Implantable medical device with real time T-wave oversensing detection

• US 20060224075A1
• Filed: 03/31/2005
• Published: 10/05/2006
• Est. Priority Date: 03/31/2005
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Gunderson, Bruce D., Patel, Amisha S., Bounds, Chad A.
• Granted Patent: US 8,942,795 B2
• Time in Patent Office: Days
• US Class Current: 600/518
• CPC Class Codes: A61B 5/35 by template matching
• CPC Class Codes: A61B 5/363 Detecting tachycardia or bradycardia
• CPC Class Codes: A61N 1/3621 for treating or preventing abnormally high heart rate
• CPC Class Codes: A61N 1/3702 Physiological parameters A61N1/365 takes precedence; evoked response A61N1/371
• CPC Class Codes: A61N 1/3925 Monitoring; Protecting

Abstract

An implantable cardioverter defibrillator (ICD) senses ventricular depolarizations (R-waves) in an electrogram signal to detect a ventricular tachycardia or fibrillation episodes. The EGM signal is also monitored in real time for characteristics that uniquely identify instances of T-wave oversensing. The ICD determines whether detection of a tachycardia or fibrillation episode is appropriate based upon counts of each of the unique characteristics evidencing T-wave oversensing.

Claims

1. A method of controlling VT and VF detection in an implantable medical device, the method comprising:

sensing R-waves in a ventricular EGM signal;

monitoring in real time on an event-by-event basis a plurality of characteristics that indicate T-wave oversensing; and

withholding detection of a VT or VF in response to the characteristics indicating presence of oversensed T-waves among the sensed R-waves.

2. The method of claim 1 wherein at least one of the characteristics is derived from a current interval and preceding intervals.

3. The method of claim 2 wherein the characteristics include a large successive difference between the current interval and an immediately preceding interval.

4. The method of claim 2 wherein the characteristics include a current interval that is approximately equal to a sum of two preceding intervals.

5. The method of claim 1 wherein the characteristics include an alternating waveform morphology.

6. The method of claim 1 wherein detection is withheld if more than one count of characteristics indicates T-wave oversensing.

7. The method of claim 1 wherein detection is withheld in response to a count of one of the characteristics reaching a value reliably indicating T-wave oversensing.

8. The method of claim 1, further comprising:

sensing ventricular events based upon the ventricular EGM signal;

measuring intervals between successive sensed events;

counting characteristics of T-wave oversensing derived with each sensed event;

determining presence of an episode requiring therapy based on the intervals; and

withholding detection of the episode if characteristic counts indicate presence of oversensed T-waves among the sensed events.

9. The method of claim 8 wherein at least one of the characteristics is derived from a current interval and preceding intervals.

10. The method of claim 9 wherein the characteristics include a large successive difference between the current interval and an immediately preceding interval.

11. The method of claim 9 wherein the characteristics include a current interval that is approximately equal to a sum of two preceding intervals.

12. The method of claim 8 wherein the characteristics include an alternating waveform morphology.

13. The method of claim 8 wherein detection is withheld if more than one characteristic count indicates T-wave oversensing.

14. The method of claim 8 wherein detection is withheld if one characteristic count has reached a value strongly indicating T-wave oversensing.

15. The method of claim 1 wherein sensing R-waves includes:

detecting R-waves from an EGM signal;

measuring each RR interval;

comparing a current RR interval to preceding RR intervals;

counting instances of large successive RR interval differences;

counting instances of a current RR interval being approximately equal to a sum of two previous RR intervals;

analyzing morphology of each R-wave detected;

counting instances of alternating morphologies;

identifying a potential ventricular tachycardia (VT) or ventricular fibrillation (VF) based on measured RR intervals; and

withholding detection of the VT or VF if the counts indicate a likelihood of T-wave oversensing.

16. The method of claim 1 wherein withholding detection of VT or VF includes:

sensing ventricular events from an EGM signal;

determining presence of an episode requiring therapy based on sensed events;

deriving, from the EGM signal, indicators of T-wave oversensing;

updating counts of the indicators with each sensed event; and

determining whether to withhold detection of the episode based on the counts.

17. An implantable medical device comprising:

at least one sensing electrode to sense an EGM signal from a heart of a patient;

a sense circuit for sensing events representing R-waves in the EGM signal; and

a processor to identify T-wave oversensing by the implantable medical device based on counts of T-wave oversensing characteristics that are updated with each sensed event.

18. The implantable medical device of claim 17 wherein the characteristics counted by the processor include a large successive difference between the current interval and an immediately preceding interval, a current interval that is approximately equal to a sum of two preceding intervals, and an alternating waveform morphology.

19. The implantable medical device of claim 17 wherein the processor withholds detection if more than one characteristic count indicates T-wave oversensing.

20. The implantable medical device of claim 17 wherein the processor withholds detection if one characteristic count has reached a value reliably indicating T-wave oversensing.

21. A computer-implemented system for detecting ventricular tachycardia and ventricular fibrillation, the system comprising:

means for operating an implantable medical device in accordance with sensed ventricular events for a plurality of cardiac cycles;

means for identifying a plurality of characteristics of T-waves oversensing by the implantable medical device;

means for updating counts of the characteristics with each sensed event; and

means for automatically withholding detection of a ventricular tachycardia or ventricular fibrillation if the counts indicate T-wave oversensing.