US20070198073A1 - Medical device with a mri-induced signal attenuating member - Google Patents

Abstract

A lead includes a conductor having a distal end and a proximal end. The lead also includes a filter circuit in the conductor. The filter circuit filters out magnetic resonance imaging induced signals.

Description

PRIORITY INFORMATION
• The present application is a divisional of co-pending U.S. patent application Ser. No. 10/972,275, filed on Oct. 22, 2004, which said co-pending U.S. patent application Ser. No. 10/972,275, filed on Oct. 22, 2004 is a divisional of U.S. patent application Ser. No. 10/077,906, filed on Feb. 19, 2002.
• The present application claims priority, under 35 U.S.C. §120, from co-pending U.S. patent application Ser. No. 10/972,275, filed on Oct. 22, 2004, said U.S. patent application Ser. No. 10/972,275, filed on Oct. 22, 2004 claiming priority, under 35 U.S.C. §120, from U.S. patent application Ser. No. 10/077,906, filed on Feb. 19, 2002, said U.S. patent application Ser. No. 10/077,906 claiming priority, under 35 U.S.C. §119(e), from U.S. Provisional Patent Application Ser. No. 60/269,817, filed on Feb. 20, 2001. The present application also claims priority, under 35 U.S.C. §120, from U.S. patent application Ser. No. 10/077,906, filed on Feb. 19, 2002, and claims priority, under 35 U.S.C. §119(e), from U.S. Provisional Patent Application Ser. No. 60/269,817, filed on Feb. 20, 2001.
• The entire contents of U.S. patent application Ser. No. 10/972,275 and U.S. patent application Ser. No. 10/077,906 are hereby incorporated by reference. The entire content of U.S. Provisional Patent Application Ser. No. 60/269,817 is hereby incorporated by reference.
FIELD OF THE PRESENT INVENTION
• The present invention relates generally to an implantable device that is immune or hardened to electromagnetic insult or interference. More particularly, the present invention is directed to implantable systems that utilize fiber optic leads and other components to hardened or immune the systems from electromagnetic insult, namely magnetic-resonance imaging insult.
BACKGROUND OF THE PRESENT INVENTION
• Magnetic resonance imaging (“MRI”) has been developed as an imaging technique adapted to obtain both images of anatomical features of human patients as well as some aspects of the functional activities of biological tissue. These images have medical diagnostic value in determining the state of the health of the tissue examined.
• In an MRI process, a patient is typically aligned to place the portion of the patient's anatomy to be examined in the imaging volume of the MRI apparatus. Such an MRI apparatus typically comprises a primary magnet for supplying a constant magnetic field (B₀) which, by convention, is along the z-axis and is substantially homogeneous over the imaging volume and secondary magnets that can provide linear magnetic field gradients along each of three principal Cartesian axes in space (generally x, y, and z, or x₁, x₂and x₃, respectively). A magnetic field gradient (ΔB₀/Δx_i) refers to the variation of the field along the direction parallel to B₀with respect to each of the three principal Cartesian axes, x_i. The apparatus also comprises one or more RF (radio frequency) coils which provide excitation and detection of the MRI signal.
• The use of the MRI process with patients who have implanted medical assist devices; such as cardiac assist devices or implanted insulin pumps; often presents problems. As is known to those skilled in the art, implantable devices (such as implantable pulse generators (IPGs) and cardioverter/defibrillator/pacemakers (CDPs)) are sensitive to a variety of forms of electromagnetic interference (EMI) because these enumerated devices include sensing and logic systems that respond to low-level electrical signals emanating from the monitored tissue region of the patient. Since the sensing systems and conductive elements of these implantable devices are responsive to changes in local electromagnetic fields, the implanted devices are vulnerable to external sources of severe electromagnetic noise, and in particular, to electromagnetic fields emitted during the magnetic resonance imaging (MRI) procedure. Thus, patients with implantable devices are generally advised not to undergo magnetic resonance imaging (MRI) procedures.
• To more appreciate the problem, the use of implantable cardiac assist devices during a MRI process will be briefly discussed.
• The human heart may suffer from two classes of rhythmic disorders or arrhythmias: bradycardia and tachyarrhythmia. Bradycardia occurs when the heart beats too slowly, and may be treated by a common implantable pacemaker delivering low voltage (about 3 V) pacing pulses.
• The common implantable pacemaker is usually contained within a hermetically sealed enclosure, in order to protect the operational components of the device from the harsh environment of the body, as well as to protect the body from the device.
• The common implantable pacemaker operates in conjunction with one or more electrically conductive leads, adapted to conduct electrical stimulating pulses to sites within the patient's heart, and to communicate sensed signals from those sites back to the implanted device.
• Furthermore, the common implantable pacemaker typically has a metal case and a connector block mounted to the metal case that includes receptacles for leads which may be used for electrical stimulation or which may be used for sensing of physiological signals. The battery and the circuitry associated with the common implantable pacemaker are hermetically sealed within the case. Electrical interfaces are employed to connect the leads outside the metal case with the medical device circuitry and the battery inside the metal case.
• Electrical interfaces serve the purpose of providing an electrical circuit path extending from the interior of a hermetically sealed metal case to an external point outside the case while maintaining the hermetic seal of the case. A conductive path is provided through the interface by a conductive pin that is electrically insulated from the case itself.
• Such interfaces typically include a ferrule that permits attachment of the interface to the case, the conductive pin, and a hermetic glass or ceramic seal that supports the pin within the ferrule and isolates the pin from the metal case.
• A common implantable pacemaker can, under some circumstances, be susceptible to electrical interference such that the desired functionality of the pacemaker is impaired. For example, common implantable pacemaker requires protection against electrical interference from electromagnetic interference (EMI), defibrillation pulses, electrostatic discharge, or other generally large voltages or currents generated by other devices external to the medical device. As noted above, more recently, it has become crucial that cardiac assist systems be protected from magnetic-resonance imaging sources.
• Such electrical interference can damage the circuitry of the cardiac assist systems or cause interference in the proper operation or functionality of the cardiac assist systems. For example, damage may occur due to high voltages or excessive currents introduced into the cardiac assist system.
• Therefore, it is required that such voltages and currents be limited at the input of such cardiac assist systems, e.g., at the interface. Protection from such voltages and currents has typically been provided at the input of a cardiac assist system by the use of one or more zener diodes and one or more filter capacitors.
• For example, one or more zener diodes may be connected between the circuitry to be protected, e.g., pacemaker circuitry, and the metal case of the medical device in a manner which grounds voltage surges and current surges through the diode(s). Such zener diodes and capacitors used for such applications may be in the form of discrete components mounted relative to circuitry at the input of a connector block where various leads are connected to the implantable medical device, e.g., at the interfaces for such leads.
• However, such protection, provided by zener diodes and capacitors placed at the input of the medical device, increases the congestion of the medical device circuits, at least one zener diode and one capacitor per input/output connection or interface. This is contrary to the desire for increased miniaturization of implantable medical devices.
• Further, when such protection is provided, interconnect wire length for connecting such protection circuitry and pins of the interfaces to the medical device circuitry that performs desired functions for the medical device tends to be undesirably long. The excessive wire length may lead to signal loss and undesirable inductive effects. The wire length can also act as an antenna that conducts undesirable electrical interference signals to sensitive CMOS circuits within the medical device to be protected.
• Additionally, the radio frequency (RF) energy that is inductively coupled into the wire causes intense heating along the length of the wire, and at the electrodes that are attached to the heart wall. This heating may be sufficient to ablate the interior surface of the blood vessel through which the wire lead is placed, and may be sufficient to cause scarring at the point where the electrodes contact the heart. A further result of this ablation and scarring is that the sensitive node that the electrode is intended to pace with low voltage signals becomes desensitized, so that pacing the patient's heart becomes less reliable, and in some cases fails altogether.
• Another conventional solution for protecting the implantable medical device from electromagnetic interference is illustrated inFIG. 1.FIG. 1 is a schematic view of an implantablemedical device12 embodying protection against electrical interference. At least onelead14 is connected to the implantablemedical device12 inconnector block region13 using an interface.
• In the case where implantablemedical device12 is a pacemaker implanted in abody10, thepacemaker12 includes at least one or both of pacing and sensing leads represented generally as leads14 to sense electrical signals attendant to the depolarization and repolarization of theheart16, and to provide pacing pulses for causing depolarization of cardiac tissue in the vicinity of the distal ends thereof.
• FIG. 2 more particularly illustrates the circuit that is used conventionally to protect from electromagnetic interference. As shown inFIG. 2,protection circuitry52 is provided using a diode array component130. The diode array consists of five zener diode triggered semiconductor controlled rectifiers (SCRs) with anti-parallel diodes arranged in an array with one common connection. This allows for a small footprint despite the large currents that may be carried through the device during defibrillation, e.g., 10 amps. The SCRs190-194 turn on and limit the voltage across the device when excessive voltage and current surges occur.
• As shown inFIG. 2, each of the zener diode triggered SCRs190-194 is connected to an electrically conductive pin34-37, respectively. Further, each electrically conductive pin34-37 is connected to a medical device contact region140-143 to be wire bonded to pads90-93 of a printed circuit board. The diode array component130 is connected to the electrically conductive pins34-37 via the die contact regions180-184, respectively, along with other electrical conductive traces of the printed circuit board.
• Other attempts have been made to protect implantable devices from MRI fields. For example, U.S. Pat. No. 5,968,083 (to Ciciarelli et al.) describes a device adapted to switch between low and high impedance modes of operation in response to EMI insult. Furthermore, U.S. Pat. No. 6,188,926 (to Vock) discloses a control unit for adjusting a cardiac pacing rate of a pacing unit to an interference backup rate when heart activity cannot be sensed due to EMI.
• Although, conventional medical devices provide some means for protection against electromagnetic interference, these conventional devices require much circuitry and fail to provide fail-safe protection against radiation produced by magnetic-resonance imaging procedures. Moreover, the conventional devices fail to address the possible damage that can be done at the tissue interface due to RF-induced heating, and they fail to address the unwanted heart stimulation that may result from RF-induced electrical currents.
• Thus, it is desirable to provide protection against electromagnetic interference, without requiring much circuitry and to provide fail-safe protection against radiation produced by magnetic-resonance imaging procedures. Moreover, it is desirable to provide devices that prevent the possible damage that can be done at the tissue interface due to induced electrical signals and due to thermal tissue damage. Furthermore, it is desirable to provide to provide an effective means for transferring energy from one point in the body to another point without having the energy causing a detrimental effect upon the body.
SUMMARY OF THE PRESENT INVENTION
• A first aspect of the present invention is a lead. The lead includes a conductor having a distal end and a proximal end and a filter circuit in the conductor, the filter circuit filtering out magnetic resonance imaging induced signals.
• Another aspect of the present invention is a lead. The lead includes a plurality of conductors, each conductor having a distal end and a proximal end, and a plurality of filter circuits, each filter circuit being in a conductor, each filter circuit filtering out magnetic resonance imaging induced signals.
• Another aspect of the present invention is a lead. The lead includes a conductor having a distal end and a proximal end; an electrode connected to the distal end of the conductor; and a filter circuit in the conductor. The filter circuit is connected in series between the conductor and the electrode. The filter circuit filters out magnetic resonance imaging induced signals.
• Another aspect of the present invention is a lead. The lead includes a conductor having a distal end and a proximal end and a filter circuit in the conductor, the filter circuit attenuating magnetic resonance imaging induced signals.
• Another aspect of the present invention is a lead. The lead includes a plurality of conductors, each conductor having a distal end and a proximal end, and a plurality of filter circuits, each filter circuit being in a conductor, each filter circuit attenuating magnetic resonance imaging induced signals.
• Another aspect of the present invention is a lead. The lead includes a conductor having a distal end and a proximal end; an electrode connected to the distal end of the conductor; and a filter circuit in the conductor. The filter circuit is connected in series between the conductor and the electrode. The filter circuit attenuates magnetic resonance imaging induced signals.
• Another aspect of the present invention is a lead. The lead includes a conductor having a distal end and a proximal end and a filter circuit in the conductor, the filter circuit limiting magnetic resonance imaging induced signals.
• Another aspect of the present invention is a lead. The lead includes a plurality of conductors, each conductor having a distal end and a proximal end, and a plurality of filter circuits, each filter circuit being in a conductor, each filter circuit limiting magnetic resonance imaging induced signals.
• Another aspect of the present invention is a lead. The lead includes a conductor having a distal end and a proximal end; an electrode connected to the distal end of the conductor; and a filter circuit in the conductor. The filter circuit is connected in series between the conductor and the electrode. The filter circuit limit magnetic resonance imaging induced signals.
• Another aspect of the present invention is a conductor having a distal end and a proximal end. The conductor consisting essentially of a filter circuit, the filter circuit filtering out magnetic resonance imaging induced signals.
• Another aspect of the present invention is a lead. The lead includes a plurality of conductors, each conductor having a distal end and a proximal end, each conductor consisting essentially of a filter circuit, each filter circuit filtering out magnetic resonance imaging induced signals.
• Another aspect of the present invention is a lead. The lead includes a conductor having a distal end and a proximal end and an electrode connected to the distal end of the conductor. The conductor consisting essentially of a filter circuit. The filter circuit is connected in series between the conductor and the electrode. The filter circuit filters out magnetic resonance imaging induced signals.
• Another aspect of the present invention is a conductor having a distal end and a proximal end. The conductor consisting essentially of a filter circuit, the filter circuit attenuating magnetic resonance imaging induced signals.
• Another aspect of the present invention is a lead. The lead includes a plurality of conductors, each conductor having a distal end and a proximal end, each conductor consisting essentially of a filter circuit, each filter circuit attenuating magnetic resonance imaging induced signals.
• Another aspect of the present invention is a lead. The lead includes a conductor having a distal end and a proximal end and an electrode connected to the distal end of the conductor. The conductor consisting essentially of a filter circuit. The filter circuit is connected in series between the conductor and the electrode. The filter circuit attenuates magnetic resonance imaging induced signals.
• Another aspect of the present invention is a conductor having a distal end and a proximal end. The conductor consisting essentially of a filter circuit, the filter circuit limiting magnetic resonance imaging induced signals.
• Another aspect of the present invention is a lead. The lead includes a plurality of conductors, each conductor having a distal end and a proximal end, each conductor consisting essentially of a filter circuit, each filter circuit limiting magnetic resonance imaging induced signals.
• Another aspect of the present invention is a lead. The lead includes a conductor having a distal end and a proximal end and an electrode connected to the distal end of the conductor. The conductor consisting essentially of a filter circuit. The filter circuit is connected in series between the conductor and the electrode. The filter circuit limits magnetic resonance imaging induced signals.
BRIEF DESCRIPTION OF THE DRAWINGS
• The present invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating a preferred embodiment and are not to be construed as limiting the present invention, wherein:
• FIGS. 1 and 2 are illustrations of conventional techniques used to protect against electromagnetic interference;
• FIG. 3 is a block diagram of one embodiment of a MRI immune cardiac assist system according to some or all of the concepts of the present invention;
• FIG. 4 is a block diagram of another embodiment of a MRI immune cardiac assist system according to some or all of the concepts of the present invention;
• FIGS. 5 through 20 are schematics of various optical sensing devices according to some or all of the concepts of the present invention;
• FIG. 21 illustrates a pressure optical transducer according to some or all of the concepts of the present invention;
• FIGS. 22 through 26 are block diagrams of various pressure optical transducers according to some or all of the concepts of the present invention;
• FIG. 27 is a partial view of a cardiac assist device according to some or all of the concepts of the present invention with an intermediate portion of the photonic catheter thereof removed for illustrative clarity;
• FIG. 28 is an enlarged partial perspective view of components located at the distal end of the photonic catheterFIG. 27;
• FIG. 29 is a detailed partial schematic view showing one construction of an electro-optical transducer according to some or all of the concepts of the present invention;
• FIG. 31 is a graph depicting a typical pulse sequence used in pacing a human heart, over an interval equivalent to a nominal 1 Hz human heartbeat;
• FIG. 32 is a similar graph depicting the pacing pulse as shown inFIG. 31, but with a much finer time scale;
• FIG. 33 is a schematic representation of a cardiac pacing lead with two electrodes;
• FIG. 34 is a schematic representation of a similar cardiac pacing lead with three electrodes;
• FIG. 35 is a schematic representation of yet another cardiac pacing lead with two pairs of electrodes;
• FIG. 36 is a graph depicting the use of pulsewidth pacing signals and interleaved periods for sensing heart activity;
• FIG. 37 is a graph depicting the operation of one embodiment according to some or all of the concepts of the present invention that gains energy efficiency by means of early termination of the pacing signal;
• FIG. 38 is a graph depicting the operation of another embodiment according to some or all of the concepts of the present invention that gains energy efficiency by means of both early termination of the pacing signal and by gradient pulsewidth power control;
• FIG. 39 is another graph of the embodiment inFIG. 38, but with alternate waveform of the pacing signal;
• FIGS. 40 through 42 are schematic circuit diagrams of a pulse generator according to some or all of the concepts of the present invention;
• FIG. 43 is a schematic circuit diagram showing one embodiment of an opto-electric coupling device according to some or all of the concepts of the present invention;
• FIGS. 44 and 45 are graphical illustrations of pulse waveforms that may be, respectively, input to and output from the opto-electric coupling device according to some or all of the concepts of the present invention;
• FIG. 46 is a schematic circuit diagram showing a second embodiment of an opto-electric coupling device in accordance with the invention;
• FIG. 47 is a schematic circuit diagram showing a constant current regulator for a laser light generator according to some or all of the concepts of the present invention;
• FIG. 48 is a detailed partial schematic view showing one construction of an electro-optical transducer according to some or all of the concepts of the present invention;
• FIG. 49 is a schematic circuit diagram of a pulse generator according to some or all of the concepts of the present invention;
• FIG. 50 is an exploded perspective view of a hermetic component housing according to some or all of the concepts of the present invention;
• FIGS. 51 through 53 are sectional axial centerline views showing alternative ways in which the component housing ofFIG. 50 can be configured;
• FIG. 54 is a perspective view of the component housing ofFIG. 50 showing details of exemplary components that may be housed therein;
• FIG. 55 is a partial exploded perspective view of a hermetic component housing according to some or all of the concepts of the present invention;
• FIGS. 56 and 57 are sectional axial centerline views showing alternative ways in which the component housing ofFIG. 55 can be configured;
• FIG. 58 is a perspective view of the component housing ofFIG. 55 showing details of exemplary components that may be housed therein;
• FIG. 59 is a partially exploded perspective view of a hermetic component housing according to some or all of the concepts of the present invention;
• FIG. 60 is a sectional view taken along the axial centerline of the component housing ofFIG. 59;
• FIG. 61 is a perspective view of the component housing ofFIG. 59 showing details of exemplary components that may be housed therein; and
• FIGS. 62 through 65 are schematics of various optical pressure transducers according to some or all of the concepts of the present invention;
• FIGS. 66 through 69 are schematics of various MRI coils for a photonic catheter according to some or all of the concepts of the present invention; and
• FIGS. 70 through 85 are schematics of various optical power transfer devices according to some or all of the concepts of the present invention.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
• As noted above, the present invention is directed to an implantable device that is immune or hardened to electromagnetic insult or interference.
• FIG. 3 illustrates a cardiac assist system that is immune or hardened electromagnetic insult or interference, namely to magnetic radiation imaging, MRI. As illustrated inFIG. 3, amain module40 includes aprocessor circuit43 that controls the operations of the cardiac assist system. Theprocessor unit43 provides control signals to apacing unit45. Thepacing unit45 produces packets of energy to stimulate theheart49 to start beating or to beat at a predetermined rate or pace. Theprocessor circuit43 also receives information about the conditions of theheart49 from asensing unit44. Thesensing unit44, through sensors or electrodes, monitors the conditions of theheart49 to provide feedback information to theprocessor circuit43.
• Atelemetry unit46 is also provided in themain module40 to provide information to theprocessor circuit43 received from sources external to the body. Lastly, atiming circuit42 is provided to communicate with anauxiliary module50 through anoptical communication interface41 in themain module40, overoptical communication channels36, such as fiber optics, and through anoptical communication interface46 in theauxiliary module50. In response to the information received from theoptical communication interface46, asignaling logic circuit47 will activate or suppress apacing unit48. In this embodiment, if there is a failure in themain module40 due to error or electromagnetic insult or interference, thesignaling logic circuit47 will detect the shutdown of themain module40 and cause theauxiliary module50 to take over the pacing of theheart49 in an asynchronous manner throughpacing unit48.
• As described above, the cardiac assist system performs synchronous cardiac assist operations through a main module. A secondary module is provided to perform asynchronous cardiac assist operations. Upon detection of an electromagnetic interference insult upon the cardiac assist system, the control circuit of the main module terminates synchronous cardiac assist operations, and the control circuit of the secondary module initiates asynchronous cardiac assist operations upon detection of the electromagnetic interference insult. The control circuit of the secondary module places the cardiac assist system in the asynchronous mode for a duration of the electromagnetic interference insult and terminates the asynchronous mode of the cardiac assist system upon detection of an absence of an electromagnetic interference insult. The control circuit of the main module terminates the synchronous mode of the cardiac assist system for the duration of the electromagnetic interference insult and re-initiates the synchronous mode of the cardiac assist system upon detection of an absence of an electromagnetic interference insult.
• FIG. 4 is a more detail schematic ofFIG. 3. InFIG. 4, a cardiac assist system is immune or hardened electromagnetic insult or interference, namely to magnetic radiation imaging, MRI. As illustrated inFIG. 4, amain module67 includes aparallel processing unit59 and primary andsecondary processors65 and63 that control the operations of the cardiac assist system. Theparallel processing unit59 provides control signals to apacing unit58. Thepacing unit58 produces packets of energy to stimulate the heart to start beating or to beat at a predetermined rate or pace through lead(s)51 andelectrode52. Theparallel processing unit59 also receives information about the conditions of theheart49 from asensor53 through lead(s)56. Thesensor53 monitors the conditions of the heart to provide feedback information to theparallel processing unit59.
• Atelemetry unit62 is also provided in themain module67 to provide information to theparallel processing unit59 received fromsources60 external to the body.Memory72 is provided for the processing of the cardiac assist system, and a primaryerror detection circuit64 is included to detect any failures in themain module67. Lastly, atiming circuit66 is provided to communicate with anauxiliary module69 through anoptical emitter68 in themain module67, overoptical communication channels70, such as fiber optics, and through a light detection and signalingcircuit73 in theauxiliary module69.
• In response to the information received from the light detection and signalingcircuit73, apacing unit74 will activate or de-activate. In this embodiment, if there is a failure in themain module67 due to error or electromagnetic insult or interference, the light detection and signalingcircuit73 will detect the shutdown of themain module67 and cause theauxiliary module69 to take over the pacing of the heart in an asynchronous manner throughpacing unit74, lead(s)55, andelectrode54.
• As described above, the cardiac assist system performs synchronous cardiac assist operations through a main module. A secondary module is provided to perform asynchronous cardiac assist operations. Upon detection of an electromagnetic interference insult upon the cardiac assist system, the control circuit of the main module terminates synchronous cardiac assist operations, and the control circuit of the secondary module initiates asynchronous cardiac assist operations upon detection of the electromagnetic interference insult. The control circuit of the secondary module places the cardiac assist system in the asynchronous mode for a duration of the electromagnetic interference insult and terminates the asynchronous mode of the cardiac assist system upon detection of an absence of an electromagnetic interference insult. The control circuit of the main module terminates the synchronous mode of the cardiac assist system for the duration of the electromagnetic interference insult and re-initiates the synchronous mode of the cardiac assist system upon detection of an absence of an electromagnetic interference insult.
• FIG. 30 illustrates a cardiac assist system that includes aprimary device housing1100. Theprimary device housing1100 includes acontrol circuit1110, such as a microprocessor integrated circuit for controlling the operations of the cardiac assist system. Thecontrol circuit1110 may select a mode of operation for the cardiac assist system based on predetermined sensed parameters. Theprimary device housing1100 may also include circuitry (not shown) to detect and isolate cross talk between device pulsing operations and device sensing operations. Thecontrol circuit1110 may isolate physiological signals using a noise filtering circuit or a digital noise filtering.
• Theprimary device housing1100 is implantable such that thecontrol circuit1110 can be programmable from a source external of theprimary device housing1100 or thecontrol circuit1110 can provide physiological diagnostics to a source external of theprimary device housing1100.
• Theprimary device housing1100 includes apower source1120. Thepower source1120 may be a battery power source in combination with a battery power source measuring circuit. In this embodiment, thecontrol circuit1110 can automatically adjust a value for determining an elective replacement indication condition of a battery power source such that the value is automatically adjusted by thecontrol circuit1110 in response to a measured level of a state of the battery power source, the measured level generated by the battery power source measuring circuit connected to the battery power source.
• Theprimary device housing1100 includes anoptical emitter1130, anoptical sensor1140, and aninterface1170 to put theprimary device housing1100 in operative communication with alead system1150.
• Theprimary device housing1100 may also include a switch (not shown), such as a reed switch or solid state switch, to place thecontrol circuit1110 into a fixed-rate mode of operation and an acoustic sensor (not shown) or near infrared sensor (not shown) to sense a predetermined acoustic signal. The switch places thecontrol circuit1110 into a fixed-rate mode of operation when the acoustic sensor or near infrared sensor senses the predetermined acoustic signal or the predetermined infrared signal.
• Theprimary device housing1100 has formed around it ashield1160 to shield theprimary device housing1100 and any circuits therein from electromagnetic interference.
• Theshield1160 may be a metallic sheath, a carbon composite sheath, or a polymer composite sheath to shield theprimary device housing1100 and any circuits therein from electromagnetic interference. Theshield1160 is further covered with a biocompatible material wherein the biocompatible material may be a non-permeable diffusion resistant biocompatible material. Theprimary device housing1100 may also include a detection circuit (not shown) to detect a phase timing of an external electromagnetic field such that thecontrol circuit1110 alters its operations to avoid interfering with the detected external electromagnetic field.
• FIG. 30 further illustrates alead system1150 connected to theprimary device housing1100. Thelead system1150 provides a communication path for information to be transported between theprimary device housing1100 and a distal location in the body. Thelead system1150 also may be a conduit of power or energy from theprimary device housing1100 to the distal location in the body.
• In the example illustrated inFIG. 30, thelead system1150 may provide a path for control signals to be transferred to the distal location of the body, such as the heart muscle tissue. These control signals are used to control the operations of asecondary device1200, such as stimulating the beating of the heart. Thelead system1150 may also provide a path for signals representing sensed biological conditions to be transferred from the distal location of the body to theprimary device housing1100 so that the functionality of the heart muscle tissue can be effectively monitored.
• Thelead system1150 may be a fiber optic based communication system wherein the fiber optic communication system contains at least one channel within a multi-fiber optic bundle. The fiber optic based communication system is covered with a biocompatible material wherein the biocompatible material is a non-permeable diffusion resistant biocompatible material.
• Thelead system1150 may also be a plurality of electrical leads that have ashield1180 therearound to prevent the electrical leads from conducting stray electromagnetic interference. Thisshield1180 may be a metallic sheath, a carbon composite sheath, or a polymer composite sheath to prevent the electrical leads from conducting stray electromagnetic interference. In addition to theshield1180 or in lieu of theshield1180, each electrical lead may include an electrical filter wherein the electrical filter removes stray electromagnetic interference from a signal being received from the electrical lead. The electrical filter may comprise capacitive and inductive filter elements adapted to filter out predetermined frequencies of electromagnetic interference. Theshield1180 is covered with a biocompatible material wherein the biocompatible material is a non-permeable diffusion resistant biocompatible material.
• The electrical leads maybe unipolar leads, bipolar leads, or a combination of unipolar and bipolar leads. Thelead system1150 may also be a combination of a fiber optic based communication system and electrical leads.
• Thelead system1150 may also include a detection circuit (not shown) to detect a phase timing of an external electromagnetic field such that thecontrol circuit1110 alters its operations to avoid interfering with the detected external electromagnetic field.
• InFIG. 30, thesecondary housing1200 includes acontrol circuit1210, such as a microprocessor integrated circuit. Thesecondary device housing1200 may also include circuitry (not shown) to detect and isolate cross talk between device pulsing operations and device sensing operations. Thecontrol circuit1210 may isolate physiological signals using a noise filtering circuit or a digital noise filtering.
• Thesecondary device housing1200 includes apower source1220. Thepower source1220 may be a battery power source or capacitor or other device for storing. Theprimary device housing1200 includes anoptical emitter1230, anoptical sensor1240, and aninterface1270 to put thesecondary device housing1200 in operative communication with thelead system1150.
• Thesecondary device housing1200 has formed around it ashield1260 to shield thesecondary device housing1200 and any circuits therein from electromagnetic interference.
• Theshield1260 may be a metallic sheath, a carbon composite sheath, or a polymer composite sheath to shield thesecondary device housing1200 and any circuits therein from electromagnetic interference. Theshield1260 is further covered with a biocompatible material wherein the biocompatible material may be a non-permeable diffusion resistant biocompatible material.
• Thesecondary housing1200 may also includeelectrodes1300 for either stimulating a tissue region or sensing biological characteristics or parameters from the tissue region. More details as to the construction of the secondary device are set forth below in the describing of distal end elements.
• As an alternative toelectrodes1300, thesecondary device housing1200 may include a sensing and stimulation system that includes optical pulsing components to deliver a stimulus of a predetermined duration and power to the desired anatomical cardiac tissue region; a sensing and stimulation system that includes optical pulsing components to deliver a stimulus of a predetermined duration and power to the desired anatomical cardiac tissue region and electrical pulsing components to deliver a stimulus of a predetermined duration and power to the desired anatomical cardiac tissue region; a hydrostatic pressure sensing components to detect physiological signals from the desired anatomical cardiac tissue region; or optical sensing components to detect physiological signals from the desired anatomical cardiac tissue region and electrical sensing components to detect physiological signals from the desired anatomical cardiac tissue region.
• Thesecondary device housing1200 may also include a detection circuit (not shown) to detect a phase timing of an external electromagnetic field such that thecontrol circuit1110 alters its operations to avoid interfering with the detected external electromagnetic field.
• Thesecondary device housing1200 may include sensors to detect a heart signal and to produce a sensor signal therefrom and a modulator to modulate the sensor signal to differentiate the sensor signal from electromagnetic interference. In the alternative, thesecondary device housing1200 may include sensors to detect a heart signal and to produce a sensor signal therefrom, and theprimary device housing1100 may include a sampling circuit to sample the sensor signal multiple times to differentiate the sensor signal from electromagnetic interference, undesirable acoustic signals, large muscle contractions, or extraneous infrared light.
• The cardiac assist system illustrated inFIG. 30 may detect an electromagnetic interference insult upon the cardiac assist system, and upon detection, thecontrol circuit1110 places the cardiac assist system in an asynchronous mode. Thecontrol circuit1110 places the cardiac assist system in the asynchronous mode for a duration of the electromagnetic interference insult and places the cardiac assist system in a synchronous mode upon detection of an absence of an electromagnetic interference insult. The electromagnetic interference insult may be detected a thermistor or other heat detector, a high frequency interference detector, a high voltage detector, or an excess current detector.
• The cardiac assist system illustrated inFIG. 30 may also provide atrial monitoring and diagnostic functions to help physicians make more precise patient management decisions. The cardiac assist system illustrated inFIG. 30 can provide bradyarrhythmia therapies that treat patients with chronic heart problems in which the heart beats too slowly to adequately support the body's circulatory needs, in addition to the monitoring of the atria (upper chambers) and ventricles (lower chambers) to enable physicians to assess atrial rhythm control and ventricular rate control.
• The cardiac assist system illustrated inFIG. 30 can also be used to provide daily atrial fibrillation measurements to assess atrial rhythm control. This information can improve a physician's ability to track disease progression, as well as the effectiveness of current device and drug therapies. The cardiac assist system illustrated inFIG. 30 can also be used to monitor of the ventricular rate during an atrial arrhythmia that helps assess ventricular rate control. This information can be viewed in a graphical snapshot format or by viewing the specific episode EGM information. The cardiac assist system illustrated inFIG. 30 can also be used to provide specific information on the frequency and duration of arrhythmias that help with risk assessment of symptoms and in determining whether a change in anticoagulation medicines is warranted.
• FIG. 27 illustrates an MRI-compatible cardiac pacemaker according to another embodiment of the present invention. The pacemaker may be wearable and is readily implemented to operate in a fixed-rate (VOO) mode. The pacemaker includes a first (main)enclosure263 that is designed to be located outside the body and connected to aproximal end268 of a photonic catheter. Adistal end273 of aphotonic catheter271 mounts a bipolar endocardial (or pericardial)electrode pair286 that includes asecond enclosure283 and athird enclosure285 separated by ashort insulative spacer284. Other electrode configurations could also be used.
• Themain enclosure263 houses a self-containedelectrical power source264, apulse generator265, and an electro-optical transducer266. Thepower source264, which may include one or more batteries, serves to deliver low energy continuous electrical power to the pulse generator. Thepulse generator265 stores the electrical energy provided by thepower source264 in one or more storage devices such as capacitors, batteries, etc., and periodically releases that energy to deliver electrical pulses to the electro-optical transducer266. The electro-optical transducer266 converts the electrical pulses into light energy and directs that energy into theproximal end268 of thephotonic catheter271.
• Themain enclosure263 is preferably formed as a sealed casing, external to the body, made from a non-magnetic metal. Note that a rate control selector and a pulse duration selector can be provided on themain enclosure263 to allow a medical practitioner to controllably stress a patient's heart by varying the rate and duration of the stimulating pulses. Note further that if thepower source264 comprises multiple batteries, these may be separately wired for independent operation and a selector switch can be provided on theenclosure263 to selectively activate each battery for use. A pair of illuminated push buttons may also be provided for testing each battery.
• Thephotonic catheter271 includes anoptical conduction pathway267 surrounded by a protectiveouter covering269. Theoptical conduction pathway267 may be constructed with one or more fiber optic transmission elements that are conventionally made from glass or plastic fiber material, e.g., a fiber optic bundle. To avoid body fluid incompatibility problems, the protective outer covering269 should be made from a biocompatible material, such as silicone rubber, polyurethane, polyethylene, or other biocompatible polymer having the required mechanical and physiological properties. The protective outer covering269 is thus a biocompatible covering. Insofar as thephotonic catheter271 must be adapted for insertion into the body, thebiocompatible covering269 is preferably a very thin-walled elongated sleeve or jacket having an outside diameter on the order of about5 millimeters and preferably as small as one millimeter or even smaller. This will render thephotonic catheter271 sufficiently slender to facilitate insertion thereof through a large vein, such as the external jugular vein.
• Theproximal end268 of thephotonic catheter271 is mounted to themain enclosure263 using an appropriate connection. Theoptical conduction pathway267 may extend into theenclosure263 for a short distance, where it terminates in adjacent relationship with the electro-optical transducer266 in order to receive light energy therefrom.
• Light emitted by the electro-optical transducer266 is directed into theproximal end268 of thephotonic catheter271, and transmitted through theoptical conduction pathway267 to thesecond enclosure283. Since thephotonic catheter271 is designed for optical transmission, it cannot develop magnetically induced or RF-induced electrical currents, as is the case with the metallic leads of conventional pacemaker catheters.
• Thesecond enclosure283 houses an opto-electrical transducer274, which converts light energy received from the distal end of thephotonic catheter271 into electrical energy. Theelectrical output side280 of the opto-electrical transducer274 delivers electrical pulses that drive the pacemaker'selectrode pair286.
• Thesecond enclosure283 is a hermetically sealed casing made from a non-magnetic metal, such as titanium, a titanium-containing alloy, platinum, a platinum-containing alloy, or any other suitable metal, including copper plated with a protective and compatible coating of the foregoing materials. Plated copper is especially suitable for thesecond enclosure283 because it has a magnetic susceptibility approaching that of the human body, and will therefore minimize MRI image degradation. Note that the magnetic susceptibility of human body tissue is very low, and is sometimes diamagnetic and sometimes paramagnetic. As an alternative to using non-magnetic metals, thesecond enclosure283 can be formed from an electrically conductive non-metal that preferably also has a very low magnetic susceptibility akin to that of the human body. Non-metals that best approach this condition include conductive composite carbon and conductive polymers comprising silicone, polyethylene, or polyurethane.
• Unlike themain enclosure263, thesecond enclosure283 is adapted to be implanted via insertion in close proximity to the heart, and in electrical contact therewith. As such, thesecond enclosure283 preferably has a miniaturized tubular profile that is substantially co-equal in diameter with thephotonic catheter271.
• As seen InFIGS. 27 and 28, the second enclosure (283,295) includes a cylindricalouter wall276 and a pair of disk-shapedend walls272 and277. Theend wall272 is mounted to thedistal end273 of thephotonic catheter271 using an appropriate sealed connection that prevents patient body fluids from contacting theoptical conduction pathway267 and from entering the second enclosure (283,295). Although thephotonic catheter271 may feed directly from themain enclosure263 to the second enclosure (283,295), another arrangement would be to provide anoptical coupling270 at an intermediate location on thephotonic catheter271. Thecoupling270 could be located so that a distal portion of thephotonic catheter271 that connects to thesecond enclosure283 protrudes a few inches outside the patient's body. A proximal portion of thephotonic catheter271 that connects to themain enclosure263 would then be connected when MRI scanning is to be performed. Note that themain enclosure263 could thus be located a considerable distance from the patient so as to be well outside the area of the MRI equipment, as opposed to being mounted on the patient or the patient's clothing.
• In an alternative arrangement, thecoupling270 could be located at themain enclosure263. Theoptical conduction pathway267 may extend into the enclosure (283,295) for a short distance, where it terminates in adjacent relationship with the opto-electrical transducer (274,289) in order to deliver light energy thereto. Light received by the opto-electrical transducer (274,289) will thus be converted to electrical energy and delivered to theoutput side280 of the opto-electrical transducer (274,289).
• Due to the miniature size of the second enclosure (283,295), the opto-electrical transducer (274,289) needs to be implemented as a miniaturized circuit. However, such components are conventionally available from commercial electronic component manufacturers. Note that the opto-electrical transducer (274,289) also needs to be adequately supported within the second enclosure (283,295).
• To that end, the second enclosure (283,295) can be filled with asupport matrix material291 that may be the same material used to form the photonic catheter's biocompatible covering269 (e.g., silicone rubber, polyurethane, polyethylene, or any biocompatible polymer with the required mechanical and physiological properties).
• As stated above, the second enclosure (283,295) represents part of an electrode pair (286,298) that delivers the electrical output of the pacemaker to a patient's heart. In particular, the electrode pair (286,298) is a tip/ring system and the second enclosure (283,295) is used as an endocardial (or pericardial) ring electrode thereof. A positive output lead (275,290) extending from theelectrical output side280 of the opto-electrical transducer (274,289) is electrically connected to thecylindrical wall276 of the second enclosure (283,295), as by soldering, welding or the like. A negative output lead (281,294) extending from theelectrical output side280 of the opto-electrical transducer (274,289) is fed out of the second enclosure (283,295) and connected to a third enclosure (285,297), which functions as an endocardial tip electrode of the electrode pair (286,298).
• The third enclosure (285,297) can be constructed from the same non-magnetic metallic material, or non-metal material, used to form the second enclosure (283,295). Since it is adapted to be inserted in a patient's heart as an endocardial tip electrode, the third enclosure (285,297) has a generally bullet shaped tip (279,293) extending from a tubular base end (278,292). The base end (278,292) preferably has an outside diameter that substantially matches the diameter of the second enclosure (283,295) and thephotonic catheter271. Note that the base end (278,292) of the third enclosure (285,297) is open insofar as the third enclosure (285,297) does not house any critical electrical components. Indeed, it mounts only the negative lead (281,294) that is electrically connected to the third enclosure's base end (278,292), as by soldering, welding, or the like.
• The material used to form the spacer (284,296) preferably fills the interior of the second enclosure (283,295) so that there are no voids and so that the negative lead (281,294) is fully captured therein.
• InFIG. 29,electrical power source303 is implemented using a pair of conventionalpacemaker lithium batteries300 providing a steady state DC output of about 3 to 9 volts. Electro-optical transducer301 is implemented with light emitting orlaser diodes304 and current limitingresistors305. Thediodes304 are conventional in nature and thus have a forward voltage drop of about 2 volts and a maximum allowable current rating of about 50-100 milliamperes, or more. If additional supply voltage is available from the power source20 (e.g., 4 volts or higher), more than one diode can be used in the electro-optical transducer for additional light energy output. The value of eachresistor305 is selected accordingly.
• By way of example, if thebatteries300produce 3 volts and the desired current through a single diode is 0.5 milliamperes, the value of the resistor should be about 2000 ohms. This would be suitable if the diode is a light emitting diode. If the diode were a laser diode, other values and components would be used. For example, a current level on the order of 100 milliamps may be required to produce coherent light output from the diode if it is a laser. Theoptical conduction pathway300 can be implemented as fiber optic bundles307, or as single fibers, driving respective arrays of photo diodes. The opto-electrical transducer28 may be implemented with six photodiodes312-317 that are wired for photovoltaic operation.
• The opto-electrical transducer309 may be implemented with a single photodiode that is wired for photovoltaic operation. The photodiodes are suitably arranged so that each respectively receives the light output of one or more fibers of the fiber optic bundles and is forward biased into electrical conduction thereby.
• Each photodiode is conventional in nature and thus produces a voltage drop of about 0.6 volts. Cumulatively, the photodiodes develop a voltage drop of about 3.3 volts across the respective positive and negative inputs a power amplifier (not shown). The photodiode develops about 0.6 volts across the respective positive and negative inputs of the power amplifier.
• FIGS. 40-42 and49 shows an alternative circuit configuration that may be used to implement the oscillator (369,372,373,439) and the power amplifier. The alternative circuit configurations are conventional in nature and do not constitute part of the present invention per se. The alternative circuit configurations are presented herein as examples of pulsing circuits that have been shown to function well in a pacemaker environment. InFIGS. 40-42, the oscillator (369,372,373,439) is a semiconductor pulsing circuit (365,370,374,441) of the type disclosed in U.S. Pat. No. 3,508,167. As described in U.S. Pat. No. 3,508,167, the contents of which are incorporated herein by reference, the pulsing circuit (365,370,374,441) forming the oscillator (369,372,373,439) provides a pulsewidth and pulse period that are relatively independent of load and supply voltage. The semiconductor elements are relegated to switching functions so that timing is substantially independent of transistor gain characteristics. In particular, a shunt circuit including a pair of diodes is connected so that timing capacitor charge and discharge currents flow through circuits that do not include the base-emitter junction of a timing transistor.
• InFIG. 46, an opto-electrical coupling device399 is shown. The opto-electrical coupling device includes opto-electrical transducer392. Ahigh quality capacitor390 delivers pulses from the opto-electrical transducers photodiode array (393-398) to atip electrode401. A return path is provided from aring electrode400. Thecapacitor390 forms part of a DCcurrent discharge system391 that also includes aresistor389. Theresistor389 is connected across thecapacitor390 to discharge it between pulses. Exemplary values for thecapacitor390 and theresistor389 are 10 microfarads and 20K ohms, respectively.
• InFIG. 47, a constantcurrent regulator402 is shown. The purpose of the constantcurrent regulator402 is to controllably drive the electro-optical transducer405 using the electrical pulse output of a pulse generator. Collectively, the constantcurrent regulator402 and the electro-optical transducer405 provide a constant current regulatedlaser light generator404. Thecurrent regulator402 uses anNPN transistor403 arranged in a common emitter configuration to drive thelaser diode404. A suitable NPN transistor that may be used to implement thetransistor403 is a switching transistor.
• Thelaser diode404 can be implemented as a standard150 milliwatt gallium arsenide laser diode. The recommended power level for driving such a device is about 100 milliwatts. The required input voltage is about 2 volts. Assuming there is a conventional diode voltage drop of about 0.7 volts across thelaser diode404, a driving current of about 140 milliamps should be sufficient to achieve operation at the desired 100 milliwatt level. However, the current through thelaser diode404 must be relatively constant to maintain the desired power output. The constantcurrent regulator402 achieves this goal.
• In particular, the base side of thetransistor403 is biased through a resister RI and a pair of diodes D1 and D2. The diodes D1 and D2 are connected between the base of thetransistor403 and ground. Each has a conventional diode voltage drop of about 0.7 volts, such that the total voltage drop across the diodes D1 and D2 is about 1.5 volts and is substantially independent of the current through the diodes (at operational current levels). This means that the base of thetransistor403 will be maintained at a relatively constant level of about 1.5 volts notwithstanding changes in the input voltage supplied from the pulse generator. The value of the resistor R1 is selected to be relatively high to reduce the current draw through the base of thetransistor403. By way of example, a value of 2500 ohms may be used for R1. Assuming a supply voltage of about 5 volts, as represented by the input pulse waveform, the current through the resistor R1 will be a negligible 1.4 milliamps.
• Importantly, the emitter side of thetransistor403 will remain at a relatively constant level of about 1 volt (assuming a base-emitter voltage drop across thetransistor403 of about 0.5 volts). A resistor R2 is placed between the emitter of thetransistor403 and ground in order to establish a desired current level through the collector-emitter circuit of thetransistor403. Note that this also represents the driving current through thelaser diode404 insofar as the laser diode is connected in series between the current regulator's supply voltage (the output of pulse generator) and the collector of thetransistor406. Since the voltage potential at the transistor emitter is about 1 volt, if R2 is selected to be a 7 ohm resistor, the resultant current level will be about 140 milliamps. This corresponds to the current level required to drive thelaser diode404 at the desired operational power level.
• InFIG. 48, an electrical power source (409,411) is implemented using a pair of conventional pacemaker lithium batteries (408,410) providing a steady state DC output of about 3 to 9 volts. The electro-optical transducers412 and416 are implemented with light emitting or laser diodes (414,415) and current limiting resistors (413,419). The diodes are conventional in nature and thus have a forward voltage drop of about 2 volts and a maximum allowable current rating of about 50-100 milliamps, or more. If additional supply voltage is available from the power source (409,411) (e.g., 4 volts or higher), more than one diode can be used in each electro-optical transducer412 and416 for additional light energy output. The value of each resistor is selected accordingly.
• By way of example, if the batteries produce 3 volts and the desired current through a single diode is 0.5 milliamps, the value of the resistor should be about 2000 ohms. This would be suitable if the diode is a light emitting diode. If the diode were a laser diode, other values and components would be used. For example, a current level on the order of 100 milliamps may be required to produce coherent light output from the diode if it is a laser. Theoptical conduction pathways417 and421 can be implemented as fiber optic bundles418 and423, or as single fibers, driving respective arrays of photodiodes.
• The opto-electrical transducer424 may be implemented with six photodiodes428-433 that are wired for photovoltaic operation. The opto-electrical transducer424 may be implemented with asingle photodiode434 that is wired for photovoltaic operation. The photodiodes are suitably arranged so that each respectively receives the light output of one or more fibers of the fiber optic bundles418 and423 and is forward biased into electrical conduction thereby.
• Each photodiode is conventional in nature and thus produces a voltage drop of about 0.6 volts. Cumulatively, the photodiodes428-433 develop a voltage drop of about 3.3 volts across the respective positive andnegative inputs426 and435 of thepower amplifier427. Thephotodiode434 develops about 0.6 volts across the respective positive andnegative inputs437 and438 of thepower amplifier427.
• InFIG. 43, a circuit diagram of an opto-electric coupling device388 is shown. The opto-electric coupling device388 includes the opto-electrical transducer376, which is assumed to be illuminated by a photonic catheter for about 1 millisecond, and left dark for about 1000 milliseconds. When illuminated, opto-electrical transducer photodiode array377-382 will produce pulses of about 3 to 4 volts across its outputs. The positive side of the photodiode array is connected via ahigh quality capacitor385 to animplantable tip electrode383 that is adapted to be implanted in the endocardium of a patient. The negative side of the photodiode array is connected to animplantable ring electrode384 that is adapted to be immersed in the blood of the patient's right ventricle. A DCcurrent discharge system387 comprising thecapacitor385 and aresistor386 is used to attenuate DC current in the tissue implanted with theelectrodes383 and384.
• Theresistor386 is connected across the outputs of the photodiode array. Theresistor386 thus grounds one side of thecapacitor385 between pulses. The return path from the implanted tissue is the through thering electrode384.
• The values of the capacitor and the resistor are selected so that the opto-electric coupling device conveys a suitable stimulating signal to the electrodes, but in such a manner as to prevent any net DC current from flowing into the implanted tissue. A long RC time constant is desired so that the square waveform of the photodiode array output is delivered in substantially the same form to the implanted tissue. For a 1 millisecond pulse, the desired RC time constant should be substantially larger than 1 millisecond. By way of example, if the capacitor has a capacitance of 10 microfarads and the resistor has a resistance of 20K ohms, the RC time constant will be 200 milliseconds. This is substantially larger than the 1 millisecond pulse length produced by the photodiode array.
• On the other hand, the RC time constant should not be so large as to prevent adequate DC current flow from the implanted body tissue into the capacitor between pulses. According to design convention for RC circuits, a period of five time constants is required in order for an RC circuit capacitor to become fully charged. Note that the selected RC time constant of 200 milliseconds satisfies this requirement if the photodiode array is pulsed at 1000 millisecond intervals, which is typical for pacemakers. Thus, there will be approximately five 200 millisecond time constants between every pulse. Stated another way, the RC time constant will be approximately one-fifth of the time interval between successive pulses.
• FIG. 44 shows the square wave electrical pulses generated by the photodiode array.FIG. 45 shows the actual electrical pulses delivered at the electrodes due to the presence of the RC circuit provided by the capacitor and the resistor. Note that the pulses ofFIG. 45 are substantially square is shape due to the RC circuit's time constant being substantially larger than the input pulse width.FIG. 45 further shows that there is a small reverse potential between pulses that counteracts DC current build up in the stimulated tissue.
• Ideally, the area A₁underneath each positive pulse ofFIG. 45 will be equal to the area A₂of negative potential that follows the positive pulse.
• Another embodiment of the present invention is the use of a photonic catheter in a MRI environment to sense the biological conditions of particular tissue regions of a patient or to stimulate particular tissue regions of the patient. Examples of photonic catheters are illustrated inFIGS. 5 through 20.
• InFIGS. 5 and 6,power supply595 and logic andcontrol unit597 enableemitter598 to transmit radiation, preferably optical radiation at wavelength λ₁throughbeam splitter900 into wave-guide601. This radiation exits the wave-guide601 and passes throughbeam splitter606 tosensor607 that converts the radiation to electrical energy. The electrical energy is used to directly power functions at the distal end oflead602, such as stimulation of internal body tissues and organs (e.g. pacing of cardiac tissues) throughelectrodes604 and603. The electrical energy is also used to power logic andcontrol unit608 or is stored in energy storage device609 (e.g. a capacitor) for later use. Proximally located elements are electrically connected through conductors. Distally locatedsensor607, logic andcontrol unit608,energy storage device609, and electrodes (604,603) are electrically connected through conductive elements.
• Asecond emitter600 transmits radiation at wavelength λ₂(λ₂≠ λ₁) throughbeam splitter901, offbeam splitter900, into wave-guide601, tobeam splitter606 andoptical attenuator605 that is mounted on a mirror. Theoptical attenuator605 is preferably made from materials such as liquid crystals whose optical transmission density is modulated by applied electrical voltage. The distally located logic andcontrol unit608 andoptical attenuator605 are powered either directly by excitation radiation or from energy stored inenergy storage element609.
• This photonic catheter can also be used withelectrodes603 and604 to capture electrical signals from the patient and direct the captured electrical signals to logical andcontrol unit608 which uses electrical energy to modulate the optical transmission density ofoptical attenuator605. Attenuated optical signals, originally emanating fromemitter600, are encoded with the electrical signals received byelectrodes603 and604 by passing through theoptical attenuator605, reflect off mirror, travel back through theoptical attenuator605, reflect offbeam splitter606 and into wave-guide601 tobeam splitters900 and901 tosensor599 that converts the encoded optical signal to an encoded electrical signal. Output fromsensor599 is sent to logic andcontrol unit597. This output is either utilized by logic andcontrol unit597 to control the radiation fromemitter598, which is typically at a high energy level and is used to stimulate distally located tissues and organs, or is relayed totransmitter596 which relays this sensory information to external sources.
• The embodiment illustrated inFIG. 7 is similar to the embodiment illustrated inFIGS. 5 and 6, with the exception that theoptical attenuator612 is mounted over the surface of the distally locatedsensor613 to take advantage of the first surface reflectance of this sensor. Radiation emitted by wave-guide610 passes throughoptical attenuator612 tosensor613 that converts the radiation to electrical energy as previously described. Radiation emitted by wave-guide610 passes throughoptical attenuator612 and reflects off the front surface ofsensor613. This reflected energy is collected bycoupling lens611 that directs the energy into wave-guide610 to a sensor at the proximal end (not shown).
• The embodiment illustrated inFIG. 8 is similar to the embodiment illustrated inFIGS. 5 and 6, with the exception that a variable reflectanceoptical reflector616 is mounted over the surface of the distally locatedsensor617. Radiation emitted by wave-guide619 passes throughoptical reflector616 tosensor617 that converts the radiation to electrical energy as previously described. Radiation emitted by wave-guide619 is reflected offoptical reflector616 and is collected bycoupling lens618 that directs the energy into wave-guide619. Preferably, the variable reflectanceoptical reflector616 would be transparent to excitation radiation.
• With respect toFIGS. 9 and 10,power supply620 and logic andcontrol unit622 enableemitter623 to transmit radiation, preferably optical radiation at wavelength λ₁throughbeam splitter624 into wave-guide626. This radiation exits the wave-guide and passes through an on-axis variable intensityoptical emitter631 tosensor632 that converts the radiation to electrical energy. The electrical energy is used to directly power functions at the distal end oflead635, such as stimulation of internal body tissues and organs (e.g. pacing of cardiac tissues) throughelectrodes627 and628; to power logic andcontrol unit633; or to store in energy storage device634 (e.g. a capacitor) for later use. Proximally located elements are electrically connected through conductors. Distally located sensor, logic and control unit, energy storage device, and electrodes are electrically connected through conductive elements.
• Logic andcontrol unit633 receives sensor input fromelectrodes627 and628 and delivers an electrical potential to variable intensityoptical emitter631 causing it to emit optical radiation at wavelength λ₂(λ₂≠λ₁) which is collected bycoupling lens630 and directed into wave-guide629, tobeam splitter624 andsensor625. The distally located logic andcontrol unit633 andoptical attenuator631 are powered either directly by excitation radiation or from energy stored inenergy storage element634.
• This photonic catheter can also be used withelectrodes627 and628 to capture electrical signals from the patient and direct the captured electrical signals to logical andcontrol unit633 that uses electrical energy to modulate the variable intensityoptical emitter631. Optical signals, emanating from variable intensityoptical emitter631, are encoded with the electrical signals received byelectrodes627 and628 and travel into wave-guide629 tobeam splitter624 tosensor625 that converts the encoded optical signal to an encoded electrical signal. Output fromsensor625 is sent to logic andcontrol unit622. This output is either utilized by logic andcontrol unit622 to control the radiation fromemitter623, which is typically at a high energy level and is used to stimulate distally located tissues and organs, or is relayed totransmitter621 which relays this sensory information to external sources.
• The embodiment illustrated inFIGS. 11 and 12 is similar to the embodiment illustrated inFIGS. 9 and 10, with the exception that the variable intensityoptical emitter646 is located off-axis. Power supply636 and logic andcontrol unit638 enableemitter639 to transmit radiation, preferably optical radiation at wavelength λ₁throughbeam splitter910 into wave-guide641. This radiation exits the wave-guide643 and passes throughbeam splitter645 tosensor647 that converts the radiation to electrical energy. The electrical energy is used to directly power functions at the distal end oflead642, such as stimulation of internal body tissues and organs (e.g. pacing of cardiac tissues) throughelectrodes650 and644; power logic andcontrol unit648; or to be stored in energy storage device649 (e.g. a capacitor) for later use.
• Proximally located elements are electrically connected through conductors. Distally locatedsensor647, logic andcontrol unit648,energy storage device649, andelectrodes650 and644 are electrically connected through conductive elements.Variable intensity emitter646 transmits radiation at wavelength λ₂(λ₂≠λ₁) offbeam splitter645 into wave-guide643 and offbeam splitter910 tosensor640. Preferably, thevariable intensity emitter646 emits optical radiation when excited by an electrical potential, and is mounted upon a mirror to direct a greater percentage of emissions into wave-guide643.
• A preferred application of the embodiment illustrated inFIGS. 11 and 12uses electrodes650 and644 to capture electrical signals and direct them to logical andcontrol unit648 which delivers electrical energy toemitter646 to emit optical radiation that is encoded with the electrical signals received byelectrodes650 and644. The encoded optical signals are directed tobeam splitter645 and into wave-guide643 tosensor640 that converts the encoded optical signal to an encoded electrical signal. Output fromsensor640 is sent to logic andcontrol unit638. This output is either utilized by logic andcontrol unit638 to control the radiation fromemitter639, which is typically at a high energy level (typically higher than radiation from emitter646) and is used to stimulate distally located tissues and organs, or is relayed totransmitter637 that relays this sensory information to external sources.
• InFIGS. 13 and 14,radiation emitter651 transmits radiation, preferably optical radiation at wavelength λ₁throughbeam splitter652 into wave-guide655. This radiation exits wave-guide656 at exit angle α and impinges uponsensor657 that converts the radiation to electrical energy. The electrical energy is used as previously described. Proximally and distally located elements are electrically connected through conductors.
• Asecond emitter658 located on or withinsensor657 transmits radiation at wavelength λ₂(λ₂≠λ₁) at cone angle β into wave-guide656 tobeam splitter652. The small size ‘d’ ofemitter658 relative to the larger size ‘D’ ofsensor658 and narrow radiation exit angle α and emission angle β enable effective coupling of radiation fromemitter651 intosensor657 and radiation fromemitter658 into wave-guide656.Optional coupling lens653 collects and directs radiation tosensor654. The distally located light source may be a solid-state laser or light emitting diode.
• InFIGS. 15 and 16,radiation emitter659 transmits radiation, preferably optical radiation at wavelength λ₁and exit angle β₁throughoptional coupling lens661 into wave-guide662. This radiation exits wave-guide663 at exit angle α₁and impinges uponsensor664 that converts the radiation into electrical energy. The electrical energy is used as previously described.
• Asecond emitter665 located on or withinsensor664 transmits radiation at wavelength λ₂at cone angle β₂into wave-guide663. This radiation exits wave-guide662 at exit angle α₂ontosensor660. Ideally, wavelength λ₂≠λ₁so that optical reflections fromcoupling lens661 or wave-guide662 do not interfere with radiation incident upondetector660. The small sizes ‘d’ ofemitters659 and665 relative to the larger sizes ‘D’ ofsensors660 and664, combined with narrow radiation exit angles α₁and α₂, and β₁and β₂, enable effective coupling of radiation into wave-guide (662,663), andsensors660 and664.
• InFIGS. 17 and 18,radiation emitter666 transmits radiation, preferably optical radiation at wavelength λ₁into wave-guide667. This radiation exits wave-guide670 and impinges uponsensor671 that converts the radiation into electrical energy. The electrical energy is used as previously described.
• A second distally locatedemitter672 transmits radiation at wavelength λ₂into wave-guide673. This radiation exits wave-guide668 onto proximally locatedsensor669. Wavelength λ₂may or may not be equal to wavelength λ₁.Light sources666 and672 include a solid-state laser or light emitting diode. Wave-guides (667,670) and (668,673) are preferably included in the same lead assembly.
• InFIGS. 19 and 20, asensor678 transparent to certain wavelengths of optical radiation is used.Radiation emitter677 transmits radiation, preferably optical radiation at wavelength λ₁throughsensor678 that is transparent to wavelength λ₁into wave-guide679 and exiting at exit angle α tosensor682 that converts the radiation to electrical energy. The electrical energy is used as previously described.
• Asecond emitter681 located on or withinsensor682 transmits radiation at wavelength λ₂(λ₂≠λ₁) at cone angle β into wave-guide680 to proximally locatedsensor678 where it is absorbed and converted into electrical energy. As before, the small size ‘d’ ofemitter681 relative to the larger size ‘D’ ofsensor682 and narrow radiation exit angle α and emission angle β enable effective coupling of radiation fromemitter677 intosensor682 and radiation fromemitter681 into wave-guide680.
• FIG. 50 illustrates another embodiment of the present invention in which a hermetic housing is constructed to provide part of anelectrode termination pair448. Theelectrode termination pair448 includes a cup-shaped structure (tip)449 acting as a tip electrode and the hermetic housing446 (ring) acting as a ring electrode. Thetip449 and thering446 are both substantially cylindrical in shape, and preferably have the same wall thickness. Note that thetip449 has a rounded nose portion and a base portion that is planar in cross-section. Thering446 has proximal and distal end portions that are both preferably planar in cross section.
• As shown inFIG. 51, thetip473 and thering463 can be made from a body-compatible, non-ferromagnetic metal such platinum, titanium or alloy of platinum or titanium. As shownFIGS. 52 and 53, the tip (497,522) and the ring (487,515) can be made of a non-metallic material, such as ceramic, and covered with electrically conductive coatings (495,520) and (480,505), respectively. The difference betweenFIGS. 52 and 53 is that all exposed surfaces of thetip497 and thering487 are coated inFIG. 52, whereas only the outer surface of thetip522 and thering515 are coated inFIG. 53.
• If a ceramic is used to form the tip and the ring, the material used is preferably a suitable biocompatible ceramic material such a ceramic of the type commonly used for joint prostheses. By way of example only, such material is available from Ceramic Components Inc. of Latrobe, Pa. To form a ceramic tip and ring, ceramic slurry can be formed into the desired shapes and fired to bake the ceramic material.
• The electrically conductive coatings (495,520) and (480,505) are preferably formed by very thinly coating the tip and the ring, as by electroplating, sputtering or other deposition technique, etc., with a suitable metal. To facilitate MRI compatibility, the metal preferably has low magnetic susceptibility, such as titanium, platinum, an alloy of titanium or platinum, or the like. Preferably, the coatings (495,520) and (480,505) are applied as thin as possible to achieve the twin goals of efficient electrical interaction with implanted tissue while minimizing interaction with MRI induced electromagnetic fields. By way of example, the thickness of the coatings (495,520) and (480,505) may range from mono-molecular thickness to sub-micron or micron level thickness.
• FIGS. 50 through 53 show the electrode termination pair (448,469,498,524) being mounted to the distal end of a photonic catheter (451,476,501). The tip and the ring are also interconnected by a short insulative stub (447,468,493,518) that is solid, generally cylindrical in shape, and made from silicone, polyurethane, polyethylene, or any other suitable biocompatible electrically insulating material. The outside diameter of the stub preferably equals the outside diameter of the tip and the ring, to facilitate efficient implantation and removal in a patient. The ends of the stub can be bonded to the tip and the ring using a suitable medical adhesive. To provide additional connection integrity, the stub can be formed with end portions (470,492,519) of reduced diameter. One end portion of the stub is received into an opening (471,494) in the base portion of the tip and bonded therein. The other end portion of the stub is received into an opening (459,485,509) in the distal end of the ring and bonded therein.
• The completed tip/ring assembly can be mounted to the distal end of the photonic catheter in similar fashion. In particular, the photonic catheter will be a generally cylindrical element whose exterior sheath (451,474,459) is made from silicone, polyurethane, polyethylene, or any other suitable biocompatible electrically insulating material. Note that the sheath could be tubular in shape, with a small center bore carrying one or more optical conductors therein. Alternatively, the sheath could be formed around the optical conductors such that the conductors are embedded, in the material of the sheath
• In either case, the outside diameter of the sheath will preferably be the same as that of the ring and can be bonded thereto using a suitable medical adhesive. To provide additional connection integrity, the sheath may be formed with a small end portion (453,477,502) of reduced diameter that is snugly received within an opening (454,478,503) in the proximal end the ring and bonded therein.
• Since the ring functions as a hermetically sealed component housing, it must be provided with hermetically sealed closures at or near the ends thereof. These closures may be provided by a pair of closure walls (465,488,516) and (461,482,513) that are secured within the interior of the ring. The closure walls can be formed from any suitable bio-compatible material capable of sealing the ring interior, including metals, polymers, and potentially other materials. To facilitate the secure hermetic attachment of the closure walls, the inside of the ring can be formed with a pair of recessed annular shoulders (456,479,504).
• There may be disposed within the ring any number of components for delivering electrical signals to, or sensing biological activity in, a body. Such components are collectively shown as a component array by reference numeral (462,486,514), and may include opto-electrical transducers, electro-optical transducers, signal processors and amplifiers, digital microprocessors, temperature sensors, R-wave sensors, partial oxygen sensors, and any number of other components. To provide electrical interaction with surrounding body tissue, a positive terminal of the component array is connected to a short metallic lead (457,483,507) made from copper or other suitable material of low magnetic susceptance.
• InFIG. 51, thelead457 is electrically connected to the ring by attaching it, as by soldering or the like, directly to the ring itself. InFIG. 52, themetallic lead483 is electrically connected to the ring by attaching it, as by soldering or the like, to an interior portion of themetallic coating480. InFIG. 53, themetallic lead507 is fed through asmall hole506 in the wall of the ring so that it may be attached to the exteriormetallic coating505, as by soldering or the like.
• A negative terminal of the component array connects to a longer metallic lead (466,489,517) that is also made from copper or other suitable material of low magnetic susceptance. This metallic lead feeds through a hermetic seal terminal (464,490,511) mounted on the closure wall. This metallic lead then extends through the material of the stub (which can be molded around the lead) and into the tip.
• InFIG. 51, the metallic lead is electrically attached, as by soldering or the like, directly to the tip itself. InFIG. 52, the metallic lead is electrically attached, as by soldering or the like, to an interior portion of the metallic coating. InFIG. 53, the metallic lead is fed through asmall hole523 in the ceramic wall of the tip so that it may be attached to the metallic coating, as by soldering or the like.
• When the tip and the ring are implanted in a patient's heart, the tip will typically be embedded in the endocardial tissue, while the ring is situated in the right ventricle, in electrical contact with the endocardium via the ventricular blood. If the photonic catheter is connected to a pacemaker, an optical pulse emanating from a photonic pacemaker pulsing unit (not shown) is sent down a fiber optic element or bundle of the photonic catheter. The fiber optic element or bundle passes into the hermetically sealed interior of the ring via a hermetic seal terminal (460,481,512). There, the fiber optic element or bundle delivers the optical pulse to the component array, which preferably includes a photodiode array. The photodiode array produces an electrical impulse that negatively drive the tip with respect to the ring at a potential of about 3-4 volts and a current level of about 3 milliamps for a total power output of about 10 milliwatts. Note that a sensing function could be added by incorporating an electro-optical transducer into the component array. Electrical sense signals would then be converted to optical signals and placed on the fiber optic element or bundle for delivery to a sensing unit (not shown).
• FIG. 54 illustrates an exemplary construction of the component array in which the array comprises aphotodiode array532 for receiving optical pacing signals from the fiber optic element or bundle525 and alight emitting diode533 for delivering optical sensing signals to the fiber optic element or bundle. Thecomponents532 and533 are mounted on acircuit substrate527 that is electrically connected to anelectrical circuit unit534 that may include transducers, amplifiers, oscillators, a microprocessor, and other devices that can assist electrical pulse delivery and biological sensing functions.
• FIGS. 55 through 57 include a modified hermetic housing to provide a unitary or integralelectrode termination pair540. Theelectrode termination pair540 includes atip539 and aring538 that are constructed as metallic coatings formed on the hermetic housing (551,565).
• An electrically conductive coating (552,566) formed at the distal end of the housing provides the tip. An electrically conductive coating (547,559) formed at the proximal end of the housing provides the ring.
• FIGS. 56 and 57 also show that the component array can be hermetically sealed within the housing via the hermetic seal. The proximal end of the housing may then be secured to the distal end of the photonic catheter, and the fiber optic element or array can be connected to the component array via the hermetic terminal. The component array is electrically connected to the tip and the ring via electrical leads.
• FIG. 58 shows an exemplary implementation of the component array within the housing. This component array configuration is identical to the component array configuration ofFIG. 55.
• InFIG. 59, a modified hermetic housing again provides a completeelectrode termination pair586. Theelectrode termination pair586 includes atip electrode584 and aring electrode582 that are constructed as electrically conductive band coatings on the hermetic housing, which is designated byreference numeral581. A shallow well562 ofFIG. 60 formed near the distal end of thehousing560 ofFIG. 60 may be used to mount thetip561. A shallow well593 ofFIG. 60 formed toward the proximal end of thehousing560 ofFIG. 60 may be used to mount thering594 ofFIG. 60.
• FIG. 61 shows an exemplary implementation of the component array within the housing. This component array configuration is identical to the component array configuration ofFIG. 54.
• The output of a typical pacemaker is illustrated inFIG. 31, which is a graph of the electrical direct current voltage (vDC) applied to the electrode or electrodes at the distal end of a cardiac pacemaker lead, as a function of time. The indicated voltage of 3 vDC is a nominal value and is typically often selected by the physician based on the type of cardiac anomaly being corrected, the physical state of the patient's heart, and other factors. However, it should be understood that this value is intended to have a safety factor of two built into it; thus the typical voltage required to pace the heart is 1.5 volts direct current, or less.
• Referring again toFIG. 31, and noting that the time axis is not to scale, the typical time between pacing events is nominally one second, or 1000 milliseconds (mS). In normal practice, using modem pacemakers, this time interval is not fixed but is variable based upon two factors. The first factor is whether or not the heart requires pacing in order to beat. The term ‘demand pacemaker’ applies to a device that senses heart activity electrically and does not send a pacing signal to the electrodes if the heart is beating on its own in a manner determined to be acceptable by the computer controller within the device, and based upon input programmed by the physician. Thus, during the time after the refractory period associated with the previous heartbeat ends321, and up to a time when the next heartbeat is required322, the pacemaker electrode is used to sense heart activity and to disable thenext pacing signal323 if the heartbeat is regular.
• The second factor associated with demand pacing is physiologic demand; modern pacemakers are designed with additional sensing and analytical capability that permits the device to monitor physiologic demand associated with physical activity or other forms of stress that would result in an elevated heartbeat in a normal human subject. In response to this heightened physiologic demand, thepacing signal323 would be generated at an earlier time than the1000 mS delay indicated inFIG. 3I.
• FIG. 32 is an expanded view similar toFIG. 31, showing thepacing signal326 over the nominal one-millisecond time interval of the actual pacing signal. The beginning of the pacing signal (319,324) and the end of the pacing signal (320,325) are shown in bothFIG. 31 andFIG. 32 for reference. Note that there is no other activity in this one millisecond time interval; more particularly there is no attempt to sense heart activity nor the heart's response to the pacing signal during the time pacing time interval between times (319,324) and (320,325). This is in part due to the fact that while a relatively modest voltage (about 3 volts) is being applied to the heart cardiac tissue by the electrodes, the voltages sensed by the pacemaker in monitoring heart activity (typically in the millivolt range) would be immeasurable using traditional techniques. In addition, the tissues surrounding the pacing electrode develop a polarization potential in response to the energy in the pacing signal; this serves to make measurements of heart activity via those same electrodes very difficult using traditional techniques. However, the interval between times (319,324) and (320,325) is very long in the context of modem computational electronic devices.
• FIGS. 33, 34, and35 are schematic representations of a cardiac pacemaker lead (327,329,333) having various electrode configurations.
• In one preferred embodiment, and referring toFIG. 33,pacemaker lead327 comprises one or more electrical conductors communicating from a connector on the body of the pacemaker device (not shown) to theelectrodes328 that are affixed by one of a number of techniques to the sensitive cardiac tissue that initiates the natural heartbeat and that is paced when necessary by the implanted pacemaker system. The configuration shown inFIG. 33 is for a bipolar pacemaker; the positive and negative terminals for electron flow through the cardiac tissue are the twoelectrodes328. It should be noted that there is an alternative configuration referred to as unipolar, and it is not shown in this figure. In the case of a unipolar configuration, there is asingle electrode328 at the heart; the return path for electron flow is through the general bulk tissue back to the case of the device itself. In either unipolar or bipolar configurations,electrodes328 are used both to pace the heart during the period between times (319,324) and (320,325) shown inFIGS. 31 and 32, but are also used to sense heart activity electrically betweentimes321 and322 shown inFIG. 31.
• In the embodiment depicted inFIG. 34,sensing electrode332 is disposed at a distance of at least about5 millimeters from pacingelectrode330 in order to provide a degree of electrical isolation between tissues that will develop a polarization potential and tissues being sensed for heartbeat activity. Similarly, in the embodiment depicted inFIG. 35,sensing electrode pair335 is disposed at a distance of at least about 5 millimeters from pacingelectrode pair334.
• In another preferred embodiment, cardiac pacemaker lead is not an electrical conductor but rather comprises one or more optical fibers that carry light energy between the pacemaker device case and the electrodes. This embodiment may be used in order to create pacemaker leads that are immune to the intense radio frequency and magnetic fields associated with magnetic resonance imaging (MRI) and which fields can in some cases result in damage to the pacemaker and/or injury or death to the pacemaker patient who inadvertently undergoes MRI diagnosis. In this embodiment electrodes are more complex than in the former embodiment; for purposes of pacing they comprise a photodiode (not shown) used to convert light energy to electrical energy within them, and in the case of sensing cardiac activity they also comprise a miniature electrical amplifier and light emitting diode source that creates an optical signal that travels from the electrode back to a pacemaker device that uses the photonic catheter of this embodiment.
• In another embodiment, and referring toFIG. 34, thepacemaker lead329 connects the pacemaker device case (not shown) to a set ofelectrodes330,331, and332 at its distal end and affixed to cardiac tissue as in the previous embodiment.Electrode331, as in the previous embodiment, is capable of either pacing the heart or sensing heart activity electrically.Electrode330 is used only to pace the heart, and is identical in its function to that part of the function of the dual-purpose electrode. In likemanner electrode332 is used only for sensing heart activity electrically, in a fashion identical to that part of the function of the dual-purpose electrode.
• The reason for the configuration shown inFIG. 34 is that the cardiac tissue immediately involved in the pacing event, and which develops a polarization potential as a result of the pacing signal, is somewhat removed physically from the cardiac tissue immediately around thesensing electrode332, thus providing some degree of isolation from polarization potential in the area where cardiac sensing is being done, but still providing ample opportunity for sensing any cardiac activity. Thus this embodiment provides the opportunity for sensing measurements to be made during dwell periods in the overall pacing signal wherein no voltage is being applied to the cardiac tissue.
• In a further embodiment, and still referring toFIG. 34,pacemaker lead329 does not contain electrical conductors but rather comprises one or more optical fibers, as described in a previous embodiment. Likewise,electrodes330 and331 have the capability to convert optical energy to electrical energy in order to pace the heart, andelectrodes331 and332 comprise electrical amplifier and electricity-to-light conversion, as is also described in the previous embodiment.
• In yet another preferred embodiment, shown inFIG. 35,pacemaker lead333 connects the pacemaker device case (not shown) to a set ofelectrodes334 and335 at its distal end and is affixed to cardiac tissue as in the previous embodiments. In this embodiment, additional separation between the volume of cardiac tissue being paced (between electrodes334) and the volume of cardiac tissue being sensed (between electrodes335) is created in order to provide further improvements in electrical isolation between those areas, thereby providing further improvement in the ability to make sensing measurements during cardiac pacing.
• In yet another embodiment, and still referring toFIG. 35,pacemaker lead333 does not contain electrical conductors but rather one or more optical fibers, as described in a previous embodiment. Likewise,electrodes334 have the capability to convert optical energy to electrical energy in order to pace the heart, andelectrodes335 comprise electrical amplifier and electricity-to-light conversion as also described in previous embodiments.
• In one preferred embodiment of the present invention, a technique of pulsewidth modulation is used to pace the heart and to provide the opportunity for real-time measurement of cardiac tissue activity.
• Referring toFIG. 36, it may be seen that apacing signal338 that begins attime341 is not a traditional square wave pulse as shown inFIGS. 31 and 32, but is a series of much faster pulses that apply avoltage337 for atime period339 and that apply no voltage duringtime period340.
• For example, iftime period339 is chosen to be two microseconds and iftime period340 is chosen to be one microsecond, a single repeat ofsequence339 and340 has a duration of three microseconds. If this sequence is repeated three hundred thirty-three times, the time interval forpulse338 will be about one millisecond, corresponding to the time interval of a single traditional pacing signal to the heart. For purposes of this illustrative example and again referring toFIG. 36,voltage337 may be chosen to compensate for the fact that no voltage is applied for one third of the time. In order for apulsewidth signal338 having 66% duty cycle as described in this illustration to deliver the same amount of electrical energy to the cardiac tissue as in asquare wave 3 volt DC pulse of 1 millisecond duration, and taking into consideration the relationship of energy to voltage in a purely resistive medium (energy is proportional to the square of the applied voltage), thevoltage337 will be chosen to be 3 volts DC multiplied by the square root of 1.5, or 3.67 volts direct current. If the frequency of pulsewidth modulatedpacing curve338 is high with respect to the reaction time of cardiac tissue, that tissue will react in the same manner to the pulsewidth modulated signal having 66% duty cycle and 3.67 volt peak signal level as it would to a square wave of the same duration at 3.0 volt.
• The foregoing example is intended to be illustrative only; in the embodiment depicted,time periods339 and340 may range from below 1 microseconds to over 100 microseconds in order to optimize the response of the system to design choices in the pacemaker device or the pacemaker lead and electrodes. In addition, this embodiment provides fortime periods339 and340 to be variable over time, both in absolute duration and in their ratio. Further, the appliedvoltage337 may be variable over time within asingle pacing signal338, or between pacing signals, as a function of changes in physiologic demand or based on changes in programmed response of the pacemaker system. For purposes of this specification, the overall signal that spans betweentimes339 and340 will be referred to as the pacing signal, the shorter signals sent to the heart in multiples will be referred to as pulses, and the much shorter signals described in this illustrative example as havingtime duration339 will be referred to as micropulses.
• Referring once again toFIG. 36, it may be seen that a cardiactissue sensing measurement343 may be carried out duringtime period342. In one embodiment,time period342 may occur any time during the pacing signal and may have any duration appropriate to making said sensing measurement. In a preferred embodiment,time period342 is selected to be shorter in duration thantime period340, and is further synchronized so as to fall withintime period340. The result is that the electrical measurement of cardiac tissue activity is done during a time period wherein there is not pacing signal applied to the tissue.
• Referring again briefly toFIGS. 33, 34, and35, it may be seen that in combination with the placement of electrodes on pacemaker lead that provides isolation between the tissue being paced and the tissue being sensed, the additional temporal isolation of sensing period from the active time period of the pulsewidth modulated pacing signal, a means is provided to measure the onset of cardiac response to the pacing signal while the signal is still being generated as a set of multiple shorter pulses.
• FIG. 37 is a graph depicting the operation of one preferred embodiment that gains energy efficiency by means of early termination of the pacing signal, but which uses a constant voltage applied to the micropulses comprising the pacing signal. The peak voltage of pulses that make up pacingsignal345 rises from zero tovoltage344 attime346, as previously shown inFIG. 36. Attime348, when a signal from heart causes cessation of the micropulsing process, thepulsewidth pacing signal345 returns to zero until the next pacing signal is commanded from the demand controller. Thearea347 depicts the additional signal that a traditional pacemaker not practicing pulsewidth pacing would send to pace the heart after the onset of a beat attime348. As discussed previously, standard clinical practice calls for a threefold safety factor in pulse duration; employing a pacemaker in a manner depicted inFIG. 37, would result in up to approximately a 65 percent reduction in energy consumption for the pacemaker system.
• FIG. 38 is a graph depicting the operation of another preferred embodiment that gains energy efficiency by means of both early termination of the pacing signal and by the additional use of gradient pulsewidth power control. As in the previous embodiment,pulsewidth pacing signal352 begins to rise from zero attime353, and the voltage of each of the micropulses rises with each micropulse cycle.FIG. 38 depicts a linear rise with time, but experimentation may result in a different algorithm that better matches the electrochemistry of cardiac tissue; thusFIG. 38 should be considered as illustrative of a variety of waveforms that may be employed to excite the heart. Attime354, when a signal from heart causes cessation of the micropulsing process, thepulsewidth pacing signal352 returns to zero until the next pacing signal is commanded from the demand controller. As in the example ofFIG. 37, thearea356 depicts the signal that a traditional pacemaker not practicing pulsewidth pacing would send to pace the heart.
• As discussed previously, standard clinical practice calls for a threefold safety factor in pulse duration. The typical twofold safety factor in applied voltage results in a power level that is four times higher than the minimum to pace the specific patient's heart. Thus in combination the joint safety factors applied to voltage and pulse duration result in an energy utilization that is twelve times higher than the minimum needed to reliably pace that individual's heart. By practicing pulsewidth pacing, which permits the cessation of the pulsewidth pacing signal virtually the instant the heart begins to beat, the energy consumption of a pacemaker may be reduced by as much as 90%.
• It should also be understood that in using a pulsewidth modulation control technique, it is not necessary to alter the actual peak voltage of the pulses that make up the pacing signal to effect an apparent change in applied voltage. If the frequency of the pulses is high enough in comparison to the response time of the circuit and the cardiac tissue through which the pacing signal is conducted, the tissue will react in the same manner as if the applied voltage were the actual peak voltage multiplied by the duty cycle. Thus, the electronic circuit may be designed to utilize a single voltage and adjust duty cycle by adjusting the ratio oftimes339 and340. This permits optimization the energy efficiency of power sources and switching circuits.
• FIG. 39 depicts an alternative overall waveform for pacingsignal360. Note that for reasons of simplicity the overall value of peak voltage is shown for pacingsignal360, and not the individual pulsewidths, as shown inFIG. 38. However, this embodiment still makes use of the high-frequency pulsewidth approach shown in greater detail inFIGS. 37 and 38. WhereasFIG. 38 depicts a linear rise with time,FIG. 39 depicts an initial rise ofpacing signal360 attime361 from 0 vDC tovoltage359, followed by a non-linear increase tovoltage358, at which time362 a heartbeat has been sensed, andpacing signal360 is cut off as in the previous embodiments described herein.
• Experimentation may result in a different algorithm that better matches the electrochemistry of cardiac tissue, and this algorithm may be developed for the specific patient during the initial post-implantation period. Thus,FIGS. 38 and 39 should be considered as illustrative of a variety of waveforms that may be employed to excite the heart, and may be made specific to the needs of each pacemaker patient.
• As in the previous embodiment depicted inFIG. 38, the use of pulsewidth modulation techniques in the embodiment depicted inFIG. 39 permits optimization of energy efficiency by adjusting duty cycle rather than adjusting actual peak voltage.
• The photonic catheter described above may be used for transmission of a signal to and from a body tissue of a vertebrate. The fiber optic bundle has a surface of non-immunogenic, physiologically compatible material and is capable of being permanently implanted in a body cavity or subcutaneously. The fiber optic bundle has a distal end for implantation at or adjacent to the body tissue and a proximal end. The proximal end is adapted to be coupled to and direct an optical signal source, and the distal end is adapted to be coupled to an optical stimulator. The fiber optic bundle delivers an optical signal intended to cause an optical stimulator coupled to the distal end to deliver an excitatory stimulus to a selected body tissue, such as a nervous system tissue region; e.g., spinal cord or brain. The stimulus causes the selected body tissue to function as desired.
• The photonic catheter further includes a photoresponsive device for converting the light transmitted by the fiber optic bundle into electrical energy and for sensing variations in the light energy to produce control signals. A charge-accumulating device receives and stores the electrical energy produced by the photoresponsive device. A discharge control device, responsive to the control signals, directs the stored electrical energy from the charge-accumulating device to a cardiac assist device associated with a heart.
• The photoresponsive device may include a charge transfer control circuit and a photodiode. The charge transfer control circuit controls a discharging of a photodiode capacitance in two separate discharge periods during an integration period of the photodiode such that a first discharge period of the photodiode capacitance provides the sensing of variations in the light energy to produce control signals and a second discharge period of the photodiode capacitance provides the converting the light transmitted by the photonic lead system into electrical energy. The first discharge period can be a shorter time duration that the time duration of the second discharge period. During the first discharge period, a control signal sensing circuit is connected to the photodiode, and during the second discharge period, the charge-accumulating device is connected to the photodiode. The charge-accumulating device may be a capacitor or a rechargeable battery.
• The photonic catheter can also transmit between the primary device housing and the cardiac assist device, both power and control signals in the form of light. A photoresponsive device converts the light transmitted by the photonic lead system into electrical energy and to sense variations in the light energy to produce control signals. A charge-accumulating device receives and stores the electrical energy produced by the photoresponsive device, and a discharge control device, responsive to the control signals, directs the stored electrical energy from the charge-accumulating device to the cardiac assist device associated with the heart.
• The photoresponsive device, in this embodiment, may include a charge transfer control circuit and a photodiode. The charge transfer control circuit controls a discharging of a photodiode capacitance in two separate discharge periods during an integration period of the photodiode such that a first discharge period of the photodiode capacitance provides the sensing of variations in the light energy to produce control signals and a second discharge period of the photodiode capacitance provides the converting the light transmitted by the photonic lead system into electrical energy. The first discharge period can be a shorter time duration that the time duration of the second discharge period. During the first discharge period, a control signal sensing circuit is connected to the photodiode, and during the second discharge period, the charge-accumulating device is connected to the photodiode. The charge-accumulating device may be a capacitor or a rechargeable battery.
• The physical realization of the photodiode functions as light-detecting elements. In operation, the photodiode is first reset with a reset voltage that places an electronic charge across the capacitance associated with the diode. Electronic charge, produced by the photodiode when exposed to illumination, causes charge of the photodiode capacitance to dissipate in proportion to the incident illumination intensity. At the end of an exposure period, the change in photodiode capacitance charge is collected as electrical energy and the photodiode is reset.
• Manipulating or adjusting the charge integration function of the photodiode can modify the creation of energy by the sensors. Charge integration function manipulation can be realized by changing of an integration time, T_int, for the photodiode. Changing the integration time, T_int, changes the start time of the charge integration period.
• Integration time, T_int, is the time that a control signal is not set at a reset level. When the control signal is not at a reset value, the photodiode causes charge to be transferred or collected therefrom. The timing of the control signal causes charge to be transferred or collected from the photodiode for a shorter duration of time or longer duration of time. This adjustment can be used to manage the charge in the photodiode so that the photodiode does not become saturated with charge as well as to manage the current output of the sensor.
• Another conventional way of manipulating the charge integration function is to use a stepped or piecewise discrete-time charge integration function. By using a stepped or piecewise discrete charge integration function, the charge in the photodiode can be further managed so that the photodiode does not become saturated with charge as well as to manage the current output of the photodiode.
• The photonic catheter can also be used to measure displacement current. Unlike a standard conduction current of moving electrons, displacement current is a measure of the changing electric field in the air, generated by the shifting voltages on the skin surface. To accurately measure this subtle current in the air without shorting it, a sensor is needed with impedance higher than that of the air gap between the body and the sensor. Otherwise, the sensor will drain the electrical signal just like an ECG contact sensor does. The sensor can be a small copper disc about a centimeter across, which can produce sensitive ECGs.
• As illustrated inFIGS. 66-69, aphotonic catheter585 may contain a sensor to detect the presence of MRI insult. Most specifically, thephotonic catheter585 may include at a distal end a logic andcontrol circuit586 connected to anamplifier587. Theamplifier587 may be connected to a single MRI coil as illustrated inFIG. 66 or to multiple MRI coils (589,590,591 . . . ) as illustrated inFIG. 67. InFIG. 68, the MRI insult sensor is encased in asleeve592 that enables theMRI coil592 to be rotatable within thephotonic catheter585. Lastly, thephotonic catheter585, as illustrated inFIG. 69, may position twoMRI coils593 and594 at predetermined angles β to each other, such as 90°. The MRI coils are located in the distal end of the photonic catheter and detects characteristics of magnetic radiation of a predetermined nature. Each coil may be designed to detect a different type of radiation.
• FIG. 21 illustrates an optical transducer including apressure sensor225 in a porousnon-conductive insert226 that is coupled to a photonic catheter or other optical communication channel.
• FIG. 22 illustrates in more detail, the pressure optical transducer device ofFIG. 21. InFIG. 22, an optical transducer device is anchored to apredetermined tissue region230, such as a cardiac muscle region, byanchors227 and229. The anchors are connected to aporous sleeve231 that houses apressure sensor228. The optical transducer device further includes a mechanical-optical transducer232, withinhousing233, to produce an optical signal corresponding to the movement ofpressure sensor228.Pressure sensor228 moves back and forth in response to pressure generate by contractions of thepredetermined tissue region230. Based on the pressure gradient produced, thepressure sensor228 will move and cause the mechanical-optical transducer232 to produce a signal containing information on the characteristics of thepredetermined tissue region230.
• InFIG. 23, an optical transducer device is anchored to apredetermined tissue region234, such as a cardiac muscle region, by aporous sleeve235 that houses apressure sensor236. The optical transducer device further includes a mechanical-optical transducer239, withinhousing237 and connected tooptical cable238, to produce an optical signal corresponding to the movement ofpressure sensor236.Pressure sensor236 moves back and forth in response to pressure generate by contractions of thepredetermined tissue region234. Based on the pressure gradient produced, thepressure sensor236 will move and cause the mechanical-optical transducer239 to produce a signal containing information on the characteristics of thepredetermined tissue region234.
• InFIG. 24, an optical transducer device is anchored to apredetermined tissue region240, such as a cardiac muscle region, by aporous sleeve241 that houses anoptical device242. Theoptical device242 produces an optical signal that reflects off thepredetermined tissue region240. Based upon the nature of the reflection,optical device242 produces optical signals corresponding to the characteristics of thepredetermined tissue region240. These optical signals are transmitted over anoptical cable244 within ahousing243.
• InFIG. 25, an optical transducer device for a cardiac region is illustrated. Anoptical device251 produces light that is fed alongfiber optics247 and250 to a ventricle area of the heart and an atrium area of the heart, respectively. The light is reflected off these areas and fed back to theoptical device251 throughfiber optics248 and249. Based upon the nature of the reflection,optical device251 produces optical signals corresponding to the characteristics of the monitored areas. Theseoptical signals252 are transmitted over anoptical cable253 to acontrol unit device254 at a proximal end of theoptical cable253.
• FIG. 26 illustrates one embodiment of an optical sensor. InFIG. 26, afiber optic bundle258 includesindividual fiber optics259. One of the fiber optics produces the reference light that is reflected offflap261 within the optical sensor. Theflap261 will move betweenstops257 and260 based on characteristics within a predetermined tissue region. As theflap261 moves onpivot262, the light is reflected at different angles and thus is collected by a different fiber in the fiber optic bundle, depending upon the angle of reflection. In this way, the characteristics of the predetermined tissue region can be measured.
• FIGS. 63 and 64 illustrate one embodiment of anoptical sensor1008. InFIGS. 63 and 64, afiber optic bundle1017 includesindividual fiber optics1013 and1016. One of thefiber optics1013 produces the reference light that is reflected offflap1014 within theoptical sensor1008. Theflap261 will move based on muscle contractions ofmuscle tissue1018 and1020 in a predetermined tissue region that is within theoptical sensor1008 throughopenings1010 and1012. As theflap1014 moves onpivot1015, the light is reflected at different angles and thus is collected by adifferent fiber1016 in the fiber optic bundle, depending upon the angle of reflection. In this way, the characteristics of the predetermined tissue region can be measured.
• FIG. 62 is an optical sensor andstimulation device1030 for a photonic catheter. InFIG. 62, the optical sensor andstimulation device1030 includes aring electrode1034 and atip electrode1032 to sense or stimulate a predetermined tissue region. Thering electrode1034 and atip electrode1032 are connected to acontrol circuit1038 that produces energy to enable thering electrode1034 andtip electrode1032 to stimulate the predetermined tissue region or enables thering electrode1034 andtip electrode1032 to sense characteristics of the predetermined tissue region. Control signals from a proximal end are communicated along afiber optic1044 and received bysensor1040.Sensor1040 also receives other light signals overchannel1044 that is converted into electrical energy to be stored for later use. The sensed characteristics of the predetermined region are transmitted bydevice1008 overfiber optic1017 to the proximal end.
• FIG. 65 illustrates apressure pulse sensor580. Cardiac tissue causes a mirror membrane to be atposition578 when the heart is in the diastolic interval because the pressure from the cardiac tissue decreases and inposition579 when the heart is in the systolic interval because the pressure from the cardiac tissue increases. When the mirror membrane is inposition579,laser light581 fromfiber optic583 is reflected alongray582 tofiber optic sensor584. The pressure is transferred to thepressure pulse sensor580 throughopenings576 and577.
• Alternatively to the electromagnetic insult immune systems described above, a system can avoid failure during magnetic resonance imaging by determining a quiet period for a tissue implantable device and generating a magnetic resonance imaging pulse during a quiet period of the tissue implantable device. Moreover, a system can avoid failure due to an external electromagnetic field source by detecting a phase timing of an external electromagnetic field or external magnetic resonance imaging pulse field and altering operations of the tissue implantable device to avoid interfering with the detected external electromagnetic field or external magnetic resonance imaging pulse field. In these instances the tissue implantable device may be a cardiac assist device.
• The concepts of the present invention may also be utilized in an electromagnetic radiation immune tissue invasive delivery system. The electromagnetic radiation immune tissue invasive delivery system has a photonic lead having a proximal end and a distal end. A storage device, located at the proximal end of the photonic lead, stores a substance to be introduced into a tissue region. A delivery device delivers a portion of the stored substance to a tissue region. A light source, in the proximal end of the photonic lead, produces a first light having a first wavelength and a second light having a second wavelength.
• A wave-guide is located between the proximal end and distal end of the photonic lead. A bio-sensor, in the distal end of the photonic lead, senses characteristics of a predetermined tissue region, and a distal sensor, in the distal end of the photonic lead, converts the first light into electrical energy and, responsive to the bio-sensor, to reflect the second light back the proximal end of the photonic lead such that a characteristic of the second light is modulated to encode the sensed characteristics of the predetermined tissue region. A proximal sensor, in the proximal end of the photonic lead, converts the modulated second light into electrical energy, and a control circuit, in response to the electrical energy from the proximal sensor, controls an amount of the stored substance to be introduced into the tissue region.
• In this embodiment, the sensed characteristic may be an EKG signal, a glucose level, hormone level, or cholesterol level. The stored substance may be a cardiac stimulating substance, a blood thinning substance, insulin, estrogen, progesterone, or testosterone.
• The MRI compatible photonic catheter, according to the concepts of the present invention, can also be utilized to illuminate a multiple sector photodiode, whose sectors are electrically connected in series so that the voltage output of each sensor is additive, thereby producing a total output voltage in excess of what would be achieved from a single sensor.
• In another embodiment of the present invention, a higher voltage and current outputs is achieved by increasing the number and size of detectors. This embodiment also provides very accurate and stable alignment of the radiation wave-guide to the sensor, and a uniform spatial intensity of the output beam that illuminates the multiple sensor sectors.
• An example of a MRI compatible photonic catheter being utilized to transfer power or energy to a tissue region located at a distal end of the catheter is illustrated inFIG. 70.FIG. 70 shows a wave-guide2001 coupled to a radiation source (not shown). The wave-guide2001 directs radiation into aradiation scattering medium2007. Attached to the surface of the radiation scattering medium2007 are multiple radiation sensors2010-2013, mounted along the axis of scattering medium2007, for receiving and converting incident radiation into electrical energy. The multiple radiation sensors2010-2013 are electrically connected in series so that the voltage output of each sensor is additive, thereby producing a total output voltage in excess of what would be achieved from a single sensor.
• The physical realization of the sensors is either a plurality of phototransistors or a plurality of photodiodes functioning as light-detecting elements. In operation, the sensor is first reset with a reset voltage that places an electronic charge across the capacitance associated with the diode. Electronic charge produced by, for example, a photodiode, when exposed to illumination, causes charge of the diode capacitance to dissipate in proportion to the incident illumination intensity. At the end of an exposure period, the change in diode capacitance charge is collected as electrical energy and the photodiode is reset.
• Manipulating or adjusting the charge integration function of the sensor can modify the creation of energy by the sensors. Charge integration function manipulation can be realized by changing of an integration time, T_int, for the sensor. Changing the integration time, T_int, changes the start time of the charge integration period.
• Integration time, T_int, is the time that a control signal is not set at a reset level. When the control signal is not at a reset value, the sensor causes charge to be transferred or collected therefrom. The timing of the control signal causes charge to be transferred or collected from the sensor for a shorter duration of time or longer duration of time. This adjustment can be used to manage the charge in the sensor so that the sensor does not become saturated with charge as well as to manage the current output of the sensor.
• Another conventional way of manipulating the charge integration function is to use a stepped or piecewise discrete-time charge integration function. By using a stepped or piecewise discrete charge integration function, the charge in the sensor can be further managed so that the sensor does not become saturated with charge as well as to manage the current output of the sensor.
• Theradiation scattering medium2007 and multiple sensors2010-2013 are mounted such that there is little or no surface of the scattering medium that is not covered by a sensor. Any areas that are not covered by sensors are preferably covered with an internally reflective coating that directs incident radiation back into thescattering medium2007 for absorption by the sensors2010-2013. Together these features ensure that the sensors2010-2013 absorb a maximum amount of radiation.
• InFIGS. 71 and 72, multiple sensors2021-2026 are alternately mounted circumferentially along the periphery of thescattering medium2007, for receiving and converting incident radiation into electrical energy. The multiple radiation sensors2021-2026 are electrically connected in series so that the voltage output of each sensor is additive, thereby producing a total output voltage in excess of what would be achieved from a single sensor.
• InFIG. 73, radiation scattering medium2031-2034 with a decreasing radiation transmission rate along the axis of the medium2031-2034 is used. A scattering medium2031-2034 with these properties would be used when sensors2035-2038 are electrically connected in series with consecutive sensors in the electrical circuit placed further along the axial direction of the scattering medium. This feature ensures that each sensor receives an equal exposure of radiation, produces a similar output current, thereby ensuring that the output current of the series circuit including all sensors is not limited by the output current of any individual sensor due to limited incident radiation.
• InFIG. 74, multiple sensors2041-2044 of varying size along the axis of thescattering medium2007 are used. By placing larger sensors towards the distal end of thescattering medium2007, these sensors2043-2044 receive an exposure of radiation equal to more proximally positioned sensors2041-2042 and therefore produce equivalent output currents, even though the radiation intensity at the distal end of thescattering medium2007 may be less than the radiation intensity at the proximal end of thescattering medium2007.
• InFIG. 75, a wave-guide2001 is coupled to a radiation source (not shown) to direct radiation into a second wave-guide2054 with multiple radiation beam splitters2050-2053 located along the optical axis of the wave-guide. Attached to the second wave-guide2054 are multiple radiation sensors2045-2048, mounted along the axis of the wave-guide2054, for receiving and converting incident radiation into electrical energy. The multiple radiation sensors2045-2048 are electrically connected in series so that the voltage output of each sensor is additive, thereby producing a total output voltage in excess of what would be achieved from a single sensor. The multiple sensors2045-2048 are mounted such that there is little or no surface of the second wave-guide2054 that is not covered by either a sensor or internally reflective coating. Together these features ensure that the sensors2045-2048 absorb a maximum amount of radiation.
• InFIG. 76, a second wave-guide2059 with beam splitters that have decreasing radiation transmission rates along the axis of the medium2059 is used. This feature would be used when sensors2055-2058 are electrically connected in series with consecutive sensors in the electrical circuit placed further along the axial direction of the wave-guide2059. Each sensor receives an equal exposure of radiation and produces a similar output current, thereby ensuring that the output current of the series circuit including all sensors is not limited by the output current of any individual sensor due to limited incident radiation.
• InFIG. 77, a wave-guide2001 is coupled to a radiation source (not shown) to direct radiation onto a stack of sensors2061-2064 such that each sensor absorbs a fraction of radiation incident upon the stack. The multiple radiation sensors2061-2064 are electrically connected in series so that the voltage output of each sensor is additive, thereby producing a total output voltage in excess of what would be achieved from a single sensor. To ensure maximum current output of the series circuit containing all sensors2061-2064, the radiation capture is increased with increasing distance into the sensor stack, which can be accomplished in several ways, including increasing sensor thickness that reduces radiation transfer through the consecutive sensors.
• InFIG. 78, a wave-guide2001 is coupled to a radiation source (not shown) to direct radiation onto a concentrically oriented array of sensors2071-2073. Multiple radiation sensors2071-2073 are electrically connected in series so that the voltage output of each sensor is additive, thereby producing a total output voltage in excess of what would be achieved from a single sensor. Each sensor has an equal area to ensure equal radiation exposure to all sensors2071-2073, thereby producing maximum current output for the series connected sensor array. This embodiment would be used when it is desirable to over-illuminate the sensor array to ensure equal radiation exposure to all sensors.
• InFIG. 79, a wave-guide2001 is coupled to a radiation source (not shown) to direct radiation onto areflective grating2084 that disperses radiation uniformly over the surface of multiple concentrically located sensors2081-2083. The multiple radiation sensors are electrically connected in series so that the voltage output of each sensor is additive, thereby producing a total output voltage in excess of what would be achieved from a single sensor.
• InFIG. 80, a wave-guide2001 is coupled to a radiation source (not shown) to direct radiation onto asingle radiation sensor2091 that is connected to multiple capacitors (C₁, C₂, C₃, . . . , C_n) electrically connected in parallel, enabling simultaneous charging of the capacitors (C₁, C₂, C₃, . . . , C_n) by the output voltage of thesingle sensor2091. The voltage of each capacitor is controlled by the duration of the single pulse of radiation incident upon the single sensor.
• InFIG. 81, the charged capacitors (C₁, C₂, C₃, . . . , C_n) are switchable to a series electrical circuit so that the voltage output of each capacitor is additive, thereby producing a total output voltage in excess of what would be achieved from a single capacitor.
• InFIG. 82, a catheter features a solid-state control circuit2094 to manage capacitor charging, switching, and discharging functions, as well as other distal control functions. Thecontrol circuit2094 is powered by electrical energy supplied by the illuminatedsensor2091. Additional features of this illustrated catheter include a housing andpacing electrodes2093 and2095.
• Variable capacitance capacitors can be utilized that are tuned to precisely match individual capacitor capacitances, thereby providing extraordinary control over output voltage and power.
• InFIGS. 81 and 82, the parallel electrical circuit ensures that each capacitor is charged to the same voltage level, ensuring a predictable output voltage when the parallel charged capacitors are connected in series and discharged. Moreover, the absence of multiple sensor sectors ensures that spatial variation in illumination intensity between sectors will not minimize the current of any one sector and thereby the entire circuit. Furthermore, the total energy dissipated by the series connected electrical circuit is determined by parameters that are easy to control; such as, the pre-selected capacitance of the capacitors (Power=CV²/2), as well as the intensity and duration of the radiation pulse and duration of the discharge pulse which are controlled by the solid state control circuit. The diameter of thesingle sensor2091 is limited only by the size of the radiation wave-guide2001. Lastly, reliability is improved due to reduced switching operations.
• InFIG. 83, a wave-guide2001 is coupled to a radiation source (not shown) to direct radiation onto asingle radiation sensor2091 that is sequentially connected to multiple capacitors (C₁, C₂, C₃, . . . , C_n) for charging. The voltage of each capacitor is controlled by the duration of the radiation pulse incident upon the surface of thesingle sensor2091.
• InFIG. 84, the capacitors (C₁, C₂, C₃, . . . , C_n) are subsequently connected in series for discharging, thereby producing a total output voltage in excess of what would be achieved from a single sensor or single capacitor. A solid-state control circuit (not shown) is utilized to manage capacitor charging, switching, and discharging functions, as well as other distal control functions. The control circuit is powered by electrical energy supplied by thesensor2091.
• The electrical measurements of the charging characteristics of each capacitor are determined prior to utilizing the catheter. This calibration information is then pre-programmed into a proximally located control circuit to determine the duration and intensity of the radiation pulse required to achieve a specific voltage across the capacitor, thereby providing a predictable output voltage when the parallel charged capacitors are connected in series and discharged.
• InFIGS. 83 and 84, the sequentially charging electrical circuit enables each capacitor to be charged with a pre-determined pulse intensity and duration, ensuring a predictable output voltage when the parallel charged capacitors are connected in series and discharged. The absence of multiple sensor sectors ensures that spatial variation in illumination intensity between sectors will not minimize the current of any one sector and thereby the entire circuit. Furthermore, the total energy dissipated by the series connected electrical circuit is determined by parameters that are easy to control; such as, the pre-selected capacitance of the capacitors (Power=CV²/2), as well as the intensity and duration of the radiation pulse and duration of the discharge pulse which are controlled by the solid state control circuit. The diameter of thesensor2091 is limited only by the size of the radiation wave-guide2001.
• InFIG. 85, the output energy of asingle radiation source3001 is split into multiple beams by radiation beam splitter3006 having multiple beam splitters3002-3005 and directed into multiple wave-guides3007-3010 to direct radiation onto multiple radiation sensors3011-3013. Redundant sensors3011-3013 are connected in series to produce a total output voltage in excess of what would be achieved from a single sensor.
• Power transfer can also be realized by a radiation source coupled to a wave-guide to direct radiation onto a single radiation sensor. This photonic system design is repeated with additional radiation sources, additional wave-guides, and additional radiation sensors. Redundant sensors are connected in series to produce a total output voltage in excess of what would be achieved from a single sensor.
• These embodiments may also utilize a variable intensity radiation source that can be used to vary the output current of the series connected sensors. Moreover, this embodiment may include a control circuit that controls the period and nature of the charge integration function of the sensors to maximize the output current of the sensors.
• It is noted that the power transfer embodiments illustrated inFIGS. 70-85 can be combined with the photonic sensing embodiments illustrated inFIGS. 5-20 such that the photonic catheter has both power transfer and sensing capabilities.
• The concepts of the present invention may also be utilized in implanted insulin pumps. Implanted insulin pumps typically consist of two major subsystems: a pump assembly for storing and metering insulin into the body, and a sensor for measuring glucose concentration. The two assemblies are typically connected by a metallic wire lead encased in a biocompatible catheter. The pump and sensor assemblies are typically located in separate locations within the body to accommodate the larger size of the reservoir and pump assembly (which is typically located in the gut), and to enable the sensor (typically located near the heart) to more accurately measure glucose concentration.
• The output of the sensor is delivered to the reservoir and pump assembly as a coded electrical signal where it is used to determine when and how much insulin to deliver into the body. The fact that the lead connecting the two assemblies is a wire lead makes it susceptible to interference from external magnetic fields, particularly the intense magnetic fields used in MRI imaging. Interference from MRI fields can induce electrical voltages in the leads that can damage the pump assembly and cause incorrect operation of the pump which could lead to patient injury possibly even death.
• Induced electrical currents can also cause heating of the lead that can also damage the pump and cause incorrect operation of the pump and injury to the patient due to pump failure as well as thermogenic injury to internal tissues and organs. Shielding of the reservoir and pump assembly and sensor assembly can reduce direct damage to these devices, but cannot prevent induced electrical voltages and currents from interfering with and damaging the devices.
• According to the concepts of the present invention, a photonic lead replaces the metallic wire connecting the reservoir and pump assembly and sensor assembly with a wave-guide such as an optical fiber. The sensor assembly is also modified to include means to transduce the electrical signal generated by the sensor into an optical signal that is then transmitted to reservoir and pump assembly over the wave-guide. This transduction means can be achieved by various combinations of optical emitters, optical attenuators, and optical sensors located in either the sensor assembly or reservoir and pump assembly.
• As noted above, the present invention is an implantable device that is immune or hardened to electromagnetic insult or interference.
• In one embodiment of the present invention as illustrated in the figures, an implantable pacemaker or a cardiac assist system is used to regulate the heartbeat of a patient. The implantable cardiac assist system is constructed of a primary device housing that has control circuitry therein. This control circuitry may include a control unit such a microprocessor or other logic circuits and digital signal processing circuits. The primary device housing may also include an oscillator, memory, filtering circuitry, an interface, sensors, a power supply, and/or a light source.
• The microprocessor may be an integrated circuit for controlling the operations of the cardiac assist system. The microprocessor integrated circuit can select a mode of operation for the cardiac assist system based on predetermined sensed parameters. In one embodiment, the microprocessor integrated circuit isolates physiological signals using an analog or digital noise filtering circuit.
• The primary device housing also can contain circuitry to detect and isolate crosstalk between device pulsing operations and device sensing operations, a battery power source and a battery power source measuring circuit. In such an embodiment the microprocessor integrated circuit can automatically adjust a value for determining an elective replacement indication condition of a battery power source. The value is automatically adjusted by the microprocessor integrated circuit in response to a measured level of a state of the battery power source. The measured level is generated by the battery power source measuring circuit that is connected to the battery power source.
• The microprocessor integrated circuit can be programmable from a source external of the cardiac assist system and can provide physiological or circuit diagnostics to a source external of the cardiac assist system.
• The microprocessor integrated circuit may also include a detection circuit to detect a phase timing of an external electromagnetic field. The microprocessor integrated circuit alters its operations to avoid interfering with the detected external electromagnetic field. Moreover, the cardiac assist system would include sensors may detect a heart signal and to produce a sensor signal therefrom and a modulator to modulate the sensor signal to differentiate the sensor signal from electromagnetic interference or a sampling circuit to sample the sensor signal multiple times to differentiate the sensor signal from electromagnetic interference, undesirable acoustic signals, large muscle contractions, or extraneous infrared light.
• The primary device housing has formed around it, in a preferred embodiment, a shield. The shield can be formed of various composite materials so as to provide an electromagnetic shield around the primary housing. Examples of such materials are metallic shielding or polymer or carbon composites such as carbon fullerenes. This shield or sheath around the primary device housing shields the primary device housing and any circuits therein from electromagnetic interference.
• The cardiac assist system also includes a lead system to transmit and receive signals between a heart and the primary device housing. The lead system may be a fiber optic based communication system, preferably a fiber optic communication system contains at least one channel within a multi-fiber optic bundle, or the lead system may be a plurality of electrical leads. The lead system is coated with electromagnetic interference resistant material.
• With respect to the electrical lead system, the plurality of electrical leads has a second shielding therearound, the second shielding preventing the electrical leads from conducting stray electromagnetic interference. The second shielding can be a metallic sheath to prevent the electrical leads from conducting stray electromagnetic interference; a carbon composite sheath to prevent the electrical leads from conducting stray electromagnetic interference; or a polymer composite sheath to prevent the electrical leads from conducting stray electromagnetic interference. The electrical leads may either be unipolar, bipolar or a combination of the two. Moreover, the lead system itself may be a combination of fiber optic leads and electrical leads wherein these electrical leads can be either unipolar, bipolar or a combination of the two.
• The lead systems may include a sensing and stimulation system at an epicardial-lead interface with a desired anatomical cardiac tissue region. The sensing and stimulation system may include optical sensing components to detect physiological signals from the desired anatomical cardiac tissue region and/or electrical sensing components to detect physiological signals from the desired anatomical cardiac tissue region. The sensing and stimulation system may also include optical pulsing components to deliver a stimulus of a predetermined duration and power to the desired anatomical cardiac tissue region and/or electrical pulsing components to deliver a stimulus of a predetermined duration and power to the desired anatomical cardiac tissue region. The sensing and stimulation system may also include hydrostatic pressure sensing components to detect physiological signals from the desired anatomical cardiac tissue region.
• Although the leads may be fiber optic strands or electrical leads with proper shielding, the actual interface to the tissue, the electrodes, cannot be shielded because the tissue needs to receive the stimulation from the device without interference. This causes the electrodes to be susceptible to electromagnetic interference or insult, and such insult can cause either damage to the tissue area or the circuitry at the other end. To realize immunity from the electromagnetic interference or insult, each electrode has an anti-antenna geometrical shape. The anti-antenna geometrical shape prevents the electrode from picking up and conducting stray electromagnetic interference.
• Moreover, the primary device housing, may include for redundancy filtering circuits as the ends of the electrical leads at the primary housing interface to remove stray electromagnetic interference from a signal being received from the electrical lead. The filters may be capacitive and inductive filter elements adapted to filter out predetermined frequencies of electromagnetic interference.
• In addition to the electromagnetic interference shielding, the primary device housing, and lead system, whether it is a fiber optic system or electrical lead system can be coated with a biocompatible material. Such a biocompatible material is preferably a non-permeable diffusion resistant biocompatible material.
• In another embodiment of the present invention as illustrated in the figures, an implantable pacemaker or a cardiac assist system is used to regulate the heartbeat of a patient. The implantable cardiac assist system is constructed of a primary device housing that has control circuitry therein. This control circuitry may include a control unit such a microprocessor or other logic circuits and digital signal processing circuits. The primary device housing may also include an oscillator, memory, filtering circuitry, an interface, sensors, a power supply, and/or a light source. In a preferred embodiment, the control circuitry including the oscillator and an amplifier operate at an amplitude level above that of an induced signal from a magnetic-resonance imaging field.
• The microprocessor may be an integrated circuit for controlling the operations of the cardiac assist system. The microprocessor integrated circuit can select a mode of operation for the cardiac assist system based on predetermined sensed parameters. In one embodiment, the microprocessor integrated circuit isolates physiological signals using an analog or digital noise filtering circuit.
• The primary device housing also can contain circuitry to detect and isolate crosstalk between device pulsing operations and device sensing operations, a battery power source and a battery power source measuring circuit. In such an embodiment the microprocessor integrated circuit can automatically adjust a value for determining an elective replacement indication condition of a battery power source. The value is automatically adjusted by the microprocessor integrated circuit in response to a measured level of a state of the battery power source. The measured level is generated by the battery power source measuring circuit that is connected to the battery power source.
• The microprocessor integrated circuit can be programmable from a source external of the cardiac assist system and can provide physiological or circuit diagnostics to a source external of the cardiac assist system.
• The cardiac assist system also includes a lead system to transmit and receive signals between a heart and the primary device housing. The lead system may be a fiber optic based communication system, preferably a fiber optic communication system contains at least one channel within a multi-fiber optic bundle, or the lead system may be a plurality of electrical leads. The lead system is coated with electromagnetic interference resistant material.
• The cardiac assist system further includes a detection circuit. The detection circuit is located in the primary device housing and detects an electromagnetic interference insult upon the cardiac assist system. Examples of such detection circuits are a thermistor heat detector; a high frequency interference detector; a high voltage detector; and/or an excess current detector. The control circuit places the cardiac assist system in an asynchronous mode upon detection of the electromagnetic interference insult by the detection system.
• With respect to the electrical lead system, the plurality of electrical leads has a second shielding therearound, the second shielding preventing the electrical leads from conducting stray electromagnetic interference. The second shielding can be a metallic sheath to prevent the electrical leads from conducting stray electromagnetic interference; a carbon composite sheath to prevent the electrical leads from conducting stray electromagnetic interference; or a polymer composite sheath to prevent the electrical leads from conducting stray electromagnetic interference. The electrical leads may either be unipolar, bipolar or a combination of the two. Moreover, the lead system itself may be a combination of fiber optic leads and electrical leads wherein these electrical leads can be either unipolar, bipolar or a combination of the two.
• The lead systems may include a sensing and stimulation system at an epicardial-lead interface with a desired anatomical cardiac tissue region. The sensing and stimulation system may include optical sensing components to detect physiological signals from the desired anatomical cardiac tissue region and/or electrical sensing components to detect physiological signals from the desired anatomical cardiac tissue region. The sensing and stimulation system may also include optical pulsing components to deliver a stimulus of a predetermined duration and power to the desired anatomical cardiac tissue region and/or electrical pulsing components to deliver a stimulus of a predetermined duration and power to the desired anatomical cardiac tissue region. The sensing and stimulation system may also include hydrostatic pressure sensing components to detect physiological signals from the desired anatomical cardiac tissue region.
• Although the leads may be fiber optic strands or electrical leads with proper shielding, the actual interface to the tissue, the electrodes, cannot be shielded because the tissue needs to receive the stimulation from the device without interference. This causes the electrodes to be susceptible to electromagnetic interference or insult, and such insult can cause either damage to the tissue area or the circuitry at the other end. To realize immunity from the electromagnetic interference or insult, each electrode has an anti-antenna geometrical shape. The anti-antenna geometrical shape prevents the electrode from picking up and conducting stray electromagnetic interference.
• Moreover, the primary device housing, may include for redundancy filtering circuits as the ends of the electrical leads at the primary housing interface to remove stray electromagnetic interference from a signal being received from the electrical lead. The filters may be capacitive and inductive filter elements adapted to filter out predetermined frequencies of electromagnetic interference.
• The primary device housing has formed around it, in a preferred embodiment, a shield. The shield can be formed of various composite materials so as to provide an electromagnetic shield around the primary housing. Examples of such materials are metallic shielding or polymer or carbon composites such as carbon fullerenes. This shield or sheath around the primary device housing shields the primary device housing and any circuits therein from electromagnetic interference.
• In addition to the electromagnetic interference shielding, the primary device housing, and lead system, whether it is a fiber optic system or electrical lead system can be coated with a biocompatible material. Such a biocompatible material is preferably a non-permeable diffusion resistant biocompatible material.
• In a third embodiment of the present invention as illustrated in the figures, a cardiac assist system includes a primary device housing. The primary device housing has a control circuit, therein, to perform synchronous cardiac assist operations. The cardiac assist system further includes a secondary device housing that has a control circuit, therein, to perform asynchronous cardiac assist operations
• A detection circuit, located in either the primary or secondary device housing and communicatively coupled to the control circuits, detects an electromagnetic interference insult upon the cardiac assist system. The detection circuit can also be located in a third device housing. Examples of such detection circuits are a thermistor heat detector; a high frequency interference detector; a high voltage detector; and/or an excess current detector.
• The detection circuit is communicatively coupled to the control circuits through a fiber optic communication system and/or through electromagnetic interference shielded electrical leads. The fiber optic communication system or the electromagnetic interference shielded electrical leads are coated with a biocompatible material.
• The control circuit of the primary device housing terminates synchronous cardiac assist operations and the control circuit of the secondary device housing initiates asynchronous cardiac assist operations upon detection of the electromagnetic interference insult by the detection system. In this system the control circuit of the secondary device housing places the cardiac assist system in the asynchronous mode for a duration of the electromagnetic interference insult and terminates the asynchronous mode of the cardiac assist system upon detection of an absence of an electromagnetic interference insult by the detection system. The control circuit of the primary device housing terminates the synchronous mode of the cardiac assist system for the duration of the electromagnetic interference insult and re-initiates the synchronous mode of the cardiac assist system upon detection of an absence of an electromagnetic interference insult by the detection system.
• The primary and secondary device housings have formed around them, in a preferred embodiment, a shield. The shield can be formed of various composite materials so as to provide an electromagnetic shield around the primary housing. Examples of such materials are metallic shielding or polymer or carbon composites such as carbon fullerenes. This shield or sheath around the primary device housing shields the primary device housing and any circuits therein from electromagnetic interference.
• In addition to the electromagnetic interference shielding, the primary and secondary device housings are coated with a biocompatible material. Such a biocompatible material is preferably a non-permeable diffusion resistant biocompatible material.
• The cardiac assist system also includes a lead system to transmit and receive signals between heart and the primary and secondary device housings. The lead system may be a fiber optic based communication system, preferably a fiber optic communication system contains at least one channel within a multi-fiber optic bundle, or the lead system may be a plurality of electrical leads. The lead system is coated with electromagnetic interference resistant material.
• With respect to the electrical lead system, the plurality of electrical leads has a second shielding therearound, the second shielding preventing the electrical leads from conducting stray electromagnetic interference. The second shielding can be a metallic sheath to prevent the electrical leads from conducting stray electromagnetic interference; a carbon composite sheath to prevent the electrical leads from conducting stray electromagnetic interference; or a polymer composite sheath to prevent the electrical leads from conducting stray electromagnetic interference. The electrical leads may either be unipolar, bipolar or a combination of the two. Moreover, the lead system itself may be a combination of fiber optic leads and electrical leads wherein these electrical leads can be either unipolar, bipolar or a combination of the two.
• The lead systems may include a sensing and stimulation system at an epicardial-lead interface with a desired anatomical cardiac tissue region. The sensing and stimulation system may include optical sensing components to detect physiological signals from the desired anatomical cardiac tissue region and/or electrical sensing components to detect physiological signals from the desired anatomical cardiac tissue region. The sensing and stimulation system may also include optical pulsing components to deliver a stimulus of a predetermined duration and power to the desired anatomical cardiac tissue region and/or electrical pulsing components to deliver a stimulus of a predetermined duration and power to the desired anatomical cardiac tissue region. The sensing and stimulation system may also include hydrostatic pressure sensing components to detect physiological signals from the desired anatomical cardiac tissue region.
• Although the leads may be fiber optic strands or electrical leads with proper shielding, the actual interface to the tissue, the electrodes, cannot be shielded because the tissue needs to receive the stimulation from the device without interference. This causes the electrodes to be susceptible to electromagnetic interference or insult, and such insult can cause either damage to the tissue area or the circuitry at the other end. To realize immunity from the electromagnetic interference or insult, each electrode has an anti-antenna geometrical shape. The anti-antenna geometrical shape prevents the electrode from picking up and conducting stray electromagnetic interference.
• In a fourth embodiment of the present invention, an implantable pacemaker or a cardiac assist system is used to regulate the heartbeat of a patient. The implantable cardiac assist system is constructed of a primary device housing that has control circuitry therein. This control circuitry may include a control unit such a microprocessor or other logic circuits and digital signal processing circuits. The primary device housing may also include an oscillator, memory, filtering circuitry, an interface, sensors, a power supply, and/or a light source.
• The microprocessor may be an integrated circuit for controlling the operations of the cardiac assist system. The microprocessor integrated circuit can select a mode of operation for the cardiac assist system based on predetermined sensed parameters. In one embodiment, the microprocessor integrated circuit isolates physiological signals using an analog or digital noise filtering circuit.
• The primary device housing also can contain circuitry to detect and isolate crosstalk between device pulsing operations and device sensing operations, a battery power source and a battery power source measuring circuit. In such an embodiment the microprocessor integrated circuit can automatically adjust a value for determining an elective replacement indication condition of a battery power source. The value is automatically adjusted by the microprocessor integrated circuit in response to a measured level of a state of the battery power source. The measured level is generated by the battery power source measuring circuit that is connected to the battery power source.
• The microprocessor integrated circuit can be programmable from a source external of the cardiac assist system and can provide physiological or circuit diagnostics to a source external of the cardiac assist system.
• The microprocessor integrated circuit may also include a detection circuit to detect a phase timing of an external electromagnetic field. The microprocessor integrated circuit alters its operations to avoid interfering with the detected external electromagnetic field. Moreover, the cardiac assist system would include sensors may detect a heart signal and to produce a sensor signal therefrom and a modulator to modulate the sensor signal to differentiate the sensor signal from electromagnetic interference or a sampling circuit to sample the sensor signal multiple times to differentiate the sensor signal from electromagnetic interference, undesirable acoustic signals, large muscle contractions, or extraneous infrared light.
• The primary device housing has formed around it, in a preferred embodiment, a shield. The shield can be formed of various composite materials so as to provide an electromagnetic shield around the primary housing. Examples of such materials are metallic shielding or polymer or carbon composites such as carbon fullerenes. This shield or sheath around the primary device housing shields the primary device housing and any circuits therein from electromagnetic interference.
• The cardiac assist system also includes a fiber optic lead system to transmit and receive signals between a heart and the primary device housing. The fiber optic communication system preferably contains at least one channel within a multi-fiber optic bundle. The lead system can be coated with electromagnetic interference resistant material.
• The optic fiber lead systems may include a sensing and stimulation system at an epicardial-lead interface with a desired anatomical cardiac tissue region. The sensing and stimulation system may include optical sensing components to detect physiological signals from the desired anatomical cardiac tissue region and/or electrical sensing components to detect physiological signals from the desired anatomical cardiac tissue region (in the electrical sensing components, electrical pulses are converted to light pulses before being transmitted over the lead system). The sensing and stimulation system may also include optical pulsing components to deliver a stimulus of a predetermined duration and power to the desired anatomical cardiac tissue region and/or electrical pulsing components to deliver a stimulus of a predetermined duration and power to the desired anatomical cardiac tissue region (in the electrical delivering components, light pulses are converted to electrical pulses after the light pulses are received from the lead system). The sensing and stimulation system may also include hydrostatic pressure sensing components to detect physiological signals from the desired anatomical cardiac tissue region.
• Although the leads are fiber optic strands, the actual interface to the tissue, the electrodes, cannot be fiber optics because the tissue needs to receive electrical stimulation from the device. This causes the electrodes to be susceptible to electromagnetic interference or insult, and such insult can cause either damage to the tissue area or the circuitry at the other end. To realize immunity from the electromagnetic interference or insult, each electrode has an anti-antenna geometrical shape. The anti-antenna geometrical shape prevents the electrode from picking up and conducting stray electromagnetic interference.
• In addition, the primary device housing and the fiber optic lead system are coated with a biocompatible material. Such a biocompatible material is preferably a non-permeable diffusion resistant biocompatible material.
• The primary device housing further includes an electronic signal generator and a controlled laser light pulse generator linked to the electronic signal generator. A fiber optic light pipe for receives the laser light pulse from the controlled laser light pulse generator at a proximal end of the fiber optic light pipe. A photodiode, at a distal end of the fiber optic light pipe converts the laser light pulse back into an electrical pulse. The electrical pulse drives the cardiac electrodes coupled to the photodiode and to a cardiac muscle.
• In a fifth embodiment of the present invention as illustrated in the figures, an implantable cable for transmission of a signal to and from a body tissue of a vertebrate is constructed of a fiber optic bundle having a cylindrical surface of non-immunogenic, physiologically compatible material. The fiber optic bundle is capable of being permanently implanted in a body cavity or subcutaneously. An optical fiber in the fiber optic bundle has a distal end for implantation at or adjacent to the body tissue and a proximal end. The proximal end is adapted to couple to and direct an optical signal source. The distal end is adapted to couple to an optical stimulator. The optical fiber delivers an optical signal intended to cause the optical stimulator located at a distal end to deliver an excitatory stimulus to a selected body tissue. The stimulus causes the selected body tissue to function as desired.
• The optical stimulator is constructed, in a preferred embodiment, is constructed of a photoresponsive device for converting the light received from the optical signal source into electrical energy and for sensing variations in the light energy to produce control signals. A charge-accumulating device, such as a CCD, receives and stores the electrical energy produced by the photoresponsive device. A discharge control device, responsive to the control signals, directs the stored electrical energy from the charge-accumulating device to the cardiac assist device associated with the heart.
• A second optical fiber has a distal end coupled to a sensor and a proximal end coupled to a device responsive to an optical signal delivered by the second optical fiber. The sensor generates an optical signal to represent a state of a function of the selected body tissue to provide feedback to affect the activity of the optical signal source.
• In a sixth embodiment of the present invention, an implantable photonic cable system is constructed from a photonic cable, a light source and a light detector. The light source and the light detector form an optical sensor unit. The photonic cable, in this embodiment, receives signals from a selected tissue area and delivering signals to the selected tissue area. The system further includes transducers.
• The light source illuminates a tissue area, and the light detector detects properties of the tissue by measuring the output of the light signals reflective from the tissue area. A hollow porous cylinder is used to attach the optical sensor unit to the tissue area. Preferably, the light source is a light emitting diode and the light detector is a photodiode comprising multiple channels. The multiple channels detect light emission at multiple wavelengths. Moreover, the optical sensor unit includes either a pressure-optical transducer or a reflective element mechanically driven by a moving part of the selected body tissue.
• In a seventh embodiment of the present invention, a cardiac assist system is constructed of a primary device housing having a control circuit therein. A shielding is formed around the primary device housing to shield the primary device housing and any circuits therein from electromagnetic interference. A lead system to transmit and receive signals between a heart and the primary device housing. A switch places the control circuitry into a fixed-rate mode of operation. A changing magnetic field sensor to sense a change in magnetic field around the primary housing. The switch places the control circuitry into a fixed-rate mode of operation when the changing magnetic field sensor senses a predetermined encoded changing magnetic field.
• In another embodiment of the present invention, a method prevents a cardiac assist system from failing during magnetic resonance imaging. A magnetic-resonance imaging system determines a quiet period for a cardiac assist system. Upon making this determination, the magnetic-resonance imaging system locks the timing of a magnetic resonance imaging pulse to occur during a quiet period of the cardiac assist system.
• In an eighth embodiment of the present invention, a cardiac assist system is constructed of a primary device housing having a control circuit therein. A shielding is formed around the primary device housing to shield the primary device housing and any circuits therein from electromagnetic interference. A lead system to transmit and receive signals between a heart and the primary device housing. A switch places the control circuitry into a fixed-rate mode of operation. An acoustic sensor senses a predetermined acoustic signal, and the switch places the control circuitry into a fixed-rate mode of operation when the acoustic sensor senses the predetermined acoustic signal.
• In a ninth embodiment of the present invention, a cardiac assist system is constructed of a primary device housing having a control circuit therein. A shielding is formed around the primary device housing to shield the primary device housing and any circuits therein from electromagnetic interference. A lead system to transmit and receive signals between a heart and the primary device housing. A switch places the control circuitry into a fixed-rate mode of operation. A near infrared sensor senses a predetermined near infrared signal. The switch places the control circuitry into a fixed-rate mode of operation when the near infrared sensor senses the predetermined near infrared signal.
• The present invention also contemplates an electromagnetic radiation immune tissue invasive stimulation system that includes a photonic lead having a proximal end and a distal end; a light source, in the proximal end of the photonic lead, to produce a first light having a first wavelength; a wave-guide between the proximal end and distal end of the photonic lead; a distal sensor, in the distal end of the photonic lead, to convert the first light into electrical energy into control signals; an electrical energy storage device to store electrical energy; and a control circuit, in response to the control signals, to cause a portion of the stored electrical energy to be delivered to a predetermined tissue region. In this embodiment, the predetermined tissue region may be, for example, a region of the spinal cord, a region of the brain, a region associated with a deep brain structure, the vagal nerve, peripheral nerves that innervate muscles, sacral nerve roots to elicit functional contraction of muscles innervated by the sacral nerve roots, sacral nerve roots associated with bladder function, a region of the cochlea, a region of the stomach, or the hypoglossal nerve.
• The present invention also contemplates an electromagnetic radiation immune tissue invasive sensing system that includes a photonic lead having a proximal end and a distal end; a light source, in the proximal end of the photonic lead, to produce a first light having a first wavelength; a wave-guide between the proximal end and distal end of the photonic lead; a distal sensor, in the distal end of the photonic lead, to convert the first light into electrical energy into control signals; an electrical energy storage device to store electrical energy; and a bio-sensor, in the distal end of the photonic lead, to sense a characteristic of a predetermined tissue region. The light source, in the proximal end of the photonic lead, produces a second light having a second wavelength. The distal sensor, in the distal end of the photonic lead and responsive to the bio-sensor, reflects the second light back the proximal end of the photonic lead such that a characteristic of the second light is modulated to encode the sensed characteristic of the predetermined tissue region. In this embodiment, the sensed characteristic may be, for example, an ECG, an EKG, an esophageal ECG, a level of oxygen, blood pressure, intracranial pressure, or temperature.
• The present invention also contemplates an electromagnetic radiation immune sensing system that includes a photonic lead having a proximal end and a distal end; a light source, in the proximal end of the photonic lead, to produce a first light having a first wavelength and a second light having a second wavelength; a wave-guide between the proximal end and distal end of the photonic lead; a bio-sensor, in the distal end of the photonic lead, to measure changes in an electric field located outside a body, the electric field being generated by the shifting voltages on a body's skin surface; and a distal sensor, in the distal end of the photonic lead, to convert the first light into electrical energy and, responsive to the bio-sensor, to reflect the second light back the proximal end of the photonic lead such that a characteristic of the second light is modulated to encode the measured changes in the electric field. In this embodiment, the measured electric field may correspond to an ECG signal. Also in this embodiment, the bio-sensor has impedance higher than an impedance of an air gap between the bio-sensor and the body.
• While various examples and embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that the spirit and scope of the present invention are not limited to the specific description and drawings herein, but extend to various modifications and changes all as set forth in the following claims.

Claims (69)

1. A lead, comprising:

a conductor having a distal end and a proximal end; and

a filter circuit in said conductor;

said filter circuit filtering out magnetic resonance imaging induced signals.

2. The lead as claimed inclaim 1, wherein said filter circuit is located at said distal end of said conductor.

3. The lead as claimed inclaim 1, wherein said filter circuit is located at said proximal end of said conductor.

4. The lead as claimed inclaim 1, wherein said filter circuit is an inductor and a capacitor.

5. The lead as claimed inclaim 4, wherein said inductor and capacitor are connected in parallel.

6. The lead as claimed inclaim 1, wherein said filter circuit is a tank circuit.

7. The lead as claimed inclaim 1, wherein the conductor is a conductor in a bipolar pacing lead circuit.

8. The lead as claimed inclaim 1, wherein the conductor is a conductor in a unipolar pacing lead circuit.

9. The lead as claimed inclaim 1, wherein the conductor is a conductor in a cardiac defibrillator lead, a deep brain stimulating lead, or a conductor in a nerve stimulating lead.

10. A lead, comprising:

a plurality of conductors, each conductor having a distal end and a proximal end; and

a plurality of filter circuits, each filter circuit being in a conductor, each filter circuit filtering out magnetic resonance imaging induced signals.

11. The lead as claimed inclaim 10, wherein each filter circuit is located at said distal end of said conductor.

12. The lead as claimed inclaim 10, wherein each filter circuit is located at said proximal end of said conductor.

13. The lead as claimed inclaim 10, wherein each filter circuit is an inductor/capacitor pair.

14. The lead as claimed inclaim 13, wherein each inductor/capacitor pair is an inductor connected in parallel with a capacitor.

15. The lead as claimed inclaim 10, wherein each filter circuit is a tank circuit.

16. The lead as claimed inclaim 10, wherein said conductors are conductors in a cardiac defibrillator lead, a deep brain stimulating lead, or a conductor in a nerve stimulating lead.

17. A lead, comprising:

a conductor having a distal end and a proximal end;

an electrode connected to said distal end of said conductor; and

a filter circuit in said conductor;

said filter circuit being connected in series between said conductor and said electrode;

said filter circuit filtering out magnetic resonance imaging induced signals.

18. The lead as claimed inclaim 17, wherein said filter circuit is an inductor and a capacitor.

19. The lead as claimed inclaim 18, wherein said inductor and capacitor are connected in parallel.

20. The lead as claimed inclaim 17, wherein said filter circuit is a tank circuit.

21. The lead as claimed inclaim 17, wherein the conductor is a conductor in a bipolar pacing lead circuit.

22. The lead as claimed inclaim 17, wherein the conductor is a conductor in a unipolar pacing lead circuit.

23. The lead as claimed inclaim 17, wherein the conductor is a conductor in a cardiac defibrillator lead, a deep brain stimulating lead, or a conductor in a nerve stimulating lead.

24. A lead, comprising:

a conductor having a distal end and a proximal end; and

a filter circuit in said conductor;

said filter circuit attenuating magnetic resonance imaging induced signals.

25. The lead as claimed inclaim 24, wherein said filter circuit is located at said distal end of said conductor.

26. The lead as claimed inclaim 24, wherein said filter circuit is located at said proximal end of said conductor.

27. The lead as claimed inclaim 24, wherein said filter circuit is an inductor and a capacitor.

28. The lead as claimed inclaim 27, wherein said inductor and capacitor are connected in parallel.

29. The lead as claimed inclaim 24, wherein said filter circuit is a tank circuit.

30. The lead as claimed inclaim 24, wherein the conductor is a conductor in a bipolar pacing lead circuit.

31. The lead as claimed inclaim 24, wherein the conductor is a conductor in a unipolar pacing lead circuit.

32. The lead as claimed inclaim 24, wherein the conductor is a conductor in a cardiac defibrillator lead, a deep brain stimulating lead, or a conductor in a nerve stimulating lead.

33. A lead, comprising:

a plurality of conductors, each conductor having a distal end and a proximal end; and

a plurality of filter circuits, each filter circuit being in a conductor, each filter circuit attenuating magnetic resonance imaging induced signals.

34. The lead as claimed inclaim 33, wherein each filter circuit is located at said distal end of said conductor.

35. The lead as claimed inclaim 33, wherein each filter circuit is located at said proximal end of said conductor.

36. The lead as claimed inclaim 33, wherein each filter circuit is an inductor/capacitor pair.

37. The lead as claimed inclaim 36, wherein each inductor/capacitor pair is an inductor connected in parallel with a capacitor.

38. The lead as claimed inclaim 33, wherein each filter circuit is a tank circuit.

39. The lead as claimed inclaim 33, wherein said conductors are conductors in a cardiac defibrillator lead, a deep brain stimulating lead, or a conductor in a nerve stimulating lead.

40. A lead, comprising:

a conductor having a distal end and a proximal end;

an electrode connected to said distal end of said conductor; and

a filter circuit in said conductor;

said filter circuit being connected in series between said conductor and said electrode;

said filter circuit attenuating magnetic resonance imaging induced signals.

41. The lead as claimed inclaim 40, wherein said filter circuit is an inductor and a capacitor.

42. The lead as claimed inclaim 41, wherein said inductor and capacitor are connected in parallel.

43. The lead as claimed inclaim 40, wherein said filter circuit is a tank circuit.

44. The lead as claimed inclaim 40, wherein the conductor is a conductor in a bipolar pacing lead circuit.

45. The lead as claimed inclaim 40, wherein the conductor is a conductor in a unipolar pacing lead circuit.

46. The lead as claimed inclaim 40, wherein the conductor is a conductor in a cardiac defibrillator lead, a deep brain stimulating lead, or a conductor in a nerve stimulating lead.

47. A lead, comprising:

a conductor having a distal end and a proximal end; and

a filter circuit in said conductor;

said filter circuit limiting magnetic resonance imaging induced signals.

48. The lead as claimed inclaim 4, wherein said filter circuit is located at said distal end of said conductor.

49. The lead as claimed inclaim 47, wherein said filter circuit is located at said proximal end of said conductor.

50. The lead as claimed inclaim 47, wherein said filter circuit is an inductor and a capacitor.

51. The lead as claimed inclaim 50, wherein said inductor and capacitor are connected in parallel.

52. The lead as claimed inclaim 47, wherein said filter circuit is a tank circuit.

53. The lead as claimed inclaim 47, wherein the conductor is a conductor in a bipolar pacing lead circuit.

54. The lead as claimed inclaim 47, wherein the conductor is a conductor in a unipolar pacing lead circuit.

55. The lead as claimed inclaim 47, wherein the conductor is a conductor in a cardiac defibrillator lead, a deep brain stimulating lead, or a conductor in a nerve stimulating lead.

56. A lead, comprising:

a plurality of conductors, each conductor having a distal end and a proximal end; and

a plurality of filter circuits, each filter circuit being in a conductor, each filter circuit limiting magnetic resonance imaging induced signals.

57. The lead as claimed inclaim 56, wherein each filter circuit is located at said distal end of said conductor.

58. The lead as claimed inclaim 56, wherein each filter circuit is located at said proximal end of said conductor.

59. The lead as claimed inclaim 56, wherein each filter circuit is an inductor/capacitor pair.

60. The lead as claimed inclaim 59, wherein each inductor/capacitor pair is an inductor connected in parallel with a capacitor.

61. The lead as claimed inclaim 56, wherein each filter circuit is a tank circuit.

62. The lead as claimed inclaim 56, wherein said conductors are conductors in a cardiac defibrillator lead, a deep brain stimulating lead, or a conductor in a nerve stimulating lead.

63. A lead, comprising:

a conductor having a distal end and a proximal end;

an electrode connected to said distal end of said conductor; and

a filter circuit in said conductor;

said filter circuit being connected in series between said conductor and said electrode;

said filter circuit limiting magnetic resonance imaging induced signals.

64. The lead as claimed inclaim 63, wherein said filter circuit is an inductor and a capacitor.

65. The lead as claimed inclaim 64, wherein said inductor and capacitor are connected in parallel.

66. The lead as claimed inclaim 63, wherein said filter circuit is a tank circuit.

67. The lead as claimed inclaim 63, wherein the conductor is a conductor in a bipolar pacing lead circuit.

68. The lead as claimed inclaim 63, wherein the conductor is a conductor in a unipolar pacing lead circuit.

69. The lead as claimed inclaim 63, wherein the conductor is a conductor in a cardiac defibrillator lead, a deep brain stimulating lead, or a conductor in a nerve stimulating lead.

Images