GB2070937A

GB2070937A - Heart stimulating apparatus

Info

Publication number: GB2070937A
Application number: GB8008102A
Authority: GB
Original assignee: ELELCTRONICS Ltd M G
Current assignee: ELELCTRONICS Ltd M G
Priority date: 1980-03-11
Filing date: 1980-03-11
Publication date: 1981-09-16
Also published as: FR2477886A1; FR2477886B1; GB2070937B

Abstract

A demand-type heart pacer can be operated in a fixed rate test mode and includes a synchroniser 4 operative to synchronise the start of the fixed rate mode to occurence of a spontaneous heart beat, thereby reducing the chance of a test rate stimulating pulse occuring during the vulnerable T-wave period. The test mode is selected by an external device 1, eg. magnetic, electromagnetic, acoustical, optical or piezoelectric. If the test mode is selected between two spontaneous beats 31, 32 (Fig. 3), synchroniser 4 responds to beat 32 to inhibit heart beat sensing circuit 6 and to cause pacer timing circuit 5 to generate stimulating pulses 33, 34 at a fixed higher-than-normal rate, the first such pulse 33 occurring at the fixed rate interval after beat 32. When a predetermined number, eg 2, of fixed rate pulses have been generated, synchroniser 4 causes timing and sensing circuits 5, 6 to revert to normal demand operation. If the request for the test mode is still being applied, synchroniser 4 causes the start of a further sequence of the predetermined number of fixed rate pulses 36, 37 to be synchronised to the spontaneous beat or demand-generated stimulating pulse 35 next following the last pulse 34 of the previous test rate sequence-this operation repeating until the test mode request is removed. Sequencer 4 may have CMOS circuitry, including a shift register to count the predetermined number of pulses (Fig. 4). The pacer can be used to terminate tachya rhythmias by applying a stimulating pulse in the diastolic period of the heat beat and repeating such pulser, or required, at predetermined intervals, the pulser being synchronised with the spontaneous heart beats. <IMAGE>

Description

SPECIFICATION Heart stimulating apparatus The present invention relates to heart stimulating apparatus, and more particularly to implantable inhibited types of heart stimulating apparatus.

Standby or demand or inhibited or synchronized type cardiac pacemakers are provided with means to covert the standby or sensing state to a fixed predeterminated pacing rate mode which permits the performance of several tests of the pacer, and of its system, such as tests of the cell or battery voltage, which is indicated by the deviation in the testing rate or/and stimulating spike width; the stimulation threshold; the electrode system malfunctions; and other parameteric measurements.

This fixed predeterminated testing rate induces competition between the cardiac spontaneous rhythm and the pacer stimulating rate.

This competition may develop a spike-on-T phenomenon, this letter is known as a cardiac vulnerable period, and may be dangerous in case of active coronary insufficiency. It is an object of the present invention to reduce this danger by introducing synchronization of the fixed testing rate with the spontaneous cardiac rhythm.

According to a first aspect of the present invention there is provided heart stimulating spikes to the heart of a patient when required, and to refrain from delivering such spikes upon sensing of normal heart beats, in combination with electrode means for sensing such spontaneous heart beats, said apparatus including externally actuted test rate mode receiver; and means for synchronizing said test rate mode to the spontaneous heart beats.

According to a second aspect of the present invention there is provided a method of terminating cardiac tachyarrhythmia which comprises synchronizing the closest time of the application of the stimulating spikes with the diastolic period of the heart beat, and repeating such application of stimulating spikes at a predetermined frequency until the desired result is attained.

Additionally, there is a need for heart stimulation in order to terminate tachyarrhythmias by reverting to normal sinus rhythm. Today this is done by stimulating the heart with high frequency electrical spikes until the desired conversion occurs. Application of the synchronization system carries the stimulation spike into the diastole period, thus, terminating the tachyarrhythmias more efficiently and without the danger of overstimulation.

There may be provided means for terminating tachyarrhythmias, in patients with implanted demand or other pacemakers, and this by means of application of heart stimulation at a predetermined higher frequency. There may be provided means for applying a stimulating spike for terminating such cardiac tachyarrhythmias, said spike being applied into the diastolic period, and means for repeating such stimulating spikes, as required, synchronized with the heart beat rate, and for repeating such stimulation at predetermined intervals.

The novel device is based on conventional circuitry, and preferable on C-MOS technology logic circuits which exert a low current drain on the energy source. Linear circuit means may also be used for such devices.

The present invention will now be described in greater detail by way of example with reference to the accompanying drawings, wherein: Figure 1 is a block diagram of one preferred form of heart stimulating apparatus; Figure 2 is a flow diagram illustrating the signal processing of the synchronizer; Figure 3 is a ECG pattern illustrating the performance of the synchronizer in the case of two predeterminated stimulating spikes, the intervals being given for reference; and Figure 4 is a logic circuit diagram based on C-MOS circuitry for n predeterminated stimulating spkes, where n is any desired integer.

Referring to Fig. 1, the heart stimulating apparatus for stimulating a heart 10 comprises: an externally activated magnetic device 1; a test mode request receiver 2; a synchronizer 4 pacer timing circuits 5; sensing circuits 6; an output spike driver 9; a gate 12; and a two way isolating gate 13. The output of the receiver 2 is fed to one input of the synchronizer 4, the second input of which receives synchronizing signals on a line 7. The output of the synchronizer 4 is applied to both the pace timing circuits 5 and the sensing circuits 6 as an inhibit control. The output of the pacer timing circuits is applied to the output spike driver 9, whose output in turn is applied to the heart 10 through the gate 13 and to gate 12 on a line 11. The heart beats from the heart 10 are sensed by the sensing circuits 6 being fed back through the two way isolating gate 13.A reset line 14 is connected between the gate 12 and the pacer timing circuits 5. Upon a request for a testing rate mode, which is made by activating the magnetic device 1 and its associated receiver 2, the synchronizer 4 responds by sensing the synchronizing signals on the line 7. These signals are of one of the following kinds: (a) either the heart beat activity segment detected by sensing circuits 6 or the stimulating spike delivered by output spike driver 9 which is fed back via the line 11. The first of these signals activates the synchronizer 4 for the predeterminated number of stimulating spikes, thus the synchronizer 4 responds by inhibiting the sensing circuits 6 via the line 8 for this period i.e. until the predeterminated number of stimulations have been executed. Simultaneously, the pacer timing circuits 5 are shifted to a higher stimulating rate.

The signal processing of the synchronizer 4 is shown in greater detail in the flow chart of Fig. 2. The shaped blocks 20, 21 and 23 indicate positions where decisions are taken.

These decisions are as follows: (a) Block 20: Has request for fixed rate test been made; (b) Block 21: Has spontaneous heart beat occurred; (c) Block 23: Has stimulating spike occurred? Block 22 relates to the step in the flow chart where the pacer timing circuits 5 emit a predetermined number of spikes at a higher rate. The precise operation of the heart stimulating apparatus will be clear from the flow chart of Fig. 2 when considered with the basic diagram of the system shown in Fig. 1 and the more detailed circuit diagram of the synchronizer shown in Fig. 4.

Referring to the typical electrocardiogram pattern shown in Fig. 3, the test duration is defined by the length 57. This demonstrates the synchronization of the pacing spikes of the testing rate to the beat 32. The predeterminated number of fixed rate stimulation spikes was determined as two. In this case the application of stimulating spikes 33, 34, and 35 is combined into one sequential pattern., The sequence of illustrated events is as follows: The interval 51 is a spontaneous R-R interval. During this interval 51, a testing rate was initiated, thus the beat 32 is the first synchronization beat upon which the synchronizer 4 inhibits sensing circuits 6 for the two stimulation intervals 52 and 53. These stimulation intervals are shorter than the pacing interval 54 and are established according to clinical requirements.The stimulating spikes 33 and 34 are generated by the pacer timing circuits 5 with the higher rate controlled by the synchronizer 4. Upon reception of the second stimulating spike 34 the synchronizer 4 inhibits the sensing circuits 6 via the line 8 and the sensing of the pacer is resumed. In this illustration no spontaneous beat was received during the basic stimulation interval 54 which led to the application of the stimulating spike 35 inherently produced by the pacer timing circuit 5. The later spike 35 converts the synchronizer 4 for two successive intervals 55 and 56 bounded by the higher rate stimulating spikes 36 and 37. Since the request of the test mode was terminated somewhere following stimulating spike 37, the synchronizer 4 stopped its intervention and from this point the pacer exhibits its normal sensing and pacing functions.The synchronizer 4 can be incorporated at any suitable combination and length of the period 57.

Fig. 4 illustrates an example of actual circuitry of the synchronizer 4 using standard C-MOS logic circuits. A shift register 63 is used as a counter for a predeterminated number of stimulations during fixed mode test.

This shift register 63 is in the reset state unless the testing mode is requested by a block 64 which is equivalent to the receiver 2 in Fig. 1. During its reset state the output Q1 is at logic zero, so that neither is the sensing inhibited nor the increased rate activated by output block 68. Upon request of the testing mode, an OR gate 66 releases the reset state of the shift register 63, so that the first arriving pulse to the CL input of the register 63, in the form of synchronizing signals 61, sets the output Q1 to logic one. The output Q1 in turn activates via the block 68 to inhibit of the sensing circuits 6 and commands a high stimulating rate of the pacer timing circuits 5.The next series of stimulating spikes will advance the shift register 63 until the output On, which is the n-1 count of the stimulating spikes, changes to logic one. The output On at logic one substitutes logic zero to input D of the register 63, thus the next spike received at the input CL will transfer the output Q1 to logic zero. This will cancel both the inhibit and increased rate control signals via the block 68 and reset the whole shift register 63 to its zero or initial position via a differentiator 67 and the OR gate 66. From this state the synchronizer 4 is awaiting for the synchronizing signal upon reception of which a fresh cycle of the synchronization is generated as described above. This will repeat as long as the testing mode is requested.

The above described heart stimulating apparatus was evaluated on a number of patients previously equipped with demand pacemakers. When the test was actuated, the synchronizer 4 gated the output from the receiver 2 and the synchronizing signals, thus controlling the pacer timing circuits 5 for a higher pacing rate and at the same time inhibiting the sensing circuits 6 for two pacing intervals per synchronization cycle. Actually upon attachment of the magnet, the first R-wave or stimulator spike, which ever occurs first, converts the pacing into a test rate mode for two consecutive spikes, at, say 100 ppm rate.

Thereafter pacing reverts to the sensing mode for one escape interval, and again upon occurence of R or of a stimulator spike, two spikes are emitted at the same or at another predetermined frequency. This can be repeated as long as required. Two consecutive spikes, at fixed intervals, are generally adequate in order to evaluate the pacemaker system. Twenty patients were connected temporarily to the above described heart stimulating apparatus invention. An average of 200 synchronized tests were made per patient and recorded for evaluation. Spike on T phenomenon was detected in less than 5 percent of the periods, compared with an average of 45 percent during conventional magnet tests. Preliminary tests indicate that the above described heart stimulating apparatus is efficient in terminating tacharrhythmias in human patients.

It will be clear that the novel concept of synchronization of the tests of the pacemaker with the heart rate and such synchronization during applications of stimulating spikes for terminating tachyarrhythmias can be applied to numerous types of pacemakers and similar instruments.

Claims

1. A heart stimulating apparatus arranged to deliver stimulating spikes to the heart of a patient when required, and to refrain from delivering such spikes upon sensing of normal heart beats, in combination with electrode means for sensing such spontaneous heart beats, said apparatus including externally actuated test rate mode receiver; and means for synchronizing said test rate mode to the spontaneous heart beats.

2. A heart stimulating device according to Claim 1, including means for pacing at a predetermined frequency and means for testing at one or more predetermined rates.

3. A heart stimulating device according to Claim 2, wherein the frequency of the rest rate is higher than that of spontaneous heart rate, or of that of the pacing frequency.

4. A device according to any one of the preceding claims, additionally including means for terminating cardiac tachyarrhythmias which comprises means for applying a stimulating spike into the diastolic period of the heart beat and for repeating such spikes, as required, at predetermined intervals, said spikes being synchronized with the spontaneous heart beats.

5. A heart stimulating device according to any one of the preceding claims wherein the testing rate is initiated by the application of an external magnetic field, by piezoelectric means, by electromagnetic waves, by acoustic means or by a light signal.

6. A method of terminating cardiac tachyarrhythmia which comprises synchronizing the closest time of the application of the stimulating spikes with the diastolic period of the heart beat, and repeating such application of stimulating spikes at a predetermined frequency until the desired result is attained.

7. A heart stimulating apparatus constructed and arranged to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.