Detection of strong static magnetic fields and MRI examination safekeeping for an implantable cardiac prosthesis

An active implantable medical device for one of cardiac stimulation, resynchronization, and defibrillation, comprising:

• an electronic circuit for a detection/stimulation of a cardiac activity;
• a first sensor for detecting a first magnetic field positioned in proximity to the device;
• a second sensor for detecting a second magnetic field positioned in proximity to the device;
• means for activating said second sensor in response to said first sensor detecting the first magnetic field and for inactivating the second sensor otherwise;
• and
• means for placing the electronic circuit in a safekeeping operating mode in response to the first sensor detecting the first magnetic field and the second sensor detecting the second magnetic field;
• wherein the means for placing the electronic circuit in a safekeeping mode further comprises:
• means, upon detection of the first magnetic field by the first sensor, for placing the electronic circuit into a magnet mode of operation without cardiac detection, and for activating the second sensor;
• and
• means, upon detection of the second magnetic field by the second sensor, for inhibiting a component of the device that is sensitive to the second magnetic field, and for placing the electronic circuit into a modified magnetic mode by modifying at least one parameter of said magnet mode of operation;
• wherein the magnet mode of operation is a mode in which the electronic circuit produces stimulation pulses at a first predetermined frequency, correlated to a charge level of a power supply of the device;
• and
• wherein the modified magnet mode is a mode in which the electronic circuit produces stimulation pulses at a second predetermined frequency, independent of the charge level of the power supply of the device.