Implantable cardiac stimulator with safe noise mode

• US 6,198,968 B1
• Filed: 06/15/1999
• Issued: 03/06/2001
• Est. Priority Date: 01/23/1998
• Status: Expired due to Term

• Current Assignee: Intermedics Incorporated
• Original Assignee: Intermedics Incorporated
• Inventors: Paul, Patrick J., Prutchi, David
• Primary Examiner(s): Schaetzle, Kennedy
• Application Number:
  US09/333,642
• Time in Patent Office: 630 Days
• Field of Search: 607/9, 607/17-24, 607/28, 607/6, 600/547, 128/901
• US Class Current: 607/9
• 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: Y10S 128/901 Suppression of noise in electric signal

Abstract

An implantable medical device for electrically stimulating the heart to beat generally includes a processor, a plurality of electrodes, a sense amplifier, a pulse generator, and a heart status monitor. The processor can determine when the patient has entered an environment of high electromagnetic interference. When this occurs, the processor forces the implantable device into a safe noise mode. While in the same noise mode (which preferably continues while the patient is experiencing the electromagnetic interference), the implantable device paces the heart on demand and inhibits pacing during the vulnerable period. The processor determines when the vulnerable period is occurring and when the heart needs to be paced by monitoring a status signal from the heart status monitor. The status signal generated by the heart status monitor preferably is not sensitive to the electromagnetic interference, and thus the processor can determine the bio-mechanical state of the heart during a cardiac cycle even in the face of high electromagnetic interference. The heart status monitor preferably includes an impedance measurement circuit, but may include any type of cardiac sensor that can generate a status signal from which the processor can determine the beginning and ending of the vulnerable period. Accordingly, even during a period of high electromagnetic interference, the implantable device can provide on demand pacing support to the patient.

Claims

1. A method for electrically stimulating a patient'"'"'s heart to beat, comprising:

pacing the heart in a first operational mode;

determining when the patient is in an environment characterized by high electromagnetic interference;

switching to a second operational mode when it is determined that the patient is in a high electromagnetic interference environment; and

pacing the heart in said second operational mode on demand.

2. The method of claim 1, wherein pacing the heart in said second operational mode includes determining the impedance of the heart.

3. The method of claim 2, wherein pacing the heart in said second operational mode further includes determining when the heart needs to be paced by monitoring the impedance of the heart.

4. The method of claim 3, wherein pacing the heart in said second operational mode further includes determining a vulnerable period for a cardiac cycle based on said impedance.

5. The method of claim 4, wherein pacing the heart in said second operational mode includes pacing the heart on demand, but not during said vulnerable period.

6. The method of claim 4, wherein pacing the heart in said second operational mode further includes determining when said heart needs to be paced by monitoring a heart status signal.

7. The method of claim 6, wherein pacing the heart in said second operational mode includes determining when said heart needs to be paced by monitoring a heart status signal provided by a cardiac sensor.

8. The method of claim 7, wherein pacing the heart in said second operational mode includes determining when said heart needs to be paced by monitoring a heart status signal provided by a pressure sensor.

9. The method of claim 7, wherein pacing the heart in said second operational mode includes determining when said heart needs to be paced by monitoring a heart status signal provided by a volume sensor.

10. The method of claim 7, wherein pacing the heart in said second operational mode includes determining when said heart needs to be paced by monitoring a heart status signal provided by a flow sensor.

11. The method of claim 6, further includes wirelessly transmitting the heart status signal to an external programmer.

12. The method of claim 1, wherein stimulating a patient'"'"'s heart to beat comprises stimulating an animal'"'"'s heart to beat.

13. A method of providing pacing for a heart, comprising:

pacing the heart in a first operational mode;

detecting the presence of noise;

pacing the heart on demand when the noise is detected, wherein pacing on demand includes;

discontinuing pacing the heart in the first operational mode;

pacing the heart based on signals received from the heart;

detecting a vulnerable period;

discontinuing pacing during the vulnerable period; and

resuming pacing on demand at the end of the vulnerable period; and

resuming pacing the heart in the first operational mode in the absence of noise.

14. The method of claim 13, wherein pacing on demand includes determining the impedance of the heart.

15. The method of claim 14, further includes determining when the heart needs to be paced by monitoring the impedance of the heart.

16. The method of claim 15, wherein determining when said heart needs to be paced includes determining when said heart needs to be paced by monitoring a heart status signal.

17. The method of claim 16, wherein determining when said heart needs to be paced includes determining when said heart needs to be paced by monitoring a heart status signal provided by a cardiac sensor.

18. The method of claim 16, wherein determining when said heart needs to be paced includes determining when said heart needs to be paced by monitoring a heart status signal provided by a pressure sensor.

19. The method of claim 16, wherein determining when said heart needs to be paced includes determining when said heart needs to be paced by monitoring a heart status signal provided by a volume sensor.

20. The method of claim 16, wherein determining when said heart needs to be paced includes determining when said heart needs to be paced by monitoring a heart status signal provided by a flow sensor.

21. The method of claim 13, further includes wirelessly transmitting the signals received from the heart to an external programmer.