GB2014858A - Programmable demand heart pacer - Google Patents

Abstract

An implantable R-wave inhibited cardiac pacer has integrated digital logic circuits including programmable registers 12, 16 (210, 262, Fig. 4) to determine the pulse rate and width. A 5-3-4 code applied by an external pulsed electromagnet to a reed switch 20 (400, Fig. 5) unlocks a digital lock 18 so that rate register 12 can be reprogrammed to any value between 30 and 120 BPM. A 5-3-2 code allows the width register 16 to be reprogrammed, and the circuitry ensures that the programmed width can only lie between set limits. If a main timing circuit failure gives rise to a rate above 130 BPM, a protection circuit 32 feeds pulses to the heart 32 at half the rate from generator 28. A refractory circuit 42 prevents the generator being reset by a heart signal for 256 or 320 msec following a sensed natural beat or a pacing pulse respectively, noise sensing circuits operating from the last 64 mec of the refractory period and the pacer operating uninhibited, at its programmed rate in the presence of noise. Closure of switch 20 by a permanent magnet causes uninhibited operation at 100, 90 or 85 BPM depending on whether the battery is new, half-discharged or should be replaced, the pacer giving six uninhibited pulses at the programmed rate on removal of the magnet. <IMAGE>