On-again, off-again physiologic-demand heart pacing

FIELD OF THE INVENTION

The instant invention is associated generally with the field of acoustic cardiography, and more specifically relates to controlling physiologic-on-demand, feedback-adjusted heartbeat-assist pacing in a heart-pacing therapy-device-equipped patient (such as a pacemaker-equipped patient) specifically through controlling the on-again, off-again heartbeat pacing behavior, or pacing pattern, of such a device. I refer herein to such a practice as physiologic-demand pacing. Those skilled in the art will recognize that this field of acoustic cardiography involves the cooperative, information-integration use of both heart sounds and ECG information processed in different ways to obtain, selectively, various important heart-functionality parameters which correlate to, and help one to understand, the hemodynamic (pumping and filling) behavior(s) of a subject's heart. Such integration characterizes and underpins important aspects of the present invention.

While it will be very evident to those skilled in the art that the methodology of the present invention may be employed successfully in a number of different heart-pacing therapy device manners of operation, a preferred and best-mode approach toward practicing the invention is disclosed herein, for illustration purposes, specifically in the context of biventricular, pacemaker pacing. As will be seen, this implementation of the invention focuses, in the related context of feedback-adjusted heart-therapy pacing, on the development and defining (computer calculation) of what is referred to herein as an acoustic cardiographic (AC) control value (also referred to as a physiologic-demand AC control value, and also as an AC Value). This AC Value “entity”, utilizing computer processing, is determined from (i.e., is based upon) one or more heart-functionality parameter(s) that are especially relevant to the heart pumping and filling functions, and is computed on the basis of key, input, physiologic information, such as heart-sound and ECG information. In this setting, the invention specifically recognizes the special, differential utility, in various circumstances, of several, important heart-functionality parameters as bases for calculating, and then employing, AC Values that are deemed to be the most useful for controlling, in an on-again/off-again sense, and in relation to the mentioned heart pumping and filling functions, the pacing operation of a (heart-therapy-device) pacemaker. These parameters are four in number. They include % LVST, S3, S4 and EMAT.

In certain circumstances, the % LVST parameter may be used as an averaged singularity for AC-Value calculation purposes. In certain other circumstances, an averaged (per parameter) and mathematically combined (both parameter averages), two-parameter combination of the S3 and EMAT parameters may be approach the most relevant for use. Still further instances may be best addressed by using other averaged and mathematically combined combinations of the four, mentioned parameters. Those skilled in the relevant medical arts will understand how to choose AC-Value basing parameters from the detailed description of the invention which is follows shortly. Non-exclusive illustrations of averaging and mathematical combining of heart-functionality parameter values involved in the calculation of AC values are given below.

Definitions

At this point, it will be useful to define certain terms and terminology which appear(s) in the text herein.

S1—The peak-to-peak measurement of the amplitude of the first heart sound (based predominantly on mitral valve closure).

S2—The peak-to-peak measurement of the amplitude of the second heart sound (based predominantly on aortic valve closure).

S3—The strength of the third heart sound based on the intensity and persistence of that sound. Conventionally, acoustic cardiography provides a value for S3 strength in the range of 1 to 10. If this value equals or exceeds 5.0, a conventional algorithm employed herein declares that a third heart sound is present. With relatively normal heart rates, the third heart sound occurs typically about 0.12- to about 0.16-seconds after the second heart sound. The most likely explanation for the production of the third heart sound is that vigorous and excessively rapid filling of blood into a stiff ventricle is suddenly halted, causing audible vibrations. In persons generally older than about 40-years, the third heart sound has been shown to indicate elevated filling pressure and systolic dysfunction. This S3 sound is associated with an abnormal diastolic filling pattern, and almost all persons with pseudonormal, or restrictive, filling patterns exhibit third heart sounds.

S4—The strength of the fourth heart sound based on the intensity and persistence of that sound. Conventionally, acoustic cardiography provides a value for S4 strength in the range of 1 to 10. The fourth heart sound occurs after T-wave onset and before the first heart sound in a cardiac cycle. The S4 sound occurs as blood enters a relatively non-compliant ventricle late in diastole because of atrial contraction, resulting in vibrations of (a) the left ventricular muscle, (b) the mitral valve structure, and (c) the left ventricular blood mass often associated with left ventricular hypertrophy due to the decreased compliance and frequency present in acute myocardial infarction. The presence of the fourth heart sound is always abnormal.

% OLVST—Left ventricular systolic time measured as the time from the mitral component of the first heart sound to the aortic component of the second heart sound. % LVST is computed as LVST divided by the dominant RR interval (the time between two consecutive R waves in an ECG signal). % LVST indicates how much of the cardiac cycle is occupied by systole (pump function) versus diastole (filling). A normal % LVST value lies usually in the range of about 35% to about 45%.

EMT—The electromechanical activation time measured from Q-wave onset (from ECG information) to the time of closure of the mitral valve within the first heart sound. The time value of EMAT reflects the time required for the left ventricle to generate sufficient force to close the mitral valve, and is therefore related to the acceleration of the pressure curve in the left ventricle.

Time for Off State—A user-selected, predetermined time interval which is begun and measured from the beginning of each time that a heart-pacing therapy device enters a sustained On State. It marks a time for switching that device from a sustained On State to an Off State, at least temporarily, in order to make a determination about whether the device should be turned back to the On State to continue applying therapy, or whether a subject's heart behavior at that point in time is such that the device may be left in an Off State for another, user-selected, predetermined, sustained period of time.

Time for On State—A user-selected, predetermined time interval which is begun and measured from the beginning of each time that a heart-pacing therapy device enters a sustained Off State. It marks a time for switching that device from a sustained Off State to an On State, at least temporarily, in order to make a determination, based upon a subject's then actual heart behavior, about whether the device should now remain in a sustained On State to resume therapy, or whether a subject's heart behavior at that point in time is such that the device may be returned to an Off state, or in certain instances, simply held in the existing on off state.

AC Value—While other approaches may be made if desired, an AC Value herein, generally, is a computer-calculated, numeric value based upon simple, common-parameter averaging, and arithmetic combining (adding, subtracting, multiplying, etc. of the respective, common-parameter averages associated with plural, different parameters), of the determined values of user-selected parameters (one or more) drawn from the list of the four, heart-functionality parameters mentioned above, acquired over a user-selected, cardiac-cycle-collection time period, such as a ten-second time period.

As an illustration, if two heart-functionality parameters (as distinguished from a singular, selected-parameter situation), A and B, have been selected to form the basis for a calculated AC Value, the respective A and B values obtained from the plural heart cycles acquired during a given cardiac-cycle-collection time period are individually averaged to produce an average A value and an average B value. These two, average, parameter-specific values are then mathematically combined as desired, for example by addition, subtraction, multiplication, etc., to produce a resulting, usable AC Value. If desired, in such a plural-parameter use situation, weighted mathematical combining may be employed to recognize differential importances relating to the selected heart-functionality parameters.

Actual AC Value—an AC Value which is calculated, in real-time, based upon a selected number of cardiac cycles acquired from a subject during implementation and operation of the methodology of the invention.

Reference AC Value—an AC Value based upon one or more of the four, mentioned, selected heart-functionality parameters, determined from data acquired from a subject at a point in time when that subject's heart appears to be operating in a normal and satisfactory manner. A Reference AC Value may also be drawn from an available database of heart-functionality data derived from a selected population of people having characteristics which are deemed to be similar to those possessed by a particular subject.

BACKGROUND OF THE INVENTION

Cardiac Resynchronization Therapy (CRT) is an effective method to decrease morbidity and mortality, and to increase quality of life in patients having severe and moderate heart failure and mechanical dyssynchrony. The implantation of a biventricular pacemaker as a heart-pacing therapy device in such patients leads to more synchronous, simultaneous contraction patterns of the right and left ventricle, and, assuming good placement of the relevant ventricular pacing lead, and optimized pacemaker settings, to an improvement in systolic performance of the heart. Such an improvement may be measured by improvements in left ventricular ejection fraction, end-diastolic volume, end-systolic volume, and end-diastolic pressure. The practice of assisting heart functionality is, of course, known to be possible through the supportive use of other aiding devices and practices, depending on the underlying root cause, or causes, for severe systolic dysfunction. Illustrations of such other devices and methods include: (a) Left Ventricular Assist Devices (LVAD) for patients with severely failing hearts waiting for heart transplants; (b) Cardiac Contractility Modulation (CCM) with very low systolic strength and no dyssynchrony; and (c) External Counter Pulsation Therapy (ECPT); etc.

At the present time, the duration for which a heart failure therapy is applied to the patient is completely empirical, and is based on a subjective assessment by the attending physician. In the case of CRT, the therapy is enabled and continued 100% after its initiation, independent of whether the therapy will change heart structure or the need for continuous activation. This independence ignores the fact that finer, more precise control over, and knowledge about, the actual time(s) that good heart functionality is made, or is, dependent upon therapy pacing, may frequently offer a much improved, overall heart-behavior condition for a heart-failure subject.

The present invention, as will be seen, avoids these prior-practice “non-independence” conditions and practices effectively by applying objectively controlled, thoughtfully staged, cardio-functionality therapy—and specifically, controlled, pacemaker (heart-pacing device) “duration” therapy—on the basis of certain, selected, key-relevance, carefully assessed cardio-function parameters.

SUMMARY OF THE INVENTION

In general terms, the present invention furnishes a therapy-duration control method involving intentional on-again, off-again, physiologic-demand heart pacing which is associated with at least one of an operationally adjustable (a) implantable, and (b) external, controllable/adjustable heart-pacing device having on and off states (On State, Off State). It is especially aimed at furnishing, through such control, an effective approach toward decreasing morbidity and mortality, and thereby increasing quality of life, in patients having severe and moderate heart failure and mechanical dyssynchrony (important heart-failure issues). The invention methodology leads significantly to control over the operation of a heart-pacing device in a manner which directly leads to more synchronous, simultaneous contraction patterns of the right and left ventricle, thus to result in an improvement in systolic performance of the heart, as reflected strongly by improvements made in left ventricular ejection fraction, in end-diastolic volume, in end-systolic volume, and in end-diastolic pressure.

The method of the invention includes the practice of gathering certain, selected categories of a person's physiologic data, including both ECG and heart acoustic data, which are (a) relevant to that person's heart functionality in the areas of concern expressed above, and (b), suitable for computing and producing an actual, heart-functionality-parameter-based, acoustic, cardiographic therapy-control (AC) value. Based on the gathered data, and using a controlled, feedback-associated combination of On and Off states in a heart-pacing device, the methodology of the invention involves recurrently adjusting the operation of that device, including adjusting the device's specific operational performance (pacing rate, pacing intensity, atrio-ventricular (AV) delay, and inter-ventricular (IV) delay) in the On State, as necessary (i.e., in an on-needed manner as will be explained herein), so as to maintain a minimum difference between such an actual AC Value, and a predetermined, reference AC Value.

In a more specific sense the present invention involves an intentional, staged on/off, physiologic-demand heart-pacing methodology using acquired ECG and heart-sound information for operationally adjusting, and for controlling the on and off states of, an implanted or external heart-pacing therapy device associated with a subject having heart failure, including the steps of: (a) selecting at least one of the heart-functionality parameters % LVST, S3, S4 and EMAT to form a basis for a calculated, acoustic cardiographic therapy (AC) value which is to be employed in relation to such adjusting and controlling; (b) based on the selecting step, establishing a desired, reference, AC Value; (c) monitoring real-time, subject ECG and heart-sound information, and periodically calculating therefrom actual AC values; (d) utilizing various, different comparisons between the actual and reference AC Values, and employing a selected feedback loop approach, controlling both (1) the On-State/Off-State status of the therapy device in a pattern of On-State and Off-State conditions, and (2) the On-State, adjusted operational pacing-rate, pacing intensity, AV delay and/or IV delay behaviors of that device, in an overall manner aimed at both (i) maintaining a minimum difference between the actual and the reference AC Values, and (ii) maximizing Off-State time in the therapy device; and (e), by such utilizing and controlling, effecting a heart-functionality-based, on-demand, therapy relationship between the subject's heart and the therapy device, wherein heart-functionality is maximized, and therapy-based heart functionality control is minimized.

In a somewhat more specific sense with respect to the calculating of an actual AC Value, and in certain, but not all, instances, the computer processing step is performed so as to obtain specifically either the % LVST heart-functionality parameter as a singularity, or the two-parameter, heart-functionality combination of S3 and EMAT as a duality. In other instances, all four of the mentioned heart-functionality parameters are employed, and in still further situations, other parameter combinations of the four, mentioned heart-functionality parameters may be used. From the descriptions of the invention given herein, those skilled in the relevant medical arts will, from observation of a particular person, and from experience, be able readily to choose which parameter or parameters to obtain, process, use for AC-Value calculation, and employ.

The predetermined, reference AC Value may, selectively, be based upon heart-functionality parameter information derived either from (a) a selected population of people, or from (b) previously acquired, subject-specific, heart-functionality information.

The methodology of the invention may further be expressed, in relation to employing the mentioned reference-comparison practice, as intervalically performing the gathering, computer-processing, and defining steps, and thereby intervalically adjusting the respective durations of the mentioned on and off states.

A more thorough understanding of the invention will be obtained by reference to the following detailed description of the preferred and best-mode embodiment of the invention in connection with the accompanying drawings.

DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a graphical, time-based presentation of ECG data, heart sounds, certain heart functions, and aspects of several parameters which are relevant to practice of the present invention.

FIG. 2 is a block/schematic diagram illustrating the overall methodology of the present therapy-duration-control invention. In particular, this figure illustrates an interruptible, operational-adjustment feedback loop which is specifically employed, when not interrupted in accordance with certain steps of the invention to enter a period of time for placing a heart-pacing therapy device in an Off State, for applying adjustments in the operation of the therapy device in accordance with determinations that are made regarding whether such an adjustment is necessary at the current time to improve detected heart functionality, and specifically, heart pumping and filling functionalities.

FIG. 3 is a block/schematic diagram picturing a portion of another feedback loop arrangement which relates partially to a block labeled “Time for Off State” illustrated in FIG. 2, specifically focused upon testing whether a switch of the heart-pacing therapy device from and On State to an Off State for a period of time is appropriate.

FIG. 4 is a block/schematic diagram which is associated with FIG. 3, and which completes an illustration of the mentioned, other feedback loop arrangement, in this case, illustrating whether, with a heart-pacing therapy device “currently” in an Off State, it would be better, or not, at this point in time to switch the therapy device to an On State.

DETAILED DESCRIPTION OF THE INVENTION

The methodology of the present, physiologic-demand pacing invention, while illustrated and specifically described herein in a setting for furnishing therapy-duration control over a biventricular pacemaker, is not limited to that particular heart-therapy device configuration and modality, and, as will be appreciated by those skilled in the art, may be applied to any one of a number of different heart-failure, heart-pacing-device therapies which lead to improvements in systolic performance, i.e., regular dual-chamber pacing, CCM, LVAD, ECPT, etc. This versatile methodology, as will be seen, uses selected physiologic parameter(s), and frequently, though not always, only one parameter (% LVST) in particular, extracted from a computerized analysis of simultaneously acquired electrocardiograms (ECGs or IEGMs) and heart sound recordings, as the (or a) central control parameter(s) relied upon to effect control over the operation of an implanted or external cardiac heart-pacing device. These parameters “operate” effectively, through computer processing, to define, through calculation, what is referred to herein as a physiologic-demand, acoustic cardiographic (AC) control value (the earlier-mentioned AC Value) which control value more directly ( than the specific underlying parameters, per se) applies pacing control to a relevant heart-pacing device, such as a pacemaker. All aspects of the invention are focused on addressing the heart-failure pumping and filling issues specifically referred to above.

Turning now to the drawings, and beginning with FIG. 1, for those who are generally skilled in the relevant art, the content of the time-based graphical display which is presented in this figure is completely familiar, and requires no particular elaboration. As will be observed, this content plainly illustrates the characteristics of the several, particular, different heart-functionality (physiologic) parameters, both electrical and acoustical, which differentially play roles in the AC-Value defining (calculating) practice of the present invention. These parameters, whose respective definitional characteristics which are relevant herein have been set forth above, include S1, S2, S3, S4, % LVST, and EMAT.

Switching attention to FIG. 2, indicated generally at 10 is a block/schematic diagram which illustrates the overall architectural layout, and the key features, of the methodology of the present invention. Methodology 10 is specifically illustrated and described herein in the context of a person—a subject—(not specifically illustrated in the drawings) who has a heart-failure (poor pumping and filling) condition, and who has been equipped with a heart-pacing device in the form of a biventricular pacemaker. Such a device may be either an implanted (internal) device, or an external device, with respect to which the features of the present invention are equally applicable. However, for invention description purposes herein, an assumption is made that such a device is of the implanted, internal category.

Also in connection with the discussion of the invention which is now to unfold, we will assume that the pacemaker which has been implanted in the mentioned subject is initially operating in an On State. More specifically we will assume that the pacemaker is effectively currently operating at the beginning of what is referred to herein as a sustained, On-State operating period whose length has been predetermined by the user, and which State will, as will shortly be explained, be terminated, at least temporarily, to place the pacemaker in an Off State for the purpose of determining whether the pacemaker should be returned to the On State, or left for another user-predetermined span of time during which it will remain in a sustained Off-State condition. The user-predetermined lengths of these mentioned, sustained On-State/Off-State time intervals, as referred to herein, are not critical to an understanding of the invention, are completely user chooseable and changeable as desired, and are programmed into a computer C (shown in FIG. 2, and mentioned more particularly below), in accordance with what appears to the user to be in the best interest of a particular subject. Accordingly, they are not discussed herein in any special detail.

Continuing with a discussion regarding FIG. 2, shown more specifically at 10 are a preferred, and best-mode, embodiment of, and manner of practicing, the methodology of the present invention. As shown in FIG. 2, methodology 10 includes seven blocks 12, 14, 16, 18, 20, 22, 24. These blocks are operatively interconnected by information and/or control communication connections represented by arrow-headed lines 28, 30, 32, 34, 36, 38, 40.

Block 12 represents the mentioned, non-illustrated-subject's heart, and block 14 represents a heart-pacing therapy device in the form, as just suggested above, of a biventricular pacemaker. Pacing pulses are delivered from pacemaker 14 to heart 12 via communication connection 28.

Blocks 16-24, inclusive, represent both structure and methodology which is implemented in an appropriately, and conventionally, algorithmically programmed digital computer (mentioned briefly above). Thus these five blocks may be understood in FIG. 2 to represent directly such a computer, and a bracket C appearing adjacent the right side of FIG. 2 represents such a computer. This same bracket may also be viewed herein as encompassing, and in part representing, an optional modification of the invention which involves the user-elective presence of a particular kind of operative association between pacemaker 14 and the mentioned computer, whereby specific information relating to certain operational parameters of the pacemaker, such as the above-mentioned pacing rate, pacing intensity, atrio-ventricular (AV) delay time, and inter-ventricular (IV) delay time operational parameters, may be fed back to the computer to indicate their respective statuses, and further to offer augmented utility in the practice of the invention.

Algorithmic programming in computer C, which programming includes, as will be seen, an architecture that is suitable for implementing all of the still-to-be-described, (a) timing-control, (b) pacing-device control, and (c) value-calculation tasks, as well as any other computational tasks that may be desired, may be structured in various different, entirely conventional ways that are all well within the skills and knowledge possessed by those generally skilled in such programming arts. This condition of readily understandable programming suited to the practice of the present invention is especially is made clear in the contexts of the teachings of the drawings presented herein, and of the operational description of the invention set forth below. Accordingly, programming details, and details of related algorithmic architecture associated with, and installed in, computer C, which details form no part of the present invention, are not elaborated herein.

Received in block 16, as delivered via communication connection 30, are ECG and heart-sound categories of information (heart-functionality information) that are acquired in conventional fashions from heart 12. One should note here that the present invention is not concerned with any specific manner or manners in which such heart-functionality information is acquired, and, accordingly, no specific details of such acquisition are set forth herein. Suffice it to say that each “event” of gathering such information takes place over a user-selectable, pre-determined, and pre-computer-programmed interval of time—the previously mentioned, illustrative cardiac-cycle-collection time period of ten-seconds—which is sufficient to permit the capture of heart data from a suitable plurality of real-time, i.e., current, cardiac cycles. For the purpose only for illustration herein, an assumption is made that ten cardiac cycles are acquired during each cardiac-cycle-collection time period of ten-seconds.

Block 16, which is labeled “Monitor and Calculate Actual AC Value”, receives and processes this ECG and heart-sound received information to calculate and identify per-cardiac-cycle values for whichever one or ones of the four, above-identified, heart-functionality parameters has been chosen by a user to be employed in the practice of this invention for effecting pacing control over the operation of pacemaker 14. For the purpose of ongoing description of the invention methodology herein, and just for single-illustration purposes, we will further assume that the parameter % LVST has been chosen as a singularity to form the basis for pacemaker-operation control, and in accordance with the invention, and within block 16, a computer calculation is thus performed to acquire an actual AC Value through a process of simple averaging of the several collected and calculated % LVST values drawn from each of the “collected” ten-cardiac-cycle streams of heart-behavior data. This calculated, actual AC Value is supplied to block 20 (labeled “Compare”) via communication connection 32.

In block 20, a comparison takes place between the just-mentioned, calculated, actual AC Value and a reference AC Value which is furnished to block 20 via communication connection 34 from block 18, wherein an appropriate location in the memory of the mentioned computer has previously stored such a reference value. The definition of reference AC Value has been provided earlier herein, and for the purpose of ongoing description of the methodology of the invention, we will assume that this reference value has been based upon previously acquired, real-time heart-functionality data derived directly from the subject, per se, during a prior span of time when medical personnel have determined that the subject's heart is performing in normal and satisfactory pumping and filling manners. This reference AC Value takes the form of a calculated, appropriately simply averaged value drawn from the collection of % LVST values acquired during a plurality (which may be ten, or more) of cardiac cycles that occurred during such a normal heart-operating period of time.

From the comparison which is produced in block 20, any difference which is detected between the actual AC Value, as calculated, and the stored, reference AC Value, is noted and supplied to block 22 via communication connection 36.

We will further assume, at this point in the description of the operation of the methodology of the present invention, that block 22, which is, at least partially, a “question-asking” block labeled “Time for Off State?” is in a condition noting that it is not yet time to interrupt the currently active, sustained, pacemaker On State, and thus develops the answer “No” to this question. This “developed” answer effectively creates a through-block-22 connection to previously mentioned communication connection 38, which supplies any such compared AC-Value difference information coming from block 20 directly to block 24 (“Adjust Pacemaker Operation”).

At this point in the invention description, and staying for a moment with block 22 before discussing the behavior of block 24, one should note the existence of a relevant, additional, arrow-headed communication connection 42 which appears fragmentarily in FIG. 2, and which extends and points downwardly from block 22. More will be said in detail about connection 42 shortly, but at this stage, it is sufficient to say that connection 42 represents that the answer to the “timing question” posed in block 22 is “Yes”. As will soon be elaborated, connection 42 extends to the block-schematic arrangement pictured in FIG. 3.

The AC-Value difference information which is passed by way of connection 38 to block 24 causes block 24 to send, by way of communication connection 40, to pacemaker 14 a control signal, or signals, which effect(s) an operational adjustment, or adjustments, as necessary, to re-form the pacing operation of the pacemaker so as to stimulate heart 12 in a manner intended to minimize the difference between a calculated, current, during-pacing-therapy, actual AC Value and the reference AC Value. This adjustment, of course, is aimed at furnishing therapy deemed most appropriate to improving the pumping and filling behaviors of heart 12. The preferred adjustments take the form of specific adjustments made in one or more of the pacing rate, the pacing intensity, the AV delay, and the IV delay operational behavior(s) of the pacemaker. Throughout the sustained On-State operating time of the pacemaker, recurrent heart-functionality monitoring, and calculating of actual AC Values, take place, followed by respective comparison activities in block 20, as explained, thereby to produce operational control adjustments as needed which are delivered by block 24 to the pacemaker in a continual feedback effort to maintain, as closely as possible, an equality of actual and reference AC Values. The frequency of recurrent monitoring and of associated actual AC Value calculations is a matter of user choice, and is programmed appropriately into computer C.

What can thus be seen is that the arrangement pictured in FIG. 2 takes the form of a pacemaker operational-adjustment (pacing rate, pacing intensity, AV delay, and IV delay) feedback loop for pacemaker 14. More particularly, it possesses the form of such a feedback loop which, on a user-selected time basis, is interruptible under the influence of block 22, as will now be explained.

Accordingly, turning attention to FIG. 3, when block 22 in FIG. 2 determines that the time (the end of the current, sustained (full-term) On-State operating condition for the pacemaker) has arrived to place pacemaker 14, at least temporarily, in an Off State, it breaks the previously existing operational-adjustment feedback loop pictured in FIG. 2, and sends a “timing associated” signal over connection 42 to an input block 44 in FIG. 3. Thus, with respect to the resulting state of the feedback loop pictured in FIG. 2, and during the time period which is about to occur wherein the pacemaker will be switched, as just mentioned temporarily at least, into an Off State, no operational-control signaling is supplied over connection 38 to pacemaker 14.

Pictured in FIG. 3, in addition to just-mentioned block 44, are seven additional blocks numbered 46, 48, 50, 52, 54, 56, 58. Associated with these blocks in FIG. 3, and for the most part establishing communication/control connections between and or from these blocks, and illustrated by arrow-headed lines, are connections 60, 62, 64, 66, 68, 70, 72, 74, 76, 78. One will also observe, by looking at both FIG. 2 and FIG. 3, that previously mentioned connection 30 which, in FIG. 2 interconnects blocks 12, 16, also interconnects block 12 in FIG. 2 and block 46 in FIG. 3.

When the just-above-mentioned “timing” signal arrives at block 44 over connection 42 from block 22, indicating that it is now time to place pacemaker 14 in an Off State, this action is performed by block 44, which then sends a signal via connection 60 to block 46—a block which is essentially the same in structure and functionality (within computer C) as previously described block 16 shown in FIG. 2. Accordingly, block 46, as was true with block 16, receives over connection 30, from a ten-cycle plurality of heart-cycles, heart-functionality ECG and heart-the sound information with respect to which it then calculates a current, Off-State actual AC Value. This Value is transmitted by connection 62 to comparison block 50 which performs in the same manner described earlier for block 20 seen in FIG. 2.

Block 48, “operating” from, and functioning as, memory within computer C, presents to block 50, via connection 64, the last-calculated, actual, On-State AC Value. In accordance with the operation of block 50, any difference which exists between these two compared AC Values is supplied via connection 66 to block 52 which is an inquiry block that asks the question about whether or not, based on the difference information (if any) now presented on connection 66, the actual AC Value now appearing on connection 62 is better than the last-calculated, actual AC Value presented by connection 64 from block 48 to block 50.

If the answer to this question is “No”, block 52 supplies over connection 68 to block 54 such an indication which then causes block 54 (a) to return (i.e., switch) pacemaker 14 to the On State, and (b) to send a signal via connection 70 to block 16 in FIG. 2 to resume operation as described earlier with regard to this figure. This “No” indication produced by block 52 thereby effectively returns the pacemaker to the beginning of another, full-length, sustained On-State operating period, whereby all of the activity previously described as being carried on in the arrangement pictured in FIG. 2 resumes as before described.

If the answer to the question asked by block 52 is “Yes”, then block 52 sends to block 56, by way of connection 72, a signal which effectively causes pacemaker 14 to be held now in, and for, the full duration of the earlier-mentioned, predetermined, sustained Off-State time period. Placement of the pacemaker in this sustained Off State is noted over connection 74 by inquiry block 58 in FIG. 3, which block asks the question regarding whether it is yet time (i.e. at the end of the current Off State condition in the pacemaker) to return the pacemaker, at least temporarily, to the On State. So long as the intended, current, sustained Off-State period for pacemaker 14 is “under way”, block 58 generates a “No” answer which is supplied via communication connection 76 to block 56 in a manner which effectively causes pacemaker 14 confirmedly to be held in the Off State.

When block 58 determines that the end of the sustained Off State for pacemaker 14 has arrived, this block generates a “Yes” answer which is communicated, as will now shortly be described, by way of communication connection 78 to a block 80 which is included in the block/schematic arrangement pictured in FIG. 4.

What can thus be seen with respect to the on/off staging and pacing operation which has just been described respecting the behavior of the arrangement shown in FIG. 3, following the activities described in relation to FIG. 2, is that, after the conclusion of a sustained On-State period of operation for pacemaker 14 (FIG. 2 condition), a determination is made regarding the normalcy and acceptability of a subject's pumping and filling heart behaviors, thus to assess whether or not full-term pacing therapy should be resumed, or whether it is now time to switch the pacemaker into an Off State to allow the subject's heart to function without therapy assistance. This decision is based upon the comparison which is made in block 50, and is very specifically based upon an assessment, through looking at comparative actual AC Values, whether to resume immediately pacemaker pacing support, or to allow the heart to continue to function without pacing support for the user-preselected nominal, sustained, full-term operating time for a pacemaker Off State. Where an Off State appears to be the appropriate methodology behavior at this point in time, a predetermined-length (full-term) Off State condition begins. When this period begins, and as will now be more fully described, the operation of the invention methodology is then placed under the control of what is pictured in FIG. 4.

Focusing attention now on FIG. 4, included in this figure, in addition to previously briefly mentioned block 80, are six additional blocks numbered 82, 84, 86, 88, 90, 92. Variously interconnecting, and extending from, the seven blocks seen in FIG. 4 are communication connections 94, 96, 98, 100, 102, 104, 106. Also connecting as shown to blocks 80, 82, 88, and 82, are previously mentioned connections 78, 30, 70, 78, respectively.

When a signal is sent via connection 78 from block 58 in FIG. 3 to block 80 in FIG. 4, this signal indicates that it is time, at least temporarily, to place pacemaker 14 in an On State. Accordingly, this signal causes block 80 to turn pacemaker 14 back to an On-State condition wherein it furnishes therapy to heart 12.

Further, following receipt of the mentioned signal over connection 78, block 80 communicates to block 82, via connection 94, that there should now take place the same monitoring and calculating activities which have previously been described as being performed in blocks 16, 46. Accordingly, block 82 (which is like blocks 16, 30), receives full “information-collection cycle” ECG and heart-sound information over connection 30 from heart 12, and calculates a new On-State actual AC Value which is then supplied via connection 96 to comparison block 86. This newly calculated actual AC Value which is, now, at least temporarily, based upon pacemaker therapy being provided to the subject's heart, is compared in block 86 with a computer stored value in block 84 of the last-calculated Off-State actual AC Value, the latter being communicated via connection 98 to block 86. What is thus now occurring in block 86 is a comparison to determine whether the last calculated actual AC Value acquired during the just-terminated Off State in the pacemaker is different from the newly calculated actual AC Value based upon switching back on of the pacemaker in accordance with the operation of block 80. Any difference in these two values noted through comparison in block 86 is supplied by connection 100 to question-posing block 88 which asks the question whether the newly calculated actual AC Value in the On State of the pacemaker is better than the last-calculated Off-State AC Value stored in block 84.

If the answer to this question is “Yes”, block 88 communicates this answer effectively via previously mentioned communication connection 70 to block 16 in FIG. 2 to place the pacemaker effectively in the same operating condition, i.e., at the beginning of a full-term, sustained On-State mode of operation, as was initially described with respect to the operation of the methodology steps pictured in FIG. 2. However, if the answer to the question posed by block 88 is “No”, this condition is communicated via connection 102 to block 90 which, at this point in time, switches and returns pacemaker 14 to the Off State to begin another full-term, sustained Off-State operating period for the pacemaker.

This condition is now communicated by way of communication connection 104 to block 92 which is a question-asking block, and which specifically asks the question whether it is yet time to conclude the sustained Off-State condition in the pacemaker, and return the pacemaker, at least temporarily, to the On-State condition. If the answer to this question is “No”, communication between blocks 92, 90 by way of connection 106 functions to maintain pacemaker 14 in the Off State. If the answer to the question is “Yes”, then this condition is communicated via connection 78 to just previously discussed block 80 appearing at the left side in FIG. 4 to begin a next “cycle” of operation in, and as described for, FIG. 4.

What one can thus see about the operation of the methodology portion of the invention which is illustrated in FIG. 4 is that a kind of feedback loop exists which possesses the tendency to maintain the pacemaker in an Off-State condition for as many of its pre-planned, full-term, sustained off-period intervals as possible—returning the pacemaker to an On-State condition only when comparison activity which takes place in block 86 indicates that an actual AC Value associated with the Off State of the pacemaker is poorer than the last-noted On-State actual AC Value.

The present invention thus proposes a unique physiologic-on-demand, heart-pacing-device operation, wherein there is a very clear propensity to invoke minimal-time operation of such a device.

Accordingly, one way of expressing the invention is to describe it as being a physiologic-demand method using acquired ECG and heart-sound information for operationally adjusting, and for controlling the on and off states of, an implanted or external heart-pacing therapy device associated with a subject having heart failure, this method including the steps of: (a) selecting at least one of the heart-functionality parameters % LVST, S3, S4 and EMAT to form a basis for a calculated, acoustic cardiographic therapy (AC) value which is to be employed in relation to the desired adjusting and controlling; (b) based on such selecting, establishing a desired, reference, AC value; (c) monitoring real-time, subject ECG and heart-sound information, and periodically calculating therefrom actual AC values; (d) utilizing various, different comparisons between the actual and reference AC values, and employing a selected feedback loop approach, controlling both the on-state/off-state status of the therapy device, and the on state, adjusted operational behavior of that device, in an overall manner aimed at both (1) maintaining a minimum difference between the actual and the reference AC values, and (2) maximizing off-state time in the therapy device; and (e), by such utilizing and controlling steps, effecting a heart-functionality-based, on-demand, therapy relationship between the subject's heart and the therapy device, wherein therapy-based heart-functionality control is minimized.

The methodology of the invention may, in the context just expressed above, more specifically be described as one wherein the above-mentioned feedback loop approach includes implementing an interruptible, operational-adjustment feedback loop, and the controlling activity includes (a) on a selected time basis periodically interrupting that loop, (b) during each such interruption, and beginning therein with the therapy device in a controlled off-state, periodically checking actual AC values in both on and off states of the therapy device so as effectively and preferentially to maintain that device in an off state until an off-state actual AC value is found by comparison to be poorer in relation to the reference AC value than the actual AC value in the on state, and then returning the therapy device to the on state, and (c), thereafter returning to the implementing step, and recurrently repeating these just (in this paragraph) mentioned (a), (b) and (c) steps.

If desired, the so far described practice of the invention may be modified by introducing information feedback, as suggested earlier herein, from pacemaker 14 to computer C so as to effect relational changes in the manner in which the operational feed back loop shown in FIG. 2 functions. Preferred feedback information, in the context of the operation of the FIG. 2 loop, is designed (conventionally) to affect at least one of pacing rate, pacing intensity, AV delay, and IV delay.

Preferably, although not necessarily, all structure, firmware and software which are relevant to the practice of the invention, including a programmable digital computer with an appropriate memory, and all operational algorithmic software, are effectively “onboard” and installed as “component parts/aspects” of the heart-pacing device which is employed.

Thus, an on-again, off-again, physiologic-demand, therapy-device-management methodology for heart pacing has been disclosed—a methodology possessing a key focus on minimizing the On-State time of an internal or external, heart-pacing therapy device. Accordingly, while a preferred and best-mode embodiment of, and manner of practicing, the invention have been illustrated and described herein, it is appreciated that further variations and modifications thereof may be made within the scope of the invention as defined in the appended claims.

On-again, off-again physiologic-demand heart pacing

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