GB1149559A - Standby cardiac pacer - Google Patents

Abstract

1,149,559. Cardiac pacer apparatus. COR DIS CORP. 20 Dec., 1966 [6 May, 1966], No. 56865/66. Heading A5R [Also in Division H3] A cardiac pacer comprises a ventricle electrode connected to a source of electric stimulating pulses with an interpulse interval conformable to the normal heart beat rate, means under the control of a sensed physiological signal and acting upon said source for inhibiting the delivery of the pulses throughout a period at least equal to said interval and commencing with the sensing of said signal, and blocking means which is actuated both by a pulse delivered as a stimulus to the ventricle and by a natural physiologic signal originating in the ventricle for preventing a sensed physiologic signal from acting upon the source until after the termination of a simulated refractory period following the delivery of the stimulus. As shown, a free running multivibrator with transistors Q 6 , Q 7 provides stimulating pulses (A, Figure 2, not shown) at a resistor R 16 which are then supplied via a transistor Q 8 and resistor R 22 to the ventricle electrode 1. The multivibrator provides a pulse when a charge on a condenser C 8 derived from the battery B 1-5 leaks away. The circuit is also arranged to amplify, through transistors Q 1 , Q 2 , a QRS cardiac signal from the electrode 1 and to pass this signal to a monostable multivibrator including transistors O 3 , Q 4 , this signal causing the monostable multivibrator to change to its metastable state and be insensitive to further signals for a period corresponding to the refractory period of the heart. The monostate multivibrator, in changing to its metastable state, also provides a pulse through a capacitor C 6 to control switches S 1 , S 2 , which then connect the condenser C 8 to a battery B 6 so that the condenser is recharged and the pulses from the multivibrator are delayed and retimed. An alternative circuit (Figure 3, not shown) similar to that described above but without the auxiliary battery B 6 is retimed to a QRS signal from the electrode 1 by arranging that this signal advances the pulses of the multivibrator Q 6 , Q;, the first advanced pulse then being blocked by a transistor Q 5 . Since stimulating pulses are fed back into the amplifier Q 1 , Q 2 , a further transistor Q 9 is arranged to disable the transistor O 5 during the provision of stimulating pulses from the multivibrator Q 6 , Q 7 when QRS signals are absent. In a second alternative circuit (Figure 4, not shown), similar to that of the first alternative, the monostable multivibrator Q 3 , Q 4 can only be triggered by a positive pulse and is sensitive to only the trailing edge of a stimulating pulse fed back from the multivibrator Q 6 , Q 7 and the resultant pulse from the changing multivibrator O 3 , Q 4 is arranged to be ineffective to alter the free running multivibrator Q 6 , Q 7 .