SE9501191A0 - Apparatus for tissue stimulation - Google Patents

Abstract

ABSTRACT The invention relates to an apparatus for tissue stimulation. A stimulation signal generating means for generates stimulation signals to the tissue. A detector means (21) acquires an electrical waveform signal corresponding to the waveform of the electrical potential at the tissue after a stimulation signal. The detector means (21) acquires a stimulation signal providing heart response of the patient's heart, and acquires a heart response waveform. The stimulation signals generating means (3) generates a stimulation signal within the heart refractory period of a patient's heart after a heartbeat in order to provide a non-capture waveform signal representing polarization phenomena from a stimulation signal without heart response. Means could be provided for generating a difference signal between the heart response waveform and the non-capture waveform signal in order to provide a waveform signal representing evoked response of the heart.

Description

BILAGOR Beskrivning, patent.krav och sammandrag 3 exenTI;ir Jsser 4 ritningar i 3 exemplar Overlatelsehandling Fulltnakt Umierfullmakt av generailuilmak: litlandsk text, Priontets'levls Ev sekvenshsta I rnaskinli.o_bar torm AVGIFT xGrundavgift 1600- Tillaggsavgit1 200:-r patentkrav over xGrundavgift 2000--ITS-granskmng Stockholm den 31 mars 199 H. ALRIHNS PITENTBYRA AR 14AL 8114M4S PATE5iT/1Y!) A All Lto. 3137 • .flyjnetVatsr% 23 • S • 103 62 STOCK■.PAi,s',1:11f:t., •4, • ICn10 19 23 AHr. A. rsIf)(-• '7' 7fi•A I_Pv•; )SA Pacesetter AB Apparatus for tissue stimulation FIELD OF THE INVENTION The present invention generally relates to an arrangement for tissue stimulation and in particular to a heart stimulating device for providing a heart stimulating signal without providing a heart response.

The inventive arrangement is, however, developed for an arrangement including a subtraction stage for generating a difference signal from a measured cardiac electrical potential curve provided by a stimulation signal having an active response from the tissue and a curve representing polarization phenomena produced in the tissue by stimulation not providing an active response from the tissue, with the stimulation being controlled dependent on an evaluation of the difference signal.

DESCRIPTION OF THE PRIOR ART U.S. Pat. No. 5,165,405 discloses a heart stimulator where the heart of a patient is stimulated by electrical stimulation pulses that are generated by a stimulation pulse generator and are supplied to the heart via an electrode arrangement. A signal curve is stored representing the stimulation of the tissue where a stimulation response of the tissue occurs. A signal curve for the compensation of the polarization components is captured when the stimulation energy happens to stimulate the tissue without stimulation response. Weighted versions of these two curves are subtracted from each other in order to evaluate the curve for evoked response.

OBJECTS OF THE INVENTION • • • :3'0: • • • • • • • • • • • • ." . • • .

It iS a primary object A. the T,resent inventl,,m tvlde apparatus giving a stimulation pulse which does not give a response from the heart in order to provide a curve representing polarization phenomena produced in the tissue by stimulation not providing an active response from the tissue, below called a non-capture curve.

It is a further object of the present invention to provide an arrangement having an improved and a high level of confidence regarding a non-capture curve, which curve could be used for compensation after a stimulation signal providing a response from the heart, referred to below as heart response capture curve.

It is still another object of the present invention to pro- vide an evoked response curve using the heart response capt- ure curve and the non-capture curve.

It is another object of the present invention to provide an arrangement for providing a non-capture curve of practically the same order of amplitude as the heart response capture curve.

Still another object of the invention is to provide an arrangement with which it is possible to provide a heart response capture curve and a non-capture curve within the same heartbeat.

It is still another object of the invention to provide an arrangemert providing a heart response capture curve and a non-capture curve using a low power consumption.

SUMMARY OF THE INVENTION These objects are achieved in an apparatus in accordance with the principles of the present invention as described in the independent claims. Further developments and features of the invention are described in the dependent claims.

According to the invention an apparatus for tissue ,t.imulat- ••• • • • • •• • • • • • • I • ion is provided comprising stimulation signal generating means for generating stimulation signals to the tissue, and detector means for acquiring an electrical waveform signal corresponding to the waveform of the electrical potential at said tissue after a stimulation signal. In order to provide an electrical non-capture waveform representing signal characterizing polarization phenomena from a stimulation signal without heart response, stimulation signal generating means are adapted to generate stimulation signals within the heart refractory period of a patient's heart after a heartbeat , and the detector means is adapted to acquire said non-capture waveform signal after the stimulation signal before the end of the heart refractory period, i.e. before the T-wave of a heartbeat.The purpose of this non-response stimulation is to monitor the stimulation polarization potentials.

The stimulation signal generating means could also be adapted to provide a stimulation signal providing heart response of the patient's heart, and the detector means adapted to acquire a heart response waveform. Means could be provided for generating a difference signal between the heart response waveform and the non-capture waveform signal, in order to provide a waveform representing evoked response. The stimulation signal for providing a non-capture waveform signal could preferably be provided 50 to 150 sec. after a heart activating stimulation signal. However, it is to be noted that the stimulation signals for providing the heart response waveform and the non-capture waveform signal can be provided during different heartbeats as well. The non-capture .• • • 'BO:waveform signal can thus be a stored signal from an earlier stimulation to provide it. • • • • yl • • The following expressions are used in the text. . . q5ispontaneous response (or beat): .

."Heart signal resulting from normal contraction without stimu- • • lation.

Evoked response: • • • • • • • • • • • • • • •11. • ••II••••• n•• ••• • :.•• •• • •••• 4 Heart signal resulting from contraction after a successful stimlat ion.

Stimulation after-potential: This is a signal generated by polarisation caused by tissue stimulation. Tissue stimulation produces Ions in the tissue at the site of an electrode position. These Ions propagate by diffusion away from the electrode site and will dissipate (by recondination) and diminish. The corresponding signal will disturb the sensing of evoked response and distort the sens- ing detector function.

Evoked response detection and spontaneous detection are two different functions. The detector implementation can however be combined (but this is not necessary). The signals are different in shape and size, especially regarding the T-wave.

A scheme for minimization of polarization potentials after a heart stimulation can be utilized dependent upon the result- ing waveform, it is also possible to store its waveform and provide compensation for the evoked response detected waveform.

The stimulation technique according to the invention could advantageously be used to evaluate the potentials after an active heart stimulation, below called after-potentials or heart response capture potentials, provided in a common heart stimulator system.

. • • Evoked response is of interest in Atrium after Atrial stimulation and in Ventricle after Ventrical stimulation. It is . •dependent on the pacing system used (or a programmed modal- 400 • • • •ity).

• •A single chamber system can be of Atrial or Ventricular type.

••• • ••• •••• * • • • • • A dual chamber system has sensing and sometimes stimulation of Atrial activity and further sensing and stimulation of the Ventricle.

:"• *.: • • ••••• • ••• ••• ••• •••••• ••••• ••••••• •• Two methods of compensation: A signal representing polarization potential is generated with opposite signs and added to the stimulated sensed signal.

The stimulated sensed signal is sampled or char- acterized, and the polarization signal is applied.

The most common (60%) pacing system is Ventricular single chamber stimulation with inhibition on spontaneous heart activity (VVI) single chamber systems (AM). Atrial single chamber systems (AAI) are less than 10%. Dual Chamber systems (DDD) are about 30%.

Two types of electrode leads are used for pacemakers: Unipolar:a single Tip electrode for both sensing and stimulation.

Bipolar:Tip and Ring electrodes having a distance of about 2 cm. Sensing is provided between Tip and Ring. Stimulation is sometimes provided between Tip and Ring and sometimes between Tip and Case, i.e. the housing of the pacer, which thus can and commonly is used as an indifferent electrode.

The invention could be used in all kinds of pacemakers and for pacemaker systems using both kinds of electrode leads mentioned above. • • • .3.0heart stimulator implanted in a patient can be studied by a • physician via telemetry. Properties of waveforms of the patient's heart can be used for control of and minimizing the ". • • •after-potentials by sensing and/or monitoring intracardial • • IEGM. Hence the sensing properties of the stimulator detector .• can be optimized and crosstalk sensing in a dual chamber ..•••device minimized.

• • • • * • • • • • •• • • • • • Since the stimulation signals to the heart for the heart response stimulation and for the non-capture stimulation can The effect of change of electrode-to-tissue parameters in a • ••.:. 1 s•.• ••••••• ••••11 • •• II••••I.II••• 4•••■111•• 6 be of the same order of magnitude, and hence the after-potential curves after these stimulations will also be of the same order of magnitude, the circuitry for making the capture and the subtraction operation could then be rather uncomp- licated. Therefore, the number of storages of after-potenti- als could be increased in relation to the ones which could be provided by the system described in the U.S. Pat. No. 5,165,405 mentioned above. Therefore, different types of evoked or spontaneous waveforms could be covered with the device according to the present invention.

Waveforms with abnormal propagation directions sometimes occur in a heart. This penomena is especially observed in some heart diseases/abnormalities, e.g. Ischemia or Tachycardia. Thus, detection of occurrence of these phenomena are of interest in order to adjust an implanted stimulator action accordingly or to just monitor for diagnostical purposes. For instance, occurrence of Tachycardia will result in changing the heart stimulator algorithms for Tachycardia treatment where defibrillation treatment could be activated when necessary.

BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of the present invention and for realizing further objects and advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings, in which: FIG. 1is a schematic block diagram of an embodiment of an apparatus for ,issue stimulation, in the form of a heart stimulator, constructed in accordance with the principles of the present invention; • • .1'■• (.15.* • ••• • • ••• • •• •• 15 •• • • a00 •• • FIG.

FIG.

FIG. 2A and213 show voltage/time diagrams of waveform signals provided after stimulation signals; 3is a schematic block diagram of afirst embodiment of a detector unit for usein the apparatus shownin FIG.1; 4is a schematic block diaqram of an embodiment of a • ' 7 • ••• •••••• •••• 7 circuit providing parameters representing a detected curve form; FIG. is a schematic block diagram of another embodiment of a circuitry providing parameters representing a detected curve form and having updating possibiliti- es.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As an exemplary embodiment of the arrangement of the invent- ion, FIG. I shows the block circuit diagram of a heart stimulator 1 for tissue stimulation, in this case the stimulation of a heart 2. The heart stimulator 1 comprises a stimulation pulse generator 3 that has its output side connected via an electrode line arrangement 4, 4' to an electrode arrangement 5, 5' applied in the heart 2 for charging the heart 2 with stimulation pulses. It is to be noted that the generator 3 may be rather complicated providing different stimulation signals at different outputs in different times adapted to the different kinds of stimulation the heart need for the electrodes sited in different places in the heart. It is to be understood that pace-pulse stimulation electrode arrangements placed in a heart could be of many different kinds, for instance one in atrium and/or one in ventricle, and that the electrodes could be unipolar or bipolar. The electrode arrangement 5, 5' only illustrates that the heart is pace-stimulated. As mentioned in the introductary part of the description, all the described pacing electrode •arrangements could be used according to the invention.

G•• However, the detection arrangements for atrial and ventricular after-potentials must be separate, if both atrial . •and ventricular stimulations are used, •• • • • ..•••Defibrillator electrodes 8, also connectr!d to the stimulation • .. -14pulse generator 3, could be provided at the heart as well, if .• .9 ••the patient suffers from a heart disease, such as '...• • . • .tachycardia, requiring defibrillation, However, it is the .. • • • stimulation via the electrode arrangement 5 and/or 5' for • • • • • pacing which is to be used in accordance with the invention, and also that electrode arrangement to be monitored.

The stimulation pulse generator 3 can be activated to deliver a stimulation pulse of the kind necessary for the patient via control line 6, which is connected to a corresponding output of a control unit 7. The duration of the respective stimulation pulse can also be set via the same line 6. In the illustrated exemplary embodiment, the control unit 7 is preferably a controller 9, for instance a sequence controller or state machine, in order to save power consumption but could also be a microprocessor having program that executes all functions of the heart stimulator stored in a read-only memory 10. A direct access storage device 11, analog or digital (RAM), is connected to the control device 9 via a data line 13, address line 15, as well as via a write-read switching line 16.

In order to be able to acquire the reaction of the heart 2 given a stimulation, the heart stimulator 1 contains a de- tector arrangement connected to the controller 7 for each electrode line arrangement 4 and/or 4'. If only one electrode line arrangement is used for an actual pacemaker only one detector arrangement is needed of course. Each detector arrangement comprises a detector unit 17, 17' having an input side connected via the electrode line arrangement 4, 4' to the electrode arrangement 5, 5' for acquiring the electrical potential in the heart tissue. This arrangement could be as simple as having only a single electrode 5 or 5' both for stimulating the heart 2 and for acquiring the reaction thereof (stimulation response). However, stimulation could be made both from an Atrium electrode and a Ventricular electrode •each by itself or in combination, and the capture could be ••• • •made between tip and ring of a bipolar electrode. The problem ••• arises, however, for all the combinations described because • the heart tissue is so highly polarized in the immediate • ."region of the stimulation electrode 5 or 5', for every ." •stimulation, that the polarization effects overlay the • • . • ••• .stimnlation response, evoked response, of the heart 2 to the . • • • degree of making it unrecognizableL This problem and the inventive solution thereof shall be set forth in greater detail below with reference to FIGs. 3 to 5. The exemplary embodiment of the inventive arrangement of FIG. 1, of course, also allows the employment of a separate stimu- lation electrode and a measuring electrode for respectively stimulating the tissue and for acquiring the stimulation response.

The curve of electrical potential for a heart response cap- ture curve in the heart tissue is acquired by the detector unit 17 or 17', or both, depending upon which kind of pacemaker used. The detector signal is supplied via an output line 18 or 18' of the detector unit 17 or 17' to a corresponding input of the control device 9. The detector unit 17 or 17' is activated or inhibited by the control device 9 via a control line 19 or 19', such that the detector 17 or 17' is activated only during a time window after an activating stimulation signal which may be composed of a plurality of individual lines for acquiring the curve of potential in the heart 2, and the detector unit 17, 17' could be set in terms of its sensitivity via a further control line 20 or 20'. Both the heart response capture curve and the non-capture curve detected by the same detector unit 17 or 17' could stored in different cells in the same storage. The structure of different embodiments of the detector unit 17 or 17' shall be set forth in greater detail below with reference to FIGs. 3 and 5. • • • used to control the detector 17, 17' to sense evoked response • • or spontaneous response, if the detector 17, 17' is a com- • •bined detector to be used for detection of both these featur- •• • • • I es.

.ZUFor detecting natural heart activities, the heart stimulator . • •••1 could contain a further detector unit 21 or 21' instead of ••• . .having a combined detector unit 17, 17' for both evoled and • 0 • • ••• •spontaneous response. The detector unit 21, 21' also has its ••. • • .. input side connected via the electrode line 4 or 4' to the However, more generally the control line 20, 20' could be electrode 5 or 5' and is connected to the control device 9 via an output line 22 or 22'.

The detector unit(s) 17, 17' can be activated or disconnected by the control device 9 via control lines 19, 19' and 20, 20'. However, in most instances a sensitivity adjustment of the two curves after stimulation could be avoided. The detector unit(s) 21, 21' serves the purpose of acquiring natural heartbeat s and inhibit a stimulation of the heart 2 from the stimulation pulse generator 3 via the control device 9, for instance for heart response stimulation as long as natural heart activity is present, and for providing non-capture stimulation only at predetermined times or when predetermined conditions occur; suppressing stimulation of the heart is known in the art and shall therefore not be set forth in greater detail below.

Finally, the heart stimulator 1 contains a telemetry unit 25 connected to the control device 9 for programming and for monitoring functions of the heart stimulator 1 and of heart parameters acquired therewith on the basis of data exchange with an external programming and monitoring device (not shown).

%SO • • • • 0 • • • • • • • • • • • • • • • • • 0 • • • • • • The stimulation signal providing heart response and the stimulation signal not providing heart response could be provided, relating to the same heartbeat , the first provided in order to stimulate the heartbeat and the second provided before the end of the refractory time after the first effective heart stimulation. The second stimulation signal has basically the same amplitude, shape, duration and antipolarizing pulses/scheme as the first one. The stimulation signal for providing and for not providing heart response should have the same mutual forn. However, a number of different stimulation signal forms common in the art could be used, such as a uniphase impulse or a biphase impulse, which either has the two impulses provided directly after each other or having a small time inverval between them. The Most preferred one is, however, the kind of biphase impulse 11 described in US-A-5,165,405 composed of a negative sub-pulse and a positive sub-pulse following thereupon after a pulse pause. The advantage of the biphase stimulation pulse over a monophase stimulation pulse (which may likewise be employed within the framework of the invention) is in the relatively fast reduction of the polarization phenomena produced in the tissue via the stimulation as a result of the positive sub-pulse following the stimulation-triggering, negative sub-pulse. Attempts to analyse the after-potentials of a stimulation complex can normally not be done due to the fact that response is provided from the stimulated heart. An analysis is needed in order to minimize the after-potentials and thus guarantee a correct detection of the evoked response from the heart as little as possible dependent on the polarization phenomena produced in the tissue by the stimulation pulse.

New analysis is needed for each change of some parameter in the stimulation impulse complex, such as amplitude, duration, antipolarization impulses (the second sub-pulse in a biphase impulse) etc. Such changes are done for instance in an autocapture pace, where compensation is needed on every new adapted energy level. Autocapture is an autosensing facility, which automatically performs a programming decrease in stimulation pulses delivered to the heart in order to determine a threshold value of the stimulation pulse providing heart response. At this autocapture test a programming decrease in output (pulse duration and/or pulse •duration) is done by the pacemaker system. When this test is terminated, the output of the stimulation generator, such as • the generator 3, returns to the initial setting. • • In accordance with the invention, an extra stimulance complex is delivered to the heart in its refractory phase, 50 to 1 - .. ••• • • msek after a stimulation providing a heart response,when needed or in regular intervals,as well as when the 0•• • stimulation parameters are changed. As mentioned above this • • • • ••• ••• • stimulation has substantially the same parameters and form as • • • • the first stimulation signal,and isineffective, i.e. the ••• • • P.• • ; ; V • • 011. •••••••••0 ••• 12 same after-polarization is obtained but without heart response. The after-polarization can then be minimized by adjusting the parameters at the antipolarization process.

Thus, the goal of the later stimulation signal at the second provision is to evoke the tissue in order to evaluate the polarisation of the stimulation after-potentials without response of the stimulation tissue (in the heart). The characteristics of the resulting waveforms or a complete sampled complex waveform is stored for comparison with the stimulated capture response. It is also within the scope of the invention to update data relating to the by averaging data (such as characterizing form) regarding resulting waveforms of the after-potentials without response from stimulations provided during the refractory phase of a plurality of heartbeat s for later use to compensate the after-potentials from a stimulation signal providing heart response in order to provide the waveform of the evoked response.

Further the waveform characteristics (amplitude, offset from baseline etc) could be used for control of antipolarizing pulse amplitude or duration in order to minimize the after-potentials.

FIG 2A and 213 show two voltage/time diagrams having different amplitude scales and time scales. They have been recorded during experiments on sheep. The lefthand curve HR in FIG 2A representing the waveform of the measured potential after a heart stimulation HRS giving a heart response, the next curve NC representing the waveform of the non-capture response to a stimulation signal provided within the heart refractory period, i.e. before the T-wave of the heartbeat signal. The stimulation signal must be provided at such distance from the T-wave, i.e. early in the refractory period, that the non-capture curve also is provided before the T-wave. However, it must be provided after the end of the heart response waveform HR, as shown in FIG. 2A. Both stimulation signals were chosen to be biphase impu.ses having the same form and amplitud,!. • 2.

•• • • ••• • * • • • ••■ • SO • • • • 13 The curves NC and HR are provided superimposed in FIG 28, which means that the curve HR is delayed in relation to the curve NC. A subtraction of the curve NC from the curve HR gives the searched evoked response (not shown).

FIG 3 shows a very simple circuitry for providing an evoked response curve representation from a heart response curve and a non-capture curve, which curves are provided near to each other, preferably within the same heartbeat , as shown in FIG 2A.

The signal from the line 4 (or 4') is first fed to a bandpassfilter 30 in order to reduce noise signal components, e.g. originating from the patient's movements and breathing as well as components originating from high frequency distur- bances. The output of the filter 30 comprises the waveforms HR and NC. The heart response waveform HR is fed to a delay circuit 31, which could have a controllable delay controlled by the control device 9. The delay is adapted to the time interval between the stimulation signals HRS and RPS. The output of the delay circuit is fed to the input of an HR-waveform detecting circuit 32 within a time window set by the control device 9. The length of the time window is related to the time of the curve HR.

The non-capture waveform NC is fed to the input of an NC-waveform detecting circuit 33 within a time window set by the control device 9 and having the same length as the time window for the circuit 32. The circuit 32 also inverts the curve waveform.

Each of the outputs from the circuits 32 and 33 are fed to a separate input of an adder 34, providing an evoked response • I curve at its output.If a compressed curveform of the evoked response curve is to be stored the output of the circuit • • is fed to a circuit for creating parameters representing the • • • • 4 • • • curveform. The parameter values are then fed to the control 0• • 0• • • • • circuit 9.

• • I• al • l • • • • • •• ••■•.••• •■■• 14 The obvious way to store a complex waveform is by sampling it, selecting a starting point, end point and a sampling speed. Such a solution for curves like HR and NC is described in the U.S. Pat. No. 5,165,405 mentioned above and could also be used in the device shown in FIG. 1 and in a simplified form for the evoked response curve in FIG. 3. Description of that technique is thus not included. However, a technique like that needs large memory area and high computer speed. The latter will undoubtedly result in high power consumption.

These difficulties could be overcome by performing some kind of data compression. A lot of data compression methods useful for an application of the descrbed kind are known to the person skilled in the art, but only one particulary suitable method is described below.

An embodiment of a first parameter computating circuit 36 shown in FIG. 4. The output from the circuit 35 is first fed to a bandpassfilter 37. The output of the filter 37 is fed to a differential circuit 38 to form the differential of the waveform signal. The output of the differential circuit is connected to a first circuit 39 detecting the extreme values (maxima and minima) of the differential signal together with the times for them. The output of the filter 37 is also directly connected to a second circuit 40 for detecting the extreme values (maxima and minima) of the waveform signal directly. The extreme values together with their timing relations are stored in a temporary storage 41 before they are fed to the control device 9. The control device 9 could then calculate other parameters from the first parameters :.1C1stored in the storage 41 in order to provide second para- meters better suited to make comparisons between curveforms . •than the ones provided in the circuit in FIG 4, as will be •." explained further below.

• • • ••••• ••• • • • • • NOS • • • • • 0 The circuit shown in FIG 4 could also be utilized for providing first compression parameters of the curves HR and NC. It is to be observed that a typical waveform from a heart within the detection window can be characterized by seven (or less) parameters by using this kind of technique instead of a sampled sequence of 40 samples or more in case of a sampled waveform signal.

As mentioned, the waveform after the stimulation signal not providing heart response could be used to update an average of the captured waveforms in a way known per se. This will significantly reduce the effect of noise and other disturbances. In this case the averaged non-capture curve NC from several heartbeat s could be used for subtracting the curve HR.

A number of waveform types preferably of the curve NC, but also of the curves HR and the evoked response curve, can be provided for and stored separately. The waveform character- istics or complete sample of a waveform could be stored in a storage in the detector unit 17, but could also be stored in the direct access storage device 11 connected to the control device 9. The waveform storage could be updated by control of the control device 9 at certain predetermined conditions, such as after detection of a certain waveform of the heart, or at predetermined intervals, or after a control signal from the telemetry unit or the like. At the occurrence of a complex waveform signal, the characteristics of this waveform is compared to each one of the stored complex waveforms. The one that best fits the just captured waveform is selected as the type of detection. Then, the microprocessor program can automatically be adjusted accordingly to provide control of the stimulation generator adapted to this type. The storage of this type of complex waveform could then be updated 9• .3(floating average). The exact way to perform features like • • this could he made in several ways obvious to the person ..skilled in the art.

• • • • • • "."However, an embodiment for performing the updating feature is • —shown in FIG. 5. The waveform signal is detected during a •••••time interval in a circuit 42 and filtered and amplified in a ••• filtering and amplifying circuit 43. First parameters of the .• • • • • .•• .waveform are created in a circuit 44. The output from the . . • . • circuit 44 are fed to the control device 9, which provides a •• -••• ••11•• ••• •••• •• • •• • ••••••• • •• •• •••416 •••• ••• 16 second parameter computation in J stage 45.

The second parameter computation could for instance be computation of inclination data of straight lines between stored times and extreme values between detected curve points pro- vided in accordance with the circuitry shown in FIG. 4.

An alternative is to make use of the fact that the curve forms have the same configuration, where only some calculat- able constants are different between detected curves re- presenting the same kind of stimulation. For example, regarding the curve NC, which could be different depending on different kinds of heart disorders, the curve form is rather simple and could be approximated in two steps, one related co the first slope from the stimulation time to the lower ex- treme value and the other from the lower extreme value continuing like an under compensated regulation curve up to a constant level. Constants approximating given curveforms to the actually derived curveform could easily be calculated.

As described, parameters from earlier derived curveforms could be stored in the storage 11. After the curve parameter calculation in step 45, the calculated parameters are successively compared to those earlier stored ones in step 46. The stored parameter complex coming closest to the parameter complex from the actually detected curve is chosen and fed to the control device 9 for giving information on the kind if actual heart disturbance. The actual parameter complex and tl-e found stored parameter complex, together with information from a number of earlier updatings, are used in a step 47 providing updating of the parameter complex according to averaging principles well known to a person skilled in the art and the averaged parameter complex is fed to the storage 11 to replace the found parameter complex. 36 While the invention has been described with reference to •••specific embodiments, it will be understood by those skilled ..

. • • Oesin the art that various changes may be made and equivalents .•• • •may be substituted for elements thereof without departin4 •• • • $ • a •••••••• 17 from the true spirit Ind scope of the invention given by the accompanying claims. In addition, modifications may be made without departing from the essential teachings of the invention as described in the accompanying claims.

Claims (12)

CLAIMS 1. An apparatus for tissue stimulation comprising: * stimulation signal generating means (3) for generating a stimulation signal to the tissue; * detector means (21) for acquiring an electrical waveform signal corresponding to the waveform of the electrical po- tential at said tissue; characterized in that the stimulation signals generating means (3) is adapted to generate the stimulation signal within the heart refractory period of a patient's heart after a heartbeat in order to provide a non-capture waveform signal representing polarization phenomena from a stimulation signal without heart response, and the detector means (21) acquires the non-capture waveform signal after the stimulation signal. 2. An apparatus according to Clain 1, in which the stimulation signal generating me,,s. (3) also provides a stimulation signal providing heart response of the patient's heart, and the detector means (21 acquires a heart response waveform, characterized by means for generating a-ference signal between the heart response waveform signal and the non-capture waveform signal in order to provide a waveform signal representing evoked response of the heart. 1. 2. • . 1. •• 3. An apparatus according to Claim 2, characterized in that . • 1. the stimulation signals generating means (3) provides the .. heart response stimulation signals and said stimulation ." . • • signals within the heart refractory period in lifferent • heartbeat periods of the heart. 4. An apparatus according to Claim 2, characterized in that ." . •the stimulation signal generating means (3) provides a first ..• • 0. 0stimulation signal providing heart response of the patient's 1. • • 4 • 0 heart before generating said stimulating signal within the :•• :••• 0.: 2. • • • •• •••• • 19 heart refractory period for the same heartbeat period. 5. An apparatus according to Claim 2 or 3, characterized in that the stimulation signal generating means provides heart response and the refractory period stimulation signals of the same order of magnitude. 6. An apparatus according to any one of the preceding claims, characterized in that the detector means (21), after each stimulation signal, detects a waveform signal during a predetermined time window. 7. An apparatus according to claim 6, characterized by storage means (11) for storirg detected waveform signals. 8. An apparatus according to claim 7, characterized by comparing means (34;46) for comparing an actual detected waveform signal (HR) after said stimulation signal providing heart response with stored waveform signals (NC) after said stimulation signals not providing heart response in said storage means (11) and choosing the one of said stored waveform signals coming closest to the actual detected waveform as the waveform character being detected. 9. An apparatus according to claim 8, characterized by means (47) for updating the waveform character being choosen with the actual detected waveform on an averaging basis. 10. An apparatus according to any one of the preceding claims, characterized by data compressing means (36;44,45) for providing parameters representing the waveform signals. 11. An apparatus accordingClaim 10, characterized in that said data compressing means ,,ncludes means (38 to 41) for only capturing the extreme values and the times for them for the detected waveform signal and a differential waveform signal of it. 1. • 2. • • 3. •• ' ••• 4. • • 5. • 6. •• 7. • • 8. • • 12. An apparatus according to any one of the preceding :; •• • : ;; ••• : ;; 1. • ••• ; 2. *: •• •••• ••• : • 3. • :• 4. • 5. .. . •• •• I .• 04 • 404, 12. An apparatus according to any one of the preceding claims, characterized in that said stimulation signal for providing a non-capture waveform signal is provided 50 to 150 msec. after a heart activating stimulation signal. :". 1. s 2. Io• • • 7, "I 3. • .4,1 4. • 5. • 6. • 7. • •• • ••• • 8. • 9. • • 10. • • 11. . • • •• • 12. • • • 13. • • • • • • •• •• • • • ••• 21 ABSTRACT The invention relates to an apparatus for tissue stimulation. A stimulation signal generating means for generates stimulation signals to the tissue. A detector means (21) acquires an electrical waveform signal corresponding to the waveform of the electrical potential at the tissue after a stimulation signal. The detector means (21) acquires a stimulation signal providing heart response of the patient's heart, and acquires a heart response waveform. The stimulation signals generating means (3) generates a stimulation signal within the heart refractory period of a patient's heart after a heartbeat in order to provide a non-capture waveform signal representing polarization phenomena from a stimulation signal without heart response. Means could be provided for generating a difference signal between the heart response waveform and the non-capture waveform signal in order to provide a waveform signal representing evoked response of the heart. lie•••••••■•■•••■••••■••••••••••••r•• ••••••••••••••••• 14. • • • 15. • 16. • • • • • I, IS ••• 17. • 11•0 18. •• 19. • • ••• ••• 20. • • • • • • • • *V • : :: ••• • 21. • ••• • • •• 22. • • •• • • •• • 23. •• 2 - DETECTOR UNIT -7– 1 STIMOLATI61-1 PULSE GEN."6 3 sraftd-ofroit CoN rit.04 E EffiFil TELEMETRY UNIT, 22 zi (t. 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