GB1484504A - Cardiac pacers - Google Patents

Abstract

1484504 Cardial pacers W GREATBATCH 7 Nov 1974 [7 Nov 1973] 48211/74 Heading A5R In a demand cardiac pacer providing pulses to an electrode 11 connected to a patient's heart, a combination of a quartz crystal oscillator 18 and a binary frequency divider 20 provides pulses at the rate e.g. of 72 per minute, and a delay switch 32 produces a signal corresponding to logical zero for a pre-determined period immediately following, and in response to, a natural heart beat sensed by the electrode 11 and thereby prevents any pulses occurring on an input line 22 of an AND gate during that period from being transmitted to the electrode 11. The delayswitch, however, produces a signal corresponding to logical one in the absence of a natural heart beat and as such, the pulses produced by the combination of the oscillator-divider are gated to the electrode 11. The delay switch comprises a full-wave rectifier including diodes (44, 46), Fig. 2 (not shown), so that the switch responds to both positive and negative natural heart beat signals, a parallel combination of a timing capacitor (50) and a timing resistor (54) determining the said pre-determined period, an inverter (66), and a transistor (60) which is non-conducting in the absence of a natural heart beat signal, but which starts conducting almost instantly following the occurrence of a natural heart beat for the said pre-determined period, which may be 0.3 secs. The quartz crystal oscillator 18 comprising a digital clock circuit, and the frequency divider 20 use integrated circuit chips. An electrode 12 at ground or reference potential, is either placed in contact with the heart or is subcutaneously connected to any other part of the body.