Patent Publication Number: US-11642065-B2

Title: System for induction-based subcutaneous insertable physiological monitor recharging

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This non-provisional patent application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent application, Ser. No. 63/135,745, filed Jan. 11, 2021, the disclosure of which is incorporated by reference. 
    
    
     FIELD 
     This application relates in general to electrocardiographic monitoring and, in particular, to system for induction-based subcutaneous insertable physiological monitor recharging. 
     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. 
     Recharging such monitors is not a trivial matter, however, as many techniques that are used for recharging batteries are not applicable when the battery is implanted in a patient and a charging wire cannot simply be connected to a battery, especially in a case of an obese patient where the implanted device is buried beneath a thick layer of fat. Those techniques that do allow for remote charging, such as inductive charging, cannot be directly translated from other industries. Whereas in many other industries the speed of recharging can be prioritized without worry of the battery or the battery&#39;s surrounding overheating, overheating is a grave concern when the battery being recharged is implanted inside a patient. Even as a slight overheating of the battery or the battery&#39;s surrounding can cause discomfort and pain to the patient; a significant overheating can damage the patient&#39;s tissues, endangering the patient&#39;s health and likely requiring a removal of the inserted monitor from the patient. Overheating of the battery can also cause the battery to explode, which may be potentially fatal for the patient. On the other hand, if the speed of recharging is too slow, the patient is inconvenienced, and is less likely to spend sufficient time recharging the monitor, increasing the chances that the monitor will fail without the charging being complete. 
     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, and that can be recharged at a high speed without endangering the patient. 
     SUMMARY 
     Long-term electrocardiographic and physiological monitoring over a period lasting up to several years in duration can be provided through a continuously-recording rechargeable subcutaneous insertable cardiac monitor (ICM. 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 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. 
     Internally, the energy harvesting module can include at least two overlapping receiving coils that are spaced to be orthogonal to each other and that have a tilt angle of substantially 45°. Such overlapping wire combination allows to minimize mutual inductance of the solenoid coils and increase the rate at which energy can be provided to the energy harvesting module. Further, the rate at which the energy is transmitted from the outside can be increased by defining in a transmitting coil a substantially triangular gap. The combination of the overlapping coils inside the ICM and the transmitting coil with the substantially triangular gap allows to substantially increase the rate at which the ICM can be recharged without overheating the ICM or the surrounding thoracic tissues of the patient. The ICM can be used for performing not only cardiac monitoring, but also other types of physiological monitoring. The energy harvesting module described and the transmitting coil can be used to charge a wide variety of implantable medical devices of a wide variety of shapes and configurations. 
     In one embodiment, a system for induction-based subcutaneous insertable cardiac monitor recharging is provided. The system includes a subcutaneous insertable physiological monitor, which includes an implantable housing comprised of a biocompatible material that is suitable for implantation within a living body; at least one pair of ECG sensing electrodes; electronic circuitry provided within the housing assembly comprising a low power microcontroller, an ECG front end circuit interfaced to the microcontroller and configured to capture cardiac action potentials sensed by the pair of ECG sensing electrodes which are output as ECG signals, and a memory electrically interfaced with the microcontroller and operable to store data regarding the ECG signals associated with substantially every heartbeat of the living body during the monitoring; and two or more overlapping inductive coils within the housing, each of the overlapping inductive coils configured to generate alternating current, at least a portion of which is used to power the electronic circuitry, upon being exposed to a magnetic field generated by a transmitting coil located outside the living body. 
     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. 
         FIG.  20    is a diagram showing overlapping receiving coils for use in the energy harvesting module to receive energy from an external transmitting coil via inductive coupling in accordance with one embodiment. 
         FIG.  21    is a diagram showing the solenoids of  FIG.  20    unwrapped in accordance with one embodiment. 
         FIG.  22    is an illustration of the tilt angle and the overlap angles on a portion of unwrapped solenoids  261 A,  261 B in accordance with one embodiment. 
         FIG.  23    is a close up of a portion of the  FIG.  21    illustrating attachments of solenoids to each other in accordance with one embodiment. 
         FIG.  24    is a diagram showing unwrapped solenoids connecting to other parts of the energy harvesting module in accordance with one embodiment. 
         FIG.  25    is a diagram showing overlapping solenoids connecting to other parts of the energy harvesting module in accordance with one embodiment. 
         FIGS.  26 A- 26 B  provide a bottom view of unwrapped solenoids being wrapped into the coils seen with reference to  FIG.  20    in accordance with one embodiment. 
         FIG.  27    is a diagram showing a transmitting coil that defines a gap shaped substantially as a triangle with rounded corners in accordance with one embodiment. 
         FIG.  28    is an outer perspective view showing an IMD that houses a configurable hardware platform for physiological monitoring of a living body in accordance with one embodiment. 
         FIG.  29    is an outer perspective view showing the central tubular body of the IMD of  FIG.  28   . 
         FIG.  30    is a side perspective view showing the semi spherical end cap (“Radome”) of the IMD of  FIG.  28   . 
         FIG.  31    is a side perspective view showing the electrically conductive semi spherical end cap (“Protectrode”) of the IMD of  FIG.  28   . 
         FIG.  32    is an inside perspective view showing the interior of the end cap of the “Protectrode” of  FIG.  31   . 
         FIG.  33    is an inside perspective view showing the interior of the end cap of the “Protectrode” of  FIG.  31   . 
         FIG.  34    is an inside perspective view showing the interior of the fully assembled “Protectrode” of  FIG.  31   . 
         FIG.  35    is an exploded perspective view showing the components of the “Protectrode” of  FIG.  31   . 
         FIG.  36    is a top plan view of a flexible circuit board for use in the IMD of  FIG.  28    in a flat, unfolded form. 
         FIG.  37    is a three-quarters perspective view of the flexible circuit board of  FIG.  36    in a semi-folded configuration. 
         FIG.  38    is an outer perspective view showing an IMD that houses a configurable hardware platform for physiological monitoring of a living body in accordance with a further embodiment. 
         FIG.  39    is a block diagram showing the microarchitecture of the IMD of  FIG.  28   . 
         FIG.  40    is a flow diagram showing a method for continuously monitoring electrocardiography for use in the IMD of  FIG.  28   . 
         FIG.  41    is a diagram showing an unrolled 3-phase coil that is composed of three receiving coils in accordance with one embodiment. 
         FIGS.  42 A and  42 B  show two views of the 3-phase coil of  FIG.  41    when rolled up in accordance with one embodiment. 
         FIG.  43    is a diagrams showing an unrolled 4-phase coil that is composed of four receiving coils in accordance with one embodiment. 
         FIGS.  44 A and  44 B  show two views of the 4-phase coil of  FIG.  42    when rolled up in accordance with one embodiment. 
         FIG.  45    is a diagrams showing an unrolled 6-phase coil that is composed of six receiving coils in accordance with one embodiment. 
         FIGS.  46 A and  46 B  show two views of the 6-phase coil of  FIG.  44    when rolled up in accordance with one embodiment. 
         FIGS.  47 A- 47 B  show a plurality of unwrapped coils in accordance with one embodiment. 
         FIG.  48    is an expanded view of the unrolled coil of  FIGS.  47 A- 47 B  in accordance with one embodiment 
         FIG.  49 A  shows a partially rolled-up coil. 
         FIG.  49 B  shows fully-rolled up coil. 
         FIG.  50    is an expanded view of the unrolled coil of  FIGS.  47 A- 47 B . 
         FIG.  51    shows fully-rolled up coil. 
         FIG.  52    a plurality of unwrapped coils in accordance with one embodiment. 
         FIG.  53    is a diagram showing a two-phase coil that needs to be wrapped around 1.5 times to create the tubular shape. 
     
    
    
     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 - 26   , other embodiments of the energy harvesting module  88  are also possible. In addition, while the power source  86  is shown as an integrated module, in a further embodiment, different components could be distributed throughout the ICM  12 . Likewise, different components of the energy harvesting module  88  could be distributed throughout the ICM  12 . 
     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 with and recharging 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. 
     Further, 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. 
     Finally, as further described below beginning with reference to  FIG.  15   , the ICM  12  can interface with devices used for recharging the ICM  12 , such as the transmission coil  263  described below or an external device  380  described below that can combine recharging and data offload capabilities. 
     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. 
     While the ICM  12  is described above as having particular features, in a further embodiment, the ICM  12  within which the energy harvesting module  88  is integrated could be other types of implantable cardiology and other physiology monitor that have a rechargeable battery or other parts of their circuitry that need to be recharged. For example, the ICM  12  could be an implantable medical device such as described in U.S. Patent Application Publication No. 20210000345, entitled “Configurable Hardware Platform For Physiological Monitoring Of A Living Body,” published Jan. 7, 2021, to Felix et al. (“the Felix Publication”), the disclosure of which is incorporated by reference. The Felix Publication discloses a configurable hardware platform for health and medical monitoring of physiology that is housed within a hermetically sealed implantable medical device (IMD). Briefly, physically, the IMD has a generally tubular shape that includes a central tubular body with rounded semi spherical end caps. When configured to measure electrocardiographic signals, the central tubular body and one of the semi spherical end caps function as electrode dipoles. The semi spherical end cap is electrically conductive yet electrically insulated from the central tubular body. As well, the outside surface of the central tubular body is partially electrically insulated, generally on the surface closest to the electrically conductive semi spherical end cap to form a non-electrically conductive inversion with only the outside surface distal to that semi spherical end cap being exposed. When placed within the central tubular body, a flexible circuit board forms three aspects of a microcontroller circuit assembly that respectively define a receiving coil for inductive charging and optional communication, a high frequency antenna for radio frequency (RF) data exchange, and a flexible circuit board containing a microcontroller and device circuitry. An onboard power source that includes a rechargeable energy cell, battery, or supercapacitor is also placed within the tubular body to one end of the flexible circuit board and, optionally, in electrical contact through a protection circuit with the electrically conductive semi spherical end cap, thereby serving as an electrical feedthrough to the flexible circuit board. The power source may be recharged through a charging and conditioning circuit interfaced with the microcontroller using a non-contact method, such as inductive charging, resonant charging, energy harvesting, thermal gradient charging, ultrasonic charging, RF-based charging or charging by ambient or driven motion. All or parts of the energy harvesting  88  could be included in the IMD disclosed by the Felix Publication to recharge the rechargeable power source. The energy harvesting module  88  could be used to supplement the energy provided by the receiving coil described in the Felix Publication, or the double-helix shaped coil  750  could be used as the power receiving coil  536  of the IMD described by the Felix publication, as further described below beginning with reference to  FIG.  28   . In a still further embodiment, part or all of the energy harvesting module  88  could be integrated into other kinds of implantable medical devices. 
     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 as part of the system  9 —in accordance with one embodiment. In this embodiment, the energy harvesting module  88  includes at least one receiving coil  261  that generates alternating current upon being exposed to a magnetic field generated by a transmitting coil  263  located outside the patient  10 . Thus, when the ICM  12  (or another form of monitor, such as the IMD  500 ,  560  described below) 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   . As further described below beginning with reference to  FIG.  20   , the energy harvesting module  88  can include multiple receiving coils positioned in a way that minimizes parasitic interactions between them. A particular configuration of the transmitting coil  263  is described below with reference to  FIG.  27   . 
     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 transmitting coil  263  that generates the magnetic field that causes the inductive coil  261  within the energy harvesting module  88 . 
     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 , such as further described in U.S. Patent Application No. 20210000344, published Jan. 7, 2021, entitled “SYSTEM AND METHOD FOR REMOTE ECG DATA STREAMING IN REAL-TIME,” to Dreiscbach et al., the disclosure of which is incorporated by reference. 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. 
     As mentioned above, the energy harvesting module  88  can include multiple receiving coils  261 A,  261 B that generate alternating current upon being exposed to a magnetic field generated by a transmitting coil  263  located outside the patient  10 . In the description below, such receiving coils are also referred to as solenoids. Having multiple receiving solenoids increases the surface area that can be used for inductive charging. However, as the fields induced by the solenoids can have parasitic effect on each other, decreasing the overall amount of current generated by them, optimizing the positioning of the solenoids relative to each other is important for increasing the rate at which the energy harvesting module  88  generates energy and at which the ICM  12  (including the IMD  500 ,  560  described below) can be recharged. For the sake of clarity, in the example below, the multiple receiving coils  261  are often described below as being two solenoids  261 A,  261 B that receive energy from the transmitting coil  263 . However, as also described below, other numbers of receiving coils  263  are possible. 
       FIG.  20    is a diagram showing a double-helix shaped receiving coil  750  formed by overlapping receiving coils  261 A,  261 B for use in the energy harvesting module  88  to receive energy from an external transmitting coil  263  via inductive coupling in accordance with one embodiment. The coils  261 A,  261 B overlap with each other and are attached to each other as further described below. The solenoids  261 A,  261 B are positioned so that the solenoidal tilt angle is 45° while the solenoids  261 A,  261 B are positioned to intersect orthogonally (perpendicularly), at a 90° angle, relative to each other. The 45° angle and the orthogonal positioning minimizes any interactions between the solenoids  261 A,  261 B, the mutual inductance of the solenoids  261 A,  261 B and any parasitic interactions between them. Together, the two solenoids  261 A,  261 B form a shape resembling a double-helix. The solenoids  261 A,  261 B could be made of polyimide copper, though other types of materials are also possible. As the interactions between the solenoids  261 A,  261 B is minimized, due to the increased surface area (when compared to a single solenoid) available for receiving energy via inductive coupling, the rate at which the combined solenoids  261 A,  261 B can be used to recharge the components of the ICM  12  is significantly higher than when a single solenoid is used. Despite the increased surface area, the amount of space that the two solenoids  261 A,  261 B occupy is insignificantly greater than occupied by a single solenoid due to the two solenoids  261 A,  261 B overlapping, thus helping to minimize the size of the ICM  12 . Further, when the housing of the ICM  12  is of a tubular shape (such as of the implantable medical device  500 ,  560  described below), the double-helical shape of the coil formed by the solenoids  261 A,  261 B allows the coil  750  to be positioned along the interior walls of the housing, thus maximizing the amount of space available within the housing for other components of the ICM  12 . The overlapping solenoids  261 A,  261 B can also be used in an energy harvesting module  88  of an ICM  12  that has a non-tubular housing. 
     The thickness of the wires (also referred to as traces or circuit traces) making up the solenoids  261 A,  261 B influences the resistance of the solenoids  261 A,  261 B (and consequently, the degree to which they heat up) as well as their inductance (and consequently their ability to receive energy). In particular, increasing the thickness decreases the resistance (making the solenoids  261 A,  261 B less likely to heat up) but also decreases the number of times the solenoids  261 A,  261 B can be wrapped each other in a limited space, which in turn decreases the inductance and the ability of the solenoids to receive energy. Thus, optimal thickness must be chosen to consider both the resistance and the inductance. In one embodiment, the wire thickness could be in the 6 mils-60 mils range (with one mil being one thousandth of an inch), though other wire thickness could also be used. 
     Depending on the length of the wires making up the solenoids  261 A,  261 B, the solenoids  261 A,  261 B can be wrapped around each other multiple times (while retaining the same orthogonal positioning described earlier), thus creating multiple layers of overlapping coils, allowing to minimize the amount of space the solenoids  261 A,  261 B occupy, and increasing the inductance of the solenoids  261 A,  261 B. As illustrated by  FIGS.  26 A- 27 B , the solenoids  261 A,  261 B shown with reference to  FIG.  20   , are wrapped around each other twice. Other number of wraparounds are possible. 
     As mentioned above, while only one pair, two solenoids  261 A,  261 B, are shown with reference to  FIG.  20   , other numbers of solenoids could be combined to further increase the surface area available for use in inductive charging. For example, additional two solenoids  261 A,  261 B could be combined with the first pair of solenoids  261 A,  261 B to form the double-helix-shaped coil  750 , resulting in the double-helix shaped coil  750  being composed of two pairs of coils  261 A,  261 B. A first additional solenoid  261 A could be wrapped around the outside surface of the first solenoid  261 B; this first additional solenoid would be aligned with solenoid  261 A, having a solenoidal tilt angle of 45° and being orthogonal to solenoid  261 B. A second additional solenoid  261 B would be wrapped around the first additional solenoid, and would be aligned with the solenoid  261 B; the second additional solenoid would have a solenoidal tilt angle of 45° and would be orthogonal with the solenoid  261 A and the first additional solenoid. Still other numbers of solenoids in the energy harvesting module  88  are possible. 
     Showing the alignment of solenoids  261 A,  261 B when they are unwrapped and not forming a coil can help visualize their arrangement.  FIG.  21    is a diagram showing the solenoids  261 A,  261 B of  FIG.  20    unwrapped in accordance with one embodiment. The unwrapped solenoids  261 A,  261 B are sine shaped, they can be wrapped to create the coils seen with reference to  FIG.  20   . As the solenoids  261 A,  261 B are wrapped around each other multiple times, the period of the sine wave by which each unwrapped portion can be represented gets longer due to having around to wrap previously wrapped portions of the solenoids  261 ,  261 B, as illustrated by  FIGS.  26 A- 26 B .  FIGS.  26 A- 26 B  provide a bottom view of unwrapped solenoids  261 A,  261 B being wrapped into the coils seen with reference to  FIG.  20    in accordance with one embodiment.  FIG.  26 A  shows the wrapping of a portion of the unwrapped solenoids  261 A,  261 B, and  FIG.  26 B  shows a result of wrapping of the solenoids  261 A,  261 B around each other a second time. As can be seen with reference to the  FIGS.  26 A- 26 B , the circumference of the circle formed by portions of the solenoids  261 A,  261 B used for the second wrapping around is greater than for the first wrapping around. To precisely predict the length of each segment of the solenoid  261 A,  261 B that is used for each wraparound, the period of the sine wave representing that segment (when unwrapped) is set to equal the circumference of the circle formed by the segment (when wrapped) when looked at from the perspective of  FIGS.  26 A- 26 B . With the circumference being determined according to the formula 2πr, the circumference of the segment of the solenoids  261 A,  261 B used for each subsequent wraparound increases due to the increased radius of the circle formed by that segment. Thus, the period of the sine wave representing each segment of the solenoids must get longer with each wraparound. Knowing this increase allows to properly size each segment of each solenoids  261 A,  261 B. In particular, to achieve optimal alignment of the solenoids, the lengths of the segments of the solenoids  261 A,  261 B used for a single wraparound must be substantially equal. 
     As previously mentioned before, the solenoidal tilt angle of the solenoids  261 A and  261 B is around 45° and the solenoids  261 A,  261 B are positioned as to intersect substantially orthogonally to each other.  FIG.  22    is an illustration of the tilt angle and the overlap angles on a portion of unwrapped solenoids  261 A,  261 B in accordance with one embodiment. When the solenoids  261 A,  261 B are wrapped, the angles are maintained. 
     The solenoids  261 A,  261 B are attached to each other in at least some portions to make sure that their positions with respect to each other are maintained.  FIG.  23    is a close up of a portion of the  FIG.  21    illustrating attachments of solenoids  261 A,  261 B to each other in accordance with one embodiment. As can be seen with reference to  FIG.  23   , the solenoids  261 A,  261 B can be attached to each other with vias  402 , though other ways of attachments and reinforcement are also possible. Also, while a particular number of vias are shown as connecting the solenoids, in a further embodiment, a different number of vias could be used. 
     Each of the solenoids  261 A,  261 B also attaches to other portions of the energy harvesting module  88 , such as a rectifier, to which the generated current is provided for recharging the power cell  87  or otherwise powering the circuitry  80  of the ICM  12 .  FIG.  24    is a diagram showing unwrapped solenoids  261 A,  261 B connecting to other parts of the energy harvesting module  88  in accordance with one embodiment. When the solenoids  261 A,  261 B are wrapped around each other and form the double-helical shape, they retain the connections to other parts of the energy harvesting module  88 , as shown with reference to  FIG.  25   .  FIG.  25    is a diagram showing overlapping solenoids  261 A,  261 B connecting to other parts of the energy harvesting module  88  in accordance with one embodiment. If the housing of the ICM  12  is tubular, one or more other portions of the energy harvesting module  88  could also be foldable to adopt a circular or partially-circular shape when the solenoids are overlapping. 
     The large surface area and the positioning of the overlapping solenoids  261 A,  261 B provides a way to increase the rate at which energy is received via inductive coupling from the transmitter coil  263  without significantly increasing the size of the energy harvesting module  88 . Further, the double-helix shape is tolerant towards misalignment with the transmitting coil  263 , thus allowing a reasonably high rate of charging even when the charging procedure is imperfect (such as when being conducted by the patient). The speed of the charging can further be increased without endangering the patient through a use of a transmitting coil that defines a triangular gap.  FIG.  27    is a diagram showing a transmitting coil  263  that defines a gap  405  shaped substantially as a triangle with rounded corners in accordance with one embodiment. The triangular gap  405  allows to provide energy via inductive charging to the energy harvesting module  88  without overheating the energy harvesting module  88 , the power cell  87 , other portions of the ICM  12 , or the surrounding thoracic tissues of the patient. The triangular gap  405  helps to compensate for misalignment between the transmitting coil  263  and the receiving coils. 
     In one embodiment, the width  407  of the entire transmitting coil  263  can be 6 inches-10 inches, with the height  406  base of the triangular gap  405  being 1 inch-3 inches. In this embodiment, changing the height  406  of the gap lower than 1 inch could increase the rate of transmission of energy too high, resulting in the ICM  12  or the patient&#39;s tissues heating up too much. Also, in this embodiment, changing the height of the gap  405  to be greater than 3 inches could make the rate of the transmission of energy to be too slow to be convenient for the patient. If the width  407  of the transmitting coil changes, the optimal height  406  of the gap  405  could also change. While the transmitting coil  263  with the triangular gap is particularly synergetic when transmitting energy to the overlapping solenoids described above, in a further embodiment, the transmitting coil  263  could also be used with other kinds of receiving coils and can be used to recharge multiple kinds of implantable medical devices. As mentioned above, the transmitting coil  263  with the gap  405  could be integrated into the external device  380 . While the overall shape of the transmitting coil  263  is substantially circular, in a further embodiment, other overall shapes could be used as long as the substantially triangular gap  405  is retained in the central portion of the transmitting coil. For example, in one further embodiment, the transmitting coil  263  could have a shape of a figure eight. 
     As also further described below, a portion (such as the double-helix shaped coil  750 ) or the entirety of the energy harvesting module  88  could be a part of the IMD described by the Felix Publication. Additional details regarding the IMD are provided below. A configurable hardware platform for health and medical monitoring of physiology is housed within a hermetically sealed, implantable medical device (IMD). The IMD provides an implanted form of ambulatory physiological monitor that offers per-heartbeat monitoring with flexible and extensible monitoring capabilities. The IMD is designed to be implanted within a living body and to operate over an extended time period while monitoring different types of patient physiology, possibly at different times and in different ways. 
     The IMD can record every heartbeat, perform live transmission or delayed transmission, which may occur, for instance, two days or longer following recordation, or live monitoring. When every heartbeat is recorded and sent, the platform does not require an analysis algorithm onboard; rather, the analysis algorithm could be implemented at a datacenter or on a cell phone to do the heavy data processing by utilizing the better computing resources available on those platforms. The IMD is equipped with one or more physiological sensors that non-exhaustively include ECG, temperature, pulse oximetry, oxygen saturation, respiration, blood glucose, blood pressure, and drug levels or any appropriate measure of disease. In a further embodiment, the IMD can also monitor non-physiological data when the IMD is equipped with an appropriate type of sensor, such as posture as derived from data measured by an actigraphy sensor, accelerometer or inertial motion sensor. Other types of sensors and forms of physiology and non-physiological data capture are possible, such as cardiac effort level, thoracic impedance, and sound recording, including ultrasonic and sub-sonic sound recording. 
     The degree of surgical invasiveness required to implant the IMD depends upon the intended situs within the body, which is at least in part dictated by the desired range of physiology to be monitored. For instance, electrocardiographic monitoring of the heart that emphasizes the propagation of low amplitude, relatively low frequency content cardiac action potentials, particularly the P-waves that are generated during atrial activation, can be efficaciously performed by implanting the IMD in a subcutaneous situs located axially and slightly to either the left or right of the sternal midline in the parasternal region of the chest. This type of subcutaneous implantation can be performed in a physician&#39;s office using a specialized implantation instrument that includes a trocar to incise the skin and form a subcutaneous tunnel, and a cannula through which the IMD is guided into place, after which the implantation instrument is withdrawn and the surgical incision is closed. 
     Specific details of the IMD&#39;s housing, electronic and support circuitry, power source, and microarchitecture will now be discussed. 
     Housing 
     Physically, the IMD has a generally cylindrical shape that includes a central tubular body with rounded semi spherical end caps, although other shapes and configurations are possible. In a further embodiment, one or both of the semi spherical end caps may be replaced pointed or semi-pointed tips to ease insertion into the body.  FIG.  28    is an outer perspective view showing an IMD  500  that houses a configurable hardware platform for physiological monitoring of a living body in accordance with one embodiment. The IMD  500  includes three primary assemblies. The main middle section of the IMD  500  is a central body  511  that can be formed from a medical grade titanium or similar medical implantation-safe material. The central body  511  has a tubular or cylindrical shape that defines an axial bore, which provides a hollow interior cavity that is open on both end caps running longitudinally over the length of the central body  511 . Other shapes having non-circular or non-spherical shapes are possible. Rounded semi spherical end caps  512  and  513  are welded or affixed to the central body  511  to form a hermetically sealed device housing. The end caps  512  and  513  can be formed in other shapes, such as pointed or semi-pointed tips. 
     The central body  511  houses a flexible circuit board, a low frequency resonant charger antenna to facilitate device recharging, and an onboard power source generally consisting of a rechargeable energy cell, battery, or supercapacitor. One of the semi spherical end caps, known as the “Protectrode”  512 , serves a dual purpose as an electrode and housing for patient and device protection components. The other semi spherical end cap, known as the “Radome”  513 , houses a high frequency antenna used for transmitting data over an RF link, using, for instance, Bluetooth or WiFi. Additionally, the “Radome”  513  could be used to house an inductive antenna and inductive link. The RF link may also be used for device calibration and configuration. In a further embodiment, the “Radome”  513  can also house physiological sensors, such as pulse oximetry and blood pressure. In a further embodiment, the optically clear “Radome”  513  may allow light or other forms of radiation to be received and transmitted through to passively facilitate collection of other vital signs, such as pulse oximetry and blood pressure. In a still further embodiment, fiber optics or lenses implanted into the “Radome”  513  may facilitate collection of vital signs by sensors housed elsewhere. 
     The IMD  500  has an overall length of approximately 5.5 cm to 8.5 cm with an outer diameter, measured across the central body  511 , of approximately 5-8 mm and a wall thickness of approximately 0.3 mm; however, other dimensions, including overall length, wall thickness, and outer diameter, are possible depending upon both the electronic circuitry and power source that need to be housed within and the types and numbers of physiological and non-physiological sensors. 
     In a further embodiment, the IMD  500  can be filled with a gas, such as argon or other inert gas. In particular, argon gas is conventionally used when welding titanium components and, when oxygen-purged into the interior of the IMD  500 , further serves to preserve the electrical components and facilitate device longevity. In addition, supporting structure, such as an acrylic rod, can be used as an internal spacer to help keep the internal components in proper position. 
     In one embodiment, the central body  511  and the “Protectrode”  512  can be micro bead blasted to respectively increase the roughness of the central body  511  to improve silicone or Parylene bonding and to increase the surface area of the “Protectrode”  512  for better signal quality. A titanium nitride coating could also be applied to dramatically increase the surface area of the device. 
     The conductive surface  518  is formed by partially insulating the outside surface of the central body  11  using a non-electrically conductive, insulating surface treatment or coating (“insulating coating”)  519 . The insulating coating  519  is generally applied on the outer surface closest to the “Protectrode”  512 , which maximizes the electrode dipole spacing. In one embodiment, the insulating coating  519  can be a chemical vapor deposited poly polymer, such as Parylene C. In a further embodiment, the insulating coating  519  can be a silicone polymer-based (polysiloxanes) coating. Alternatively, both forms of coatings, poly polymer and silicone polymer, could be employed. Poly polymers exhibit superior moisture resistance and insulation resistance properties, but are susceptible to damage from scratches and scrapes. Silicone polymer coatings form a durable protective layer and, when applied over a poly polymer coating, such as Parylene C, can protect the underlying coating from scratches and scrapes during insertion, repositioning, or removal of the IMD  500 . 
     The end  522  of the central body  511  closest to the conductive surface  518  interfaces to the “Radome”  513 . In one embodiment, the high frequency antenna is a separate component that is contained within the “Radome”  513 . Here, the high frequency antenna can be held in place by filling the cavity of the “Radome”  513  with a filler material, such as acrylic, urethane, glass, or similar material, and the high frequency antennal is interfaced to a flexible circuit board via an electrical contact  520  that can be soldered or bonded to the high frequency antenna. In a further embodiment, the high frequency antenna is formed on a foldable “ear” section of the flexible circuit board and routed into the “Radome”  513  assembly. 
     In one embodiment, when configured to measure electrocardiographic signals, the “Protectrode”  512  and an exposed, conductive surface  518  of the central body  511  function as an electrode dipole. Other forms of electrode dipoles are possible.  FIG.  29    is an outer perspective view showing the central body  11  of the IMD  500  of  FIG.  1   . The end cap  14  of the “Protectrode”  12  forms one electrode. An exposed, conductive surface  18  of the central body  11  distal to the “Protectrode”  12  forms the other electrode. The metallic case of the power source provides an electrical feedthrough from the “Protectrode”  12  to a flexible circuit board, thereby simplifying construction. 
     “Radome” 
     Informally, the non-electrically conductive semi spherical end cap forms a “Radome” (radar dome)  13  that serves as a housing for a high frequency antenna used for RF data exchange.  FIG.  30    is a side perspective view showing the semi spherical end cap (“Radome”) of the IMD  500  of  FIG.  28   . A high frequency antenna  534  for data exchange is housed within the “Radome”  513 . Note that more than one high frequency antenna could be included. The “Radome”  513  is an assembly that includes an electrically insulated semi sphere  517  formed from a medical implantation-safe grade material, such as acrylic, glass, ruby crystal, or ceramic, and a metallic weld ring  521  formed from a medical grade titanium or similar medical implantation-safe metal. These parts are bonded together using pressure fitting, brazing, laser welding, or electron beam welding. In a further embodiment, the high frequency antenna is defined as part of a flexible circuit board or folded metal shape, folded wire, or other similar structure, as further described infra. 
     “Protectrode” 
     Informally, the electrically conductive semi spherical end cap forms a “Protectrode” (feeder electrode)  512  that serves a dual purpose as an electrode and as housing for patient and device protection components.  FIG.  31    is a side perspective view showing the electrically conductive semi spherical end cap (“Protectrode”) of the IMD  500  of  FIG.  28   . The “Protectrode”  512  is an assembly that includes an electrically conductive semi sphere  514  formed from a medical grade titanium or similar medical implantation-safe conductor, an insulator ring  515  formed from a medical implantation-safe grade material, such as acrylic, glass, ruby crystal, or ceramic, and a metallic weld ring  516 , which can include a chamfered edge  523  to facilitate welding to the central body  511 , formed from a medical grade titanium or similar medical implantation-safe metal. These parts are bonded together with heat fitting, press fitting, brazing, epoxy adhesive, silicon adhesive or other similar bonding agent. 
     The construction details of the “Protectrode”  512  will now be discussed.  FIG.  32    is an inside perspective view showing the interior of the end cap  514  of the “Protectrode”  512  of  FIG.  31   . In one embodiment, a set of concave dimples  526  is formed along an inside shelf surface of the end cap  514 . The dimples  526  increase surface area and thereby facilitate adhesion of the end cap  514  to the insulator ring  515 , they also resist circular rotation.  FIG.  33    is an inside perspective view showing the interior of the end cap  514  of the “Protectrode”  512  of  FIG.  31   . A circumferential groove  525  is longitudinally defined within a cavity  524  inside the end cap  514 . The groove  525  provides a mounting location for a circuit board  527 . The edges of the circuit board  527  are plated with a set of electrically conductive coatings  528  that include, starting from the circuit board  527  and proceeding outward, copper, nickel (thickly applied), palladium (thinly applied), and gold (of medium thickness), although other materials and combinations of layers are possible. The conductive coatings  528  are necessary to ensure against a galvanic reaction between the copper traces of the circuit board  527  and the titanium shell of the end cap  514 . The “Protectrode” may be filled with epoxy or a similar material such as silicon to increase strength and dielectric breakdown properties and provide resistance to corrosion. The filler also will bond with the insulator when the insulator is made out of a brittle material such as ruby, glass or ceramic. The adhesive will hold in place the brittle material should the material fracture during an extreme impact event, such as a car crash. 
       FIG.  34    is an inside perspective view showing the interior of the fully assembled “Protectrode”  512  of  FIG.  31   . The edges of the circuit board  527  contact the “Protectrode”  512  along the groove  525 . The edges of the circuit board  527  contact the “Protectrode”  512  in two places, in the groove  525  along the end cap  514  and in the groove  525  along the metallic weld ring  516  (the groove  525  is formed along only one side of the metallic weld ring  516 , but could be formed along both sides). 
       FIG.  35    is an exploded perspective view showing the components of the “Protectrode” of  FIG.  31   . The circuit board  527  includes a protection circuit  535  for the electrode dipole. The insulator ring  515  electrically isolates these two contact points, thereby allowing the protection circuit  535  to interface with both electrodes, that is, the “Protectrode”  512  and the conductive surface  518 . 
     Flexible Circuit Board 
     The primary electrical structure of the IMD  500  is made out of a single flexible circuit board, which effectively eliminates many inter-circuit board connections and the delicate construction required to create them. 
     Folded Shape 
     The flexible circuit board  530  resembles a piece of origami paper that is folded into final shape, which is expected to increase device longevity and reliability by simplifying the design and eliminate the commonly-encountered failure points found in traditional designs.  FIG.  36    is a top plan view of a flexible circuit board  530  for use in the IMD  500  of  FIG.  28    in a flat, unfolded form. The flexible circuit board  530  is formed out of a single piece of flexible circuit board substrate defining a flexible circuit board  530  for placement of the microcontroller and device circuitry, a pair of vertically disposed foldable “ears”  532  provided on opposite ends of the flexible circuit board  530 , and a foldable (or rollable) area  533  that acts as a receiving coil for inductive power coupling. On one end of the flexible circuit board  530 , a foldable ear  532  connects to a power source and the feedthrough provided by the power source&#39;s case. On the other end of the flexible circuit board  530 , the foldable ear  532  either connects to a high frequency antenna that is a separate component contained within the “Radome”  513  or the foldable ear  532  itself forms the high frequency antenna  523 . The flexible circuit board  530  can include circuit traces on all sides, or multiple layers covered by an insulating layers to maximize space utilization. In one embodiment, the receiving coil&#39;s circuit traces are copper, although other types of conductive materials could be used. 
       FIG.  37    is a three-quarters perspective view of the flexible circuit board  530  of  FIG.  36    in a semi-folded configuration. When placed within the central tubular body, the flexible circuit board  530  forms three aspects  531  of a microcontroller circuit assembly that respectively define a receiving coil  536  for energy capture, a pair of inter-device connecting ears  532 , and a printed circuit board  537  containing a low power microcontroller and device circuitry operable to execute under modular micro program control as specified in firmware. The flexible circuit board  530  can be folded into a triangular shape or horseshoe shape (not shown) and each of the inter-device connecting ears  532  are folded angularly inward towards the triangular ends of the triangular shape  534 . The foldable area  533  is either folded or rolled around the triangular shape of the flexible circuit board  530  and ears  532 . Other shapes may be possible, including other variations on “ears” or extensions to the flexible circuit board  530 . 
     Receiving Coil 
     A power receiving coil  536  is formed by folding (or rolling) the foldable (or rollable) area  533  (shown in  FIG.  36   ) circumferentially about the triangular or horseshoe shape that contains the microcontroller and device circuitry. As further described below, the power receiving coil  536  may be composed of multiple individual receiving coils. The foldable (or rollable) area  533 , however, is longer than the flexible circuit board  530  and is defined, when installed inside the IMD  500 , to extend for substantially the entire longitudinal length of the tubular body  511 . The receiving coil  536  uses planar trace construction to maximize the capture of magnetic flux and provides insulation between the positive and negative electrode poles of the IMD  500 . In further embodiments, signals can be routed from the spherical end caps through the antenna. As well, additional sensors can be implanted in the antennas. 
     In one embodiment, the receiving coil  536  that is used for gathering energy to recharge the power source is connected to a clamping diode array and fusible link. In the presence of extreme electromagnetic environments, the protection diode array will limit the voltage across the antenna protecting the device charging circuitry. If the diode array is overwhelmed for a long enough period of time, the fusible link will open to protect the patient from the effects of device heating due to excessive charging energy received from the receiving coil. The fusible link may optionally be constructed out of a resettable overcurrent device, thermally actuated device, or fusible current limiting device. 
     In a further embodiment, the foldable (or rollable) area  533  is defined to form, when installed inside the IMD  500 , a diagonal antenna that (not shown) will limit dead zones by creating a spiral where the two halves of the receiving coil connect. A standard square-shaped receiving coil could potentially lead to an RF dead zone in certain orientations. The diagonal antenna has a wide track and is overlaid, so that there are two overlapping areas, which should result in efficient flux capture for fields passing through the antenna. 
     In one embodiment, the high frequency antenna, when formed on a foldable ear  532  of the flexible circuit board  530 , can be folded in different ways to create a range of antenna shapes. Note that more than one high frequency antenna could be used. The antenna is completely integrated into the flex circuit, which eliminates feedthrough that also translates into much better energy coupling. 
     In one embodiment, the receiving coil is sandwiched between the central tubular body  511 , which can be a titanium cylindrical enclosure, and the case of the power source, described infra, which can also be a cylindrical titanium battery case. During inductive charging, eddy currents are induced in the titanium battery case. The eddy currents can raise the temperature of the IMD  500  and can reduce charge efficiency. This effect can be countered by reflecting the low frequency charging magnetic field into the low frequency energy receiving antenna with the increase in efficiency resulting in less heating. A ferrite coating or ferrite sheet can be applied to the outside casing of the power source to increase charge transfer efficiency by reflecting energy back into the receiving coil. Since the energy is reflected, less heating of the power source will occur during inductive charging due to decreased eddy currents. 
     Forming the power receiving coil  536  by folding or rolling the flexible circuit board provides several benefits over conventional implantable device design. First, the folding or rolling of the flexible circuit board affords a thin design that facilitates patient comfort by enabling compact packaging, resulting in an smaller device than would otherwise be available in a comparably rechargeable design. Second, the wide aspect ratio of the power receiving coil, when compared with to a traditional wire coil, allows a low loss element, thereby decreasing device heating. Moreover, the low loss element enables quicker charging through higher energy reception without excessive heating. Third, the unique shape enables injectable implantation technique that are not possible with traditional planar coils. Finally, the completely integrated design of the printed circuit board containing the microcontroller and related circuitry and the receiving coil simplifies device design, decreases weight, improves device longevity, and increases patient safety by virtue of requiring fewer parts and no discrete interconnections using, for instance, soldered wires or circuit traces. 
     As mentioned above, the power receiving coil  536  can be formed by multipole individual coils. In particular, the power coil  536  could be the double-helix shaped coil  750  described above with reference to  FIG.  20 - 26 B , with the one or more pairs of overlapping coils  261 A,  261 B making up the coil  750  having a title angle of substantially 45° and each coil  261 A,  261 B in that pair being orthogonal to the other coil  261 A,  261 B in the pair. The coils  261 A,  261 B could be rolled up from a flat state to form the double-helix coil  750  as part of rolling up the circuit board. 
     The power coil  536  could also be formed by other kinds of coils, including single-phase coils, poly-phase coils, single-layer coils, and multi-layer coils. As described further below, all of these coils can be rolled up into a tubular shape suitable for use in the IMD  500 . Poly-phase coil include multiple individual coils that can act as receiving coil for inductive charging. Due to the different positions of the receiving coils in the poly-phase coil, even when the poly-phase coil assumes angular orientations that would other be misaligned with the transmitting coil, at least one of the receiving coils would be in position to efficiently couple with the transmitting coil and receive energy that could be used for powering the circuitry of the IMD  500  (including recharging the power source of the IMD  500 ). Thus, such poly-phase coils can compensate for the misalignment of the transmitting coil (such as the transmitting coil  263 ), facilitating quick recharging of the IMD  500  even in the hands of an inexperienced user. Multi-layered coils have an increased inductive coupling efficiency compared to single-layer coils; both a poly-phase coil and a single-phase coil can be multi-layered. Finally, coils that are both single-phase and single-layered can be useful in recharging an implantable monitor that for some reason cannot be rotated, with the fixed position and simplified structure of the coil allowing to position the transmitting coil (such as the transmission coil  263  or a transmission coil of another shape) in a way that would increase the charging speed. 
     All of the receiving coils in a poly-phase coil are wound up in the same direction (such as clockwise, though other directions are also possible) to avoid magnetic coupling between receiving coils.  FIG.  41    is a diagram showing an unrolled 3-phase coil  701  that is composed of three receiving coils  261  in accordance with one embodiment. The 3-phase coil  701  also includes an interconnect region  702  that is used to connect the coil  701  and provide the current generated by the coil  701  to other parts of the IMD  500  (such as to the clamping diode array and the fusible link) —while in this and several other FIGURES below, some of the terminals on the interconnect region are not shown as connected to the receiving coils  261 , the connections are present and are visible from other views (similarly to what is illustrated in  FIGS.  47 A- 47 B ). The 3-phase coil can be rolled up along the axis  703  shown with dashed lines.  FIGS.  42 A and  42 B  show two views of the 3-phase coil  701  of  FIG.  41    when rolled up in accordance with one embodiment. The dashed arrow  704  shows the magnetic flux vector. The tubular shape of the rolled up coil  701  allows the coil  701  to conveniently fit within the tubular housing of the IMD  500 . Numeral  751  denotes the last trace in the spiral of each coil  701 —following the last trace  751 , there is a layer transition and trace runs towards the interconnect. In the interests of clarity, numeral  751  is shown only with reference to one of the coils  261  on  FIG.  41   , but the same numeral could be used for the same elements on  FIG.  41    and all subsequent FIGURES depicting the receiving coils. 
     Other numbers (both even and odd numbers) of receiving coils  261  in a poly-phase coil are also possible. For example, a poly-phase coil could include four and six receiving coils  261 .  FIG.  43    is a diagrams showing an unrolled 4-phase coil  705  that is composed of four receiving coils  261  in accordance with one embodiment. Similarly to above, the coil  705  includes an interconnect region  702  that is used to connect the coil  705  and provide the current generated by the coil  702  to other parts of the IMD  500  (such as to the clamping diode array). The 4-phase coil  705  can be rolled up along the axis  703  shown with dashed lines.  FIGS.  44 A and  44 B  show two views of the 4-phase coil  705  of  FIG.  42    when rolled up in accordance with one embodiment. The dashed arrow  704  shows the magnetic flux vector. The tubular shape of the rolled up coil  705  allows the coil to conveniently fit within the tubular housing of the IMD  500 . 
       FIG.  45    is a diagrams showing an unrolled 6-phase coil  706  that is composed of six receiving coils  261  in accordance with one embodiment. Similarly to above, the coil  706  includes an interconnect region  702  that is used to connect the coil  706  and provide the current generated by the coil  702  to other parts of the IMD  500  (such as to the clamping diode array). The 6-phase coil  706  can be rolled up along the axis  703  shown with dashed lines.  FIGS.  46 A and  46 B  show two views of the 6-phase coil  706  of  FIG.  44    when rolled up in accordance with one embodiment. The dashed arrow  704  shows the magnetic flux vector. The tubular shape of the rolled up coil  706  allows the coil to conveniently fit within the tubular housing of the IMD  500 . 
     Still other shapes of the unrolled coils that roll-up into a tubular state that can be used inside the IMD  500  are also possible.  FIGS.  47 A- 47 B  show a plurality of unwrapped coils  710 - 718  in accordance with one embodiment.  FIG.  47 A  shows the coils  710 - 718  from one side (“top”) and  FIG.  47 B  shows the coils  710 - 718  from an opposite side (“bottom”) to one shown with reference to  FIG.  47 A . The coils can be rolled up into the tubular shape similar to what is seen with reference to  FIGS.  42 A-B ,  44 A-B, and  46 A-B, and act as the receiving power couple  536 . All of the coils  710 - 718  include interconnect region  702  (numeral marked only on coil  716  in the interest of clarity) and all of the coils  710 - 718  include at least one individual receiver coils  261  (numeral marked only on coil  713  in the interest of clarity). 
     A detailed description of the coils  710 - 718  is given below. In those coils that are described as multi-layered, all of the spiral orientations are in the same direction so that the generated current would not be cancelled out. Coil  711  includes is a single-phase, single layer coil, including only a single coil  261  on a top, and a direct return path to the interconnect  702  on the bottom. Coil  712  includes a coil on top layer and a coil on the bottom layer that are electrically connected through a via. Coil  714  is single-layered and flag-shaped and includes a single coil  261  on top, with a direct return path to the interconnect region  702  on the bottom. Coil  715  is multi-layered and flag-shaped, including a coil  261  on top layer and a coil  261  with the same pattern bottom layer, with the layers being electrically connected. Coil  710  is single-layered and includes three staggered independent coils  261  on top with simple return paths (to the interconnect region  702 ) and is a poly-phase coil, Coil  713  is multi-layered and poly-phase, includes three staggered independent coils  261  on top layer and three independent staggered coils  261  on the bottom layer, each coil  261  in top layer being electrically connected (through vias) to the opposite coil  261  in the bottom layer. Coil  717  is single-layered and poly-phase and includes three independent coils  261  on top with simple return paths (to the interconnect region  702 ). Coil  718  is multi-layered includes three independent coils  261  on top layer and three independent coils  261  on bottom layer, each coil  261  in top layer being electrically connected (through vias) to the opposite coil  261  in the bottom layer. Coil  716  includes two independent coils  261  on top, with simple return paths to the interconnect region  702 . 
     As mentioned above, all of the coils  710 - 718  can be rolled up in a tubular shape.  FIGS.  48  and  49 A -B illustrate the rolling up of the coil  714  of  FIG.  47 A- 47 B .  FIG.  48    is an expanded view of the unrolled coil  715  of  FIGS.  47 A- 47 B .  FIG.  49 A  shows a partially rolled-up coil  715 .  FIG.  49 B  shows fully-rolled up coil  715 . Similarly,  FIGS.  50 - 51    illustrate the rolling up of the coil  710  of  FIG.  47 A- 47 B .  FIG.  50    is an expanded view of the unrolled coil  710  of  FIGS.  47 A- 47 B .  FIG.  51    shows fully-rolled up coil  710 . The line  742  indicates fold geometry. 
     Still other coil shapes that can be rolled up into the tubular shape and used as the power receiving coil  536  are possible.  FIG.  52    a plurality of unwrapped coils  720 - 728  in accordance with one embodiment. All of the coils  720 - 728  include interconnect region  702  (numeral marked only on coil  724 —connections to the interconnect region  702  not shown in  FIG.  52    are visible from the opposite side) and all of the coils  710 - 718  include at least one individual receiver coils  261  (numeral marked only on coil  723 ). Coils  726 - 728  must be double-wrapped when folded into the tubular shape. Coil  726  is single-layered, Coil  728  is multi-layered, and Coil  727  has different wire trace thickness (with the center portion having a thicker wire trace thickness and side portions having thinner wire trace thickness). Coil  720  is single-layered and only includes one individual coil  261 . Coil  721  is multi-layered. Coil  724  is identical to Coil  721 . Coil  725  is single-layered and has a smaller trace width than in other designs shown. Coils  722  and  723  are poly-phase coils, composed of three individual coils  261 . The Coil  722  is double-layered, and the Coil  723  is single-layered. Coils  720 - 725  are only single-wrapped to form the tubular shape. 
     While the above-described coil designs are either double or single-wrapped to create the tubular shape, in a further embodiment, other numbers of wrappings are possible.  FIG.  53    is a diagram showing a two-phase coil  731  that needs to be wrapped around 1.5 times to create the tubular shape. The coil  731  includes two individual receiving coils  261  (with one being a part of the bottom layer that is not shown). 
     One or more of the coils described above with reference to  FIGS.  41 - 53    and the double-helix shaped coil  750  could be combined within a single implantable monitor (such as the monitor  500 ). Further, while the coils that can form the power receiving coil  536  fit the tubular housing of the IMD  500 , in a further embodiment, they could be used in a different kind of implantable physiological monitor. The coils that can form the power receiving coil  536  can be recharged using the transmitting coil  263 , though other shapes of transmission coils are also possible. Further, as described above, the monitor being recharged (including the IMD  500 ) could offload gathered data while the external device  380  that includes both energy transmitting and data download capabilities as described above. 
     Power Source and Charging Circuit 
     A power source that includes an inductively-rechargeable energy cell, battery, or supercapacitor is also placed within the IMD  500  to one end of the flexible circuit board  530  and in electrical contact with the electrically conductive semi spherical end cap  513 , thereby serving as an electrical feedthrough to the flexible circuit board  530 . The power source may be recharged through a charging and conditioning circuit interfaced with the microcontroller using a non-contact method, such as inductive charging, resonant charging, energy harvesting, thermal gradient charging, ultrasonic charging, RF-based charging or charging by ambient or driven motion including vibration. When recharging using inductive coupling, the transmitting circuit  263  can be used, though use of other circuits is also possible. Low frequency charging circuits are most efficient at transmitting energy through solid objects. When a charging circuit operates, vibrations are induced in the coils used in the charger as well as surrounding conductive objects. However, these vibrations, if within the human audible hearing range (or a close multiple thereof) create sound. 
     A traditional charging circuit uses a single frequency to transmit power. If the frequency or a major harmonic thereof is within the audible human hearing range, a single tone that humans can find very annoying could result. To overcome this issue, traditional charging circuits operate above the human audible hearing range. However, instead of using a single frequency for charging, a low frequency charging circuit could also modulate the charging waveform at audible frequencies that result in a pleasant sound for the user, so as to allow the technical benefits of low frequency charging without causing annoyance to humans. 
     Modulation of frequencies requires receive and transmit circuitry with higher bandwidth to accommodate the frequency shifts efficiently. The modulation can cause decreased circuit Q (“quality”), which can be overcome by using a variable capacitor or other automatic tuning circuit to ensure sufficient resonance as the frequency changes. For example, if the frequency changes, tuning may be required to restore satisfactory coupling. The automatic tuner circuit could predict the value needed to achieve resonance or a high Q factor based on the input frequency, or alternatively could employ a feedback system to self-tune as the input frequency changes. The automatic tuner circuit could further be employed to efficaciously control charging to decrease overall charging time. Differences in devices, patients and their environment will modify the Q factor of the system. An automatic turning circuit can automatically compensate for these changes. 
     In a still further embodiment, a feedback circuit or system could be further employed to automatically compensate for changes in the environment and patient load. The feedback circuit would tune charging based on input energy. Alternatively, the feedback circuit method is to know what is coming and instantly auto tune the charging circuitry based on the pattern that will be sent shortly to the IMD  500 . 
     The feedback system could also be used to provide positive feedback to the patient. For instance, the modulation frequency could produce a very “futuristic” sound, such as a low to high frequency ramp, which repeats at a predetermined interval, or could even play a song, perhaps of the patient&#39;s choosing. Further, the modulation frequency could be used to signal to the user the state of the device, such as charging, error condition, or completion of charging. 
     Encasement 
     The power source may optionally be encased in a metallic cylindrical case that also functions as an electrical feedthrough, where the outside of the power source case is used as a conductor to the electrode connection. Conventional IMDs are typically rectangular or prismatic in shape. A cylindrical shape offer several advantages, including patient comfort, power source design, accommodations for different types of antennae, and improved insertability and ease of explant. 
     The actual electrode contact area forms a hollow dome to absorb any swelling that might occur during the extremely unlikely event of a catastrophic power source failure. A set of feedthroughs, arranged in a possible pattern of [+/Temp/−/chassis] is provided to provide increased safety, reduction of leakage currents and ease of assembly. 
     In one embodiment, the power source case is electro polished to improve the ability of the receiving coil  536  to slide over the power source case during installation. In a further embodiment, the head of the power source, that is, the end of the power source that faces outwards away from the flexible circuit board  530  and replaces the “Protectrode” assembly. The head is formed of thin titanium and shaped as a dome to serve as an electrode and provide internal relief for power source expansion if a failure occurs. 
     Chemistry 
     In one embodiment, the power source can use lithium titanate (LTO) technology. Alternatively, other power source or battery technologies such as Lithium Cobalt Oxide, Lithium Manganese Oxide, Lithium Nickel Manganese Cobalt Oxide, Lithium Iron Phosphate, Lithium Nickel Cobalt Aluminum Oxide, Nickel Cadmium or Nickel Meta Hydrate could be employed. 
     To accommodate complete discharge without oxidation of the power source collector, the copper collector typically found in a power source could be replaced by a corrosion resistant metal, such as stainless steel, titanium, gold or platinum. Furthermore, a collector could be made of a standard base metal and plated to increase corrosion resistance. This combination of materials could be copper, nickel, palladium, gold or titanium, gold, or stainless steel, gold or any appropriate combination thereof to provide the necessary degree of corrosion resistance and zero volt life. The surfaces of the materials and platings could be roughened to increase surface area and provide better charge and discharge characteristics. 
     Scalloped Electrodes 
     The proximity of the high frequency antenna  534  to the conductive surface  18  exposed on the outside surface of the tubular body  511  can, in some circumstances, pose a risk of ECG signal degradation.  FIG.  38    is an outer perspective view showing an IMD  560  that houses a configurable hardware platform for physiological monitoring of a living body in accordance with a further embodiment. The electrode  561  formed as part of the “Protectrode” section of the IMD  560  and the electrode  562  formed on the outer surface of the tubular body  511  are shaped with scalloped cutouts on their respective inward facing aspects. The electrode formation minimizes potential parasitic coupling of the electrodes  561  and  562  to ground strips that are used for the high frequency antenna return. In addition, the shape of the “Protectrode” electrode  561  increases the performance and durability of the ceramic to titanium weld joints, when used, to join the “Protectrode”  512  to the tubular body  511 . 
     Microarchitecture 
     The operation of the IMD  500 , including data capture, analysis, and communication, is controlled by a programmable microcontroller.  FIG.  39    is a block diagram showing the microarchitecture  540  of the IMD  500 . The microcontroller is remotely interfaceable over a wireless radio frequency (RF) data communications link using the high frequency antenna  534  that is housed within the “Protectrode”  512 , which enables the IMD  500  to provide continuous heartbeat-by-heartbeat monitoring and to be remotely reconfigured or reprogrammed to utilize one or more of the physiological sensors. 
     Microcontroller 
     In one embodiment, a low power, high efficiency microcontroller  541 , such as a microcontroller from the RL78 family of microcontrollers offered by Renesas Electronics Corp., Tokyo, Japan, can be used. Architecturally, the microcontroller is built around a Harvard architecture that physically separates signal and storage pathways for instructions and data storage. The microcontroller operates under a dedicated microprogram stored as microcode within a non-volatile memory device, rather than a general purpose operating system, which aids in efficient operation and longer power source life, although in a further embodiment, an operating system including a real time operating system, could be used. Note that there is memory located on the microcontroller as well as externally and program instructions are expected to be stored in the microcontroller&#39;s flash memory. 
     Additional Components 
     The microcontroller  541  is interfaced to components, both integrated and off-chip, that provide continuous and extensible monitoring capabilities to the IMD  500 . A voltage regulation/charge control circuit  48  is interfaced to the low frequency resonant charger antenna  547  and the microcontroller  541 , which together regulate and control the charging of the power source  549 . An integrated Bluetooth system-on-a-chip (SoC) transceiver circuit  542  is similarly interfaced to the high frequency antenna  534  and the microcontroller  541  to provide data communications capabilities to the IMD  500 . An electrode dipole is formed by electrodes  545  and  546 , which are interfaced to an analog front end (AFE)  544  and to the microcontroller  541  to effect electrocardiographic monitoring. In one embodiment, temperature, actigraphy, and motion sensing are respectively provided through a temperature sensor  550 , Hall effect switch  551 , and accelerometer  552 . Finally, monitoring data, including continuous ECG data awaiting offloading, are stored in mass storage  553  in the form of random access memory. 
     Paradigm 
     Purpose-build IMDs, such as implantable cardiac monitors (ICMs), are specifically designed to address a range of potential conditions which would be observable over an expected patient population. Thus, typical ICMs require power hungry and complex signal filters, which are able to detect R-wave intervals on a very high percentage of the patient population. Practically, however, the majority of the patient population does not need extreme filtering. As a result, dramatic power savings are possible if a signal filter could be selected that is appropriate for a given patient and for patients with special needs, strong signal filtering can be selected to reduce false positives at the cost of high power consumption and frequent recharging. 
     Here, the IMD  500  implements a configurable hardware platform based on a reprogrammable microcontroller that can be supplemented with additional physiological sensors, including an SpO 2 , sensor, a blood pressure sensor, a temperature sensor, respiratory rate sensor, a glucose sensor, an air flow sensor, and a volumetric pressure sensor, and non-physiological sensors, including an accelerometer and inertial motion sensor. Through the microcontroller  41 , the sensors can be selectively activated over the implantation lifetime, whether in real time or during reprogramming, to tailor the monitoring of the patient to ongoing diagnostic needs. 
     The microcontroller-based design also affords the flexibility to choose signal filtering and processing algorithm options tailored to each patient. This microarchitecture allows the best patient experience by eliminating designs that adopt a one-size-fits-all approach and which are dominated by considerations of accommodating the hardest cases. The microarchitecture further accommodates changes to patient morphology; modifications to the filtering software can be selected dynamically and updated in the field as a configuration update that is pushed by a physician from the “cloud,” that is, the server paradigm that virtualizes server-side functionality as a service widely available through access to the internet or other wide-area data communications network. 
     In a further embodiment, the transceiver  542  can be used in conjunction with the microcontroller to communicate with ingestible sensors, such as offered by Proteus Digital Health, Inc., Redwood City, Calif. Ingestible sensors are pills made of biocompatible materials, which combine remote monitoring microelectronics with medication or inert materials that can safely be taken by a patient. Typically, an ingestible sensor is activated by gastric fluids dissolving or acting upon its surface, after which the sensor begins to measure gastro-intestinal tract physiology and, possibly, other types of physiology. Ingestible sensors that are capable of communicating wirelessly, such as over Bluetooth, Medradio, or via WiFi, are available as a real-time-capable alternative to standalone ingestible sensors that store recorded physiology onboard the device. This wireless-capable class of ingestible sensors allows the sensory data to be captured in real time. Moreover, these types of ingestible sensors aAcan be coupled with the IMD  500 ; thus, a patient can be monitored for medication compliance by providing accurate, time-correlated data that can be used to evaluate non-adherence and to provide positive reinforcement. The patient&#39;s caregiver can be notified in real time as to a patient&#39;s behavior with respect to adhering to prescribed medication. 
     The platform described facilitates the monitoring of every heartbeat in contrast to conventional non-rechargeable platforms, which typically do not have enough power to store and transmit each heartbeat. In addition to monitoring each heartbeat, since the heartbeats are offloaded, the heartbeats may be analyzed by an intelligent algorithm not located in the platform proper, which allows for better recognition of arrhythmias and disease conditions, as the complexity of the algorithm is not limited by the amount of power available to the analyzing device. 
     The IMD  500  continuously monitors the patient&#39;s heart rate on a heartbeat-by-heartbeat basis and physiology.  FIG.  40    is a flow diagram showing a method  600  for continuously monitoring electrocardiography for use in the IMD  500  of  FIG.  28   . Initially, following successful implantation, the microcontroller  541  executes a power up sequence (step  101 ). During the power up sequence, the voltage of the power source  549  is checked, the state of the mass storage (flash memory)  553  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  602 - 614 ) is continually executed by the microcontroller  541 . During each iteration (step  602 ) of the processing loop, the AFE  544 , through the electrode dipole created by electrodes  545  and  546 , continually senses electrocardiographic signals; additionally, patient physiology is sampled at appropriate intervals, depending upon the sampling frequency selected for the particular type of physiology being sensed (step  503 ). One or more types of physiology can be sensed at any given time. The type and sampling rate of physiology are selectively activated over the lifetime of the IMD  500  via the microcontroller through programmatic control, which in turn, determines the hardware device being utilized. For instance, reading patient temperature once each minute would require activation of the temperature sensor  550 . A similar approach to sensing non-physiological data, such as position or posture, is followed mutatis mutandis. 
     A sample of the ECG signal and, at appropriate intervals, physiology, are read (step  604 ) by the microcontroller  61  by sampling the AFE  544  and appropriate physiology sensing hardware. Each sampled ECG signal and each of the physiology signals, in quantized and digitized form, are temporarily staged in a buffer (step  605 ), pending compression preparatory to storage in the mass storage  553  (step  606 ). Following compression, the compressed ECG digitized samples are again buffered (step  607 ), then written to the mass storage  553  (step  608 ) using the communications bus. Processing continues (step  614 ), so long as storage space remains available in the mass storage  553 , after which the processing loop is exited. Still other operations and steps are possible. 
     The IMD  500  processes sensing signals generated by ingestible sensors follow a similar methodology as with processing monitored physiology, with two important distinctions. First, ingestible sensors are typically activated upon ingestion and thereafter generate monitoring data only during the time in which they are present in the patient&#39;s digestive tract. Second, ingestible sensor data is generally time-sensitive, where the correlation of the time of signal generation and time of day is of notable interest in itself, whereas physiological data is typically seen in the context of other physiological events, such as SpO 2 , which is significant with reference to cardiac events. 
     Concurrently, the IMD  500  can offload stored monitoring data to a datacenter or other external device. The data is offloaded in a conceptually-separate execution thread as part of the iterative processing loop (steps  602 - 614 ) continually executed by the microcontroller  541 . If an offloading event occurs (step  609 ), the IMD  500  connects to a mobile device (step  610 ), such as a smart phone or cellular-enabled tablet, and the stored samples are sent from the mass storage  553  to the mobile device (step  511 ). In turn, the mobile device relays the uploaded ECG and physiology samples to the datacenter. Alternatively, the IMD  500  can connect directly to the datacenter, provided the transceiver  542  is sufficiently capable. The mass storage  553  is cleared (step  512 ) and the IMD  500  disconnects from the mobile device (step  513 ) upon completion of the sending of the stored samples. Processing continues (step  514 ). Still other operations and steps 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.