Switched safety protection circuit for an AIMD system during exposure to high power electromagnetic fields

An active implantable medical device (AIMD), comprising:

• a) a conductive device housing for the AIMD, the housing containing tissue-stimulating or biological-sensing circuits;
• b) an implantable lead comprising at least one leadwire having a length extending between and to a proximal end electrically connected to the medical device including the tissue-stimulating or biological-sensing circuits and an electrode configured for tissue-stimulating or biological-sensing at or near a distal end of the leadwire;
• c) an energy dissipating surface provided by the device housing;
• d) at least one diversion circuit electrically connected from the leadwire to the device housing;
• and
• e) at least one switch that is actuatable in response to a magnetic resonance B0 field sensor to electrically connect the leadwire to the tissue-stimulating or biological-sensing circuits for the medical device in the absence of an MRI static magnetic field and, in the presence of an MRI static magnetic field, to electrically disconnect the leadwire from the tissue-stimulating or biological-sensing circuits and to connect the tissue-stimulating or biological-sensing circuits to the device housing at a position that is either spaced apart or at the same location as where the diversion circuit is connected thereto as the energy dissipating surface,
• f) wherein regardless the position of the switch:
• i) at relatively high frequencies attendant to the medical device being subjected to an RF pulse field, the diversion circuit act as a relatively low impedance circuit between the leadwire and the energy dissipating surface, and
• ii) at relatively low frequencies attendant to the medical device being subjected to an MRI gradient field, the diversion circuit acts as an relatively high impedance circuit between the leadwire and the energy dissipating surface.

An implantable medical device, comprising:

• a) a conductive device housing for the medical device, the housing containing tissue-stimulating or biological-sensing circuits;
• b) an implantable lead comprising at least one leadwire having a length extending between and to a proximal end electrically connected to the medical device including the tissue-stimulating or biological-sensing circuits and an electrode configured for tissue-stimulating or biological-sensing at or near a distal end of the leadwire;
• c) an energy dissipating surface provided by the device housing;
• d) at least one diversion circuit electrically connected from the leadwire to the device housing;
• and
• e) at least one switch that is selectively actuatable in response to programmable telemetry to electrically connect the leadwire to the tissue-stimulating or biological-sensing circuits for the medical device in the absence of an MRI static magnetic field and, in anticipation of being in the presence of an MRI static magnetic field, to electrically disconnect the leadwire from the tissue-stimulating or biological-sensing circuits and to connect the tissue-stimulating or biological-sensing circuits to the device housing at a position that is either spaced apart or at the same location as where the diversion circuit is connected thereto as the energy dissipating surface,
• f) wherein regardless the position of the switch:
• i) at relatively high frequencies attendant to the medical device being subjected to an RF pulse field, the diversion circuit acts as a relatively low impedance circuit from the leadwire to the energy dissipating surface, and
• ii) at relatively low frequencies attendant to the medical device being subjected to an MRI gradient field, the diversion circuit acts as a relatively high impedance circuit between the leadwire and the energy dissipating surface.

An implantable medical device, comprising:

• a) a conductive device housing containing tissue-stimulating or biological-sensing circuits;
• b) an energy dissipating surface provided by the device housing;
• c) at least one frequency variable impedance diversion circuit electrically connected between a terminal and the device housing;
• and
• d) at least one switch that is actuatable in response to a magnetic resonance B0 field sensor to electrically connect the terminal for an implantable lead to the tissue-stimulating or biological-sensing circuits for the medical device in the absence of an MRI static magnetic field and, in the presence of an MRI static magnetic field, to electrically disconnect the terminal from the tissue-stimulating or biological-sensing circuits and to connect the tissue-stimulating or biological-sensing circuits to the device housing at a position that is either spaced apart or at the same location as where the diversion circuit is connected thereto as the energy dissipating surface,
• e) wherein regardless the position of the switch:
• i) at relatively high frequencies attendant to the medical device being subjected to an RF pulse field, the diversion circuit acts as a relatively low impedance circuit from the leadwire to the energy dissipating surface, and
• ii) at relatively low frequencies attendant to the medical device being subjected to an MRI gradient field, the diversion circuit acts as a relatively high impedance circuit between the leadwire and the energy dissipating surface.