GB1316291A - Electronic heart pacing apparatus - Google Patents

Abstract

1316291 Pacemakers MEDTRONIC Inc 11 June 1970 [12 June 1969 7 Jan 1970] 28297/70 Heading A5R [Also in Division H3] A demand type heart pacemaker includes means for sensing natural heartbeats, means for generating stimulating pulses at a selected repetition rate in the absence of natural heartbeats, and means responsive to the occurence of a natural heartbeat for delaying the generation of the next output pulse until a waiting period greater than the inter-pulse period of pulses at said selected rate has expired following the sensing of the natural heartbeat. When the pacer is uninhibited, a capacitor 35 charges until it reaches a potential at which a transistor 30 conducts, discharging capacitor 35 and resulting in conduction of a transistor 15 to discharge a capacitor 74 through the heart. In such operation a capacitor 39 remains charged and said selected rate is determined by the charging time of capacitor 35, which capacitor is large compared to an R.F. by-pass capacitor 34, the output pulse-width being determined by the time taken for a capacitor 28 to charge sufficiently to turn off a transistor 20. A natural heart beat is detected by an amplifier comprising transistors 65, 60 and 48 and causes a transistor 40 to turn on to discharge capacitors 39 and 35. Capacitor 39 is thus charged via resistors 36, 37 with capacitor 35 thus lengthening the time needed for capacitor 35 to charge to turn on transistor to said waiting period. In the absence of further natural heart beats, stimulating pulses following the first stimulating pulse after the detected beat are all separated by said inter-pulse period. A circuit comprising diode 79 and transistor 55 prevents the pacer from being inhibited by its own output pulses. The normal stimulating pulse repetition rate may be adjusted by adjusting resistor 36 and said waiting period may be altered by varying the valve of capacitor 39. In the presence of repetitive noise signals occurring at a rate above the upper limit of normal heart beat rates, the timing circuit comprising capacitor 35 is at first reset by transistor 40, but continuous resetting is prevented by charging of a capacitor 44 by detected noise signals of one polarity to block passage of further signals of this polarity to transistor 40, noise signals of the opposite polarity being shunted by a diode. In the presence of such noise signals the pacer provides asychronous stimulation at a rate lower than the normal rate and at a repetition rate which is approximately equal to the sum of said waiting period and a refractory period of the heart-beat sensing amplifier. In a modified embodiment, Figure 2 (not shown), the timing period of a timing circuit of the stimulating pulse generator is changed from an intrinsic valve obtaining in the presence of natural heart beats to a shorter timing period in the absence of natural heart beats by charging a capacitor (103) from both a power supply and from a previously charged capacitor (111) in such absence, but only from the power supply in such presence.