Method And Apparatus For Providing Synchronized Stimulus And Coupled Stimulation From An Implanted Heart Stimulator Having A Constant Rhythm

Abstract

An apparatus which provides an electromagnetic field in synchronization with the occurrence of a detected heart function potential is located outside of a patient's body in which a heart stimulator having a constant rhythm frequency generator has been implanted. The implanted generator is magnetically coupled within the electromagnetic field so as to be responsive to the occurrence thereof. An electrical heart stimulus in synchronization with the detected potential is thereby enforced from the implanted generator in response to the occurrence of the field. Coupled stimulation is provided by the apparatus by routing the detected signal along an additional branch path which includes a delay line. The delayed signal provides a second electromagnetic field a preselected delayed time after the provision of the synchronized field whereby a synchronized heart stimulus and a second, coupled heart stimulus are provided in response to a single detected heart function potential.

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a consolidated continuation-in-part of U.S. Pat. applications, Ser. No. 853,843, filed Aug. 28, 1969, now abandoned, and Ser. No. 853,882, filed Aug. 28, 1969, now abandoned.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for obtaining an electrical heart stimulus in synchronization with a heart function potential from an implanted heart stimulator having constant rhythm, and a method of obtaining coupled stimulation thereby.

2. Description of the Prior Art

Prior art implanted heart stimulators, or as they are commonly termed, cardiac pacers, are normally of the constant rhythm type, having a constant rhythm frequency generator, or blocking oscillator for emitting an electrical stimulus to the heart. In such pacers, a single impulse signal is emitted at a preset interval by the pacer in order to stimulate the heart. This single impulse stimulates the heart to cardiac contraction at a constant rhythm or frequency. If spontaneous heart function potentials, which are the electrical manifestations which accompany cardiac contractions, appear in a patient having a constant rhythm pacemaker implanted in his body, the stimulator pulses can cause an interference with the patient's own heart rhythm. This phenomenon may bring about dangerous disturbances, such as ventricular fibrillation, if the ventricle is the portion of the heart being stimulated.

Prior art methods of correcting for this interference of stimulator pulses with the patient's own, or natural heart rhythm have involved surgical removal and exchange of the stimulator, which must often be urgently carried out, or pharmacological treatment, by administering drugs for the purpose of inhibiting a generation of heart function potentials until such generation no longer interferes with stimulator pulses. Another and more drastic prior art solution to this problem is to provide a very large electric shock to the heart in order to totally depolarize the heart. The heart then totally discharges and stops, and then commences beating again at a different rate, hopefully in step with the stimulator.

However, these prior art solutions do not totally solve the problem of interference since a surgical exchange of stimulators, or pacers may cause additional complications and cannot always be accomplished due to the condition of the patient or a lack of facilities at the time the emergency occurs, while pharmacological therapy does not produce reliable effects. Furthermore, electrical shock treatment is a drastic remedy and one not normally favored if others are available.

Coupled stimulation, that is stimulation in which a heart function potential is detected and a delayed signal, or stimulus is emitted to the heart sometime thereafter in order to produce a depolarization of the heart without producing a mechanical contraction of the heart, is well known. Such coupled stimulation is normally provided by means of applicances provided outside the patient's body rather than by a pacer. Moreover, for such a pacer of the constant rhythm variety, the problems previously enumerated such as interference, may occur. Prior art pacers are not, therefore, able to provide stimulator pulses in synchronization with a patient's spontaneously appearing heart function potentials as well as a second, coupled stimulation thereafter.

The present invention overcomes these disadvantages of the prior art.

SUMMARY OF THE INVENTION

An apparatus for providing an electrical stimulus for a heart from a pacer having a constant rhythm frequency generator is provided. The heart stimulus is provided in synchronization with an occurrence of a heart function potential of the heart. Means are provided to detect the occurrence of the heart function potential and to trigger a generation of a first synchronized electromagnetic field in response thereto. The generator is magnetically coupled within the first electromagnetic field and the synchronized heart stimulus is enforced therefrom in response to the occurrence of the first field.

Additional means may also be provided, in conjunction with the first electromagnetic field providing means, if provision of a second electromagnetic field to the generator in response to the occurrence of the single heart function potential is desired. This additional means includes a delay means for delaying the triggering of the generation of the second electromagnetic field for a preselected interval after the generation of the first synchronized electromagnetic field whereby coupled stimulation is provided. The implanted generator is responsive to both the first and second electromagnetic fields to enforce the occurrence of the coupled heart stimuli, one in synchronization with the heart function potential, and the other at a preselected interval thereafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the preferred embodiment of the present invention;

FIG. 2 is a block diagram of an alternative embodiment of the present invention;

FIG. 3 is a partial schematic diagram of the embodiment shown in FIG. 1;

FIGS. 4-a through 4-c are graphical illustrations of signal phenomena associated with the embodiment shown in FIG. 1; and

FIGS. 5-a through 5-c are graphical illustrations of signal phenomena associated with the embodiment shown in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings in detail, and especially to FIG. 1 thereof which is a block diagram of the preferred embodiment of the present invention. As shown and preferred, the present invention includes an electromagnetic field providing means, generally referred to by the reference numeral 10 having an impulse generator portion 12 and a detection and synchronization portion 14. The impulse generator portion 12 of the electromagnetic field providing means 10 includes a power supply circuit 16 which is conventional and is shown in greater detail in FIG. 3.

The power supply circuit 16 (FIG. 3) preferably includes a step-down power transformer 18 having a primary winding 19 and a pair of secondary windings 20 and 26, each forming a part of a power supply source. Secondary winding 20 together with a diode 22 and an electrolytic capacitor 24, form one power supply source, and secondary winding 26 together with a diode 28 and an electrolytic capacitor 30 forms another power supply source which is a low-voltage power supply source. The portion of the power supply circuit 16 including secondary winding 20 is connected to a charging circuit 32 which preferably is a capacitive charging circuit consisting of a resistor-capacitor combination 34-36 (FIG. 3) for a purpose to be described in greater detail hereinafter. The portion of the power supply circuit 16 including secondary winding 26 is connected to an amplifier 38 of the detection and synchronization portion 14 of the electromagnetic field providing means 10, in a manner to be described in greater detail hereinafter.

The output of the charging circuit 32 is connected to an electromagnetic field generator 40 which, as shown and preferred in FIG. 3, includes an armature 42 of a relay 44, which acts as a switch to enable or disable the electromagnetic field generator 40, and an induction coil 46 for providing an electromagnetic field therefrom. Preferably, during use, the induction coil 46 which is preferably applied to the body of the patient above the location of a conventional implanted pacer is located so as to be magnetically coupled to a constant rhythm frequency generator 48 of the pacer (not shown). The solenoid portion 50 of the relay 44 is connected in a triggering circuit 52, such as a conventional Schmitt trigger circuit configuration as shown and preferred in FIG. 3, with the solenoid 50 of the relay 44 connected to the collector 54 of an output transistor stage 56 of the trigger circuit 52.

The detection and synchronization portion 14 of the electromagnetic field providing means 10 includes a heart function potential detector 58, such as an electrode connected to the heart of the patient in which the pacer (not shown) is implanted. Amplifier 38, preferably, has an input thereof connected to the electrode 58, which is either implanted in or located near the heart of the patient in which a pacer is implanted, in order to amplify the detected heart function potential. The amplifier 38, which is preferably a conventional transistor amplifier, preferably has the output thereof connected to a conventional refractory circuit 60 which, as will be explained in greater detail hereinafter, renders the electromagnetic field providing means 10 insensitive to external stimuli for a predetermined interval. Preferably, the output of the refractory circuit 60 is connected to a conventional synchronization circuit 62, the output thereof which is in turn connected to the input of the triggering circuit 52.

OPERATION

The operation of the electromagnetic field providing circuit 10 of the present invention is as follows. Referring now to FIGS. 4-a through 4-c, the total electric signal detected by the electrode 58 includes a stimulator pulse portion 64 as well as a stimulated heart function potential pulse portion 66. Spontaneous heart function potentials such as those illustrated by 68, 70 and 72, which are due to the abnormal operation of the heart without the aid of the implanted pacer, are also shown in FIG. 4-a.

The electrical signal from the heart is detected by electrode 58 and amplified in the amplifier 38. The amplified signal is then transmitted to the refractory circuit 60 which, after having passed the detected signal, blocks the signal conduction path for a preselected interval in a conventional manner, so as to render the electromagnetic field providing means 10 insensitive to external stimuli subsequently detected by electrode 58 during this blocking interval. In this manner, the circuit 10 is protected against excitation as a result of feedback of the pulse triggered from the pacer or the stimulated heart function potential resulting therefrom. This refractory period is provided during the occurrence of the resultant synchronized heart stimulus and the resultant heart response thereto.

The detected signal, after having passed through the refractory circuit 60, enables the synchronization circuit 62 which, in a conventional manner, provides a signal to the triggering circuit 52. When a signal is received by the triggering circuit 52, it in turn causes the generation of a pulse, via output stage 56, through the solenoid 50 of the relay 44. Relay 44 is thereby activated and the relay armature 42 is operated to close the circuit in generator 40. This completes the circuit to the induction coil 46 of the electromagnetic field generator 40 from the charging circuit 32. This causes the capacitor 36, which has been charged during the interval when the relay 44 was not activated and an open circuit to coil 46 was thereby provided, to discharge through coil 46. The discharge of capacitor 36 provides an impulse through coil 46 which impulse causes a generation of an electromagnetic field thereby providing a pulse 74, such as shown in FIG. 4-b.

The electromagnetic field which is created by the discharge through coil 46 provides a pulse to the constant rhythm frequency generator 48 of the implanted pacer due to the magnetic coupling of the induction coil 46 to the constant rhythm frequency generator 48. This pulse, which is in synchronization with the detected heart function potential in turn enforces the generation of a pulse from the implanted generator which is in synchronization with the detected heart function signal, such as shown in FIG. 4-c.

For purposes of illustration, we shall now describe the operation of the circuit 10 of the present invention in the time period from t.sub. 1 through t.sub. 6. As was previously mentioned, the detected heart function signal at t 1 (FIG. 4-a) represents a combination of the stimulator pulse 64 together with the stimulator heart function potential 66. This causes a generation of a pulse 74 (FIG. 4-b) due to the electromagnetic field at coil 46 which in turn enforces combined pulse 76 (FIG. 4-c) from the constant rhythm frequency generator 48 in synchronization with the detected heart function signal 64-66. Assuming the constant rhythm frequency generator to have the period T, where T represents the time interval between the stimulator pulses of the pacer, if no spontaneous heart function potentials occur during this period, such as represented by the time interval from t.sub. 1 to t.sub.2/3.sub.2, then the previously described operations of detection, creation of an electromagnetic field and enforcement of a synchronized stimulating pulse represented by the signals 78, 80 and 82, respectively, occur in the manner previously described.

If a spontaneous heart function potential, such as represented by signal 68 (FIG. 4-a) occurs during the time interval T between the normal constant rhythm stimulator pulses generated by the implanted generator 48, such as at t.sub. 3, this heart function potential 68 is detected by electrode 58 and as was previously described with reference to the detected combined heart function signal 64-66 causes the generation of a trigger pulse by trigger circuit 52 which closes the relay 44. This causes the generation of an electromagnetic field through coil 46 due to the discharge of capacitor 36 thereby providing a pulse 84. The electromagnetic field through coil 46 enforces the occurrence of a heart stimulating pulse 86 from the constant rhythm frequency generator 48 in synchronization with the occurrence of heart function potential 68 thereby correcting for the occurrence of the spontaneous heart function potential 68 and preventing any interference thereto.

The constant rhythm frequency generator 48 is automatically reset so as to thereafter provide another stimulating pulse after the time interval T in a continuous manner from the occurrence of the last generated pulse until this rhythm is interrupted by another spontaneous heart function potential. If this occurs a synchronized pulse is enforced and the constant rhythm frequency generator 48 resets once again. The occurrence of another spontaneous heart function potential before the completion of the preset time interval T is illustrated at t.sub. 4 by signal 70. When this occurs, pulses 88 and 90 are subsequently produced in the manner previously described with reference to the production of the pulses 84 and 86. Combined signal 92 (FIG. 4-a) at time interval t.sub. 5 represents the occurrence of a heart function signal after the normal preset time interval T, and resultant pulses 94 and 96 are produced thereby. Finally, if another spontaneous heart function potential 72 occurs prior to the completion of the preselected time interval T of the constant rhythm frequency generator 48, an electromagnetic field is generated once again through coil 46 thereby providing a pulse 98 which field in turn enforces the occurrence of a synchronized heart stimulating pulse 100, such as illustrated at t.sub. 6.

COUPLED STIMULATION

Referring now to FIG. 2, a circuit, generally referred to by the reference numeral 102, capable of providing coupled stimulation in a preferred manner to be described in greater detail hereinafter is shown. The circuit 102 includes an impulse generator portion 104 which is preferably identical with the impulse generator portion 12 previously described with reference to the embodiment of FIG. 1 and will not be described in greater detail hereinafter. Suffice it to say, the impulse generator portion 104 includes a power supply circuit 16, a charging circuit 32, an electromagnetic field generator 40 and a triggering circuit 52 connected together in the manner previously described with reference to the embodiment shown in FIG. 1.

The circuit 102 for providing coupled stimulation preferably also includes a detection and synchronization portion 106 which is preferably substantially identical with the detection and synchronization portion 14 of the embodiment shown in FIG. 1. However, in addition to the normal interconnection between the refractory circuit 60 and the synchronization unit 62, an additional interconnection through a delay circuit 108, such as a conventional delay line, is provided for a purpose to be described in greater detail hereinafter. The detection and synchronization portion 106 includes a detector or electrode 58, an amplifier 38 which is connected to the power supply circuit 16, the refractory circuit 60, a direct connection therefrom to the synchronization circuit 62 and a connection from the refractory circuit 60 through delay circuit 108 to the synchronization unit 62. The synchronization unit 62 has its output in turn connected to the triggering circuit unit 52, as in the embodiment previously described with reference to FIG. 1.

COUPLED STIMULATION OPERATION

Referring now to FIGS. 2 and 5-a through 5-c, the operation of the circuit 102 to provide coupled stimulation from a pacemaker having a constant rhythm will now be described. The operation of this circuit 102 with respect to the provision of a heart stimulating pulse from a constant rhythm frequency generator 48 in synchronization with the occurrence of a heart function potential of the heart is similar to that previously described with reference to the operation of the embodiment shown in FIG. 1. However, in addition to the provision of the synchronized heart stimulating pulse, a second, delayed heart stimulating pulse is produced, in a manner to be described in greater detail hereinafter, in response to the occurrence of the same heart function potential to which the synchronized heart stimulating pulse is responsive.

The hart function signal, such as represented by the combined signal 110 (FIG. 5-a) which includes a stimulator pulse portion 112 and a stimulated heart function potential 114, is detected by means of electrode 58. This detected signal 110 is transmitted to the amplifier 38 where it is amplified. After amplification, this detected signal is then transmitted to the refractory unit 60 which thereafter, for a preselected interval termed the refractory period, blocks the signal conduction path to inhibit the response of the circuit 102 to external stimuli, as was previously described with reference to the embodiment shown in FIG. 1.

After passing through the refractory circuit 60, the detected signal 110 is then passed directly to the synchronization unit 62 and, over a separate signal conduction path to the delay circuit 108. The detected signal which was passed directly to the synchronization unit 62 in turn is passed to the triggering circuit 52 where it in turn causes the generation of a pulse at the output stage 56 thereof. The pulse from output stage 56 operates relay 44 to close the circuit between the induction coil 46 of the electromagnetic field generator 40 and the charging circuit 32 thereby discharging the capacitor 36. This provides a pulse through the induction coil 46 to create an electromagnetic field which causes the generation of a pulse 116 (FIG. 5-c). The constant rhythm frequency generator 48 which is magnetically coupled to the induction coil 46, as was previously mentioned with reference to the embodiment shown in FIG. 1, thereby enforces a generation of a heart stimulating pulse 118 (FIG. 5-c) in synchronization with the detected heart function signal 110 due to the occurrence of the electromagnetic field through coil 46.

Simultaneously, the delay unit 108 delays the detected heart function signal 110 passing thereto over the separate conduction path for a preselected interval represented by T.sub.d. The delayed signal is then passed to the synchronization unit 62 and in turn to the triggering unit 52 where it functions similarly to the undelayed detected signal previously described to cause the generation of a trigger pulse at the output stage 56 of the triggering circuit 52. This trigger pulse operates the relay 44 once again to close the circuit to coil 46 and discharge capacitor 36 therethrough thereby creating a second electromagnetic field and causing the generation of another pulse 120 (FIG. 5-b). This second electromagnetic field results in the enforcement of another heart stimulating pulse 122 from the constant rhythm frequency generator 48 at the end of the delay interval T.sub.d.

In this manner, the synchronization unit 62 and in consequence, the triggering unit 52 are controlled twice in a time interval equal to the delay time T.sub.d thereby causing the generation of two successive electromagnetic fields through coil 46 in this time interval T.sub.d. Coupled stimulation is thereby provided from the constant rhythm frequency generator 48 with one stimulating pulse being enforced in synchronization with the detected heart function signal and the second pulse being enforced at a delayed time thereafter.

For purposes of illustration, we shall now describe the operation of the circuit 102 to provide coupled stimulation during the time interval from t.sub. 1 to t.sub. 8 as shown in FIGS. 5-a through 5-c. Assuming the period of the constant rhythm frequency generator 48 to be T, then if no spontaneous heart function potential occurs during this period T, then the combined heart function signal represented by 124 (FIG. 5-a) is detected in the circuit 102 which thereby operates as was previously described to provide successive electromagnetic fields in the delay period T.sub.d. This produces associated pulses 126 and 128, respectively, and resultant coupled heart stimulating pulses 130 and 132, as is illustrated at t.sub. 3 and t.sub. 4.

If as illustrated at t.sub. 5, a spontaneous heart function potential 134 occurs prior to the completion of the preset constant rhythm period T, then the circuit 102 operates to cause the generation of a first electromagnetic field in synchronization with the occurrence of the spontaneous heart function potential 134 resulting in a pulse 136 and a synchronized heart stimulating pulse 138 from the constant rhythm frequency generator 48. Furthermore, a second electromagnetic field will be generated through coil 46 due to operation of the delay circuit 108 to provide resultant pulses 140 and heart stimulating pulse 142 within the delay interval T.sub.d thereby providing coupled stimulation from the pacer due to pulses 138 and 142. The constant rhythm frequency generator 48 will reset after the occurrence of the last stimulating pulse 142 therefrom so as to commence generating a stimulating pulse after the time interval T measured from the generation of the last pulse 142. Thereafter, as is illustrated at t.sub.7, when a combined heart function signal 144 occurs, a pair of successive electromagnetic fields resulting in pulses 146 and 148 respectively and coupled heart stimulating pulses 150 and 152 within the delay interval T.sub.d occurs, as is illustrated at t.sub. 7 and t.sub. 8.

By utilizing the method and apparatus of the present invention, interference from the rhythm of the heart with the rhythm of the stimulator due to an occurrence of spontaneous heart function potentials is minimized. Furthermore, by utilizing the method and apparatus of the present invention to provide coupled stimilation, the force of the heart systole can be increased and the heart rhythm frequency may be lessened such as by depolarizing the heart with the second heart stimulating signal of the coupled stimulating pair of signals so as to render the heart refractory to the next successive spontaneous generated heart function potential.

It is to be understood that the above described embodiments of the present invention are merely illustrative of the principles thereof and numerous modifications and embodiments of the invention may be derived within the spirit and scope thereof.

Claims

What is claimed is:

1. A method of providing an electrical stimulus for a heart from an implanted heart stimulator having a constant rhythm frequency generator, said stimulus being in synchronization with an occurrence of a heart function potential, comprising the steps of

providing a first electromagnetic field to said generator in response to the occurrence of said heart function potential from said heart, and

enforcing an occurrence of said synchronized heart stimulus from said generator in response to the occurrence of said first electromagnetic field.

2. A method in accordance with claim 1 wherein said providing step includes the steps of detecting the occurrence of said heart function potential, and triggering a generation of said first electromagnetic field in response to said detected heart function potential.

3. A method in accordance with claim 1 wherein said providing step includes the step of providing a refractory period during the occurrence of said synchronized heart stimulus and a resultant heart response thereto.

4. A method in accordance with claim 1 wherein said enforcing step includes the step of magnetically coupling said generator within said first electromagnetic field.

5. A method in accordance with claim 1 wherein said providing step includes the step of providing a second electromagnetic field to said generator in response to the occurrence of said heart function potential from said heart.

6. A method in accordance with claim 5 wherein said providing step further includes the step of providing said second electromagnetic field a preselected interval after the provision of said first electromagnetic field.

7. A method in accordance with claim 6 wherein said enforcing step includes the step of enforcing an occurrence of a second electrical heart stimulus from said generator in response to the occurrence of said second electromagnetic field.

8. A method in accordance with claim 5 wherein said enforcing step includes the step of magnetically coupling said generator within said first and second electromagnetic fields.

9. An apparatus for providing an electrical stimulus for a heart from an implanted stimulator having a constant rhythm frequency generator, said stimulus being in synchronization with an occurrence of a heart function potential of said heart, comprising

means for providing a first electromagnetic field to said generator in response to the occurrence of said heart function potential from said heart, said generator including means responsive to said first electromagnetic field for enforcing an occurrence of said synchronized heart stimulus.

10. An apparatus in accordance with claim 9 wherein said first electromagnetic field providing means includes means between said first electromagnetic field providing means and said generator means for magnetically coupling said generator within said first electromagnetic field.

11. An apparatus in accordance with claim 9 wherein said first electromagnetic field providing means includes means for detecting the occurrence of said heart function potential, and means for triggering a generation of said first electromagnetic field in response to said detected heart function potential.

12. An apparatus in accordance with claim 11 wherein said first electromagnetic field providing means further includes means for providing a refractory period during the occurrence of said synchronized heart stimulus and a resultant heart response thereto.

13. An apparatus in accordance with claim 11 wherein said first electromagnetic field providing means further includes a capacitive charging means and a means for discharging said charging means, said discharge means including electromagnetic means, said triggering means being operatively associated with said discharge means for causing the operation of said electromagnetic means in synchronization with said detected heart function potential.

14. An apparatus in accordance with claim 9 wherein said first electromagnetic field providing means includes means for providing a second electromagnetic field to said generator in response to the occurrence of said heart function potential from said heart, said generator responsive means further including means responsive to said second electromagnetic field for enforcing an occurrence of a second heart stimulus.

15. An apparatus in accordance with claim 14 wherein said first electromagnetic field providing means includes means for detecting the occurrence of said heart function potential, and means for triggering a generation of said first and second electromagnetic fields in response to said detected heart function potential, said second electromagnetic field providing means including delay means operatively connected between said detecting means and said triggering means for delaying the generation of said second electromagnetic field due to said triggering means for a preselected interval after the generation of said first electromagnetic field due to said triggering means, said synchronized heart stimulus and said second heart stimulus providing coupled stimulation for said heart.

16. An apparatus in accordance with claim 14, wherein said first electromagnetic field providing means includes means between said first electromagnetic field providing means and said generator means for magnetically coupling said generator within said first and second electromagnetic fields whereby coupled stimulation is provided for said heart.