Patent GB-1352638-A (GB)
Title: Pacemaker
IPC: A61N1/05
Filed: 1971-04-19
Abstract: 1352638 Demand pacemakers F ZACOUTO 19 April 1971 [24 March 1970 2 July 1970 4 Sept 1970 4 Jan 1971] 24748/71 Heading A5R A demand pacemaker has a stimulating pulse generator producing stimulating pulses I, Fig. 1, at regular intervals X in the absence of a spontaneous systole (S.S. hereafter) and is controlled by means having a time delay circuit to delay occurence of a stimulating pulse for a waiting period Y upon detection of an S.S., the waiting period commencing at the detention of said S.S. and the length of said period being adjustable and determined in accordance with the pattern of occurence of the spontaneous systoles. In first form, parts A and B, Fig. 2, with or without part C, the length of the waiting period Y is dependent on the length of the time interval K between the detected S.S. and the directly preceding stimulated or spontaneous heart signal, Y being an increasing function of K over at least a substantial part of the range of variation of K. In a second form, the part C, Fig. 2, is connected to a known demand pacer which normally supplies stimulating pulses with a predetermined regular period in the absence of detected heart signals and gives a fixed waiting period K after each S.S. However, the part C intervenes to produce stimulation at a faster rate for a predetermined period if the part C counts a predetermined number of spontaneous systoles deemed to be dangerous within a predetermined number of all heart signals, spontaneous or stimulated, and if this occurs the waiting period between the last counted dangerous systole, giving rise to the faster stimulation, and the first of the faster rate simulating pulses is shorter than said fixed waiting period. The part C may also be used with the part A when the part A determines the waiting period unless the part C intervenes to stimulate at the faster rate. Y may be a continuous or discontinuous function of K and may decrease as K increases over a part of the range of K. Means are provided to inhibit actuation of the time delay circuit during a fixed period of between 200 and 400 m.sec., which is greater than the refractory period of the cardiac muscle, following each pulse I. The device may include means for identifying systoles of ventricular origin and for transmitting signals to means for adjusting the length of the period Y. Means may be included for detecting the average intranyocardial pressure in order to vary the amplitude of the pulses I and/or the period X or the relationship of Y to K if said pressure varies. The pressure detector may form part of a branch of an intraventricular catheter (602), Figs. 19-20 (not shown), located in the left ventricle and camprising a microdetector of pressure (610) surrounded by a liquid (611) and a flexible envelope (613) enclosing the liquid. An embodiment of the invention, Fig. 2, comprises parts A, B, and C. Part B has a cardiac catheter 1, electrodes 2, an input amplifier 3, filter 5, trigger 6, a monostable multivibrator M57 having a 5 m.sec. unstable period, a detector conductor 8, and a stimulating pulse generator 10 controlled by the parts A and C. Part A may comprises gates ET1, ET2, ET3, OU1, OU2, Figs. 3 and 4 (not shown), monostable multivibrators MS1 to 7, and a pulse generator 12 normally generating pulses at intervals of X=900 m.sec. and having a capacitance (CC) connected to a programmable unijunction transistor (PUT). In the absence of an S.S. generator 12 controls generator 10, via a shaping monostable M56, to produce pulses I. A time delay control device 16 includes a capacitor (CD) charged through a variable resistor, the potential on (CD) being applied via impedance adaptor 17 to the transistor (PUT). For 400 m.sec. following a pulse I gates ET1, ET2 and ET3 are blocked. devices A1, A2 inhibiting device 16 and generator 12 respectively for the first 200 m.sec. of this 400 m.sec. F or 350 m.sec. after the 400m.sec. gate ET2 is open and gates ET1, ET3 closed. After this 350 m.sec. ET1 is open and ET2, ET3 closed for 150 m.sec. 500 m.sec. after the start of charging the potentials on capacitor (CC), (CD), which start charging at different potentials, Vo and Vo' and have different charging rates, become equal and transistor (PUT) initiates a pulse I starting a new cycle of 900 m.sec. If an S.S. occurs during the first 400 m.sec. of a normally 900 m.sec. cycle operation of the device is not affected. If the S.S occurs between 400 and 750 m.sec., generator 12 is inhibited and capacitor (CC) starts charging again at potential Vo._ The later the S.S. the longer the potential on capacitor (CC) takes to equal that on capacitor (CD), i.e. period Y increases with K. The 750 m.sec. time period is selected to define the moment at which an S.S. is estimated to be no longer dangerous. If a delayed S.S. occurs after 750 m.sec., generator 12 is inhibited for 600 m.sec. via MS2 and capacitor (CC) does not charge but capacitor (CD) will have reached its peak potential during this time. Y is thus 600 m.sec. plus the time for capacitor (CC) to reach the peak potential of capacitor (CD) which is set at 700 m.sec. If an S.S. occurs between K=400 and 750 m.sec., a waiting period Y commences and if a further S.S. occurs before 350 m.sec. of period Y have elapsed anew waiting period Y commences. If the further S.S. occurs when MS4 is stable but MS5 is unstable, a waiting period Y=1300 m.sec. is started. If the further S.S. occurs when MS1, MS3, MS4 and MS5 are all stable a waiting period of 900 m.sec starts. If a third S.S. occurs before the end of this 900 m.sec a new waiting period of 900 m.sec. starts. Thus if tachycardia appears under these conditions the device does not intervene. Numerous other embodiments of the part A are described. ..The Part C, Fig. 2, comprises a step-by-step integrator 512, which counts all spontaneous and stimulated systoles up to a predetermined number and then resets itself and also resets a counter S16 counting only dangerous, i.e. premature, systoles passing via a gate, such as ET2 in the part A in Fig. 3, and a gate ET4. Part C also comprises flip-flops FF2, FF3, FF4, a gate OU20, an integrator 518, which when not cut-out integrates a potential over 15 secs. after which a pulse is emitted at 519, a pulse generator 520, trasmitting pulses via a line 11' to control the generator 10 in part B, and inhibitors A10, A20, A30. If counter 516 counts a predetermined number of dangerous systoles before being reset by integrator 512, which number is adjustable by switch K10, integrator 512 is inhibited and generator 520 operates to control generator 10 to produce pulses I at an adjustable rate between 90 and 150 p.p.min. for a period controlled by integrator 518 following which integrator 518 resets integrator 512 and counter 516 and inhibits generator 520, generator 10 then being controlled as normally by the part A. A push button K3 allows control of generator 10 by generator 520 to be stopped before expiry of the full period determined by integrator 518. Push button K2 allows generator 520 to be started before the predetermined number of premature systoles has been counted. The part C may be adapted to give a temporary increase in stimulation pulse frequency which takes place in several steps.