Implantable cardiac pacemaker having therapeutic and diagnostic functions.

0001The invention relates to an implantable pacemaker capable of fulfilling, in addition to its normal therapeutic function of automatic stimulation of the patient's cardiac insufficiency, a function of a posteriori control of the state and the degree of dependence of the patient with respect to the pacemaker ensuring this. therapeutic function.

0002Today, it is common to implant pacemakers fulfilling a therapeutic function in a patient with cardiac insufficiencies which could have been previously diagnosed, precisely with a view to overcoming these cardiac insufficiencies. In other cases, the diagnosis does not make it possible to demonstrate with sufficient certainty the cardiological origin of the disorders from which the patient suffers. In these hypotheses, there is just as much risk of not implanting a stimulator as of implanting one. In addition, it is hardly possible, a posteriori, to control the state and the degree of dependence of the patient compared to the pacemaker therefore the objective utility of this one.

0003We already know, to solve this problem, entirely extra-corporeal and elsewhere bulky recording devices. These are therefore troublesome and do not usually give reliable results.

0004The invention aims <img file="EP0004243A2_D0001.tif" />she offers a cardiac stimulator <img file="EP0004243A2_D0002.tif" />to be associated with a cardiac probe, comprising the box and in this means automatically ensuring the normal therapeutic function of the pacemaker with a view to overcoming the cardiac insufficiencies of the patient, characterized by the fact that it includes inside of the housing of the means ensuring a function of control, a posteriori, of the state and the degree of dependence of the patient in relation to cardiac stimulator ensuring its therapeutic function and, by the fact that these internal means ensuring a control function are controlled by removable external control means.

0005The other characteristics of the invention will result from its description which follows with reference to the arrexes drawings in which:<ul id="ul0001" list-style="none"><li>Figure 1 is a schematic view illustrate a cardiac st lator according to the invention; Figure 2 a schematic view of the logic module part pacemaker; Figure 3 is a schematic view illustrating the operation of the stimulator according to the general program; FIG. 4A is a diagram illustrating a possible sequence of the phases of a control program; FIG. 4B is a diagram illustrating another possible sequence of a program. control ; FIGS. 5A, 5B, 5c are three diagrams illustrating the records obtained thanks to the stabilizer according to the invention.</li></ul>

0006According to the invention, an implantable pacemaker is proposed, intended to be associated with a cardiac probe, not shown, comprising a housing, not shown, and in this means means ensuring automatically the normal therapeutic function of the pacemaker by joining the patient's heart failure. In addition, the tutor compotes, inside the same means housing asstructing a function of a posteriori control of the state and damage._ré dependence of the patient on the pacemaker ensuring its therapeutic function. External control means control the means fulfilling the control function.

0007The means fulfilling the therapeutic and control functions comprise: two electrodes 1a, 1b, intended to be connected to the cardiac probe by suitable means; an autonomous electrical energy source 2 such as a battery provided with connections 3a and 3b, one of which, ie 3a, for example is connected to the electrode la. Between the connections 3a and 3b, the following elements are placed in parallel: an amplifier 4 and its filter 5; a level 6 detector; a magnetic relay 7; a logic module 8; and an output stage 9 connected by a connection 10 to the electrode 1b. Connections 11, 12, 13, 14 respectively connect the amplifier 4 and its filter 5 to the level detector 6, the latter to the logic module 8, the magnetic relay 7 also to the logic module 8 and the latter on the stage of exit 9.

0008The amplifier 4 and its filter 5 have the function of amplifying and filtering the signals which are detected on the electrodes la, Ib. Its amplification coefficient is in particular of the order of 500 in tension approximately. The filter 5 is in particular of the low-band type centered on a frequency equal to or close to 60 hertz.

0009The level detector 6 operates a switching operation when the level at the output of the amplifier 4 and of the filter 5 exceeds a preset value, for example of approximately 0.5 volts. It follows from this device that any signal detected on the electrodes, tuned to the pass band and whose amplitude once amplified, will exceed the switching threshold of the detector 6, causes the switching of the latter.

0010The logic module 8, which will be described in more detail below, has the function of developing stimulation pulses in synchronization with the signals at the output of the level detector 6.

0011The output stage 9 has the function of delivering to the electrodes la, lb, pulses calibrated and shaped according to the signals at the output of the logic module 8.

0012The magnetic relay 7, in particular in the form of a flexible blade switch, is normally in the open circuit position. This relay is capable of being switched to the closed circuit position by removable external control means, in particular magnetic means, and in particular a member producing a magnetic field such as a permanent magnet.

0013The logic module 8 comprises a central unit 15, a memory 16 connected to the central unit 15 by a "bus" circuit 17 and comprising two registers Rp and Ri; a clock 18, a voltage doubling circuit 19 between the hoiloge and on the one hand, the central unit 15 and, on the other hand, the memory 16 an "OR" logic gate 20 connected to the "interruption" input 21 of the central unit 15, and, at the output of the level detector 6 and at the relay 7, via the connections 12 and 13. The door 20 is also connected to the two "indicator" inputs 22, 23 of the central unit 15. The central unit is naturally connected to the output stage 9 by 14.

0014All these circuits are preferably produced using MOS transistor technology. This notably allows operation at very low supply voltages and low current consumption at low frequency.

0015The clock 18 is made in any suitable manner. In particular, it is an oscillator produced from logic inverters and a resistance-capacitance circuit. It is supplied by the battery via a decoupling capacitor. Its frequency of oscillation depends on the charging time of the capacitor up to the threshold of the logic step.

0016The voltage doubler is produced using two capacitors arranged alternately in parallel and in series at the oscillation frequency of the clock. A sufficient supply voltage is thus obtained for the logic module even when the voltage of the clock supply battery decreases.

0017The central unit by microprocessor operates in a conventional manner on the basis of control logic, an arithmetic and logic calculation unit, program and data registers and an accumulator register. It carries out a program the instructions of which are written in the memory, the progress of which is controlled by the clock 18.

0018As already mentioned, the stimulator, as just described in its functional elements, can fulfill its normal and habitual therapeutic function which corresponds to a general program and, also, a control function corresponding to a particular program.

0019The characteristics of the general program are as follows:<ul id="ul0002" list-style="none"><li>In the absence of autonomous cardiac activity detected on the electrodes, the device emits stiumation pulses at a known and determined regular period T, in particular between 500 and 1,300 milliseconds for example.</li></ul>

0020Any detection of an autonomous cardiac activity on the electrodes, causes the simultaneous recycling of the device for a new period T.

0021After each stimulation pulse, or each wave corresponding to an autonomous cardiac activity, a so-called "refractory" period runs such that any wave detected during this specified period causes the recycling of the stimulator. If, however, a first wave is detected during this period, the refractory period is extended by a second refractory period. This arrangement is such that the electromagnetic parasites having a repetition period less than the refractory period do not cause the stimulator to be recycled.

0022If the magnetic relay 7 is short-circuited by the action of the external control means, the recycling is made inoperative and the stimulator permanently emits pulses with the period T.

0023In FIG. 3, the operation of the stimulator according to the general program is illustrated.

0024In Al is represented an autonomous wave. No autonomous cardiac activity following this wave Al, the stimulator emits, at the end of the period T, a stimulation pulse Sl. Similarly, no autonomous wave appearing the stimulator emits, at the end of the period T after S1, a stimulation pulse S2. If, at the end of a time tl less than T, an autonomous cardiac wave A2 appears, the pacemaker is recycled from this moment. If after wave A2, an autonomous cardiac wave A3 appears at the end of a time t2 less than T, the pacemaker is still recycled to A3. If therefore, after A3, a cardiac pause appears which is at least equal to T, the pacemaker emits a stimulation pulse S3, at the end of the period T after A3. The impulse. sion S3 runs the refractory period of duration_T . We observe that the wave s1 intervening after S3, in the refractory period_T, does not cause the stimulator to be recycled so that a stimulation pulse appears after S3, at the end of the period T. Similarly, the S3 pulse causes a refractory period of duration to run. _T during which a wave s2 appears which on the one hand does not cause the recycling of the stimulator and on the other hand causes a second refractory period of the same duration to run _T during which a s3 wave may appear which, like s2, does not cause the stimulator to be recycled.

0025The specific program has the following characteristics:

0026- The first stimulation pulse is delivered after a cardiac pause due to a lack of autonomous cardiac activity for a duration 2T equal to twice the normal stimulation period (For example, if the period T is equal to 1,000 milliseconds, the stimulator will wait 2,000 milliseconds before stimulating.<ul id="ul0003" list-style="none"><li>- After this first stimulation pulse, a second stimulation pulse is issued in the absence of any autonomous cardiac activity after a duration of 2T.</li><li>- When a first and a second successive pulse such as those which have just been described have been delivered, the stimulator emits successive pulses at a period T.</li><li>- As long as a first and a second successive pulse have not been emitted, as indicated previously, the stimulator operates according to the particular program described. On the contrary, as soon as the stimulator has emitted the first and second successive pulses, as described, it operates not according to the particular program but according to the general program already described.</li></ul>

0027FIGS. 4A and 4B illustrate two possible sequences of the particular program.

0028In FIG. 4A, there is at Al an autonomous wave. In the absence of cardiac activity, the first stimulation pulse SI appears at the end of a duration 2T after Al. In A2 appears an autonomous heart wave at the end of a duration less than 2T after S1, of even with regard to the autonomous wave A3 successive to A2. Given the appearance of waves A2 and A3, the stimulator is re-cycled and the stimulation pulse S2 appears in the event of a cardiac pause at least equal to 2T. The successive autonomous waves A4, A5 and A6 follow the stimulation pulse S2 and therefore predict the recycling of the stimulator. In this hypothesis, the stimulation pulses S1 and S2 constitute two first isolated pulses in the sense that the pulse S2 does not constitute a second pulse successive to the pulse S1.

0029In FIG. 4B, another possible operation is shown in which there is A'l an autonomous heart wave, in S'l a stimulation pulse occurring after a duration 2T from A'l Si, after the pulse S ' l, no autonomous cardiac activity appears (unlike ace that we have seen previously in A2 and A3 with reference to FIG. 4A) and this, for a period equal to 2T, the pacemaker emits a second stimulation pulse S'2 successive to S'l and separated from the latter in the time of 21, 61 at the end of the S'2 implusion, no autonomous cardiac activity appears and this during a duration equal to T the sttaletaur emits S'3 a stimulation pulse at the end of the period T after S'2. At this time, the pacemaker follows the heart program so that it normally emits pulses at period T, in the absence of any autonomous cardiac activity. For example, it is illustrated in A'2, an autonomous cardigaue wave occurring after S'3, at the end of a duration less than T. The stimulator therefore recycles from A'2 and emits for example in S '4, after a duration T after A'2, a stimulation stimulation. In this case, the stimulator emitted in S'1, S'2, and S'3, three successive strokes according to the particular program. As already mentioned, in the case of FIG. 4A, the device has not emitted successive pulses according to the particular program, continues to apply the latter. On the other hand, in the case of pure 4B fi, the stimulator stops working according to the particular program and works according to the program

0030the number of stimulation pulses delivered is recorded in the register Rp of memory 16. More precisely, are recorded in the register Rp:<ul id="ul0004" list-style="none"><li>either the number of stimulation pulses delivered if the stimulator has never delivered at least two successive pulses or a first and a second pulse according to the particular program. This case corresponds to the assumption in Figure 4A. In this case, the two pulses S1 and S2 are recorded. These two impulses correspond to the two times when the patient has had a pause._eventricular with a duration greater than twice and less than four times the stimulation period. In this case, the pulse S1 corresponds to the ventricular pause A1, A2 and the stimulation pulse S2 to the ventricular pause A3, A4 which both effectively have a duration at least equal to 2T and less than 4T.</li></ul>

0031Or the number of successive stimulation pulses delivered. This hypothesis corresponds to FIG. 4B where the three successive pulses S'1, .S'2 and S'3 are emitted. This number characterizes the duration of the first ventricular pause greater than 4T. In this case, it is the ventricular pause A'1, A'2 which, in the case of FIG. 4B, has a duration of between 5T and 6T.

0032The values ​​entered in the Rp register are as follows: a first isolated stimulation pulse will write 1. A second isolated stimulation pulse will write 2. A third isolated stimulation pulse will write 3 and so on for the isolated stimulation pulses. If, for example, after the third isolated stimulation pulse, the device emits a successive stimulation pulse, it will be entered in the register not 4 but 2. In other words, the content of the register Rp is reset to 2, as soon as a second successive pulse is delivered. If after this pulse, the device emits other successive pulses, these will be respectively noted 3,4, etc.

0033Registration ceases in one of the following two cases:<ul id="ul0005" list-style="none"><li>Appearance of autonomous cardiac activity after at least two successive stimulation pulses delivered.</li></ul>

0034Filling the capacity of the Rp register.

0035The register Ri is in correspondence with the register Rp and indicates whether the stimulation pulses whose number is entered in Rp are of the isolated type (case of FIG. 4a if the stimulator has not delivered two successive pulses) or successive (case in Figure 4B).

0036Reading of the recordings is carried out as follows:<ul id="ul0006" list-style="none"><li>Thanks to the removable external control means such as a permanent magnet, the magnetic relay 7 is switched to the closed circuit position.</li></ul>

0037The succession of stimulation periods obtained is then measured.

0038In the case where no recording has taken place, we obtain a representation such as that illustrated in FIG. 5A where the second wave is separated from the first by 2T and the successive waves separated from each other by the period T .

0039Assuming that the stimulator has recorded several isolated stimulation pulses, a representation is obtained such as FIG. 5B which corresponds to the recording of two stimulation pulses, in this case, the following successive time intervals are obtained: 2T , 2T, 2T, T, T, T, etc.

0040In the case where several successive stimulation pulses have been recorded, a recording of the type shown in FIG. 5C is obtained for two successive pulses. The succession of pulses is then done according to the time intervals T, 2T, 2T, T, T, etc.

0041It is therefore clear that the only examination of the records makes it possible, by measuring the intervals between the pulses, to determine whether these correspond to successive pulses or to isolated pulses. We can therefore deduce, as we saw previously, on the one hand, the number of times the patient has had a cardiac pause of a duration greater than twice and less than four times the stimulation period and, on the other hand, the length of the first cardiac pause lasting more than four times the stimulation period. These elements therefore make it possible to control the state and the degree of dependence of the patient in relation to his pacemaker.

0042There are also provided means for erasing the recordings and declutching the recording mechanism externally controlled.