GB1108858A - Multimode cardiac pacer - Google Patents

Abstract

1,108,858. Transistor oscillator circuits. CORDIS CORPORATION. 20 Dec., 1966 [6 May, 1966], No. 56864/66. Heading H3T. [Also in Division A5] Cardiac pacer apparatus comprises a source able to generate electric pulses at a preset rate conformable to the normal heart beat, connections for applying the pulses to the patient's heart, and connections for applying a potential obtained from the heart so as to advance the timing of the pulses from the source. The potential may be obtained from the atrium or the ventricle of the heart and the apparatus may include a switch S to select one of these potentials. As shown, but with the switch S at the contact B, the apparatus receives a P-wave signal from the atrium electrode and this is passed through a transistor amplifier Q 1 , Q 2 and a blocking condenser C 4 to a monostable multivibrator Q 3 , Q 4 which serves as an atrioventricular (A-V) delay simulator. The signal causes the multivibrator to switch to its metastable state from which it returns (after 0À12 secs.) and then delivers a negative pulse through a diode D 3 to cause transistors Q 5 , Q 6 in a free-running multivibrator to conduct. An output pulse (about two milliseconds) is passed from the multivibrator, through a tap 2 on the resistors R 16 , R 20 , and a power transistor Q 7 to an electrode 3 at the ventricle. In the absence of a P-wave signal advancing the pulse generation, the free-running multivibrator delivers a pulse to the heart about 70 times per minute. The refractory period of the heart is simulated by the diode D 3 which, each time the transistors Q 5 , Q 6 conduct, is biased so that it is non- conductive and a further stimulating pulse cannot be generated until (e.g. 0À325 seconds later) the biasing charge has leaked away from the capacitors C 9 , C 10 . If the P-wave signal from the patient's heart is weak, the switch S may be moved to the position A, so that the apparatus provides either regular pulses derived from the free-running multivibrator, or pulses initiated by the QRS-wave signal received at the ventricular electrode 3. In any mode of operation, the apparatus does not provide a pulse to the heart while the multivibrator Q 3 , Q 4 is in its metastable state or during the refractory period determined by the bias on the diode D 3 . The entire pacer apparatus, including the mercury battery B1-B5, may be implanted in the patient's body and the switch S may be operated by magnetic, thermal, radio, or video means, or by mechanical shock. The electrode 4 located in the patient's abdomen may comprise a metal shield surrounding the implanted apparatus.