Implantable Defibrillator Arrangement

1. Field of the Invention

The present invention is directed to an implantable defibrillator arrangement, and in particular such an arrangement making use of a capacitor and an inductance for generating an electrical defibrillation pulse.

2. Description of the Prior Art

In implantable defibrillator arrangments, as exemplified by U.S. Pat. No. 4,834,100, it is conventional to provide a capacitor in an implantable housing, the capacitor being connectable for charging to a voltage source in the housing via a controllable switch arrangement, and also being connectable through an inductance to electrodes arranged in the region of the heart, by means of electrode leads, for generating an electrical defibrillation pulse and supplying the pulse to the heart tissue. In the arrangement disclosed in U.S. Pat. No. 4,834,100, the capacitor is connectable through a controllable switch arrangement either to a voltage source or, in series with an inductance, to two electrode terminals. Electrode leads are connectable outside of the capsule housing to the terminals, the leads terminating in electrodes which are placed at or in the heart of a patient. The capacitor is charged to a prescribed charging voltage as long as the capacitor is connected to the voltage source. For releasing an electrical defibrillation pulse to the heart, the capacitor is briefly connected, via the inductance, to the electrodes by means of switch arrangement, causing a biphase current pulse in the form of a highly attenuated oscillation to be generated. Such a pulse shape has proven particularly effective with respect to the energy required for defibrillation.

The shape of the oscillation is defined by the values of the capacitance of the capacitor, the inductance, and the electrical impedance of the heart tissue between the electrodes. This electrical impedance is substantially dependent on the particular type of electrodes employed, including their shape and their positioning relative to the heart. The defibrillation pulse supplied by this known defibrillator system can therefore significantly deviate from a waveform which is considered optimum, dependent upon which electrodes are employed and on the positions of the electrodes.

It is an object of the present invention to provide a defibrillator arrangement wherein a defibrillation waveform is generated using a capacitance and an inductance which enables optimization of the defibrillation pulses to be made in a simple manner, even with use of different electrodes and electrode arrangements.

The above object is achieved in accordance with the principles of the present invention in a defibrillator system of the type described above wherein the inductance is contained in a second, separate implantable housing, which is provided with terminals for connecting the inductance in the path of one of the electrode leads. Such a separate housing, containing an inductance selected for generating an optimum defibrillation pulse given the type of electrodes provided for a particular patient and their arrangement at the heart, can be connected at the time of implantation. Such an optimization can also be made in a defibrillator arrangement that has already been implanted, without having to remove the entire arrangement, because replacement of the separate capsule housing containing the inductance is all that is required. The separate housing, because it contains only the inductance, has particularly small outside dimensions and therefore can be implanted at body locations which are easily accessible for later replacement. It is also possible to make use of the separate housing to convert defibrillators designed for generating monophase pulses, whether already implanted or not, into an arrangement which generates biphase defibrillation pulses.

The possibilities for optimizing the defibrillation pulse with respect to different electrodes and electrode arrangements can be further improved in another embodiment of the invention wherein at least one further, passive electrical component is connected between the terminals in the second, separate housing in addition to the inductance. This further component may be a capacitor or a resistor connected either in series or in parallel with the inductance.

In a further embodiment of the invention, the separate housing has at least one additional terminal for a further electrode, and contains at least one additional, passive electrical component which is connected together with the inductance to form a current divider circuit, which divides the defibrillation pulse supplied by the capacitor into different sub-currents for the respective electrodes. Using this arrangement, upon the generation of a defibrillation pulse, the electrical current density is distributed in the heart muscle in a manner adapted to the arrangement (positioning) of the electrodes and thus be distributed so that the current can penetrate the thickest zones of the heart muscle, which form the main portion of the heart muscle mass, in order to achieve reliable defibrillation. Again, existing defibrillators, implanted or otherwise, which are designed only for the connection of two electrodes can be correspondingly retrofitted.

As noted above, the second, separate housing can have relatively small exterior dimensions, and therefore it is subject to far fewer limitations as to the implantation location in the human body than the main (first) capsule housing, which contains the voltage source and the capacitor. In a further embodiment of the defibrillator arrangement of the invention, the separate housing has a surface with at least regions thereof which are electrically conductive, the surface (or regions thereof) functioning as one of the electrodes of the defibrillator arrangement. The second, separate housing can then be implanted at or in the proximity of the heart and additionally assumes the function of a defibrillator electrode.

A plurality of such second, separate housings, each having an inductance of a different value therein, or further combinations of passive electrical components in addition to the inductance, can be provided to the physician to expand his or her choices for selecting an inductance or component combination best suited to the particular electrode arrangement being employed at the time.

FIG. 1 is a schematic diagram of a first embodiment of a defibrillator arrangement having first and second housings, constructed in accordance with the principles of the present invention.

FIG. 2 is a schematic diagram showing a further embodiment of a current divider circuit in the second housing in portion of a defibrillator arrangement constructed in accordance with the principles of the present invention.

FIG. 3 is a schematic diagram of a third embodiment of a second housing forming an electrode, in a portion of a defibrillator arrangement constructed in accordance with the principles of the present invention.

An implantable defibrillator 1 is shown in FIG. 1, the defibrillator 1 being of the conventional type for generating monophase defibrillation pulses. The defibrillator 1 includes a capsule housing 2, adapted for in vivo implantation in a patient, containing a capacitor 3. The capacitor 3 is connected via a switch arrangement 5, controllable by a control unit 4, either to a voltage source 6 or to two externally accessible electrode terminals 7 and 8. The electrode terminals 7 and 8 are connected via electrode leads 9 and 10 to two electrodes 12 and 13 placed at a heart 11. An inductance 14 is connected in the path of the electrode lead 9, the inductance 14 being contained in a second, separate housing 15. The housing 15 has a terminal 16 which is connected via a first section 18 of the electrode 9 to the output terminal 7 of the defibrillator 1. The housing 15 also has a terminal 17 which is connected via a second section 19 of the electrode lead 9 to the electrode 12.

The housings 2 and 15 each consist of tissue-compatible material, for example titanium, and the terminals 7, 8, 16 and 17 are in the form of insulated bushings extending through the metal housing. The separate housing 15, however, may alternatively consist of plastic, for example silicone, in order to more simply integrate the housing 15 into the electrode lead 9. The housing 15 may have a shape other than shown in the drawing, to facilitate implantability.

As long as the capacitor 3 is connected to the voltage source 6 via the switch arrangement 5, it will be charged to a prescribed charging voltage. For releasing an electrical defibrillation pulse to the heart 11, the capacitor 3 is briefly connected by the switch arrangement 5 to the electrodes 12 and 13 via the inductance 14. This causes the generation of a biphase current pulse in the form of a highly attenuated oscillation. The shape of the current pulse is defined by the values for the capacitance of the capacitor 3, the inductance 14, and the impedance of the heart tissue between the electrodes 12 and 13. Because the value for the impedance of the heart tissue between the electrodes 12 and 13 changed dependent on the size and arrangement of the electrodes at the heart 11, the defibrillation pulse supplied to the heart 11 can deviate from a pulse shape which is considered optimum with respect to defibrillation effectiveness. This deviation can be counteracted in a simple manner by selecting a suitable value for the inductance 14, so that the second, separate housing 15 having the selected inductance 14 must merely be initially implanted together with the defibrillator 1, or can be implanted in a patient as a replacement, or addition to, an existing defibrillator arrangement. Because the separate housing 15 can have relatively small dimensions, it can be implanted at a location in the body which is easily accessible for replacement.

For further optimization of the defibrillation pulse, a further, passive electrical component (not shown in FIG. 1) in the form of a resistor or a capacitor can be provided in the second separate housing 15, in addition to the inductance 14. This further, passive electrical component can be connected either in series with the inductance 14 or in parallel with the inductance 14 between the terminals 16 and 17. This is shown below in FIG. 3 in an exemplary embodiment.

As shown in FIG. 2, the further, passive electrical component 20 (a capacitor in this case) can be arranged between the electrode leads 9 and 10, for which purpose the second, separate housing 15 is provided with further terminals 21 and 22 for the electrode lead 10. Moreover, the separate housing 15 shown in FIG. 2 contains an additional, passive electrical component 23 (in the form of a resistor) which is connected at a one side to the terminal 16 connected via the lead section 18 to the defibrillator 1 (not shown in FIG. 2). The other side of the component 23 is connected to an additional terminal 24 for a further electrode 25 placed at the heart 11. This arrangement achieves, when generating a defibrillation pulse, a distribution of the electrical current density in the heart muscle according to the arrangement of the electrodes 12, 13 and 25 and dependent on the values for the components 14, 20 and 23. The current density is preferably distributed so that current penetrates the thickest zones of the heart muscle which form the main part of the heart muscle mass in order to achieve reliable defibrillation.

An exemplary embodiment is shown in FIG. 3 of the second, separate housing 15 wherein a region 26 of the housing surface is fashioned as an electrode, by virtue of being connected via a capacitor 27 to a voltage tap of a series circuit consisting of the inductance 14 and a resistor 28, which is disposed between the terminals 16 and 17. The use of the housing 15, with the aforementioned region 26, as one electrode of the defibrillator arrangement is facilitated by the small dimensions of the housing 15, which permit the housing 15 to be placed in or near the heart without difficulty.

The exemplary embodiments show the structure of the separate housing 15 in schematic illustrations. The housing shape can be altered dependent on the implantation location in the body of the patient, as may be considered preferable.

Lastly, the illustrated selection and arrangement of the passive components 14, 20, 23, 27 and 28 are considered only as examples among a plurality of further possible combinations.

Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.