System and method for estimating electrical conduction delays from immittance values measured using an implantable medical device

• US 8,208,999 B2
• Filed: 05/28/2008
• Issued: 06/26/2012
• Est. Priority Date: 04/04/2007
• Status: Expired due to Fees

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Inventors: Wenzel, Brian Jeffrey, Panescu, Dorin, Naware, Mihir, Siou, Jeffery
• Primary Examiner(s): Vivlemore, Tracy
• Application Number:
  US12/127,963
• Publication Number:
  US 20090299211A1
• Time in Patent Office: 1,490 Days
• Field of Search: None
• US Class Current: 600/509
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 5/0002 Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network A61B5/07 takes precedence; transmission systems for measured values G08C; transmission H04B; transmission of digital information H04L; wireless communication networks H04W
• CPC Class Codes: A61B 5/002 Monitoring the patient using a local or closed circuit, e.g. in a room or building A61B5/0017 takes precedence
• CPC Class Codes: A61B 5/0215 by means inserted into the body catheters A61M25/00
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61B 5/4839 combined with drug delivery
• CPC Class Codes: A61B 5/686 Permanently implanted devices, e.g. pacemakers, other stimulators, biochips A61B5/6861 takes precedence
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence
• CPC Class Codes: A61B 5/7282 Event detection, e.g. detecting unique waveforms indicative of a medical condition A61B5/4094, A61B5/4818, A61B5/349, A61B5/0823 take precedence
• CPC Class Codes: A61B 5/7405 using sound
• CPC Class Codes: A61B 5/742 using visual displays A61B5/339 takes precedence
• CPC Class Codes: A61B 5/746 Alarms related to a physiological condition, e.g. details of setting alarm thresholds or avoiding false alarms alarms per se G08B
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance

Abstract

Techniques are provided for estimating electrical conduction delays with the heart of a patient based on measured immittance values. In one example, impedance or admittance values are measured within the heart of a patient by a pacemaker or other implantable medical device, then used by the device to estimate cardiac electrical conduction delays. A first set of predetermined conversion factors may be used to convert the measured immittance values into conduction delay values. In some examples, the device then uses the estimated conduction delay values to estimate LAP or other cardiac pressure values. A second set of predetermined conversion factors may be used to convert the estimated conduction delays into pressure values. Techniques are also described for adaptively adjusting pacing parameters based on estimated LAP.

Claims

1. A method for estimating cardiac pressure within a patient using an implantable medical device, the method comprising:

detecting a value representative of electrical immittance within the heart of the patient; and

estimating an electrical conduction delay in the heart of the patient from the value representative of immittance.

2. The method of claim 1 wherein detecting a value representative of electrical immittance includes:

detecting a value representative of electrical admittance; and

converting the value representative of electrical admittance into a value representative of electrical impedance.

3. The method of claim 1 wherein detecting a value representative of electrical immittance includes:

detecting a value representative of electrical impedance; and

converting the value representative of electrical impedance into a value representative of electrical admittance.

4. The method of claim 1 wherein detecting a value representative of electrical immittance includes:

measuring a raw impedance signal (Z₀) along at least one sensing vector passing through the heart of a patient in which the device is implanted; and

determining an average impedance value (Z) from the raw impedance signal (Z₀).

5. The method of claim 4 wherein estimating the electrical conduction delay from the average impedance value (Z) includes:

determining conversion factors for converting average impedance values to delay values within the patient; and

applying the conversion values to the average impedance values to estimate the conduction delay.

6. The method of claim 5 wherein applying the conversion values to the average impedance to estimate the conduction delay includes calculating:

Delay=α

*Z²+β

*Z+δ

where α

, β and

δ

are the conversion factors and wherein Z represents average impedance along a given vector passing through the heart of the patient.

7. The method of claim 5 wherein applying the conversion values to the average impedance to estimate the conduction delay includes calculating:

Delay=α

₁*Z₁²+β

₁+Z₁+α

₂*Z₂²+β

₂*Z₂+δ

where α

₁, β

₁, α

₂, β

₂ and δ

are the conversion factors and wherein Z₁ represents average impedance along a first vector passing through the heart of the patient and Z₂ represents average impedance along a second, different vector passing through the heart of the patient.

8. The method of claim 5 further including an initial calibration step for determining the conversion factors for converting average impedance values to delay values for the particular patient.

9. The method of claim 3 wherein detecting a value representative of electrical admittance includes:

measuring a raw admittance signal (Y₀) along at least one sensing vector passing through the heart of a patient in which the device is implanted; and

determining the average admittance value (Y) from the raw admittance signal (Y₀).

10. The method of claim 9 wherein estimating the electrical conduction delay from the average admittance value includes:

determining conversion factors for converting average admittance values to delay values within the patient; and

applying the conversion values to the average admittance value to estimate the conduction delay.

11. The method of claim 10 wherein applying the conversion values to the average admittance value to estimate the conduction delay includes calculating:

Delay=α

*Y²+β

*Y+δ

where α

, β and

δ

are the conversion factors and wherein Y represents average admittance along a given vector passing through the heart of the patient.

12. The method of claim 10 wherein applying the conversion values to average admittance value to estimate the conduction delay includes calculating:

Delay=α

₁*Y₁²+β

₁+α

₂*Y₂²+β

₂*Y₂+δ

where α

₁, β

₁, α

₂, β

₂ and δ

are the conversion factors and wherein Y₁ represents average admittance along a first vector passing through the heart of the patient and Y₂ represents average admittance along a second, different vector passing through the heart of the patient.

13. The method of claim 10 further including an initial calibration step for determining the conversion factors for converting average admittance values to delay values for the particular patient.

14. The method of claim 1 further including estimating cardiac pressure within the patient from the estimated electrical conduction delay.

15. The method of claim 14 wherein estimating cardiac pressure within the patient includes estimating left atrial pressure (LAP).

16. The method of claim 1 wherein estimating cardiac pressure within the patient from the estimated electrical conduction delay includes:

retrieving predetermined conversion factors from a memory of said implantable medical device for converting the conduction delay to cardiac pressure; and

estimating cardiac pressure within the patient from the electrical conduction delay by applying the conversion factors to the conduction delay.

17. The method of claim 16 wherein retrieving predetermined conversion factors includes retrieving slope and baseline values representative of a linear relationship between cardiac pressure and the conduction delays.

18. The method of claim 16 wherein estimating cardiac pressure includes calculating:

Cardiac Pressure=Delay*Slope+Baseline.

19. The method of claim 17 further including an initial calibration step for determining the slope and baseline values that are representative of the linear relationship between the conduction delay and cardiac pressure for the particular patient.

20. The method of claim 1 further including controlling therapy based on the estimated cardiac pressure.

21. The method of claim 1 further including determining a measure of cardiac function based on the estimated cardiac pressure.

22. The method of claim 1 further including tracking heart failure based on the estimated cardiac pressure.