IMPLANTABLE MEDICAL DEVICE RESPONSIVE TO MRI INDUCED CAPTURE THRESHOLD CHANGES

• US 20100087892A1
• Filed: 09/28/2009
• Published: 04/08/2010
• Est. Priority Date: 10/02/2008
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Wika, Kevin G., Stubbs, Scott R.
• Granted Patent: US 8,571,661 B2
• Time in Patent Office: Days
• US Class Current: 607/28
• CPC Class Codes: A61N 1/371 Capture, i.e. successful stimulation
• CPC Class Codes: A61N 1/3712 Auto-capture, i.e. automatic adjustment of the stimulation threshold
• CPC Class Codes: A61N 1/3718 Monitoring of or protection against external electromagnetic fields or currents
• CPC Class Codes: A61N 1/3943 for threshold determination

Abstract

Energy delivered from an implantable medical device to stimulate tissue within a patient'"'"'s body is controlled. An electrical signal used to stimulate the tissue is changed from a first energy state to a second energy state during a magnetic resonance imaging (MRI) scan. The energy delivered is maintained at the second energy state after the MRI scan. A capture threshold of the tissue is then measured, and the energy delivered to the tissue is adjusted based on the measured capture threshold of the tissue.

Claims

1. A method for controlling energy delivered from an implantable medical device to stimulate body tissue within a patient, the method comprising:

changing energy delivered to stimulate the tissue from a first energy state to a second energy state during a magnetic resonance imaging (MRI) scan;

maintaining the energy delivered at the second energy state after the MRI scan;

measuring a capture threshold of the tissue; and

adjusting the energy delivered based on the measured capture threshold of the tissue.

2. The method of claim 1, wherein the measuring and adjusting steps are repeated until the energy delivered returns to the first energy state.

3. The method of claim 1, wherein the measuring and adjusting steps are repeated until the measured capture threshold remains substantially unchanged for a programmed number of capture threshold measurements.

4. The method of claim 1, wherein measuring the capture threshold of the tissue comprises:

delivering a sequence of pacing pulses of varying magnitude to the tissue; and

sensing a response of the tissue to the pacing pulses.

5. The method of claim 1, wherein measuring the capture threshold of the tissue comprises:

delivering a sequence of pacing pulses of varying duration to the tissue; and

sensing a response of the tissue to the pacing pulses.

6. The method of claim 1, wherein the measuring and adjusting steps are performed by the implantable medical device.

7. The method of claim 1, wherein the measuring and adjusting steps are controlled by an external device in communication with the implantable medical device.

8. The method of claim 1, wherein the second energy state has a signal magnitude and/or duration greater than the first energy state.

9. A method for controlling energy delivered from an implantable medical device to stimulate body tissue within a patient, the method comprising:

delivering energy having a first energy level to stimulate the tissue;

detecting magnetic resonance imaging (MRI) scan fields;

increasing the energy delivered from the first energy level to a second energy level;

maintaining the energy delivered at the second energy level after the MRI scan fields are no longer detected;

measuring a capture threshold of the tissue; and

adjusting the energy delivered by the implantable medical device based on the measured capture threshold of the tissue.

10. The method of claim 9, wherein the measuring and adjusting steps are repeated until the level of energy delivered by the implantable medical device is returned to the first energy level.

11. The method of claim 9, wherein measuring the capture threshold of the tissue comprises:

delivering a sequence of pacing pulses of varying magnitude to the tissue; and

sensing a response of the tissue to the pacing pulses.

12. The method of claim 9, wherein the measuring and adjusting steps are performed by the implantable medical device.

13. The method of claim 9, wherein the measuring and adjusting steps are controlled by an external device in communication with the implantable medical device.

14. An implantable medical device comprising:

a lead including an electrode adapted to electrically stimulate body tissue;

sensing circuitry operable to receive signals through the lead based on electrical activity of the tissue;

therapy circuitry operable to deliver electrical stimulation to the tissue through the lead, wherein the sensing and therapy circuitry is further operable to measure a capture threshold of the tissue;

magnetic field detection circuitry operable to detect magnetic resonance imaging (MRI) scan fields; and

control circuitry operable to set energy delivered by the therapy circuitry to stimulate the tissue from a normal energy state to an MRI mode energy state when the magnetic detection circuitry detects the MRI scan fields, and, after the magnetic field detection circuitry no longer detects the MRI scan fields, to adjust the energy delivered based on the measured capture threshold of the tissue.

15. The implantable medical device of claim 14, wherein the control circuitry maintains the energy delivered by the therapy circuitry at the MRI mode energy level for a period of time after the magnetic field detection circuitry no longer detects the MRI scan fields.

16. The implantable medical device of claim 14, wherein the control circuitry repeatedly adjusts the energy delivered based on the measured capture threshold until the energy delivered returns to the normal energy state.

17. The implantable medical device of claim 14, wherein, to measure the capture threshold, the therapy circuitry delivers a sequence of pacing pulses of varying magnitude and/or duration to the tissue, and the sensing circuitry senses a response of the tissue to the pacing pulses.

18. The implantable medical device of claim 14, wherein the sensing circuitry measures the capture threshold of the tissue and the control circuitry adjusts the energy delivered in response to a control signal from an external device.

19. The implantable medical device of claim 14, wherein the sensing circuitry, therapy circuitry, magnetic field detection circuitry, and control circuitry are included in a pulse generator.

20. The implantable medical device of claim 14, and further comprising:

communication circuitry operable to communicate information about the measured capture threshold.