Cardiac Sensing by Implantable Medical Devices During Magnetic Resonance Imaging

• US 20080228092A1
• Filed: 03/14/2007
• Published: 09/18/2008
• Est. Priority Date: 03/14/2007
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Wedan, Steven R.
• Granted Patent: US 7,853,318 B2
• Time in Patent Office: Days
• US Class Current: 600/509
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: A61B 5/076 Permanent implantations telemetry using implanted circuitry A61B5/0031; implanted stimulators for therapy A61N1/3605, A61N1/362, A61N1/372
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: A61N 1/37 Monitoring; Protecting
• CPC Class Codes: A61N 1/3718 Monitoring of or protection against external electromagnetic fields or currents

Abstract

Embodiments of the invention can include a method for reducing MRI interference from a physiological electrical signal received in an implantable medical device. The method can include the steps of amplifying the physiological electrical signal with a high bandwidth amplifier and sampling the amplified physiological electrical signal at a sampling frequency of at least 8 kHz to obtain a first high-frequency sequence of samples. The method can further includes the steps of processing the first high-frequency sequence of samples to identify a signal artifact that is characteristic of MRI interference and creating a second high-frequency sequence of samples by reducing the signal artifact characteristic of MRI interference from the first sequence of samples. Embodiments can also include a method of determining a heart rate from a physiological electrical signal received in an implantable medical device. Embodiments can also includes an implantable medical device that receives and processes a physiological electrical signal. Other embodiments are also described herein.

Claims

1. A method of determining a heart rate from a physiological electrical signal received in an implantable medical device, the method comprising:

(i) receiving an input associated with the presence of an environment that tends to cause corruption of a physiological electrical signal; and

(ii) initiating a mode of operation for reducing corruption of the physiological electrical signal, the mode of operation comprising

(a) amplifying the physiological electrical signal with an amplifier of an implantable medical device having a bandwidth of at least 4 kHz;

(b) sampling the amplified physiological electrical signal at a sampling frequency of at least 8 kHz to obtain a first sequence of samples;

(c) processing the first sequence of samples to identify a superposed signal artifact characteristic of MRI interference;

(d) reducing the superposed signal artifact from the first sequence of samples to form a second sequence of samples; and

(e) processing the second sequence of samples to identify the timing of heart contractions.

2. The method of claim 1, where the environment that tends to cause corruption of a physiological electrical signal comprises magnetic resonance imaging.

3. The method of claim 1, where the input comprises receiving a signal by telemetry.

4. The method of claim 3, where the telemetric signal is initiated by a person who is aware of the presence of an environment that tends to cause corruption of an electrical signal.

5. The method of claim 1, where the input comprises receiving a signal from a magnetic field sensor.

6. The method of claim 1, where the input comprises receiving a signal from a sensor configured to measure induced currents within a conductive loop.

7. A method for reducing MRI interference from a physiological electrical signal received in an implantable medical device, the method comprising:

amplifying the physiological electrical signal with an amplifier of an implantable medical device having a bandwidth of at least 4 kHz;

sampling the amplified physiological electrical signal at a sampling frequency of at least 8 kHz to obtain a first sequence of samples;

processing the first sequence of samples to identify a signal artifact characteristic of MRI interference; and

creating a second sequence of samples by reducing the signal artifact characteristic of MRI interference from the first sequence of samples, the second sequence continuous in time.

8. The method of claim 7, where the step of sampling the physiological electrical signal comprises sampling the signal at a frequency between about 8 kHz and 100 kHz.

9. The method of claim 7, where the step of processing the first sequence of samples comprises using digital signal processing techniques.

10. The method of claim 9, where the digital signal processing technique comprises linear filtering.

11. The method of claim 9, where the digital signal processing technique comprises non-linear filtering.

12. The method of claim 9, where the digital signal processing technique comprises a heuristic technique.

13. The method of claim 7, further comprising the step of determining cardiac activity from the second sequence of samples.

14. The method of claim 7, where the step of sampling the amplified physiological electrical further comprises converting the amplified signal from analog to digital.

15. A method of calculating a heart rate from a physiological electrical signal received in an implantable medical device, the method comprising:

amplifying the physiological electrical signal with an amplifier of an implantable medical device having a bandwidth of at least 4 kHz;

sampling the amplified physiological electrical signal at a sampling frequency of at least 8 kHz to obtain a first sequence of samples;

processing the first sequence of samples to identify a superposed signal artifact characteristic of MRI interference;

reducing the superposed signal artifact from the first sequence of samples to form a second sequence of samples; and

processing the second sequence of samples to identify the timing of heart contractions.

16. The method of claim 15, where the step of sampling the physiological electrical signal comprises sampling the signal at a frequency between about 8 kHz and 100 kHz.

17. The method of claim 15, where the step of processing the first sequence of samples comprises using digital signal processing techniques.

18. The method of claim 17, where the digital signal processing technique comprises linear filtering.

19. The method of claim 17, where the digital signal processing technique comprises non-linear filtering.

20. The method of claim 17, where the digital signal processing technique comprises a heuristic technique.

21. The method of claim 15, where the step of sampling the amplified physiological electrical signal further comprises converting the amplified signal from an analog signal to a digital signal.

22. An implantable medical device that receives and processes a physiological electrical signal, the implantable medical device comprising:

(i) a conductor for transmitting the physiological electrical signal from body tissue to the implantable medical device; and

(ii) physiological signal processing circuitry for identifying heart contractions from the physiological electrical signal, the signal processing circuitry including;

(a) a first amplifier for amplifying the physiological electrical signal received from the conductor having a bandwidth of at least 4 kHz;

(b) a first analog to digital converter for sampling the amplified physiological electrical signal at a sampling frequency of at least 8 kHz to obtain a first sequence of samples;

(c) a digital signal processor configured to process the first sequence of samples to identify a superposed signal artifact characteristic of MRI interference and further configured to reduce the superposed signal artifact from the first sequence of samples to form a second sequence of samples; and

(d) cardiac activity detection circuitry configured to process the second sequence of samples to identify heart contractions.

23. The implantable medical device of claim 22, further comprising:

(i) a sensor configured to detect the presence of an environment that tends to cause corruption of a physiological electrical signal;

(ii) a second amplifier for amplifying the physiological electrical signal received from the conductor;

(iii) a second analog to digital converter for sampling the amplified physiological electrical signal from the second amplifier at a sampling frequency less than about 1 kHz; and

(iv) a switch to selectively couple either the first analog to digital converter or the second analog to digital converter to the digital signal processor, where the switch is configured to couple the first analog to digital converter to the digital signal processor in response to the detection of the presence of an environment that tends to cause corruption of a physiological electrical signal.