GB1424355A - Cardiac pacers - Google Patents

Abstract

1424355 Synchronous heart pacers KENT CAMBRIDGE MEDICAL Ltd 8 March 1973 [11 March 1972] 11501/72 Heading A5R [Also in Division H3] A synchronous heart pacer has electrodes 7 for sensing P-waves, electrodes 5, 6 for sensing QRS signals, gating means 12 which responds to the signals from electrodes 5, 6, 7 by blocking any similar simultaneously occurring signals so that only a pure P-wave signal without a QRS component passes to an output connection from gate 12 to electrodes 5, 6 and controls stimulation of the heart via electrodes 5, 6, and delay means 15 which introduces an A-V delay between sensing of the P-wave and stimulation of the heart via electrodes 5, 6. The electrodes may be disposed on a catheter 1 for insertion via a vein into the heart so that a tip electrode 5 and electrode 6, 1 cm. therefrom, lie in the right ventricle and electrodes 7, 1cm. apart and 12 cm. from the tip, lie in the atrium. More than two electrodes may be provided for each of the atrium and ventricle, or only one for each with a common indifferent return electrode. Atrial electrode signals pass via a variable gain amplifier 8 to give rise to corresponding pulses at the output of a generator 9. Similarly a generator 11 gives rise to output pulses corresponding to QRS complex signals and these output pulses block in the circuit 12, any output of circuit 9 occurring during a QRS complex. The unblocked pulses from circuit 9 act via control circuits, including the A-V delay circuit 15, on a pulse generator 16 to synchronise ventricular stimulating pulses produced thereby to the natural heart rate. The output pulses of generator 16 pass to an output amplifier 19, having a variable gain giving 20 mA. maximum amplitude pulses, via an inhibiter 18 which inhibits ventricular stimulating pulse generation for a period, e.g. 360 m.sec., after each detected QRS signal, which period extends over the T-wave. If the natural P-wave rate rises above an upper rate limit, the pacemaker reverts to a mode in which stimulating pulses are normally produced at said upper rate. If the natural P-wave rate falls below a lower rate limit, the pacemaker produces stimulating pulses at said lower rate. In a modification. Fig. 4 (not shown), a circuit may be selectively switched to a mode in which, when the pacer operates at the upper rate limit mode, the circuit omits a generated stimulating pulse each time this pulse falls behind the corresponding preceding P-wave by more than a predetermined amount to re-synchronise the circuit to the natural heart beat. Amplifier 19 includes an optical link for electrical isolation purposes. The timing of the various pulse lengths and spacings may be effected by use of multivibrator circuits or by using digital circuits with clock counters. A direct connection (not shown in Fig. 1) between circuit 11 and generator 16 produces a demand-mode of operation.