GB1350016A - Cardiac pacer device apparatus and method of testing thereof - Google Patents

Abstract

1350016 Pacemakers AMERICAN HOSPITAL SUPPLY CORP 1 Feb 1972 [31 Jan 1972] 4460/72 Heading A5R An implantable pacemaker is operative to supply the heart with stimulating pulses in the absence of natural heart-beats and with non- stimulating pulses in the presence of natural heart-beats, the non-stimulating pulses being detectable externally of the patient by means which prefereably gives an audible warning to indicate that the pacer is in working order when the heart is working normally. Signals from a ventricle electrode 10 are passed via an amplitude-limiter 12 to an amplifier 13, comprising transistors Q1-Q3, and thence to a pulse rectifier 14 comprising diode 41 and transistor Q5, which are operative in the presence of a positive pulse on electrode 10, and diode 36 and transistor Q4 which, together with transistor Q5 are operative in the presence of a negative pulse on electrode 10. Detected signals pass from rectifier 14 to a monostable multivibrator 15 comprising transistors Q6, Q7 and having an output on line 16 to an oscillator 18 and an outlet on line 17 to a monostable multivibrator 19. In the absence of a natural heartbeat, oscillator 18 is free-running, the capacitor 76 charging until it reaches a potential at which transistors Q10, Q11 conduct and capacitor 76 is discarged unitil its potential is too low to keep transistors Q10, Q11 conducting, the potential on capacitor 76 at which Q10, Q11 conduct being determined by a potential divider comprising resistors 80, 81, the potential divider being adjustable by means of a switch S so that when the switch is open or closed oscillator 18 generates pulses at 70 or 90-95 p.p.m. respectively. The output of oscillator 18 passes to an input A of a pulse shaping circuit 20 and in the absence of a natural heartbeat causes transistor Q16 in an amplifier 21 to conduct for about 1 m. sec. to discharge capacitor 100 through the heart to cause stimulation thereof. In the resence of a natural heartbeat the signal on line 16 causes premature resetting of oscillator 18 giving a signal at input A of circuit 20 in synchronism with the natural heartbeat, and the signal on line 17 causes the monostable multivibrator 19 to pass a signal to input B of circuit 20 causing a transistor Q14 therein to conduct, the inputs at A and B resulting in transistor Q16 conducting, and capacitor 100 discharging through the heart for only about 10 microsecs, the pulse to the heart having insufficient energy for stimulation but having a relatively large high-frequency content allowing it to be distinguished by the external detector. Oscillator 18 has a refractory period of about 300 m. sec. after it is reset during which it is not capable of being responsive to a signal detected on electrode 10, thereby reducing the sensitivity of the pacemaker to noise signals having a repetition rate greater than about three pulses per sec.