US3857399A

US3857399A - Heart pacer

Info

Publication number: US3857399A
Application number: US00126069A
Authority: US
Inventors: F Zacouto
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-03-24
Filing date: 1971-03-19
Publication date: 1974-12-31
Anticipated expiration: 1991-12-31

Abstract

Device for stimulating the heart comprises means for producing stimulating pulses at regular intervals and means responsive to spontaneous heart signals for controlling the transmission of said pulses to the heart in dependence upon the timing and magnitude of the spontaneous heart signals and/or the average intramyocardial pressure. In the absence of spontaneous heart signals, stimulating pulses are produced at predetermined intervals. When spontaneous heart signals occur, an adjustable waiting period is introduced in which to allow a second spontaneous signal instead of a stimulating pulse. The duration of the waiting period is varied as a function of the interval of time which separates two consecutive spontaneous detected signals (i.e., not separated by any artificially induced heart signal).

Description

Zacouto [111 3,857,399 [451 Dec. 31, 1974 HEART PACER' [76] Inventor: Fred Zacouto, 16, rue de la Convention, Paris l5eme, France 9/1972 Cole 128/419 P Primary Examiner-William E. Kamm Attorney, Agent, or Firm-Brisebois & Kruger 57 ABSTRACT Device for stimulating the heart comprises means for producing stimulating pulses at regular intervals and means responsive to spontaneous heart signals for controlling the transmission of said pulses to the heart in dependence upon the timing and magnitude of the spontaneous heart signals and/or the average intramyocardial pressure. In the absence of spontaneous heart signals, stimulating pulses are produced at predetermined intervals. When spontaneous heart signals occur, an adjustable waiting period is introduced in whichto allow a second spontaneous signal instead of a stimulating pulse. The duration of the waiting period is varied as a function of the interval of time which separates two consecutive spontaneous detected signals (i.e., not separated by any artificially induced heart signal).

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PATEHTEU 8 1 I914 SHEU OBBF 15 pyggmgg miss 1 I974 SHEET IOUF 15 HEART PACER SUMMARY OF THE INVENTION This invention relates to a method and apparatus for the electrical stimulation of the cardiac muscle.

Known devices for electrically stimulating the cardiac muscle include demand heart pacers which normally stimulate the cardiac muscle at a given frequency by transmitting thereto stimulating impulses at predetermined intervals corresponding to that frequency. When a spontaneous electrical signal (called a heart signal) from the cardiac muscle occurs which is detected by the electrodes and corresponds, for example, to a cardiac systole, the stimulation is interrupted after this signal for a constant waiting period regardless of whether the spontaneous systole is early or late, and regardless ofthe nature of this systole. Such devices, while currently in use, have a number of disadvantages.

In particular, they offer only an unpersonalized rerhythm to be established when it should on the contrary provide corrective intervention.

It is an object of the present invention to provide a process and apparatus making it possible to adapt the artificial electrical stimulation to the instantaneous condition of the cardiac muscle so as to supply a stimulating-response which takes into account whether the spontaneous systoles are or are not dangerous.

Another object of the invention is to provide a method and apparatus making it possible to take the cardiac muscle under control when a rapid and dangerous spontaneous rhythm tends to become established.

Another object of the invention is to provide a method and apparatus making it possible to let the heart beat at its own characteristic rhythm when nondangerous delayed spontaneous systoles occur.

Another object of the invention is to provide a process and apparatus for temporarily increasing the frequency of the stimulation when a dangerous rhythm tends to become established.

Another object of the invention is to differentiate the responses in dependence on whether the detected electrical signals are of ventricular or auricular origin.

Another object of the invention is to also provide means for adapting. the stimulating response to the hemodynamic conditions and/or the intramyocardial pressure.

Another object of the invention is to provide inexpensive and reliable devices .which may be simply adjusted to adapt the responses of the devices very precisely to the instantaneous state of the cardiac patient.

Yet another object of the invention is to provide a device of very simple construction, which is very reliable and consumes very little electrical energy so that it may be implanted in the body.

Other objects and advantages of the invention will appear from reading the following description of the invention, with reference to the accompanying drawings in which:

FIG. I is a schematic view of an electrocardiogram illustrating theprocess according to the invention;

FIG. 2 is a general schematic view ofa device accord- 2. ing to the invention comprising three parts A, B and C; FIG. 3 is an alternative embodiment of the part A;

FIG. 4 is a detailed circuit'dia gram of the apparatus shown in FIG. 3;

FIGS. 5 and 6 are graphical representations illustrating the operation of the device of FIG. 3;

FIG. 7 shows another embodiment of the part A; FIG. 8 is a circuit diagram of the delay means of FIG. 7;

FIG. 9 is a diagramatic representation illustrating the operation of FIG. 7;v

FIG. 10 shows another embodiment of the device of FIG. 7 adapted to detect ventricular systoles;

FIG. 11 is a diagram illustrating the operation of FIG. 10;

FIG. 12 is another embodiment of the apparatus of part A;

FIG. 13 is a circuit diagram of the device shown in FIG. 12;

FIG. 14 is a diagram illustrating the operation of the device shown in FIG. 12;

FIG. 15 shows another embodiment of the part A;

FIG. [6 schematically illustrates yet another embodiment of the part A;

FIG. 17 illustrates an example ofthe function Y of K;

FIg. 18 is a circuit diagram of the part C;

FIGS. 19, 20 and 21 show a device responsive to the intramyocardial pressure;

FIG. 22 is a schematic view of another embodiment of the part A; and

FIG. 23 is a diagram illustrating the operation of the device of FIG. 22. I

GENERAL DESCRIPTION OF THE PROCESS It is the object of the invention to provide a method of electrically stimulating the cardiac muscle by means of an automatic device comprising one or more stimulating and detecting electrodes, in which method electrical stimulating impulses having a predetermined frequency are transmitted to the cardiac musclein the absence of a spontaneous systole, and the transmission of a stimulating electrical impulse is'delayed for a predetermined waiting period when a spontaneous systole of at least a certain type occurs after a stimulating im pulse. The waiting period may be of two different durations, at least the shortest of which is less than, or at most equal to, the predetermined period, and the choice of one of the two durations is determined by the interval of time separating the spontaneous systole from the stimulating impulse which directly preceded it. The selected duration of said waiting period is an at least partially increasing function of said interval of time.

FIG. 1 represents an electrocardiogram illustrating the process according to the invention. On this electrical cardiogram three spontaneous systoles SS are shown. After the third spontaneous systole, there is no further spontaneous systole and, in a conventional manner, the device waits a certain period of time .I. When no systole occurs during this time, the automatic device, of the demand heart pacer type, transmits a in the absence of the appearance of extrasystoles or spontaneous systoles. After the third pulse I, a new spontaneous systole SS, is produced, which is separated from the immediately preceding pulse 1 by an interval of time K,. From this moment, in accordance with the invention, a waiting period is permitted to pass which is represented on the drawing by Y,. The drawing also shows at I the moment at which the next stimulating pulse would have taken place if SS, had not taken place. If, as shown on the drawing, no new spontaneous systole appears during the period Y,, the apparatus emits a stimulating pulse l, at the end of this period. Since no new spontaneous systole appears after I,, the device resumes its stimulation at the intervals X by transmitting pulses I as shown on the drawing. If, after such a pulse I, for example the first one on the drawing, a new spontaneous systole SS appears, a new waiting period Y, is initiated and if no spontaneous systole occurs during this time, a stimulating pulse 1 is transmitted to the cardiac muscle at the end of the delay period Y2.

In accordance with the invention, the waiting period Y (such as Y, or Y may have any one of several different values, these values being preferably the smaller as the interval of time, such as K, or K separating the spontaneous systole from the preceding stimulating pulse is the smaller. As shown on the drawing, the value Y, is smaller than the value Y because the period K, is less than the interval K More exactly, it willbe seen on the example shown on the drawing that Y, is less than the period X, and Y, is greater than the period X. Of course Y, and Y may both be less than the interval -X. On the other hand, in accordance with the invention, Y is an increasing function of K, when K increases over a part at least of its range of variation. Neverthe-,

less, in certain particular applications, Y may be a decreasing function of K over a certain part of the range of variation ofK.

When, before the end ofthe waiting period, generally represented by Y, a new spontaneous systole takes place, a new waiting period is established. In a first embodiment, this new waiting period is selected, like the length of the waiting period Y, as a function, this time of the interval of time separating the new spontaneous systole from the preceding spontaneous systole such as SS, or $8,. In a second embodiment of the invention, this new-waiting period is, on the contrary, fixed, and preferably equal to the predetermined stimulating period (X on the drawing). This means that if two directly consecutive spontaneous systoles take place, the second systole is treated as a stimulating pulse and the normal rhythm of stimulation at the predetermined intervals X is resumed.

In one particular embodiment of the invention the different values (such as Y, and Y of the waiting period are discontinuous, the highest values being generally attained for the longest delayed spontaneous systoles and the lowest values for the most premature systoles. Thus, by way of example, if the predetermined interval X is 900 milliseconds, the waiting period Y is 600 milliseconds if the interval of duration K separating the spontaneous systole from the immediately preceding stimulating impulse is less than or equal to 500 milliseconds, but equal to 800 milliseconds if K is between 550 and 750 milliseconds, and equal to 1,100 milliseconds ifK is between 750 and 900 milliseconds. The three different values of the waiting period are thus respectively 600, 800 and 1,100 milliseconds. It will be seen that in this particular example the highest value of the waiting period is longer than the interval X. It could, however, be equal to or less than this period. In all cases, as has already been said, the smallest value, at least, of the waiting period, is less than or exactly equal to the duration of the interval X.

However, in a preferred embodiment of the invention, the different values of the waiting period are arranged in a continuous manner and the waiting period is then a continuous, generally increasing, function of the interval of time separating the last pulse from the consecutive spontaneous systole. This function may, however, have steps, especially when the interval approaches the value of said predetermined period X, or on the contrary, when the interval K becomes very small.

Nevertheless, in certain applications, the continuous function Y of X may have a decreasing portion over a certain portion of the range of variation of K.

By way of example, FIG. 17 shows the graphical representation of this function. The ordinate shows the duration Y of the waiting period before stimulation, while the abscissa, decreased by 400 milliseconds, (for reasons of expediency hereinafter explained) shows the interval separating a spontaneous systole from the directly preceding stimulating pulse. The abscissa thus shows the value K-400 milliseconds. This curve may comprise horizontal segments, especially for the highest values of Y, which moreover, be greater than the period X.

When the largest values of the waiting period Y are greater than X, that is to say, greater than the period of stimulation in the absence of a spontaneous systole, the value of the interval K beneath which Y is less than X and above which Y is greater than X lies preferably in the second half of the period X which follows the stimulating pulse I directly preceding the spontaneous systole which causes a waiting period. This limiting value is shown at m on FIG. 2. Naturally, if Y is a continuous function of K, Y is equal to X and K is equal to the distance separating I from m.

In one embodiment of the process according to the invention the waiting period is always greater than the interval separating a spontaneoussystole from the immediately preceding stimulating pulse, or, in an alternative form already mentioned, from the immediately preceding spontaneous systole. This means that Y is greater than K. On the contrary, in another form of the invention, Y is always less than K. In this particular embodiment, it is obviously impossible to have in the electrocardiogram three spontaneous systoles SS separated from each other by identical periods of time, as shown at the left of FIG. 2. This alternative has the advantage of insuring energetic taking in hand of the cardiac muscle while leaving it the least possible time within which to produce spontaneous systoles. However, in a third embodiment, Y may be greater than K when K is large and less than K when K is small. It is thus possible to check premature spontaneous systoles while lengthening the waiting period for delayed spontaneous systoles, so as to encourage the cardiac muscle to beat at its own characteristic rhythm, but at a frequency which is not too high.

As has been seen above, the process according to the invention is put in operation when a spontaneous systole of at least a certain type appears. By systole" is meant any electrical signal of sufficient strength received on at least one of the electrodes, regardless of whether there is or is not a contraction of the cardiac muscle. Thus, in a preferred embodiment of the invention, the process takes into account only those spontaneous systoles which occur after the end of the refractory period of the cardiac muscle, and the systoles which take place during this period are not taken into account. This refractory period is, for a normal cardiac rhythm, for example on the order of 300 to 400 milliseconds after a spontaneous systole or an electrosystole. However, according to the invention, the choices of the type of spontaneous systole which is taken into account may also be a function either of the shape of the systole on the electrocardiogram or of the origin of the spontaneous systole. Thus, the systoles of a certain type may, for example, be limited to ventricular extrasystoles, which are often the most dangerous.

In this .case, the detecting electrode may, in accordance with the invention, amount to a waveform discriminator (which will be hereinafter described) or a plurality of electrodes may be used which are located in, or in contact with, the cardiac muscle, the first electrode exciteddetermining the origin of this spontaneous systole..

In accordance with an improved form of the invention, the stimulating pulse normally. delivered, or delivered after a waiting period according to the invention, may be at least doubled or its strength may be automatically adjusted, to increase it if a spontaneous systole appears, when the interval of time K is smaller. This assures more certain electrical control of the cardiac muscle, the electrical conductivity of which varies as a function of the instantaneous frequency of the. systoles.

In accordance with another improvement of the in-' vention the basic stimulating frequency, that is to say the predetermined period X, is increased in a temporary manner. Y'may also be diminished simultaneously to adapt it to this new period X. These alternatives may be selected in dependence on various factors as will be seen from the following.

Thus, if it is found that, despite the variation in the waiting period Y, too large a number of spontaneous systoles are produced, these spontaneous systoles are automatically counted, and when, for a predetermined number of systoles one has counted too large a number of spontaneous systoles, the base period X is automatically decreased.

In another alternative, this base period varies as a function of the intramyocardial pressure detected, as will be hereinafter described. It is also possible to detect by suitable pick-up means the hemodynamic characteristics so as to regulate the rhythm and shape of the stimulating pulses and to the waiting period.

GENERAL DESCRIPTION OF THE APPARATUS The invention alsorelates to a device for carrying out i the aforesaid process and comprises stimulating means controlled by a time base to deliver at a predetermined frequency electricalpulses for stimulating the cardiac muscle through at least one preferably cardiac elecmost equal to the predetermined waiting period, means for detecting spontaneous cardiac systoles comprising at least one preferably cardiac electrode and for conducting electrical pulses corresponding to the spontaneous systoles detected to said time delay means to initiate said waiting period, which corresponds to the state in which the delay means are found at this instant, and means to shift said time delay means successively from one of said states into the other as a function of the time which has elapsed since tht last stimulating pulse. Said stimulating means may be any conventional means adapted to transmit a stimulating pulse so at least one electrode when actuated by'said time base, or by said time delay means, at the end of the waiting period.

The time base may also be of a conventional type. It is thus possible to use as a time base, for example, a capacitance which charges itself periodically through a load resistance and actuates, when charged to a sufficiently high potential, a device such as a programmable unijunction transistor. It is also possible to use an astable switch or multi-vibrator which periodically initiates the stimulation. It is also possible, as an alternative, to use as a time base a pulse generator operating at a given frequency'and associated with any suitable counting means, for example, a flip-flop counter or step-by-step integrator. This counter when the number of predeter mined pulses has been counted, causes the emission of a stimulating pulse.

The delay means are responsive to the spontaneous systole pulses coming from the detecting means and may be in either'of two'different states, so as to initiate the waiting period corresponding to their state at the moment at which they are actuated, and actuate said stimulating means at the end of said waiting period. It is thus possible to use as delay means two condensers (i.e., capacitors), each comprising a charging resistor, and both connected to trigger means such, for example, as a programmable unijunction transistor, with one of g the condensers charging from an initial potential slightly higherthan the initial potential of the other condenser, but increasing in potential more slowly the other condenser, so that the potential of this other condenser in time overtakes thepotential of the first condenser, thus actuating a device such as the unijunction transistorpThe later the second condenser starts charging after the first condenser has begun to charge, the longer the time which will be required for it to overtake the potential of the first condenser. In this embodiment, the state of the delay means is thus determined by the potential which has beenattained by the said first condenser at the moment at which a spontaneous systolic pulse occurs to initiate charging of the second condenser. Of course, instead of using the charging periods of the condensers, it is possible to use their discharge periods.

In another embodiment of the invention, said delay means may consist of a single condenser associated with a discharge resistance. This condenser is charged through a charging resistance which may be the same as the discharge resistance, but which is preferably different. When a spontaneous systolic pulse takes place the charging of the condenser is interrupted and the condenser discharges through the discharge resistance up to the point at which the potential reaches a fixed value from which, through appropriate means, it causes a stimulating pulse to beproduced. It will be appreciated that the higher the charging potential is when this I pulse takes place, the longer the discharge to the fixed charged during the occurrence of a spontaneous systole.

In another embodiment of the invention said time delay means comprise several monostable multivibrators having different periods in the unstable state, at least one of which is less than said predetermined waiting period. These different multivibrators are connected to a electronic actuated rotary switch directing the spontaneous successive systolic pulses as a function of time to the different monostable multivibrators. The state of these time delay means is thus determined by the position of the rotary electronic switch.

In another embodiment of the invention, the delay means comprises a digital pulse counter. Said pulse counter counts a certain number of pulses from a pulse generator and, when it has counted the last of these pulses, actuates the stimulating means. The number of pulses which said counter must count is for example, determined by another number of pulses which has been previously counted, the state of said delay means being thus determined by the number of pulses previously counted and thus by the state of the counter.

This means for changing the state of one of said delay means as a function of the time elapsed since the last stimulating pulse may also be made in various ways. Thus they may comprise a source of potential and a charging resistance associated with a capacitance. The charging of said capacitance starts at the moment at which an electrical stimulating pulse takes place, or, as an alternative, at a predetermined time after such a pulse. The potential attained by said capacitance at the moment at which a spontaneous systole is detected thus determines thestate of the associated delay means, for example, a discharge resistance associated with the capacitance.

Thus when the delay means comprises two condensers, the means for changing the delay means from one state to another comprise a source of energy and the charging resistance of the slower condenser. The same is true of the variation utilizing only a single condenser.

In the variation in which said delay means comprises several monostable multivibrators which are made successively responsive, said means for changing the state -of one of these delay means comprises means advancing the rotary electronic switch at a predetermined speed from an initial position corresponding to the occurrence of a stimulating pulse. The means for changing the time delay means from one state to another may also comprise digital means including a pulse generator and a counter, for example one which is automatically reset to zero at each stimulating pulse. Beginning when a stimulating electrical pulse takes place, the counter recommences to count the pulses which it receives from the pulse generator. When a spontaneous systole occurs, the state of the time delay means is determined by the number of pulses counted. When the time delay means also comprise a counter, this second counter counts a number of pulses determined by the number of pulses which has previously been counted up to that time by the first counter. The number of pulses counted by the second counter may be, for example, the same as the number previously counted, in which case the waiting period may be equal to or different from the interval of time separating a spontaneous systole from the artificial electrosystole immediately preceding it. Of course, in all embodiments, it is advantageously possible to use common electrical or electronic components, for example for the time base, and/or delay means, and/or means for changing the state of any of the delay means.

The means for detecting spontaneous systoles comprises at least one detecting electrode, which may be the same as the stimulating electrode, and which is adapted to detect cardiac electrical phenomena. Preferably, temporary cut-off means are provided to avoid detection of the cardiac systole directly provoked by an articifical electrostimulation ES. Cut-off means may also be provided to prevent the detection of any cardiac electrical phenomena during a fixed time which follows a stimulating pulse ES, so as to avoid taking into account phenomena which take place during the refractory periods of the cardiac muscle. Finally, said detecting means may comprise different selecting means making it possible to insure the transmission to the delay means of only these pulses received from particular systoles, either as a function of the moment at which such a systole takes place, or as a function of its origin (auricular or ventricular). This is made possible by utilizing two electrodes and determining the position of the electrode which first detected the electrical phenomenon of this systole, or by using means responsive to a characteristic of the electrical systolic pulse, such as its shape, length, amplitude, etc.

The device which has been described may take several forms. It may be that a spontaneous systole detected which has triggered the time delay means will be followed by a second spontaneous systole before the end of the waiting period. In a first embodiment of the invention means are provided to return the different electronic components of the device to their original state so that a second systole is considered by the device exactly like an artificial stimulating pulse.

In another variation of the invention however, means may be provided to again trigger the time delay means to provide a waiting period corresponding to the state in which said provide a waiting period corresponding to the state in which said time delay means is found at the moment at which the second systole takes place. In this case said time delay means are preferably divided into two parts as will be hereinafter seen.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A. FIRST EMBODIMENT This first embodiment relates to a device comprising two condensers which are charged at two different speeds, the potential of one condenser being adapted to overtake the potential of the other condensenThis device is described with reference to FIGS. 2, 3, 4, 5

and 6.

Referring first to FIG. 2, the device according to the invention comprises three parts, A, B and C, of which only parts A and B will now be described. Part C is hereinafter described since it is not indispensable to the operation of parts A and B. Part B comprises an intracardiac catheter I which terminates in several electrodes 2, certain of which are positive, while others are negative. These electrodes 2 act both as detectors and as stimulators for the cardiac muscle. The electrodes 2

Claims

1. Method of electrically stimulating the cardiac muscle by means of an automatic device comprising heart stimulating and detecting means, which method comprises the steps of: A. detecting spontaneous heart signals, B. transmitting electrical stimulating pulses to the cardiac muscle at predetermined intervals in the absence of a spontaneous heart signal, C. sensing the time between the occurrence of an electrical stimulating pulse and the detection of a directly successive spontaneous heart signal, D. suspending the transmission of an electrical stimulating pulse for one of at least two waiting periods when a spontaneous heart signal is detected after a stimulating pulse, the length of at least one of said at least two waiting periods being no greater than said predetermined inverval, and E. selecting said one of at least two waiting periods in dependence upon said sensed time, the length of said selected waiting period being an increasing function of said sensed time over at least part of the range of variation of said sensed time.

2. A method according to claim 1 comprising the step of initiating a fixed further waiting period upon the detection of a spontaneous heart signal directly consecutive to a previous spontaneous heart signal.

3. A method according to claim 2 in which said fixed further waiting period is equal to said predetermined interval.

4. A method according to claim 1 comprising the steps of identifying those spontaneous heart signals which are of ventricular origin and initiating one of said waiting periods upon the detection of a heart signal of ventricular origin.

5. A method according to claim 4 which comprises the step of initiating a waiting period upon the detection of a heart signal of non-ventricular origin, the length of said waiting period for a heart signal of non-ventricular origin being different from that for the heart signals of ventricular origin.

6. Method as claimed in claim 1 which further comprises the steps of periodically counting all heart signals up to a predetermined total number, simultaneously counting the number of at least that portion of said spontaneous heart signals which are of an identifiable type, and temporarily decreasing the length of said predetermined intervals when the number of dangerous heart signals counted is greater than a predetermined number, said dangerous heart signals counted being those which take place after a period of time at least as great as the refractory period of the cardiac muscle and before the elapse of a fixed period greater than half of said predetermined interval.

7. Process as claimed in claim 6 in which said identifiable signals are those of dangerous typE and only said dangerous signals are counted simultaneously.

8. Process according to claim 6 in which twelve heart signals are counted and said predetermined regular interval is decreased when the number of dangerous heart signals counted during the time required to count said twelve heart signals is greater than a number between 1 and 3 inclusive.

9. A method according to claim 1 further comprising the steps of: A. sensing the time between the detection of a spontaneous heart signal and the detection of a directly successive second spontaneous heart signal, B. suspending the transmission of an electrical stimulating pulse for one of at least two different further waiting periods when said directly successive second spontaneous heart signal is detected and C. selecting said one of at least two further waiting periods in dependence upon said sensed time immediately preceding the detection of said directly successive second spontaneous heart signal, the length of said selected waiting period being an increasing function of the sensed time preceding the detection of said directly successive second heart signal over at least part of its range of variation.

10. A method according to claim 9 wherein said time subsequent to the detection of a spontaneous heart signal is measured by dividing it into at least two consecutive time durations.

11. A method according to claim 1 wherein said time consecutive to the occurrence of an electrical stimulating pulse is measured by dividing it into at least two consecutive time durations.

12. A method according to claim 11 in which said time subsequent to the occurrence of a stimulating pulse is divided into a plurality of consecutive identical time durations, each of which corresponds to a particular length of said waiting period.

13. A method according to claim 12 in which said time subsequent to the detection of a spontaneous heart signal is divided into a plurality of consecutive identical time durations, each of which corresponds to a particular length of said waiting period.

14. A method as claimed in claim 1 comprising the further step of avoiding said suspension of a transmission of an electrical stimulating pulse when a spontaneous heart signal is detected in a fixed period following each stimulating pulse, said fixed period being greater than the refractory period of the cardiac muscle.

15. A method as claimed in claim 14 in which said fixed period is between 200 and 400 milliseconds.

16. Method as claimed in claim 1 which comprises the step of sensing the time between two directly consecutive heart signals and initiating after the last of said sensed heart signals a variable period before transmitting the next stimulating pulse, said period increasing when said time interval increases and decreasing when said time interval decreases.

17. A method as claimed in claim 1 which comprises the steps of sensing the average value of the intramyocardial pressure and varying at least one of a. the intensity of the stimulation, and b. the relationship between said waiting period and said interval of time in dependence on said average value.

18. In a heart pacing method for electrically stimulating a cardiac muscle by means of an automatic device comprising heart stimulating and detecting means, said method comprising the steps of detecting spontaneous heart signals, starting a waiting period after the detection of a spontaneous heart signal, producing an electrically stimulating pulse at the end of said waiting period when no further spontaneous signal has been detected within said waiting period, and transmitting said stimulating pulse to the cardiac muscle, the improvement comprising the steps of: A. measuring the time subsequent to the detection of a spontaneous heart signal, and B. adjusting the length of said waiting period in dependence upon the measured time which corresponds to the detection of the corresponding spontaneous heart signal, the adjustEd value of said waiting period being an at least partially increasing function of said measured time.

19. An improvement as claimed in claim 18 wherein said time subsequent to the detection of a spontaneous heart signal is measured by dividing it into a plurality of consecutive time durations.

20. An improvement as claimed in claim 18 further comprising the step of avoiding said suspension of transmission of an electrical stimulating pulse when a heart signal is detected in a fixed period following the previous detected spontaneous heart signal, said fixed period being greater than the refractory period of the cardiac muscle.

21. An improvement as claimed in claim 18 further comprising the step of adjusting the length of said waiting periods to be shorter than said measured time.

22. An improvement as claimed in claim 18 further comprising a step of avoiding the adjustment of the length of said waiting period when the corresponding spontaneous heart signal occurs in a fixed period following a previous detected spontaneous heart signal and being greater than the refractory period of the cardiac muscle.

23. A demand type heart pacer comprising: A. detection and stimulation leads adapted to be connected to a heart, B. detecting means for detecting spontaneous heart signals, said detecting means being connected to said detection leads, C. pulse generator means connected to said stimulating leads and providing a stimulating pulse upon control thereof, D. pulse generator control means connected to said pulse generator means and including a time-base circular means operable to cause stimulating pulses from said pulse generator means at predetermined regular intervals in the absence of detected spontaneous heart signals, said time base circuit means being responsive to said detection means to cause staggering of said period upon detection of a spontaneous heart signal, said pulse generator control means further comprising: D1. time sensing means for sensing a time interval between a stimulating pulse and a successive detected spontaneous signal D2. time delay means for providing a variable waiting period after detection of a spontaneous heart signal, said time delay means being connected to said time sensing means and being responsive thereto for giving to said waiting period a value which is an at least partially increasing function of said time interval sensed by said time sensing means, one at least of said values being at most equal to said regular intervals, said time sensing means and time delay means being both connected to said detection means.

24. Device as claimed in claim 23 in which said time delay means comprises: A. a single capacitor (C, C3) associated with a discharge resistance and a trigger (PUT) connected to trigger the stimulation when the discharge potential of said capacitor attains a predetermined value, B. means for changing said delay means into at least two different states for each of which said waiting period has a different value comprising a charging resistance associated with said capacitor to charge said capacitor from its initial potential, and C. means (A202, A111, A222, Q3, Q4) to interrupt the charging and commence the discharging when a spontaneous heart signal of at least a certain type takes place, said capacitor being associated with trigger means (116) connected to trigger the stimulation when the charging potential of said capacitor has reached a predetermined potential.

25. Device as claimed in claim 24 in which said trigger means is responsive to the final value of the potential attained by said capacitor for triggering the transmission of a stimulating pulse and thus constitutes the time base.

26. Device as claimed in claim 25 in which said trigger means is a programmable unijunction transistor.

27. Device as claimed in claim 26 comprising means (121) for rapidly discharging and begiNning the recharging of said capacitor when a spontaneous heart signal takes place during the discharge.

28. Device according to claim 23 which comprises a bistable means (FF100) connected, on the one hand, to the detecting means to be switched into one position and, on the other hand, to a trigger (116) responsive to the charging and discharging potentials of the capacitor to be switched into another position when the potential of the capacitor becomes less than a predetermined value during its discharge, said bistable means being connected to cause the slow discharge of said capacitor through its discharge resistance when switched by the detecting means and cause the rapid discharge of said capacitor and the transmission of a stimulating pulse when switched by said trigger.

29. Device according to claim 28 in which said bistable multivibrator (FF100) is also connected to one input of a first gate (ET104), the other input of which is connected to the detecting means to open said gate during the discharge of said capacitor into its discharge resistance, said gate being connected to means (121) to rapidly discharge said capacitor without the transmission of a stimulating pulse, upon the detection of a spontaneous heart signal during the time said bistable multivibrator is in the position assuring the slow discharge of said capacitor.

30. Device according to claim 29 comprising means actuated by the detecting means to connect said bistable means to a second gate (ET102) connected on the one hand to the detecting means and on the other hand to gate actuating monostable means (MS102) for opening said second gate during a period less than said predetermined interval, said means also comprising a third gate (ET103) connected to open at the end of the open period of said second gate (ET102), the output of said third gate (ET103) being so connected to said device for rapidly discharging said capacitor as to abruptly discharge said capacitor without the transmission of a stimulating pulse when said third gate is open.

31. Device as claimed in claim 30 in which said third gate (ET103) is connected to said means for rapidly discharging the capacitor without the transmission of a stimulating pulse through monostable delay means (MS103) adapted to actuate said means (121) after a fixed time.

32. Device according to claim 30 in which the detecting means are connected to a fourth gate (ET100), said fourth gate being closed after a stimulating pulse for a period at least as great as the refractory period of the cardiac muscle by monostable means which is temporarily actuated by the stimulating pulse and connected to temporarily switch said gate actuating monostable means (MS102), temporarily opening first said first gate leading to said bistable means, and closing said third gate (ET103), after which said third gate (ET103) is opened, and said first gate leading to said bistable means is closed.

33. Device according to claim 24 which comprises means connected to the detecting means for selecting those heart signals of ventricular origin and directing them to the time delay means (HV1), said selecting means comprising a trigger (246) supplying a square wave signal when the detection potential resulting from the presence of a heart signal exceeds a predetermined value (U), said trigger being connected to switch, at the beginning of said square wave signal, monostable means (MS207) supplying, while switched, a potential to means (C201, D201, R201) which inhibits the transmission toward the time delay means of a terminal pulse when said monostable is not returned to its stable position, and permits the transmission of said terminal pulse from the trigger to said time delay means when the end of said signal supplied to said trigger takes place after the return of said monostable means to its stable position.

34. Device as claimed in claim 33 which comprises second time delay means for determining waiting periods different from those of said first mentioned time delay means, said second time delay means being connected to inhibiting means (C202, R202, D202) actuated by the potential transmitted by said monostable means to permit the transmission of the terminal pulse of said trigger to said second time delay means when said monostable has not returned to its stable position and prevent said transmission to the second time delay means when said terminal pulse from said trigger takes place after the return of said monostable to its stable position.

35. Device as claimed in claim 23 in which said time delay means comprises a plurality of monostable multivibrators having different unstable periods, at least one of which is shorter than said predetermined interval, said means for changing their state rendering said multivibrators successively responsive to the detecting means.

36. Device as claimed in claim 35 in which said means for changing state comprises a plurality of gates, the output of each gate leading to one of said monostable multivibrators, each of said gates having an input connected to said detecting means and another input connected to means for successively opening said gates.

37. Device as claimed in claim 23 in which said time delay means comprise a digital pulse counter (C400), a pulse generator being connected to supply pulses to said pulse counter from the moment at which a spontaneous heart signal takes place, and a memory determining the number of pulses to be counted prior to said stimulation.

38. Device as claimed in claim 37 which comprises at least one pulse generator (414), an adder-subtracter (C400) connected to said pulse generator, means for initiating the stimulation during the return to zero of said adder-subtracter, and control means (FF400) bringing said adder-subtracter into counting position at each stimulating pulse and switching said adder-subtracter to subtracting position when a spontaneous heart signal takes place.

39. Device as claimed in claim 38 in which said central means comprises a flip-flop (FF400) responsive to the detecting means.

40. Device as claimed in claim 39 in which said flip-flop connects said adder-subtracter to an oscillator (412) during said subtraction and said oscillator is connected to transmit the subtracting pulses thereto at an instanteous frequency different from the frequency of its adding pulses.

41. Device as claimed in claim 23 in which said time delay means comprises a pair of time delay devices connected to said detecting means by an alternating electronic directing means responsive to the spontaneous heart signals, a first one of said time delay devices being connected to initiate a variable waiting period promptly upon the detection of a spontaneous heart signal, while said heart signal simultaneously actuates means for changing the state of the other time delay means to permit it to initiate a variable waiting period when a new spontaneous heart signal is detected before the end of the waiting period of said first time delay device.

42. In a device as claimed in claim 23, the improvement which comprises first means for periodically counting a predetermined number of detected heart signals, second means for simultaneously counting the number of spontaneous heart signals, and means responsive to second counting means for temporarily decreasing the predetermined interval between stimulating pulses, said first counting means being connected to reset said second counting means to zero upon the return of the first counting means to zero.

43. Device as claimed in claim 42 comprising a bistable means and means for transmitting a switching pulse to said means when said second counting means have counted a number of spontaneous heart signals greater than the predetermined number, means connecting said bistable means to said fiRst counting means to reset it to zero when said bistable means is switched by said second counting means and means connecting said bistable means to said means for temporarily decreasing said predetermined interval of stimulation.

44. Device as claimed in claim 43 in which said means for temporarily decreasing said predetermined interval comprise a time base transmitting cardiac stimulating pulses at regular intervals less than said predetermined interval and control means (518) for alternately initiating and interdicting the operation of said time base, said control means being themselves actuated by the switching of said bistable means and being connected in turn to a second input of said bistable means to switch back said bistable means at the moment of interdiction of said time base.

45. Device as claimed in claim 44 in which said control means (518) are also connected to said second counting means to reset it to zero at the end of the duration of the operation of said time base (520).

46. Device according to claim 45 in which said second counting means are connected to means for identifying and selecting dangerous spontaneous heart signals which take place after a period of time at least as great as the refractory period of the cardiac muscle and before the elapse of a fixed period greater than half of said predetermined interval.

47. Device according to claim 23 in which the detecting means comprise a device responsive to the intramyocardial pressure including an intramyocardial element having a pressure detector surrounded by a liquid enclosed in a flexible envelope, said pressure detector being connected to at least one conductor leading to means responsive to the average pressure detected to strengthen the stimulation in the case of an increase in said average pressure.

48. Device as claimed in claim 47 comprising an intraventricular catheter in which said pressure detector is positioned in a trans-septal branch of said catheter.

49. Device as claimed in claim 48 in which said envelope is made of cloth having a very fine mesh.

50. Device as claimed in claim 47 in which said envelope is an impermeable membrane.

51. Device as claimed in claim 47 in which said liquid is polyvinyl pyrrolidone.

52. The device of claim 23 wherein said detection means comprises inhibition means for preventing transmission to said pulse generator control means after each stimulating pulse during a fixed period at least equal to the refractory period of the heart.

53. The device of claim 23 wherein said time delay means is divided into at least two different circuit means each of which, when selectively actuated, provides a waiting period different from the waiting periods of the others of said circuit means, said detection means comprising at least two different gate means, each gate means being connected to one of said circuit means, amd gate control means responsive to said pulse generator means for opening said gates successively after occurrence of a stimulating pulse, each of said gates being closed when the successive gate is opened.

54. Devices as claimed in claim 53 in which said gate control means comprises two monostable circuits connected to each other to switch successively one after the other.

55. Method of electrically stimulating the cardiac muscle by means of an automatic device comprising heart stimulating and detecting means, which method comprises the steps of: A. detecting spontaneous heart signals, B. transmitting electrical stimulating pulses to the cardiac muscle in the absence of a spontaneous heart signal, C. sensing the time between the occurrence of an electrical stimulating pulse and the detection of a directly successive spontaneous heart signal, D. suspending the transmission of an electrical stimulating pulse for one of at least two different waiting periods, when a spontaneous heart signal is detected after a stimulating pulse, E. selecting the length of said one waiting period in Dependence on said sensed time, the length of said waiting period being shorter than said sensed time.

56. A method according to claim 55 further comprising the steps of A. measuring the time consecutive to the detection of a spontaneous heart signal, B. suspending the transmission of an electrical stimulating pulse for one of at least two different waiting periods, when a spontaneous heart signal is detected after a previous spontaneous heart signal, C. selecting the length of said waiting period in dependence upon the time measure which corresponds to the detection of said spontaneous heart signal, the selected value of said waiting period being shorter than said measured time as an increasing function of said measured time.

57. In a demand type heart pacer comprising detection and stimulating leads adapted to be connected to a heart, detection means for detecting spontaneous heart signals, said detection means being connected to said detection leads, pulse generator means for providing, when actuated, a stimulating pulse to said stimulator leads, and pulse generator control means responsive to said detection means to start a waiting period on occurrence of each detected spontaneous heart signal before controlling said pulse generator means to cause a stimulating pulse, the improvement wherein said pulse generator control means comprises a time delay means divided in at least two different circuit means which, when selectively actuated, each provides a waiting period different from the waiting periods of the others of said circuit means, said detection means comprising at least two different gate means, each gate means being connected to one of said circuit means, and gate control means responsive to said pulse generator means for opening successively said gates after occurrence of a stimulating pulse, each of said gates being closed when the successive gate is opened.

58. A demand type heart pacer comprising: A. detection and stimulation leads adapted to be connected to a heart, B. detection means for detecting spontaneous heart signals, said detection means being connected to said detection leads, C. pulse generator means connected to said stimulating leads and providing a stimulation pulse upon control thereof, D. pulse generator control means connected to said pulse generator means and comprising time delay means providing a base waiting period after occurrence of a stimulating pulse and operating said pulse generator means at the end of said base waiting period when no spontaneous heart signal has been detected during said base waiting period, said time delay means comprising time sensing means connected to said detection means and responsive to the time interval separating a stimulation pulse from a directly successive spontaneous heart signal, for causing said time delay means to provide, upon detection of a spontaneous heart signal, a variable waiting period, the value of which is an at least partially increasing function of said time interval sensed by said time sensing means, one at least of said values being at most equal to the length of said base waiting period.

59. The device of claim 58 wherein: A. said time sensing means comprises: A1. a first capacitor, A2. a charging resistance connected to said first capacitor, A3. means for charging said first capacitor through said charging resistance, and B. wherein said time delay means further comprises: B1. a second capacitor, B2. a charging resistance connected to said second capacitor, B3. means for charging said second capacitor through said charging resistance, B4. a triggering means connected to said first and second capacitors and responsive to a predetermined potential difference between said first and second capacitors to cause a stimulating pulse from said pulse generator means, and B5. means connected To said detection means for resetting said second capacitor on the occurrence of a spontaneous heart signal detection, C. there being further provided means for resetting said first and second capacitors on the occurrence of a stimulating pulse and inhibiting charging of said second capacitor for a fixed time interval on the occurrence of said stimulating pulse.

60. The device of claim 59 comprising: A. a first and a second gate connected to said detection means, B. gate control means responsive to said pulse generator means for opening successively said first gate and said second gate after occurrence of a stimulating pulse, said first gate being closed when said second gate is being opened, said first and second gates being connected to said second capacitor for resetting said capacitor on occurrence of a spontaneous heart signal when one of said gates is in opened condition, and said second gate being connected to a further means for temporarily inhibiting charging of said second capacitor on occurrence of a spontaneous heart signal when said second gate is in opened condition.

61. The device of claim 60 in which said gate control means comprises at least two monostable circuits connected to each other to switch successively one after the other.