System and method for predicting a heart condition based on impedance values using an implantable medical device

• US 20050216067A1
• Filed: 12/15/2004
• Published: 09/29/2005
• Est. Priority Date: 03/26/2004
• Status: Active Grant

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Inventors: Min, Xiaoyi, Bornzin, Gene A., Park, Euljoon
• Granted Patent: US 7,272,443 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 1/371 Capture, i.e. successful stimulation

Abstract

Techniques are provided for predicting the onset of a heart condition within a patient based on impedance measurements. Briefly, overloads in fluid levels in the thorax and in ventricular myocardial mass within the patient are detected based on impedance signals sensed using implanted electrodes. The onset of certain heart conditions is then predicted based on the overloads. For example, pulmonary edema arising due to diastolic heart failure is predicted based on the detection of on-going overloads in both fluid levels and ventricular mass. Ventricular hypertrophy is detected based on an on-going ventricular mass overload without a sustained fluid overload. Various other heart conditions may also be predicted based on specific combinations of recent or on-going overloads. Evoked response is exploited to corroborate the predictions. Appropriate warning signals are generated and preemptive therapy is initiated.

Claims

1. A method for predicting the onset of a heart condition within a patient having an implantable medical device, the method comprising the steps of:

detecting impedance values representative of thoracic fluid levels within the patient;

detecting impedance values representative of ventricular mass within the patient; and

predicting the onset of the medical condition within the patient based on the values representative of thoracic fluid levels in combination with the values representative of ventricular mass.

2. The method of claim 1 wherein the step of detecting values representative of thoracic fluid levels is performed to detect a fluid overload and wherein the step of detecting values representative of ventricular mass is performed to detect mass overload.

3. The method of claim 2 wherein the implantable medical device includes a device can and is coupled to a cardiac electrode implanted in the heart and wherein the step of detecting fluid overload is performed by detecting a sustained decrease in cardiac electrode-can impedance over a predetermined period of time.

4. The method of claim 3 wherein the cardiac electrode is selected from a group including right ventricular (RV) tip, RV ring, RV coil, left ventricular (LV) tip, LV ring, LV coil, and supraventricular (SVC) coil electrodes.

5. The method of claim 3 wherein the predetermined period of time is at least three days.

6. The method of claim 3 wherein the decrease is at least ten percent of a previous cardiac electrode-can impedance value.

7. The method of claim 2 wherein the implantable medical device is coupled to a right ventricular (RV) electrode and a left ventricular (LV) electrode and wherein the step of detecting a mass overload is performed by detecting an increase in RV-LV impedance over a first mass overload threshold amount.

8. The method of claim 7 wherein the RV electrode is a tip, ring or coil electrode and wherein the LV electrode is a tip, ring or coil electrode.

9. The method of claim 7 wherein the first threshold amount is set to at least ten percent greater than that of a previous RV-LV impedance value.

10. The method of claim 7 further including the step of detecting a recent drop in ventricular mass by detecting a decrease in RV-LV impedance below a second mass overload threshold following an increase above the first threshold.

11. The method of claim 2 wherein the step of predicting the onset of a heart condition is performed based on the values representative of sustained fluid overloads in combination with the values representative of on-going ventricular mass overloads and recent decreases in ventricular mass overloads.

12. The method of claim 11 wherein the step of detecting ventricular evoked response and where the step of predicting the onset of a heart condition additionally exploits changes, if any, in ventricular evoked response.

13. The method of claim 12 the step of predicting the onset of a heart condition includes the step of identifying the combination of a sustained fluid overload without an on-going ventricular mass overload and without a recent decrease in ventricular mass overload and with either a constant of decreased evoked response as being indicative of an increased likelihood of the onset of pulmonary edema due to systolic heart failure (SHF) within the patient.

14. The method of claim 12 the step of predicting the onset of heart condition includes the step of identifying the combination of a sustained fluid overload along with an on-going ventricular mass overload and an increased evoked response as being indicative of an increased likelihood of onset of pulmonary edema due to diastolic heart failure (DHF) within the patient.

15. The method of claim 12 the step of predicting the onset of heart condition includes the step of identifying the combination of a sustained fluid overload without an on-going ventricular mass overload but with a decreased evoked response as being indicative of an increased likelihood in the onset of SHF within the patient.

16. The method of claim 12 the step of predicting the onset of heart condition includes the step of identifying the combination of a sustained fluid overload along with an on-going ventricular mass overload and either an increased evoked response or a lack of change in evoked response as being indicative of an increased likelihood of onset of DHF within the patient.

17. The method of claim 12 wherein the step of predicting the onset of heart condition includes the step of identifying the combination of a lack of sustained fluid overload along with an on-going ventricular mass overload and an increased evoked response as being indicative of an increased likelihood of onset of ventricular hypertrophy within the patient.

18. The method of claim 12 wherein the step of predicting the onset of heart condition includes the step of identifying the combination of a lack of sustained fluid overload along with an on-going ventricular mass overload and an increased evoked response as being indicative of an increased likelihood of onset of ventricular hypertrophy within the patient.

19. The method of claim 12 wherein the step of predicting the onset of heart condition includes the step of identifying the combination of a lack of sustained fluid overload and a lack of an on-going ventricular mass overload is along with a recent drop in ventricular mass and a decrease in evoked response from a previously elevated level as being indicative of an increased likelihood of progression of mixed heart failure within the patient.

20. The method of claim 12 wherein the step of predicting the onset of heart condition includes the step of identifying the combination of a decrease in evoked response without an on-going ventricular mass overload and without any recent drop in ventricular mass as being indicative of an increased likelihood of ventricular dilation within the patient.

21. The method of claim 1 further including the step of delivering warning signals in response to a prediction of the onset of a heart condition.

22. The method of claim 1 further including the step of storing diagnostic information indicative of a prediction of the onset of a heart condition.

23. The method of claim 1 further including the step of initiating preemptive pacing in response to the prediction of the onset of heart condition.

24. The method of claim 1 wherein all steps are performed by the implanted device.

25. The method of claim 1 wherein the step of predicting the onset of a heart condition is performed by an external programmer device based on signals received from the implanted device.

26. A system for predicting the onset of a heart condition within a patient using an implantable medical device, the system comprising:

a fluid overload detection unit operative to detect impedance values representative of changes in fluid levels within the thorax of the patient;

a ventricular mass overload detection unit operative to detect impedance values representative of changes in ventricular mass of the patient; and

an overload-based prediction unit operative to predict the onset of a heart condition within the patient based on the values representative of fluid overload in combination with the values representative of ventricular mass.

27. A system for predicting the onset of a heart condition within a patient using an implantable medical device, the system comprising:

means for detecting impedance values representative of fluid overloads within the thorax of the patient;

means for detecting impedance values representative of ventricular mass of the patient; and

means for predicting the onset of a heart condition within the patient based on the values representative of fluid overload in combination with the values representative of ventricular mass; and

means for generating warning signals based on a prediction of the onset of the heart condition.