GB1416176A - Demand pacemakers - Google Patents

Abstract

1416176 Cardiac pacemakers MEDTRONIC INC 7 Nov 1972 [11 Nov 1971] 51369/72 Heading A5R A demand pacemaker has means for inhibiting a stimulation pulse in response to a natural heartbeat, means for progressively decreasing the energy of successive stimulation pulses which occur following or in response to a stimulated heartbeat and means for increasing the energy of a stimulating pulse in response to failure of a preceding pulse to stimulate the heart provided that the preceding pulse has energy less than the maximum stimulation pulse energy. A pulse generator 15 including a timing device emits periodic pulses and is reset by a signal from an amplifier 11 which senses natural or induced heart pulses so that the generator 15 only emits signals when the heart is not beating naturally or stimulated or the sensing mechanism is inoperative. The amplifier 11 is connected to the heart by an electrode 12 and a common electrode 26 of large area to prevent polarisation effects, the common electrode also being used with a second electrode 25 for stimulating the heart. An emission of a pulse by the generator 15, a transistor 20 powered by a battery connected by a positive lead 22 through an output voltage capacitor 29 and a negative lead 32 through a second transistor 31 produces a stimulation pulse. A second pulse generating circuit, comprising transistors 36, 42 together with a timing capacitor 48 and a reset transistor 50, provides in response to a signal from the generator 15, when a heartbeat has not been stimulated and sensed, a signal to the transistor 31 which thus produces an 'escape' pulse which charges the output capacitor 29 so that the next stimulation pulse is of increased amplitude. In the event that a heartbeat is stimulated, the generator 15 is inoperative, the second generating circuit will not operate and the energy of the next stimulating pulse provided by the capacitor 29 will be reduced. In an alternative circuit the collectors of the transistor 31 Figure 2 not shown, and the output transisitor 20 are connected by a lead (81) and a diode (80) so that when the heart misses a beat and the generator 15 emits a signal, a maximum energy pulse is applied to it within 100 millisecs at the same time as the capacitor 29 is recharged for increasing the energy of the stimulating pulses above the threshold value.