CARDIAC OUTPUT ENHANCED PACEMAKER

Abstract: This invention is an apparatus for heart pacing with cardiac output modification, including one or more electrodes (27, 29) which apply electrical signals to muscle. Signal generation circuitry (26) applies an excitatory electrical pulse to at least one of the one or more electrodes to pace the heart and a non-excitatory stimulation pulse to at least one of the one or more electrodes to modify the cardiac output. Preferably the circuitry synchronizes the non-excitatory stimulation pulse with the pacing pulse.

Description: CARDIAC OUTPUT ENHANCED PACEMAKER FIELD OF TH E INVENTION The present invention relates generally to cardiac therapeutic devices, and specifically to cardiac pacemakers. BACKGROUND OF THE INVENTION The heart is a muscular pump whose mechanical activation is controlled by electrical stimulation generated at the right atrium and passed to the entire heart In a normal heart the electrical stimulation originates as action potentials in a group of pacemaker cells lying in a sino-atrial (SA) node in the right atrium In certain heart diseases, either congenital or acquired, natural pacing is replaced or assisted by artificial pacing induced by an implanted pacemaker. Pacemakers known in the art provide artificial excitatory pulses to the heart tissue, to control the heart rhythm. Cardiac output, i.e , the output of the heart per unit time, is the product of stroke volume and heart rate. Hence, variations in cardiac output can be produced by changes in cardiac rate or stroke volume. The stroke volume can be influenced, for example, by changing the efficacy of cardiac contraction, by changing the length of the cardiac muscle fibers, and by changing contractility of cardiac muscle independent of fiber length The heart rate and rhythm influence the cardiac output both directly and indirectly, since changes in the rate and rhythm also affect myocardial contractility The human body normally regulates the cardiac output in response to physiological needs, mainly by changing the heart rate, as during physical exercise, and/or by adapting the stroke volume. Under pathological condition-,, however, some of the regulatory mechanisms may be damaged. Artificially paced hearts typically lose more than 30% of their normal cardiac output, presumably due to loss of efficient contraction under artificial, as opposed to natural, electrical stimulation. In the context of the present patent application, this reduction is referred to as pacing-induced cardiac output (PICO) loss Moreover, when pacing is indicated, it is frequently in the wake of heart disease, particularly ischemic heart disease (IHD), including cases of myocardial infarction (MI), which in itself reduces the cardiac output. Such reduction is referred to in the context of the present patent application as global cardiac output (GCO) loss While electronic pacemakers can inciease caidiac output temporarily by increasing the heart rate, this increase is at the expense of gieatei eneigv expenditure by the heart muscle, which the heart disease patient cannot generally sustain Although modem pacemakers may include stimulation at two oi moie points and allow optimization of the excitatory pulse amplitudes, rate and timing, they do not address dnectly the loss of cardiac output caused by the pacing, nor do they address the loss due to cardiac pathology These losses are mainly related to reduction in the stroke volume, which caidiac pacing tends to exacerbate Defibrillators are useful in treating arrhythmia when it occui s (although they are painful to the patient and traumatic to the heart), but they piovide no long-term amelioration of cardiac insufficiency Thus, none of the tieatments known in the ait allow effective, long-term regulation of cardiac output, because they aie aimed at controlling the heart rate and do not address the need to increase the stioke volume and the efficiency of contraction of the heart The electiomechanical properties of the heart, as well as methods known in the art for influencing these pioperties, aie moi e fully descπbed in the ''Backgiound of the Invention" section of PCT patent application PCT/IL97/00012, which is assigned to the assignee of the present patent application, and whose disclosui e is incoi oi ted hei em by l eference SUMMARY OF T HE INVENTION The inventors have found that by applying non-excitatoiy electπcal stimulation pulses to cardiac muscle segments, appiopi lately timed w ith lespect to the heart's electπcal activation, it is possible to regulate the caidiac output It is therefoie an object of the piesent invention to piovide devices that allow both artificial heart pacing and effectiv e l egulation of ai dia * . output, and pai ticulai ly devices that increase the cardiac output by enhancing the heart's stioke volume The present invention thus piovides appaiatus foi heart pacing with cardiac output regulation, including one oi moi e implantable electrodes, which apply electrical signals to cardiac muscle segments, and signal genei tion cii cuitiy, which applies an excitatory electrical pulse to at least one of the one oi moi e electi odes to pace the heart and a non-excitatory stimulation pulse to at least one of the one oi moie electiodes to regulate the cardiac output Another aspect of the pi esent invention i claics to method for heart pacing with cardiac output enhancement, including implanting one oi moi e electiodes in a subject's heart, applying an excitatory electrical pulse to at least one of the one oi moie electrodes to pace the heart; and applying a non-excitatory stimulation pulse to at least one of the one or more electrodes to regulate an efficacy of cardiac contraction. The term "non-excitatory electrical stimulation," in the context of the present patent application and in the claims, refers to electrical pulses that do not induce new activation potentials to propagate in cardiac muscle cells. Rather, such pulses affect the response of the heart muscle to the action potentials, by modulating cell contractility within selected segments of the cardiac muscle. Specifically, as described in the above-mentioned PCT patent application PCT/IL97/00012 and incorporated herein by reference, the inventors have found that by applying non-excitatory electrical stimulation pulses of suitable strength, appropriately timed with respect to the heart's electrical activation, the contraction of the selected segments can be increased or decreased, thus increasing or decreasing the stroke volume of the heart. This finding forms the basis for the present invention. According to preferred embodiments of the present invention, the non-excitatory stimulation pulse is coupled to the activity of a pacemaker, and in various embodiments, the non-excitatory stimulation pulse is synchronized by pacing pulses generated by the pacemaker. In other embodiments of the present invention, one or more sensors are provided in the apparatus to sense local activity in the heart tissue, to enable the non-excitatory stimulation pulse to be triggered independently of the pacemaker, particularly when the pacemaker is inactive for a period of time, as is know n in the an, for example, with regard to VVI and DDD pacemakers. In preferred embodiments of the present invention, a cardiac output enhanced pacemaker (COEP) comprises a pacing unit and a non-excitatory stimulation unit. The pacing unit provides pacing pulses to the heart muscle for controlling the heart rate, as is known in the art. The non-excitatory stimulation unit provides stimulation pulses to at least a segment of the heart muscle, synchronized with the pacing pulses, so as to enhance the response of the muscle to the pacing pulses, preferably to increase the heart's stroke volume. Each of the two units comprises one or more electrodes to be implanted in a subject's heart and signal generation circuitry coupled thereto. The circuitry is preferably encased in an implantable case, similar to those used in pacemakers known in the art, and preferably uses a similar type of battery as a power source. Thus, in preferred embodiments of the pi esent invention, the COEP device applies both excitatory electrical stimulation, to pace the heart by generating activation potentials in the cardiac muscle tissue, and non-excitatory stimulation, to control the response of the muscle to the activation potentials In this l espect, the device differs fundamentally from pacemakers and other implantable cardiac electronic devices known in the art, which provide only excitatory stimulation When the COEP is used to pace the heart, the activation of the heart with respect to the pacing is substantially the same as it would be if an ordinary pacemaker were used. By applying non-excitatory stimulation to the heart, however, the COEP allows cardiac output to be regulated to demand by controlling the stroke volume, as well as the heart rate. It is preferably used to compensate for the loss of cardiac output that commonly results from the pacing, and may also be used to treat problems of low cardiac output due to other cardiac pathologies Preferably, the COEP device can be controlled to apply both excitatory and non- excitatory stimulation together, or to apply either excitatory or non-excitatory stimulation alone, depending on the therapeutic needs and condition of the patient Thus, for example, the excitatory stimulation could be applied at substantially all hours of the day and night, while the non-excitatory stimulation is applied only during daytime hours, when the patient needs a boost in cardiac output, or at any other desired limes Parameters of the excitatory and non- excitatory stimulation are preferably adjusted together, so as to cooperatively achieve a desired therapeutic effect Although in describing some aspects of the present invention, the pacing and non- excitatory stimulation units are, for clarity of explanation, referred to as separate entities, in some preferred embodiments of the present invention, these units are implemented using a common, preferably integrated, electronic circuiti \ Similarly , in some preferred embodiments of the present invention, the same electrodes may be used to apply both the pacing and non- excitatory stimulation pulses Furthermore, while preferred embodiments of the present invention are described herein with reference to the COEP device, certain aspects of the present invention may be accomplished by suitably modifying and/or leprogramming an existing pacemaker, so as to apply non-excitatory stimulation pulses in addition to the pacing pulses that the pacemaker normally generates It will be appi eciated that such embodiments and modifications fall within the scope of the pi esent invention In some preferred embodiments of the present invention the pacing unit comprises multiple pacing electrodes to allow for pacing optimization, as is known in the art More generally, it will be understood that the pi inciples of the present invention may be applied to produce COEP devices that apply non-excitatory stimulation to achieve cardiac output regulation in conjunction with any suitable mode of pacing, including adaptive and rate- responsive pacing modes known in the art In preferred embodiments of the present invention, the non-excitatoty stimulation unit comprises electrodes having a relatively large contact area with the heart, preferably at least 5 mm2, more preferably at least 1 cm-, most preferably at least 4 cm-, and preferably comprising carbon or another conductive material Alternatively or additionally, the non-excitatory stimulation unit may comprise a plurality of stimulation electrodes, preferably a stimulation net, comprising a plurality of interconnected, addressable electrodes, covering a substantial heart segment, such that the size of the segment of the heart to which a non-excitatory signal is applied may be modulated Considerations relating to the design of the electrodes and various preferred embodiments thereof are described m the abov e-mentioned ' 012 PCT application and the PCT patent application filed on even date, entitled "Cardiac Output Controller," and incorporated herein by reference. Although generally the non-excitatory stimulation unit is triggered responsive to the pacing pulses generated by the pacing unit, in some preferred embodiments of the present invention, the COEP comprises one or more sensors, preferably sensing electrodes, which sense local electrical activity in the heart tissue Alternatively or additionally, one or more of the stimulation electrodes may also serve as sensing electrodes The signals sensed by the sensing electrodes are received by the circuitry and are used to trigger the non-excitatory stimulation unit and, alternatively or additionally, may be used by the pacing unit in adaptive pacing modes. Additionally, the circuitry may analyze the signals, for example, to determine the QT interval, so as to adjust the stimulation pulses responsive thereto Further alternatively, a body surface electrode may be used to detect an ECG signal, which is then used to synchronize the non-excitatory stimulation pulses Other types of sensors may also be used for this purpose, for example, a pressure sensor or other mechanical sensor in or on the heart, which senses heart muscle activity. In some preferred embodiments of the present invention, one or more of the pacing electrodes and one or more of the non-excitatory stimulation electrodes are placed in two or more different heart chambers. Preferably, the pacing electrode is implanted in the right ventricle and the non-excitatory stimulation electrode, in the left ventricle Alternatively, all electrodes may be located in the same chambei of the heart Further alternatively, one or more of the electrodes may be placed epicardially, on an outer wall of one of the chambers, or may be implanted in the myocardium. In a preferred embodiment of the present invention, the non-excitatory stimulation electrodes are placed on the heart wall in close proximity to coronary blood vessels. The inventors have found that placing the electrodes in proximity to the blood vessels generally increases the effectiveness of the non-stimulatory excitation pulses in enhancing stroke volume and contraction efficiency. In some preferred embodiments of the present invention, optimal placement of the electrodes is determined with reference to a map of local cardiac activity and/or viability. Preferably, before insertion of the electrodes, a map of the heart is produced, for example, an electrophysiological map, as described in U.S. Patent 5,568,809, or a phase-dependent geometrical map, as described in PCT Patent Application PCT/IL97/0001 1 , which is assigned to the assignee of the present patent application, both of which documents are incorporated herein by reference The electrodes are then positioned responsive to the map. Alternatively or additionally, at the time of implantation of the electrodes, their positions are varied and the results of the variation on hemodynamics are observed, in order to find optimal, fixed positions for the electrodes. In some preferred embodiments of the present invention, the non-excitatory stimulation pulse is applied between the pacing and the non-excitatory stimulation electrodes. Alternatively, the non-excitatory stimulation pulse may be applied between the non-excitatory stimulation electrode and the signal generation circuitry case or across a bipolar non-excitatory stimulation electrode. In some preferred embodiments of the present invention, the extent of change in cardiac output is controlled by changing the characteristics of the non-excitatory stimulation pulse. This is achieved by changing the strength of the electrical signal applied to the heart, i.e., the pulse voltage or current, the pulse timing, the pulse duration and the pulse waveform and frequency thereof, as described in the '012 PCT application, mentioned above In particular, the inventors have found that the shape of the non-excitatory signal can determine the magnitude of an increase or decrease in cardiac output In alternative preferred embodiments of the present invention, the COEP device may further include one or more physiological sensors, such as, for example, blood flow rate detectors, ventricular pressure detectors, etc , in order lo assess cardiac output and to adjust its regulation as needed Such adjustment may be pei foimed internally, by the signal generation circuitry itself Alternatively, an external telemetry unit may monitor physiological parameters related to the operation of the COEP device, and may then repiogram the device in response to the values of the parameters Further aspects of the present invention are also described in the above-mentioned PCT patent application entitled "Cardiac Output Contiollei ," filed on even date and incorporated herein by reference Other aspects of the use of the COEP device are described further in a PCT patent application entitled, "Apparatus and Method for Controlling the Contractility of Muscles," filed on even date (docket no 4424/WO/97), which is assigned to the assignee of the present patent application, and whose disclosuie is incorpoiated herein by reference Preferred embodiments of the piesent invention may also be used in conjunction with suitable drugs, as described in a PCT patent application entitled "Drug-Device Combination for Controlling the Contractility of Muscles" (docket no 4425ΛVO/97), and in conjunction with devices and methods for pi eventing cardiac fibrillation, as described in a PCT patent application entitled "Fencing of Cardiac Muscles" (docket no 4437/WO/97), both filed on even date and assigned to the assignee of the present application The disclos ies of these applications are also incoi porated hei ein by lefei ence There is therefore provided, in accordance with a preferred embodiment of the present invention, apparatus for heart pacing with caidiac output modification, including one or more electrodes, which apply electrical signals to cardiac muscle segments; and signal generation circuit! y, which applies an excitatoiy electrical pulse to at least one of the one or more electrodes to pace the heart and a non-excitatory stimulation pulse to at least one of the one oi more electiodes to modify the cai diac output Preferably, the cii cuitt y synchi oni/cs the non- excitatotv, stimulation pulse with the pacing pulse, most preferably by introducing a predetermined time offset between the pacing pulse and the non-excitatory stimulation pulse In a pieferred embodiment of the invention, the circuitry generates a sequence of multiple non-excitatory stimulation pulses, at predetermined respective delays relative to the pacing pulse Preferably, the one oi moi e electi odes include a bipolar non-excitatory stimulation electrode, across which the non-cxcιtatoι \ stimulation pulse is applied Additionally or alternatively, the one or more electrodes include a pacing electrode and a non-excitatory stimulation electrode, and the non-excitatory stimulation pulse is applied between the non-excitatory stimulation electrode and the pacing electrode Preferably, the signal generation circuitry is encased in an implantable case, and the non- excitatory stimulation pulse is preferably applied between one of the one or more electrodes and the implantable case In a preferred embodiment of the invention, the apparatus includes at least one sensor, which senses cardiac activity, preferably an electrode, which senses cardiac electrical activity The sensor is coupled to the signal generation circuitry, which generates the pulses responsive thereto Preferably, the signal generation circuitry interrupts application of the excitatory pulse, while generating the non-excitatory pulse responsive to the sensor Additionally or alternatively, the circuitry detects a QT interval in the cai diac electrical activity Further additionally or altei natively, the sensoi includes a pressure sensoi and/or a flow rate sensor and/or an oxygen sensoi and/or a temperature sensor Preferably, the signal generation circuitry varies one or more parameters of the non- excitatory stimulation pulse, from the group of parameters including voltage, current, duration, timing delay, waveform and waveform frequency Additionally or alternatively, after the non-excitatory stimulation pulse, the signal generation circuitry generates another pulse of opposite polarity to the stimulation pulse, which is applied to the cardiac muscle segment b\ the non-excitatory stimulation electrode Preferably, the one or more electrodes include at least one non-excitatory stimulation electrode having an area of at least 5 mm-, moi e preferably at least 1 cm-, and most preferably at least 4 cm- In a preferred embodiment of the invention, the at least one non-excitatory stimulation electrode includes a net of addressable electrodes In a further preferred embodiment, the signal generation circuitrv varies the extern of a portion of the area of the heart segment to which the non-excitatory stimulation pulse is applied In another preferred embodiment of the invention, the apparatus includes a telemetry unit, which receives data indicative of cardiac function and programs the signal generation circuitry to adjust the pulses responsive to the data Preferably, application of the non-excitatory stimulation pulse engenders an increase in the cardiac output or, alternatively, a decrease in the cardiac output Additionally or alternatively, application of the non-excitatory stimulation pulse increases an efficiency of cardiac contraction There is further provided, in accordance with a preferred embodiment of the present invention, a method for heart pacing with modification of cardiac contraction, including: applying one or more electrodes to a subject's heart, conveying an excitatory electrical pulse to at least one of the one or more electrodes to pace the heart, and conveying a non-excitatory stimulation pulse to at least one of the one or more electrodes to modify an efficacy of cardiac contraction Preferably, conveying the non-excitatory stimulation pulse includes synchronizing the pulse with the excitatory pacing pulse, pi eferably by controlling a time offset of the pulse relative to the pacing pulse In a preferred embodiment of the invention, conveying the excitatory and non-excitatory pulses includes conveying the pulses to a common one of the one or more electrodes Preferably, applying the one or moi e electrodes includes implanting a pacing electrodes in a first chamber of the heart and implanting a non-excitatory stimulation electrode in another chamber Alternatively or additionally, applying the one or more electrodes includes implanting a plurality of electrodes in a single chamber of the heart, and/or implanting at least one non- excitatory stimulation electrodes in each of a plurality of chambei s of the heart Further alternatively or additionally applying the one oi more electrodes includes fixing an electrode to the epicai ium In a preferred embodiment of the invention, the method includes applying at least one sensor to the subject's body, which senses cardiac activity, and conveying the non-excitatory stimulation pulse includes generating a pulse responsive to the activity Preferably, applying the at least one sensor includes implanting at least one sensing electrode in the heart Further preferably, generating the pulse includes detecting a QT interval in an electrical signal received bv the sensing electrode and generating a pulse responsive thereto Preferably, the method includes intei ruptmg the conveyance of the excitatory pulse while conveying the non-excitatory pulse responsive to the activity Additionally or alternatively, applying the at least one sensor includes applying a body surface electrode to the subject Further additionally or alternatively, applying the at least one sensor includes applying a flow sensor and/or a pressure sensor and/or an oxygen sensor and/or a temperature sensor. In a preferred embodiment of the invention, generating the pulse includes receiving signals from the sensor via telemetry, and varying a parameter of the pulse responsive thereto. Preferably, applying the electrodes includes applying electrodes so as to convey the non-excitatory pulse to a segment of the heart having an area of at least 5 mm-, more preferably at least 1 c ^, and most preferably at least 4 cm-. In a preferred embodiment of the invention, conveying the non-excitatory pulse includes varying an area of the heart to which non-excitatory pulses are applied. Preferably, conveying the non-excitatory pulse includes varying one or more parameters of the pulse from the group of parameters including voltage, current, duration, timing delay, waveform and waveform frequency Further preferably, after conveying the non-excitatory pulse to the at least one of the one or more electrodes, another pulse of opposite polarity thereto is conveyed to the electrodes. Preferably, modifying the efficacy includes increasing the cardiac output, or alternatively, decreasing the cardiac output Additionally or alternatively, modifying the efficacy includes enhancing the efficiency of cardiac contraction The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings in which: BRIEF DESCRIPTION OI Til l. DRAWI NGS Fig. 1 is a schematic illustration showing a cardiac output enhanced pacemaker (COEP) device, in accordance with a preferred embodiment of the present invention; Fig. 2A is a schematic illustration showing implantation of the device of Fig 1 within a patient's heart and chest, in accordance with a preferred embodiment of (he present invention; Fig. 2B is a schematic, sectional illustration of the heart, into which pacing and non- excitatory stimulation electrodes are inserted, in accordance with an alternative embodiment of the present invention; Fig. 2C is a schematic, sectional illustration of the heart, to which pacing and non- excitatory stimulation electrodes are applied, in accordance with still another alternative embodiment of the present invention, Fig 2D is a schematic lllusti ation showing an integrated pacing and stimulation electrode unit, in accoi dance with anothei pi eferi ed embodiment of the pi esent invention, Fig 3 is a schematic block diagram showing signal generation circuitry used in the device depicted in Fig 1 , in accordance with a preferi ed embodiment of the pi esent invention, Fig 4 is a flow chart illustiatmg a method ol artificial pacing with cardiac output enhancement, in accoi dance with pieferred embodiments of the pi esent invention, Fig 5 is a schematic illustration showing pacing and no -excitatoiy stimulation pulses applied by a COEP device to the patient's heart, in accordance with a pieferred embodiment of the present invention, and Figs 6-30 are electronic schematic diagrams show ing circuitry foi use in the device of Fig 1, in accordance with a piefened embodiment of the pi esenl inv ention DETAI LED DESCRIPTION OF PREFERRED EM BODIM ENTS Fig. 1 is a schematic illustration of a COEP device 20, for enhancing cardiac output in a paced patient, comprising a control unit case 26, a pacing electrode 29, and a non-excitatory stimulation electrode 27 Electrode 27 preferably comprises a large-area conductive electrode, for example, a pyro-carbon or vitreous carbon electrode, having an area of at least 5 mnv--, as described in the above-mentioned "Cardiac Output Controller" patent application, but may alternatively comprise any type of implantable electrode suitable for this purpose. Pacing electrode 29 may comprise any suitable type of pacing electrode known in the art. Preferably, electrodes 27 and 29 are coated with an anticoagulant, preferably in a time- release form, or elute the anticoagulant into the heart tissue, to prevent clot formation on and around the electrodes Such electrodes may be produced in a manner similar to steroid-eluting electrodes known in the art, for example, the Medtronic CAPSURE model 4003 electrode, described in The foundations of Cardiac I'aciny, by Sutton and Bourgeois, p. 73, which is incorporated herein by reference Control unit case 26, which is implanted in the patient's chest, similar to implantable pacemaker controllers known in the art, contains signal generation circuitry 22 (illustrated in Fig. 3 below and described with reference thereto). Circuitry 22 drives non-excitatory stimulation electrode 27 to apply a non-excitatory stimulation pulse to cardiac muscle tissue. The pulse is initiated by a trigger impulse generated by the circuitry, preferably in response to and in synchronization with a pacing pulse applied by pacing electrode 29 to the subject's heart It will be understood that although device 20 is shown in the figure as comprising only one pacing electrode 29 and one non-excitatory stimulation electrode 27, in other preferred embodiments, COEP devices may comprise multiple pacing and stimulation electrodes, of various types and sizes. Furthermore, in still other preferred embodiments, a single electrode may be used for both pacing and non-excitatory stimulation In the embodiment shown in Fi 1 , device 20 also includes an optional sensing electrode 25, which receives local electrυgram signals from the heart tissue Alternatively, one or more of electrodes 27 and 29 may also serve as sensing electrodes for this purpose. The electrogram is received by signal generation circuitry 22, which regulates the non-excitatory stimulation responsive thereto Fig. 2A is a schematic illustration showing electrodes 27 and 29 implanted in heart 32 of a patient 40, in accordance with a preferred embodiment of the present invention. Optional sensing electrode 25 is omitted from this figure Pacing electi ode 29 is pi eferably implanted on the septum in right ventricle 34, whereas non-excitatory stimulation electrode 27 is implanted in the wall of left ventricle 36 Electrodes 27 and 29 are connected by wires passing through appropriate blood vessels to implantable case 26, w hich is pi efeiably implanted in the patient's chest After application of a pacing pulse by electiode 29, COEP device 20 generates a stimulation pulse, which is applied to electiode 27, preferably so as to inciease the contraction of at least the segment of the wall of ventricle 36 with which electiode 27 is in contact, thus increasing the ventricular stroke volume The embodiment of Fig 2A also includes an optional telemetry unit 28, in communication with circuitry 22 in case 26 Pιeferabl\ cncuitry 22 includes an electronic memory, as is known in the ai t, which l eceives and stoi es values of electrophysiological parameters related to the functioning of device 20 relemeti unit 28 reads and analyzes these parameters, and repi ogi ams cu cuitiy 22 lesponsive thei eto, so as to optimize the functioning of the COEP device Fig 2B is a schematic, sectional lllusti ation showing heart 32, in which additional electrodes have been implanted, in accordance w ith an alternative preferred embodiment of the present invention In this embodiment, a plui ahh of non-excitatory stimulation electrodes 38 are implanted in left ventricle 36, so as to stimulate an extended area of the ventricular wall Preferably, these electi odes form an addiessable net, so that the extent of the area of the wall that is stimulated may be varied oi modulated, and/or so that the relative timing of stimulation pulses applied to different ones of the plurality of electiodes may be varied Electrode nets and modulation of the stimulated ai ea and the timing of stimulation pulses ai e described further in the above-mentioned '"Cardiac Output Controller ' PCT patent application, incorporated herein by reference The ai ea and timing ai e pi efei ablv, adμisied to give an optimal enhancement of cardiac output The embodiment shown in Fig 2B also includes multiple pacing electrodes 39 in right ventricle 34, and sensing electrode 25 at the apex of left ventncle 36 A further physiological sensor 43, for example, a flow sensoi oi piessui e sensoi , is placed in the aorta Signals from sensor 43 are likewise conveyed to cucuiti y 22 in case 26, for use in assessing ventricular contraction, so that the stimulation applied by electi odes 8 may be adiusted to give a desired enhancement of cardiac output Foi example, the intensity, dm ation, aiea extent and/or delay (relative to pacing pulses applied to electiodes 39) of the non-excitatoiy stimulation pulses applied by the electrodes may be varied until the desired enhancement is achieved. It will be understood that electrode 25 and sensor 43 may both be placed in other locations in the heart, as well, besides those shown in Fig. 2B Fig. 2C is a schematic, sectional illustration of heart 32, to which electrodes have been fixed in accordance with still another preferred embodiment of the present invention. In this case pacing electrode 39 is implanted in right atrium 35. Non-excitatory stimulation electrodes 38 are implanted surgically on the epicardium of left ventricle 36 Although Figs. 2A-2C show certain specific placements of the pacing and non- excitatory stimulation electrodes, it will be understood that other electrode placements are also possible. For example, particularly in cases of severe cardiac insufficiency, non-excitatory stimulation electrodes may also be placed in or on an epicar ial surface of the right ventricle, and/or of one or both atria, preferably using a thorascope or other minimally-invasive surgical method. Similarly, pacing electrodes may be placed in m o. three or all four chambers of the heart, in accordance with methods of multi-chamber pacing known in the art Additionally or alternatively, at least some of the pacing and non-excitatory stimulation electrodes may be "floating electrodes," as are known in the art, which are not fixed to the heart wall and can move within a heart chamber. The optimal electrode placement in each case may be a function of the particular pathological condition of the heart, and may preferably be ascertained by mapping the heart before placement of the electrodes, as described above The non-excitatory stimulation electrodes may also be inserted and positioned in the heart's blood vessels, as described in the above-mentioned "C ardiac Output Controller " PCT patent application. Fig. 2D is a schematic illustration of a stimulation probe 46, for use in conjunction with COEP device 20, in accordance with an alternative embodiment of the present invention. Probe 46 includes a pacing electrode 47, preferably unipolar, and two non-excitatory stimulation electrodes 48, between which the non-excitatory pulse is applied The probe may be implanted in a single chamber of the heart, thereby simplifying the task of electrode placement Alternatively, because probe 46 is long, narrow and, preferably, flexible, it may be inserted into one of the heart's blood vessels Fig. 3 is a schematic block diagram showing signal generation circuitry 22, in accordance with a preferred embodiment of the present invention Circuitry 22 comprises a non-excitatory stimulation section 100 and a pacing section 120, as well as an optional sensing unit 1 10 and detection circuit 104. Optionally, circuitry 22 also communicates with a telemetry and external programming unit, such as telemetry unit 28, shown in Fig 2A In a standard mode of operation, pacing section 120 and stimulation section 100 are triggered to apply pulses to pacing electrode 29 and stimulation electrode 27, respectively, responsive to a pulse generator 122 in section 120. The pulse generator may be programmed and controlled to pace the heart in substantially any mode of pacing known in the art, for example, DDD, DDDR and VVI modes. Circuitry 22 may also operate in an adaptive mode, however, responsive to electrogram signals received from sensing electrode 25, or to ECG signals from a body surface electrode In this mode, unit 1 10 receives and conditions the electrogram signals Detection circuit 104 receives the conditioned signals and senses an activation w aveform in the electrogram, as is known in the art, and generates a trigger pulse responsive thereto. The trigger pulse is conveyed to stimulation section 100 Pacing section 120 continues to operate under the control of pulse generator 122, as in the standard mode described above Sensing unit 1 10 includes signal blanking unit 101 and signal blank logic 102 and a differential amplifier/ signal conditioning circuit 103 The blanking operates to block the input to detection circuit 104 while the output of pacing section 120 or stimulation section 100 is active, to prevent the system from generating trigger pulses due to stimulation artifacts. Pacing section 120 includes pulse generator 122 and constant current units (CCU) 125 and 126. The CCU's generate output pacing pulses responsive to the trigger received from pulse generator 122 The output pulses are applied io pacing electrode 29, as well as to one or more optional additional pacing electrodes, u.s show n, for example, in Fig 2B When multiple pacing electrodes are used, a delay unit 127 allow s the relative timing of the pacing pulses applied to the electrodes to be controlled and adjusted Stimulation section 100 comprises a trigger divider 105, which generates a modified trigger pulse in response to input trigger pulses from pulse generator 122 or from detection circuit 104, or alternatively from external trigger input 30 The trigger divider allows a user of device 20 to select whether the stimulation pulse w ill be applied at every heart beat or only once in a predetermined number of beats Section 1 00 further includes signal generators 106 and 107, which generate voltage signals of predefined characteristics, as described below, in response to the modified trigger pulse, and constant current units (CCU) 108 and 109, which convert input voltage signals from the signal generators to output current pulses. Two stimulation output channels are shown in Fig. 3, enabling different stimulation pulses to be applied to two or more different stimulation electrodes. It will be appreciated, however, that only one of the channels need be used or alternatively, that additional channels may be added to drive additional stimulation electrodes. Fig. 4 is a flow chart, which illustrates a method for enhancing cardiac output in a paced patient using COEP device 20, according to a preferred embodiment of the present invention. Pacing parameters and non-excitatory stimulation parameters are initially input to fit the patient's condition. The device is set so that stimulation section 100 operates in either the standard, self-triggered mode or the adaptive mode, responsive to electrogram or ECG signals received from the heart. In either case, a trigger pulse is generated by pulse generator 122 and is applied to CCU 125 (and optionally, after a delay, to CCV 126), which produces a pacing pulse output to electrode 29 A trigger pulse is likewise input to non-excitatory stimulation section 100, whereby CCU 108 and, optionally, CCU 109 generate non-excitatory stimulation pulses having predefined or user-defined characteristics, which are applied to the heart by non- excitatory stimulation electrode 27 Optionally, electrical or other physiological signals are received from the heart, for example, by electrode 25 and/or sensor 43, as shown in Fig 2B These signals are used in adjusting the pacing and/or non-excitatory stimulation parameters to be applied in subsequent cycles. The signals may either be processed and used on-line, within circuitry 22, or they may be transferred to telemetry unit 28, which analyzes the signals and reprograms the circuitry accordingly. Fig. 5 is a schematic illustration of pulses applied to heart 32 by device 20, including a pacing pulse 60, applied by pacing electrode 29, and a non-excitatory stimulation pulse 51 , applied by stimulation electrode 27, in accordance with a preferred embodiment of the present invention. As shown in the figure, pacing pulse 60 is preferably initiated immediately upon generation of the trigger pulse by pulse generator 122 The amplitude and duration of the pacing pulse are in accordance with principles of cardiac pacing known in the art In some preferred embodiments of the present invention the regulation of cardiac output is achieved by varying certain characteristics of pulse 5 1 Non-excitatory stimulation energy is applied to stimulation electrode 23 in the form of a baseline pulse 53, having a baseline amplitude, indicated by an arrow- 54 in Fig. 5, of preferably 0. 1 lo 10 inA, optionally up to 50 mA, and a duration, indicated by an arrow 52, preferably ranging between 1 and 300 msec, most preferably between 10 and 80 msec. Preferably, signal generators 106 and 107 are controlled to provide a delay, indicated by an arro 50 in Fig. 5, of between 1 and 500 msec between the trigger input and the onset of pulse 53. Pulse 53 is preferably followed by another pulse of opposite polarity (not shown in the figure) to prevent problems of tissue polarization and electrode degradation, as described in the above-referenced l 012 PCT application and mentioned above. Preferably, a waveform 58 having a frequency of up to 10 kHz and amplitude, indicated by an arrow 56, up to or comparable to the baseline amplitude is superimposed on the baseline amplitude of pulse 53. Although waveform 58 is shown here as a square wave, any other suitable waveform may be used, for example, a sinusoid or sawtooth wave. The appropriate amplitude, duration, delay, waveform, etc., of non-stimulatory pulse 5 1 are preferably adjusted to provide a desired increase or, alternatively, a decrease, in (he cardiac output. Non-excitatory stimulation pulse 1 may be applied to heart 32 along various electrical paths. For example, in one preferred embodiment, described with reference to Fig. 2 A, stimulation electrode 27 operates as a unipolar electrode, and pulse 51 is applied between electrode 27 and case 26, which is preferably made of an electrically conductive material. Alternatively, the pulse may be applied between stimulation electrode 27 and pacing electrode 29. Further alternatively, referring now to Fig 2B. multiple stimulation electrodes 38 may operate in a bipolar mode, whereby pulse 5 1 is applied between a pair of the electrodes. Figs. 6-29 are electronic schematic diagrams illustrating circuitry for use in implementing the functions of circuitry 22, in accordance with a preferred embodiment of the present invention. As shown in Figs 6A and 6B, the circuitry includes an ECG processor 130, a first CCU section 140, a second CCU section 142 and main control circuit 150, which together perform the functions of circuitry 22, as shown in Fig. 3 and described with reference thereto. Figs. 7 through 29 are circuit diagrams showing details of the implementation of the elements of Figs. 6 A and 6B. These diagrams are considered sufficient in and of themselves to enable one skilled in the art to practice the present invention Various aspects of these diagrams are described hereinbelow. Figs. 7A, 7B and 7C illustrate main control circuit 150, which is based on a microcontroller MPU 1 , preferably an 805 I -type microcontroller, as is known in the art. The microcontroller receives user commands via a communications interface, for example, to program parameters of the stimulation pulses to be applied It controls other elements of circuitry 22 via a data bus, marked AD0-AD7 Figs. 8A and 8B show details of ECG processor 130, which receives electrical signals from the patient's body and processes them to generate trigger pulses, as described above, for driving the non-excitatory stimulation ECG processor 130 includes an ECG amplifier 152, an ECG signal conditioning unit 154, an A/D converter 156, and a detection controller 158. ECG amplifier 152 is shown in detail in Fig. 9, and comprises a differential preamplifier and programmable gain amplifier and blanking unit Signal conditioning unit 1 54, shown in Figs 10A and I OB, includes programmable high-pass, low-pass and notch filters, selectable by means of a clock generator, and also including an analog switch for bypassing the notch filter. A D converter 1 56 is shown in Fig. I I Figs I 2A and I 2B illustrate controller 1 58, including another 8051 -type microcontroller MPU2, which analyzes the ECG signal and generates the trigger pulse Figs. 13 A, 13B and 13C illustrate first CCU section 140, which generates two channels of non-excitatory stimulation pulses CCU section 140 includes two control units 162 and 164, waveform generators 166 and 168, power units 170 and 1 74, and a waveform selector 172. Figs. 14A and 14B show details of waveform generator 166, which drives a first one of the two non-excitatory channels, while Figs I 7A and 17B show waveform generator 168, which is substantially similar to generator 166 and drives the second channel Figs 15A, 15B and 15C illustrate control unit 162, which receives and scales the waveform from generator 166. Fig. 15C shows timing control logic common to both control units 162 and 164 Figs 18A, 18B, 18C and 18D illustrate control unit 164. wherein Figs I 8 Λ and 18B show waveform scaling circuitry similar to that in Figs. I 5A and 15B Figs 18C and 18D include circuitry for controlling the relative delays of the pulses generated by the two stimulation channels Figs 16 and 19 show details of power units 1 74 and 178, respectively, and Fig 20 illustrates wave selector 176. Fig. 21 shows second CCU section 142, including two CCU channels 180 and 182, for generating pacing pulses at predetermined rates and a relative delay therebetween, similar to pacemakers known in the art Figs 22A, 22B and 22C show details of channel 180. Figs 23A and 23B show details of channel 182, which is switched by the same sw itch and counters as channel 180 (shown in Fig 22B) Figs. 24, 25A, 25B, 26, 27A and 27B show details of isolation circuitry, which is used when circuitry 22 is to be run while connected to external power. Fig. 28 illustrates a battery charging circuit. Figs. 29 and 30 show front and rear panel connections, respectively. Although in some of the preferred embodiments described above, for example, as shown in Fig. 2A, circuitry 22 is shown as being contained within an implantable case 26, the specific implementation of the circuitry exemplified by Figs 6-30 is better suited to be contained in an external, bedside case, in accordance with the best mode of the invention practiced at present. It will be understood that the circuitry of Figs 6-30 can be suitably altered and miniaturized to fit in an implantable case, using methods and electronic devices known in the art, particularly such as are currently used in implantable pacemakers. On the other hand, under some circumstances, pacing and non-excitatory stimulation may be best accomplished using such an external, bedside case, hen the heart must be paced and/or the cardiac output regulated temporarily, for example, during recovery from infarction or surgery. It will be appreciated that the preferred embodiments described above are cited by way of example, and the full scope of the invention is limited only by the claims I

Claims: CLAIMS 1 . Apparatus for heart pacing with cardiac output modification, comprising one or more electrodes, which apply electrical signals to cardiac muscle segments; and signal generation circuitry, which applies an excitatory electrical pulse to at least one of the one or more electrodes to pace the heart and a non-excitatory stimulation pulse to at least one of the one or more electrodes to modify the cardiac output. 2. Apparatus according to claim 1 , wherein the circuitry synchronizes the non-excitatory stimulation pulse with the pacing pulse 3. Apparatus according to claim 2, w herein the circuitry introduces a predetermined time offset between the pacing pulse and the non-excitatory stimulation pulse 4. Apparatus according to claim 3, wherein the circuitry generates a sequence of multiple non-excitatory stimulation pulses, at predetermined respective delays relative to the pacing pulse. 5. Apparatus according to any of the preceding claims, wherein the one or more electrodes comprise a bipolar non-excitatory stimulation electrode, across which the non-excitatory stimulation pulse is applied 6. Apparatus according to any of claims 1 -4, wherein the one or more electrodes comprise a pacing electrode and a non-excitatory stimulation electrode, and herein the non-excitatory stimulation pulse is applied between the non-excitatory stimulation electrode and the pacing electrode 7. Apparatus according to any of claims 1 -4, wherein the signal generation circuitry is encased in an implantable case 8 Apparatus accoidmg to claim 7, wheie the non-excitatory stimulation pulse is applied between one of the one oi more electiodes and the implantable case 9 Apparatus according to any of claims 1-4, and composing at least one sensor, which senses cardiac activity, wheiem the sensoi is coupled to the signal genei ation circuitry, which generates the pulses lesponsive theieto 10 Apparatus accoidmg to claim 9 wheiem the signal genei ation circuitry interrupts application of the excιtatoι\ pulse while geneiating the non-excιtatoι \ pulse lesponsive to the sensor 11 Apparatus according to claim 9, wheiem the at least one sensoi comprises an electrode, which senses cardiac electncal activity 12 Apparatus accoidmg to claim I 1 wheiem the cucuitiy detects a QT interval in the cardiac electrical activity 13 Apparatus accoidmg to claim 9, wheiem the sensoi comprises a piessuie sensor 14 Apparatus accoidmg to claim 9 wheiem the sensoi compiises a flow t ate sensor 15 Apparatus accoidmg to claim 9, wheiem the sensoi compiises an oxygen sensor 16 Appaiatus accoidmg to claim 9, whet cm the sensoi composes a tempei tuie sensor 17 Apparatus accoidmg to any of claims 1-4 wheiem the signal genei ation cncuitry vanes one or more paiameteis of the stimulation pulse, from the gioup of parameters including voltage, cunent duration, timing dela \ wa efoim and wavefoim fiequency 18 Apparatus accoidmg to any of claims 1-4, wheiem afiei the non-excitatoiy stimulation pulse, the signal geneiation cucuitiy geneiates anothei pulse of opposite polarity to the stimulation pulse, which is applied to the caidiac muscle segment by the non-excitatory stimulation electiode 19 Apparatus according to any of claims 1-4, wheiem the one oi moie electrodes comprise at least one non-excitatoiy stimulation electiode having an aiea of at least 5 mm^ 20 Apparatus according to claim 19, wheiem the at least one non-excitatory stimulation electrode applies the stimulation pulse to a heart segment having an aiea of at least 1 cm^ 21 Apparatus accoidmg to claim 20 wheiem the at least one non-excitatory stimulation electrode comprises a net of addiessable electiodes 22 Apparatus accoidmg to any of claims 1-4, wheiem the signal geneiation circuitry varies the extent of a portion of the aiea of the heart segment to which the non-excitatory stimulation pulse is applied 23 Appaiatus accoidmg to anv, of claims 1-4, and composing a telemetiy unit, which receives data indicative of caidiac function and piogiams the signal geneiation circuitry to adjust the pulses lesponsive to the data 24 Apparatus according to any of claims 1-4 wheiem application of the non-excitatory stimulation pulse cngendeis an inciease in the caidiac output 25 Apparatus accoidmg to an\ of claims 1-4, wheiem application of the non-excitatory stimulation pulse engenders a deciease in the caidiac output ->"> 26. Apparatus according to any of claims 1 -4, wherein application of the non-excitatory stimulation pulse increases an efficiency of cardiac contraction 27. A method for heart pacing with modification of cardiac contraction, comprising: applying one or more electrodes to a subject 's heart; conveying an excitatory electrical pulse to at least one of the one or more electrodes to pace the heart; and conveying a non-excitatory stimulation pulse to at least one of the one or more electrodes to modify an efficacy of cardiac contraction. 0 28. A method according to claim 27, wherein conveying the non-excitatory stimulation pulse comprises synchronizing the pulse with the excitatory pacing pulse 29. A method according to claim 28, wherein synchronizing the non-excitatory stimulation 5 pulse comprises controlling a time offset of the pulse relative to the pacing pulse. 30. A method according to any of claims 27-29, wherein conveying the excitatory and non- excitatory pulses comprises conveying the pulses lo a common one of the one or more electrodes. 0 31. A method according to any of claims 27-29, wherein applying the one or more electrodes comprises implanting a pacing electrodes in a first chamber of the heart and implanting a non-excitatory stimulation electrode in another chamber. !5 32. A method according to any of claims 27-29, wherein applying the one or more electrodes comprises implanting a plurality of electrodes in a single chamber of the heart. 33 A method according to any of claims 27-29, wheiem applying the one or more electrodes compiises implanting at least one non-excitatoiy stimulation electiodes in each of a plurality of chambeis of the heart 34 A method accoidmg to any of claims 27-29, wheiem applying the one or more electrodes comprises fixing an electiode to the epicardium 35 A method accoidmg to any of claims 27-29, and composing applying at least one sensor to the subiect's bod 1 ), which senses caidiac activity and wheiem conveying the non- excitatory stimulation pulse compiises genei at ing a pulse lesponsive to the activity 36 A method accoidmg to claim 35 heiem applying the at least one sensoi comprises implanting at least one sensing electiode in the heart 37 A method accoidmg to claim 36, wheiem genciating the pulse comprises detecting a QT interval in an electiical signal ieceived by the sensing electiode and generating a pulse responsive thereto 38 A method according to claim 5, and composing intemipting the conveyance of the excitatory pulse while conveying the non-excitatoiy pulse lesponsive to the activity 39 A method accoidmg to claim 35, wheiem applying the at least one sensoi comprises applying a body surface electiode to the subiect 40 A method accoidmg to claim 35 wheiem applying the at least one sensor comprises applying a flow sensor 41 A method accoidmg to claim 35 wheiem applying the at least one sensor comprises applying a piessuic sensoi 42 A method according to claim 35, wheiem applying the at least one sensor comprises applying an oxygen sensoi 43 A method according to claim 35, wherein applying the at least one sensor comprises applying a temperature sensor 44 A method according to claim 35, wheiem genei atmg the pulse comprises receiving signals fiom the sensoi via telemeti y, and vaiy g a paiametei of the pulse lesponsive thereto 45 A method accoi dmg to any of claims 27-29, whei em applying the electiodes comprises applying electi odes so as to convev, the non-excitatoi y pulse to a segment of the heart having an area of at least 5 mm- 46 A method accoidmg to claim 45, whei em applying the electrodes comprises applying electrodes so as to convey the non-excitatoi y pulse to a segment of the heart having an area of at least 1 cm 2 47 A method accoi dmg to claim 46, whei em applying the electi odes comprises applying electrodes so as to convev, the non-excitatoiy pulse to a segment of the heart having an area of at least 4 cm 2 48 A method accoi dmg to an\ of claims 27-29 w hei em conveying the non-excitatory pulse compi ises varying an ai ea of the heart to w hich non-excitatoi y pulses ai e applied 49 A method accoidmg to an \ of claims 27-29, whei e conveying the non-excitatory pulse comprises varying one oi moie pai ametei s of the pulse fiom the gi oup of paiameters including voltage, cui rent, duration, timing delay, wav efoi m and w vefoi m fiequency 50 A method accoi dmg to composing aftei conveying the non- excitatory pulse to the at least one of the one oi moi e electi odes, conveying anothei pulse of opposite polarity theieto to the electi odes 51. A method according to any of claims 27-29, wherein modifying the efficacy comprises increasing the cardiac output 52. A method according to any of claims 27-29, wherein modifying the efficacy comprises decreasing the cardiac output. 53. A method according to any of claims 27-29, wherein modifying the efficacy comprises enhancing the efficiency of cardiac contraction

Inventors: BEN-HAIM SHLOMO, DARVISH NISSIM, FENSTER MAIER, MIKA YUVAL, BEN-HAIM, SHLOMO, DARVISH, NISSIM, FENSTER, MAIER, MIKA, YUVAL
Applicants: BEN HAIM SHLOMO, DARVISH NISSIM, FENSTER MAIER, MIKA YUVAL, NEW TECHNOLOGIES SA YSY LTD, BEN-HAIM, SHLOMO, DARVISH, NISSIM, FENSTER, MAIER, MIKA, YUVAL, NEW TECHNOLOGIES (SA-YSY) LTD.
Application year: 1997
Main classification: A61N1
IPC codes: A61B17, A61N1