Patent Application
20130035736
The invention generally relates to implantable cardiac stimulation devices such as pacemakers and implantable cardioverter-defibrillators (ICDs) and, in particular, to techniques for controlling paired pacing achieved via postextrasystolic potentiation (PESP).
PESP therapy is a pacing therapy wherein extra stimulation pulses are delivered by a pacemaker or other suitable device during (or sometimes just outside of) a relative myocardial refractory period following paced or intrinsic depolarization. The extra PESP stimulus causes the heart muscle to depolarize a second time but does not cause significant contraction of the muscle. The second depolarization acts on the sarcoplasmic reticulum to release an additional bolus of calcium. It is generally believed that the additional intracellular calcium ions provide for increased contractility. Another consequence of the extra stimulus provided during the relative refractory period is to extend the overall refractory interval, which slows the heart and allows the pacemaker to control the heart rate. During actual delivery of PESP pulses, as with all stimulation pulses, the pacemaker blanks or blocks its sensing channels so as not to misinterpret the electrical stimulus as being an intrinsic electrical signal (i.e. an electrical signal arising from the myocardial tissue.)
Note that, following a paced or intrinsic depolarization, pacemakers typically track a refractory interval that includes both an absolute refractory period and a subsequent relative refractory period. During the absolute refractory period, a second myocardial depolarization cannot be triggered, regardless of the amplitude of extra stimulus, because the myocardial tissue is not susceptible to further electrical stimulus at that time. Hence, PESP pulses are not delivered during the absolute refractory period. During the subsequent relative refractory period, a second depolarization can be triggered with a sufficiently large stimulation pulse but not with a pulse of otherwise normal pulse amplitude. Accordingly, PESP pulses are typically delivered during the relative refractory period (or sometimes just beyond it) using a stimulation pulse of nominal pulse amplitude to trigger depolarization without contraction.
PESP can be implemented in accordance with either “paired pacing” or “coupled pacing” techniques. With paired pacing, the additional PESP pulse is delivered following a paced depolarization. With coupled pacing, the additional stimulation is delivered following an intrinsic depolarization. Paired and coupled pacing techniques are discussed in U.S. Published Patent Application No. 2010/0094371 of Bornzin et al., entitled “Systems and Methods for Paired/Coupled Pacing” and in U.S. patent application Ser. No. 11/929,719, also of Bornzin et al., filed Oct. 30, 2007, entitled “Systems and Methods for Paired/Coupled Pacing and Dynamic Overdrive/Underdrive Pacing.”
PESP may be used to enhance cardiac resynchronization therapy (CRT) by increasing contractility beyond what is typically achieved by merely restoring synchrony. PESP may be used to slow the ventricles during atrial fibrillation (AF) because PESP tends to prolong the refractory interval. That is, the additional depolarization during the relative refractory period caused by the PESP pulse has the effect of extending the overall refractory interval. The longer refractory interval acts to block the conduction of rapid atrial impulses associated with AF. PESP thus can provide for rate control during AF. A secondary benefit may be enhanced contractility for patients with AF and heart failure. Further, PESP may be used to treat patients with low ejection fraction (EF) and narrow QRS heart failure (i.e. a form of heart failure wherein the electrical signals associated with ventricular depolarization (QRS complexes) are shorter than usual.) PESP may be used to treat their cardiac insufficiency. Still further, PESP may be used to treat heart failure with preserved EF. Patients with heart failure with preserved EF can benefit because PESP enhances the rate of relaxation.
Hence, PESP can be particularly useful in patients with poor EF, which might not be corrected by standard CRT or medicinal (Rx) therapy. Possible candidates include: (1) CRT non-responders (which currently represent ˜30% of CRT device patients); (2) patients with narrow QRS (<120 ms) currently not indicated for standard CRT; (3) diastolic heart failure (HF) patients not indicated for device therapy; and (4) AF patients with rapidly conducted heart beats. These and other clinical problems may be helped by the benefits of PESP, which can include: (a) reduce rate to allow for longer filling time; (b) increased EF; and (3) reduced rate during rapidly conducted AF.
One issue to be addressed with PESP is how best to determine the pacing rate for paired pacing. This is important since the paired pacing rate will determine cardiac output (CO). If the device paces too slowly during paired pacing, then overall CO might not meet the physiological demand of the patient due to on-going patient activity. In this regard, if the rate is too low, then even though the PESP-driven stroke volume (SV) might be higher than that of normal sinus rhythm, the CO still might not meet the physiological demands of the patient, particularly during activity that is more strenuous. (For coupled pacing, where PESP pulses are coupled to intrinsic depolarizations, the heart beats at its intrinsic rate and hence the device need not determine a separate PESP rate.) Another issue is that paired pacing, if performed at a rate that is too high, may consume too much oxygen, which can be a problem particularly within heart failure patients. For these and other reasons, at least some patients who are candidates for paired pacing do not currently receive paired pacing.
Accordingly, it would be desirable to provide techniques for addressing these and other concerns and it is to this end that aspects of the invention are generally directed.
In an exemplary embodiment, a method is provided for use with an implantable cardiac stimulation device equipped to deliver paired pacing via PESP. In accordance with an exemplary method, a current activity level of the patient is detected during paired pacing. The cardiac output (CO) level needed to maintain the patient's current activity level is determined during paired pacing with reference, e.g., to pre-stored lookup tables relating activity levels with corresponding minimum necessary CO levels for the particular patient. A minimum or target paired pacing rate sufficient to achieve the CO level is then determined based, e.g., on stroke volume (SV) derived from cardiogenic impedance (also referred to as intra-cardiac impedance). Paired pacing is then delivered at the determined paired pacing rate, thereby assuring that the paired rate is sufficient to meet the current physiological demands of the patient but is not set higher than needed.
In an exemplary embodiment where the implanted device is a pacemaker, ICD or CRT device, the current activity level of the patient is detected during paired pacing using an accelerometer. The accelerometer output value is applied to a pre-stored lookup table that relates accelerometer values to corresponding CO levels for the patient to thereby readout a target CO value, which represents the minimum necessary CO needed to meet the physiological demand within the patient at the current activity level. To determine the paired rate needed to achieve the target CO level, the device estimates the current SV within the patient from a cardiogenic impedance signal (Z(i)) based, for example, on an examination of delta (Z(i)) or area (Z(i)). Once the current SV has been ascertained, the device divides CO by SV to determine the paired pacing rate needed to achieve the target CO level to meet the current physiological demands of the patient. The procedure is repeated as needed to update the paired rate based on changes in activity, stroke volume or other factors. For example, the procedure might be repeated every few cardiac cycles or might be repeated whenever a significant change is detected in activity level, stroke volume or other parameters.
An initial calibration procedure may be performed to determine the relationship between activity level and corresponding cardiac output levels for the particular patient for use in populating the lookup table. The initialization procedure is performed without any on-going paired pacing (or other pacing.) In one example, the intrinsic heart rate of the patient is tracked while parameters representative of cardiogenic impedance (Z) are detected and while patient activity is tracked using an accelerometer. Stroke volume is estimated from cardiogenic impedance, then CO is estimated by multiplying SV by the intrinsic heart rate. The estimated CO is stored in the lookup table along with the corresponding output value (XLS) from the accelerometer to thereby relate CO to activity within the patient at a particular activity level. This procedure is repeated for various activity levels throughout a range of patient activity to thereby populate the lookup table. For example, the patient might be instructed to exercise at each of various activity levels under clinician supervision to thereby generate a set of CO values and corresponding accelerometer output values for populating the lookup table. The initialization/calibration procedure can be performed by the device itself, if so equipped, or by an external system such as a device programmer operated under clinician supervision.
Rather than using a lookup table, other equivalent means for relating cardiac output to patient activity can instead be employed, such as computational devices that use functional equations to relate CO to patient activity. If so, the parameters defining those equations can be ascertained during the initialization procedure based on linear regression or other suitable techniques. Also, it should be understood that whenever cardiogenic/intracardiac impedance is detected, other suitable electrical parameters could instead be employed, such as admittance, conductance or immittance.
System and method implementations are described herein.
Features and advantages of the described implementations can be more readily understood by reference to the following description taken in conjunction with the accompanying drawings.
The following description includes the best mode presently contemplated for practicing the invention. This description is not to be taken in a limiting sense but is made merely to describe general principles of the invention. The scope of the invention should be ascertained with reference to the issued claims. In the description of the invention that follows, like numerals or reference designators will be used to refer to like parts or elements throughout.
The pacer/ICD is programmed using an external programming device 14 under clinician control. Programming commands can specify, for example, the circumstances under which paired pacing should be activated within the patient, the time delay between the pulses of each pair and the amplitudes of the pulses. At other times, the pacer/ICD may be in communication with a beside monitor or other diagnostic device such as a personal advisory module (PAM) that receives and displays data from the pacer/ICD, such as diagnostic data representative of the efficacy of paired pacing. In some embodiments, the bedside monitor is directly networked with a centralized computing system, such as the HouseCall™ system or the Merlin@home/Merlin.Net systems of St. Jude Medical, which can relay diagnostic information to the clinician.
Beginning at step 200 of
At step 208 of
If an external system is performing the calibration procedure of
At step 212, at each of the different activity levels, the system estimates the current SV of the heart of the patient from the changes in cardiogenic impedance detected within in individual heartbeats based, e.g., on delta(Z(i)) or area(Z(i)) or using other suitable techniques. Otherwise conventional techniques may be used to estimate SV from impedance. See, for example, impedance-based techniques discussed in U.S. Published Patent Application 2011/0046691 of Bjorling et al., entitled “Implantable Heart Stimulator determining Left Ventricular Systolic Pressure.”
At step 214, at each of the different activity levels, the system determines the current CO (abbreviated “K”) of the heart of the patient by multiplying the SV estimated at step 212 by the corresponding intrinsic heart rate detected at step 200 to thereby generate a set of values of K as a function of activity (XLS) throughout a range of patient activity levels. For example, for each unique XLS value (XLS(i)), the system calculates: CARDIAC OUTPUT=STROKE VOLUME (SV)×HEART RATE based on the corresponding SV and heart rate to obtain a CO value (K(i)) for each i. The resulting CO values may be regarded as the minimum CO needed by the patient to maintain the corresponding level of activity. As can be appreciated, for a given level of activity, a set of CO values obtained over time at that activity level can be averaged together to provide a more robust estimate of the true CO required by the patient at that particular level of activity.
At step 216, the system then stores the accelerometer values XLS (or, preferably, XLS·SEC, where XLS·SEC represents the accelerometer output signals summed or integrated over time such as over one cardiac cycle) and the corresponding CO values (K(i)) over the range of changing activity levels to thereby quantify the relationship between CO and activity levels within the patient for use during subsequent paired pacing. Within
At step 220, the system can repeat the calibration/initialization procedure to update or replace the values within the lookup table. This may be done periodically (such as every month or two), on-demand (based on clinician control) or automatically in response to detection of an episode of ischemia within the patient (or recovery from ischemia) or in response to other significant changes within the patient, such as progression or regression of heart failure. A variety of techniques may be employed to detect ischemia in the patient. See, for example, U.S. Patent Application 2011/0004111 of Gill et al., entitled “Ischemia Detection using Intra-Cardiac Signals”; U.S. Pat. No. 6,108,577 to Benser, entitled “Method and Apparatus for Detecting Changes in Electrocardiogram Signals;” and U.S. Pat. No. 7,610,086 to Ke et al., entitled “System and Method for Detecting Cardiac Ischemia in Real-Time using a Pattern Classifier Implemented within an Implanted Medical Device.” A variety of techniques may be employed to track heart failure. See, for example, U.S. Pat. No. 7,676,260 to Koh, entitled “Implantable Cardiac Stimulation Device that Monitors Progression and Regression of Heart Disease Responsive to Differences in Averaged Electrograms and Method” and U.S. Pat. No. 7,171,271 to Koh et al., entitled “System and Method for Evaluating Heart Failure using an Implantable Medical Device based on Heart Rate During Patient Activity.”
Hence,
Beginning at step 300 of
At step 302, during paired pacing, the pacer/ICD tracks accelerometer output values (XLS) and cardiogenic/intracardiac impedance values (Z).
At step 310 of
Note that in the example of
Hence,
Although primarily described with respect to examples having a pacer/ICD, other implantable medical devices may be equipped to exploit the techniques described herein, such as standalone CRT devices or CRT-D devices (i.e. a CRT device also equipped to deliver defibrillation shocks.) CRT and related therapies are discussed in, for example, U.S. Pat. No. 6,643,546 to Mathis, et al., entitled “Multi-Electrode Apparatus and Method for Treatment of Congestive Heart Failure”; U.S. Pat. No. 6,628,988 to Kramer, et al., entitled “Apparatus and Method for Reversal of Myocardial Remodeling with Electrical Stimulation”; and U.S. Pat. No. 6,512,952 to Stahmann, et al., entitled “Method and Apparatus for Maintaining Synchronized Pacing”. See, also, U.S. Patent Application No. 2008/0306567 of Park et al., entitled “System and Method for Improving CRT Response and Identifying Potential Non-Responders to CRT Therapy” and U.S. Patent Application No. 2007/0179390 of Schecter, entitled “Global Cardiac Performance.” The techniques described herein may also be applicable to systems equipped for multi-site LV (MSLV) pacing, such as systems using quad-pole leads or the like. See, for example, techniques described in U.S. Patent Application 2011/0022112 of Min, entitled “Systems and Methods for Determining Ventricular Pacing Sites for use with Multi-Pole Leads.”
It should be understood that the “optimal” pacing rates obtained using the techniques described herein are not necessarily absolutely optimal in a given quantifiable or mathematical sense. What constitutes “optimal” depends on the criteria used for judging the resulting performance, which can be subjective in the minds of some clinicians. The paired pacing rates determined by the techniques described herein represent, at least, “preferred” pacing rates. Clinicians may choose to adjust or alter the rates for particular patients, at their discretion.
For the sake of completeness, an exemplary pacer/ICD will now be described, which includes components for performing or controlling the functions and steps already described.
With reference to
To sense left atrial and ventricular cardiac signals and to provide left chamber pacing therapy, pacer/ICD 10 is coupled to a CS lead 524 designed for placement in the “CS region” via the CS os for positioning a distal electrode adjacent to the left ventricle and/or additional electrode(s) adjacent to the left atrium. As used herein, the phrase “CS region” refers to the venous vasculature of the left ventricle, including any portion of the CS, great cardiac vein, left marginal vein, left posterior ventricular vein, middle cardiac vein, and/or small cardiac vein or any other cardiac vein accessible by the CS. Accordingly, an exemplary CS lead 524 is designed to receive atrial and ventricular cardiac signals and to deliver left ventricular pacing therapy using at least a left ventricular (LV) tip electrode 526 and a LV ring electrode 525, left atrial pacing therapy using at least a left atrial (LA) ring electrode 527, and shocking therapy using at least a LA coil electrode 528. With this configuration, biventricular pacing can be performed. Although only three leads are shown in
A simplified block diagram of internal components of pacer/ICD 10 is shown in
At the core of pacer/ICD 10 is a programmable microcontroller 560, which controls the various modes of stimulation therapy. As is well known in the art, the microcontroller 560 (also referred to herein as a control unit) typically includes a microprocessor, or equivalent control circuitry, designed specifically for controlling the delivery of stimulation therapy and may further include RAM or ROM memory, logic and timing circuitry, state machine circuitry, and I/O circuitry. Typically, the microcontroller 560 includes the ability to process or monitor input signals (data) as controlled by a program code stored in a designated block of memory. The details of the design and operation of the microcontroller 560 are not critical to the invention. Rather, any suitable microcontroller 560 may be used that carries out the functions described herein. The use of microprocessor-based control circuits for performing timing and data analysis functions are well known in the art.
As shown in
The microcontroller 560 further includes timing control circuitry (not separately shown) used to control the timing of such stimulation pulses (e.g., pacing rate, AV delay, atrial interconduction (inter-atrial) delay, or ventricular interconduction (V-V) delay, etc.) as well as to keep track of the timing of refractory periods, blanking intervals, noise detection windows, evoked response windows, alert intervals, marker channel timing, etc., which is well known in the art. Switch 574 includes a plurality of switches for connecting the desired electrodes to the appropriate I/O circuits, thereby providing complete electrode programmability. Accordingly, the switch 574, in response to a control signal 580 from the microcontroller 560, determines the polarity of the stimulation pulses (e.g., unipolar, bipolar, combipolar, etc.) by selectively closing the appropriate combination of switches (not shown) as is known in the art.
Atrial sensing circuits 582 and ventricular sensing circuits 584 may also be selectively coupled to the right atrial lead 520, CS lead 524, and the right ventricular lead 530, through the switch 574 for detecting the presence of cardiac activity in each of the four chambers of the heart. Accordingly, the atrial and ventricular sensing circuits 582, 584 may include dedicated sense amplifiers, multiplexed amplifiers or shared amplifiers. The switch 574 determines the “sensing polarity” of the cardiac signal by selectively closing the appropriate switches, as is also known in the art. In this way, the clinician may program the sensing polarity independent of the stimulation polarity. Each sensing circuit 582, 584 preferably employs one or more low power, precision amplifiers with programmable gain and/or automatic gain control, bandpass filtering, and a threshold detection circuit, as known in the art, to selectively sense the cardiac signal of interest. The automatic gain control enables pacer/ICD 10 to deal effectively with the difficult problem of sensing the low amplitude signal characteristics of atrial or ventricular fibrillation. The outputs of the atrial and ventricular sensing circuits 582, 584 are connected to the microcontroller 560 which, in turn, are able to trigger or inhibit the atrial and ventricular pulse generators 570, 572, respectively, in a demand fashion in response to the absence or presence of cardiac activity in the appropriate chambers of the heart.
For arrhythmia detection, pacer/ICD 10 utilizes the atrial and ventricular sensing circuits 582, 584 to sense cardiac signals to determine whether a rhythm is physiologic or pathologic. As used in this section, “sensing” is reserved for the noting of an electrical signal, and “detection” is the processing of these sensed signals and noting the presence of an arrhythmia. The timing intervals between sensed events (e.g., AS, VS, and depolarization signals associated with fibrillation which are sometimes referred to as “F-waves” or “Fib-waves”) are then classified by the microcontroller 560 by comparing them to a predefined rate zone limit (i.e., bradycardia, normal, atrial tachycardia, atrial fibrillation, low rate VT, high rate VT, and fibrillation rate zones) and various other characteristics (e.g., sudden onset, stability, physiologic sensors, and morphology, etc.) in order to determine the type of remedial therapy that is needed (e.g., bradycardia pacing, antitachycardia pacing, cardioversion shocks or defibrillation shocks).
Cardiac signals are also applied to the inputs of an analog-to-digital (A/D) data acquisition system 590. The data acquisition system 590 is configured to acquire intracardiac electrogram signals, convert the raw analog data into a digital signal, and store the digital signals for later processing and/or telemetric transmission to an external device 16. The data acquisition system 590 is coupled to the right atrial lead 520, the CS lead 524, and the right ventricular lead 530 through the switch 574 to sample cardiac signals across any pair of desired electrodes. The microcontroller 560 is further coupled to a memory 594 by a suitable data/address bus 596, wherein the programmable operating parameters used by the microcontroller 560 are stored and modified, as required, in order to customize the operation of pacer/ICD 10 to suit the needs of a particular patient. Such operating parameters define, for example, the amplitude or magnitude, pulse duration, electrode polarity, for both pacing pulses and impedance detection pulses as well as pacing rate, sensitivity, arrhythmia detection criteria, and the amplitude, waveshape and vector of each shocking pulse to be delivered to the patient's heart within each respective tier of therapy. Other pacing parameters include base rate, rest rate and circadian base rate.
Advantageously, the operating parameters of the implantable pacer/ICD 10 may be non-invasively programmed into the memory 594 through a telemetry circuit 600 in telemetric communication with the external device 16, such as a programmer, transtelephonic transceiver or a diagnostic system analyzer. The telemetry circuit 600 is activated by the microcontroller by a control signal 606. The telemetry circuit 600 advantageously allows intracardiac electrograms and status information relating to the operation of pacer/ICD 10 (as contained in the microcontroller 560 or memory 594) to be sent to the external device 16 through an established communication link 604. Pacer/ICD 10 further includes an accelerometer or other physiologic sensor or sensors 608, sometimes referred to as a “rate-responsive” sensor because it is typically used to adjust pacing stimulation rate according to the exercise state of the patient.
However, physiological sensor(s) 608 can be equipped to sense any of a variety of cardiomechanical parameters, such as heart sounds, systemic pressure, etc. As can be appreciated, at least some these sensors may be mounted outside of the housing of the device and, in many cases, will be mounted to the leads of the device. Moreover, the physiological sensor 608 may further be used to detect changes in cardiac output, changes in the physiological condition of the heart, or diurnal changes in activity (e.g., detecting sleep and wake states) and to detect arousal from sleep. Accordingly, the microcontroller 560 responds by adjusting the various pacing parameters (such as rate, AV delay, V-V delay, etc.) at which the atrial and ventricular pulse generators, 570 and 572, generate stimulation pulses. While shown as being included within pacer/ICD 10, it is to be understood that the physiologic sensor 608 may also be external to pacer/ICD 10, yet still be implanted within or carried by the patient. A common type of rate responsive sensor is an activity sensor incorporating an accelerometer or a piezoelectric crystal and/or a 3D-accelerometer capable of determining the posture within a given patient, which is mounted within the housing 540 of pacer/ICD 10. Other types of physiologic sensors are also known, for example, sensors that sense the oxygen content of blood, respiration rate and/or minute ventilation, pH of blood, ventricular gradient, etc.
The pacer/ICD additionally includes a battery 610, which provides operating power to all of the circuits shown in
As further shown in
In the case where pacer/ICD 10 is intended to operate as an implantable cardioverter/defibrillator (ICD) device, it detects the occurrence of an arrhythmia, and automatically applies an appropriate electrical shock therapy to the heart aimed at terminating the detected arrhythmia. To this end, the microcontroller 560 further controls a shocking circuit 616 by way of a control signal 618. The shocking circuit 616 generates shocking pulses of low (up to 0.5 joules), moderate (0.5-10 joules) or high energy (11 to 40 joules or more), as controlled by the microcontroller 560. Such shocking pulses are applied to the heart of the patient through at least two shocking electrodes, and as shown in this embodiment, selected from the left atrial coil electrode 528, the RV coil electrode 536, and/or the SVC coil electrode 538. The housing 540 may act as an active electrode in combination with the RV electrode 536, or as part of a split electrical vector using the SVC coil electrode 538 or the left atrial coil electrode 528 (i.e., using the RV electrode as a common electrode). Cardioversion shocks are generally considered to be of low to moderate energy level (so as to minimize pain felt by the patient), and/or synchronized with an R-wave and/or pertaining to the treatment of tachycardia. Defibrillation shocks are generally of moderate to high energy level (i.e., corresponding to thresholds in the range of 6-40 joules), delivered asynchronously (since R-waves may be too disorganized), and pertaining exclusively to the treatment of fibrillation. Accordingly, the microcontroller 560 is capable of controlling the synchronous or asynchronous delivery of the shocking pulses.
Insofar as PESP pacing is concerned, the microcontroller includes on on-board activity-based PESP controller 601 operative to detect a current activity level of the patient during paired pacing; determine a cardiac output level needed to maintain the current activity level of the patient during paired pacing; and determine a paired pacing rate sufficient to achieve the cardiac output level. To this end, the controller includes an activity level detection/tracking system 603, which may operate in conjunction with accelerometer 608, to assess the current level of activity of the patient. A cardiac output/paired pacing evaluation system 605 determines the cardiac output level needed to maintain the current activity level during paired pacing with reference, for example, to an XLS/cardiac output lookup table 607 (or functional equivalent) within memory 594. A Z-based stroke volume detection system 609 estimates the current SV for the heart of the patient based, for example, on impedance signals measured using circuit 612. An activity-based paired pacing rate determination system 611 determines the paired pacing rate needed to meet the CO level determined by system 605 by, for example, dividing CO by SV to yield a preferred/optimal paired pacing rate. A paired pacing controller 613 controls the delivery of paired pacing via the various pulse generators. Additionally, for the sake of completeness, a coupled pacing controller 615 is also shown.
To initialize or calibrate the data stored in lookup table 607, an on-board activity-based paired pacing calibration/initialization system 617 is provided. Additionally or alternatively, these functions may be performed by an external activity-based paired pacing calibration/initialization system 619, which transmits the lookup table data (or functional equivalents) to the device for storage within device memory. A CRT/MSLV controller 621 is also shown within the microcontroller of the device to control CRT and/or MSLV pacing. For multi-site left ventricular (MSLV) pacing, additional terminals may be required to accommodate additional multi-site stimulation electrodes of a multi-polar LV lead, such as a quad-pole lead.
Any diagnostic data pertinent to PESP pacing can be stored in memory 594 for eventual transmission to an external system. In the event any warnings are needed, such as warnings pertaining to PESP pacing, such warnings can be delivered using an onboard warning device, which may be, e.g., a vibrational device or a “tickle” voltage warning device.
Depending upon the implementation, the various components of the microcontroller may be implemented as separate software modules or the modules may be combined to permit a single module to perform multiple functions. In addition, although shown as being components of the microcontroller, some or all of these components may be implemented separately from the microcontroller, using application specific integrated circuits (ASICs) or the like.
In general, while the invention has been described with reference to particular embodiments, modifications can be made thereto without departing from the scope of the invention. Note also that the term “including” as used herein is intended to be inclusive, i.e. “including but not limited to.”
