SYSTEM AND METHOD FOR DETECTING PULMONARY EDEMA BASED ON IMPEDANCE MEASURED USING AN IMPLANTABLE MEDICAL DEVICE DURING A LEAD MATURATION INTERVAL

• US 20100305641A1
• Filed: 05/28/2009
• Published: 12/02/2010
• Est. Priority Date: 05/28/2009
• Status: Active Grant

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Inventors: Xi, Cecilia Qin, Pillai, Ajit
• Granted Patent: US 8,473,054 B2
• Time in Patent Office: Days
• US Class Current: 607/17
• CPC Class Codes: A61B 5/0538 invasively, e.g. using a catheter
• CPC Class Codes: A61N 1/3627 for treating a mechanical deficiency of the heart, e.g. congestive heart failure or cardiomyopathy
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: A61N 1/3702 Physiological parameters A61N1/365 takes precedence; evoked response A61N1/371

Abstract

Techniques are provided for use by implantable medical devices such as cardiac resynchronization therapy (CRT) devices for detecting pulmonary edema based on transthoracic impedance sensed using cardiac pacing/sensing leads, wherein detection can be performed while lead maturation occurs. Briefly, the implantable device determines whether the leads are within an initial post-implant interval following implant during which lead maturation generally occurs. The device then detects pulmonary edema or related medical conditions within the patient based on transthoracic impedance using a set of detection parameters adjusted for use during the post-implant interval. Thus, rather than “blanking” impedance data during lead maturation, the device instead detects and processes impedance during this period to identify possible episodes of pulmonary edema so that appropriate measures can be undertaken, such as delivery of warnings or titration of appropriate medications.

Claims

1. A method for use with an implantable medical device for implant within a patient along with at least one lead, the method comprising:

determining whether the lead is within an initial post-implant interval following lead implant during which lead maturation occurs;

detecting values representative of transthoracic impedance within the patient using the lead; and

detecting a medical condition within the patient during the initial post-implant interval based on transthoracic impedance using a set of detection parameters for use within the post-implant interval.

2. The method of claim 1 wherein determining whether the lead is within the post-implant interval includes:

determining the duration of the post-implant interval by adding a lead maturation period to a long-term average window duration; and

tracking an amount of time since lead implant to determine whether the lead is within the post-implant interval.

3. The method of claim 2 wherein the duration of the lead maturation period is about one month and the long-term average window duration is initially about two-weeks.

4. The method of claim 1 wherein detecting a medical condition is performed to detect pulmonary edema (PE).

5. The method of claim 1 wherein detecting a medical condition within the patient during the post-implant interval includes:

retrieving a set of detection parameters for use following the post-implant interval;

adjusting the parameters for use during the post-implant interval; and

detecting an episode of the medical condition by applying the adjusted detection parameters to values representative of transthoracic impedance detected during the post-implant interval.

6. The method of claim 5 further including detecting an episode of the medical condition within the patient following the post-implant interval by applying the non-adjusted detection parameters to values representative of transthoracic impedance detected after the post-implant interval.

7. The method of claim 5 wherein the set of detection parameters include a long-term average window duration, a short-term average window duration, and a detection threshold.

8. The method of claim 7 wherein adjusting the parameters for use during the post-implant interval is performed to adjust the duration of the long-term average window based on time since implant.

9. The method of claim 8 wherein the duration of the long-term average is adjusted during the post-implant interval to increase linearly relative to its retrieved value.

10. The method of claim 8 wherein the duration of the long-term average is adjusted during the post-implant interval to increase nonlinearly relative to its retrieved value.

11. The method of claim 8 wherein the duration of the long-term average is adjusted during the post-implant interval to increase stepwise relative to its retrieved value by fractional steps.

12. The method of claim 7 wherein adjusting the parameters for use during the post-implant interval is performed to adjust the detection threshold based on time since implant.

13. The method of claim 12 wherein the value of the detection threshold is adjusted during the post-implant interval to increase linearly relative to its retrieved value.

14. The method of claim 12 wherein the value of the detection threshold is adjusted during the post-implant interval to increase nonlinearly relative to its retrieved value.

15. The method of claim 12 wherein the value of the detection threshold is adjusted during the post-implant interval to increase stepwise relative to its retrieved value by fractional steps.

16. The method of claim 7 wherein detecting an episode of the medical condition includes:

determining both a long-term average and a short-term average of transthoracic impedance during the post-implant interval based on adjusted values of the window duration parameters;

accumulating a detection index based on a comparison of the short-term average to the long-term average, wherein the index is increased if the short-term average is below the long-term average; and

detecting the episode of the medical condition by determining whether the index exceeds the detection threshold.

17. A system for use with an implantable medical device for implant within a patient along with at least one lead, the system comprising:

a post-implant interval tracking unit operative to determine whether the lead is within an initial post-implant lead maturation-based interval following lead implant;

a transthoracic impedance detector operative to detect values representative of transthoracic impedance; and

an impedance-based medical condition detector operative to detect a medical condition within the patient during the initial post-implant interval based on transthoracic impedance using a set of detection parameters for use within the post-implant interval.

18. The system of claim 17 wherein the detection unit is further operative to detect a medical condition within the patient following the post-implant interval based on transthoracic impedance using a set of detection parameters that differ from those used during the post-implant interval.

19. The system of claim 17 wherein the implantable medical device is equipped to deliver cardiac resynchronization therapy (CRT).

20. The system for use with an implantable medical device for implant within a patient along with at least one lead, the system comprising:

means for determining whether the lead is within an initial post-implant lead maturation-based interval following lead implant;

means for detecting values representative of transthoracic impedance within the patient;

means for detecting a medical condition within the patient during the initial post-implant interval based on transthoracic impedance using a set of detection parameters for use within the post-implant interval; and

means for detecting a medical condition within the patient following the initial post-implant interval based on transthoracic impedance using a set of detection parameters that differ from those used during the post-implant interval.