input (such as magnetic or radio waves) that allows the energy harvesting module  88  to produce electrical energy. For example, the energy transmission module  381  can include a radio transmitter that radiates radio waves captured by the antenna  330 . The energy transmission can also include, alternatively or in addition to the radio transmitter, the further inductive coil  263  that generates the magnetic field that causes the inductive coil  261  within the energy harvesting module  283 . 
     Further, the external device  380  includes a data download module  382 , which uses an internal wireless transceiver to wirelessly download data collected by the ICM  12  by interfacing with the wireless transceiver  85  of the ICM  12 . The downloading of the data can happen simultaneously to the energy transmission module  381  supplying the input to the energy harvesting module  88  of the ICM, allowing to reduce the time that the external device  380  would need to be held next to the patient  10 . The downloaded physiological data can in turn wirelessly forwarded by the external device  380  for further processing, such as to the server  94 . The external device  380  can also perform processing of the downloaded data, as described above with reference to  FIG.  12   , prior to transmitting the data to the server  14 . The external device  380  further includes components necessary for the functioning of the modules  381  and  382  and other processing, such as a processor, memory, and either an internal source of power, or a connection to an external source of power. 
     In addition, while the external device is shown as a puck with reference to  FIG.  19   , in a further embodiment, other configurations of the external device  380  are possible. For example, the external device  380  could be shaped as a wand. Still other configurations of the external device are possible. 
     While the invention has been particularly shown and described as referenced to the embodiments thereof, those skilled in the art will understand that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope.