GB1030380A - Cardiac pacer - Google Patents

Abstract

1,030,380. Electromedical apparatus. CORDIS CORPORATION. Nov. 24, 1964, No. 47726/64. Heading A5R. An electrical cardiac pacer circuit comprises an input responsive to a P-wave signal generated by the heart on contraction of the atrium to produce a trigger signal, which is delayed by a time corresponding to the normal interval between the auricular and ventricular systoles, and an output for producing a stimulation signal, the input and output being connected by means including an oscillator for causing the output signal to be synchronized with the delayed trigger signal. The heart is connected by a sensing electrode so that the P- wave signal is transmitted through amplifiers 10, 20 to a one-cycle multivibrator delay circuit 30. The transistor T 3 of the multivibrator is normally conducting and reception of the amplified signal causes the multivibrator to reverse slates so that the transistor T 4 conductor for a period determined by a capacitor C 5 and a resistor R 5 . During this period the multivibrator is insensitive to further signals from the heart. While the transistor T 4 conducts, a signal is transmitted to the blocking oscillator 40, the positive initial pulse being blocked by a diode D 2 and the negative pulse at the end of the conduction period of the transistor T 4 passing to the oscillator 40 as a delayed trigger signal. The oscillator 40 comprises a free-running multivibrator in which transistors T 5 , T 6 normally alternately conduct to provide stimulating impulses of a desired frequency. During normal operation, the blocking oscillator 40 receives the trigger impulse when transistor T 6 is conducting to render the delay circuit 30 inoperative for a predetermined period. However, reception of the trigger impulse when transistor T 5 conducts causes transistor T 6 to conduct, thus reducing to a desired new value the period of the oscillator 40. The stimulating impulse is transmitted via a pulse generator 50, comprising normally cut off transistors T 7 , T 8 arranged in a common feedback loop, and an amplifier 60 to the ventricle. The shunt transistor T 10 prevents a signal derived from the stimulating impulse received by the ventricle from influencing the operation of the circuit. If the P-wave signals or the input circuits 10, 20, 30 fail, the oscillator 40 provides stimulating impulses at its natural frequency, e.g. 60 pulses per minute. The circuit and batteries B 1 to B 5 are enclosed in a casing implanted in the patient's body, the casing being conductive to provide a local ground connection 61. The batteries are associated with a charging circuit (Fig.3 not shown) including a full-wave diode rectifier and an inductance, in which a rectified changing current may be produced by applying an alternating magnetic field to the outside of the body.