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

• US 8,818,506 B2
• Filed: 10/08/2013
• Issued: 08/26/2014
• Est. Priority Date: 01/09/2009
• Status: Active Grant

• Current Assignee: Sorin CRM SAS (MicroPort Scientific Corp.)
• Original Assignee: Sorin CRM SAS (MicroPort Scientific Corp.)
• Inventors: Legay, Thierry
• Primary Examiner(s): Koharski, Christopher D
• Assistant Examiner(s): CAREY, MICHAEL JAMES
• Application Number:
  US14/049,061
• Publication Number:
  US 20140039568A1
• Time in Patent Office: 322 Days
• Field of Search: 607/11, 607/63
• US Class Current: 607/11
• CPC Class Codes: A61N 1/37 Monitoring; Protecting
• CPC Class Codes: A61N 1/3718 Monitoring of or protection against external electromagnetic fields or currents
• CPC Class Codes: A61N 1/3925 Monitoring; Protecting
• CPC Class Codes: G01R 33/288 Provisions within MR facilities for enhancing safety during MR, e.g. reduction of the specific absorption rate [SAR], detection of ferromagnetic objects in the scanner room

Abstract

An implantable medical device detects a strong static magnetic field associated with an MRI imaging instrument and operates in a safekeeping operating mode. The device includes an electronic circuit for the detection/stimulation of a cardiac activity, a weak field sensor detecting the presence of a first magnetic field of a permanent magnet being located in proximity to the device, a strong field sensor detecting the presence of a second magnetic field of an MRI imaging instrument during the course of an MRI examination.

Claims

1. A method for operating an active implantable medical device, the method comprising:

determining whether a first magnetic field is detected in proximity to the device using a first sensor;

determining whether a second magnetic field is detected in proximity to the device using a second sensor;

wherein the second sensor is activated in response to a determination that the first magnetic field is detected in proximity to the device;

operating the active implantable medical device in a safe operating mode in response to a determination that both the first magnetic field and the second magnetic field are detected in proximity to the device; and

wherein the first and second magnetic fields are different.

2. The method of claim 1, further comprising:

deactivating the second sensor in response to a determination that the first magnetic field is not detected in proximity to the device.

3. The method of claim 2, wherein:

activating the second sensor comprises connecting a power source to the second sensor; and

deactivating the second sensor comprises disconnecting the power source from the second sensor.

4. The method of claim 1, further comprising:

preventing the active implantable medical device from operating in the safe operating mode unless both the first magnetic field and the second magnetic field are detected.

5. The method of claim 1, further comprising:

inhibiting a component of the active implantable medical device that is sensitive to the second magnetic field in the safekeeping operating mode.

6. The method of claim 1, further comprising:

operating the active implantable medical device in a magnet operating mode in response to a determination that the first magnetic field is detected and the second magnetic field is not detected; and

transitioning into the safe operating mode in response to a determination that the second magnetic field is detected when operating in the magnet operating mode, wherein transitioning into the safe operating mode comprises modifying at least one operating parameter of the magnet operating mode.

7. The method of claim 1, wherein determining whether the first magnetic field is detected comprises determining whether a level of the first magnetic field measured by the first sensor exceeds a first threshold value;

and

wherein determining whether the second magnetic field is detected comprises determining whether a level of the second magnetic field measured by the second sensor exceeds a second threshold value;

wherein the second threshold value is greater than the first threshold value.

8. The method of claim 1, wherein the first magnetic field is associated with a permanent magnet and the second magnetic field is associated with a magnetic resonance imaging device.

9. The method of claim 1, wherein the first magnetic field is a static magnetic field having a level of at least 1 mT and the second magnetic field is a static magnetic field having a level of at least 0.25 T.

10. The method of claim 1, further comprising:

producing stimulation pulses at a first frequency in response to a determination that the first magnetic field is detected, wherein the first frequency is a function of a level of charge in a power supply for the active implantable medical device; and

producing stimulation pulses at a second frequency in response to a determination that the second magnetic field is detected, wherein the second frequency is not a function of the level of charge in the power supply for the active implantable medical device.

11. An active implantable medical device comprising:

a first sensor configured to detect a first magnetic field in proximity to the device;

a second sensor configured to detect a second magnetic field in proximity to the device; and

an electronic circuit configured to determine whether the first magnetic field is detected by the first sensor, to determine whether the second magnetic field is detected by the second sensor, and to operate the active implantable medical device in a safe operating mode in response to a determination that both the first magnetic field and the second magnetic field are detected;

wherein the electronic circuit is configured to activate the second sensor in response to a determination that the first magnetic field is detected in proximity to the device; and

wherein the first and second magnetic fields are different.

12. The active implantable medical device of claim 11, wherein the first sensor is at least one of:

a coil having a core that saturates in the presence of the first magnetic field, a giant magnetic resistance (GMR) device, and a Hall effect sensor.

13. The active implantable medical device of claim 11, wherein the second sensor is a MAGFET type sensor integrated with the electronic circuit.

14. The active implantable medical device of claim 11, wherein the electronic circuit is configured to:

deactivate the second sensor in response to a determination that the first magnetic field is not detected in proximity to the device.

15. The active implantable medical device of claim 14, wherein:

activating the second sensor comprises connecting a power source to the second sensor; and

deactivating the second sensor comprises disconnecting the power source from the second sensor.

16. The active implantable medical device of claim 11, wherein the electronic circuit is configured to:

prevent the active implantable medical device from operating in the safekeeping operating mode unless both the first magnetic field and the second magnetic field are detected; and

inhibit a component of the active implantable medical device that is sensitive to the second magnetic field in the safekeeping operating mode.

17. An active implantable medical device comprising:

a first sensor configured to detect a weak magnetic field having a level exceeding a first threshold value;

a second sensor configured to detect a strong magnetic field having a level exceeding a second threshold value, wherein the second threshold value is higher than the first threshold value; and

an electronic circuit configured to operate the active implantable medical device in a safekeeping operating mode in response to the first sensor detecting the weak magnetic field and the second sensor detecting the strong magnetic field;

wherein the electronic circuit is configured to inhibit a component of the active implantable medical device that is sensitive to the strong magnetic field in the safekeeping operating mode; and

wherein the electronic circuit is further configured to activate the second sensor in response to a determination that the weak magnetic field is detected in proximity to the device.

18. The active implantable medical device of claim 17, wherein the electronic circuit is configured to operate the active implantable medical device in the safekeeping operating mode only when both the weak magnetic field and strong magnetic field are detected.

19. The active implantable medical device of claim 17, wherein the weak magnetic field is associated with a permanent magnet and the strong magnetic field is associated with a magnetic resonance imaging device.

20. The active implantable medical device of claim 17, wherein the electronic circuit is configured to:

produce stimulation pulses at a first frequency when only the weak magnetic field is detected, wherein the first frequency is based on a measured variable and

produce stimulation pulses at a second frequency when both the weak magnetic field and the strong magnetic field are detected, wherein the second frequency is not based on a measured variable.