Implantable Medical System With Optical Communication Between a Treatment Site and a Therapy-Generating Apparatus

1. Field of the Invention

The present invention is directed to an implantable medical system, for administering therapy in vivo to living tissue, of the type including an implantable therapy-generating apparatus connected to a treatment site remote from the apparatus, as well as to such a medical system having at least two separate implantable therapy-generating apparatus, with the capability of communicating between the two implanted apparatuses.

2. Description of the Prior Art

Many types of implantable medical devices, such as pacemakers and defibrillators, are employed in systems for connection to living tissue for sensing tissue functions or for treating the tissue. The devices can be implantable or extracorporeal. The devices are connected to the living tissue by metallic conductors. A plurality of such devices can be used in a single system, each device being connected to the living tissue, and the implanted devices being interconnected with metallic conductors so that information can be exchanged between the devices.

Metallic leads can cause problems, particularly in implanted systems. A conductor used to transmit pacemaker pulses between a pacing pulse generator and a treatment site may, for example, pick up a defibrillation pulse generated by another device, thereby resulting in a spurious detection of cardiac activity, and may also damage the pacemaker electronics. The metallic conductors are usually contained in an insulating sheath made of a polymer, such as silicone, to keep the leads from having any effect on the surrounding tissue which is not to be sensed or stimulated. The requirement for such an insulating sheath means that the lead cannot be made as thin as is desirable.

It is an object of the present invention to provide a medical system of the type described above wherein the number of metallic conductors is minimized.

Such a medical system is achieved in accordance with the principles of the present invention by employing at least one optical conductor having a proximal end connected to a therapy-generating device and a distal end which is disposed at a location remote from the therapy-generating apparatus. A first converter or transducer is disposed at the proximal end of the optical conductor for converting optical signals into electrical signals and/or for converting electrical signals into optical signals. A second converter is located at the distal end of the optical conductor, for converting optical signals into electrical signals and/or for converting electrical signals into optical signals. A further component of the medical system is disposed at the distal end of the optical conductor, and receives and/or transmits signals to and/or from the therapy-generating apparatus via the optical conductor. The further component may be an electrode for administering therapy in the form of electrical energy to tissue at the treatment site, or may be a sensor for obtaining physiological information about tissue in the region of the treatment site, or may be a further medical device, such as another therapy-generating apparatus, with information being exchanged between the therapy-generating apparatus and the further therapy-generating apparatus.

By employing an optical conductor for carrying signals and/or energy, metallic conductors are not needed for most connections between medical a therapy-generating apparatus and living tissue, or between different medical devices.

The component disposed at the distal end of the optical conductor may include a first electrode surface and a second electrode surface, both connected to the second converter, so that electrical signals generated by the second converter are delivered to the living tissue via the first electrode surface as well as via the second electrode surface.

The system of the invention may be employed, for example, for delivering stimulation pulses to a heart, and would thus replace known electrode systems for pacemakers employing metallic conductors. For this purpose, the pacing electronics of the pacemaker would supply an electrical signal to the first converter located at the proximal end of the optical conductor, which would then be converted into a light pulse which would be transmitted via the optical conductor to the second converter located at the distal end. The second converter would then convert the optical pulse into an electrical pulse for stimulating the tissue.

Alternatively, or in addition to the above example, the first and second electrode surfaces disposed at the distal end of the optical conductor and connected to the second converter may be employed as a sensor, so that electrical signals sensed between the first electrode surface and the second electrode surface are supplied to the second converter, which generates an optical signal which is transmitted to the first converter via the optical conductor. The optical signal is then converted into an electrical signal and is appropriately analyzed in a known manner.

This embodiment permits living tissue to be sensed without the use of metallic conductors. If a combination of the above two embodiments is used in the context of a pacemaker, a heart can therefore be stimulated and sensed without the use of any metallic conductors whatsoever. The component connected at the distal end of the optical conductor may additionally include a third electrode surface and a fourth electrode surface, both connected to the second converter, so that electrical signals sensed between the third electrode and fourth electrode surfaces can be supplied to the second converter to generate an optical signal which is transmitted to the first converter via the optical conductor. With two pairs of electrode surfaces, one pair can be used exclusively for emitting stimulation pulses, and the other pair can be used exclusively for sensing. The system can then include means for automatically checking as to whether an emitted stimulation pulse has achieved a desired effect, i.e., whether it induces an appropriate tissue response.

Preferably, the distance between the electrode surfaces in a pair of electrodes is less than 2 mm.

With a short distance between the electrode surfaces in a pair, the current needed to stimulate tissue would not have to be very high in order to depolarize one or several cardiac tissue cells, which would be sufficient to initiate a depolarization wave which stimulates all of the cardia tissue.

In a further embodiment of the invention, the component connected at the distal end of the optical conductor is an additional medical device, and information is transmittable between this additional medical device and the aforementioned therapy-generating apparatus via the optical conductor.

Particularly in implantable systems utilizing a plurality of devices, it is advantageous if information transmission between the devices is as free of noise as possible. This is achieved in accordance with the invention by the use of optical signals, which are unaffected by electromagnetic fields in the environment, thereby making the information transfer more reliable.

As used herein the term "implantable system" refers to a system which includes at least some components which are implantable, but does not necessarily require that all components of this system be implantable. An "implantable system" may include one or more extracorporeal components.

FIG. 1 is a schematic illustration of an embodiment of a medical system constructed in accordance with the principles of the present invention.

FIG. 2 shows an enlarged, detailed view of a tip electrode for stimulating and sensing heart tissue constructed in accordance with the principles of the present invention.

FIG. 3 shows a detailed, enlarged view of a contact plug for connection to a pacemaker or a defibrillator, constructed in accordance with the principles of the present invention.

FIG. 4 shows a detailed, enlarged view of a further embodiment of a connection for an optical conductor to a pacemaker or a defibrillator, constructed in accordance with the principles of the present invention.

A medical system 2, shown in FIG. 1, includes a pacemaker 4 connected to a heart 6 by an electrode element 8. The pacemaker 4 has a housing 4a of a size permitting implantation in the body of a subject. The electrode element 8 and the pacemaker 4 are connected to each other by means of a first optical line 10, which carries signals and energy between the pacemaker 4 and the electrode element 8. Heart tissue can be sensed, or induced to trigger a heartbeat, via the electrode element 8. The medical system 2 also includes a defibrillator 12, which is also connected to the heart 6. The defibrillator 6 has a housing 6a of a size permitting implantation in the body of the subject. A first defibrillation electrode 14 and a second defibrillation electrode 16 are positioned so as to surround the heart 6. The defibrillation electrodes 14 and 16 are connected to the defibrillator 12 by respective first and second metallic conductors 18 and 20. If the heart 6 exhibits fibrillation, The heart 6 can be defibrillated by means of the defibrillator 12 delivering a defibrillation pulse across the first defibrillation electrode 14 and the second defibrillation electrode 16. The pacemaker 4 and the defibrillator 12 are interconnected by a second optical line 22, so those components can exchange information.

FIG. 2 shows the structure of an exemplary embodiment of the electrode element 8 in greater detail. The electrode element 8 includes an electrode body 24, preferably made of a biocompatible polymer or another type of electrically insulating material. A first electrode surface 26 and a second electrode surface 28 are disposed at the exterior of the electrode body 24. The electrode surfaces 26 and 28 are positioned close to each other, for example, at a distance of 0.5 mm. This reduces the stimulation energy needed to trigger a heartbeat. A photodiode 30 is electrically connected to both of the electrode surfaces 26 and 28. The photodiode 30 is positioned so that optical signals, carried by a first optical conductor 32 in the optical lead 10, are incident on the photodiode 30 and are converted therein into pulses of electrical energy. These energy pulses are delivered to surrounding tissue via the first electrode surface 26 and the second electrode surface 28. A light-emitting diode 34 is also disposed in the electrode body 24. The light-emitting diode 34 emits light signals when electrical signals arising in the heart tissue are picked-up by the first electrode surface 26 and the second electrode surface 28. These generated optical signals are incident on an end face of a second optical conductor 36 contained in the optical line 10. The first optical conductor 32 and the second optical conductor 36 may be interleaved to form a helical coil, which proceeds the length of the first optical line 10. If the optical conductors 32 and 36 are made of a biocompatible, optical polymer, they can be helically coiled with a very small diameter, thereby making the first optical line 10 thinner than a corresponding metallic conductor contained in an insulating sheath.

A contact plug 38 is shown in FIG. 3, which is intended for detachable connection of the optical conductors 32 and 36 to the pacemaker 4. The contact plug 38 has a first contact surface 40 and a second contact surface 42 which are both in electrical contact with pacemaker electronics (not shown). A light-emitting diode 44 is connected across the first contact surface 40 and the second contact surface 42, so that it emits optical signals onto an end face of the first optical conductor 32, which are transmitted along the first optical conductor 32. A photodiode 46 is disposed to receive optical signals carried by the second optical conductor 36, and converts the received signals into electrical signals.

FIG. 4 shows an alternative structure for achieving contact between the optical conductors and the remainder of the medical device. In this embodiment, a contact socket 48, which may be present as part of the pacemaker 4 and/or as part of the defibrillator 12, has a receiver receptacle 50, into which a contact plug 52 can be inserted. The contact plug 52 has a guide key 54, in the form of a ridge or projection, to ensure correct insertion of the contact plug 52 into the receiver receptacle 50. Within the contact socket 48, a photodiode 56 is disposed to receive the optical signals carried by a first optical conductor 58. A light-emitting diode 60 is also disposed in the contact socket 48, which emits optical signals to be carried by a second optical conductor 62. The photodiode 56 and the light-emitting diode 60 are connected to an electronics unit 64 which may be, for example, the pacemaker electronics or the defibrillator electronics.

Although further 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.