Implantable defibrillator systems and methods with mitigations for saturation avoidance and accommodation

• US 8,712,523 B2
• Filed: 12/11/2009
• Issued: 04/29/2014
• Est. Priority Date: 12/12/2008
• Status: Active Grant

• Current Assignee: Cameron Incorporated (Schlumberger NV)
• Original Assignee: Cameron Incorporated (Schlumberger NV)
• Inventors: Sanghera, Rick, Allavatam, Venugopal, Palreddy, Surekha, Warren, Jay A.
• Primary Examiner(s): Layno, Carl H
• Assistant Examiner(s): ANTHONY, JESSICA LYNN
• Application Number:
  US12/636,575
• Publication Number:
  US 20100152799A1
• Time in Patent Office: 1,600 Days
• Field of Search: 607 27- 28, 607 4- 5, 607/9
• US Class Current: 607/27
• CPC Class Codes: A61N 1/048 Electrodes characterised by a specific connection between lead and electrode
• CPC Class Codes: A61N 1/0504 Subcutaneous electrodes
• CPC Class Codes: A61N 1/0563 specially adapted for defibrillation or cardioversion
• CPC Class Codes: A61N 1/3702 Physiological parameters A61N1/365 takes precedence; evoked response A61N1/371
• CPC Class Codes: A61N 1/3704 Circuits specially adapted therefor, e.g. for sensitivity control
• CPC Class Codes: A61N 1/3968 Constructional arrangements, e.g. casings A61N1/375 takes precedence
• CPC Class Codes: A61N 1/3987 characterised by the timing or triggering of the shock

Abstract

Methods and implantable devices that address response to, or avoidance of, likely non-cardiac voltages including after potentials from external or internal stimulus. Also, methods of operation in implantable medical devices, the methods configured for identifying saturation of input circuitry and mitigating the effects of such saturation. Also, implantable cardiac stimulus or monitoring devices that include methods for identifying saturated conditions and mitigating the effects of such saturation.

Claims

1. An implantable cardiac stimulus device (ICSD) comprising electrodes for capturing signals and operational circuitry configured for analyzing captured signals, wherein the operational circuitry is configured to identify saturation of input signals by the following method:

detecting an event in a captured signal, wherein the event is detected if captured signal amplitude exceeds a detection threshold;

analyzing the detected event for characteristics indicating saturation; and

if the detected event has characteristics indicating saturation, identifying the detected event as saturated and engaging a mitigation in response to the saturation;

wherein the operational circuitry is configured such that, in the step of analyzing the detected event for characteristics indicating saturation, the following steps are performed;

across a defined period of time, signal samples are analyzed to identify a largest signal sample during the defined period of time and to determine whether;

i) the signal samples are all of a single polarity;

ii) the largest signal sample exceeds a saturation amplitude threshold; and

iii) the largest signal sample occurs within a predetermined number of samples of the start of the defined period of time;

and if each of i), ii) and iii) is true, the operational circuitry determines that the detected event has characteristics indicating saturation.

2. The ICSD of claim 1 wherein the operational circuitry is configured such that the mitigation comprises activation and operation of a dynamic Heuristic filter (DHF) operated by the operational circuitry as follows:

on activation, the DHF is initialized with an initial period of operation that defines how often a Heuristic filter is called;

when the Heuristic filter is called, a feature of analog-to-digital conversion (ADC) is adjusted to move an average ADC output toward a quiescent point;

at a defined DHF call interval, the DHF period of operation is recalculated by analyzing the distance of a typical ADC output from the quiescent point;

wherein the average ADC output is calculated using an average of a selected number, N, of ADC outputs, and the typical ADC output is calculated using an average of a selected number, M, of ADC outputs.

3. The ICSD of claim 2 wherein the operational circuitry is configured such that the step of periodically recalculating the DHF period of operation either:

decreases the DHF period of operation when the typical ADC output is relatively farther from the quiescent point;

or

increases the DHF period of operation when the typical ADC output is relatively closer to the quiescent point.

4. The ICSD of claim 1 wherein the operational circuitry is configured such that the mitigation response comprises excluding a detected event that has characteristics indicating saturation from further analysis, including rate calculation and rhythm analysis.

5. An implantable cardiac stimulus device (ICSD) comprising electrodes for capturing signals and operational circuitry configured for analyzing captured signals, wherein the operational circuitry is configured to identify saturation of input signals by the following method:

detecting an event in a captured signal, wherein the event is detected if captured signal amplitude exceeds a detection threshold;

analyzing the detected event for characteristics indicating saturation; and

if the detected event has characteristics indicating saturation, identifying the detected event as saturated and engaging a mitigation in response to the saturation;

wherein the operational circuitry is configured such that, in the step of analyzing the detected event for characteristics indicating saturation, the following characteristics are analyzed;

whether the detected event is associated with a signal amplitude that crosses a saturation amplitude threshold; and

if so, whether less than a saturation threshold number of signal turning points occur during a predetermined period of time associated with the detected event.

6. An implantable cardiac stimulus device (ICSD) comprising electrodes for capturing signals and operational circuitry configured for analyzing captured signals, wherein the operational circuitry is configured to identify saturation of input signals by the following method:

detecting an event in a captured signal, wherein the event is detected if captured signal amplitude exceeds a detection threshold;

analyzing the detected event for characteristics indicating saturation; and

if the detected event has characteristics indicating saturation, identifying the detected event as saturated and engaging a mitigation in response to the saturation;

wherein the operational circuitry is configured such that, in the step of analyzing the detected event for characteristics indicating saturation, the following characteristics are analyzed;

whether the detected event is associated with a signal amplitude that crosses a saturation amplitude threshold; and

if so, whether less than a saturation threshold number of signal inflection points occur during a predetermined period of time associated with the detected event.

7. An implantable cardiac stimulus device (ICSD) comprising electrodes for capturing signals and operational circuitry configured for analyzing captured signals, wherein the operational circuitry is configured to identify saturation of input signals by the following method:

detecting an event in a captured signal, wherein the event is detected if captured signal amplitude exceeds a detection threshold;

analyzing the detected event for characteristics indicating saturation; and

if the detected event has characteristics indicating saturation, identifying the detected event as saturated and engaging a mitigation in response to the saturation;

wherein the operational circuitry is configured such that the mitigation response comprises applying a signal to the inputs to the system to reduce saturation energy at the inputs.

8. An implantable cardiac stimulus device (ICSD) comprising electrodes for capturing signals and operational circuitry configured for analyzing captured signals, wherein the operational circuitry is configured to identify saturation of input signals by the following method:

detecting an event in a captured signal, wherein the event is detected if captured signal amplitude exceeds a threshold;

analyzing the detected event for characteristics indicating saturation; and

if the detected event has characteristics indicating saturation, identifying the detected event as saturated and engaging a mitigation in response to the saturation;

wherein the mitigation comprises activation and operation of a dynamic Heuristic filter (DHF) operated by the operational circuitry as follows;

on activation, the DHF is initialized with an initial period of operation that defines how often a Heuristic filter is called;

when the Heuristic filter is called, a feature of analog-to-digital conversion (ADC) is adjusted to move an average ADC output toward a quiescent point;

the DHF period of operation is periodically recalculated in view of the distance of a typical ADC output from the quiescent point;

the average ADC output is calculated using an average of a selected number, N, of ADC outputs, and the typical ADC output is calculated using an average of a selected number, M, of ADC outputs; and

the step of periodically recalculating the DHF period of operation either;

decreases the DHF period of operation when the typical ADC output is relatively farther from the quiescent point;

or increases the DHF period of operation when the typical ADC output is relatively closer to the quiescent point; and

wherein in the step of analyzing the detected event for characteristics indicating saturation, signal samples within a predetermined time interval are analyzed to identify a largest signal sample and to determine whether;

i) the signal samples are all of a single polarity;

ii) the largest signal sample exceeds a saturation amplitude threshold; and

iii) the largest signal sample occurs within a predetermined number of samples of the start of the defined period of time;

and if each of i), ii) and iii) is true, the operational circuitry determines that the detected event has characteristics indicating saturation.

9. A method of operation in an implantable cardiac stimulus device (ICSD) comprising electrodes for capturing signals and operational circuitry configured for analyzing captured signals, the method comprising:

detecting an event in a signal captured using the electrodes, wherein the event is detected if captured signal amplitude exceeds a threshold;

analyzing the detected event for characteristics indicating saturation; and

if the detected event has characteristics indicating saturation, identifying the detected event as saturated and engaging a mitigation in response to the saturation;

wherein, in the step of analyzing the detected event for characteristics indicating saturation, it is determined whether, across a defined period of time, rectified signal samples all have amplitudes that are in excess of a saturation threshold and, if so, the operational circuitry determines that the detected event has characteristics indicating saturation; and

wherein the mitigation comprises activation and operation of a dynamic Heuristic filter (DHF) operated by the operational circuitry as follows;

on activation, the DHF is initialized with an initial period of operation that defines how often a Heuristic filter is called;

when the Heuristic filter is called, a feature of analog-to-digital conversion (ADC) is adjusted to move an average ADC output toward a quiescent point; and

periodically recalculating the DHF period of operation in view of the distance of a typical ADC output from the quiescent point;

wherein the average ADC output is calculated using an average of a selected number, N, of ADC outputs, and the typical ADC output is calculated using an average of a selected number, M, of ADC outputs.

10. The method of claim 9 wherein the step of periodically recalculating the DHF period of operation either:

decreases the DHF period of operation when the typical ADC output is relatively farther from the quiescent point;

or

increases the DHF period of operation when the typical ADC output is relatively closer to the quiescent point.

11. The method of claim 9 wherein the mitigation response comprises applying a signal to the inputs to the system to reduce saturation energy at the inputs.

12. A method of operation in an implantable cardiac stimulus device (ICSD) comprising electrodes for capturing signals and operational circuitry configured for analyzing captured signals, the method comprising:

detecting an event in a signal captured using the electrodes, wherein the event is detected if captured signal amplitude exceeds a threshold;

analyzing the detected event for characteristics indicating saturation; and

if the detected event has characteristics indicating saturation, identifying the detected event as saturated and engaging a mitigation in response to the saturation;

wherein, in the step of analyzing the detected event for characteristics indicating saturation, the following steps are performed;

across a defined period of time, signal samples that are analyzed to identify a largest signal sample during the defined period of time and to determine whether;

i) the signal samples are all of a single polarity;

ii) the largest signal sample exceeds a saturation amplitude threshold; and

iii) the largest signal sample occurs within a predetermined number of samples of the start of the defined period of time;

and if each of i), ii) and iii) is true, the operational circuitry determines that the detected event has characteristics indicating saturation.

13. A method of operation in an implantable cardiac stimulus device (ICSD) comprising electrodes for capturing signals and operational circuitry configured for analyzing captured signals, the method comprising:

detecting an event in a signal captured using the electrodes, wherein the event is detected if captured signal amplitude exceeds a threshold;

analyzing the detected event for characteristics indicating saturation; and

if the detected event has characteristics indicating saturation, identifying the detected event as saturated and engaging a mitigation in response to the saturation;

wherein, in the step of analyzing the detected event for characteristics indicating saturation, the following characteristics are analyzed;

whether the detected event is associated with a signal amplitude that crosses a saturation amplitude threshold; and

if so, whether less than a saturation threshold number of signal turning points occur during a predetermined period of time associated with the detected event.

14. A method of operation in an implantable cardiac stimulus device (ICSD) comprising electrodes for capturing signals and operational circuitry configured for analyzing captured signals, the method comprising:

detecting an event in a signal captured using the electrodes, wherein the event is detected if captured signal amplitude exceeds a threshold;

analyzing the detected event for characteristics indicating saturation; and

if the detected event has characteristics indicating saturation, identifying the detected event as saturated and engaging a mitigation in response to the saturation;

wherein, in the step of analyzing the detected event for characteristics indicating saturation, the following characteristics are analyzed;

whether the detected event is associated with a signal amplitude that crosses a saturation amplitude threshold; and

if so, whether less than a saturation threshold number of signal inflection points occur during a predetermined period of time associated with the detected event.

15. A method of operation in an implantable cardiac stimulus device (ICSD) comprising electrodes for capturing signals and operational circuitry configured for analyzing captured signals, the method comprising:

detecting an event in a signal captured using the electrodes, wherein the event is detected if captured signal amplitude exceeds a threshold;

analyzing the detected event for characteristics indicating saturation; and

if the detected event has characteristics indicating saturation, identifying the detected event as saturated and engaging a mitigation in response to the saturation;

wherein, in the step of analyzing the detected event for characteristics indicating saturation, it is determined whether, across a defined period of time, rectified signal samples all have amplitudes that are in excess of a saturation threshold and, if so, the operational circuitry determines that the detected event has characteristics indicating saturation;

wherein the mitigation response comprises excluding a detected event that has characteristics indicating saturation from further analysis, including rate calculation.

16. A method of operation in an implantable cardiac stimulus device (ICSD) comprising electrodes for capturing signals and operational circuitry configured for analyzing captured signals, the method comprising:

detecting an event in a signal captured using the electrodes, wherein the event is detected if captured signal amplitude exceeds a threshold;

analyzing the detected event for characteristics indicating saturation; and

if the detected event has characteristics indicating saturation, identifying the detected event as saturated and engaging a mitigation in response to the saturation;

wherein;

the mitigation comprises activation and operation of a dynamic Heuristic filter (DHF) operated by the operational circuitry as follows;

on activation, the DHF is initialized with an initial period of operation that defines how often a Heuristic filter is called;

when the Heuristic filter is called, a feature of analog-to-digital conversion (ADC) is adjusted to move an average ADC output toward a quiescent point;

the DHF period of operation is periodically recalculated in view of the distance of a typical ADC output from the quiescent point;

the average ADC output is calculated using an average of a selected number, N, of ADC outputs, and the typical ADC output is calculated using an average of a selected number, M, of ADC outputs; and

the step of periodically recalculating the DHF period of operation either;

decreases the DHF period of operation when the typical ADC output is relatively farther from the quiescent point;

or increases the DHF period of operation when the typical ADC output is relatively closer to the quiescent point;

in the step of analyzing the detected event for characteristics indicating saturation, the following steps are performed;

across a defined period of time, signal samples are analyzed to identify a largest signal sample during the defined period of time and to determine whether;

i) the signal samples are all of a single polarity;

ii) the largest signal sample exceeds a saturation amplitude threshold; and

iii) the largest signal sample occurs within a predetermined number of samples of the start of the defined period of time; and

if each of i), ii) and iii) is true, the operational circuitry determines that the detected event has characteristics indicating saturation.

17. A method of cardiac event detection in an implantable cardiac stimulus system, the implantable cardiac stimulus system including operational circuitry configured for implantation in a patient and electrodes coupled to the operational circuitry, the method comprising:

the operational circuitry capturing a signal from the electrodes coupled thereto;

the operational circuitry analyzing the captured signal to detect a potential cardiac event;

the operational circuitry analyzing the detected potential cardiac event to determine whether the captured signal is likely saturated;

if the captured signal is likely saturated, the operational circuitry ignoring the detected potential cardiac event; and

if the captured signal is likely saturated, the operational circuitry responding to the likely saturated event by providing a signal to the input circuitry of the implantable cardiac stimulus system to offset the saturation.

18. The method of claim 17 wherein the step of analyzing the captured signal includes the operational circuitry performing analog-to-digital conversion of the captured signal and the method further comprises, if the captured signal is likely saturated, the operational circuitry adjusting the analog-to-digital conversion to drive output of the analog-to-digital conversion toward a predetermined quiescent point.