GB1517328A - Cardiac pacer devices - Google Patents

Abstract

1517328 Cardiac pacers VITATRON MEDICAL BV 21 Nov 1975 47935/75 Heading A5R A demand type cardiac pacer includes means for detecting the occurrence of natural heartbeats and inhibiting the delivery of stimulus signals when they are detected, means for delivering stimulus signals over a range of rates including a predetermined normal rate, and means for reducing the rate of stimulus signals within a predetermined range below the normal rate for a plurality of delivered stimulus signals, so that natural heartbeats at a rate lower than the normal rate can be searched for and detected. In a circuit comprising a clock generator 10 and a counter 12 which produces stimulating pulses at a normal rate of 70 p.p.m. at the pacer electrodes, a counter 14 connected to the generator provides an input to a multivibrator 15, when it has counted 60 normal pulses to initiate the search period. The multivibrator 15 is thus rendered unstable and causes gate 17 to block pulses from the generator 12 and transmits multivibrator pulses via a gate 16 and a delay 18 to the pacer electrodes by way of gates 19, 20. The delay is such that two pulses at a rate of 52 p.p.m. reach the pacer electrodes, each pulse resetting the counter 12. Then, the multivibrator changes its state and ends the search period and in the absence of a detected heartbeat, pulses are supplied by the counter 12 to the heart at the normal rate. A detected heartbeat faster than the normal rate causes the counter 12 to be reset and continue. A natural heartbeat in the range 54-70 p.p.m. causes clock pulses to be fed to a counter 22 which counts at a rate of 52 p.p.m. and continually resets the counter 22. If there is no natural beat in the range 54-70 p.p.m. two stimulus pulses are generated but the gate 11 is enabled and the gate 12 disenabled thus reconnecting the counter 12 for normal operation. In an alternative analog circuit, the periodic searching is carried out every 5 minutes as determined by a counter (32), Fig. 2 (not shown) while stimulating signals are generated at a frequency below the normal rate but determined by a function generator (34). The function generator (34) may reduce the frequency linearly from 70 p.p.m. to 54 p.p.m. and back again over a period of 20 seconds as determined by a circuit (33). The programmed search is terminated by a natural heartbeat which resets the normal signal counter (31) and the 5 minute counter (32). A heartbeat in the range 54-70 p.p.m. resets a counter 42 but subsequent absence of such a heartbeat causes the counter (31) to supply normal rate pulses to the electrodes.